El Yunque National Forest Atlas is a collaborative effort by the International Institute of Tropical Forestry and El Yunque National Forest to provide upto-date maps and analyses of spatial information of an important natural reserve in Puerto Rico and the only tropical forest in the National Forest System of the United States. El Yunque National Forest Atlas serves as a companion tool to the El Yunque National Forest 2014 Forest Plan Assessment Report, Phase One, under the U.S. Department of Agriculture (USDA), Forest Service 2012 Planning Rule. The assessment documents current ecological, socioeconomic, and cultural conditions of the forest and the surrounding landscape, as part of the El Yunque National Forest management plan revision process, which will establish requirements and constraints to make management decisions within the forest. The El Yunque National Forest 2014 Forest Plan Assessment Report is available at: https://go.usa.gov/cS5Tk.
Tropical forests play a critical role in carbon and water cycles at a global scale. Rapid climate change is anticipated in tropical regions over the coming decades and, under a warmer and drier climate, tropical forests are likely to be net sources of carbon rather than sinks. However, our understanding of tropical forest response and feedback to climate change is very limited. Efforts to model climate change impacts on carbon fluxes in tropical forests have not reached a consensus. Here, we use the Ecosystem Demography model (ED2) to predict carbon fluxes of a Puerto Rican tropical forest under realistic climate change scenarios. We parameterized ED2 with species-specific tree physiological data using the Predictive Ecosystem Analyzer workflow and projected the fate of this ecosystem under five future climate scenarios. The model successfully captured interannual variability in the dynamics of this tropical forest. Model predictions closely followed observed values across a wide range of metrics including aboveground biomass, tree diameter growth, tree size class distributions, and leaf area index. Under a future warming and drying climate scenario, the model predicted reductions in carbon storage and tree growth, together with large shifts in forest community composition and structure. Such rapid changes in climate led the forest to transition from a sink to a source of carbon. Growth respiration and root allocation parameters were responsible for the highest fraction of predictive uncertainty in modeled biomass, highlighting the need to target these processes in future data collection. Our study is the first effort to rely on Bayesian model calibration and synthesis to elucidate the key physiological parameters that drive uncertainty in tropical forests responses to climatic change. We propose a new path forward for model-data synthesis that can substantially reduce uncertainty in our ability to model tropical forest responses to future climate.
Climate change models predict more frequent and severe droughts in the humid tropics. How drought will impact tropical forest carbon and greenhouse gas dynamics is poorly understood. Here we report the effects of the severe 2015 Caribbean drought on soil moisture, oxygen, phosphorus (P), and greenhouse gas emissions in a humid tropical forest in Puerto Rico. Drought significantly decreases inorganic P concentrations, an element commonly limiting to net primary productivity in tropical forests, and significantly increases organic P. High-frequency greenhouse gas measurements show varied impacts across topography. Soil carbon dioxide emissions increase by 60% on slopes and 163% in valleys. Methane (CH4) consumption increases significantly during drought, but high CH4 fluxes post-drought offset this sink after 7 weeks. The rapid response and slow recovery to drought suggest tropical forest biogeochemistry is more sensitive to climate change than previously believed, with potentially large direct and indirect consequences for regional and global carbon cycles.
Seasonally dry tropical forest (SDTF) of the Caribbean Islands (primarily West Indies) is floristically distinct from Neotropical SDTF in Central and South America. We evaluate whether tree species composition was associated with climatic gradients or geographical distance. Turnover (dissimilarity) in species composition of different islands or among more distant sites would suggest communities structured by speciation and dispersal limitations. A nested pattern would be consistent with a steep resource gradient. Correlation of species composition with climatic variation would suggest communities structured by broad-scale environmental filtering.
Seasonally dry tropical forest (SDTF) of the Caribbean Islands (primarily West Indies) is floristically distinct from Neotropical SDTF in Central and South America. We evaluate whether tree species composition was associated with climatic gradients or geographical distance. Turnover (dissimilarity) in species composition of different islands or among more distant sites would suggest communities structured by speciation and dispersal limitations. A nested pattern would be consistent with a steep resource gradient. Correlation of species composition with climatic variation would suggest communities structured by broad-scale environmental filtering.
Tropical forests are subject to seasonal hurricanes resulting in cycles of canopy opening and deposition of litter, followed by periods of recovery and canopy closure. Herein, we review two studies of litter-based communities in Puerto Rico; (i) a survey of bromeliad invertebrates in three montane forest types along an elevational gradient in 1993–1997, during a period of canopy recovery after two severe hurricanes, and the results compared with those from a resurvey in 2010, and (ii) a large scale canopy trimming experiment in the lower montane (Tabonuco) forest designed to simulate an hurricane event, and to separate the effects of canopy opening from debris deposition. Measurements of changes in invertebrate community parameters and decay rates of litter were made in a litter bag experiment as part of this major experiment. As the canopy closed, during the periods of study, bromeliad density reduced, especially in the Tabonuco forest. This was associated with a decline in both alpha and gamma invertebrate diversity, which appears to have involved the loss of rarer species. In the Tabonuco forest, two endemic bromeliad specialists were not found during resampling in 2010, though the most common species were remarkably stable over the two decades. Canopy opening significantly altered the diversity, biomass, and composition of litter communities, irrespective of litter deposition. It particularly reduced organisms responsible for comminution of litter and increased the activity of fungivores and microbiovores. Both studies showed that canopy disturbance, either indirectly or directly, adversely affects invertebrate diversity and detrital processing.
The impact of Hurricane Maria on the U.S. Caribbean was used to study the causes of remotely-sensed spatial variation in the effects of (1) vegetation index loss and (2) landslide occurrence. The vegetation index is a measure of canopy ‘greenness’, a combination of leaf chlorophyll, leaf area, canopy cover and structure. A generalized linear model was made for each kind of effect, using idealized maps of the hurricane forces, along with three landscape characteristics that were significantly associated. In each model, one of these characteristics was forest fragmentation, and another was a measure of disturbance-propensity. For the greenness loss model, the hurricane force was wind, the disturbance-propensity measure was initial greenness, and the third landscape characteristic was fraction forest cover. For the landslide occurrence model, the hurricane force was rain, the disturbance-propensity measure was amount of land slope, and the third landscape characteristic was soil clay content. The model of greenness loss had a pseudo R2 of 0.73 and showed the U.S. Caribbean lost 31% of its initial greenness from the hurricane, with 51% lost from the initial in the Luquillo Experimental Forest (LEF) from Hurricane Maria along with Hurricane Irma. More greenness disturbance was seen in areas with less wind sheltering, higher elevation and topographic sides. The model of landslide occurrence had a pseudo R2 of 0.53 and showed the U.S. Caribbean had 34% of its area and 52% of the LEF area with a landslide density of at least one in 1 km2 from Hurricane Maria. Four experiments with parameters from previous storms of wind speed, storm duration, rainfall, and forest structure over the same storm path and topographic landscape were run as examples of possible future scenarios. While intensity of the storm makes by far the largest scenario difference, forest fragmentation makes a sizable difference especially in vulnerable areas of high clay content or high wind susceptibility. This study showed the utility of simple hurricane force calculations connected with landscape characteristics and remote-sensing data to determine forest susceptibility to hurricane effects.
We quantified long-term successional trajectories of canopy arthropods on six tree species in a tropical rainforest ecosystem in the Luquillo Mountains of Puerto Rico that experienced repeated hurricane-induced disturbances during the 19-yr study (1991–2009). We expected: 1) differential performances of arthropod species to result in taxon- or guild-specific responses; 2) differences in initial conditions to result in distinct successional responses to each hurricane; and 3) the legacy of hurricane-created gaps to persist despite subsequent disturbances. At least one significant effect of gap, time after hurricane, or their interaction occurred for 53 of 116 analyses of taxon abundance, 31 of 84 analyses of guild abundance, and 21 of 60 analyses of biodiversity (e.g., richness, evenness, dominance, and rarity). Significant responses were ∼60% more common for time after hurricane than for gap creation, indicating that temporal changes in habitat during recovery were of primary importance. Both increases and decreases in abundance or diversity occurred in response to each factor. Guild-level responses were probably driven by changes in the abundance of resources on which they rely. For example, detritivores were most abundant soon after hurricanes when litter resources were elevated, whereas sap-suckers were most abundant in gaps where new foliage growth was the greatest. The legacy of canopy gaps created by Hurricane Hugo persisted for at least 19 yr, despite droughts and other hurricanes of various intensities that caused forest damage. This reinforces the need to consider historical legacies when seeking to understand responses to disturbance. http://ee.oxfordjournals.org/content/ee/early/2017/01/03/ee.nvw155.full.pdf
Hurricanes generate disturbances in forests such as canopy opening, fallen trees and leaves which in turn alter physicochemical characteristics of the habitat, as well as, decomposer activity. Litter decomposition depends primarily on the interaction among climate, litter quality and biota; as a consequence any change in habitats will result in changes in these factors. Identifying the changes in the fungal community structure in soil and forest floor litter can help understand the factors that influence ecosystem recovery.
Decades of studies have shown that soil macrofauna, especially earthworms, play dominant engineering roles in soils, affecting physical, chemical, and biological components of ecosystems. Quantifying these effects would allow crucial improvement in biogeochemical budgets and modeling, predicting response of land use and disturbance, and could be applied to bioremediation efforts. Effective methods of manipulating earthworm communities in the field are needed to accompany laboratory microcosm studies to calculate their net function in natural systems and to isolate specific mechanisms. This chapter reviews laboratory and field methods for enumerating and manipulating earthworm populations, as well as approaches toward quantifying their influences on soil processes and biogeochemical cycling.
The study of altitudinal gradients has made enduring contributions to the theoretical and empirical bases of modern biology. Unfortunately, the persistence of these systems and the species that compose them is threatened by land-use change at lower altitudes and by climate change throughout the gradients, but especially at higher altitudes. In this review, we focus on two broad themes that are inspired by altitudinal variation in tropical montane regions: (1) dimensions of biodiversity and (2) metacommunity structure. Species richness generally decreased with increasing altitude, although not always in a linear fashion. Mid-altitudinal peaks in richness were less common than monotonic declines, and altitudinal increases in richness were restricted to amphibian faunas. Moreover, gradients of biodiversity differed among dimensions (taxonomic, phylogenetic and functional) as well as among faunas (bats, rodents, birds) in the tropical Andes, suggesting that species richness is not a good surrogate for dimensions that reflect differences in the function or evolutionary history of species. Tropical montane metacommunities evinced a variety of structures, including nested (bats), Clementsian (rodents, bats, gastropods), quasi-Clementsian (reptiles, amphibians, passerines) and quasi-Gleasonian (gastropods) patterns. Nonetheless, composit
Land-use change is a key driver of the global biodiversity crisis and a particularly serious threat to tropical biodiversity. Throughout the tropics, the staggering pace of deforestation, logging, and conversion of forested habitat to other land uses has created highly fragmented landscapes that are increasingly dominated by human-modified habitats and degraded forests. In this chapter, we review the responses of tropical bats to a range of land-use change scenarios, focusing on the effects of habitat fragmentation , logging , and conversion of tropical forest to various forms of agricultural production. Recent landscape-scale studies have considerably advanced our understanding of how tropical bats respond to habitat fragmentation and disturbance at the population, ensemble, and assemblage level. This research emphasizes that responses of bats are often species and ensemble specific, sensitive to spatial scale , and strongly molded by the characteristics of the prevailing landscape matrix . Nonetheless, substantial knowledge gaps exist concerning other types of response by bats. Few studies have assessed responses at the genetic , behavioral , or physiological level, with regard to disease prevalence , or the extent to which human disturbance erodes the capacity of tropical bats to provide key ecosystem services . A strong geographic bias, with Asia and, most notably, Africa, being strongly understudied, precludes a comprehensive understanding of the effects of fragmentation and disturbance on tropical bats. We strongly encourage increased research in the Paleotropics and emphasize the need for long-term studies , approaches designed to integrate multiple scales, and answering questions that are key to conserving tropical bats in an era of environmental change and dominance of modified habitats (i.e., the Anthropocene).
Decaying coarse woody debris can affect the underlying soil either by augmenting nutrients that can be exploited by tree roots, or by diminishing nutrient availability through stimulation of microbial nutrient immobilization. We analyzed C, N, microbial biomass C and root length in closely paired soil samples taken under versus 20–50 cm away from large trunks of two species felled by Hugo (1989) and Georges (1998) three times during wet and dry seasons over the two years following the study conducted by Georges. Soil microbial biomass, % C and % N were significantly higher under than away from logs felled by both hurricanes (i.e., 1989 and 1998), at all sampling times and at both depths (0–10 and 10–20 cm). Frass from wood boring beetles may contribute to early effects. Root length was greater away from logs during the dry season, and under logs in the wet season. Root length was correlated with microbial biomass C, soil N and soil moisture (R = 0.36, 0.18, and 0.27, respectively; all p values < 0.05). Microbial biomass C varied significantly among seasons but differences between positions (under vs. away) were only suggestive. Microbial C was correlated with soil N (R = 0.35). Surface soil on the upslope side of the logs had significantly more N and microbial biomass, likely from accumulation of leaf litter above the logs on steep slopes. We conclude that decaying wood can provide ephemeral resources that are exploited by tree roots during some seasons.
Decaying wood is related to nutrient cycling through its role as either a sink or source of nutrients. However, at micro scales, what is the effect of decaying logs on the physical, chemical, and biotic characteristics of the soil underneath? We took samples from a 0 to 5 cm depth under and a 50 cm distance away from decaying logs (Dacryodes excelsa and Swietenia macrophylla at 2 stages of decay, and measured soil temperature, total and available nutrients, and root length in a tropical wet forest. We found decaying wood affected physical, chemical, and biotic properties of the underlyingsoil. Soil temperature was less variable under the decaying logs than away from the logs. Soil under the decaying wood had fewer roots, and lower NO3 and Mg2+ availability than samples collected a distance of 50 cm away from the logs. Tree species and decay stage were important factors defining the effect of decaying wood on the distribution of available nutrients. Ca2+, Mg2+, and K+ levels were higher in the soil associated with the youngest logs, and were higher near S. macrophylla logs. Heavy metals were also higher in the soil located near the younger logs independent of the species; other metal ions such as Al3+ and Fe3+ were higher in the soil associated with D. excelsa and the oldest logs. These results indicate decaying wood can contribute to and generate spatial heterogeneity of soil properties.
Resource utilization by earthworms affects soil C and N dynamics and further colonization of invasive earthworms. By applying 13C-labeled Tabebuia heterophylla leaves and 15N-labeled Andropogon glomeratus grass, we investigated resource utilization by three earthworm species (invasive endogeic Pontoscolex corethrurus, native anecic Estherella sp, and native endogeic Onychochaeta borincana) and their effects on soil C and N dynamics in Puerto Rican soils in a 22-day laboratory experiment. Changes of 13C/C and 15N/N in soils, earthworms, and microbial populations were analyzed to evaluate resource utilization by earthworms and their influences on C and N dynamics. Estherella spp. utilized the 13C-labeled litter; however, its utilization on the 13C-labeled litter reduced when cultivated with P. corethrurus and O. borincana. Both P. corethrurus and O. borincana utilized the 13C-labeled litter and 15C-labeled grass roots and root exudates. Pontoscolex corethrurus facilitated soil respiration by stimulating 13C-labeled microbial activity; however, this effect was suppressed possibly due to the changes in the microbial activities or community when coexisting with O. borincana. Increased soil N mineralization by individual Estherella spp. and O. borincana was reduced in the mixed-species treatments. The rapid population growth of P. corethrurus may increase competition pressure on food resources on the local earthworm community. The relevance of resource availability to the population growth of P. corethrurus and its significance as an invasive species is a topic in need of future research.
Revertir la perdida y degradación de bosques a nivel global requerirá la restauración forestal a escala de paisaje y a largo plazo. Esta estrategia ofrece beneficios sociales, ambientales, y económicos que pueden sustentar poblaciones rurales, mitigar efectos del cambio climático, aumentar la seguridad alimenticia, y proteger suelos y cuencas. A pesar del demostrado alcance y viabilidad de la regeneración natural como herramienta de restauración de paisajes degradados, la mayoría de proyectos de restauración se han enfocado en plantaciones. En la mayoría de los casos se ha ignorado la regeneración natural como una opción viable. En esta edición especial de Biotropica presentamos una colección de 16 artículos que ilustran las dimensiones ecológicas, económicas y sociales de la restauración de bosques a nivel de paisaje (FLR). FLR es un enfoque a la restauración relativamente nuevo que aspira a recuperar la integridad ecológica de paisajes deforestados ó degradados y al mismo tiempo aumentar el bienestar humano. Los artículos documentan como la regeneración natural, tanto pasiva como activa, puede lograr beneficios sociales y ecológicos. FLR se enfoca en las poblaciones que viven y trabajan en el paisaje y cuyo bienestar la restauración puede mejorar y diversificar. Dada la magnitud de degradación forestal y la necesidad de mitigar el cambio climático y sustentar el bienestar humano, es fundamental aprovechar el potencial de la regeneración natural para conseguir las ambiciosas metas que motivan iniciativas globales de restauración.
A major global effort to enable cost-effective natural regeneration is needed to achieve ambitious forest and landscape restoration goals. Natural forest regeneration can potentially play a major role in large-scale landscape restoration in tropical regions. Here, we focus on the conditions that favor natural regeneration within tropical forest landscapes. We illustrate cases where large-scale natural regeneration followed forest clearing and non-forest land use, and describe the social and ecological factors that drove these local forest transitions. The self-organizing processes that create naturally regenerating forests and natural regeneration in planted forests promote local genetic adaptation, foster native species with known traditional uses, create spatial and temporal heterogeneity, and sustain local biodiversity and biotic interactions. These features confer greater ecosystem resilience in the face of future shocks and disturbances. We discuss economic, social, and legal issues that challenge natural regeneration in tropical landscapes. We conclude by suggesting ways to enable natural regeneration to become an effective tool for implementing large-scale forest and landscape restoration. Major research and policy priorities include: identifying and modeling the ecological and economic conditions where natural regeneration is a viable and favorable land-use option, developing monitoring protocols for natural regeneration that can be carried out by local communities, and developing enabling incentives, governance structures, and regulatory conditions that promote the stewardship of naturally regenerating forests. Aligning restoration goals and practices with natural regeneration can achieve the best possible outcome for achieving multiple social and environmental benefits at minimal cost.
Naturally regenerating and restored second growth forests account for over 70% of tropical forest cover and provide key ecosystem services. Understanding climate change impacts on successional trajectories of these ecosystems is critical for developing effective large-scale forest landscape restoration (FLR) programs. Differences in environmental conditions, species composition, dynamics, and landscape context from old growth forests may exacerbate climate impacts on second growth stands. We compile data from 112 studies on the effects of natural climate variability, including warming, droughts, fires, and cyclonic storms, on demography and dynamics of second growth forest trees and identify variation in forest responses across biomes, regions, and landscapes. Across studies, drought decreases tree growth, survival, and recruitment, particularly during early succession, but the effects of temperature remain unexplored. Shifts in the frequency and severity of disturbance alter successional trajectories and increase the extent of second growth forests. Vulnerability to climate extremes is generally inversely related to long-term exposure, which varies with historical climate and biogeography. The majority of studies, however, have been conducted in the Neotropics hindering generalization. Effects of fire and cyclonic storms often lead to positive feedbacks, increasing vulnerability to climate extremes and subsequent disturbance. Fragmentation increases forests’ vulnerability to fires, wind, and drought, while land use and other human activities influence the frequency and intensity of fire, potentially retarding succession. Comparative studies of climate effects on tropical forest succession across biogeographic regions are required to forecast the response of tropical forest landscapes to future climates and to implement effective FLR policies and programs in these landscapes.
Synthetic unit hydrographs (SUHs) are useful numeric models developed to predict empirical unit hydrograph parameters as a function of watershed characteristics. These statistical equations usually relate peak flow and timing to watershed characteristics. Once produced, a SUH estimates a storm hydrograph at the outlet of a watershed for a given excess precipitation amount. A sub class of SUHs is the Geographic Unit Hydrographs (GUH), which is informed by the geographic properties of basins (i.e. average slope, average land use, annual precipitation). Recent GUH models use geographic information systems (GIS) allow scientist and engineers to model the flow path and velocity to calculate the runoff response of that basin. This Tropical Geographic Unit Hydrograph (tGUH) model is developed for a specific tropical island environment, and includes an analytical methodology to derive required empirical coefficients directly from observed geographic characteristics, which in turn can provide a more consistent runoff estimate between users. Additionally, with the tGUH described here, unit hydrograph parameters are found to be sensitive to non-stationary parameters including land use (attributable to anthropogenic change) and annual precipitation change (attributable to climate change).
Local habitat size has been shown to influence colonization and extinction processes of species in patchy environments. However, species differ in body size, mobility, and trophic level, and may not respond in the same way to habitat size. Thus far, we have a limited understanding of how habitat size influences the structure of multitrophic communities and to what extent the effects may be generalizable over a broad geographic range. Here, we used water-filled bromeliads of different sizes as a natural model system to examine the effects of habitat size on the trophic structure of their inhabiting invertebrate communities. We collected composition and biomass data from 651 bromeliad communities from eight sites across Central and South America differing in environmental conditions, species pools, and the presence of large-bodied odonate predators. We found that trophic structure in the communities changed dramatically with changes in habitat (bromeliad) size. Detritivore?:?resource ratios showed a consistent negative relationship with habitat size across sites. In contrast, changes in predator?:?detritivore (prey) ratios depended on the presence of odonates as dominant predators in the regional pool. At sites without odonates, predator?:?detritivore biomass ratios decreased with increasing habitat size. At sites with odonates, we found odonates to be more frequently present in large than in small bromeliads, and predator?:?detritivore biomass ratios increased with increasing habitat size to the point where some trophic pyramids became inverted. Our results show that the distribution of biomass amongst food-web levels depends strongly on habitat size, largely irrespective of geographic differences in environmental conditions or detritivore species compositions. However, the presence of large-bodied predators in the regional species pool may fundamentally alter this relationship between habitat size and trophic structure. We conclude that taking into account the response and multitrophic effects of dominant, mobile species may be critical when predicting changes in community structure along a habitat-size gradient.
Communities of invertebrate animals in lower canopy and saxicolous tank bromeliads, originally studied in 1993–1997, were resampled along an elevational gradient in tabonuco, palo colorado, and dwarf or cloud forest in Puerto Rico in 2010. These Puerto Rican montane rain forests were impacted strongly by hurricanes in 1989 and 1998, so the surveys in the 1990s represented 4–8 yr of post-hurricane recovery, whereas our recent survey represents 12 yr of post-hurricane recovery. At most elevations, species diversity, both within individual bromeliads and at the forest scale, declined between the 1990s and 2010. This decline in diversity between decades is associated with reductions in bromeliad density as the canopy progressively closed during recovery from hurricane damage. The observed decline in alpha and gamma diversity appears to have involved the loss of rarer species, as might be expected from standard metapopulation theory. By contrast, the most common species were remarkably stable in abundance, composition, and frequency of occurrence over the two decades. In the lowermost tabonuco forest, two endemic bromeliad specialists, restricted to bromeliads for their entire life cycle, were not found on resampling. This study also demonstrates that, at least in Puerto Rico, sets of ten plants from each forest were sufficient to monitor bromeliad invertebrate populations and their diversity over time.Las comunidades de animales invertebrados en el dosel menor y las bromelias tanque saxícolas, estudiadas originalmente entre los años 1993–1997, fueron re-muestreadas a lo largo de un gradiente altitudinal en Tabonuco, Palo Colorado, y en bosque enano o nublado en Puerto Rico en el año 2010. Estos bosques húmedos montanos de Puerto Rico se vieron muy afectados por los huracanes en los años 1989 y 1998, por lo que los estudios realizados en la década del 1990 representaron 4.8 años de recuperación post- huracán, mientras que nuestro reciente inventario representa doce años de la recuperación posterior a los huracanes. La diversidad de especies, tanto dentro de individuos de bromelias, y a nivel del bosque, disminuyó entre los años 1990 y 2010 en la mayoría de las elevaciones. Esta disminución de la diversidad entre décadas, se asocia con reducciones en la densidad de bromelias, mientras el dosel se cierra de forma progresiva durante el proceso de recuperación de daños ocasionados por huracanes. El descenso observado en la diversidad alfa y gamma parece implicar la pérdida de especies raras, como era de esperarse según la teoría estándar de la meta-población. Por el contrario, las especies más comunes fueron notablemente estables en abundancia, composición, y en la frecuencia de ocurrencia en más de dos décadas. En las partes más bajas del bosque Tabonuco, dos bromelias endémicas especializadas, restringidas a las bromelias durante todo su ciclo de vida, no se encontraron en el re-muestreo. Este estudio también demuestra que, al menos en Puerto Rico, series de diez plantas de cada bosque fueron suficientes para monitorear las poblaciones de invertebrados de bromelias y su diversidad a través del tiempo.
Coastal ecosystems are complex and species rich, but are vulnerable to degradation from a variety of anthropogenic activities. Nevertheless, information on inter-tidal community composition in the Caribbean Basin and at other oceanic sites is lacking. Such information is essential to developing a more comprehensive understanding of rocky inter-tidal systems and their responses to global change. The goals of this study were to determine the relative importance of environmental (wave power density, wave height), habitat (e.g. algal cover, slope, complexity of rock surfaces) and anthropogenic (distance to roads, population density) factors associated with the structure of local assemblages at multiple shore heights and the regional metacommunity of mobile invertebrates on oceanic rocky inter-tidal habitats. Environmental characteristics associated with habitat complexity (algal cover, rock surface complexity) and human population density were most strongly associated with abundance and biodiversity of invertebrates. Species richness was positively correlated with surface complexity, but abundance was negatively correlated with both surface complexity and per cent algal cover. By contrast, abundance of invertebrates was positively correlated with human population density, and diversity was negatively correlated with human population density. Abundance of invertebrates was greatest in the mid inter-tidal zone, whereas diversity was greatest in the lower inter-tidal zone. Metacommunity structure was Gleasonian, but the gradient along which species turnover occurred was correlated with measures of wave exposure, rather than anthropogenic activity. Unlike in previous studies, mostly at mainland sites, human activity primarily altered dominance patterns of communities, while having relatively little effect on species richness or composition.
Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human-ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.
Creation of the National Ecological Observatory Network (NEON) provides unparalleled opportunities for continental-scale research and synthesis in aquatic sciences. Organizers of the NEON aquatic network will equip sites at 29 streams or small rivers across bioclimatic regions of the USA to measure O2 dynamics, aquatic community structure, and aquatic chemistry for up to 3 decades. Data will be collected via a suite of sensors and traditional measurements of a wide range of variables with standardized techniques. The availability of such data will usher in a new era for aquatic scientists, who can use the data to understand the influence of major drivers of stream ecosystem structure and function at regional to continental scales. This rich data stream also will present challenges for the aquatic community. These challenges include interpreting field measurements at distant sites, analysis and management of large data sets, development of appropriate tools for synthesis, and changes in the culture of aquatic science. With the advent of NEON, the most successful aquatic scientists in the coming decades will be equally versed in field measurements and sophisticated analysis of large data sets.
Intense hurricanes disturb many tropical forests, but the key mechanisms driving post-hurricane forest changes are not fully understood. In Puerto Rico, we used a replicated factorial experiment to determine the mechanisms of forest change associated with canopy openness and organic matter (debris) addition. Cascading effects from canopy openness accounted for most of the shifts in the forest biota and biotic processes, which included increased plant recruitment and richness, as well as the decreased abundance and diversity of several animal groups. Canopy opening decreased litterfall and litter moisture, thereby inhibiting lignin-degrading fungi, which slowed decomposition. Debris addition temporarily increased tree basal area. Elevated soil solution nitrate was a dominant response after past hurricanes; this effect only occurred in our experiment with simultaneous canopy-opening and debris treatments. Although debris is an important carbon and nutrient source, short-term responses to cyclonic storms appear to be largely driven by canopy opening.
Aim:Tropical forests store 25% of global carbon and harbour 96% of the world's tree species, but it is not clear whether this high biodiversity matters for carbon storage. Few studies have teased apart the relative importance of forest attributes and environmental drivers for ecosystem functioning, and no such study exists for the tropics.Location:Neotropics.Methods:We relate aboveground biomass (AGB) to forest attributes (diversity and structure) and environmental drivers (annual rainfall and soil fertility) using data from 144,000 trees, 2050 forest plots and 59 forest sites. The sites span the complete latitudinal and climatic gradients in the lowland Neotropics, with rainfall ranging from 750 to 4350 mm year−1. Relationships were analysed within forest sites at scales of 0.1 and 1 ha and across forest sites along large-scale environmental gradients. We used a structural equation model to test the hypothesis that species richness, forest structural attributes and environmental drivers have independent, positive effects on AGB.Results:Across sites, AGB was most strongly driven by rainfall, followed by average tree stem diameter and rarefied species richness, which all had positive effects on AGB. Our indicator of soil fertility (cation exchange capacity) had a negligible effect on AGB, perhaps because we used a global soil database. Taxonomic forest attributes (i.e. species richness, rarefied richness and Shannon diversity) had the strongest relationships with AGB at small spatial scales, where an additional species can still make a difference in terms of niche complementarity, while structural forest attributes (i.e. tree density and tree size) had strong relationships with AGB at all spatial scales.Main conclusions:Biodiversity has an independent, positive effect on AGB and ecosystem functioning, not only in relatively simple temperate systems but also in structurally complex hyperdiverse tropical forests. Biodiversity conservation should therefore be a key component of the UN Reducing Emissions from Deforestation and Degradation strategy.
A simplified soil–plant–atmosphere–continuum model of carbon starvation and hydraulic failure is developed and tested against observations from a drought-manipulation experiment in a woodland dominated by piñon pine (Pinus edulis) and juniper (Juniperus monosperma) in New Mexico. The number of model parameters is reduced using allometric relationships. The model can represent more isohydric (piñon) and more anisohydric (juniper) responses. Analysis of the parameter space suggests four main controls on hydraulic failure and carbon starvation: xylem vulnerability curve, root:shoot area ratio, rooting depth and water use efficiency. For piñon, an intermediate optimal (1.5–2 m2 m−2) tree leaf area index reduces the risk of hydraulic failure. For both piñons and junipers, hydraulic failure was relatively insensitive to root:shoot ratio across a range of tree LAI. Higher root:shoot ratios however strongly decreased the time to carbon starvation. The hydraulic safety margin of piñons is strongly diminished by large diurnal variations in xylem/leaf water potential. Diurnal drops of water potential are mitigated by high maximum hydraulic conductivity, high root:shoot ratio and stomatal regulation (more isohydric). The safety margin of junipers is not very sensitive to diurnal drops in water potential so that there is little benefit in stomatal regulation (more anisohydric). Narrower tracheid diameter and a narrower distribution of tracheid diameters reduce the risk of hydraulic failure and carbon starvation by reducing diurnal xylem water potential drop. Simulated tree diameter-dependent mortality varies between these two species, with piñon mortality decreasing with increasing tree size, whereas juniper mortality increases with tree size. Juvenile piñons might thus be overimpacted by water stress. Copyright © 2015 John Wiley & Sons, Ltd.
Tropical reforestation (TR) has been highlighted as an important intervention for climate change mitigation because of its carbon storage potential. TR can also play other frequently overlooked, but significant, roles in helping society and ecosystems adapt to climate variability and change. For example, reforestation can ameliorate climate-associated impacts of altered hydrological cycles in watersheds, protect coastal areas from increased storms, and provide habitat to reduce the probability of species' extinctions under a changing climate. Consequently, reforestation should be managed with both adaptation and mitigation objectives in mind, so as to maximize synergies among these diverse roles, and to avoid trade-offs in which the achievement of one goal is detrimental to another. Management of increased forest cover must also incorporate measures for reducing the direct and indirect impacts of changing climate on reforestation itself. Here we advocate a focus on “climate-smart reforestation,” defined as reforesting for climate change mitigation and adaptation, while ensuring that the direct and indirect impacts of climate change on reforestation are anticipated and minimized.
Leaf litter represents an important link between tree community composition, forest productivity and biomass, and ecosystem processes. In forests, the spatial distribution of trees and species-specific differences in leaf litter production and quality are likely to cause spatial heterogeneity in nutrient returns to the forest floor and, therefore, in the redistribution of soil nutrients. Using mapped trees and leaf litter data for 12 tree species in a subtropical forest with a well-documented history of land use, we: (1) parameterized spatially explicit models of leaf litter biomass and nutrient deposition; (2) assessed variation in leaf litter inputs across forest areas with different land use legacies; and (3) determined the degree to which the quantity and quality of leaf litter inputs and soil physical characteristics are associated with spatial heterogeneity in soil nutrient ratios (C:N and N:P). The models captured the effects of tree size and location on spatial variation in leaf litterfall (R2 = 0.31–0.79). For all 12 focal species, most of the leaf litter fell less than 5 m away from the source trees, generating fine-scale spatial heterogeneity in leaf litter inputs. Secondary forest species, which dominate areas in earlier successional stages, had lower leaf litter C:N ratios and produced less litter biomass than old-growth specialists. In contrast, P content and N:P ratios did not vary consistently among successional groups. Interspecific variation in leaf litter quality translated into differences in the quantity and quality (C:N) of total leaf litter biomass inputs and among areas with different land use histories. Spatial variation in leaf litter C:N inputs was the major factor associated with heterogeneity in soil C:N ratios relative to soil physical characteristics. In contrast, spatial variation soil N:P was more strongly associated with spatial variation in topography than heterogeneity in leaf litter inputs. The modeling approach presented here can be used to generate prediction surfaces for leaf litter deposition and quality onto the forest floor, a useful tool for understanding soil–vegetation feedbacks. A better understanding of the role of leaf litter inputs from secondary vegetation in restoring soil nutrient stocks will also assist in managing expanding secondary forests in tropical regions.Read More: http://www.esajournals.org/doi/full/10.1890/15-0112.1
Identifying the processes that maintain highly diverse plant communities remains a central goal in ecology. Species variation in growth and survival rates across ontogeny, represented by tree size classes and life history stage-specific niche partitioning, are potentially important mechanisms for promoting forest diversity. However, the role of ontogeny in mediating competitive dynamics and promoting functional diversity is not well understood, particular in high-diversity systems such as tropical forests. The interaction between interspecific functional trait variation and ontogenetic shifts in competitive dynamics may yield insights into the ecophysiological mechanisms promoting community diversity. We investigated how functional trait (seed size, maximum height, SLA, leaf N, and wood density) associations with growth, survival, and response to competing neighbors differ among seedlings and two size classes of trees in a subtropical rain forest in Puerto Rico. We used a hierarchical Bayes model of diameter growth and survival to infer trait relationships with ontogenetic change in competitive dynamics. Traits were more strongly associated with average growth and survival than with neighborhood interactions, and were highly consistent across ontogeny for most traits. The associations between trait values and tree responses to crowding by neighbors showed significant shifts as trees grew. Large trees exhibited greater growth as the difference in species trait values among neighbors increased, suggesting trait-associated niche partitioning was important for the largest size class. Our results identify potential axes of niche partitioning and performance-equalizing functional trade-offs across ontogeny, promoting species coexistence in this diverse forest community.
Question Understanding how the relative importance of different community assembly processes changes during secondary succession of diverse systems remains elusive. Functional and phylogenetic approaches that place species along continuous axes of niche differentiation and evolutionary relatedness, however, are deepening our understanding of the mechanisms that drive successional dynamics. We ask whether successional shifts in the functional and phylogenetic composition of post-agricultural tropical forests provide evidence for niche partitioning or competitive dominance hierarchies as drivers of successional change. Location Subtropical wet forests, Puerto Rico. Methods We combined data on four functional traits [leaf dry mass per area (LMA), wood density (WD), maximum height (Hmax), seed dry mass] and a well-resolved molecular phylogeny to characterize taxonomic, functional and phylogenetic composition of sapling and adult tree communities along a regionally replicated chronosequence. We used a null model approach to assess how functional and phylogenetic diversity change with forest age. Results Corresponding increases of community-weighted mean LMA, Hmax and seed mass with forest age reflected a shift in dominance of species with acquisitive resource-use strategies and small seeds towards species with more conservative resource use and larger seeds. A negative relationship between forest age and local diversity of Hmax and seed mass suggested increased importance of competitive hierarchies for light capture and shade-tolerant regeneration in older forests. In contrast, the colonization of palms in older forest plots led to a positive relationship between forest age and local phylogenetic diversity, suggesting functional convergence of distantly related lineages on traits that confer competitive dominance under low resource conditions. Conclusions We linked both functional and phylogenetic dimensions of community diversity with successional trajectories of post-agricultural tropical forests. Contrasting patterns of these dimensions of diversity shed light on the underlying community assembly processes. We argue that integrating traits and phylogeny with specific hypotheses about physiological and historical mechanisms is essential for advancing our understanding of the drivers of community change during succession.
In natural systems, organisms are simultaneously engaged in mutualistic, competitive, and predatory interactions. Theory predicts that species persistence and community stability are feasible when the beneficial effects of mutualisms are balanced by density-dependent negative feedbacks. Enemy-mediated negative feedbacks can foster plant species coexistence in diverse communities, but empirical evidence remains mixed. Disparity between theoretical expectations and empirical results may arise from the effects of mutualistic mycorrhizal fungi. Here, we build a multiprey species/predator model combined with a bidirectional resource exchange system, which simulates mutualistic interactions between plants and fungi. To reach population persistence, (1) the per capita rate of increase of all plant population must exceed the sum of the negative per capita effects of predation, interspecific competition, and costs of mycorrhizal association, and (2) the per capita numerical response of enemies to mycorrhizal plants must exceed the magnitude of the per capita enemy rate of mortality. These conditions reflect the balance between regulation and facilitation in the system. Interactions between plant natural enemies and mycorrhizal fungi lead to shifts in the strength and direction of net mycorrhizal effects on plants over time, with common plant species deriving greater benefits from mycorrhizal associations than rare plant species.
It has been proposed that the large soil carbon (C) stocks of humid tropical forests result predominantly from C stabilization by reactive minerals, whereas oxygen (O2) limitation of decomposition has received much less attention. We examined the importance of these factors in explaining patterns of C stocks and turnover in the Luquillo Experimental Forest, Puerto Rico, using radiocarbon (14C) measurements of contemporary and archived samples. Samples from ridge, slope, and valley positions spanned three soil orders (Ultisol, Oxisol, Inceptisol) representative of humid tropical forests, and differed in texture, reactive metal content, O2 availability, and root biomass. Mineral-associated C comprised the large majority (87 ± 2%, n = 30) of total soil C. Turnover of most mineral-associated C (66 ± 2%) was rapid (11 to 26 years; mean and SE: 18 ± 3 years) in 25 of 30 soil samples across surface horizons (0–10 and 10–20 cm depths) and all topographic positions, independent of variation in reactive metal concentrations and clay content. Passive C with centennial–millennial turnover was typically much less abundant (34 ± 3%), even at 10–20 cm depths. Carbon turnover times and concentrations significantly increased with concentrations of reduced iron (Fe(II)) across all samples, suggesting that O2 availability may have limited the decomposition of mineral-associated C over decadal scales. Steady-state inputs of mineral-associated C were statistically similar among the three topographic positions, and could represent 10–25% of annual litter production. Observed trends in mineral-associated Δ14C over time could not be fit using the single-pool model used in many other studies, which generated contradictory relationships between turnover and Δ14C as compared with a more realistic two-pool model. The large C fluxes in surface and near-surface soils documented here are supported by findings from paired 14C studies in other types of ecosystems, and suggest that most mineral-associated C cycles relatively rapidly (decadal scales) across ecosystems that span a broad range of state factors.
Humid tropical forest soils are characterized by warm temperatures, abundant rainfall, and high rates of biological activity that vary considerably in both space and time. These conditions, together with finely textured soils typical of humid tropical forests lead to periodic low redox conditions, even in well-drained upland environments. The relationship between redox and biogeochemical processes has been studied for decades in saturated environments like wetlands and sediments, but much less is known about redox dynamics in upland soils. The goal of this study was to understand the spatial variability of redox sensitive biogeochemistry within and across two forest types at the ends of a high rainfall gradient (3500 to 5000 mm y−1) in the Luquillo Experimental Forest, Puerto Rico. The two sites differed significantly in average soil chemical and physical properties, but the scale of variability was similar across sites, with greater variability in soil gas concentrations than extractable Fe and P. Soil P and Fe pools and trace gas concentrations were more strongly correlated with each other and exhibited more spatial structure at the wetter site. While the within-site relationships among these redox sensitive variables were typically weak, the relationships across sites were much stronger. We provide a conceptual model that elucidates how the strength of the relationships between indicators of redox-sensitive biogeochemical processes depends on the spatial scale of analysis.
The amphidromous shrimp Xiphocaris elongata(Guérin-Méneville, 1855) has a long rostrum in the presence of predatory fishes and a short rostrum above steep waterfalls where predatory fishes are absent, i.e., typically above waterfalls. Prior experiments showed that elongated rostrum in X. elongatais induced by chemical signals from the predatory fish Agonostomus monticola. We tested the hypothesis that in addition to rostrum length there are other morphometric differences between long-rostrum (LR) and short-rostrum (SR) X. elongata. We measured the post-orbital carapace length and pleon length of LR and SR shrimp and weighed both shrimp morphs. LR shrimp have significantly longer and heavier pleons than the SR shrimp. These allometric differences may affect the behavior of X. elongatashrimp in ways that, in turn, affect their interactions with predators and the environment. Our study demonstrates the importance of taking pleon measurements when studying crustaceans given that these measurements have been mostly overlooked, and may provide insight of environmental influences on crustacean morphology and behavior. This research provides data of the differences between prey phenotypes, which may alter their life-histories and interactions with the environment.
Urbanization influences a range of factors related to stream health, including the hydrologic regime, water quality, and riparian conditions that lead to negative effects on terrestrial and aquatic ecosystems. However, impacts on freshwater decapods from urbanization of tropical streams have not been reported. We hypothesized that changes in decapod communities in watersheds with different levels of urbanization are related to changes in physical stream habitats caused by different land uses and their effects on water discharge. The impacts of land use on the physico-chemical characteristics of streams and freshwater decapod communities were evaluated in three watersheds characterized by low, moderate and high-intensities of urbanization in Puerto Rico. For the low and moderately developed urban watersheds, decapod species richness ranged from 10 to 11 species; the highly urbanized watershed only had 4 species. Macrobrachium faustinum and Xiphocaris elongata were the most ubiquitously species and were found in all watersheds. Multivariable analysis of physical characteristics and densities of the decapod families resulted in one axis that explained 80 % of the total variation among the watersheds and was correlated with stream discharge. The effect of discharge is likely a result of frequent high flows that sustain habitats with high concentrations of dissolved oxygen and low concentrations of pollutants. An increase in physico-chemical parameters were observed from the LUW to the HUW. These results indicate that the decapod communities were most likely influenced by land use and environmental conditions that affected erosional aspects related to water discharge and water quality in the highly impacted watersheds.
SUMMARY1. Growth rates of individual freshwater shrimp of the species Atya lanipes and Xiphocaris elongata were measured in a second-order stream in the Luquillo Experimental Forest in Puerto Rico over 10 years (1997-2007). Shrimp living at lower altitudes in warmer water and wider stream channels with more algal and detrital foods were predicted to grow and reproduce more rapidly.2. Shrimp were marked and recaptured periodically in pools located at three altitudes to determine whether temperature affected growth rates among individual A. lanipes and X. elongata.3. Mean annual water temperatures ranged from 20 to 24 °C with the uppermost pool being cooler than the lower pools. Mean annual growth rates for Atya and Xiphocaris were 0.27 and 0.1 mm carapace length, respectively, for all three populations.4. Differences in growth were partially influenced by how each species obtains its food. Atya is a filter feeder and scraper and has continuous access to suspended organic particles and biofilms. The slower growth rate forXiphocaris elongata is most likely a result of the wider range in quality and accessibility of food resources.5. Differences in pool morphology and depths probably affected differences in food availability. Increased leaf litter retention in the deeper upper and lower pools probably increased shrimp growth rates, while washout of leaf litter from the relatively shallow, elongate mid-altitude pool decreased Atya lanipes growth rates.6. These long-lived, slow-growing shrimp species transform a wide range of organic materials into their biomass. Because of the slow growth rates of these detritivores shrimp, tropical storms, hurricanes, droughts or other disturbances could have persistent, long-term impacts on detrital processing and on the populations of their predators.
Web-spinning spiders that inhabit stream channels are considered specialists of aquatic ecosystems and are major consumers of emerging aquatic insects, while other spider taxa are more commonly found in riparian forests and as a result may consume more terrestrial insects. To determine if there was a difference in spider taxa abundance between riverine web-spinning spider assemblages within the stream channel and the assemblages 10 m into the riparian forest, we compared abundances for all web-spinning spiders along a headwater stream in El Yunque National Forest in northeast Puerto Rico. By using a nonmetric dimensional scaling (NMDS) abundance analysis we were able to see a clear separation of the two spider assemblages. The second objective of the study was to determine if aquatic insects contributed more to the diet of the spider assemblages closest to the stream channel and therefore stable isotope analyses of δ (15)N and δ (13)C for web-spinning spiders along with their possible prey were utilized. The results of the Bayesian mixing model (SIAR) however showed little difference in the diets of riverine (0 m), riparian (10 m) and upland (25 m) spiders. We found that aquatic insects made up ∼50% of the diet for web-spinning spiders collected at 0 m, 10 m, and 25 m from the stream. This study highlights the importance of aquatic insects as a food source for web-spinning spiders despite the taxonomic differences in assemblages at different distances from the stream.
Streams have been impacted by human activities in a variety of ways. Over time, these ecosystems become dominated by the most resilient species, with significant losses in the natural components that provide valuable ecosystem services to people. In impacted streams, the loss of ecosystem services often is not recognized until the stream has already been dramatically altered. In this study, I provide data on the natural distribution of freshwater decapods and the status of decapod communities in streams with different land use histories. I reviewed the decapod distribution for the Caribbean to provide an update of the species that inhabit the freshwater systems. I determined the presence of 18 species of decapods in Puerto Rico and concluded that these decapods follow the island-species relationship in the Caribbean. Also, I present data associated with decapod community dynamics in watersheds with different urban development. As, expected the highly urban watershed had lower diversity and density of decapods than the medium and low urban watersheds. The variations in decapod communities among watersheds correlated with the degradation of the physical-chemical environments and clearing of the riparian zones. I compare the food webs among streams with different human impacts. Specific influences of point/nonpoint sources of N could be iv distinguished in food web components. This shows to an effect of human activities on the stream and watershed. In addition, I determined the effect of abiotic and biotic factors on the growth of A.lanipes (0.27 mm) and X.elongata (0.1 mm) over the 10-year period of study. The results showed that these species transform a wide range of organic materials into their biomass. Finally, I developed a series of education projects which promote the understanding and knowledge of freshwater ecosystems; interactions and the organisms that inhabit these systems. The results showed an increasing interest about freshwater fauna and ecosystems. I concluded that: a) the distribution of freshwater decapods in the Caribbean islands follows the area-species relationship; b) urbanization represents one of the many distinct land uses that affect habitat structure, energy sources and biotic interactions; and c) it’s necessary to present the results of our research to the general public in ways that are easily understood.
This work presents basic information on tropical lichenology. It also describes general aspects about the ecology and biodiversity of these organisms in eight forest ecosystems present along an elevational radient in northeastern Puerto Rico. These ecosystems consist of elfin woodlands, palo colorado, sierra palm, tabonuco, lowland moist, dry, mangrove, and Pterocarpus forests. Lichen communities are mainly described in terms of general ecological attributes (e.g., species richness, common species, etc.). Basic information about the environment and vegetation found in these forests is also provided. The information presented is supplemented with field and microscopic photographs of species and their habitats.
Appraising the social-ecological processes influencing the inflow, transformation, and storage of materials and energy in urban ecosystems requires scientific attention. This appraisal can provide an important tool for assessing the sustainability of cities. Socio-economic activities are mostly responsible for these fluxes, which are well manifested in the household unit. Human behavior associated with cultural traditions, belief systems, knowledge, and lifestyles are important drivers controlling the transfer of materials throughout the urban environment. Within this context, we explored three aspects of household consumption and waste disposal activities along the Río Piedras Watershed in the San Juan metropolitan area of Puerto Rico. These included: the source of food consumed by residents, recycling activities, and trends in connection to the municipality’s sewerage system. We randomly interviewed 437 households at six sites along the watershed. We also conducted analysis to estimate accessibility to commercial food services for residents in the study areas. Our surveys revealed that nearly all interviewed households (~97 percent) consumed products from supermarkets. In neighborhoods of the upper portion of the watershed, where residential density is low with large areas of vegetative cover, more than 60 percent of residents consumed food items cultivated in their yards. Less than 36 percent of residents in the in densely urbanized parts of the lower portion of the watershed consumed items from their yards. Accessibility to commercial stores for food consumption contrasted among study sites. Recycling activities were mostly carried out by residents in the lower portion of the watershed, with better access to recycling programs provided by the municipality. The surveys also revealed that only 4 to 17 percent of residences in the upper watershed are connected to the sewerage system while the large majority uses septic tanks for septic water disposal. For these residents wastewater from house maintenance is disposed of directly into the environment. In the lower portion of the watershed all residents were connected to the sewerage system. Our study suggests the need to understand human behavioral attitudes in the acquirement and processing of resources, as a tool to generate informed-based strategies promoting sustainable consumption and disposal patterns.
We sampled tank bromeliads and censused their invertebrate fauna at four elevations on the small Caribbean island of Saba. We expected that invertebrate communities would show a strong response to the elevational gradient, as found on the larger island of Puerto Rico, but there was no difference in overall animal abundance, species richness, or biomass in bromeliads at the different sites. A weak rainfall gradient and relatively recent anthropogenic disturbance may be reasons for the lack of elevational response. The structure of the community in dry forest bromeliads was different from in the wetter forests, due to the dominance of the larvae of one particular species (Forcipomyoa antiguensis). The aquatic larvae of some bromeliad-specialist genera (e.g., Monopelopia, Corethrella, Wyeomyia, and Scirtes) common in the other Caribbean and mainland sites were absent from Saba. Their absence may be due to the target island effect, which reduces the chances of successful immigration and survival on small islands.
We analyzed responses of canopy arthropods on seven representative early and late successional overstory and understory tree species to a canopy trimming experiment designed to separate effects of canopy opening and debris pulse (resulting from hurricane disturbance) in a tropical rainforest ecosystem at the Luquillo Experimental Forest Long-Term Ecological Research (LTER) site in Puerto Rico. We expected that either canopy opening or added debris would result in increased abundances of certain scale insects and other hemipterans, and thereby affect arthropod diversity. Six of thirteen arthropod taxa tested showed significant responses to treatments as main effects or interactions. No taxon responded significantly to trim treatment alone. The red wax scale, Ceroplastes rubens (on Manilkara bidentata), was significantly less abundant in treatments with added debris than in treatments without added debris, and salticid spiders (on Sloanea berteriana) were significantly more abundant in treatments with added debris than in other treatments. Canopy trimming generally did not have a significant effect on assemblage diversity, whereas debris deposition significantly increased diversity on three late successional tree species. A number of significant treatment interactions were observed. Overall, the debris pulse had a greater effect on canopy arthropods than did canopy opening, suggesting that changes in plant condition resulting from nutrient availability associated with debris deposition have a greater effect on canopy arthropods than do the more direct and immediate changes in abiotic conditions resulting from canopy opening.
In this study, we used a replicated factorial design to separate the individual and interacting effects of two main components of a severe hurricane – canopy opening and green debris deposition on leaf litter decay in the tabonuco forest in the Luquillo Mountains of Puerto Rico. We quantify changes in percent mass remaining (PMR), the concentration and absolute amounts of various chemical elements using fresh (green) and senesced leaf litter contained in litterbags of two different mesh sizes. Mass loss was significantly slowed by canopy trimming. There was no significant effect of debris treatment on the PMR of the litter. Canopy trimming increased the percent of initial N, Al, Ca, Fe, and Mg remaining and decreased the percent of initial Mn remaining compared with not trimmed plots. Debris addition increased the percent of initial N and P remaining and decreased the percent of initial Al, and Fe remaining in the decomposing litter compared to no debris added plots. Of the elements studied, only Al and Fe accumulated above 100% of initial. Accumulation of Al and Fe in the canopy trimmed and no debris plots is most likely dominated by the adsorption of these ions onto the surfaces of the decaying litter. Overall, P showed a rapid initial loss during the first 0.2 yr followed by steady loss. Nitrogen was lost steadily from leaf litter. The PMR of fresh and senesced litter was significantly affected by mesh size, with a higher mass remaining in small mesh bags. Fresh litter decayed faster than senesced litter; following patterns of initial N and P concentrations (higher in the former litter type). We found a significantly negative correlation between the Margalef index of diversity for the litter arthropods contained in the litterbags and the PMR, suggesting functional complexity is an important determinant of decay in this forest. Our results imply hurricanes can differentially impact litter decomposition and associated nutrient release via canopy opening and litter inputs.