Advancements in the understanding of spatiotemporal gradients in tropical landscapes: A Luquillo focus and global perspective

TitleAdvancements in the understanding of spatiotemporal gradients in tropical landscapes: A Luquillo focus and global perspective
Publication TypeBook Chapter
Year of Publication2013
AuthorsGonzález, G, Willig, MR, Waide, RB
Book TitleEcological Bulletins 54: Ecological gradient analyses in a tropical landscape
Series TitleEcological Bulletins
PublisherJohn Wiley & Sons
Accession NumberLUQ.1104
Keywordsspatial gradients

Background The Luquillo Mountains have served as a focal point for people since pre-Columbian times. The Taíno Indians in Puerto Rico believed that the spirit of Yuquiyú – god of order, after which El Yunque National Forest (or Luquillo Experimental Forest) is named – dwelled and protected the people from Juracán (the phonetic name given by the Spanish settlers to the god of chaos and disorder believed to control the weather, particularly hurricanes). The chapters in this book illustrate how the Luquillo Mountains continue to serve as a focal point for understanding climate and for using our knowledge to better plan for and ‘protect’ people from climate-induced disturbances in the future. The juxtaposition of a rise in elevation from sea level to nearly 1100 m over the course of 10 km, the tropical climate, and the location of the Luquillo Mountains on the easternmost of the Greater Antilles, exposed to moisture laden trade winds, gives rise to gradients in rainfall, temperature, and seasonality that have structured ecological systems and human use of the landscape. Assessing the patterns and mechanisms of control along gradients that are often interdependent requires thoughtful analyses from many perspectives, rigorous experimental design, and long-term study. The value in understanding these gradients arises because knowledge is the basis for independently predicting responses to changes in rainfall, temperature, seasonality, storm intensity or frequency, and human use of the landscape. Gradient analysis uses spatial measures of physical, chemical, and biological properties of the environment to understand the spatiotemporal dynamics of species, biological communities, biogeochemical fluxes, and ecosystem properties. The study of environmental gradients traces its history to the origins of the discipline of ecology (Clements 1904, Gleason 1917, Shelford 1951, Andrewartha and Birch 1954, Odum 1959). Indeed, the relation between environmental gradients and the distribution of organisms and communities is a favorite topic of ecologists and biogeographers, and papers on the subject abound in the literature. Much of this work focuses on environmental gradients that arise in concert with changes in elevation, such as temperature and rainfall (Whittaker 1967). Thus, studies of montane ecosystems are frequent in the literature on environmental gradients, and tropical mountains, because of their high biodiversity compared to those in temperate latitudes, provide an excellent laboratory for examining ecological responses to environmental change. The chapters in this book take advantage of gradients that exist in the Luquillo Mountains, one of the most intensively studied tropical landscapes in the world (Brokaw, et al. 2012). Moreover, the work described in this book furthers the studies of ecological gradients that have been undertaken in other parts of the tropics (Olson 1963, Terborgh 1977, Patton and Smith 1992, Stevens 1992, Lieberman et al. 1996, Schneider et al. 1999, Givnish 2001, 2002, Smith et al. 2001, Ogden and Thorpe 2002, McCain 2005, Presley et al. 2012 ). The extensive literature on environmental gradients provides a general conceptual framework for studies in the Luquillo Mountains. For example, formulation of an energy-based mechanism tha provided insight into how individuals and species respond to gradients (Hall et al. 1992) stimulated development of a conceptual model for the Luquillo LTER program that uses the concept of gradients to link landscape-scale patterns and processes with disturbance regimes (Willig and Walker 1999, Waide and Willig 2012). In this model, spatial gradients of environmental factors in the landscape are dynamic. Disturbance modifies environmental conditions so that any location in the landscape is subject to a range of environmental conditions over time. The distribution and abundance of individuals and species are determined by the tolerances to this range of conditions. Much of the work reported in this volume has been stimulated by this conceptual model. Yet, the way human actions interact with the environment at all scales (e.g. global warming, urban heat island effect, land use, roads and landslides, and water extraction) make future scenarios difficult to predict. The elevational and climatic gradients within the Luquillo Mountains and northeastern Puerto Rico provide a natural in situ simulation of climate change, as a difference of about 5°C in mean annual temperature and more 3000 mm in mean annual precipitation occur from the top of the Luquillo Mountains to the coast. Thus, the use or exploration of the elevation gradient as a proxy for climate change can be a practical and informative way to study climate change scenarios, or to conduct experiments based on translocation manipulations. Manipulative experiments along elevation gradients could focus on populations, communities or ecosystem processes, and can be designed to anticipate and understand the effects of warming and drying.