Luquillo LTER

We census seedlings once each year, in 360 1 m² subplots. Three subplots are grouped together around each of 120 seed traps in the LFDP. Seed traps are located at 8 m intervals along pre-existing trails and 8 m from on either side of the trail. The three seedling subplots are located 2 m from each seed trap at polar coordinates chosen in a stratified random manner (i.e., between 1-120 degrees, 121-240, and 241-360) but rejecting locations that fell in pre-existing trails.

Data are recorded during the annual dry season from January to April. Plot substrate (leaves, bare soil, rock, herbs, dead wood, live wood), is assessed for each plot, with percent coverages estimated to the nearest 5% and totaling 100%. The number of grasses and Heliconia sp. culms are also counted in each plot, and the height of the tallest grass and all Heliconia culms is measured from the ground to the tip of the blade/tallest leaf. A densiometer is used to take measurements of canopy cover directly above the center of each seedling plot. General gap size is assessed by looking up at the tree canopy overhead and recording whether seedlings see a large (many large tree crowns missing), medium (several large tree crowns missing), small (one large tree crown missing), or no gap.

In each plot, all woody-stemmed (lianas included) new recruits and surviving seedlings >0 cm (i.e., there is no lower size threshold) and less than 1 cm diameter at 130 cm height are identified to species (using a six letter code, and marked with permanent, uniquely numbered tags. Seedlings for which species cannot be determined are labeled as “Unknown.” The predominant substrate on which that the seedling is growing is noted. Seedling height (excepting palms) is measured from the ground (or root collar or seed if that is visible) along the length of the stem to the apical meristem. For all seedlings >= 10 cm in height, the diameter is measured at the widest axis of the base of the stem. For stems >=130 cm in height, the diameter at 130 cm is also recorded. For plants with multiple stems, height is measured only for the tallest stem. The location of each seedling is mapped relative to other seedlings and the plot boundaries. Old tags found on the ground or on dead stems are removed from the plot, and tags that cannot be located are recorded as “Not Found.” We continue to follow seedlings that grow to exceed 1 cm diameter at a height >=130 cm.

 For palms, seedling height is measured as the distance from the ground to the tip of the tallest/longest leaf. Stem height of palms is recorded from the ground to the top of the stem between the last pair of leaf scars, below where the oldest frond is attached. Diameter of palms is measured at the widest part of the base. When the palm has an obvious woody stem that is clear of dead fronds, a second diameter measurement at the top of the stem, or at 1.3 m, whichever is lower.

For woody* vines rooted in the plot height is measured as the length from the ground along the vine to the apical meristem (or the highest point that can be measured) or the point where the vine leaves the plot. If the height/length of the vine is >=1.3 m (within the plot), the diameter is also measured at 1.3 m.

 Comments are recorded indicating if a seedling stem is broken or has died back, if there is evidence of herbivory or lack of leaves altogether, and tag numbers of large trees with census tags that are located within the seedling plot.

Seedling identifications have been made by Maria Aponte (2007-2008), John Bithorn (2007-2010), Christopher Nytch (2010-2011), and Alejandro Miró Co (2011), in addition to volunteers who have learned some of the identification characteristics well. This FDP is described in greater detail at http://luq.lternet.edu/research/luquillo-forest-dynamics-plot-lfdp.

* One herbaceous vine, Dioscorea polygonoides, is included in the dataset as well.