Rising to 1075 m in elevation, the Luquillo Mountains present a gradient of climate and vegetation change that extends through five life zones from subtropical moist forest to lower montane rain forest (Ewel & Whitmore 1973). Forest communities extend along the gradient from mid-elevation (200-600 m asl) tabonuco forest through palo colorado forest (600-900 m) to elfin woodland (900-1075 m; Fig. 2.2). Palm forest, an edaphic formation, occurs at all elevations. We will collect long-term (80 yr) data on changes in the distribution of organisms and process rates along this gradient to examine the integrated effects of warming, drying, and more frequent disturbance over the range of biotic and abiotic conditions (Hypotheses 1 and 4). We measure changes in vegetation structure and composition every six years in three series of Long-Term Elevation Plots (LTEP) placed at 50 m intervals of elevation in three watersheds (Mameyes, Icacos, and Sonadora). In the Sonadora watershed, we compare upland forest types to adjacent palm forest to separate the effects of forest community composition and the abiotic environment (Willig et al. 2013, Table 3.2). We also monitor climate, rainfall chemistry, diameter increment, and litterfall in the Sonadora watershed.
Soil properties and plant species composition have been measured in these plots (Barone et al. 2008); we have also conducted biogeochemical and decomposition experiments along the elevation gradient as part of previous LTER research (Silver et al. 1999, McGroddy & Silver 2000, Dubinsky et al. 2010, Hall & Silver 2015). We began long-term studies of changes in plant and gastropod communities in LUQ III (Willig et al. 2013, Willig & Presley 2016), and established baseline measurements for most of the variables in Table 3.2 last year (Fig. 3.2) before Hurricanes Irma and Maria struck in September. Funds from a RAPID award are being used to conduct post-hurricane tree damage assessments in the LTEP, and other variables will be resampled during the next year and into Year 1 of LUQ VI to capture hurricane effects, and again in Year 5, the regularly scheduled timing for the LTEP census. We will continue to measure the variables in Table 3.2 at six-year intervals until the end of the century to examine the effects of changes in environmental drivers (see Hypotheses 1 and 4) on populations, communities, and key ecosystem characteristics.