?13C ?15N American tropics Anthropocene C/N C/P Ca/Al relationship Caribbean El Yunque National Forest Forest Service Guánica Long-Term Ecological Research Luquillo Experimental Forest N/P ratios Nearctic-Neotropical Puerto Rico Tropical Forest Conservation Tropical Forest Management Tropical Forestry Research U.S. Forest Service Planning Rule adaptive management allometry and N/P ratios annual cycle basal area biomass carry over effects cities climate change communications