Tree Growth Responses to Long-Term Fertilization in a Lowland Tropical Rainforest

Trees play an important role in the global carbon cycle since they use carbon to build biomass and they release oxygen as a by-product of photosynthesis. Thus, understanding which environmental factors influence tree growth and survival is crucial in predicting how forest ecosystems will respond to global changes. Two factors that can affect a tree’s growth are 1) availability of the most limited soil nutrient and 2) a tree’s species or size. I leveraged data from a long-term (12 yrs) nitrogen (N) and phosphorus (P) nutrient addition experiment in Costa Rica. Using mixed linear models in RStudio v.3.5.1., I investigated how the different fertilizers, species, and diameter at breast height (dbh) affected growth rates of trees. I found that overall, there were no significant fertilizer effects. However, smaller trees (dbh) grew more in the N, then NP and then P treatments relative to the control. Larger trees (>15 cm dbh), grew more in the N treatment only. There was a strong species effect but because species respond differently to fertilizers, results “cancel out”, resulting in a lack of net responses to fertilizer at the community level.