Effects of nutrient manipulation (NUMEX) on the performance of tropical montane trees and interactions with climate variation and ENSO-related weather extremes
Final Report Abstract
The effects of higher rates of atmospheric N and P deposition on the biological diversity and ecosystem functioning of tropical ecosystems are still poorly understood and our knowledge of N and P limitation in tropical forest ecosystems is still limited, but it will be of critical importance to know the effects of increased nutrient availability to conserve these ecosystems. Tropical mountain ecosystems and their vegetation are considered to be especially sensitive to global environmental change. Effects of continued nutrient addition have been investigated along an elevational transect of Andean forests in southern Ecuador within the Ecuadorian NUtrient Manipulation EXperiment (NUMEX). NUMEX started in January 2008 adding moderate amounts of N (50 kg ha^-1 yr^-1), P (10 kg ha^-1 yr^-1), and N and P to representative stands at 1000, 2000 and 3000 m. The study area in S Ecuador is characterized by nutrient poor soils and highly diverse montane forests. Using information on tree functional traits we could show that tree growth responses are highly species-specific and that not all tree species respond with increased growth rates to higher nutrient availability. We conclude that continued nutrient deposition will most likely change species composition and forest structure of the studied montane forests. For fine litter production we found a strong variation between study sites and study years. In addition to higher litter nutrient concentrations after fertilization we found higher litterfall during dry periods (characterized by high vapour pressure deficit) which could be associated with El Niño events. Similar to mature trees the tree seedlings responded species-specifically to nutrient addition and there was no consistent adaptation to the changed environment. Leaves of seedlings and mature trees of some species respond to the higher nutrient availability with higher leaf nutrient concentrations, but these shifts needed some years to become visible. Overall, tropical montane forests are species-rich, highly dynamic ecosystems dominated by long-living organism and a period of ten years is still a short study interval compared to the lifetime of most tropical montane trees. Although some effects of nutrient addition became detectable rapidly (e.g. foliar properties), the expected shifts in tree species composition and resulting mayor changes in ecosystem functioning could need decades to become visible. An important indication of future changes in the composition of the forests is the declining growth performance of tree species with conservative functional traits. The results of the NUMEX highlight the importance of coordinated long-term experimental approaches in species-rich tropical forests.
Publications
- (2018) Contrasting species responses to continued nitrogen and phosphorus addition in tropical montane forest tree seedlings. Biotropica 50(2): 234-245
Cárate-Tandalla D, Camenzind T, Leuschner C & Homeier J
(See online at https://doi.org/10.1111/btp.12518) - (2018) Functional traits determine tree growth and ecosystem productivity of a tropical montane forest: Insights from a long-term nutrient manipulation experiment. Global Change Biology 24(1):399-409
Báez S & Homeier J
(See online at https://doi.org/10.1111/gcb.13905)
