Factors controlling the productivity of tropical Andean forests: climate and soil are more important than tree diversity

Abstract

Abstract. Theory predicts positive effects of species richness on the productivity of plant communities through complementary resource use and facilitative interactions between species. Results from manipulative experiments with tropical tree species indicate a positive diversity–productivity relationship (DPR), but the existing evidence from natural forests is scarce and contradictory. We studied forest aboveground productivity in more than 80 humid tropical montane old-growth forests in two highly diverse Andean regions with large geological and topographic heterogeneity and related productivity to tree diversity and climatic, edaphic and stand structural factors with a likely influence on productivity. Main determinants of wood production in the perhumid study regions were elevation (as a proxy for temperature), soil nutrient (N, P and base cation) availability and forest structural parameters (wood specific gravity, aboveground biomass). Tree diversity had only a small positive influence on productivity, even though tree species numbers varied largely (6–27 species per 0.04 ha). We conclude that the productivity of highly diverse Neotropical montane forests is primarily controlled by thermal and edaphic factors and stand structural properties, while tree diversity is of minor importance.

Forest productivity is determined by climate and stand properties rather than species diversity

“…Second, DPR is related to the definition of plant community productivity. Previous research showed that the relationship between species diversity and productivity was weak when only tree productivity was considered, but the relationship between species diversity and productivity was obvious when litter productivity was added (Homeier and Leuschner 2021). In this study, the productivity of forest trees was calculated, but litter productivity was not assessed.…”

“…Controlled experiments have shown a positive relationship between species diversity and productivity (Huang 2018;Schnabel et al 2019). However, these results are difficult to extrapolate to subtropical old-growth forests due to the young age of these tree plantations (Homeier and Leuschner 2021). Thus, the relationship between species diversity and productivity in natural communities is still unclear.…”

“…Biotic controls related to stand structural properties and the functional composition of a community can also affect forest productivity (Engbersen et al 2022). Some studies found that forest NPP increased with standing aboveground biomass (Homeier and Leuschner 2021;Lohbeck et al 2015). Moreover, the biomass of trees is closely related to DBH and tree height.…”

“…Tree height determines the ability of individual plants in the community to compete for light. Variation in leaf functional traits such as leaf mass per area (LMA) and foliar nitrogen (N) content should be major determinants of NPP (Finegan et al 2015;Homeier and Leuschner 2021;van de Weg et al 2014;Fyllas et al 2017;Luyssaert et al 2007), because they influence the radiation interception the photosynthetic capacity of the canopy. However, these leaf traits were affected by the stand density, which changes the light intensity (Vitória et al 2019).…”

Aboveground carbon stocks, woody and litter productivity along an elevational gradient in the Rwenzori Mountains, Uganda

“…The positive relationship between species richness and productivity is a result of efficient resource use by a diversity of species because of niche differentiation and facilitation (Loreau et al, 2001). In a recent study by Homeier and Leuschner (2021), in a highly species-rich Neotropical montane forest, productivity was primarily controlled by thermal and edaphic factors, and stand structure properties, while diversity had only a minor effect.…”