Is tropical montane forest heterogeneity promoted by a resource‐driven feedback cycle? Evidence from nutrient relations, herbivory and litter decomposition along a topographical gradient

Abstract

Summary1. Ridges of tropical mountains often differ strikingly from neighbouring ravines in terms of forest structure, productivity and species composition. This heterogeneity is poorly understood despite its critical role in biodiversity maintenance, carbon and nutrient budgets. 2. We examined measures of tree biomass and productivity, foliage and litter quality (nutrient concentrations, specific leaf mass, phenolics), herbivory and leaf litter decomposition in each six plots laid out in upper and lower slope position in a tropical montane moist forest in southeastern Ecuador. 3. Productivity, quality of foliage and litter as well as herbivory were significantly lower in upper slope position, and closely correlated with soil nutrient concentrations and accumulated humus. The decomposition of upper slope leaf litter (decomposition rate k) was substantially lower than in litter from lower slope forest, whereas the site of decomposition (slope position) only had a marginal effect on the decomposition rate. 4. Our results suggest that the differences in stand structure, productivity, foliar quality, herbivory and decomposition between slope positions are ultimately due to stronger nutrient limitations in upper slope forest. We propose a general conceptual model that explains origin and maintenance of contrasting forest types along topographical gradients through down-slope fluxes of nutrients and water, and a nutrient-driven positive feedback cycle.

Performance of Seedlings of a Shade-Tolerant Tropical Tree Species after Moderate Addition of N and P

“…Increased leaf damage through herbivory after P addition was also reported by Santiago et al (2012) in Panama where the proportion of herbivory in seedlings was higher after P or K addition. Werner and Homeier (2015) found a positive correlation of eaten leaf area with both foliar N and P concentrations in a montane forest close to our study site. All these studies show that herbivore choice is strongly driven by resource quality (i.e., nutrient content and palatability of leaves).…”

The carbon fluxes in different successional stages: modelling the dynamics of tropical montane forests in South Ecuador

“…1) •ha −1 for basal area and 2,300 individuals per hectare for overall stem density. All inventory plots have no sign of human impact and are therefore assumed to be in an old growth state (Leuschner et al 2013;Werner and Homeier 2015). A detailed description of the forest inventories used for model calibration (lower slope/ravine forest only) can be found in Additional file 1: Appendix A.…”

“…Trees that died within this time period were excluded. The method of upscaling these plots to 1 ha is discussed in Werner and Homeier (2015) and resulting values are shown in Table 1. Carbon flux estimations from field data (e.g.…”

“…where S fast , S slow , S dead and S mort (tc•ha −1 ) represent the (Werner and Homeier 2015) field measurements (matrixplots) used for comparison (Werner and Homeier 2015) field measurements from Peru (Plot VII) used for comparison (Girardin et al 2010 …”

“…Another data set from Werner and Homeier (2015) for the ravine forest was used for validation. The last two columns are exemplary data sets for other montane forests in Peru with similar behaviours stocks of rapidly decaying, slowly decaying, dead and newly added dead biomass through mortality.…”