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

1. 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 and 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.

1. 热带山地山脊的森林结构、生产力与物种组成往往与邻近沟谷存在显著差异。尽管这种异质性在生物多样性维持、碳与养分预算中发挥着关键作用，但其相关机制仍未得到充分阐释。
2. 我们在厄瓜多尔东南部的热带山地湿润森林（tropical montane moist forest）中，于上坡位与下坡位各设置6块样地，对树木生物量与生产力、叶片及凋落物品质（养分浓度、比叶质量、酚类物质含量）、植食水平以及叶片凋落物分解情况开展了测定。
3. 上坡位的生产力、叶片与凋落物品质以及植食水平均显著低于下坡位，且与土壤养分浓度及腐殖质累积量密切相关。上坡位叶片凋落物的分解速率k显著低于下坡位森林的凋落物，而分解位点（坡度位）对分解速率仅存在微弱影响。
4. 研究结果表明，不同坡度位之间林分结构、生产力、叶片品质、植食水平以及分解过程的差异，归根结底源于上坡位森林更强的养分限制作用。我们提出了一个通用概念模型，该模型通过养分与水分的下坡通量，以及养分驱动的正反馈循环，解释了地形梯度上迥异森林类型的起源与维持机制。