The influence of structural, functional, and species diversity to temporal stability of productivity and efficiency of resource use in a tropical tree diversity experiment

由于过去的森林砍伐和生态系统退化，热带和亚热带地区有很大的造林需求和潜力。混种种植提供了一个机会，可以建立比单一种植更高产的森林，并提供更高水平的生态系统服务。然而，尚未充分研究多样化植树是否实际上更能抵御干旱，以及它们是否比单一栽培更有效地利用养分和水，特别是在热带地区。在这里，我们打算利用这一独特的机会来分析巴拿马最近收获的“沙丁鱼”树木多样性实验，其中16年是同类中最古老的一个。拟议项目的总体目标是确定树木邻里多样性是否具有稳定作用，树木相互作用发生的规模，对树木的生产力和资源利用动态（水和养分）随着时间的推移。具体而言，我们假设：（a）随着多样性的增加，生产力和资源利用的互补性增加（物种，结构，功能）的树木邻里和随着时间的推移，B）生产力和资源利用的时间变化下降和稳定性增加的多样性，c）结构多样性和物种丰富度独立和直接影响生产力和资源利用的个别树木，和d）在干旱时期，随着生物多样性的增加，木本生物量生产、水利用效率和营养方面的互补性也在增加。为了验证这些假设，我们将分析近150棵树的茎盘，以确定生物量增量，元素浓度，以及个别树木年轮中的C和O同位素。对于这些树木，这源于实验地块与1，2，3，或5个树种，我们将确定在正常或潮湿和干燥的年份，木材生物量生产，水分利用和树木的营养的邻域多样性的影响。这将是第一项研究，评估这些响应变量的组合，在每年的决议，并在一个相对较长的时间段（16年）在热带树木。建议分析中期树木多样性的影响，在潮湿和非常干燥的时期是特别相关的未来人工林的背景下，预计气候变化。这项研究的结果将表明，混交林是否能够生产出养分和水成本较低、干旱风险较低的木材。

Owing to past deforestation and ecosystem degradation there is a large need and potential for afforestation in tropical and subtropical regions. Mixed-species plantations offer an opportunity to establish forests that may be more productive and offer ecosystem services at a higher level compared to monocultures. However, whether diverse tree plantations are in fact more resilient to droughts and whether they use nutrients and water more efficiently than monocultures has not been sufficiently studied, in particular not in tropical regions. Here we intend to use the unique opportunity to analyse the recently harvested “Sardinilla” tree diversity experiment in Panama, with 16 years the oldest one of its kind. The overall objective of the proposed project is to determine whether there is a stabilizing effect of tree neighbourhood diversity, the scale at which tree-tree interactions occur, on the productivity and resource use dynamics (water and nutrients) of trees over time. Specifically we hypothesize that: a) complementarity of productivity and resource use increases with increasing diversity (species, structural, functional) of tree neighbourhoods and over time, b) the temporal variation in productivity and resource use declines and stability increases with diversity, c) structural diversity and species richness independently and directly affect the productivity and resource use of individual trees, and d) during drought periods, complementarity regarding woody biomass production, water-use efficiency, and nutrition increases with increasing diversity. To test these hypotheses, we will analyse stem discs from almost 150 trees to determine the biomass increment, element concentrations, and C and O isotopes in individual tree growth rings. For these trees, which originate from experimental plots with 1, 2, 3, or 5 tree species, we will determine the influence of neigbourhood diversity on wood biomass production, water use and nutrition of trees during normal or wet and dry years. This will be the first study that assesses these response variables in combination, at an annual resolution, and over a relatively long time period (16 years) in tropical trees. The proposed analyses of me-dium-term tree diversity effects during wet and very dry periods is particularly relevant for future plantations against the background of projected climate change. Results from this study will indicate whether mixed tree plantations can produce wood with lower nutrient and water costs and at lower risks with regard to droughts.