Data from: Soil-mediated filtering organizes tree assemblages in regenerating tropical forests

1.Secondary forests are increasingly dominant in human-modified tropical landscapes, but the drivers of forest recovery remain poorly understood. Soil conditions influence plant community composition, and are expected to change over a gradient of succession. However, the role of soil conditions as an environmental filter driving community assembly during forest succession has rarely been explicitly assessed.

2.We evaluated the role of stand basal area and soil conditions on community assembly and its consequences for community functional properties along a chronosequence of Atlantic forest regeneration following sugar cane cultivation. Specifically, we tested whether community functional properties are related to stand basal area, soil fertility and soil moisture. Our expectations were that edaphic environmental filters play an increasingly important role along secondary succession by increasing functional trait convergence towards more conservative attributes.

3.We sampled soil and woody vegetation features across 15 second-growth (3-30 years) and 11 old-growth forest plots (300 m² each). We recorded tree functional traits related to resource-use strategies (specific leaf area, SLA; leaf dry matter content, LDMC; leaf area, LA; leaf thickness, LT; and leaf succulence, LS) and calculated community functional properties using the community-weighted mean (CWM) of each trait and the functional dispersion (FDis) of each trait separately and all traits together.

4.With exception of LA, all leaf traits were strongly associated with stand basal area; LDMC and SLA increased, while LT and LS decreased with forest development. Such changes in LDMC, LT and LS were also related to the decrease in soil nutrient availability and pH along succession, while soil moisture was weakly related to community functional properties. Considering all traits, as well as leaf thickness and succulence separately, FDis strongly decreased with increasing basal area and decreasing soil fertility along forest succession, presenting the lowest values in old-growth forests.

5.Synthesis. Our findings suggest that tropical forest regeneration may be a deterministic process shaped by soil conditions. Soil fertility operates as a key filter causing functional convergence towards more conservative resource-use strategies, such as leaves with higher leaf dry mass content.

1. 次生林在受人类活动改造的热带景观中日益占据主导地位，但森林恢复的驱动机制仍未得到充分阐明。土壤状况会影响植物群落组成，并预计会沿演替梯度发生变化。然而，土壤状况作为环境过滤因子在森林演替过程中驱动群落构建的作用，却鲜有明确的评估。
2. 我们针对甘蔗种植后大西洋森林次生演替的时间序列样地，评估了林分断面积与土壤状况对群落构建及其群落功能属性的影响。具体而言，我们检验了群落功能属性是否与林分断面积、土壤肥力及土壤湿度相关。我们的假设为：沿次生演替梯度，土壤环境过滤因子的作用会逐渐增强，促使功能性状向更保守的资源利用策略趋同。
3. 我们在15个次生林样地（林龄3-30年）与11个原始林样地中采集土壤与木本植被数据，每个样地面积为300平方米。我们记录了与资源利用策略相关的树木功能性状：比叶面积（specific leaf area, SLA）、叶干物质含量（leaf dry matter content, LDMC）、叶面积（leaf area, LA）、叶厚度（leaf thickness, LT）以及叶肉质性（leaf succulence, LS）；并分别基于单个性状以及所有性状的组合，计算了群落加权平均（community-weighted mean, CWM）与功能离散度（functional dispersion, FDis）。
4. 除叶面积外，所有叶功能性状均与林分断面积显著相关；随着森林发育，叶干物质含量与比叶面积升高，而叶厚度与叶肉质性则降低。叶干物质含量、叶厚度与叶肉质性的上述变化，也与沿演替梯度土壤养分有效性与pH值的下降相关，而土壤湿度与群落功能属性的相关性则较弱。综合所有性状以及单独分析叶厚度与叶肉质性时，功能离散度均随林分断面积增大与土壤肥力下降而显著降低，在原始林样地中达到最低值。
5. 研究总结。我们的研究结果表明，热带森林恢复可能是由土壤条件主导的确定性过程。土壤肥力作为关键的环境过滤因子，驱动功能性状向更保守的资源利用策略趋同，例如拥有更高叶干物质含量的叶片。