Department of Biology, University of Missouri-St. Louis, St. Louis, Missouri, United States of America.
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, United States of America.
PLoS One. 2019 Nov 11;14(11):e0224896. doi: 10.1371/journal.pone.0224896. eCollection 2019.
Large trees, here defined as ≥60 cm trunk diameter, are the most massive organisms in tropical rain forest, and are important in forest structure, dynamics and carbon cycling. The status of large trees in tropical forest is unclear, with both increasing and decreasing trends reported. We sampled across an old-growth tropical rain forest landscape at the La Selva Biological Station in Costa Rica to study the distribution and performance of large trees and their contribution to forest structure and dynamics. We censused all large trees in 238 0.50 ha plots, and also identified and measured all stems ≥10 cm diameter in 18 0.50 ha plots annually for 20 years (1997-2017). We assessed abundance, species diversity, and crown conditions of large trees in relation to soil type and topography, measured the contribution of large trees to stand structure, productivity, and dynamics, and analyzed the decadal population trends of large trees. Large trees accounted for 2.5% of stems and ~25% of mean basal area and Estimated Above-Ground Biomass, and produced ~10% of the estimated wood production. Crown exposure increased with stem diameter but predictability was low. Large tree density was about twice as high on more-fertile flat sites compared to less fertile sites on slopes and plateaus. Density of large trees increased 27% over the study interval, but the increase was restricted to the flat more-fertile sites. Mortality and recruitment differed between large trees and smaller stems, and strongly suggested that large tree density was affected by past climatic disturbances such as large El Niño events. Our results generally do not support the hypothesis of increasing biomass and turnover rates in tropical forest. We suggest that additional landscape-scale studies of large trees are needed to determine the generality of disturbance legacies in tropical forest study sites.
大树（这里定义为树干直径≥60 厘米）是热带雨林中最庞大的生物，对森林结构、动态和碳循环具有重要意义。热带森林中大树木的现状尚不清楚，有报道称其数量在增加，也有报道称其数量在减少。我们在哥斯达黎加的拉塞尔瓦生物站的一个古老热带雨林景观中进行了抽样调查，以研究大树的分布和表现及其对森林结构和动态的贡献。我们对 238 个 0.50 公顷的样地中的所有大树进行了普查，并在 18 个 0.50 公顷的样地中每年对直径≥10 厘米的所有茎干进行识别和测量，时间跨度为 20 年（1997-2017 年）。我们评估了大树的丰富度、物种多样性和树冠状况与土壤类型和地形的关系，测量了大树对林分结构、生产力和动态的贡献，并分析了大树的十年期种群趋势。大树占茎干的 2.5%，约占平均基部面积和估计地上生物量的 25%，并产生了约 10%的估计木材产量。树冠暴露度随茎干直径的增加而增加，但可预测性较低。与斜坡和平原上较贫瘠的地方相比，大树在较肥沃的平坦地的密度约高出一倍。在研究期间，大树的密度增加了 27%，但这种增加仅限于较肥沃的平坦地。大树和较小茎干的死亡率和繁殖率不同，这强烈表明大树的密度受到过去气候干扰的影响，如大的厄尔尼诺事件。我们的研究结果一般不支持热带雨林生物量和周转率增加的假说。我们建议需要进行更多的景观尺度的大树研究，以确定在热带森林研究地点中干扰遗产的普遍性。
