Tropical forests are globally important for biodiversity conservation and climate change mitigation but are being converted to other land uses. Conversion of seasonally dry tropical forests (SDTF) is particularly high while their protection is low. Secondary succession allows forests to recover their structure, diversity and composition after conversion and subsequent abandonment and is influenced by demographic rates of the constituent species. However, how these rates vary between seasons for different plant sizes at different successional stages in SDTF is not known. The effect of seasonal drought may be more severe early in succession, when temperature and radiation are high, while competition and density-dependent processes may be more important at later stages, when vegetation is tall and dense. Besides, the effects of seasonality and successional stage may vary with plant size. Large plants can better compete with small plants for limiting resources and may also have a greater capacity to withstand stress. We asked how size-dependent density, species density, recruitment and mortality varied between seasons and successional stages in a SDTF. We monitored a chronosequence in Yucatan, Mexico, over six years in three 0.1 ha plots in each of three successional stages: early (3–5 years-old), intermediate (18–20 years-old) and advanced (>50 years-old). Recruitment, mortality and species gain and loss rates were calculated from wet and dry season censuses separately for large (diameter > 5 cm) and small (1–5 cm in diameter) plants. We used linear mixed-effects models to assess the effects of successional stage, seasonality and their changes through time on demographic rates and on plant and species density. Seasonality affected demographic rates and density of large plants, which exhibited high wet-season recruitment and species gain rates at the early stage and high wet-season mortality at the intermediate stage, resulting in an increase in plant and species density early in succession followed by a subsequent stabilization. Small plant density decreased steadily after only 5 years of land abandonment, whereas species density increased with successional stage. A decline in species dominance may be responsible for these contrasting patterns. Seasonality, successional stage and their changes through time had a stronger influence on large plants, likely because of large among-plot variation of small plants. Notwithstanding the short duration of our study, our results suggest that climate-change driven decreases in rainy season precipitation may have an influence on successional dynamics in our study forest as strong as, or even stronger than, prolonged or severe droughts during the dry season.

中文翻译：

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热带干旱森林中大小依赖植物人口率的季节性和演替动态

热带森林对于生物多样性保护和减缓气候变化具有全球重要意义，但正在转变为其他土地用途。季节性干燥热带森林 (SDTF) 的转化率特别高，而它们的保护率很低。次生演替允许森林在转换和随后的废弃后恢复其结构、多样性和组成，并受组成物种人口比例的影响。然而，对于 SDTF 中不同演替阶段的不同植物大小，这些比率如何在季节之间变化尚不清楚。季节性干旱的影响在连续早期可能更严重，当温度和辐射高时，而竞争和密度依赖过程可能在后期更重要，当植被高大茂密时。除了，季节性和演替阶段的影响可能因植物大小而异。大型植物可以更好地与小型植物竞争限制资源，也可能具有更大的承受压力的能力。我们询问了 SDTF 中不同季节和演替阶段的大小依赖性密度、物种密度、补充和死亡率如何变化。我们在墨西哥尤卡坦半岛的三个 0.1 公顷地块中监测了 6 年多时间序列的三个演替阶段：早期（3-5 岁）、中期（18-20 岁）和晚期（> 50 岁-老的）。对于大型（直径 > 5 厘米）和小型（直径 1-5 厘米）植物，通过湿季和旱季普查分别计算补充、死亡率和物种增加和损失率。我们使用线性混合效应模型来评估演替阶段的影响，季节性及其随时间在人口率和植物和物种密度方面的变化。季节性影响大型植物的人口率和密度，表现为早期湿季补充率和物种增加率高，中期湿季死亡率高，导致植物和物种密度相继增加，随后随后的稳定。小植物密度在仅仅 5 年的土地废弃后稳步下降，而物种密度随着演替阶段而增加。物种优势的下降可能是造成这些对比模式的原因。季节性、演替阶段及其随时间的变化对大型植物有更大的影响，可能是因为小型植物的地块间变异较大。尽管我们的研究时间很短，