Data from: Effects of light and topography on regeneration and coexistence of evergreen and deciduous tree species in a Chinese subtropical forest

1. Evergreen broad-leaved forests are widely distributed in eastern Asia with evergreen (EBL) and deciduous (DBL) broad-leaved tree species coexisting under the same climatic regime, raising questions as to the underlying mechanisms. Since EBL and DBL species differ in leaf lifespan, a key component of resource economic strategies, their coexistence might be attributed to regeneration niche partitioning across habitats varying in resource supply.
2. We investigated the effects of variation in insolation and topography on regeneration of EBL and DBL species in a subtropical evergreen broad-leaved forest of eastern China after an ice storm that caused severe canopy disturbance.
3. Using a mixed-effects modeling framework and census data from 2011 to 2014 on 8548 wild seedlings of 123 species, we quantified habitat preferences of EBL and DBL species during post-disturbance regeneration and how their survival and height relative growth rates varied among habitats.
4. The relative density of DBL seedlings (proportional to all seedlings) was greater in habitats with greater (canopy gaps) compared to lesser (understory) insolation and increased with canopy gap size. However, DBL seedlings were not more frequent in higher (valleys) compared to lower (ridges) fertility habitats. Although DBL seedlings exhibited larger differences in growth between higher and lower resource habitats than EBL seedlings, their growth rates did not increase with canopy gap size. Seedlings of EBL species had high survival in all habitats, but larger DBL seedlings survived equally well on ridges. Consequently, the relative density of DBL seedlings declined in valleys, so that by 2014 it became more similar in valley and ridge habitats, whereas it remained higher in gaps than in the understory, and especially in larger gaps.
5. Synthesis. Specialization on contrasting topographic habitats is considered the primary mechanism mediating coexistence between DBL and EBL species. Our results, however, suggest this may not always be true, since seedlings of DBL and EBL species partitioned regeneration niches based on light more so than topography. We propose that coexistence of DBL and EBL species can strongly depend upon canopy disturbance to create a mosaic of habitat patches, including high light gaps favoring regeneration of DBL species.

1. 常绿阔叶林广泛分布于东亚地区，在同一气候条件下，常绿阔叶（Evergreen Broad-leaved, EBL）与落叶阔叶（Deciduous Broad-leaved, DBL）树种共存，这一现象引发了学界对其潜在共存机制的探讨。鉴于常绿阔叶与落叶阔叶树种在叶寿命（资源经济策略的核心组分之一）上存在显著差异，二者的共存或许可归因于资源供给各异的生境间的更新生态位分化。
2. 本研究针对中国东部一处经历过引发严重冠层干扰的冰风暴后的亚热带常绿阔叶林，探讨了光照与地形异质性对常绿阔叶与落叶阔叶树种更新过程的影响。
3. 本研究采用混合效应模型（mixed-effects modeling）框架，结合2011至2014年间对123个物种共8548株野生幼苗的普查数据，量化了干扰后常绿阔叶与落叶阔叶树种的生境偏好，以及二者的存活率和株高相对生长速率在不同生境间的差异。
4. 落叶阔叶树种幼苗的相对密度（以所有幼苗总数为基准）在光照更强的生境（林窗，canopy gaps）中显著高于光照较弱的生境（林下，understory），且随林窗面积增大而升高。然而，落叶阔叶树种幼苗在高肥力生境（山谷，valleys）中的出现频率并未显著高于低肥力生境（山脊，ridges）。尽管相较于常绿阔叶树种幼苗，落叶阔叶树种幼苗在高、低资源供给生境间的生长差异更为显著，但其生长速率并未随林窗面积增大而提升。常绿阔叶树种幼苗在所有生境中均保持较高的存活率，而较大株型的落叶阔叶树种幼苗在山脊生境中也可获得同等的存活概率。由此可见，落叶阔叶树种幼苗在山谷生境中的相对密度有所下降，至2014年，山谷与山脊生境中的落叶阔叶幼苗相对密度已较为接近；而林窗生境中的落叶阔叶幼苗相对密度仍高于林下生境，尤其在面积更大的林窗中优势更为明显。
5. 综合分析：以往研究认为，针对截然不同的地形生境的生态位特化，是介导常绿阔叶与落叶阔叶树种共存的核心机制。但本研究结果表明，这一结论并非普适——相较于地形因子，常绿阔叶与落叶阔叶树种幼苗的更新生态位分化更多地基于光照条件。本研究提出，常绿阔叶与落叶阔叶树种的共存，在很大程度上依赖于冠层干扰所形成的生境斑块镶嵌体，其中高光照林窗可促进落叶阔叶树种的更新过程。