Pasture trees contribute to structural heterogeneity and plant distributions in post-agricultural forests decades after canopy closure

Questions: Open-grown shade trees retained in pastures are legacies of agricultural history that influence recolonization dynamics and create structural heterogeneity in post-agricultural forests. This work addresses the long-term influence of pasture trees on forest structure and composition. I ask: Do signs of successional nucleation in microhabitat, structure and composition near pasture trees persist decades after canopy closure? If so, does variation primarily reflect seed deposition or environmental facilitation?

Location: Southeastern Ohio, USA

Methods: Thirteen open-grown trees greater than 70 cm in diameter in second-growth forests 40-90 years old were selected as study sites. Trees, saplings, herbs, and environmental variables were sampled and compared at three positions around each tree: under the canopy, at the dripline, and in the forest matrix.

Results: Soil pH was lower and coarse woody debris most abundant under pasture tree canopies. Stems >10 cm in diameter...

研究问题：牧场上留存的开阔遮荫树木是农业历史的遗留物，它们会影响退耕后森林的群落重建动态，并造就其结构异质性。本研究聚焦于牧场遗留树木对森林结构与物种组成的长期影响。本研究提出的问题为：牧场树木周边的微生境、结构与物种组成中是否存在演替成核的痕迹，且该痕迹能在林冠郁闭数十年后依然留存？若确实留存，那么这种差异主要源于种子沉积还是环境促进作用？
研究地点：美国俄亥俄州东南部
研究方法：选取13株胸径大于70厘米的开阔生长树木作为研究样点，这些树木位于40~90年生的次生林中。在每株树木周边的三个位置——林冠下方、林冠滴水线处以及森林基质中，分别对乔木、幼树、草本植物以及环境变量进行采样与对比分析。
研究结果：牧场树木林冠下方的土壤pH值更低，且粗木质残体储量最为丰富。胸径大于10厘米的茎干……