Data from: Topsoil removal through scarification improves natural regeneration in high-graded Nothofagus old-growth forests

1.High grading by removing the majority of trees with superior timber quality has led to loss of productivity and biodiversity in forests. Typically, after high grading, little attention is given to tree regeneration. Thus, undesirable understory vegetation often dominates for a long time, leading to stagnation in forest recovery and so-called arrested succession. In such settings, managing understory vegetation using topsoil removal through scarification has been proposed as a restoration tool to encourage tree regeneration. 2.We investigated the effectiveness of topsoil removal as a restoration technique in high-graded Nothofagus old-growth forests in the Chilean Andes. In these forests, high grading often leads to understories being dominated by dense thickets of native bamboo, Chusquea culeou. These understory conditions typically delay succession by preventing tree regeneration. 3.T-tests were used to compare vegetation development in areas with topsoil removal against those without. Non-parametric multiplicative regression (NPMR) was used to investigate which environmental variables were mainly related to regeneration of different plant groups (short and long-lived early and late-seral tree species) and C. culeou abundance in areas with and without topsoil removal. 4.Topsoil removal improved the regeneration of early-seral tree species and constrained C. culeou. In areas without topsoil scarification, higher abundances of C. culeou were reflected in a higher transmitted radiation and litter cover. In these areas, the presence of early-seral tree species was related to higher soil water content and transmitted radiation. However, topsoil removal altered these response patterns for early-seral trees. For instance, the interaction between higher soil water content and more exposed mineral soil was reflected in a higher likelihood of finding early-seral tree seedlings. 5.Synthesis and applications. Topsoil removal was a successful restoration tool for overcoming arrested succession in Nothofagus old-growth forests in the Chilean Andes by encouraging the regeneration of early-seral trees in high-graded forests. Contrasting environmental conditions of pre- and post-topsoil removal allowed insights into the processes and mechanisms responsible for forests with arrested succession and for succession progression. This understanding provides guidance regarding the range of conditions under which topsoil removal can be used as a successful restoration practice.1. 优材择伐（high grading）——即伐除绝大多数优质用材林木的森林经营方式——已造成森林生产力与生物多样性的显著丧失。通常在优材择伐作业完成后，人们对林木更新的关注极少，导致不良林下植被往往长期占据群落优势位，进而引发森林恢复停滞，即所谓的演替停滞（arrested succession）。针对此类林分，已有研究提出采用松土整地移除表层土壤的方式管控林下植被，将其作为促进林木更新的修复手段。 2. 本研究针对智利安第斯山脉中经优材择伐的南山毛榉（Nothofagus）原始老龄林，探究了表层土壤移除作为修复技术的实际效果。此类林分经优材择伐后，林下植被往往以密集丛生的本土竹类——库斯奎竹（Chusquea culeou）为绝对优势种；这类林下生境会通过阻碍林木更新，显著延缓森林演替进程。 3. 本研究采用t检验（T-tests）对比了实施表层土壤移除与未实施该措施样地的植被发育差异；同时采用非参数乘性回归（Non-parametric multiplicative regression, NPMR），解析了在实施与未实施表层土壤移除的样地中，哪些环境变量主要与不同植物类群（短寿与长寿的早期演替、晚期演替树种）的更新以及库斯奎竹的种群丰度相关。 4. 研究结果表明，表层土壤移除可有效促进早期演替树种的更新，并抑制库斯奎竹的种群扩张。在未进行土壤松土整地的对照样地中，库斯奎竹的丰度越高，对应的透射辐射与枯落物覆盖度也越高；在此类样地中，早期演替树种的出现与更高的土壤含水量及透射辐射呈显著正相关。然而，表层土壤移除彻底改变了早期演替树种的这类环境响应模式：例如，较高的土壤含水量与更裸露的矿质土壤之间的交互作用，可显著提升早期演替树种幼苗的出现概率。 5. 综合与应用：表层土壤移除是一项成功的修复手段，可通过促进智利安第斯山脉中经优材择伐的南山毛榉原始老龄林内早期演替树种的更新，有效克服演替停滞问题。表层土壤移除前后截然不同的环境条件，为解析演替停滞林分与演替推进林分的形成过程与内在机制提供了关键契机。该研究结果可为表层土壤移除作为有效修复实践的适用条件范围提供科学指导依据。