Data from: Ten-year responses of ground-dwelling spiders to retention harvest in the boreal forest

The Ecosystem Management Emulating Natural Disturbances (EMEND) project tests the hypothesis that varying levels of green tree retention maintain and retain forest biodiversity better than conventional clear-cutting. We studied epigaeic spiders to assess biodiversity changes two, five and ten years following a range of partial retention harvests (clear-cut, 10-75% retention) and unharvested controls in four boreal mixedwood cover-types. A total of 56, 371 adult spiders representing 220 species was collected using pitfall traps. Lasting effects on forest structure were proportional to harvest intensity. These changes strongly influenced spider richness, abundance and species composition, as well as assemblage recovery. Distinctive assemblages were associated with disturbance level, especially with partial harvests (≤50% retention), and these were dominated by open-habitat species even ten years after harvest. Assemblages were more similar to those of controls in the highest (75%) retention treatment, but significant recovery toward the structure of pre-disturbance assemblages was not detected for any prescription in any cover-type. Although early responses to retention harvest suggested positive effects on spider assemblages, these are better explained as lag effects after harvest because assemblages were less similar to those of unharvested controls five years post-harvest, and only minor recovery was observed ten years following harvest. Retention of forest biodiversity decreased over time, especially in conifer stands and the lower (10-50%) retention treatments. Overall, retention harvests retained biodiversity and promoted landscape heterogeneity somewhat better than clear-cutting; however, there was a clear gradient of response and no retention ‘threshold’ for conservation can be recommended on the basis of our data. Furthermore, results suggest that retention harvest prescriptions should be adjusted for cover-type. We show that low retention ameliorated impacts in broadleaved forests characteristic of earlier stages in mixedwood succession, but only higher retention was associated with less impact in successionally older conifer forests. Although these short-term responses (10 years) of spider assemblages support use of retention harvests, understanding the true conservation merit of these practices, relative to conventional approaches, requires evaluation over longer time scales, with work more focused on recovery of biodiversity than on its preservation after harvest.模拟自然干扰生态系统管理（Ecosystem Management Emulating Natural Disturbances, EMEND）项目旨在验证以下假说：相较于传统皆伐作业，不同程度的保留木留存管理更能维持并保护森林生物多样性。本研究针对地表蜘蛛展开调查，以评估在四种北方混交林林分类型中，实施一系列部分保留木采伐作业（包括皆伐、10%~75%留存率处理）及未采伐对照样地后，第2、5、10年的生物多样性变化情况。研究团队采用陷阱法共采集到56371头成年蜘蛛，隶属于220个物种。森林结构所受的长期影响与采伐强度呈正相关，这些结构变化显著影响了蜘蛛的物种丰富度、种群数量、物种组成以及类群恢复进程。独特的蜘蛛类群与干扰程度密切相关，尤其是在部分采伐（留存率≤50%）的样地中，即便在采伐后10年，这类样地的蜘蛛类群仍以开阔生境物种为优势类群。留存率最高（75%）的处理样地的蜘蛛类群与未采伐对照样地更为相似，但在所有林分类型中，未检测到任何一种采伐方案能使类群结构恢复至采伐前水平。尽管部分保留木采伐的早期响应显示其对蜘蛛类群存在积极影响，但这一结果更应被解释为采伐后的滞后效应：因为在采伐后5年，样地蜘蛛类群与未采伐对照样地的相似度反而更低，且在采伐后10年仅观察到极轻微的类群恢复。森林生物多样性的留存水平随时间推移逐渐下降，尤其在针叶林林分以及10%~50%低留存率处理样地中更为明显。总体而言，保留木采伐在生物多样性留存与景观异质性提升方面均优于皆伐作业；但本研究结果显示物种响应存在清晰的梯度变化，基于我们的数据，无法推荐适用于保护的留存率阈值。此外，研究结果表明，采伐方案应根据林分类型进行调整。研究发现，低留存率处理可缓解混交林演替早期阶段典型阔叶林所受的干扰影响，但仅高留存率处理能降低演替后期针叶林所受的干扰程度。尽管蜘蛛类群的这一短期（10年）响应支持保留木采伐的应用，但相较于传统采伐方式，要明确这类实践真正的保护价值，还需要更长时间尺度的评估，且未来研究应更侧重于生物多样性的恢复，而非采伐后的单纯留存。