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.

模拟自然干扰的生态系统管理（Ecosystem Management Emulating Natural Disturbances，简称EMEND）项目旨在检验如下科学假说：相较于传统皆伐，不同强度的活立木保留（green tree retention）方案能更有效地维持并保护森林生物多样性。本研究以地表蜘蛛（epigaeic spiders）为研究对象，针对4类北方混交林林分类型，在实施一系列部分保留采伐（涵盖皆伐、10%~75%保留率采伐）及未采伐对照处理后，分别于第2、5、10年评估其生物多样性变化。研究采用陷阱诱捕法（pitfall traps）共采集到56371只成年蜘蛛，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比关系，此类结构变化显著影响了蜘蛛的物种丰富度、个体多度及物种组成，同时也对蜘蛛类群组合的恢复过程产生作用。不同干扰强度对应特征鲜明的蜘蛛类群组合，尤其是保留率≤50%的部分采伐处理组，即便在采伐后10年，该类组合仍以开阔生境物种为优势类群。保留率最高（75%）的处理组，其蜘蛛类群组合与未采伐对照更为相似，但本研究未在任意林分类型的任一采伐方案中，检测到类群组合向采伐前结构的显著恢复。

尽管采伐后早期的类群响应显示保留采伐对蜘蛛类群具有积极作用，但这一结果更应被解释为采伐后的滞后效应：采伐后第5年，类群组合与未采伐对照的相似度反而降低，且在采伐后第10年仅观察到极轻微的恢复。森林生物多样性的留存水平随时间推移逐渐下降，尤其在针叶林林分及保留率较低（10%~50%）的处理组中更为显著。

总体而言，相较于皆伐，保留采伐在一定程度上更能留存生物多样性并提升景观异质性；但物种响应存在清晰的梯度特征，基于本研究数据，无法推荐适用于生物多样性保护的保留率“阈值”。此外，研究结果表明，采伐方案应根据林分类型进行针对性调整。本研究显示，低保留率采伐可缓解混交林演替早期典型阔叶林所受的干扰影响，而仅高保留率采伐才能在演替后期的针叶林林分中减轻干扰效应。

尽管蜘蛛类群的短期（10年）响应支持保留采伐的应用，但相较于传统采伐方式，要明确这类实践的真实保护价值，还需要更长时间尺度的评估，且未来研究应更聚焦于生物多样性的恢复而非采伐后的单纯留存。