Effects of Management Intervention on Post-Disturbance Community Composition: An Experimental Analysis Using Bayesian Hierarchical Models

As human demand for ecosystem products increases, management intervention may become more frequent after environmental disturbances. Evaluations of ecological responses to cumulative effects of management interventions and natural disturbances provide critical decision-support tools for managers who strive to balance environmental conservation and economic development. We conducted an experiment to evaluate the effects of salvage logging on avian community composition in lodgepole pine (Pinus contorta) forests affected by beetle outbreaks in Oregon, USA, 1996–1998. Treatments consisted of the removal of lodgepole pine snags only, and live trees were not harvested. We used a Bayesian hierarchical model to quantify occupancy dynamics for 27 breeding species, while accounting for variation in the detection process. We examined how magnitude and precision of treatment effects varied when incorporating prior information from a separate intervention study that occurred in a similar ecological system. Regardless of which prior we evaluated, we found no evidence that the harvest treatment had a negative impact on species richness, with an estimated average of 0.2–2.2 more species in harvested stands than unharvested stands. Estimated average similarity between control and treatment stands ranged from 0.82–0.87 (1 indicating complete similarity between a pair of stands) and suggested that treatment stands did not contain novel assemblies of species responding to the harvesting prescription. Estimated treatment effects were positive for twenty-four (90%) of the species, although the credible intervals contained 0 in all cases. These results suggest that, unlike most post-fire salvage logging prescriptions, selective harvesting after beetle outbreaks may meet multiple management objectives, including the maintenance of avian community richness comparable to what is found in unharvested stands. Our results provide managers with prescription alternatives to respond to severe beetle outbreaks that continue to occur across extensive portions of the dry forests of western North America.

随着人类对生态系统产品的需求持续攀升，环境扰动后开展管理干预的频次或将进一步提升。评估管理干预与自然扰动的累积效应对生态系统的影响，可为致力于统筹生态保护与经济发展的管理者提供关键决策支持工具。我们于1996年至1998年在美国俄勒冈州开展实验，评估抢救性采伐（salvage logging）对受甲虫虫害暴发侵扰的扭叶松（Pinus contorta）林鸟类群落组成的影响。本次实验的处理组仅移除扭叶松枯立木，未采伐活立木。我们采用贝叶斯分层模型（Bayesian hierarchical model）量化了27种繁殖鸟类的栖息动态，并纳入监测过程中的变异因素。同时，我们探究了当纳入来自相似生态系统中另一项干预研究的先验信息时，处理效应的幅度与精度会发生何种变化。无论采用何种先验信息，均未发现采伐处理对物种丰富度产生负面影响的证据；采伐林分的物种丰富度估计值较未采伐林分平均高出0.2至2.2种。对照组林分与处理组林分的平均相似性估计值介于0.82至0.87之间（数值1代表一对林分完全相似），这表明处理组林分并未出现因采伐措施而形成的全新物种组合。24种（占比90%）鸟类的处理效应估计值为正，但所有情况下的可信区间均包含0值。本研究结果表明，与多数火灾后抢救性采伐方案不同，甲虫虫害后的选择性采伐或可兼顾多项管理目标，包括维持与未采伐林分相当的鸟类群落丰富度。针对北美西部干旱森林广泛持续发生的严重甲虫虫害，本研究结果可为管理者提供可供选择的应对方案。