Biomass harvests in boreal forests: minimizing environmental impacts and maximizing benefits

生物燃料的生物质收获已经成为加拿大林业经济的一项重要活动。然而，生物质收获和森林更新如何才能最好地维持和支持生物多样性和生态系统功能，同时保持现场生产力和促进林分更新，目前仍不确定。此外，缺乏可用来衡量不同管理战略对生物多样性和生态系统功能的影响的环境成本和收益的工具。我们将以中部北方森林为重点，探讨与传统的只收获树干和野火相比，生物质收获如何影响立地生产力、生物量生产、碳储存、土壤温室气体通量、林分反照率和生物多样性；并将研究经济和生态目标之间的权衡。我们将检验如下假设：(1)与替代方案相比，生物量采集可能损害场地生产力、林分更新、生物量生产、碳储存、土壤温室气体通量和生物多样性；(2)干扰后促进恢复植被的森林更新可以减轻生物量采集的潜在负面影响，或者，如果不更新森林，负面影响可能加剧；(3)生态系统可能对土地利用集约化表现出非线性反应，从而在作业层面上可能确定生态损失有限或没有生态损失的管理方案，这些方案仍然满足经济收益。重点抓好两种主要森林类型：粗、中沙质土壤上的马尾松生态系统和中部地区中质土壤上的白杨、云杉混交林。从机械上理解资源利用和营林处理与林分发展之间的相互作用，以及北方针叶林的经济效益、生态功能和生物多样性之间的权衡，将使我们能够为林业部门提出建议，说明如何设计管理制度，使负面生态影响降至最低，同时保持立地生产力和促进林分更新。

Biomass harvesting for biofuels has become an important activity for Canada's forestry economy. However, it remains uncertain how biomass harvesting and forest renewal can best maintain and support biodiversity and ecosystem functions while maintaining site productivity and promoting stand regeneration. In addition, there is lack of tools that can be used to measure the environmental costs and benefits of different management strategies in terms of their impacts on biodiversity and ecosystem functions. Focusing on central boreal forests, we will address how biomass harvesting, compared with conventional stem-only harvesting and wildfire, affect site productivity, biomass production, and carbon storage, soil greenhouse gas fluxes, stand albedo, and biodiversity,; and will examine tradeoffs among economic and ecological objectives. We will test the hypotheses that: (i) biomass harvesting may compromise site productivity, stand regeneration, biomass production, carbon storage, soil GHG fluxes, and biodiversity in comparison with alternatives; (ii) forest renewal that promote revegetation after disturbance can mitigate the potentially negative effects of biomass harvesting, and alternatively, negative impacts may be compounded without forest renewal; (iii) ecosystems may show nonlinear responses to land-use intensification, and thus management options with limited or no ecological losses that still satisfy economic gains may be identified at the operational level. We will focus our efforts on two dominant forest types: jack pine ecosystems on coarse and medium sandy soils and mixedwoods of trembling aspen and spruce on mesic soils in the central region. A mechanistic understanding of the interactions between resource use and silvicultural treatments with stand development and the tradeoffs between economic benefits, ecological functions, and biodiversity in boreal forests will allow us to make recommendations for the forest sector on how to design management regimes that minimize negative ecological impacts while maintaining site productivity and promoting stand regeneration.