Data from: Effects of harvesting of increasing intensities on genetic diversity and population structure of white spruce

Forest harvesting of increasing intensities is expected to have intensifying impacts on the genetic diversity and population structure of postharvest naturally regenerated stands by affecting the magnitude of evolutionary processes, such as genetic drift, gene flow, mating system, and selection. We have tested this hypothesis for the first time by employing widely distributed boreal white spruce (Picea glauca) as a model and controlled, replicated experimental harvesting and regeneration experiment at the EMEND project site (http://www.emendproject.org). We used two approaches. First, genetic diversity and population structure of postharvest natural regeneration after five harvesting treatments (green tree retention of 75%, 50%, 20%, and 10%, and clearcut) were assessed and compared with those of the unharvested control (pristine preharvest old-growth) in two replicates each of conifer-dominated (CD) and mixed-wood (MW) forest, using 10 (six EST (expressed sequence tag) and four genomic) microsatellite markers. Second, genetic diversity and population structure of preharvest old-growth were compared with those of postharvest natural regeneration after five harvesting treatments in the same treatment blocks in one replicate each of CD and MW forests. Contrary to our expectations, genetic diversity, inbreeding levels, and population genetic structure were similar between unharvested control or preharvest old-growth and postharvest natural regeneration after five harvesting treatments, with clearcut showing no negative genetic impacts. The potential effects of genetic drift and inbreeding resulting from harvesting bottlenecks were counterbalanced by predominantly outcrossing mating system and high gene flow from the residual and/or surrounding white spruce. CD and MW forests responded similarly to harvesting of increasing intensities. Simulated data for 10, 50, and 100 microsatellite markers showed the same results as obtained empirically from 10 microsatellite markers. Similar patterns of genetic diversity and population structure were observed for EST and genomic microsatellites. In conclusion, harvesting of increasing intensities did not show any significant negative impact on genetic diversity, population structure, and evolutionary potential of white spruce in CD and MW forests. Our first of its kind of study addresses the broad central forest management question how forest harvesting and regeneration practices can best maintain genetic biodiversity and ecosystem integrity.

随着采伐强度不断提升，森林采伐（forest harvesting）对采伐后天然更新林分（naturally regenerated stands）的遗传多样性（genetic diversity）与种群结构（population structure）的影响预计将持续加剧，该影响通过调控遗传漂变（genetic drift）、基因流（gene flow）、交配系统（mating system）与选择（selection）等进化过程的作用强度而实现。本研究首次以广泛分布的北方白云杉（Picea glauca）为模式物种，依托EMEND项目站点（http://www.emendproject.org）的控制性重复采伐与更新实验平台，对该假说开展验证。本研究采用两种研究方案：其一，在针叶林主导（conifer-dominated, CD）与混交林（mixed-wood, MW）各设置两个重复样地，采用10个微卫星标记（microsatellite markers，含6个表达序列标签（expressed sequence tag, EST）标记与4个基因组微卫星标记），对5种采伐处理（活立木保留率分别为75%、50%、20%、10%，以及皆伐（clearcut））后的天然更新林分的遗传多样性与种群结构进行评估，并与未采伐对照（unharvested control，即原始采伐前老龄林（old-growth））开展对比；其二，在针叶林主导与混交林各一个重复样地的同一处理区块内，比较采伐前原始老龄林与5种采伐处理后天然更新林分的遗传多样性与种群结构。与本研究的初始预期相悖，未采伐对照或采伐前原始老龄林，与5种采伐处理后的天然更新林分之间的遗传多样性、近交水平（inbreeding levels）与种群遗传结构均无显著差异，皆伐未表现出任何负面遗传影响。采伐瓶颈（genetic bottlenecks）引发的遗传漂变与近交潜在效应，被以异交为主的交配系统（outcrossing mating system）以及来自残留和/或周边白云杉的高基因流所抵消。针叶林主导与混交林对不同强度采伐的响应模式相似。针对10、50与100个微卫星标记的模拟数据（simulated data）所得结果，与基于10个微卫星标记的实证研究结果一致。表达序列标签与基因组微卫星标记也呈现出相似的遗传多样性与种群结构模式。综上，在针叶林主导与混交林生态系统中，采伐强度的提升并未对白云杉的遗传多样性、种群结构以及进化潜力产生显著负面影响。这项同类首创的研究回应了森林管理领域的核心共性问题：森林采伐与更新实践应如何最优地维持遗传生物多样性（genetic biodiversity）与生态系统完整性（ecosystem integrity）。