Abstract
Changes in the light availability in forests generated by diversified retention patterns (e.g., clear cut, partial harvest) have been shown to strongly filter the plant species present. Modified soil microsite conditions due to post-harvest site preparation (e.g., mechanical site preparation, prescribed fire) might also be an important determinant of plant diversity. The objective here was to detect how retention pattern and post-harvest site preparation act as filters that explain the understory functional diversity in boreal forests. We also assessed whether these effects were dependent on forest attributes (stand type, time since fire, and time since harvest). We retrieved data from seven different studies within 101 sites in boreal forests in Eastern Canada. Our data included forests harvested with two retention patterns: careful logging and clear cut, plus unharvested control forests. Three post-harvest site preparation techniques were applied: plow or disk trenching after careful logging, and prescribed fire after clear cut. We collected trait data (10 traits) representing plant morphology, regeneration strategy, or resource utilization for common species. Our results demonstrated significant variation in functional diversity after harvest. The combined effect of retention pattern and site preparation was the most important factor explaining understory diversity compared to retention pattern only and forest attributes. According to RLQ analysis, harvested forests with site preparation favored traits reflecting resistance or resilience ability after disturbance (clonal guerilla species, geophytes, and species with higher seed weight). Yet harvested forests without site preparation mainly affected understory plant species via their light requirements. Forest attributes did not play significant roles in affecting the relationship between site preparation and functional diversity or traits. Our results indicated the importance of the compounding effects of light variation and soil disturbance in filtering understory diversity and composition in boreal forests. Whether these results are also valid for other ecosystems still needs to be demonstrated.
Highlights
Forest management practices induce long-lasting changes in the distribution of stand types in forested landscapes and the distribution of biota within them [1]
We modeled the responses of the three functional diversity indices (FRic, Functional evenness (FEve), and functional divergence (FDiv)) and community-weighted mean to variables that related to the retention pattern and its combined effect with post-harvest site preparation, as well as to variables related to forest attributes: stand type, time since fire, or time since harvest
The results showed that clear cut only (CCOL) and careful logging only (CLOL) forests were favored by midshade2019, tolerant species, and unharvested forests were favored by mega and meso phanerophyte12and
Summary
Forest management practices induce long-lasting changes in the distribution of stand types in forested landscapes and the distribution of biota within them [1]. Soil protection, and tree regeneration led to the development of alternative retention patterns (e.g. partial harvesting, careful logging, continuous-cover forestry) that have less conspicuous effects on forest ecosystems than clear cuts [5,6,7,8]. Retention forestry is defined as an approach to forest management based on the long-term retention of structures and organisms, such as live and dead trees and small areas of intact forest, at the time of harvest [8]. The variation in understory light availability, generated by different retention patterns in a region, has been shown to be a dominant filter affecting post-harvest understory plant composition and diversity [9,10,11,12]
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