Bryophyte abundance, diversity and composition after retention harvest in boreal mixedwood forest

Abstract

Variable‐retention harvest is widely recognized as an alternative to more intensive methods such as clear‐cutting. However, present information is inadequate to judge the impact of variable retention on biodiversity of indigenous forest organisms intolerant of canopy removal, such as forest‐inhabiting bryophytes. We examined how bryophyte species cover, richness, diversity and composition change with time in response to a broad range of dispersed retention harvest treatments (2% [clear‐cut], 10%, 20%, 50%, 75% retention of original basal area) contrasted with uncut controls [100% retention]) in broadleaf deciduous, mixedwood and conifer‐dominated boreal forests in North West Alberta, Canada. Bryophytes were studied in 432 permanent sample plots within 72 compartments before harvest and at 3, 6 and 11 years after harvest. Clear‐cut and lower (10% and 20%) retention levels resulted in lower cover and richness of bryophytes than in unharvested control compartments in mixed and conifer‐dominated forests, but less so in deciduous‐dominated forests, which generally supported low cover and richness. Species composition in each forest type varied along the gradient of harvesting intensity; clear‐cuts and lower levels of retention supported similar composition, as did control plots and those representing higher retention levels. Over time, the retention harvest treatments became more similar to uncut controls. Synthesis and applications. Variable‐retention harvests can better maintain bryophyte biodiversity in managed boreal mixedwood forests, as compared to clear‐cuts. We found the efficacy of retention harvest scaled with harvest intensity. Higher levels of retention better moderated the negative impacts of harvesting on bryophyte assemblages across all forest types. Our results suggest, however, that even 10% retention will facilitate faster post‐harvest recovery of bryophytes, as compared to clear‐cutting.

Bryophytes in fir waves: Forest canopy indicator species and functional diversity decline in canopy gaps

“…The extant gradients in temperature, substrate, and understory vegetation across fir waves triggered only relatively small changes in bryophyte community composition (i.e., species abundance) and functional metrics (and no changes in the total cover or depth of the bryophyte mat), suggesting that bryophyte communities at these high elevations are relatively resistant to the naturally occurring fir‐wave dynamics. Resistance of bryophyte communities has been reported also for some other temperate forest ecosystems experiencing natural gap dynamics (e.g., Baldwin & Bradfield, ; Promis et al., ), although bryophyte communities have been shown to be sensitive to larger‐scale disturbance (e.g., Dovčiak et al., ; Bartels, Macdonald, Johnson, Caners, & Spence, ). Bryophyte community resistance to natural disturbance in high‐elevation fir forests may be explained by relative constancy of moisture along the gap‐forest gradient as moisture stress can be one of the most limiting drivers of bryophyte abundance in montane forests (Wolf, ).…”

Recovery of a boreal ground‐beetle (Coleoptera: Carabidae) fauna 15 years after variable retention harvest

“…Short‐term impacts of retention harvests on forest biodiversity have been widely studied. We know, for example, that retention harvests can effectively maintain forest‐dependent plants and beetles in managed landscapes (Baker et al., 2016), and that retention patches serve as potential refugia for bryophytes and lichens (Bartels, Macdonald, Johnson, Caners, & Spence, 2018; Perhans et al., 2009). Harvest intensity also influences ground‐beetle populations and the structure of carabid assemblages in boreal mixedwood forests, with assemblage structure seeming to recover faster with increasing forest retention (Jacobs, Work, & Spence, 2008; Work et al., 2013).…”

“…Although any logging prescription can undoubtedly have significant and long‐lasting effects on biodiversity (Lindenmayer & Franklin, 2002), only a few studies have examined long‐term responses of biotic assemblages to retention harvest at particular sites (Baker et al., 2015; Bartels et al., 2018; Halpern, Halaj, Evans, & Dovciak, 2012; Pinzon, Spence, Langor, & Shorthouse, 2016; Roberts, D'Amato, Kern, & Palik, 2016). Since a central goal of retention harvest as a tactic under the modern ‘sustainable forest management’ approach (Baker et al., 2013; Lindenmayer, Margules, & Botkin, 2000) is to conserve and facilitate recovery of biodiversity to pre‐harvest conditions, long‐term studies are needed to evaluate the extent to which retention harvest meets these goals.…”

Terrestrial Bryophyte and Lichen Responses to Canopy Opening in Pine-Moss-Lichen Forests

“…Caners et al [27] reported that increased canopy retention correlated to increased bryophyte epiphyte richness and abundance, but there was some loss of species in areas where variable retention occurred when compared to the undisturbed forest. Likewise, Craig and Macdonald [28] showed similar results for the vascular plant understory and for bryophytes as a whole [29]. However, a study in Finland could not demonstrate that tree retention preserved the pre-harvest vegetation nor post-harvest succession [30].…”

“…This study was based on the concerns that changes in the ground lichen cover (especially reindeer lichens) of aging pine-dominated forests may decrease habitat suitability for caribou [20,30,32,33]. Additionally, clear-cut logging, which has long been a standard practice in western Canada, has severe consequences for the ground layer of bryophytes and lichens [29,34,35] and may conflict with caribou recovery efforts [31,36]. The project was initiated in 1997 to evaluate the value of commercial thinning as a tool for maintaining or improving caribou habitat suitability.…”