Abstract
Sweet birch (Betula lenta L.) is aggressively recruiting in temperate forest understories of the eastern United States and often dominates the post-disturbance seedling community, diminishing diversity and hindering sustainable silviculture. The type and timing of silvicultural actions affect birch recruitment via their effects on seedling recruitment, survival, and growth. Here, we examine birch regeneration under two contrasting treatment sequences: pre- versus post-shelterwood harvest herbicide application (H–S vs. S–H) in combination with white-tailed deer (Odocoileus virginianus Zimmerman) browsing (fenced vs. unfenced) at 22 sites in northwestern Pennsylvania, USA. Additionally, we examine how treatments interact with additional site factors, including potential propagule sources and site productivity (i.e., integrated moisture index). We found the S–H sequence initially reduced birch density by 71% relative to the H–S sequence; however, the magnitude of this reduction waned over five growing seasons. Furthermore, birch proliferated following the H–S sequence only where mature birch were present. Deer browsing reduced birch height by 29% relative to fenced areas protected from browsing; however, by the fifth growing season birch seedlings were over twice as tall as other hardwood species across all treatments. Finally, increasingly mesic sites enhanced birch height growth. In sum, although post-harvest herbicide (S–H) provides short-lived control over birch, land managers should also consider browse pressure, seed source, and site productivity, as these may enhance or diminish the efficacy of post-shelterwood herbicide sequence effects on birch.
Highlights
Within the last two decades, sweet birch (Betula lenta L.; hereafter, birch) has emerged among the few species that consistently and abundantly recruit into mesophytic and northern hardwood forests of the eastern United States
Initial (2014) birch seedling densities were 71% lower in areas treated with the S–H sequence relative to the herbicide-shelterwood sequence (H–S) sequence; seedling densities were statistically equivalent between treatments by 2015 and grew even more equitable by 2017
Within the H–S sequence areas, birch established at high densities only where residual birch existed in the overstory (Table 1; Figure 2)
Summary
Within the last two decades, sweet birch (Betula lenta L.; hereafter, birch) has emerged among the few species that consistently and abundantly recruit into mesophytic and northern hardwood forests of the eastern United States. Birch may be considered a ‘super-generalist’ (sensu [9]) in that it possesses wide amplitude in key traits that confer recruitment, survival, and growth advantages under a variety of conditions, including recently disturbed stands This versatility is, perhaps, most evident in its shade tolerance, which has been categorized as intolerant to intermediate [10,11], yet research demonstrates birch seedlings are able to survive and grow even under extremely low light levels (i.e.,
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