Early Regeneration and Structural Responses to Patch Selection and Structural Retention in Second-Growth Northern Hardwoods

Abstract. Many managed northern hardwood forests are characterized by low-diversity tree regeneration. Small harvest gaps, competition from shrub-herb vegetation, and browsing by white-tailed deer (Odocoileus virginianus) contribute to this pattern, but we know little about how these factors interact. With a stand-scale experiment, we examined the effects of gap size (0-3234 m 2 ), vegetation (weeded:unweeded), and deer (fenced:unfenced) on seedling growth and survival for 18 tree species. With increasing gap size and light, shrub-herb vegetation density increased, while deer browsing on seedlings in unweeded plots decreased. Fenced:weeded seedlings of all species increased in height up to 35-45% light, with optimal growth in large-group selection and patch cut harvest gaps. Height growth rank order among tree species changed between gap sizes, but growth varied little in small, low-light gaps. Instead, a low-light survival (i.e., shade tolerance) vs. high-light growth tradeoff we observed is likely more important for species sorting of gap sizes. Shrub-herb vegetation decreased seedling survival and growth, especially in larger harvest gaps, shifting gap size optima to smaller gaps, but had little effect on growth/survival rank order among species. In contrast, deer had strong impacts on growth rank order, especially in larger gaps where species differences in growth potential were trumped by differences in deer browsing pressure responses. However, contrary to their consistently negative main effects, vegetation and deer had two positive interacting effects: dense shrub-herb vegetation in large gaps protected seedlings of faster-growing species from browsing and deer browsing of shrub-herb vegetation modestly increased light and growth of short, suppressed, browsing-avoided species. In summary, harvest gap size-mediated light availability, shrub-herb vegetation, and deer herbivory had strong interacting effects on tree seedling interspecific performance ranks and intraspecific optimal gap sizes. For management, a broad range of harvest gap sizes and rapid establishment of tree regeneration (naturally or planted) to minimize shrub-herb competition should increase tree diversity in forests with few deer. However, with deer browsing pressure, a more limited set of lesser-browsed species are likely to recruit successfully regardless of gap size, except in large patch cut gaps, where recruitment of faster-growing, shade-intolerant species is possible.

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“…, D'Amato et al. ). However, in larger gaps, the superior height growth rates of intolerant species (Beaudet and Messier , Walters et al.…”

Section: Discussionmentioning

confidence: 98%

“…Other factors affecting the composition and density of seedling populations in NH forests include a scarcity of decaying wood and mineral soil substrates required by small seeded species (e.g., paper birch, yellow birch, hemlock) (D'Amato et al. , Willis et al. ) and a lack of local seed sources (Caspersen and Saprunoff ).…”

Section: Discussionmentioning

confidence: 99%

Managing for diversity: harvest gap size drives complex light, vegetation, and deer herbivory impacts on tree seedlings

et al. 2016

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“…), and is a preferred regeneration site for many species of tree and shrub (Harmon and Franklin , D'Amato et al. ). Prior research in older forests has highlighted the potential for long‐term disruption to dead wood recruitment and accumulation as a result of active management (Duvall and Grigal , Debeljak , Silver et al.…”

Section: Discussionmentioning

confidence: 99%

Medium‐term effects of active management on the structure of mature Douglas‐fir (Pseudotsuga menziesii) stands

Williams

Powers

2019

Ecosphere

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Citation: Williams, N., and M. Powers. 2019. Medium-term effects of active management on the structure of mature Douglas-fir (Pseudotsuga menziesii) stands.Abstract. We developed an observational study to (1) examine differences in the structure of mature Douglas-fir stands representing thinned, structural retention harvest and unmanaged conditions, and (2) assess the extent to which active management in mature stands expedites development of old-growth structure, relative to two old-growth indices. Time since treatment averaged 38 and 22 yr in thinned and retention harvest conditions, respectively, and stand age ranged from 106 to 193 yr when sampled. Differences in stand structure were apparent between all three management conditions, with attributes associated with stumps, live tree diameter diversity, understory vegetation, and vertical foliage structure being the strongest individual drivers of these differences. Mean old-growth index scores were lower than expected of true old-growth for each of the management conditions examined here, but were not significantly different between thinned and unmanaged stands. Our results suggest thinning in mature stands may promote certain elements of old-growth structure, including foliage height diversity, but also indicate the need for provisions against the depletion of dead wood resources. Stumps are an understudied dead wood structure, and in actively managed mature stands, our results imply that stumps may provide a degree of functional substitution where down log availability is low.

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“…Based on the literature (for example, [52][53][54] and [41]), we chose variables that have been shown to influence regeneration dynamics. Predictor variables included in the model were percent leaf litter, percent browse, Direct Site Factor (DSF, obtained through analysis of hemispheric photographs), and Curtis relative-density (RD) structure index [55].…”

Section: Discussionmentioning

confidence: 99%

“…Although all three treatments in the FEMDP shared structural retention as an objective, they differed in harvest approach, for example in the degree of uniform vs. variable density tree marking, silvicultural gap size and configuration, and amount of live and dead tree retention [6,9,41]. The treatments included two conventional uneven-aged prescriptions, single-tree selection (STS) and group selection (GS), which retain post-harvest structure at the high end of the range of retention parameters typical for selection harvesting in the region ( Table 2).…”

Section: Methodsmentioning

confidence: 99%

Regeneration Responses to Management for Old-Growth Characteristics in Northern Hardwood-Conifer Forests

Gottesman¹

2017

Forests

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Successful tree regeneration is essential for sustainable forest management, yet it can be limited by the interaction of harvesting effects and multiple ecological drivers. In northern hardwood forests, for example, there is uncertainty whether low-intensity selection harvesting techniques will result in adequate and desirable regeneration. Our research is part of a long-term study that tests the hypothesis that a silvicultural approach called "structural complexity enhancement" (SCE) can accelerate the development of late-successional forest structure and functions. Our objective is to understand the regeneration dynamics following three uneven-aged forestry treatments with high levels of retention: single-tree selection, group selection, and SCE. Regeneration density and diversity can be limited by differing treatment effects on or interactions among light availability, competitive environment, substrate, and herbivory. To explore these relationships, manipulations and controls were replicated across 2 ha treatment units at two Vermont sites. Forest inventory data were collected pre-harvest and periodically over 13 years post-harvest. We used mixed effects models with repeated measures to evaluate the effect of treatment on seedling and sapling density and diversity (Shannon-Weiner H'). The treatments were all successful in recruiting a sapling class with significantly greater sapling densities compared to the controls. However, undesirable and prolific beech (Fagus americana) sprouting dominates some patches in the understory of all the treatments, creating a high degree of spatial variability in the competitive environment for regeneration. Multivariate analyses suggest that while treatment had a dominant effect, other factors were influential in driving regeneration responses. These results indicate variants of uneven-aged systems that retain or enhance elements of stand structural complexity-including old-growth characteristics-can generally foster abundant regeneration of important late successional tree species depending on site conditions, but they may require beech control where beech sprouting inhibits desired regeneration.

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Early Regeneration and Structural Responses to Patch Selection and Structural Retention in Second-Growth Northern Hardwoods

Cited by 28 publications

References 36 publications

Managing for diversity: harvest gap size drives complex light, vegetation, and deer herbivory impacts on tree seedlings

Managing for diversity: harvest gap size drives complex light, vegetation, and deer herbivory impacts on tree seedlings

Medium‐term effects of active management on the structure of mature Douglas‐fir (Pseudotsuga menziesii) stands

Regeneration Responses to Management for Old-Growth Characteristics in Northern Hardwood-Conifer Forests

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