Introduction: Ecology and silviculture of temperate mixedwood forests

Mixedwood forest composition, or co-dominance of hardwood and softwood species, has been interpreted as both stable and unstable. Through review of existing theory, we propose a conceptual model to understand mixedwood compositional stability in boreal and temperate forests of eastern North America. We first review the current theory that the strength of neighborhood effects (i.e. species ability to self-replace under their own canopy) is essential to understanding stability, such that when self-replacement is strong for both dominant hardwood and softwood species, composition is stable except at extreme disturbance severities. In contrast, when mixedwood forests are dominated by negligible or weak affinities to self-replace, composition is unstable and sensitive to changes in disturbance. Our new concept further posits that both change in the disturbance severity and in its vertical direction are essential to understanding stability. For example, where moderate-severity surface fires (which impact forests from below) cease and are replaced by moderate-severity blowdowns (which impact forests from above), instability can occur even when disturbance severity is unchanged. We therefore pose and discuss an extension to current theory to provide a new unifying concept of stability for mixedwood forests and, more broadly, for mixed-species forests.

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Light dynamics and free-to-grow standards in aspen-dominated mixedwood forests

The Forestry Chronicle ◽

10.5558/tfc78137-1 ◽

2002 ◽

Vol 78 (1) ◽

pp. 137-145 ◽

Cited By ~ 52

Author(s):

Victor J Lieffers ◽

Bradley D Pinno ◽

Kenneth J Stadt

Keyword(s):

Leaf Area Index ◽

Key Words ◽

Leaf Area ◽

Light Transmission ◽

Stand Density ◽

Canopy Gaps ◽

Light Competition ◽

Area Index ◽

Mixedwood Forests ◽

Key Words Competition

This study examines light competition between aspen and spruce during the sequence of aspen development. Leaf area index and light transmission were measured or estimated for aspen stands from 2 to 125 years old. Light transmission was lowest at 15-25 years, and in some stands, transmission was less than 5% of above-canopy light. Hypothetical aspen stands with various stem configurations and heights were developed, and positions were identified that would meet or fail Alberta free-to-grow (FTG) standards. Light transmission was estimated at each position with the MIXLIGHT forest light simulator. Positions in canopy gaps or at the northern sides of canopy gaps had higher light. In general, however, there was little difference in available light between positions that met or failed FTG criteria. Stand density and size of aspen trees appears to be a better index to predict light transmission and spruce success in juvenile aspen stands than current FTG criteria. Key words: competition, free to grow, hardwood, spruce, light

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Long-term development of transition hardwood and Pinus strobus - Quercus mixedwood forests with implications for future adaptation and mitigation potential

Forest Ecology and Management ◽

10.1016/j.foreco.2021.119654 ◽

2021 ◽

Vol 501 ◽

pp. 119654

Author(s):

Peter W. Clark ◽

Anthony W. D'Amato

Keyword(s):

Pinus Strobus ◽

Mitigation Potential ◽

Mixedwood Forests ◽

Adaptation And Mitigation

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Contemporary status, distribution, and trends of mixedwoods in the northern United States

Canadian Journal of Forest Research ◽

10.1139/cjfr-2020-0467 ◽

2021 ◽

Author(s):

Lance A. Vickers ◽

Benjamin Knapp ◽

John M Kabrick ◽

Laura S. Kenefic ◽

Anthony W. D'Amato ◽

...

Keyword(s):

United States ◽

New England ◽

Analysis Data ◽

Specific Information ◽

Forest Types ◽

Forest Inventory And Analysis ◽

Mixedwood Forests ◽

Contemporary Status ◽

Northern United States ◽

Abundance And Distribution

As interest in managing and maintaining mixedwood forests in the northern United States (US) grows, so does the importance of understanding their abundance and distribution. We analyzed Forest Inventory and Analysis data for insights into mixedwood forests spanning 24 northern US states from Maine south to Maryland and westward to Kansas and North Dakota. Mixedwoods, i.e., forests with both hardwoods and softwoods present but neither exceeding 75-80% of composition, comprise more than 19 million hectares and more than one-quarter of the northern US forest. They are most common in the Adirondack-New England, Laurentian, and Northeast ecological provinces but also occur elsewhere in hardwood-dominated ecological provinces. These mixtures are common even within forest types nominally categorized as either hardwood or softwood. The most common hardwoods within those mixtures were species of Quercus and Acer and the most common softwoods were species of Pinus, Tsuga, and Juniperus. Although mixedwoods exhibited stability in total area during our analysis period, hardwood saplings were prominent, suggesting widespread potential for eventual shifts to hardwood dominance in the absence of disturbances that favor regeneration of the softwood component. Our analyses suggest that while most mixedwood plots remained mixedwoods, harvesting commonly shifts mixedwoods to either hardwood- or softwood-dominated cover types but more specific information is needed to understand the causes of these shifts.

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Spatial Patterns of Canopy Disturbance and Shortleaf Pine in a Mixedwood Forest

Forest Science ◽

10.1093/forsci/fxab017 ◽

2021 ◽

Author(s):

J Davis Goode ◽

Justin L Hart ◽

Daniel C Dey ◽

Scott J Torreano ◽

Stacy L Clark

Keyword(s):

Spatial Structure ◽

Spatial Patterns ◽

Natural Disturbance ◽

Shortleaf Pine ◽

Ecosystem Goods And Services ◽

Goods And Services ◽

Mixedwood Forests ◽

Canopy Disturbance ◽

Tree Spatial Pattern ◽

Neighborhood Scale

Abstract The spatial structure of forest ecosystems is dominated by the horizontal and vertical distribution of trees and their attributes across space. Canopy disturbance is a primary regulator of forest spatial structure. Although the importance of tree spatial pattern is widely acknowledged as it affects important ecosystem processes such as regeneration and recruitment into the overstory, quantitative reference spatial conditions to inform silvicultural systems are lacking. This is especially true for mixedwood forests, defined as those that contain hardwoods and softwoods in the canopy. We used data from a preexisting network of plots in a complex-stage mixedwood stand to investigate the influence of canopy disturbance on stand and neighborhood-scale spatial patterns. We reconstructed canopy disturbance history and linked detected stand-wide and gap-scale disturbance events to establishment and spatial patterns of shortleaf pine. The majority of shortleaf pine establishment coincided with stand-wide or gap-scale disturbance. Shortleaf pine was clustered at the stand scale but was randomly distributed at the neighborhood scale (i.e. five tree clusters), which was a legacy of the historical disturbance regime. These results may be used to improve natural disturbance-based silvicultural systems to restore and maintain mixedwood forests for enhanced resilience and provisioning of ecosystem goods and services. Study Implications: Shortleaf pine was clustered into compositionally distinct patches within the oak-pine stand. Based on our findings, we recommend managers of stands with patchy species composition consider silvicultural systems that focus on patches. This approach acknowledges the effects of intrastand spatial variability of biophysical conditions and interactions with stochastically occurring canopy disturbances on regeneration and recruitment. Patch clearcuts with reserves could be implemented with the openings correspondent to microsites that favor regeneration of shortleaf pine. Similar potential approaches could be seedtree, irregular shelterwood, and other regeneration methods suited to stand conditions and the silvics of the species of interest.

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Understory species interactions in mature boreal mixedwood forests

Botany ◽

10.1139/b10-062 ◽

2010 ◽

Vol 88 (10) ◽

pp. 912-922 ◽

Cited By ~ 6

Author(s):

Virginia Chávez ◽

S. Ellen Macdonald

Keyword(s):

Environmental Factors ◽

Species Interactions ◽

Common Species ◽

Herbaceous Layer ◽

Competition Intensity ◽

Understory Species ◽

Mixedwood Forests ◽

Natural Logarithm ◽

Cornus Canadensis ◽

Herb Species

We explored interactions among plant growth forms in the understory of mature boreal mixedwood forests in western Canada by investigating the competitive influence of erect shrubs on herbs (forbs and grasses). We established 10 pairs of plots; all erect shrubs were removed in one plot of each pair (removals) and left intact in the other plot (controls). Two years later, we harvested all aboveground biomass of the herbaceous layer (herb biomass: this included graminoids, forbs, trailing shrubs, and species with a woody base but not woody stems) from the 20 plots. We tested for significant differences in understory species biomass and composition between control and removal plots and examined the influence of 25 environmental factors on species composition of the herbaceous layer. Competition intensity was measured by the natural logarithm of response ratio (ln RR) index based on herb biomass. After erect shrub removal, there was a significant increase in herb biomass, mostly due to an increase of the most common species (e.g., Cornus canadensis Linnaeus, Linnaea borealis Linnaeus). The values of competition intensity (ln RR) varied among herb species but were, overall, positive, indicating a release from competition following shrub removal. Composition of the herbaceous layer was significantly different between removal and control plots and was also significantly related to seven environmental factors, which explained 40% of the variation in composition. Our study suggests that there is asymmetric competition for light between erect shrub and herb species in boreal ecosystems.

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