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Adaptation Actions for Mixedwood Forests in New England and New York

Mixedwood forests in New England and New York are already being affected by climate change and this creates challenges for sustaining the ecological, economic, and cultural benefits that the forests provide. There are many adaptation management actions that can address these key challenges. Adaptation actions are informed by site-specific conditions, including historical land-use legacies, and local manager knowledge and expertise.

A group selection harvest with leave trees in a mixedwood stand.
A group selection harvest in a mixedwood stand on the Green Mountain National Forest.

Climate Change and Mixedwood (Spruce-Fir-Northern Hardwood) Forest Ecoystems

Spruce-fir-northern hardwood mixedwood forests are typically located below 2,400 feet on moderate to well-drained, shallow soils on lower mountain slopes and flats, often in the transition zone between northern hardwood and montane spruce-fir forests. The canopy is typically dominated by red spruce and yellow birch, with components of beech, sugar maple, and white ash at nutrient-rich sites. Balsam fir, red maple, and paper birch are sometimes present. Nearly all of these forests have been harvested in the past. In highly degraded sites where spruce was selectively removed, the resulting canopy is dominated by northern hardwood species with spruce and fir more common in the understory. Mixedwood forests occur across a variety of sites in New England and New York with a range of past management regimes, which means that climate change will affect forests in different ways. Information from this section is summarized from a vulnerability assessment for regional forests.

Climate Change Impacts

Moderate-High Vulnerability

  • Mixedwood forests have limited tolerance to changes in precipitation and hydrologic conditions.
  • Sites with a higher risk of drought stress could impair tree regeneration or shift tree species composition toward the few hardwood species found in these areas.
  • Many of the dominant conifer species are expected to decline by the end of the century, particularly balsam fir.
  • Warmer temperatures may allow balsam and hemlock woolly adelgid to increase while dampening the effects of the eastern spruce budworm. Spruce budworm may be a threat to regeneration, especially if it coincides with other stressors. Beech bark and beech leaf disease may spread and cause more damage in climate-stressed forests.
  • Changes in herbivore populations may also have substantial effects on forest growth and composition.

Adaptive Capacity of Mixedwood Forests

Adaptive capacity is defined as the range of potential climate impacts a forest is exposed to and how well it can cope with these potential impacts.

These factors may increase adaptive capacity in mixedwood forests:

  • These forests are dominated by a mix of hardwood and softwood species which increases overall tree species diversity and reduces vulnerability to spruce budworm and other climate stressors.
  • Impacts from climate change are projected to be less severe at higher latitudes.

These factors may decrease adaptive capacity in mixedwood forests:

  • These forests tend to have a very limited suite of tree species physiologically adapted to the moisture and nutrient conditions found in these areas, including a limited number of different conifer species, making them particularly vulnerable to the loss of a given species due to climate change and associated impacts.
  • Past management has degraded many mixedwood stands, resulting in a canopy dominated by hardwood species over historically dominant conifers, reducing species diversity and options of recovery pathways in the face of climate change.

Site-level Considerations for Mixedwood Forests

Site-level factors could make a mixedwood stand more or less vulnerable to climate change, and the considerations below include some site-level factors that could increase or reduce risk.

risk matrix high risk to low risk
Site-level Considerations for Mixedwood by Risk
Site-level consideration High-risk condition Low-risk condition
Overstory composition There are low amounts of historically dominant conifer species (i.e., red spruce) present in the canopy due to past selective harvesting. Red spruce and other conifers make up more than 25% of the canopy in addition to hardwood species.
Regeneration Regeneration is limited by a lack of suitable seedbed conditions, altered disturbance regimes, herbivory, or competition from native or non-native species. Regeneration on site is not limited by seedbed conditions, herbivory, or competing vegetation.
Forest Structure The stand has low age class diversity and homogenous canopy structure such that conifers in the understory are stagnant. The stand is uneven-aged and has a diversity of age and size classes, canopy gaps, and sufficient amounts of downed deadwood.
Soils The site has nutrient-rich soils where hardwood species may outcompete softwoods more frequently. The site has nutrient-poor soils which are able to sustain a mix of softwood and hardwood species.
Hydrology The natural hydrology is disrupted by ditches, roads, culverts, or other alterations and may cause greater hydrologic fluctuations, including altering soil moisture patterns in wet/sensitive soils. The natural hydrology has been maintained and can buffer impacts from changes in precipitation and water table.
Insects and Disease There are high amounts of tree damage and mortality from forest pests (e.g., spruce budworm, balsam woolly adelgid, beech bark disease). The site is close to known infestations of non-native insects and pathogens. Few trees display signs of damage or mortality from insects and pathogens. The site is distant from known infestations of non-native insects and pathogens.

Adaptation Actions for High-Risk Site Conditions in Mixedwood Forests

A wide variety of actions are available for responding to climate change. This section presents examples of adaptation actions to address high-risk conditions in mixedwood forests. For each example, the corresponding adaptation approaches from the Forests or Forested Watersheds Adaptation Menus are identified in parentheses. Adaptation demonstration projects that use these actions are also highlighted to help as a starting point for managers who are exploring actions to take on the lands that they manage.

  • For stands with primarily hardwood overstory and sufficient softwood (red spruce, hemlock) advance regeneration, create regeneration openings across 10-20% of the stand to release pockets of advance regeneration. This can take the form of initial entries for expanding gap and continuous cover irregular shelterwoods, that retain diverse seed sources and provide regeneration environments for a wide range of hardwood and softwood species (Approach 5.2, 5.3, 10.2).
  • For stands with primarily hardwood overstory and limited softwood advance regeneration:
    • Focus activities on releasing and maintaining existing conifers present and establishing advance regeneration over time (i.e., crop-tree release of conifers currently overtopped by hardwood species in the canopy, use of group selection to establish spruce advance regeneration). Scarification of group openings and follow-up release of red spruce seedlings will ensure establishment and recruitment over time (Approach 5.2).
    • If conifer seed sources are not present, consider enrichment planting in group openings.
  • Retain a variety of species and age classes (Approach 5.1, 5.2).

  • Close and revegetate old logging roads (Approach 1.2, Forested Watershed Menu 6.4).
  • Identify restricted areas (sensitive and inoperable areas) for winter harvesting and no harvesting to minimize damage to soil and roots and prevent rutting (Approach 1.1).
  • Retain permanent retention patches and riparian buffers within harvest stands (Approach 1.3).
  • Upgrade water crossings to manage high-volume flood events (Forested Watershed Menu 6.1).

  • Retain canopy trees exhibiting resistance to insects and diseases on site (e.g., spruce bark beetle, spruce budworm, hemlock woolly adelgid, beech bark disease; Approach 2.1) .
  • Use regeneration harvests that sustain options for threatened species on site as mature canopy trees and in the regeneration layer (e.g., group selection and irregular shelterwoods; Approach 2.1, 5.3).
  • Encourage a diverse mix of canopy species through intermediate treatments and regeneration harvests (Approach 9.1, 9.2).
  • Plant species sharing similar ecological and cultural values to threatened species, which are also future climate-adapted (e.g., white pine, red spruce-southern genotypes; Approach 9.1, 9.7).


Silvicultural Strategies in Mixedwood Forests

The following video provides more information on adaptation in mixedwood forests. View the presentation, “Strategies for Managing Compositionally Degraded Mixedwood Stands” by Laura Kenefic, USDA Forest Service Northern Research Station.



Adaptation in Action

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This is part of a collection on Northern Forest Ecosystems in New England and New York.

Browse additional strategies for Northern Forest Ecosystems

Acknowledgments

This collection of resources was created by partners from the Northern Institute of Applied Climate Science, the University of Vermont, the Forest Stewards Guild, and the USDA Northern Forests Climate Hub who developed the content, original concept, and layout. Funding for this project was provided by the Northeastern States Research Cooperative. We thank the reviewers from the U.S. Fish and Wildlife Service, Lyme Timber, Baskahegan Company, Dartmouth College Woodlands, and other managers and scientists that provided feedback. The Northern Institute of Applied Climate Science (NIACS) is a collaborative, multi-institutional partnership led and supported by the USDA Forest Service.

If you have questions or are interested in learning more, contact project manager Tony D’Amato (awdamato@uvm.edu) or Samantha Myers (smyers3@uvm.edu).