NHRI’s Sustainable Hardwood Management IS Adaptive Silviculture

The following article is an adaptation of NHRI's latest technical note by Storm Robinson, MScF. It is a synthesis of New Brunswick climate change predictions and the first product in our Adaptive Silviculture for New Brunswick’s Mixed and Hardwood Forests toolkit for practitioners; Adaptation to Climate Change in New Brunswick. To access the full technical note, click here.?

What do we mean by NHRI’s sustainable hardwood management IS adaptive silviculture? For over 10 years now, our small research center has been perfecting the most appropriate silviculture prescriptions for mixed and hardwood stands; stands that face degradation, species composition changes, regeneration concerns, and more. These are the same issues that are expected to become more severe under a changing climate. Our silviculture decision keys are based on quality of the stand and desired regeneration and allow for adaptive and results-based management at each harvest entry.??

The purpose of this technical note is to:

• Assist practitioners in understanding the impact of the latest climate predictions on wood supply
• Present adaptive management and adaptive silviculture frameworks (ASCC) including pathways to resistance, resilience, or transition
• Relate the NHRI’s Silviculture Prescription System (SPS) to those frameworks in preparation for future adaptive silviculture work in hardwood and mixedwood stands of New Brunswick.

Most, if not all of the future predictions for forest composition and wood supply rely mostly on climate data and some natural disturbance factors. These are created to paint a worst-case scenario if New Brunswick was to remain passive with our management. The sustainability of our forests relies on active management to not only maintain our wood supply, but also to add resilience in both productive and protected forests to the unprecedented changes that are very likely to occur in our province. If unmitigated, some of these changes include:?

Much of the impacts of climate change on hardwoods will be different according to the ecoregion of concern (Fig 2). Specifically, the lowland ecoregions, including most of eastern and southern portions of the province except for the cooler Fundy coast, could suffer the highest warming. In the worst-case scenario, winter temperatures may increase by 3.8 - 6.6 °C on average. Southern regions of New Brunswick may experience winter average temperatures above the freezing point by the end of this century.?

An NHRI tool to predict climate change by EcoRegion in NB; showing the change in average annual temperature from 2020 to 2080 under RCP 4.5 scenario: Explore the tool here: https://csrno.ca/climat/ecodistricts/.?

Changes in species composition will, in most cases, change the targeted end products for producers, influence annual allowable cuts (AAC’s), and shorten or lengthen rotation age. The scenarios explored in the quest to assess climate adaptive strategies on wood supply are explained fully in Lantz et al. (2022).?

With adaptive management in mind, silviculturists present four adaptive silviculture approaches with tactics that can be applied at the stand level.?

Actions for Practitioners

To see if your stand qualifies for the NHRI SPS (Silviculture Prescription System), always run the master key. The SPS is created to help inform decisions such as which stands require more intervention than others. For example, it considers stand quality and regeneration concerns such as beech competition. A summary of SPS regimes is in Table 1 and 2.

Recommended SPS treatments under the adaptive silviculture framework:?

1. Passive adaptation: Passive adaptation is letting nature dictate what species assemblage results from the effects of a changing climate. There is no recommended SPS for this method, as no action is taken.?

?This stand regenerated to American beech following a partial harvest because it contained a large proportion of it before treatment. Adopting a better silviculture regime would have resulted in a much better cohort of future trees. This is a good example that sound silviculture practices are the best tools for managing under a changing climate.

2. Increase resistance to stress: Increase the ability of stand/forest to remain unchanged when challenged by disturbances. The most appropriate SPS prescription is single with group selection (SGS). Reduce competition for moisture, nutrients, and light. Encourage multi-aged/multi-size structure and maintain high quality across all size classes. Maintain/increase vigour and quality of residual trees while maintaining current productivity levels consistent with product type. Alter forest structure to reduce risk or severity of wildfire, wind, and ice damage by focusing on maintaining low-risk residual trees. Thinning to increase pest and drought resistance is also a good recommendation.

This stand has regenerated to yellow birch, a desired species that will adapt well to climate change. Even-aged and two aged silviculture systems are good tools to avoid the promotion of less desired species such as beech, fir and red maple.

3. Promote resilient stands: Enable forests/stands to rebound from disturbances. Our recommended SPS prescription is group selection (SGS) where appropriate. Maintain patch reserves, adjust rotation length to decrease period of time the stand is vulnerable to insects, pests and pathogens. Maintain appropriate gap sizes for your desired regenerative species to prevent undesired regeneration (e.g. American beech or invasive species). With that concept, CTA or UTA are also viable options. Increase stand structure, species functional diversity and functional redundancy as insurance against disturbances that are species or cohort specific. Promote the regeneration of highly adaptable species. Manage for wildlife and herbivory to promote regeneration of desired species.?

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?A continuous cover Irregular Shelterwood System (ISS) establishment cut was carried out in a sugar maple–yellow birch stand to reduce the dominance of beech regeneration and produce high-quality yellow birch and sugar maple. This adds resilience by maintaining an irregular structure, promoting healthy regeneration, and having control over residual species composition. For more information on irregular shelterwood, see our Spring 2024 edition of the Leaflet.

4. Active transition: Intentionally accommodate change to enable ecosystems to adaptively respond to changing conditions. Many of our irregular shelterwood (two-age) and shelterwood SPS prescriptions can work in transition including CTA, UTA, OSH, USH, RST. On top of the right prescription, we also suggest researching the many tools of adaptive silviculture such as assisted migration – introduce new species or new genotypes of the same species from different climates that are more adapted to future conditions (planting seeds from seedlots that were growing in 2°C to 4°C warmer climates). Increase proportion of planted species (> 20% composition) that are not currently on the site that are better adapted to future climate. Keeping in mind that hardwood plantations, if successful, can be an investment of between $5000 and $10000 per hectare if you are able to find a high potential site.?

A high-quality walnut plantation out of Indiana, U.S.A. with an investment of over $10,000 per hectare. New Brunswick is not ready for this warm-adapted species now, but with increasing temperatures and transitional management, it may soon become a more attainable reality.

Prioritizing active management to promote healthy regeneration, using sugar maple as an example, remains crucial. Without exemplary best management practices, the species has little chance to adapt. Sugar maple faces competition from raspberry and intolerant hardwoods when the canopy is too open, and from prolific American beech regeneration (which becomes infected with beech bark disease) in closed canopies. Understanding the initial quality of your tolerant hardwood stand is crucial for adapting your management prescriptions. Therefore, we recommend returning to SPS 2.0 and following each of the five steps, as regeneration and stand quality concerns will only be exacerbated by climate change.?

What's Next?

• Next up in our adaptive silviculture toolkit will be a technical note on setting and prioritizing climate-smart management objectives. This includes surveying a panel of experts from federal and provincial governments, Adaptive Silviculture for Climate Change network directors, researchers, and site managers, and other adaptive silviculture/assistant migration experts on recommended strategies to reach management goals such as timber, biodiversity, resistance, resilience and transition. We expect it’s release before Fall 2024 and appreciate everyone who has agreed to participate.??
• Also, keep your eyes peeled for our summer edition of the Leaflet that will bring in experts to discuss their experiences and expertise in adaptive silviculture.? ?

Robinson, Storm. (2024) “Adaptive Silviculture for New Brunswick’s Mixed and Hardwood Forests: Adaptation to Climate Change in New Brunswick."???

To access this technical note, click here.?

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