Petawawa Research Forest – Adaptive Silviculture for Climate Change Research Trial

The ASCC-PRF trial focuses on developing, testing, and demonstrating strategies for adapting the region’s white pine forests to climate change. This forest type was selected because it is important ecologically and economically in the region, it is the most prevalent forest type at the PRF, and it was not yet represented at other sites within the ASCC Network.

White pine forest stands are seldom pure, and commonly contain varying amounts of red pine, red oak, maples, aspen, birch, balsam fir and spruce. These stands are typically managed under the uniform shelterwood system which includes 1-3 partial harvests (preparatory, seed cut, first removal) designed to support regeneration establishment by providing a seed source for new seedlings and regulating light conditions to mitigate insect and disease attacks on young white pine. Once the white pine regeneration has surpassed a height of 6 meters (20 ft), the threat of white pine weevil damage (larval feeding kills the leader and causes poor form) is minimized and the remaining overstory is harvested leaving a single age stand to grow to maturity. The number of harvests will depend on the starting stand condition, composition, and basal area. Stands with lower pine components often have only the seed cut and a final removal. The seed cut is scheduled in mature stands of 80-100 years old. The final removal harvest can often occur 20-30 years after the seed cut. The goal of the uniform shelterwood system is to re-establish productive, white pine dominated stands. These are the desired future condition (DFC).

Treatments for ASCC-PRF were developed with the expectation of starting with mature white pine stands that were ready for harvest and renewal activities. The objectives of renewal activities are to establish productive forests that generate similar ecological (e.g. habitat) and economic (e.g. timber products) goods and services as the original stands.

ASCC-PRF has five treatment options: Resistance, Resilience, Transition, Untreated Control, and “Business as Usual” Control. With the exception of the Untreated Control, broad management objectives of each treatment are to harvest and regenerate the stands in a manner that will regrow healthy, productive forests that are capable of delivering similar ecosystem goods and services as provided by the original stands.

Each of the Resistance, Resilience and Transition treatments utilize assisted migration of tree species as an adaptation strategy. Identifying regions where the future climate of the PRF will match historical climate normal was guided using Natural Resources Canada’s SeedWhere model(https://cfs.cloud.nrcan.gc.ca/seedwhere/index.php?randNum=33262&lang=e). The SeedWhere modelling work and eventual seed sourcing and procurement was completed through a contract with the Forest Gene Conservation Association (https://fgca.net/).

• Resistance: The resistance treatment includes management options to achieve the desired future condition (DFC) using the uniform shelterwood system but aims to increase climate change resistance by expanding the genetic diversity of the regenerating stands. Seedlings will be planted using locally sourced seed as well as white pine seed sourced from three zones that have historical climates that match the projected future climate of the PRF (periods: 2011-2040, 2041-2070, 2071-2100) under RCP 8.5. These seedlings are expected to be better adapted to future conditions at the PRF.
• Resilience: The Resilience treatment will use a regionally novel silviculture system to achieve a similar DFC, but one that is better able to rebound from disturbances. An expanding gap, irregular shelterwood system will create a multi-age stand structure that will maintain the presence of seed producing trees on site at all times. Harvested gaps will be 50 m in diameter and distributed to cover 20% of the stand area. Overall diversity will be increased by planting multiple species within harvested gaps (white pine, red oak, and white oak). Genetic diversity will be expanded by sourcing the seed from locations with a climate similar to the 2011-2040 and 2041-2070 climate periods at PRF, under RCP 8.5. Gaps will be expanded every 15-20 years which will allow the choice of species and their sources to be revisited based on climate conditions at the time.
• Transition: The transition treatment actively facilitates change to create a climate-adapted forest. The clearcut with seed trees system will be used to facilitate the planting of local red pine, white oak suitable for the 2011-2040 period (RCP 8.5), red pine and red oak suitable for the 2041-2070 period (RCP 8.5), and planting a novel species, pitch pine, to replace the white pine component of the stands. Overall, the diversity of trees will be increased through the addition of white oak and pitch pine, and the genetic diversity of local species will be increased by planting climate adapted sources of red pine and red oak. The range of pitch pine currently extends only to the just north of the Canadian-US border (e.g., Kingston, ON) so this will be an assisted long-distance migration strategy for pitch pine. This species is well adapted to the dry and shallow growing conditions expected for the future at the PRF, modelled under the RCP 8.5.
• Un-treated reference conditions (no action): Under the untreated reference conditions, mature stands representing the DFC will be allowed to respond to climate change without direct silvicultural management intervention.
• “Business as usual” Control: This treatment represents the application of standard operational strategies and approaches used to regenerate the forest and achieve the DFCs in 80-100 years. Primarily these include using the uniform shelterwood system and planting seedlings grown from local sources of seed.

Following the requirements of the ASCC Network, each of the adaptation treatments will be replicated four times on the Petawawa Research Forest and have a minimum treatment area of 8 ha for each replicate.

Candidate white pine dominated stands were identified based on availability under the PRF sustainable forest management plan. Suitability for the project (e.g., accessible, composition, operability) was determined using stand attributes from the PRF’s enhanced forest inventory and by ground surveys. In total nearly 200 hectare of forest was selected for the study across four blocks and representing a range of productivity and moisture conditions.

Seven long-term measurement plot locations were randomly allocated to each treatment area across the gradient of productivity (3 classes of pre-harvest basal area) and moisture conditions (3 classes of topographic wetness index).

Pre-treatment assessments were conducted in summer 2021 to benchmark: composition and abundance of the overstory, saplings and shrub layer, and the ground layer and substrates; the quantity of coarse woody debris; and carbon and nutrient pools in the soils. The same data will be collected after the completion of renewal activities, and at fixed times into the future (e.g., 5 years) to be able to describe changes in the stands.

Tree marking was completed prior to harvest to identify trees that were not to be harvested. Harvesting activities were completed during the winter of 2021-22 by an external contractor. Feller bunchers harvested the trees. Tree limbs were removed prior to tree stems being removed from the forest by skidders.

For the purpose of slash management and seedbed creation, mechanical site preparation was completed during July and August 2022 in the Resistance, Transition and “Business as Usual” Control treatments. Skidders with front mounted rakes pushed the logging debris into small piles. Slash levels in harvested gaps of the Resilience did not warrant mechanical site preparation.

Chemical site preparation is scheduled for all harvested treatments in the summer of 2023. This will reduce competition to regeneration from rapidly growing herbaceous, shrub, and less desirable trees species. A glyphosate-based herbicide will be applied from a skidder.

Tree planting is scheduled for September of 2023. The different species and sources will be planted as a random mixture at target densities of 1250 to 1760 trees per hectare, depending on the treatment. A numbered pin will mark and identify the species and seed source of each planted tree within the measurement plots. This will permit the survival and growth of each to be tracked.

As part of the project development, collaboration with research partners from many institutions will be used to investigate the effectiveness of the different silvicultural treatments aimed at creating adaptive ecosystems. Given the long-term status of ASCC-PRF, monitoring is an essential component. Depending on the treatment, final rotation will take place in 60-100 years. To support the ongoing research, some of the monitoring items include:

• Regeneration of planted seedlings
• Residual tree survival and growth
• Vegetation diversity
• Microclimate conditions
• Hydrology and catchment data
• Coarse woody debris
• Carbon and nutrient pools
• Bird and wildlife activity

Natural Resources Canada is preparing for site preparation and tree planting activities in 2023, and the first post-establishment data collection in 2024. The study sites are expected to support and attract additional short- and long-term investigations as well as collaborations with internal and external partners. Future data collection will focus on tree regeneration, forest growth, forest health, and carbon and nutrient fluxes to allow ASCC-PRF to participate in network-wide analytical initiatives. Knowledge exchange activities will be an important part of this project. The study will be a destination for many field tours and the subject of many presentations, reports, and peer-reviewed publications. It is expected that ASCC-PRF will contribute to policy development related to forest management in Ontario and beyond.

Link to Full Case Study