Tree-mendous Places: Using GIS to Optimize Forest Restoration in Canada
Trees can be powerful allies in the fight against climate change, pulling carbon from the air and storing it as they grow. Forests also provide many other benefits to nature and people, like habitat for at-risk species, clean water, and opportunities for recreation. Canada launched a federal program called 2 Billion Trees (2BT) in 2021 to help the country reach its climate objectives by planting trees, as well as reach goals to benefit people and at-risk species. But where exactly should those trees go?
Nature United is a Canadian conservation organization working to accelerate nature’s role in mitigating rapid climate change. Termed “natural climate solutions,” these efforts include forest restoration or protection of important carbon stores like old forests and peatlands. To support implementation of 2BT and its effectiveness as a natural climate solution, Nature United teamed up with federal agencies, academic institutions, and other nonprofit organizations to conduct a new analysis to identify where planting trees can provide optimal climate, human well-being, and biodiversity benefits while also minimizing costs related to implementation or alternative land uses. This analysis, recently published in One Earth, shows that many co-benefits are possible, but not simultaneously at the same sites. Indeed, it can be challenging to achieve multiple goals in the same site and the analysis demonstrates trade-offs among these goals. For example, areas well-suited for nature-based recreation tend to have lower costs associated with planting and land but host fewer at-risk species or have slower tree growth (which means less carbon storage). Because of trade-offs like this, ensuring that tree planting occurs at diverse sites and for different priority reasons across the country is an important strategy for optimizing co-benefits. By choosing multiple sites for restoration, each with different objectives related to co-benefits, the full range of co-benefits from planting trees can be achieved.
The analysis also identifies important synergies that can inform Canada’s forest restoration efforts. For example, many areas of high tree growth also host high numbers of at-risk species, highlighting an opportunity for restored forests to achieve both climate and biodiversity goals. The Mixedwood Plains of southern Ontario are home to dozens of species that are in decline and may be in danger of extinction, including birds like the Canada Warbler. Trees in this well-populated area can grow and store carbon quickly, so planting trees here can provide clean water to communities, habitat for animals, and lower carbon in the atmosphere.
The team’s first step in conducting the analysis was to identify the full potential area suitable for restoration. This “area of opportunity” includes places (1) historically forested but converted to other land uses, such as pastures, or (2) that experienced natural disturbances like wildland fire that did not successfully regrow trees on their own. We excluded high-quality agricultural lands to avoid conflicts with food production, as well as areas where trees are not naturally dominant, like native grasslands, to avoid potential failed plantings or negative impacts on biodiversity. We also excluded areas that already hold enough trees or where tree planting is already required by law, so that restoration is “additional” to the status quo. We excluded areas at high elevations or at very high northern latitudes, which are hard to plant and have limited ability to store carbon due to slow growth rates. Areas not compatible with tree planting, such as urban environments or areas covered in water and ice, were omitted.
We used ArcGIS Pro 3.1 to compile data layers at the same extent and resolution, perform geoprocessing tasks such as transforming coordinate systems, and extract relevant pixels as described above, with a final resampling of all layers to 300-m resolution.
We determined that 19.1 million hectares are suitable for restoration of forest cover in Canada, far more than the 1.2 million hectares needed to plant 2BT. We performed an optimization analysis of eight scenarios of forest restoration to determine the places in the area of opportunity where 2BT can best achieve different objectives. These scenarios prioritized various aspects of restoration such as high growth rates, low cost, and close distance to the nearest road for accessibility and ease of planting. We also explored scenarios to maximize co-benefits to people, like providing freshwater and nature-based recreation, as well as co-benefits to nature, such as areas important to ecological connectivity that allow the free movement of animals. While this optimization analysis was done outside of the Esri environment using the prioritizr package in R, ArcGIS Pro allowed for the creative visualization of results. To help spread the word about the findings, we created an online data explorer using Esri Instant Apps to allow anyone to easily see where opportunities lie for planting trees.
With the help of these tools, we are sharing our findings with practitioners, policymakers, and the public to support targeted forest restoration in optimal locations and enhance how planting trees across Canada can achieve both climate and biodiversity goals while benefiting people and nature. Wherever landscapes need help to once again become forests, each tree is a step closer to achieving the diverse goals that people have for new plantings.
