What space technology can reveal about Canadian forests

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Have you ever wondered how forest researchers know how many trees are in a country as large as Canada? Look up, way up, because the answer lies in space.

Guy Strickland is a remote sensing and geographic information analyst at the Canadian Forest Service. He’s researching a new, sky-high method to model and inventory Canada’s forests so scientists can better understand what’s happening back on Earth at ground level. “Having an accurate forest inventory is an important part of forest management,” says Guy. “That’s how we can monitor and report changes in forests and gain knowledge on which to base forest management policies and land-use decisions.”

For instance, knowing how tree species are distributed across the landscape and how this distribution may have changed over time can help forest science researchers monitor the effects of a changing climate in a very clear, focused way. And with this detailed information in hand, forest managers and decision makers can then take preventive action sooner and more effectively than before.

Forest ecosystems are under increasing pressures, particularly due to climate change. As a result, there are increasing requirements for forest inventories to provide detailed qualitative and quantitative assessments of various features, such as the prevalence of particular tree species and the overall distribution of trees in our forests. But there are two related problems: first, finding a way that’s cost-effective and can be consistently applied over Canada’s large land mass and our 3.48 million square kilometres of forests; second, doing this while at the same time providing sufficient amounts of detailed spatial and temporal data. That’s where satellite technology comes in.

The Landsat program is a series of Earth-observing satellite missions jointly managed by NASA and the U.S. Geological Survey since 1972. The collection of information is straightforward: Landsat satellites can provide the data to efficiently monitor land use and to document land change. But handling this information is more complicated, and using Landsat data in Canada was challenging at first, for two reasons: limited access to the data and the complexity of storing and processing large numbers of images. These difficulties were resolved, however, when the Landsat archive became freely available online in 2008, advancing the way scientists are able to do research.

“Access to the detailed imagery allows us to develop cost-effective ways to obtain a large-scale picture of Canada’s forests,” says Guy.

And with more than 40 years of data available from Landsat sensors, researchers can analyze forest changes over time. This ability is important not only for better understanding the impact of forest disturbances, such as pests and wildfires, but also for assessing the variation in tree populations over specific time periods. The resulting information is vital for shaping forest management policies and practices in the future.

As well as the Landsat satellite imagery, forest researchers have another essential resource in Canada’s National Forest Inventory (NFI). This photographic inventory provides information on the state of Canada's forests and a continuous record of how forests are changing over time. It does so by measuring a network of 20,000 sampling points across Canada, with 2-km-square photo plots located within a national 20-km-square sampling grid. By combining this NFI data with Landsat imagery, Guy and his colleagues developed an approach to extend some specific data in the Canadian NFI over a large area.

Taking the boreal forest region of Newfoundland and Labrador, Guy and his team modelled and assessed changes in the presence or absence of trees and in tree species distributions over a 25-year period from 1985–2010. They applied both the NFI and Landsat data to refine algorithms and create models that extend that information beyond what the NFI reveals by itself.

This approach marked a real innovation: researchers had never worked with data from multi-year NFI photo plots and multi-year Landsat satellites quite like this to efficiently develop models and produce time-series mapping and area assessments. In doing so, Guy and his team were able to develop new models to produce annual maps covering the boreal forest of Newfoundland and Labrador.

And since this approach uses data sets that are consistent across the country, it has the potential to be applied not just in a single province but on a national scale — and thus to serve as a highly valuable resource for Canadian forest management, science and policy, now and into the future.

Learn more about Guy Strickland’s work on ResearchGate The National Forest Inventory Satellite Forest Information for Canada