In Northern, permafrost-impacted systems, tree species distributions are strongly influenced by permafrost (i.e. perennially cryotic ground) distribution, which in the discontinuous zone is changing rapidly. Using remote sensing methods, we have demonstrated increased rates of permafrost degradation and the importance of landscape configuration on rates of thaw. At the individual level, we have identified root dysfunction and resulting reduction in sap flow as a key driver of reduced tree growth and, ultimately, tree death in response to permafrost thaw. Finally, field-based observation of unusually high levels of gall-inducing mite herbivory has led to the initiation of research focusing on the impacts of galling on forest structure and dynamics. We demonstrated important interactions between the physiological response of trees to galling and the habitat on which they occur; in other words, abiotic stress exacerbates the negative impact of herbivory, a pattern that we also recently demonstrated in species-rich tropical assemblages. In 2012, we established the Scotty Creek Forest Dynamics Plot, a 20.8ha mapped plot within the zone of discontinuous permafrost. This plot will provide a critical framework for understanding changing boreal forest dynamics, composition and structure with permafrost thaw. It is the first boreal site within the CTFS-ForestGEO network (http://www.forestgeo.si.edu), a network of 61 plots in tropical and temperate forests in 24 countries. The addition of our boreal plot facilitates direct comparisons of tropical, temperate and boreal forest dynamics, which will advance our understanding of responses of different forest types to global change and drivers of latitudinal biodiversity gradients.
The sub-Arctic tundra is rapidly transitioning into taller shrub-dominated communities. This change is largely attributed to climate warming, which drives increases in shrub growth and recruitment, shifts in plant community composition and structure, local reductions in biodiversity, and increases in primary productivity with the potential to drive strong feedbacks on the climate system such as alterations to carbon and water cycling. Shrubbing also results in physical changes in the environment that are thought to feed back positively on shrubbing and associated changes. One key physical change is the increased capture of snow by shrub patches during blowing snow events, which insulates the ground leading to warmer winter soil temperatures. Despite these recognized and profound changes in the structure and function of the tundra as shrubbing progresses, we know surprisingly little about the drivers of shrub distribution on the landscape or the impacts of landscape position on the resulting structural and functional changes associated with shrubbing. Such knowledge will facilitate an improved understanding of the implications of shrubbing for water cycling, litter and nutrient inputs to drainage channels and streams, and tundra diversity. To enhance our understanding of the drivers and implications of shrub distribution, we are working at a tundra site north of Inuvik called Trail Valley Creek to: 1) determine associations of shrub distribution with topographic features at the landscape level over the last 60 years; 2) quantify structure and composition of plant communities in shrub and adjacent tundra patches; and 3) quantify productivity and water use in different shrub species and relate this to landscape position and hydrological feedbacks.
Fire as a natural process is important to maintaining boreal ecosystems. In 2014, 3.4 million ha of forested lands were impacted by wildfires in the NWT, which makes this the largest fire season in the NWT’s history. The fires were concentrated in the region around Great Slave Lake and thus affected the majority of the population in the Territory. A wide range of ecosystems was impacted by these fires spanning several distinct ecoregions and the environmental gradients that each of these represent. The 2014 fire season was long and intense and the impacts of this event will have long-lasting but uncertain impacts for the communities and ecosystems of this region. Climate change is predicted to increase the frequency of these extreme fire years and as such, governments and communities must build the knowledge and capacity to adapt to these changing conditions. Presently predictions about the behavior of fires and their impacts on the affected ecosystems are based upon our understanding of more southerly boreal forests; there is thus a pressing need to improve our understanding of the response of high latitude boreal ecosystems to fire. We have begun to ask questions about the implications of wildfire in the range of boreal forests in the NWT.