TRCA Terrestrial Monitoring: What are the Plants and Animals Telling Us?

A number of both good and bad news stories have been brought to our attention in the recent Terrestrial Long-term Monitoring, Spatial and Temporal Trends 2008-2014 report produced by TRCA’s Environmental Monitoring and Data Management team. Using data collected from long-term monitoring sites, the report uses specific measures of biodiversity to provide an update on how TRCA’s wetland, forest and meadow communities are changing over time, as well as examining the differences in ecological health between urban and rural sites.

What are the Data Telling Us?


The good news is that TRCA’s regional forests consist primarily of native trees (83%) in healthy condition with very few showing signs of severe decline (1.6%). It is expected, however, that the current low tree mortality rate (approximately 0.5% dying each year) will likely climb in the future as a result of the damage inflicted by the spread of the Emerald Ash Borer and by the December 2013 ice storm that hit Toronto and the surrounding region.

TRCA terrestrial monitoring team studying plant and animal species in a forest area

Garlic mustard, a non-native plant that is displacing native groundcover, is also increasing across the regional forest plots, especially in urban sites. Urbanization has led to more generalist forest flora communities, containing fewer sensitive species and more exotic species such as garlic mustard.

Overall forest birds are proving more susceptible to impacts in urban areas compared to meadow or wetland bird communities. The number of forest-dependent birds was lower in urban forests compared to rural ones, including Regional Species of Conservation Concern.

Most concerning is the serious decline of sensitive ground-nesting birds (e.g. ovenbird) at rural sites. Birds that nest and forage on the ground are extremely susceptible to urbanization e.g. the proliferation of informal trails bring increased traffic and noise from hikers and off-leash dogs.


There has been a slight increase in sensitive meadow bird species within rural sites, despite an overall decline in abundance of meadow-dependent species across the region since 2008. This decline is cause for concern as it mirrors the downward spiral of grassland breeding bird populations across North America since the 1960’s, as reported by the North American Breeding Bird Survey.

TRCA terrestrial monitoring team studying plant and animal species in a meadow area

This downhill trend is thought to be a result of many factors including habitat fragmentation in rural landscapes, which in turn contributes to higher predation rates.


Frogs and toads, as well as the number of wetland-dependent birds, appear to be stable. The only species showing potential signs of decline over the past 7 years are the more sensitive wood frog and grey treefrog.

Overall regional monitoring sites in urban areas are occupied by fewer amphibians and contain less sensitive species when compared to rural sites. Spring peeper populations seem to be the most impacted by urbanization in the region, with very few found in the more developed sites.

A frog photographed by the TRCA terrestrial monitoring team in a wetland area

Urban areas are generally less favourable environments for amphibians because of the increased density of roads. Mortality from cars is a huge threat for many amphibian species who travel to find suitable breeding and overwintering habitat in adjacent forests and wetlands. Amphibians are also particularly sensitive to increased chloride (i.e. road salt) that enters wetlands from stormwater run-off.

Wetland plant communities are also showing strong, negative impacts of urbanization and the further spread of invasive common buckthorn in wetland edges needs closer surveillance.


This report shows that while many of the measures of biodiversity analyzed in this report appear to be stable over time, almost all are showing impairment due to urbanization. If the jurisdiction foresees the conversion of more rural land to urban land uses, we will expect to see drastic declines in ecosystem health in the years to come.

More research needs to be done on development and land-use planning that maintains habitat for sensitive species while still meeting the demands of a growing population. By continuing long-term monitoring across our watersheds we can inform conservation land management to negative trends in ecosystem health and provide a window of opportunity to reverse any downward trends.

Did you know? TRCA’s Environmental Monitoring and Data Management team is currently involved in two preliminary roadside ecology studies that should help in the development of wildlife crossing structures and other mitigation measures in key amphibian habitat hotspots.

Monitoring Matters! Through scientific data collection, TRCA’s Environmental Monitoring and Data Management team tell the stories about the changes affecting the natural areas and watercourses within our regions. For more information, please visit our website, follow us on Twitter, subscribe to our Monitoring Matters e-newsletter, or visit our YouTube playlist.