Forest ecosystems with a high diversity of tree species are more resilient to diseases and invasive pests. As we’ve seen with ash trees, when few species make up the majority of the urban forest and one of these common species is threatened 
Additionally, an increase in native plant diversity increases overall biodiversity. Bird and insect diversity increase in areas where there are native tree species, as opposed to areas with non-native tree species. That’s because these trees and animals have co-evolved together and mutually benefit one another.
Our planting events in York and Durham Regions will increase tree and shrub diversity while also decreasing the amount of invasive plant species. Effectively, naturalizing the planted area. As time goes on, the trees and shrubs will mature into healthy and thriving additions to the urban forest, providing essential food and shelter to urban wildlife and many benefits to local residents. This is why tree planting and stewardship activities can have such a large impact on the urban forest.
However, in order to ensure our naturalization efforts at each site are effective in the long-term, we need to have a way to assess the impact of our tree planting and stewardship over time. If, after a couple of years, the native species we planted are thriving, leading to an overall healthy site (an established and diverse population of native species, not overrun by invasive species), we can expect the site to mature into a healthy and sustainable section of the urban forest. However, naturalized sites in urban areas face many threats, including lack of water, pollution, vandalism and being overrun by invasive species, to name a few. As such, we need to be open to the possibility that our efforts may not always lead to immediate success and must put measures in place to recognize this and amend it.
We developed a five-year monitoring program to address this:
- Monitoring takes place before and during each planting event and then two-years and five-years after each planting event.
- During the first visit, we create monitoring plots that cover at least five percent of the planting site. We record the location of each plot and count and identify all the trees and shrubs present in them to establish baseline information for each site. We also identify any invasive plant species in each plot and document how abundant they are.
- At each subsequent visit, we return to each plot and collect the same data, as well as survival rate and plant health.
- With the data collected at each visit, we can infer overall site health and development through time. If any site is not developing as we would expect, we can adaptively manage and improve our future efforts, which may include additional stewardship activities (such as additional mulching or invasive plant removal) to support the native species planted.
Tree planting events began this fall at three sites in Richmond Hill. Work on Durham Region sites will begin in 2021. If you want to help us with our planting and stewardship work, register to become a LEAF volunteer!
Brian Millward is the Stewardship Coordinator at LEAF.
Our community planting and stewardship events are supported by Ontario Power Generation, the Regional Municipality of York, the City of Richmond Hill and Grandtrees Climate Solutions.