Impacts of Deer Overpopulation Part 3 of 3: Community Impact

Published by Rob Underhill on 08/28/2024 09/16/2024

This is the third and final part in a three-part series on the impacts of deer overpopulation on SḴŦAḴ | Mayne Island. In the first two instalments of this series, we explored the ways in which deer overpopulation reduces biodiversity and the ability of local ecosystems to respond to change. In this final instalment, we will discuss how these impacts affect the human community on the island.

Some impacts to our community from deer overpopulation are obvious to anyone who has tried their hand at home gardening on SḴŦAḴ | Mayne Island. The supposedly deer proof plants recommended by friends living in other places are quickly gobbled up, and this is a hot topic in grocery store lineups and across the fence with the neighbour, resulting in comments like, “they ate my daffodils!” While having your prize flowers eaten is annoying, the impacts to our community go deeper than you may realize.

Flood Control

The fall 2021 rainfall event in the Pacific Northwest was significant and devastating. It was primarily caused by a series of atmospheric rivers, which are narrow corridors of concentrated moisture in the atmosphere. These atmospheric rivers brought heavy rainfall to the region from November 13-15, 2021. Though impacts to communities in larger watersheds such as the Fraser Valley were more significant, our community here on SḴŦAḴ | Mayne Island was also affected. In a matter of hours, small seasonal creeks were overflowing their bounds, creating new and unpredictable water courses. As fast-moving surface water flowed across the land, it carried soil with it, in many cases eroding hillsides and banks, not to mention flooding more than a few basements and septic fields. You may be wondering, what does this have to do with deer?

Deer overpopulation has resulted in a big decrease in plants that grow in the understory of our forests. These plants hold together the soil, spread out the flow of surface water, and slow down water flow during peak rainfall events. Spreading and slowing the water acts to reduce its power to cause erosion.

Groundwater Recharge

Slowing and spreading out water isn’t just important for preventing erosion, it’s also important for recharging the groundwater our community relies on. Unfortunately, past land development on SḴŦAḴ | Mayne Island has largely failed to consider natural surface flow. Instead, we have relied on ditching and draining to make the water go where we want on a site-by-site basis, protecting infrastructure such as roads and homes from seasonal flooding and creating drier valley bottoms for hay and grazing pastures. However, this pattern of ditching and draining acts to funnel water together and keep it moving off the island, which is the opposite of what we want from a groundwater recharge perspective.

While deer are not responsible for land development, overgrazing by deer in the remaining natural areas reduces the ability of those areas to naturally slow, spread, and absorb water.

Resilience to Forest Fire

I recently attended a workshop on how we can make communities in the Southern Gulf Islands more resilient to forest fires. It was a great workshop and was attended by the right mix of indigenous knowledge holders, emergency response professionals, land managers, and ecologists.

Some of the ideas coming together in the workshop were about how we can reduce fire severity and rates of spread by managing fuels in our forests. One accepted practice to accomplish this in young, dense second growth conifer forests (where trees are often small and tightly packed together) is to create gaps in the coniferous canopy to encourage the growth of less flammable deciduous trees and shrubs. Under normal deer browse conditions, these deciduous species will regenerate on their own. I (and others from Gulf Islands with deer overpopulation) pointed out that deer overpopulation is preventing the natural regeneration of those desired deciduous species, so fencing would need to be installed and maintained to achieve the desired results, increasing the cost of fire mitigation practices. Deer fencing is expensive to install and maintain, as many landholders on SḴŦAḴ | Mayne Island have learned.

Costs of Fencing – Food and Forests

The Mayne Island Conservancy has installed about 3km of deer fencing around habitat restoration projects. This adds a huge cost to our restoration efforts, and means we achieve less with the limited resources we have than we could. This is the same situation for anyone growing vegetables or fruit, whether it’s a kitchen garden or commercial farm. The largest barrier for local food production is the cost of producing food at a small scale and on high-value property. Small producers are hard pressed to offer prices competitive with food produced by larger, more mechanized farms, or in places with a lower cost of living and associated wages. The added cost of installing and maintaining deer fencing around crops makes growing food here even more expensive.

Decreased Carbon Storage

We all have a part to play in solving the global climate crisis, even our small community here on SḴŦAḴ | Mayne Island. Retaining natural vegetation is the easiest way for us to contribute, since it literally involves doing nothing: plants naturally absorb CO₂ from the atmosphere and incorporate it into their tissues as they grow. Unfortunately, deer overgrazing reduces the carbon storage and sequestering capacity of natural areas by reducing the amount of plant material in the forest and preventing the regrowth of plants. This means that areas set aside for nature conservation are not contributing to climate change mitigation as well as they could be.

Indigenous Use of Plants

Heavy deer browse limits opportunities for indigenous use of native plants when those plants are reduced in abundance and diversity. University of British Columbia researcher Peter Arcese and others found that higher deer abundance reduced culturally significant plant species. For SḴŦAḴ | Mayne Island, which is about 2,200 hectares in area, Dr. Arcese’s research suggests we would need to reduce the total number of deer on the island to around 180 in order to maximize plant biodiversity. There are currently no accurate estimates of the total number of deer on SḴŦAḴ | Mayne Island. In the few places on the island where the Conservancy has used pellet (deer poop) counts and the shape of oceanspray to estimate local deer abundance, the results indicate a relative abundance of 0.5-2 deer/ha. This means that in some places on the island, we may have 25x the number of deer that would historically have lived here before all the cougars were killed and the fallow deer were introduced. To read the technical report on those studies click here.

Check out the full three-part series on the impacts of deer overpopulation here.