Our Wild Ones mission is to promote the use of native plants in a wide array of landscapes. Why? Because native plants are necessary, and powerfully effective, to heal and extend sustainable, diverse biological communities of flora and fauna. Native plants run our ecosystems. They are the plants that have formed mutually beneficial relationships with native wildlife over millennia of co-evolution. These relationships are at the heart of productive and sustainable wildlife habitats. Fostering native plants, according to Wild Ones honorary director and mission guru Doug Tallamy (also Professor of entomology and wildlife ecology at the University of Delaware), helps “nature take its course”, restores “nature’s relationships”, and engages us in making choices “for the greater good”. You can read more here: https://tinyurl.com/mr25akaf.
Given our mission, we immediately recognize the necessity of doing what we can to root out (literally) invasive plants, or at least (when eradication is not possible) to manage them as best we can. If invasive plants are not checked, they spread and compete with the native plants that are the engine of our ecosystem. This much is incontrovertible.
But how, then, should we consider the problem of too many deer in our environment? We know that there are too many deer (in southern Michigan and elsewhere), a problem that adversely affects humans – think deer-car collisions, crop losses, the spread of ticks – and the deer themselves, many of which die from starvation and the devastating, fatal chronic wasting disease and epizootic hemorrhagic disease (and also car crashes). At WO, our focus is to support individuals and organizations in creating plant ecologies that sustain all the different lives within them – plants, bugs and other insects, birds, amphibians, fish, mammals, fungi, and even microorganisms. In this context, our concern about deer is focused on the direct threat to biodiversity arising from damage to plants caused by excessive browsing, and also related harms to soil and water.
In the early 1900s, deer had disappeared in southeast Michigan. They were reintroduced, and there was migration from “up north”, in the 1920s. Herds grew, and by the 1940s, deer populations crashed due to overabundance and starvation. In our current times, we again have an overabundance in urban areas, with current numbers believed to be higher (in Michigan and throughout the US) than in pre-European settlement times. Deer herds have grown because increased agriculture offers them more forage, major predators have been extirpated, “edge” habitats between natural and urban areas are favorable to deer, winters have been warmer overall, and there are fewer hunters.
White-tailed deer favor white pine, red pine, maple, oak, beech, eastern cedars, and even woody shrubs in winter, and they will turn to herbaceous shrubs and forbs (herbaceous perennials) as the weather warms. When there are too many deer, forest understory growth, and growth in similar stands in natural areas, is destroyed. The trees and plants cannot regenerate themselves because they cannot grow faster than the rate at which they are browsed – they end up nibbled to stubs. Native forbs frequently get replaced by invasive species that do not support insect life or soil health. Without trees and forbs, bee and butterfly populations drop, along with their larvae and caterpillars on which birds depend. Tallamy has referred to the loss of insect life we are currently experiencing as “insect apocalypse”. A single pair of breeding chickadees needs between 6,000 – 9,000 caterpillars to rear a single clutch of young – we can easily see that an insect apocalypse very quickly becomes a bird apocalypse. In addition, when trees and shrubs are browsed to the ground, ground-nesting birds lose their habitat, and often their lives. Carbon sequestration in the soil is dramatically reduced, and rivers are deprived of cooling shade, extending the harm to aquatic life.
And it isn’t just forests and nature preserves that suffer. Much of WO’s focus is on residential yards, typically in urban and suburban settings. Our yards play a crucial part in maintaining biodiversity and serving as a linked habitat for wildlife of almost all kinds (except large predatory mammals, for the most part). A 2005 study estimated that lawn in the continental U.S. totals more than 63,000 square miles, or about 40 million acres, an area three times larger than that given over to any irrigated crop: https://tinyurl.com/nha6bjb3. Most of what we commonly call “lawn”, as a general rule, is made up of non-native grasses that depend highly on fertilizers and pesticides, and do not support a diversity of wildlife. If even half of these lawn acres are converted to wildlife-friendly native plants, we will have created a powerful defense against the risks of apocalyptic extinctions: https://tinyurl.com/bddk29ze. But deer do their harms in these urban and suburban settings, as almost all gardeners know. Native plants are their favorites.
Two different experiences may help us think about this problem.
The Ann Arbor Cull
One experience is the story of Ann Arbor’s recent deer cull. From 2016-2020, Ann Arbor maintained a deer management program, which included monitoring deer numbers, conducting area-limited sharpshooter culling of certain herds, and sterilizing a smaller number of deer: https://tinyurl.com/bdd8zu72. The cull produced promising results, although a 2019-2020 study of its effects concluded that although browse levels were reduced, they were still too high to allow oak tree regrowth and forest replacement, suggesting that a future cull might be necessary. The study summary is here: https://tinyurl.com/2p9aefmz. Also during that period, a group of Wild Ones members organized a special effort dedicated to deer management, the Washtenaw Citizens for Ecological Balance (or wc4eb, for short). A good informational website was created as part of this effort, and can be viewed here: https://tinyurl.com/5n8u2264. However, the city program was not renewed after 2020, and among the casualties was any effort to gather data regarding deer herd sizes or ongoing deer impacts on vegetation in our area.
The University of Michigan ES George Reserve
Another story was described when Ann Arbor was considering whether to fund the deer cull in 2016, or to delay it. University of Michigan Professor of Ecology and Evolutionary Biology Christopher William Dick supported allocating the funds sooner rather than later, and in so doing he summarized the experience at University of Michigan’s ES George reserve, in Livingston County:
“In 1930 six whitetail deer were introduced in the reserve. In six years that number increased to 160 deer. UM biologists learned about the exponential growth rates of whitetail deer. They also noted that deer overabundance destroyed the forest understory and stopped forest regeneration. In order to maintain ecological balance, UM has periodically culled its deer herd since the early 1940s.”
Of added interest is that the reduced number of individuals in the George Reserve herd helped stave off the spread of ticks and the diseases they carry, and in this way culling the herd actually helped the remaining deer and overall health of the herd. The herbaceous plants and native tree seedlings in the Reserve rebounded and have become a lush forest understory. This has led to deer management decisions in some years to forego culling, as unnecessary. You can see Dr. Dick’s comments here: https://tinyurl.com/c7t6a4nh.
Deer impact the composition of vegetation in our natural areas and suburban yards. Deer influence habitat for birds and other wildlife, and their breeding. They alter the number of caterpillars, pollinators, and birds in their environment. Deer also change the quality of soil, through compaction, and because reduced herbivory results in bleaching certain nutrients at the soil surface. https://tinyurl.com/4m5wajfy. So here is the challenge: What is the best management of local deer populations, and what is an appropriate decision-making process for resolving deer management controversies?
One thing is for sure – ignoring the issue will undermine our best efforts to create sustainable and healthy natural environments.