Local in Ann Arbor

Hepatica acutiloba (photo by R.W. Smith) Spring, beech-maple forests.

The land speaks in flowers.    

— Shawn Severance

Wildflowers are a major source of delight in a stroll through natural areas.  Indeed, a reason many of us choose to “take a stroll in the woods” is that a season of flowers has arrived.

Jeffersonia diphylla (Twinleaf). Early spring, rich forest. Photo by C. Peirce.

But flowers have a much more important role in nature than to provide us a momentary pleasure. The beauty and scents are part of a pollination strategy for seed production.  Some flowers are pollinated by visiting butterflies, some by bees, and some by flies.  Night-blooming flowers are pollinated by moths. Tubular red flowers are often pollinated by hummingbirds.  All this flower sex makes for an important source of food for the pollinators.

Mitella diphylla (Bishop’s Cap), spring, rich forest. Photo by C. Peirce.

Trillium flexipes (Drooping Trillium) Spring, rich forest. Photo by Ann Arbor Natural Preservation

Yes, we are talking again about the food web, or as we have called it, the web of life.  Not only do the flowers feed their pollinators, but the fruits and seeds that the flowers produce are often important food sources for small mammals and birds.  The insects fed by flowers in turn are important in the diet of frogs and toads, snakes, and birds. The amphibians, birds and small mammals are the prey for raptors (birds) and sometimes larger mammals.  But it begins with the flowers.

The Impact of Deer on the Natural Landscape

Campanula americana, photo by Ann Arbor Natural Preservation. Summer, openings in deciduous forest.

Lysimachia terrestris (Swamp-candles), photo by R.W. Smith. Mid-summer, marshes and fens.

Those of us who love the natural world often see a wild place as a whole – the trees, the smaller plants, the small and larger mammals, the birds, the insects.  The concept of the ecosystem is fundamental to ecology; all the parts fit together, including the inanimate physical setting.  The food web is an integral part of that ecosystem and helps define the relationships within it.  But because the white-tailed deer is increasing out of bounds and is consuming a far greater proportion of the food resources in local ecosystems, they cause a degradation of the whole, making it less supportive of all the other living beings in it, and ultimately of the deer themselves (the carrying capacity is exceeded).

Aster laevis (Smooth Aster) fall, dry wood edges, prairies. Photo by B.S. Walters.

The problem is that deer have very demanding nutritional requirements.  They need approximately seven pounds of high-quality food a day (amounts will vary according to life cycle state).  As this study from the University of Missouri extension explains,  the diet needs to be relatively high in protein (15-20%), especially during antler formation and lactation.  They don’t get by on nibbling leaves or grazing on grass.   They eat tender buds and rapidly growing tips of plants, because that is where the protein is.  Their browsing can take out whole stands of saplings and young herbaceous plants (called forbs). One of the general effects of deer overbrowsing is the loss of both the numbers of plant species (diversity) and of the numbers of the plants themselves.  It is said that the quality of the plant community has declined. As shown in this long-term study from Wisconsin (overview) (scholarly paper) an area browsed by deer is likely to contain mostly ferns (not eaten by deer), grasses and sedges, and some non-native or invasive plants.   Even the species of plants that did seem able to co-exist with the deer were shorter and smaller. Tree regeneration was severely limited (seedlings did not survive).

Carex prasina (Drooping sedge), photo by A. A. Reznicek. Spring, wet deciduous woods. (Wind pollinated)

An alarming observation that the Wisconsin researchers made was to point out that many or most of the surviving plants employ “abiotic” pollination. This is usually wind-pollinated (grasses and sedges are wind-pollinated, as are trees, and ferns produce windborne spores).  They speculated that this could be because of loss of the animal pollinators “by altering the abundance and quality of plant food resources and habitat available to pollinators and songbirds”.  A circular causation here – if a plant species becomes too sparse, it may be difficult for pollen from another plant to reach it, especially if the pollinator is not present, partly because there weren’t enough flowers to feed the pollinator, so its population would decline…   But note that the nutritional value of the surviving vegetation to deer is also limited.

The language of flowers

So in conclusion, the absence of flowers is both an early indication of deer overabundance and an injury to the ecosystem resulting from it.  Aldo Leopold had a strong empathy for ecosystems and nearly personalized them in his concept of “the land”.  As we reviewed earlier,  he spoke of an ethic in which the land (the whole community of living things) was to be loved and respected.  If we view the entire community as an entity to be preserved, we should note this symptom (of lost flowers) with concern.  Washtenaw County Parks naturalist Shawn Severance, who has been involved for some years with studying the natural plant communities of Washtenaw County parks and natural areas, said it this way:  “The land speaks in flowers.”    Yes, and it is trying to tell us something.

Photographs of flowers are by permission of the photographers and of  University Michigan Herbarium.  They should not be copied without permission (ask at info@michiganflora.net).   All species shown here were found at Ann Arbor’s Bird Hills Nature Area at some time in the past and have a high conservation coefficient (are considered high-value species).

UPDATE: As of November, 2019, the City of Ann Arbor deer management program is up for reauthorization. This will be the 5th year. A major objective of this program has been the protection of plants in our natural areas. Happily, the City has contracted with Jacqueline Courteau, an independent consultant (NatureWrite, LLC) who is a specialist in deer-vegetation interaction. She has been assessing the levels of deer browse for some years. Her latest study has just been made available on the City’s site. It is Deer Browse Study Key Metrics 2018 and contains data from bioassays Courteau conducted for several years. She used both red oak seedlings (since oak is a favorite browse of deer) and three wildflower species, two goldenrods (Solidago caesia, bluestem goldenrod; Solidago flexicaulis, zigzag goldenrod); and  heart-leaved aster (Symphotrichum cordifolium).  She also used fenced and unfenced plots to assess the condition of Trillium grandiflorum, one of our best-loved spring wildflowers and a known deer browse indicator. Her conclusions are somewhat alarming for us flower lovers. She found that deer seemed to prefer wildflowers to oak seedlings.

These browse levels suggest that, overall, deer prefer wildflowers, and will eat a higher proportion of wildflower plants than of oak seedlings—providing evidence that, in Ann Arbor sites, oaks are of lower preference to deer, whatever their palatability rating. Because deer browse levels on oaks are lower than on wildflowers, using oak seedlings as an indicator of deer impacts will generally underestimate damage to wildflowers overall.

The summary results are shown in a handout Deer Impact Final Summary 2018-19-1 for a talk to be given at the UM Herbarium. Here is the summary graphic.

Note that for each test species, the outline is filled with color in proportion to the amount browsed. Trillium is treated slightly differently; most reports use a pink color to indicate the flower, but in Mary Beth Doyle Park the green color indicates the number of plants.

All in all, these studies indicate that the deer management program has lessened the pressure on the native vegetation, but it is still severe. We are not out of the “woods” yet.

This entry was posted on May 31, 2015 at 7:51 pm and is filed under Sustainability. You can subscribe via RSS 2.0 feed to this post's comments. You can comment below, or link to this permanent URL from your own site.