In cooperation with Baldwin-Wallace College
The Impact of Deer Browsing and Flowering Plant Abundance on the Reproductive Success of Mayapple
Mayapple is an herb that grows in forests throughout the Midwest. It is pollinated by a variety of bees. As forests have been cleared and converted to other uses, there has been growing concern that pollinator populations would decline.
In a previous study, scientists at Baldwin-Wallace College compared 3 areas across northern Ohio in which forest cover varied from more than 50% (Lake County), to 15-20% (Lorain County), to less than 10% (Henry County). The decline in forest cover corresponded to an increase in the intensity of row crop agriculture across these counties. Instead of revealing a relatively low rate of pollination and fruit production in Henry County, the Baldwin Wallace Study found that Henry County plants had the highest rate of pollination and fruit production.
The absence of the predicted relationship among deforestation, agriculture and mayapple reproductive success leaves unanswered the question of what, in fact, controls variation in mayapple reproduction. One factor that may influence reproductive success is the density of other flowering plants in the vicinity of mayapple. Mayapple does not produce nectar and does not attract large numbers of insects. Other plants growing in the vicinity of mayapple may produce nectar and attract insects that then inadvertently visit and pollinate mayapple flowers.
In 2006, study results showed that the Henry County sites had a higher density of flowering, non-mayapple plants than the Lake County sites. This difference could be caused by the impact of deer browsing. In Henry County, deer can focus their browsing on crop and forage plants that are often very high in mineral content from crop fertilization. In Lake County, deer may have fewer options because of more extensive forest cover and much less agriculture. In Cleveland Metroparks, our vegetation survey has demonstrated that excessive browsing by deer can eliminate forest herb populations.
In spring 2008, Baldwin Wallace faculty and undergraduate students began an examination of the combined impact of deer browsing and the availability of non-mayapple magnet plants on the pollination and fruit production of mayapple in Cleveland Metroparks. Observations indicate that substantial variation in deer browsing exists, and in areas of high deer impact, mayapple actually seems to thrive given a low preference for browsing by deer. Because the researchers can identify mayapple populations in areas of both relatively high and low deer impact, they will be able to compare pollination and fruit production levels as a function of deer impact and specifically in terms of the density of flowering plants that might attract pollinators.