We found that in forest ecosystems fragmented by anthropogenic development, deer activity varied between forest and meadow patches, and the patch type that deer preferred varied depending on season. Interestingly, deer preferred anthropogenic meadow patches during seasons when resources were abundant across the landscape (i.e., spring and summer), and deer did not prefer forest patches during any time of year. We suspect that deer patch preference varied among seasons due to shifts in plant phenology and structure throughout the year, which can consequentially change the nutritional benefits and costs that a patch confers to a herbivore (Moore et al. 2010; Middleton et al. 2018). Additionally, meadow patches may have provided deer with a patch type where they felt less at risk to predation due to shorter vertical vegetation that can conceal predators such as coyotes, thus deer could decrease vigilance behavior (Donadio and Buskirk 2016; Gulsby et al. 2018). Ultimately, we suggest that anthropogenically introduced meadow habitats will help to support overabundant deer populations by providing deer with a supplemental foraging opportunity that exceeds the value of adjacent forest landscapes that can be degraded due to heavy browsing pressure.
We initially expected that deer would have the greater activity densities in the forest patches due to forbs and woody vegetation being more nutritionally beneficial than grasses (i.e., higher crude protein and energy - Demment and Van Soest 1985, du Toit and Owen-Smith 1989, Wigley et al. 2015). However, we did not find that deer preferred forest patches during any season. Instead, we found that deer preferred meadow patches in spring and summer, likely due to an abundance of green forage that was available in meadows compared to the forest understories. We predicted that forest patches would possess an abundance of high-quality broad-leafed trees and herbaceous plants for deer to consume, but found that the forest patches possessed an abundance of bare ground, and provided relatively few shrubs and juvenile trees that are nutritionally beneficial for deer. When deer persist at high densities, forest understories become highly degraded due to heavy browsing, and no longer possess an abundance of high-quality forage (Rooney and Waller 2003té et al. 2004; Goetsch et al. 2011; Pendergast et al. 2016). Deer densities that are greater than approximately 5 deer km2 are considered harmful to understory plant species (Alverson et al. 1988; Russell et al. 2001; McShea 2012). In the vicinity of our study in northeast Ohio, previous estimates of deer densities were approximately 36 deer km2 and were predicted to increase (Shafer-Nolan 1997; Fulton et al. 2004). Therefore, due to heavy browsing pressure from deer populations at high densities, the understories in the forest patches where we measured activity densities likely did not confer much foraging benefit to deer.
In addition to degraded forests, our result that deer preferred meadows in the spring and summer can be explained by the abundant and high-quality forage that we found in the meadow patches and better lines of sight to detect predators. The plant species that had the greatest associations with the meadow patches were species that are non-native and frequently associated with agricultural land use (e.g., smooth brome [Bromus inermis], white clover [Trifolium repens], bluegrass [Poa spp.]) (Johnson et al. 1987; Ellis-Felege et al. 2013). Cultivated forage species such as these generally have a high crude protein content and can provide wildlife high-quality foraging opportunities (Johnson et al. 1987; Dykes et al. 2020). Additionally, many cultivated forage species associated with meadows are grasses and therefore possess little to no plant secondary metabolites such as tannins or polyphenols to defend against herbivory (Orians and Ward 2010; Ward et al. 2020). Moreover, there was a greater availability of forage in the meadows, which was reflected by open ground being more abundant in forest plots. Therefore, the generalist foraging behavior of deer enabled them to use the more beneficial meadow patch during spring and summer.
Whereas coyotes primarily prey upon neonate deer (Vreeland et al. 2004; Kilgo et al. 2010, 2014) and hunting is not permitted in our study sites, meadow patches may have provided deer with a patch type where they felt less at risk to predation. Deer are most susceptible to predation from coyotes during the neonate and juvenile life stages; the risk of predation decreases as fawns grow and become more mobile (Vreeland et al. 2004; Rohm et al. 2007). Shorter vegetation enables prey species to visually detect predators more easily (Donadio and Buskirk 2016; Chen et al. 2021). Thus, during spring and summer when females are accompanied by fawns, deer activity may have been greater in meadow patches due a more open line-of-sight that affords a better ability to detect predators than forests that may obscure predators due to dense vertical vegetation.
During autumn, deer did not significantly prefer any patch type, and deer activity in the forest patch was relatively similar to deer activity in the meadow patch. We suspect that phenological changes in the vegetation in both the meadow and forest patches were responsible for these shifts in deer activity densities. During autumn in temperate regions, grasses, forbs and other understory species have matured and begun to senesce. As plants mature, the crude protein content deteriorates and becomes much less desirable forage to herbivores (Fryxell 1991; Van Soest 2018; Geremia et al. 2019). At this time of year, the vegetation that was present in the meadow patches was much less beneficial to deer than it was during the spring and summer months, thus explaining a decrease in deer activity in the meadow when compared to spring and summer activity densities. Additionally, as the vegetation in the meadow deteriorated in quality during autumn, masting crops such as acorns, hickory nuts and walnuts, that are a valuable foraging resource for deer and other wildlife (Harlow et al. 1975; Eagle and Pelton 1983; Elston and Hewitt 2010), became available in the forest. The forest patches at our sites consisted primarily of mixed hardwoods, of which the primary mast trees were shagbark hickory (Carya ovata) and various oak species (Quercus spp.). While forests were not significantly preferred by deer in autumn, an increase in masting crop availability likely contributed to the similar deer activity between the forest and meadow patches.
During winter, we did not discern any difference in deer activity densities in relation to patch type. In regions that experience harsh winters with cold temperatures and regular snowfall, such as northeast Ohio where this study took place, high-quality foraging opportunities for deer are scarce across all patch types because herbaceous food items have fully senesced and are of poor nutritional quality (Schmitz 1992; Van Soest 2018). Moreover, masting crops that were available during autumn have mostly been consumed by other wildlife or cached by small mammals, and are not a reliable food source (Wolff 1996; Fay et al. 2023). When there is a lack of food present on the landscape, deer employ a broad foraging strategy in which they decrease selectivity to meet their dietary needs (Berteaux et al. 1998; Dumont et al. 2005). Therefore, we expect that deer were not selective in their patch use during winter (when forage quality was likely at its lowest) and used multiple patch types across the entire landscape, rather than foraging in a single patch that may confer only minimal benefit. Moreover, because deer benefit from using agriculture as a resource subsidy during winter months (Vercauteren and Hygnstrom 1998; Grovenburg et al. 2010) it is possible that deer relocated out of the parks where we collected data and increased their activity in surrounding agricultural areas instead.
Due to the effects of global climate change, many temperate regions are predicted to experience longer, hotter summers and shorter, warmer winters with less snow (Kreyling 2010; Piao et al. 2019; Wang et al. 2021). This means that vegetation in these regions will remain green and more nutritionally beneficial to deer and other herbivores for longer periods throughout the year (Piao et al. 2019). Moreover, throughout much of North America, anthropogenic development is expanding, and deer will have increasing access to anthropogenically introduced meadow habitats in suburban and fragmented landscapes. A scenario in which non-native meadows become more abundant and growing periods increase in duration will increase forage opportunities for deer and may serve to support high-density deer populations. We suggest that in suburban landscapes where deer populations are overabundant, managing meadow patches to be less desirable to deer (e.g., seeding less nutritionally beneficial plants) may decrease the quality of landscape to deer and help reduce deer abundance.