The Influence of Native Deer on Forest Fauna-A Systematic Map

Abstract

Deer are the most abundant large herbivores in temperate and boreal forests across the Northern Hemisphere. They are ecosystem engineers known to alter understory vegetation and future tree species composition by selective browsing. Also, deer have strong impacts on faunistic groups, often mediated by vegetation. The ongoing loss of faunal biodiversity in forests worldwide can be exacerbated by high deer population densities. Adapted deer management for the purpose of forest biodiversity conservation requires a holistic understanding of deer-fauna relationships. In this systematic map, we examine the existing literature assessing the effects of deer on faunal communities in boreal and temperate forests. Our aim is to synthesize currently described trends and identify research gaps for our understanding of deer as biotic drivers of forest communities. We reviewed 64 studies on how the abundance, species richness, or diversity of faunal taxa responded to different levels of deer abundance or density in forest ecosystems across the Northern Hemisphere. In total, we found almost 400 individual reported effects of nine native deer species on forest-dwelling faunal communities. However, our systematic map reveals that comprehensive synthesis of the current literature remains a challenge. Published studies often do not report contextual data essential for comparison and meta-analysis, for example, deer density, forest management, and predation pressure. Moreover, the methodological approaches of the included studies often only account for potential linear effects of deer on fauna, likely oversimplifying the complexity of direct and indirect effects that deer can have on their ecosystem. We recommend that multi-level enclosure experiments be applied to assess the impact on faunal taxa. This approach combines robust causal inference with the potential straightforward comparison and replication between deer species, forest types, and system productivity, which will facilitate the utilization of the results in future research and management.

Keywords: abundance; cervids; community; fauna; forest; species richness.

FIGURE 1

Flowchart of systematic literature screening process.

FIGURE 2

Histogram of the year of publication for the studies included into the review.

FIGURE 3

Map displaying the distribution of study locations of included studies in the Northern Hemisphere.

FIGURE 4

Sankey plot displaying the frequency of individual deer species studied and the respective distribution among biomes and forest types, as well as the frequency in which deer species were studied exclusively or in areas also inhabited by other deer species.

FIGURE 5

Reported effects for vertebrate taxa. Black bars indicate effects on faunal abundance, gray faunal species richness, and green faunal diversity. Effects for bird guilds include nesting guilds while feeding guilds and categories like “forest specialists” or “migrants” are reported under “Other birds.”

FIGURE 6

Reported effects for the influence on deer on invertebrate taxa. Black bars indicate effects on faunal abundance, gray faunal species richness, and green faunal diversity. The response “Invertebrates in general” also includes effects that were reported for arthropods. “Arachnida” does not include spiders as these are reported individually. The category of “Other invertebrates” includes groups like Collembola and Turbellaria. The category of “Web building spiders” also includes weavers. The category of “Other insects” includes orders like Hemiptera, Psocoptera, or Blattodea. The category of “Other beetles” mostly includes other beetle families such as Staphylinidae, Curculionidae, Cerambycidae, or Leiodidae.

FIGURE 7

Sankey plot displaying the frequency of which faunal taxa were studied in relation to deer feeding type, methodological approach, and forest type. The method “index‐gradient” refers to studies using continuous indices, for example, from pellet counts as indirect variables representing deer abundance.