Assessing plant community composition fails to capture impacts of white-tailed deer on native and invasive plant species. Issue 4 (8th June 2017)

• Record Type: Journal Article
• Authors: Nuzzo, Victoria; Dávalos, Andrea; Blossey, Bernd
• Is Part Of: AoB plants. Volume 9:Issue 4(2017)
• Publication Date: 2017-06-08
• Subjects: Deer herbivory -- deer management -- earthworms -- forest understory -- invasive species -- multiple stressors -- plant community; Plants -- Periodicals; Botany -- Periodicals; 580.5
• DOI: 10.1093/aobpla/plx026
• Languages: English
• ISSNs: 2041-2851

Abstract

Abstract : Excessive herbivory by native deer can reduce abundance of native vegetation and increase non-native vegetation, but how does the forest recover when deer are excluded or numbers are reduced? The expectation is that understory vegetation will return to a previously diverse condition, but this is not always the case. We found that community-level monitoring captured both change and lack of change in vegetation cover, height, species richness, and response of common species, but failed to capture response of uncommon species. In contrast, monitoring of target species favored by deer indicated increased plant size and reproduction when deer were reduced or excluded. We conclude that measuring individual plants (growth, flowering and reproductive success) provides a sensitive and powerful assessment of forest understory responses to deer management. Abstract: Excessive herbivory can have transformative effects on forest understory vegetation, converting diverse communities into depauperate ones, often with increased abundance of non-native plants. White-tailed deer are a problematic herbivore throughout much of eastern North America and alter forest understory community structure. Reducing (by culling) or eliminating (by fencing) deer herbivory is expected to return understory vegetation to a previously diverse condition. We examined this assumption from 1992 to 2006 at Fermilab (Batavia, IL) where a cull reduced white-tailed deer ( Odocoileus virginianus ) abundance in 1998/1999 by 90 % from 24.6 to 2.5/km 2, and at West Point, NY, where we assessed interactive effects of deer, earthworms, and invasive plants using 30 × 30 m paired fenced and open plots in 12 different forests from 2009 to 2012. We recorded not only plant community responses (species presence and cover) within 1 m 2 quadrats, but also responses of select individual species (growth, reproduction). At Fermilab, introduced Alliaria petiolata abundance initially increased as deer density increased, but then declined after deer reduction. The understory community responded to the deer cull by increased cover, species richness and height, and community composition changed but was dominated by early successional native forbs. At West Point plant community composition was affected by introduced earthworm density but not deer exclusion. Native plant cover increased and non-native plant cover decreased in fenced plots, thus keeping overall plant cover similar. At both sites native forb cover increased in response to deer reduction, but the anticipated response of understory vegetation failed to materialize at the community level. Deer-favoured forbs ( Eurybia divaricata, Maianthemum racemosum, Polygonatum pubescens and Trillium recurvatum ) grew taller and flowering probability increased in the absence of deer. Plant community monitoring fails to capture initial and subtle effects of reduced or even cessation of deer browse on browse sensitive species. Measuring responses of individual plants (growth, flowering and reproductive success) provides a more sensitive and powerful assessment of forest understory responses to deer management.