Individual and interactive effects of white-tailed deer and an exotic shrub on artificial and natural regeneration in mixed hardwood forests
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Individual and interactive effects of white-tailed deer and an exotic shrub on artificial and natural regeneration in mixed hardwood forests
Charlotte F. Owings 1
Douglass F. Jacobs 1
Joshua M. Shields 0
Michael R. Saunders 1
Michael A. Jenkins 1
Guest Editor: David Gorchov
0 Manistee Conservation District , 8840 Chippewa Highway, Bear Lake, MI 49614 , USA
1 Department of Forestry and Natural Resources, Purdue University , 715 West State Street, West Lafayette, IN 47906 , USA
Underplanting tree seedlings in areas where natural regeneration is limited may offer a tool by which desired overstory composition can be maintained or restored in forests. However, invasive plant species and ungulate browsing may limit the effectiveness of underplanting, and in-turn, the successful restoration of forest ecosystems. Individually, the invasive shrub Lonicera maackii and browsing by white-tailed deer (Odocoileus virginianus) have been found to negatively affect the regeneration of native tree species in the Midwestern United States, but few studies have examined their interactive or cumulative effects. Using exclosures and shrub removal at five sites, we examined the effects of white-tailed deer and L. maackii both on underplanted seedlings of Castanea dentata and Quercus rubra and on the composition, species richness and diversity of naturally regenerated native tree seedlings. Individually, both deer and L. maackii had negative effects on the survival of underplanted seedlings, but we identified no interactive effects. The presence of L. maackii or deer alone resulted in similar declines in the survivorship of Q. rubra seedlings, but the presence of deer alone resulted in lower survival of C. dentata seedlings than the presence of L. maackii alone. Lonicera maackii reduced light levels, increased seedling moisture stress and decreased relative basal diameter growth for Q. rubra seedlings. Deer reduced the relative growth in height of underplanted C. dentata and Q. rubra seedlings and increased moisture stress of C. dentata seedlings. No effects of L. maackii or deer were found on soil or foliar nitrogen or the overall abundance, species richness and diversity of naturally regenerated seedlings. However, L. maackii and white-tailed deer did affect the abundance of individual tree species, shifting composition of the regeneration layer towards shade tolerant and unpalatable and/or browse tolerant species.
Ecological restoration; field experiment; forest development; herbivory; invasive plants; moisture stress; natural and artificial regeneration; ungulates
Introduction
Successful regeneration of overstory species is integral
to maintaining forest systems in a time of ecological
change
(Reyer et al. 2015)
. However, overabundant
ungulate populations and the spread of invasive plants
pose a threat to the regeneration of ecologically and
economically valuable native tree species in many parts
of the world
(Coomes et al. 2003; Vavra et al. 2007;
Jacobs et al. 2015)
. The negative effects of ungulates
and invasive plants are typically more pronounced in
fragmented landscapes, where forests exist as small
patches within a matrix of agriculture and exurban
development
(Minor et al. 2009; Hurley et al. 2012)
. Within
North America, the Midwestern United States offers an
archetype of a fragmented landscape altered by invasive
plants
(Luken 1997; Oswalt et al. 2015)
and a frequently
overabundant ungulate species
(white-tailed deer;
Anderson 1997; Hurley et al. 2012)
.
In the last century, white-tailed deer abundance has
increased as a result of reduced predation, greater
forage from agriculture and tree plantings and increased
edge habitat
(C oˆte´ et al. 2004)
. White-tailed deer
preferentially browse certain species, altering forest dynamics
over time by shifting composition towards species that
are unpalatable or browse-tolerant
(Rooney and Waller
2003; Rossell et al. 2005)
. White-tailed deer alter nutrient
cycling by preferentially browsing plants that have
nutrient-rich tissue, over time, increasing the abundance
of nutrient-poor species which decompose more slowly
(Ritchie et al. 1998; C oˆte´ et al. 2004)
. White-tailed deer
alter nitrogen cycling by increasing the amount of
available nitrogen in the soil through faeces and urine and by
altering plant composition, and thus litter quality,
through herbivory
(Hobbs 1996; Ritchie et al. 1998;
Murray et al. 2013)
. Ultimately, composition and
structure of forests are altered as heavily browsed species
such as oak (Quercus spp.) are lost, and the regeneration
layer is dominated by less-preferred or browse-tolerant
species such as Fraxinus americana or Prunus serotina
(Tilghman 1989; Rossell et al. 2005)
.
In addition to ungulates, natural regeneration of
native tree seedlings can be limited by competition with
other species, in particular invasive plan (...truncated)