Individual and interactive effects of white-tailed deer and an exotic shrub on artificial and natural regeneration in mixed hardwood forests

AoB PLANTS, Jul 2017

Owings, Charlotte F., Jacobs, Douglass F., Shields, Joshua M., Saunders, Michael R., Jenkins, Michael A.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

Individual and interactive effects of white-tailed deer and an exotic shrub on artificial and natural regeneration in mixed hardwood forests

AoB PLANTS Downloaded from 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 plants. Amongst invasive plants species, shrubs are often the most problematic in forests because they form thick understory layers that are alien structural elements in many forests and overtop woody seedlings (Merriam and Feil 2002; Webster et al. 2006; Shields et al. 2015a) . For example, one species of invasive shrub that limits the natural regeneration of native tree seedlings is Lonicera maackii (Hutchinson and Vankat 1997; Collier et al. 2002; Gorchov and Trisel 2003 Shields et al. 2015b) , which was first cultivated in the United States in the late 1800s and has now spread to 28 states (Luken and Thieret 1994; USDA, NRCS 2015) . Lonicera maackii is a superior competitor to many native species, grows rapidly, has extensive roots near the soil surface that facilitate the uptake of nutrients and water, and possesses an extended leaf phenology compared with native species (Gould and Gorchov 2000; Hutchinson and Vankat 1997; McEwan et al. 2010; Pfeiffer and Gorchov 2015) . In addition, L. maackii has been found to alter nutrient cycling in invaded areas through accelerated release of litter N resulting from a lower C:N ratio and more rapid litter decomposition than native species (Blair and Stowasser 2009; Poulette and Arthur 2012; Schuster and Dukes 2014) . These alterations could align the release of nitrogen with the expanded growing season of invasive shrubs such as L. maackii, potentially furthering its competitive advantage (Blair and Stowasser 2009; Schuster and Dukes 2014) . Quercus rubra and Castanea dentata are two economically and ecologically valuable tree species that have limited natural regeneration across their extensive historic range in eastern North America. Quercus rubra has experienced widespread regeneration failure as a result of fire suppression (Brose et al. 2014) and herbivory by overabundant populations of white-tailed deer (Buckley et al. 1998; Castleberry et al. 1999; Rooney and Waller 2003) , resulting in drastic increases in the dominance of shadeand browse-tolerant mesophytic species in forest understories (Abrams 1992; Brose et al. 2001, 2014) . Castanea dentata has largely disappeared from its historically extensive range as the result of chestnut blight (Cryphonectria parasitica), a pathogen introduced in the early 1900s (Paillet 2002) . The loss of this foundation species spurred research efforts to develop a blightresistant hybrid though backcross breeding with Castanea mollissima, an Asian species (Jacobs et al. 2013) . The resulting seedlings are primarily C. dentata genetically (>90 %) and may offer an opportunity to restore C. dentata to native forests as restoration prescriptions are developed (Burnham 1986; Diskin et al. 2006; Jacobs et al. 2013) . In the long-term, restoring degraded forests in fragmented landscapes may depend upon artificial regeneration techniques, such as underplanting, to increase the importance of desired species in hardwood forests (Dey et al. 2012) . Underplanting can reduce the amount of site preparation necessary for restoration, thus decreasing the amount of resources needed to restore forested areas (Belair et al. 2014) . Underplanting can be used in areas with low abundance of natural regeneration and may allow management to function on controlled time scales as the technique does not require the long process VC The Authors 2017 of fostering natural regeneration (Loftis 1990; Paquette et al. 2006) . For species such as Q. rubra, seedling growth is optimized under partial canopy (often created by shelterwood harvest) and the underplanting of seedlings can provide advanced regeneration before initial openings are created (Loftis 1990) . Recent work has shown that the growth of C. dentata seedlings exhibit a similar response to partial canopy removal and outperform other species, including Q. rubra, when underplanted (Belair et al. 2014) . While underplanting is a useful restoration tool, obstacles such as herbivory from wildlife and competition from other species may reduce the successful establishment and growth of underplanted seedlings (Dey et al. 2012). While the impacts of L. maackii and white-tailed deer on native tree seedlings have been studied individually, less is known about their combined effects. Lonicera maackii in the understory could help to physically protect tree seedlings from deer browsing by providing cover, but may also create a microenvironment that inhibits the germination, establishment, growth and survival of seedlings. Aronson and Handel (2011) suggested that management of invasive plants and white-tailed deer may be necessary for the natural regeneration of native canopy trees to persist. In a study of the effects of honeysuckle and white-tailed deer on the survival of sugar maple seedlings, Loomis et al. (2015) found that, individually, both honeysuckle and white-tailed deer negatively affected seedling survival, but no significant interaction between the two factors was found. Active management methods, such as underplanting, protecting planted tree seedlings from herbivory and removing invasive shrubs may be necessary to restore forested areas in which both invasive shrub species and white-tailed deer are present. In this study, our objectives were to examine the individual and combined impacts of L. maackii and whitetailed deer on underplanted Q. rubra and C. dentata seedlings, as well as on the composition of naturally regenerated seedlings of woody species. We conducted our study in five forests within the glaciated till plain of IN, USA (Table 1). Typical of the Midwest region, forests in this area largely consist of small fragments within an agricultural matrix. Deer hunting occurred on three of our sites and in the matrix surrounding the remaining two sites. We did not observe evidence of heavy deer browse (browse lines, lack of native woody understory in areas without dense L. maackii, extirpation of lily species; Waller and Alverson 1997) at any of our sites. For our study design, we utilized two treatments: deer exclusion and honeysuckle removal. We hypothesized that white-tailed deer and L. maackii would collectively have more negative impacts on forest seedlings than either treatment alone. However, when both treatments were considered individually, we further hypothesized that L. maackii would have a greater suppressive effect on seedlings than deer, but would also mitigate the direct effects of deer. Specifically, due to above and below competition created by high stem densities of L. maackii in invaded sites, we predicted (i) growth, survival and foliar nitrogen content of underplanted seedlings would be lower and water stress higher in the presence of L. maackii alone than in the presence of deer alone. However, we predicted that (ii) the rate of browsing of underplanted seedlings outside of the exclosures would be lower under the protective cover of L. maackii. We also predicted that (iii) acute competition created by the presence of L. maackii alone would result in lower abundance, richness and diversity of naturally regenerated seedlings than in the presence of deer alone. Methods Study areas This study was conducted at five sites within the glaciated region of IN, USA: (i) Martell Experimental Research Forest (Martell); (ii) Vigo County Park District property (Terre Haute); (iii) Ross Biological Reserve (Ross); (iv) Purdue University Department of Forestry and Natural Resources Lugar Farm (Lugar Farm) and (v) a privately owned woodlot (Pursell; Table 1). Sites were within mature secondary deciduous forests that were heavily invaded by L. maackii and in which L. maackii was the dominant invasive species (Shields et al. 2015a) . The age and level of L. maackii invasion, soil type and overstory composition varied across the five sites (Table 1). Two 80 80 m areas were designated at each of the five study sites. In one 80 80 m area, all woody invasive plant species were removed between November 2010 and March 2011 at four sites (Terre Haute, Ross, Lugar Farm and Pursell) and in February 2013 at the remaining site (Martell). The second 80 80 m area was untreated and served as a reference area (Shields et al. 2015b) . Lonicera maackii was removed by either cutting the shrub at the base using a brush saw or loppers and treating the stump with herbicide (20 % Garlon 4 VR triclopyr, 1 % Stalker VR imazapyr and 79 % Ax-it VR basal oil), or by manually pulling small shrubs (single stems < 80 cm height) out of the ground (Shields et al. 2015b) . After cutting, large shrubs were then removed from the site. New and re-sprouted shrubs were re-treated by cutting and applying herbicide on the cut surface in the summer of 2014 to maintain the removal areas. In the spring of 2013, two 20 40 m units were established in each 80 80 m removal and reference area. VC The Authors 2017 300 Study site Lat/long Annual Dominant overstory species Soils Invasion L. maackii Deer precip. age density visits (cm/yr) (years) (stems/ha) ...................................................................................................................................................................................................................... Lugar Farm 40 250N 86 570W 97.03 Robinia pseudoacacia, Juglans nigra Silt loams 35 3135 6 863 19 One of the two units was randomly selected as a deer exclosure area and a 2.5-m tall fence was constructed around the exterior to prevent white-tailed deer from accessing the unit. Small mammals, however, were able to enter the exclosure beneath the fence. Fences were checked periodically for damage and repaired as necessary. No fence was constructed around the second 20 40 m unit, allowing deer to access these areas. After fence construction, each study site contained four treatment combinations: (i) L. maackii removed and accessible to deer, (ii) L. maackii removed and deer excluded, (iii) L. maackii present and accessible to deer and (iv) L. maackii present and deer excluded. A severe windstorm on 17 November 2013 resulted in heavy damage to the removal area at the Lugar Farm site. The storm resulted in windthrow of over half the forest canopy, resulting in increased light availability and large inputs of woody debris. Debris was cut and removed from around the planted seedlings and natural regeneration transects in the two removal subunits to allow deer access comparable to the pre-storm condition. In the reference area, which was largely undamaged, selected trees were girdled in the spring of 2014 in order to create similar openings in the canopy to those in the removal areas while preserving the dense L. maackii shrub cover. Tree seedling study species and underplanting Each treatment unit was divided length-wise into two sections. One of the sections was randomly assigned for 13 23 18 30 tree seedling planting and the other was assigned for the sampling of natural regeneration. For planting, we obtained 800 one-year-old bareroot Q. rubra and C. dentata seedlings that were produced according to standard operational nursery practices (Jacobs 2003) at Vallonia State Tree Nursery in southern Indiana. Twenty seedlings of each species were planted by hand in two lines spaced 2 m apart in each study unit in April of 2014. Within lines, the two species were randomly mixed and seedlings were planted 1.5 m apart. To allow establishment, competing vegetation was removed by hand within a meter of each seedling at the beginning of the study. Seedling characteristics and browse Survival, height and basal diameter (to the nearest 0.01 mm) were measured for each seedling at the beginning and end of the growing season. The presence of deer and rabbit browse was also recorded. Rabbit browse was distinguished from deer browse by examining the browsed area on the stem of the underplanted seedling. Rabbit browsed seedlings had clean and angled cuts while seedlings browsed by deer were more scraped and jagged in appearance. To confirm the presence of deer at each of the sites, two trail cameras (HC600 Hyperfire, RECONYX, Inc., Holmen, WI, USA) were placed in the two non-exclosure (removal and reference outside) subunits at each of the study sites during June and September 2014 and images were examined for deer. Total deer visits ranged from 19 at Lugar Farm to 86 at Ross (Table 1). VC The Authors 2017 Seedling moisture stress and foliar nutrient concentration Pre-dawn plant moisture stress was measured for five randomly selected seedlings per species from each of the units during 12–15 August 2014. One leaf was collected from each seedling at approximately the same location along the stem and the leaf xylem water potential was determined using a pressure chamber (Model 600, PMS Instruments, Corvallis, OR, USA; Waring and Cleary 1967) . After moisture stress measurements were taken, collected leaves were dried at 65 C for 48 h. The dried samples were then ground in a ball mill. Foliar N concentration was determined for each foliar sample using an elemental analyzer (ECS 400, Costech Analytical Technologies, Inc., Valencia, CA, USA). Light measurements and soil N availability To determine the amount of photosynthetically active radiation (PAR) in each study unit, PAR measurements were taken using a light ceptometer (LP-80 AccuPAR Ceptometer, Decagon Devices, Inc., Pullman, WA, USA) in July 2015. All measurements were made 1 m above the ground on cloudless days between 1 h prior and 1 h after solar noon. PAR measurements were taken in an open field adjacent to each study site to determine the ambient PAR (Grayson et al. 2012) . Within the study units, PAR readings were taken above every fifth underplanted seedling. Twelve soil subsamples from 0 to 20 cm depth were collected from each of the four treatment subunits using a soil probe. Four composite samples were formed by pooling three soil samples randomly chosen from the same subunit. Samples were refrigerated and then sent to Brookside Laboratories, Inc. (New Bremen, OH, USA) and tested for total nitrogen (NO3 and NH4; Nelson and Sommers 1996; McGeehan and Naylor 1988) . Natural tree regeneration In the section of the treatment unit assigned to natural regeneration, three 10 m-long permanent transects were established with each transect spaced a minimum of 5 m from the next nearest transect. Five 1 m2 quadrats were placed every other meter along the right side of each 10 m transect. Woody stems <50 cm in height were tallied by species within the 1-m2 quadrats during late July/early August 2013, 2014 and 2015. The stem and species tallies were used to determine the density, species richness and species diversity of naturally regenerating woody stems for each unit. Woody vines were not included in the tally. Calculations and statistical analyses For each underplanted seedling, relative changes in height and basal diameter were calculated by determining the change in height and basal diameter over the course of the growing season (height/basal diameter in fall – height/basal diameter in spring) and dividing this value by the initial height and initial basal diameter, respectively. For the relative change in height and basal diameter analyses, dead trees were excluded. Negative values of relative growth in basal diameter were excluded from analyses as likely being a reflection of dead seedlings. Relative changes in growth data (height and basal diameter) were transformed using an arcsine square root transformation to improve normality. Percent ambient PAR was calculated by dividing the PAR value recorded above every fifth seedling by the average ambient PAR value from 15 readings (Grayson et al. 2012) . These values were log-transformed to improve normality for statistical analyses. The species richness, evenness and diversity of naturally regenerating seedlings were calculated from the natural regeneration quadrat data. Species richness was calculated as the number of unique species per transect and species diversity was calculated using the Shannon Diversity Index. Species diversity, evenness and richness were calculated using the software PC-ORD 5 (McCune and Mefford 2011) . Species within the same genus were grouped together for analysis because many individual species did not occur across all study sites. These groupings included Carya spp., Quercus spp. and Ulmus spp. All statistical analyses were performed using R statistical software (R Core Team 2013) and significance was determined at a ¼ 0.05. The R statistical packages ‘survival’ and ‘coxme’ (Therneau 2015) were used to determine the fixed effects of L. maackii, white-tailed deer, their interaction, and the random effect of site on the survival of the underplanted C. dentata and Q. rubra seedlings. The ‘coxme’ and ‘survival’ packages were used to analyse survival using a Cox proportional hazards model to determine differences in the relative risk of mortality amongst treatments from the beginning to the end of the study. Generalized linear mixed effects models were performed using the R package ‘lme4’ (Bates et al. 2015) to determine the fixed effects of L. maackii, white-tailed deer, their interaction, and the random effect of study site on foliar and soil nitrogen concentration, moisture stress, browse, natural regeneration, PAR and underplanted seedling growth (basal diameter and height). Time (year of measurement) was also included as a factor in the natural regeneration analyses as these data represented changes across three years (2013, 2014 and 2015) while the data for the underplanted seedlings VC The Authors 2017 500 represented change over one year or one time point of measurement. Each site was considered as a replicate in our analyses. A Poisson distribution was used to model natural regeneration density, an inverse Gaussian distribution was used to model moisture stress, and all other measurements were modelled using a normal distribution. Data from Ross were excluded from the plant moisture stress and foliar N analyses as one of the treatments had no trees with foliar tissue to measure. However, we were still able to compare plant moisture stress and foliar N across all four treatments at the other four sites (Farm, Martell, Pursell and Terre Haute). Because of the large number of statistical tests performed in our comparisons of natural regeneration density by species, we adjusted P-values (q-values, Pike 2011) with a graphically-sharpened procedure based on control of the false discovery rate (FDR; Benjamini and Hochberg 1995, 2000) . In recent years, multiple comparison techniques based upon FDR have been used more frequently in ecological experiments as an alternative to traditional controls of family-wise error rate because FDR-based techniques retain statistical power while keeping the proportion of false discoveries small relative to all significant results (Verhoeven et al. 2005; Pike 2011) . Results Survival of underplanted seedlings Supporting our hypothesis, the greatest survival for both species was in the treatment combination where L. maackii was removed and deer were excluded, while the lowest survival for both species was in the reference areas outside of the exclosures where only 10 % of seedlings survived after two growing seasons (Fig. 1, Table 2). There was no significant interaction between L. maackii and white-tailed deer for the survival of either species. For C. dentata, the second highest survival rate was in areas in which L. maackii was present and deer were excluded, countering our prediction that L. maackii alone would have a greater impact on survival than deer alone. Lonicera maackii removal areas outside the exclosures exhibited the next lowest survival rate. For Q. rubra, survival did not differ between the treatment in which L. maackii was present inside the exclosures and where it was removed outside the exclosures (Fig. 1). Seedling characteristics and browse The presence or absence of L. maackii outside of the deer exclosures did not significantly impact the number of underplanted seedlings of either species browsed by the end of the study, a finding that did not support our prediction that L. maackii would protect seedlings from browsing (Table 2). We observed a significant difference in relative height during the first growing season, with white-tailed deer having a negative effect on growth in height for seedlings of both species (Fig. 2, Table 2). While L. maackii did not have a significant effect on height for Q. rubra, there was a significant interaction between L. maackii and deer on height for C. dentata, with greater height growth in the treatment without L. maackii and deer (Table 2), supporting our prediction that seedlings would grow best when deer and L. maackii were absent. However, the next greatest height growth occurred in the treatment with L. maackii and without deer (Fig. 2, Table 2) and the least growth in height for C. dentata occurred in the two treatments in which deer had access (Fig. 2, Table 2), countering our prediction that L. maackii would have greater effects on height growth than deer. Deer did not have an effect on growth in basal diameter for either underplanted species. There was no difference amongst treatments in relative change in basal diameter VC The Authors 2017 for C. dentata (Fig. 3). For Q. rubra, relative change in basal diameter was greater in the areas where L. maackii was present (Fig. 3). The high mortality of seedlings in some of the treatments during the second growing season did not allow us to examine changes in basal diameter or height over the second growing season. VC The Authors 2017 700 Seedling moisture stress, PAR, and foliar and soil N Plant moisture stress was greater where L. maackii was present for both species of underplanted seedlings and outside the exclosures (deer present) for C. dentata (Fig. 4; Table 2). Percent ambient PAR was lower in areas in which L. maackii was present compared with where it was removed (Table 3). There was no difference in PAR between the exclosed and unexclosed areas within the L. maackii removal and reference areas (Tables 2 and 3). No significant difference was found in foliar nitrogen concentration amongst the treatments for either the Q. rubra or C. dentata underplanted seedlings (Table 2). There was also no significant differences in soil nitrogen amongst the treatments (Tables 2 and 3). Natural regeneration Contrary to our predictions, neither the presence of L. maackii nor white-tailed deer had an effect on the overall density of native tree seedlings across treatments. There was also no effect of L. maackii or white-tailed deer on the species richness, evenness, or diversity of naturally regenerated tree seedlings (Table 4). No invasive tree seedlings were encountered in our units. Amongst individual species, the density of Acer saccharum, a highly shade-tolerant species, was greater where L. maackii was present than where it was removed (Tables 4 and 5, while the density of P. serotina was greater in the areas where L. maackii was removed (Table 5). Regardless of treatment, the density of P. serotina decreased over time. There was a significant interaction of L. maackii and time on the density of F. americana, with F. americana density decreasing over time in the L. maackii reference areas, but increasing in the removal areas. In contrast, the densities of F. americana and Ulmus spp. increased significantly outside of the exclosures over the course of the study and declined inside. The only significant interaction between whitetailed deer and L. maackii was for the density of Ulmus spp., which was greater in the treatment with L. maackii and white-tailed deer and did not differ amongst the other three treatments (Table 4). VC The Authors 2017 Discussion Survival and growth of underplanted seedlings Our finding that the presence of L. maackii and deer resulted in the lowest survival of underplanted seedlings of C. dentata and Q. rubra supported our hypothesis and the results of other studies that examined the individual effects of L. maackii and white-tailed deer and found each to have negative effects on the survival of naturally regenerating native tree seedlings (Loomis et al. 2015; Gorchov and Trisel 2003; Rossell et al. 2005) . The increased survival of underplanted seedlings in areas in which L. maackii was removed and white-tailed deer excluded is likely due to a number of factors. In our study, percent ambient PAR was lower in the areas in which L. maackii was present. Both Q. rubra and C. dentata seedlings have intermediate tolerance of shade, but are intolerant of heavy shade (Crow 1988; Joesting et al. 2009) . Thus, the reduced light levels in the L. maackii reference areas may have contributed to lower survival of the underplanted seedlings in the heavily shaded reference areas. Furthermore, reducing midstory basal area can promote growth and establishment of Q. rubra and C. dentata seedlings (Loftis 1990; Brown et al. 2014) . The removal of L. maackii in our study may have had a similar effect resulting in increased light availability to the underplanted seedlings, especially at sites with high preremoval densities of mature L. maackii (Table 1). Overall, our results illustrated that, contrary to our prediction, the negative individual effects of deer on survival and height growth of underplanted seedlings were greater than those of L. maackii. One of the mechanisms by which white-tailed deer may have reduced survival of the underplanted seedlings is by reducing seedling height and photosynthetic tissue through browse. Other studies have found that height of naturally regenerating seedlings is greater in areas in which deer have been excluded or in areas with lower deer abundance (Horsley et al. 2003; Aronson and Handel 2011; Shelton et al. 2014) . Gorchov and Trisel (2003) proposed that L. maackii may deter browsing of native seedlings by white-tailed deer. However, contrary to our prediction, we did not find a difference in the percent of underplanted seedlings browsed in non-exclosure areas by the end of the study. However, relative growth in height was greater with the exclusion of deer for both species of underplanted seedling, indicating that there was a negative effect of browsing on underplanted seedling growth. We observed no effect of L. maackii on relative growth in height for Q. rubra, but did find an interactive effect of L. maackii and deer on C. dentata, with underplanted seedling height being greatest where both were removed followed by where honeysuckle was present, but deer were excluded, indicating a stronger negative effect of deer. An effect of L. maackii on basal diameter was found for Q. rubra underplanted seedlings, with greater growth in areas in which L. maackii was removed. This finding may be a result of the higher PAR in the removal areas allowing for greater growth. The lower survival of the underplanted seedlings in areas with deer and L. maackii may have been, in part, a result of increased seedling moisture stress in our study. VC The Authors 2017 900 Moisture stress of the underplanted seedlings was greater in the areas in which L. maackii was present for both species of underplanted seedlings, and for C. dentata, was greater in the areas accessible to deer. We predicted that moisture stress would be greater in areas with L. maackii, which reduces soil moisture and throughfall, potentially resulting in less water available to seedlings (Pfeiffer and Gorchov 2015) . Precipitation during the two weeks prior to our measurements was almost twice the normal amount (U.S. Climate Data 2015) , potentially having an impact on our results as underplanted seedlings may not have been under as high of stress as that which may typically occur under drier conditions. Despite this increased rainfall, we still detected differences in moisture stress, suggesting that deer may be increasing moisture stress of the underplanted seedlings through herbivory. The increased moisture stress created by the presence of L. maackii and deer likely has a stronger effect on mortality and growth during the periodic meteorological droughts that occur in the Midwestern United States (Mallya et al. 2013) . Natural regeneration Contrary to our predictions, neither L. maackii nor whitetailed deer had a significant effect on the overall density, richness or diversity of naturally regenerating native seedlings. In contrast, other studies have found reduced Table 5 Density (stems/hectare 6 1 SE) of native tree seedlings across sites averaged across sampling periods from fall 2013 to 2015 in the treatments where L. maackii was present (L. maackii) and removed (no L. maackii). Superscript letters next to the species represent significant interactions between L. maackii and time (T) and deer (D). P-values for density were adjusted for multiple comparisons with a graphically sharpened procedure to control the false discovery rate (Benjamini and Hochberg 1995) . Density (stems/ha) ...................................................................................................... Species L. maackii No L. maackii P-value ...................................................................................................... Acer saccharum 8960 6 1940 640 6 200 0.005 Carya spp. Celtis occidentalis Fraxinus americanaT Liriodendron tulipiferaT Prunus serotina Quercus spp. Sassafras albidum Ulmus spp.D native tree seedling density, richness, diversity and survival under L. maackii (Collier et al. 2002) and in areas in which white-tailed deer are present (Tilghman 1989; Rossell et al. 2005; Aronson and Handel 2011; VC The Authors 2017 Frerker et al. 2014) . While both L. maackii and whitetailed deer can individually have negative effects on native tree seedling survival and density, Gorchov and Trisel (2003) suggested that there may be an interaction between L. maackii and white-tailed deer in which L. maackii protects seedlings from browse and increases their survival. However, we found no interactive effect of white-tailed deer and L. maackii on overall seedling density, richness or diversity in our study. The short time period in which our exclosures were in place may not have allowed us to detect changes in overall density and diversity resulting from deer herbivory. While L. maackii was removed from the sites up to three years prior to the beginning of the study, deer had only been excluded for 2.5 years by the end of the study. While changes in herbaceous-layer diversity richness and diversity have been found to occur quickly (1 year) after L. maackii removal (Shields et al. 2015b) , changes in the herbaceous layer following deer exclusion may take longer to manifest (10þ years) and may not be detectable over shorter periods (Griggs et al. 2006; Collard et al. 2010; Frerker et al. 2014; Waller 2014) . In addition, while deer population densities in our study areas were likely representative of densities across much of the Midwest, our sites do not have the long history of heavy overabundance documented in studies from other regions (Horsley et al. 2003; Griggs et al. 2006) . Therefore, changes across our sites following deer exclusion may be subtler and slower to develop. However, the high rate of browse on the underplanted seedlings in our study shows that deer are affecting regeneration. Furthermore, the contemporary regeneration layer of forests across the Midwest reflects the cumulative effects of a regional deer population that is likely in excess of historic levels (Coˆte´ et al. 2004). Other studies have observed suppressed regeneration as a result of lower light (Luken and Thieret 1994) , allelopathy (Dorning and Cippollini 2006) , and reduced soil moisture (Pfeiffer and Gorchov 2015) beneath L. maackii. In our study, the areas in which L. maackii was removed experienced large increases in the cover and height of herbaceous species (Freeman 2015), which may have reduced the survival of naturally regenerated seedlings through intensified competition as has been observed with natural regeneration of pine species (Cain 1991; Pitt et al. 2009, 2010) . While there was no effect of L. maackii or white-tailed deer on total native seedling density, richness or diversity, density and relative density differed for individual species and groups. Prunus serotina density was greater where L. maackii was removed, while A. saccharum density was lower in the absence of L. maackii. Shields et al. (2015b) found increases in P. serotina immediately following the removal of L. maackii across four of the sites in this study (our Martell site was not included in the study). While the high fecundity of this species allows it to produce high densities of seedlings, they are unlikely to grow out of the regeneration layer without canopy disturbance. While A. saccharum in our study may be able to reproduce under L. maackii cover, we did not assess the survival of individual seedlings. A recent study by Loomis et al. (2015) found no difference in A. saccharum survival after one year between plots where L. maackii was present and where it was removed, suggesting that the high shade tolerance of the species may allow it to persist under L. maackii cover. While we did not observe significant effects of deer or L. maackii on seedlings of Quercus species, densities of this genus were low across our study sites and likely precluded our ability to detect differences. Through time, the density of two species groups, Ulmus spp. and F. americana, decreased inside the exclosures while increasing outside. While F. americana is browsed by deer (Tilghman 1989) , the species can remain abundant in the presence of white-tailed deer and may be more tolerant of browse than many other tree species, allowing its density to remain high outside of the exclosures (Rossell et al. 2005; Jenkins et al. 2014) . Similar to F. americana, the density of Ulmus spp. was greater outside the exclosures than inside (Table 4). Density of this species displayed a significant interaction between L. maackii and deer, with greater relative density in the presence of both L. maackii and deer. In areas of high deer populations, Ulmus spp. can be a frequently browsed species (Pogge 1967); however, in areas of lower deer abundance, it may be avoided when other more palatable species are available (LaGory et al. 1985; Sotala and Kirkpatrick 1972) . Conclusions Tree recruitment is a critical mechanism for the maintenance of ecological resilience in forests (Reyer et al. 2015) . However, maintaining successful regeneration of native forests has become increasingly difficult in this era of global change. Shifts in the historical abundance of browsing ungulate populations and spread of invasive plant species are frequently identified as paramount challenges to forest regeneration worldwide, particularly in fragmented landscapes. As in many other forests, the effects of ungulate herbivory, invasive plants and altered disturbance regimes were highly evident across our study sites. We observed natural regeneration layers that were dominated by late seral and browse tolerant species. The presence of VC The Authors 2017 110 L. maackii favoured only the most shade tolerant species (A. saccharum) and the added effects of deer pushed seedling-layer composition towards F. americana and Ulmus spp. However, F. americana and Ulmus spp. are unlikely to persist in the future canopy of these forests due to the effects of introduced insects and disease (Lovett et al. 2016) . Under these conditions of depauperate natural regeneration, underplanting offers a potential, albeit expensive, technique to begin the restoration of desired species to degraded forests. Our study found that the removal of L. maackii increased understory light levels in a way similar to a technique offered by Loftis (1990) to regenerate oak species on mesic sites. This technique mechanically reduces the density of the midstory to increase light levels and foster the survival and growth of advance regeneration, which is ultimately released when canopy openings are created. Using a similar sequence, L. maackii removal, in conjunction with underplanting, could be a first step in restoring degraded hardwood forests. However, our results showed that the presence of deer had a greater negative effect on the survivorship of C. dentata seedlings than shading by L. maackii. The low survival of both underplanted species in the presence of deer and L. maackii demonstrates that both deer and L. maackii must be managed if restoration efforts are to be successful. Sources of Funding This research was supported with funds from the Department of Forestry and Natural Resources and the Hardwood Tree Improvement and Regeneration Center at Purdue University and the USDA McIntire-Stennis Cooperative Forestry Program (project IND011533MS). Contributions by the Authors This article was derived from the MS thesis of C.F.O., who was co-advised by D.F.J. and M.A.J. Study design was a collaborative effort of D.F.J., J.M.S., M.R.S. and M.A.J. C.F.O. performed the analyses and led the writing effort. D.F.J. and M.A.J. contributed text and all authors edited the manuscript. Conflicts of Interest Statement None declared. Acknowledgements We thank Lindsay Keitzer, Brad Graham, Patrick Duffy, Rob Quackenbush, Jenny Lesko, Kyle Earnshaw, Mike Szuter, Mercedes Uscola, Safi Khurram, Carmen Dobbs, Joe Littiken, Keeli Curtis, Allison Hyrcik, Heather Pasley, Josh Sloan and Taylor Owings for their help with various aspects of this project. We also thank Bryan Murray, Nathan Lichti and Rongong Zhang for their assistance with statistics, Sally Weeks for her help with species identification, and Tim Smyser, Liz Flaherty and Mike Saunders for their assistance with the Reconyx cameras. We thank Brian Beheler and Michael Loesch-Fries for their help with the construction and maintenance of exclosures and for cleaning up one of our sites after a severe windstorm knocked down over 30 trees. We also thank Brent Pursell, the Vigo County Park District and the Purdue University Department of Biological Sciences for allowing access to their properties and Kevin Gibson and three anonymous reviewers for their helpful comments on earlier drafts of this paper. Literature Cited VC The Authors 2017 VC The Authors 2017 130 Abrams MD. 1992 . Fire and the development of oak forests - in eastern North America, oak distribution reflects a variety of ecological paths and disturbance conditions . Bioscience 42 : 346 - 353 . Anderson RC . 1997 . Native pests: the impacts of deer in highly fragmented habitats . In: Schwartz MW, ed. Conservation in highly fragmented landscapes. New York: Chapman and Hall, 117 - 134 . Aronson MFJ , Handel SN . 2011 . Deer and invasive plant species suppress forest herbaceous communities and canopy tree regeneration . Natural Areas Journal 31 : 400 - 407 . Bates D , Maechler M , Bolker B , Walker S. 2015 . Fitting linear mixedeffects models using lme4 . Journal of Statistical Software 67 : 1 - 48 . Belair ED , Saunders MR , Bailey BG . 2014 . Four-year response of underplanted American chestnut (Castanea dentata) and three competitors to midstory removal, root trenching, and weeding treatments in an oak-hickory forest . Forest Ecology and Management 329 : 21 - 29 . Benjamini Y , Hochberg Y. 1995 . Controlling the false discovery rate - a practical and powerful approach to multiple testing . Journal of the Royal Statistical Society: Series B 57 : 289 - 300 . Benjamini Y , Hochberg Y. 2000 . On the adaptive control of the false discovery rate in multiple testing with independent statistics . Journal of Educational and Behavioral Statistics 25 : 60 - 83 . Blair BC , Stowasser A. 2009 . Impact of Lonicera maackii on decomposition rates of native leaf litter in a southwestern Ohio woodland . Ohio Journal of Science 109 : 43 - 48 . Brose P , Schuler T , Van Lear D , Berst J. 2001 . Bringing fire back: the changing regimes of the Appalachian mixed-oak forests . Journal of Forestry 99 : 30 - 35 . Brose P , Dey DC , Waldrop TA . 2014 . The fire-oak literature of eastern North America: synthesis and guidelines . Gen. Tech. Rep. NRS-135 . Newton Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station, 98p . Brown CE , Bailey BG , Saunders MR , Jacobs DF . 2014 . Effects of root competition on development of chestnut and oak regeneration following midstory removal . Forestry 87 : 562 - 570 . Buckley DS , Sharik TL , Isebrands JG . 1998 . Regeneration of northern red oak: positive and negative effects of competitor removal . Ecology 79 : 65 - 78 . Burnham CR . 1986 . Chestnut hybrids from USDA breeding programs . Journal of the American Chestnut Foundation 1 : 8 - 12 . Cain MD. 1991 . Woody and herbaceous competition effects on the growth of naturally regenerated loblolly and shortleaf pines through 11 years . New Forests 14 : 107 - 125 . Castleberry SB , Ford WM , Miller KV , Smith WP . 1999 . White-tailed deer browse preferences in a southern bottomland hardwood forest . Southern Journal of Applied Forestry 23 : 78 - 82 . Collard A , Lapointe L , Ouellet JP , Crete M , Lussier A , Daigle C , Coˆ te ´ SD. 2010 . Slow responses of understory plants of mapledominated forests to white-tailed deer experimental exclusion . Forest Ecology and Management 260 : 649 - 662 . Collier MH , Vankat JL , Hughes MR . 2002 . Diminished plant richness and abundance below Lonicera maackii, an invasive shrub . American Midland Naturalist 147 : 60 - 71 . Coomes DA , Allen RB , Forsyth DM , Lee WG . 2003 . Factors preventing the recovery of New Zealand forests following control of invasive deer . Conservation Biology 17 : 450 - 459 . Coˆ te´ SD , Rooney TP , Tremblay J , Dussault C , Waller DM . 2004 . Ecological impacts of deer overabundance . Annual Review of Ecology, Evolution, and Systematics 35 : 113 - 147 . Crow TR . 1988 . Reproductive mode and mechanisms for selfreplacement of northern red oak (Quercus rubra) - a review . Forest Science 34 : 19 - 40 . Dey DC , Gardiner ES , Schweitzer CJ , Kabrick JM , Jacobs DF . 2012 . Underplanting to sustain future stocking of oak (Quercus) in temperate deciduous forests . New Forests 43 : 955 - 978 . Diskin M , Steiner KC , Hebard FV . 2006 . Recovery of American chestnut characteristics following hybridization and backcross breeding to restore blight-ravaged Castanea dentata . Forest Ecology and Management 223 : 439 - 447 . Dorning M , Cipollini D. 2006 . Leaf and root extracts of the invasive shrub, Lonicera maackii, inhibit seed germination of three herbs with no autotoxic effects . Plant Ecology 184 : 287 - 296 . Freeman C. 2015 . Vegetation and underplanting response to Amur honeysuckle invasion and deer herbivory in mixed hardwood forests . Thesis , Purdue University, West Lafayette, IN, USA. Frerker K , Sabo A , Waller D. 2014 . Long-term regional shifts in plant community composition are largely explained by local deer impact experiments . PLoS ONE 9:e115843; doi:10 .1371/journal. pone. 0115843 . Gorchov DL , Trisel DE . 2003 . Competitive effects of the invasive shrub, Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings . Plant Ecology 166 : 13 - 24 . Gould AMA , Gorchov DL . 2000 . Effects of the exotic invasive shrub Lonicera maackii on the survival and fecundity of three species of native annuals . American Midland Naturalist 144 : 36 - 50 . Grayson SF , Buckley DS , Henning JG , Schweitzer CJ , Gottschalk KW , Loftis DL . 2012 . Understory light regimes following silvicultural treatments in central hardwood forests in Kentucky, USA . Forest Ecology and Management 279 : 66 - 76 . Griggs JA , Rock JH , Webster CR , Jenkins MA . 2006 . Vegetative legacy of a protected deer herd in Cades Cove, Great Smoky Mountains National Park . Natural Areas Journal 26 : 126 - 136 . Hobbs NT , 1996 . Modification of ecosystems by ungulates . Journal of Wildlife Management 6 : 695 - 713 . Horsley SB , Stout SL , De Calesta DS . 2003 . White-tailed deer impact on the vegetation dynamics of a northern hardwood forest . Ecological Applications 13 : 98 - 118 . Hurley PM , Webster CR , Flaspohler DJ , Parker GR . 2012 . Untangling the landscape of deer overabundance: reserve size versus landscape context in the agricultural Midwest . Biological Conservation 146 : 62 - 71 . Hutchinson FT , Vankat JL . 1997 . Invasibility and effects of Amur honeysuckle in Southwestern Ohio Forests . Conservation Biology 11 : 1117 - 1124 . Jacobs DF . 2003 . Nursery production of hardwood seedlings . Purdue University Cooperative Extension Service, FNR-212. West Lafayette, IN, 8p . Jacobs DF , Dalgleish HJ , Nelson CD . 2013 . Tansley review A conceptual framework for restoration of threatened plants: the effective model of American chestnut (Castanea dentata) reintroduction . New Phytologist 197 : 378 - 393 . Jacobs DF , Oliet JA , Aronson J , et al. 2015 . Restoring forests: what constitutes success in the twenty-first century? New Forests 46 : 601 - 614 . Jenkins LH , Jenkins MA , Webster CR , Zollnerd PA , Shields JM . 2014 . Herbaceous layer response to 17 years of controlled deer hunting in forested natural areas . Biological Conservation 175 : 119 - 128 . Joesting HM , McCarthy BC , Brown KJ . 2009 . Determining the shade tolerance of American chestnut using morphological and physiological leaf parameters . Forest Ecology and Management 257 : 280 - 286 . LaGory MK , LaGory KE , Taylor DH . 1985 . Winter browse availability and use by white-tailed deer in southeastern Indiana . Journal of Wildlife Management 49 : 120 - 124 . Loftis DL. 1990 . A shelterwood method for regenerating red oak in the southern Appalachians . Forest Science 36 : 917 - 929 . Loomis JD , Matter SF , Cameron GN . 2015 . Effects of invasive Amur honeysuckle (Lonicera maackii) and white-tailed deer (Odocoileus virginianus) on survival of sugar maple seedlings in a Southwestern Ohio forest . American Midland Naturalist 174 : 65 - 73 . Lovett GM , Weiss M , Liebhold AM , et al. 2016 . Nonnative forest insects and pathogens in the United States: impacts and policy options . Ecological Applications 26 : 1437 - 1455 . Luken JO , 1997 . Conservation in the context of non-indigenous species . In: Schwartz MW, ed. Conservation in highly fragmented landscapes. New York: Chapman and Hall, 117 - 134 . Luken JO , Thieret JW . 1994 . Amur honeysuckle, its fall from grace . BioScience 46 : 18 - 24 . Mallya G , Zhao L , Song XC , Niyogi D , Govindaraju RS . 2013 . 2012 Midwest drought in the United States . Journal of Hydrologic Engineering 18 : 737 - 745 . McCune B , Mefford MJ . 2011 . PC-ORD . Multivariate analysis of ecological data. Version 6 (computer program) . MjM Software , Gleneden Beach, OR , USA. McEwan RW , Arthur-Paratley LG , Rieske LK , Arthur MA . 2010 . A multiassay comparison of seed germination inhibition by Lonicera maackii and co-occurring native shrubs . Flora 205 : 475 - 483 . McGeehan SL , Naylor DV . 1988 . Automated instrumental analysis of carbon and nitrogen in plant and soil samples . Communications in Soil Science and Plant Analysis 19 : 493 - 505 . Merriam RW , Feil E. 2002 . The potential impact of an introduced shrub on native plant diversity and forest regeneration . Biological Invasions 4 : 369 - 373 . Minor ES , Tessel SM , Engelhardt KAM , Lookingbill TR , 2009 . The role of landscape connectivity in assembling exotic plant communities: network analysis . Ecology 9 . 1802 - 1809 . Murray BD , Webster CR , Bump JK , 2013 . Broadening the ecological context of ungulate-ecosystem interactions: the importance of space, seasonality, and nitrogen . Ecology 9 . 1317 - 1326 . Natural Resources Conservation Service . 2016 . United States Department of Agriculture. Web Soil Survey . http://websoilsur vey. (16 November 2015 ). Nelson DW , Sommers LE , 1996 . Total carbon, organic carbon and organic matter . In: Bartels JM , et al., ed. Methods of soil analysis: Part 3. Chemical methods. 3rd edn. Madison, WI: ASA and SSSA Book Series 5 , 961 - 1010 . Oswalt CM , Fei S , Guo Q , Iannone BV , Oswalt S , Pijanowski B , Potter KM . 2015 . A subcontinental view of forest plant invasions using national inventory data . Neobiota 24 : 49 - 54 . Paillet FL , 2002 . Chestnut: history and ecology of a transformed species . Journal of Biogeography 2 . 1517 - 1530 . Paquette A , Bouchard A , Cogliastro A. 2006 . Survival and growth of underplanted trees: a meta-analysis across four biomes . Ecological Applications 16 : 1575 - 1589 . Pfeiffer SS , Gorchov DL . 2015 . Effects of the invasive shrub Lonicera maackii on soil water content in eastern deciduous forest . American Midland Naturalist 173 : 38 - 46 . Pike N. 2011 . Using false discovery rates for multiple comparisons in ecology and evolution . Methods in Ecology and Evolution 2 : 278 - 282 . Pitt DG , Comeau PG , Parker WC , et al. 2010 . Early vegetation control for the regeneration of a single-cohort, intimate mixture of white spruce and trembling aspen on upland boreal sites . Canadian Journal of Forest Research 40 : 549 - 564 . Pitt DG , Morneault A , Parker WC , Stinson A , Lanteigne L , 2009 . The effects of herbaceous and woody competition on planted white pine in a clearcut site . Forest Ecology and Management 2 . 1281 - 1291 . Pogge FL . 1967 . Elm as deer browse . Journal of Wildlife Management 31 : 354 - 356 . Poulette MM , Arthur MA . 2012 . The impact of the invasive shrub Lonicera maackii on the decomposition dynamics of a native plant community . Ecological Applications 22 : 412 - 424 . R Core Team . 2013 . R: A language and environment for statistical computing . R Foundation for Statistical Computing , Vienna, Austria. http://www.R-project. org (16 November 2015 ). Reyer CPO , Brouwers N , Rammig A , et al. 2015 . Forest resilience, tipping points and global processes . Journal of Ecology 103 : 1 - 4 . Ritchie ME , Tilman D , Knops JMH , 1998 . Herbivore effects on plant and nitrogen dynamics in oak savanna . Ecology 7 . 165 - 177 . Rooney TP , Waller DM . 2003 . Direct and indirect effects of whitetailed deer in forest ecosystems . Forest Ecology and Management 181 : 165 - 176 . Rossell CR , Gorsira B , Patch S. 2005 . Effects of white-tailed deer on vegetation structure and woody seedling composition in three forest types on the Piedmont Plateau . Forest Ecology and Management 210 : 415 - 424 . Schuster MJ , Dukes JS . 2014 . Non-additive effects of invasive tree litter shift seasonal N release: a potential invasion feedback . Oikos 123 : 1101 - 1111 . Shelton AL , Henning JA , Schultz P , Clay K. 2014 . Effects of abundant white-tailed deer on vegetation, animals, mycorrhizal fungi, and soils . Forest Ecology and Management 320 : 39 - 49 . Shields JM , Jenkins MA , Saunders MR , Zhang H , Jenkins LH , Parks AM . 2014 . Age distribution and spatial patterning of an invasive shrub in secondary hardwood forests . Forest Science 60 : 830 - 840 . Shields JM , Jenkins MA , Saunders MR , Gibson KD , Zollner PA , Dunning JB . 2015a . Influence of intensity and duration of invasion by Amur honeysuckle (Lonicera maackii) on mixed hardwood forests of Indiana . Invasive Plant Science and Management 8 : 44 - 56 . Shields JM , Saunders M , Gibson K , Zollner P , Dunning J , Jenkins M. 2015b . Short-term response of native flora to the removal of non-native shrubs in mixed-hardwood forests of Indiana, USA . Forests 6: 1878 - 1896 . Sotala DJ , Kirkpatrick CM . 1972 . Foods of white-tailed deer, Odocoileus virginianus , in Martin County, Indiana. American Midland Naturalist 89 : 281 - 286 . Therneau T. 2015 . A Package for Survival Analysis in S. version 2 .38,¼survival. Tilghman N. 1989 . Impacts of white-tailed deer on forest regeneration in northwestern Pennsylvania . The Journal of Wildlife Management 53 : 524 - 532 . U.S. Climate Data . 2015 . http://www.usclimatedata. com/ (9 December 2015 ). USDA , NRCS. 2015 . The PLANTS Database . National Plant Data Team, Greensboro , NC 27401 -4901 U.S.A. http://plants.usda. gov (16 November 2015 ). Vavra M , Parks CG , Wisdom MJ . 2007 . Biodiversity, exotic plant species, and herbivory: the good, the bad, and the ungulate . Forest Ecology and Management 246 : 66 - 72 . Verhoeven KJF , Simonsen KL , McIntyre LM . 2005 . Implementing false discovery rate control: increasing your power . Oikos 108 : 643 - 647 . Waller D. 2014 . Effects of deer on forest herb layers , In: Gilliam FS, ed. The herbaceous layer in forests of eastern North America . New York: Oxford University Press, 369 - 399 . Waller DM , Alverson WS . 1997 . The white-tailed deer: a keystone herbivore . Wildlife Society Bulletin 25 : 217 - 226 . Waring RH , Cleary BD . 1967 . Plant moisture stress: evaluation by pressure bomb . Science 155 : 1248 - 1254 . Webster CR , Jenkins MA , Jose S. 2006 . Woody invaders and the challenges they pose to forest ecosystems in the eastern United States . Journal of Forestry 104 : 366 - 374 .

This is a preview of a remote PDF:

Owings, Charlotte F., Jacobs, Douglass F., Shields, Joshua M., Saunders, Michael R., Jenkins, Michael A.. Individual and interactive effects of white-tailed deer and an exotic shrub on artificial and natural regeneration in mixed hardwood forests, AoB PLANTS, 2017, DOI: 10.1093/aobpla/plx024