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Eastern deciduous forests are changing in species composition and diversity outside of classical successional trajectories. Three disturbance mechanisms appear central to this phenomenon: fire frequency is reduced, canopy gaps are smaller, and browsers are more abundant. Which factor is most responsible is a matter of great debate and remains unclear, at least partly because few studies have simultaneously investigated more than one process. We conducted a large-scale experiment in mesophytic forests of West Virginia, USA, to test three key hypotheses: (1) the fire hypothesis (fire suppression limits diversity to few shade-tolerant, fire-intolerant species that replace and suppress many fire-tolerant species); (2) the gap hypothesis (small gaps typical of today's forests promote dominance of a few shade-tolerant species); and (3) the browsing hypothesis (overbrowsing by deer limits diversity to a few unpalatable species). We tested these hypotheses using a factorial experiment that manipulated surface fire, large canopy gap formation (gap size ∼255 m 2 ), and browsing by deer, and we followed the fates of >28 000 seedlings and saplings for five years. Understory tree communities in control plots were dominated (up to 90%) by Fagus grandifolia , averaging little more than two species, whereas overstories were diverse, with 10-15 species. Fire, large canopy gaps, and browsing all dramatically affected understory composition. However, our findings challenge views that fire and large canopy gaps can maintain or promote diversity, because browsers reduced the benefits of gaps and created depauperate understories following fire. Consequently, two major disturbances that once promoted tree diversity no longer do so because of browsing. Our findings appear to reconcile equivocal views on the role of fire and gaps. If browsers are abundant, these two disturbances either depress diversity or are less effective. Alternatively, with browsers absent, these disturbances promote diversity (three- to fivefold). Our results apply to large portions of eastern North America where deer are overabundant, and we provide compelling experimental evidence that historical disturbance regimes in combination with low browsing regimes typical of pre-European settlement forests could maintain high tree species diversity. However, restoring disturbances without controlling browsing may be counterproductive.

Chaenotheca balsamconensis is described as new to science based on collections from the Great Lakes and Appalachians of eastern North America (Maine, New Brunswick, North Carolina, Ontario, Prince Edward Island and Québec), and one population from western North America (British Columbia). It is distinguished from other species of Chaenotheca by its restriction to Trichaptum abietinum as a substrate, almost exclusively immersed thallus, smooth ascospores, and the presence of a KOH+ red pigment in the stalk. Large-scale conifer fatalities in eastern North America have increased the available habitat for T. abietinum, which has likely caused a boom in the population of C. balsamconensis.

During foraging, moose break stems of numerous saplings in order to lower shoot tips to a height they can reach. Both stem-breaking and bedding occur throughout the range of moose and these behaviors together create disturbed patches, which increase habitat heterogeneity forest-wide. Here, we explore this phenomenon in two ways: a case study in which we quantify the size of moose beds and evaluate the physical and taxonomic extent of stem breaking for more than 300 broken trees at seven sites in western Massachusetts and Connecticut, and a literature review on stem-breaking. In our case study, moose broke the stems of 17 deciduous woody species and were twice as likely to snap main stems rather than lateral stems. After breaking a stem, moose browsed shoot tips 96% of the time. Moose snapped primarily shade-intolerant or intermediately tolerant species (92%); the frequency of broken shade-intolerant trees was 2–4 times greater than the frequency of their occurrence in the stand, and the only shade-tolerant species moose broke were shrubs or understory tree species. We measured the 10 moose beds that we encountered; they ranged in size from 1.5–3.4 m2 (mean = 2.5 m2). We performed a systematic review of stem breaking by moose throughout their range and found 14 publications that characterized stem-breaking by moose in Europe and North America. These studies typically focused on a few tree species of economic importance, on how stem-breaking increased forage access to the tips of broken trees, or how moose damage in general redirected or delayed succession. The one report of stem-breaking across all species found 1% of all trees were broken, while as many as 60% of individuals of preferred species were broken at sites in both North America and Europe. Stem-breaking contributes to keeping some forest stands in an earlier stage of succession, and bedding may create small patches of crushed vegetation that may enhance local plant diversity at small spatial scales. Thus, our findings and review support previous research that characterize moose as ecosystem engineers, keystone species, or both.

1. Ungulate browsers, when at high densities, are major drivers of vegetation change in forests world-wide. Their effects operate via a variety of generalizable mechanisms related to plant palatability and relative growth rate with respect to browsing pressure. 2. Though such impacts are obviously long-lasting when they determine composition of tree regeneration, we document in a unique long-term (30 year) experiment that biological legacies of initial deer density persist in the understorey herbaceous vegetation at least 20 years after deer densities were equalized. 3. We sampled understorey vegetation in former clear-cut areas where density of white-tailed deer (Odocoileus virginianus) was manipulated (3.9–31.2 deer km–2) for 10 years (1979–1990), and stands experienced ambient deer density (ca. 10–12 deer km–2) for the next 20 years (1990–2010) to determine whether initial deer density treatments still influenced understorey vegetation in 30-year-old, closed-canopy forests. 4. Stands initially (1979–1990) exposed to higher deer densities had ca. five times higher fern cover and three times the seedling and forb cover in 2010, as well as significantly lower angiosperm species density, compared to stands initially exposed to lower deer densities. 5. These results appear driven by deer avoidance of ferns, allowing them to expand at high deer density and sequester sites for decades. 6. Synthesis. Our long-term, experimental results show unequivocally that elevated deer densities cause significant, profound legacy effects on understorey vegetation persisting at least 20 years. Of relevance regionally and globally where high deer densities have created depauperate understoreys, we expect that deer density reduction alone does not guarantee understorey recovery; stands may need to be managed by removing recalcitrant understorey layers (e.g. ferns).

1. Most research on dynamics and impacts of plant invasions has evaluated patterns and effects over brief time periods (i.e. <4 years). As such, little is known about the persistence of invasions and their long-term impacts on native species. 2. To experimentally evaluate longer-term effects of invasions, we established field plots with native tree and herbaceous species and then invaded half of the plots with the most widespread invasive grass in the eastern United States (Microstegium vimineum). Over 8 years, we quantified invader and native plant biomass, native plant diversity, and tree density and size. 3. Microstegium was dominant during the first 4 years of the experiment, constituting more than 60% of herbaceous plant biomass in the plots, and native herbaceous biomass was 57% lower and diversity was 44% lower in invaded vs. control plots. However, both Microstegium and herbaceous native species declined in later years. By the end of the experiment, Microstegium was only 2% of community biomass, and there was no difference in native herbaceous biomass in invaded and control plots. 4. We applied a fire treatment in years 6 and 7 to test if repeated disturbance is required to maintain invader dominance and to evaluate how this common management practice in eastern US forests affected invasive and native plants. Tree density was 65% lower and tree diameters were 28-51% smaller on average in fire-treated compared with control quadrants, resulting in significantly greater light availability in fire-treated areas. Consequently, Microstegium and native herbaceous species biomass increased significantly where fire was applied. However, only native species were persistent, and after 8 years, Microstegium was nearly absent, regardless of the fire treatment. 5. Synthesis. The invasive grass was initially abundant and suppressed native species, but invader decline over time corresponded with succession to native herbaceous species dominance when fire was applied, and to native tree dominance without fire such that after 8 years, the initial effects of invasion were no longer apparent. Thus, our data provide some of the first experimental evidence that while the initial effects of plant invasions can be dramatic, invaders and their impacts may decline over time.

Increasing rates of atmospheric deposition of nitrogen (N) present a novel threat to the biodiversity of terrestrial ecosystems. Many forests are particularly susceptible to excess N given their proximity to sources of anthropogenic N emissions. This study summarizes results of a 25‐yr treatment of an entire central Appalachian hardwood forest watershed via aerial applications of N with a focus on effects of added N on the cover, species richness, and composition of the herbaceous layer. Research was carried out on two watersheds of the Fernow Experimental Forest (FEF), West Virginia. The long‐term reference watershed at FEF (WS4) was used as a reference; WS3 was experimentally treated, receiving three aerial applications of N per year as (NH4)2SO4 totaling 35 kg N ha−1 yr−1, beginning in 1989. Cover of the herbaceous layer (vascular plants ≤1 m in height) was estimated visually in five circular 1‐m2 subplots within each of seven circular 400‐m2 sample plots spanning all aspects and elevations of each watershed. Sampling was carried out in early July of each of the following years: 1991, 1992, 1994, 2003, and 2009—2014, yielding 10 yr of data collected over a 23‐yr period. It was anticipated that the N treatment on WS3 would decrease species richness and alter herb layer composition by enhancing cover of a few nitrophilic species at the expense of numerous N‐efficient species. Following a period of minimal response from 1991 to 1994, cover of the herb layer increased substantially on N‐treated WS3, and remained high thereafter. There was also a coincidental decrease in herb layer diversity during this period, along with a sharp divergence in community composition between WS4 and WS3. Most changes appear to have arisen from unprecedented, N‐mediated increases of Rubus spp., which are normally associated with the high‐light environment of openings, rather than beneath intact forest canopies. These findings support the prediction that N‐mediated changes in the herbaceous layer of impacted forests are driven primarily by increases in nitrophilic species.

1. While many ecosystems depend on fire to maintain biodiversity, non-native plant invasions can enhance fire intensity, suppressing native species and generating a fire-invasion feedback. These dynamics have been observed in arid and semi-arid ecosystems, but fire-invasion interactions in temperate deciduous forests, where prescribed fires are often used as management tools to enhance native diversity, have rarely been investigated. 2. Here we evaluated the effects of a widespread invasive grass on fire behaviour in eastern deciduous forests in the USA and the potential effects of fire and invasions on tree regeneration. We planted native trees into invaded and uninvaded forests, quantified fuel loads, then applied landscape-scale prescribed fires and no-burn controls, and measured fire behaviour and tree seedling and invasive plant performance. 3. Our results show that fires in invaded habitats were significantly more intense, including higher fire temperatures, longer duration and higher flame heights, even though invasions did not alter total fuel loads. The invasion plus fire treatment suppressed native tree seedling survival by 54% compared to invasions without fire, and invasions reduced natural tree recruitment by 66%. 4. We also show that invasive plant biomass did not change from one season to the next in plots where fire was applied, but invader biomass declined significantly in unburned reference plots, suggesting a positive invasive grass-fire feedback. 5. Synthesis and applications. These findings demonstrate that fire-invasion interactions can have significant consequences for invaded temperate forest ecosystems by increasing fire intensity and reducing tree establishment while promoting invasive plant persistence. To encourage tree regeneration and slow invasive spread, we recommend that forest managers remove invasions prior to applying prescribed fires or avoid the use of fire in habitats invaded by non-native grasses.

Amur honeysuckle (Lonicera maackii) is an exotic invasive shrub that is rapidly expanding into forests of eastern North America. This species forms a dense forest understory, alters tree regeneration, negatively affects herb-layer biodiversity, and alters ecosystem function. In a second-growth forest in central Kentucky, we examined the timing and production of leaf litter and compared litter chemistry, decay rates, and microbial community colonization of Amur honeysuckle to that of two native trees, white ash (Fraxinus americana) and hickory (Carya spp.). The distribution of Amur honeysuckle was clumped, allowing us to compare differences in decomposition under and away from Amur honeysuckle shrubs. Amur honeysuckle leaf litter had significantly higher nitrogen, lower C:N, and lower lignin than the other species, and decomposition rates were greater than 5 x faster. Despite the much higher rate of Amur honeysuckle decomposition compared with the native species (p < 0.0001), decomposition of all species was significantly slower (p = 0.0489) in sites located under Amur honeysuckle shrubs. Nitrogen concentration increased through time in decomposing Amur honeysuckle litter; however, total mass of N rapidly declined. We found the initial microbial community on leaf litter of Amur honeysuckle was distinct from two native species and although all microbial communities changed through time, the microbial community of Amur honeysuckle remained distinct from native communities. In summary, a distinct microbial community that may originate on Amur honeysuckle leaves prior to senescence could explain the rapid decay rates.

The habitat quality of urban forest patches is determined by the composition and structure of vegetation which in turn affects the quality of trophic resources and shelter provided for wildlife species. In addition, urban development in the landscape surrounding forest patches can affect species' movement between patches, further influencing habitat quality. Understanding how species respond to variation in habitat quality among urban forest patches is especially important for species that contribute to ecosystem services and disservices for urban residents. Here, we assessed habitat quality provided by urban forest patches for white‐footed mice (Peromyscus leucopus) because they are one of the key reservoir species for Lyme disease and they influence disease dilution ecosystem services provided by mammal communities. We examined variation in vegetation composition and structure in forest patches across a gradient of landscape‐scale urban development in and around Philadelphia, PA, USA. In particular, we focused on shifts in vegetation composition and structure associated with invasive understory shrubs given their prevalence in our study system. We then quantified the numerical (index of relative abundance) and morphological responses of white‐footed mice to variation in habitat quality. While we observed no significant effects of environmental variables on our index of mouse relative abundance in forest patches, environmental variables associated with vegetation structure and composition were associated with shifts in mouse morphology. Most notably, mice were larger at sites with more invasive shrub species. This indicates that invasive understory shrubs may be creating higher‐quality habitat for white‐footed mice. Because larger‐bodied mice are likely to feed more ticks, this result has significant implications for Lyme disease dynamics in urban areas, such as amplified transmission.

Fire is a disturbance that serves to maintain the diverse mosaic of vegetation in the Eastern Deciduous Forest. However, our ability to reconstruct fire occurrence from hardwood tree scars still lags far behind our expertise in reconstructing fire history from conifers in the western United States. This study examines the fidelity of fire scaring in multiple tree species in the Big Oaks National Wildlife Refuge in Indiana, which is located in the central hardwood region of the Eastern Deciduous Forest. All 15 species, except for red oak, showed evidence of past fires, and most samples recorded multiple fire events. No fire scars were recorded in the latewood of the samples. Most of the fires scars occurred in the earlywood (May) suggesting the dormant season fires are likely associated with fires in March to April before the growing season begins. No synchronous fires were recorded across all sites, but fires occurred in 1981, 1982, 1984, 1985, and 1988 across multiple sites. This suggests that these were larger spreading fires. Establishment pulses were documented in association with fire events in 1981, 1984, and 1995, suggesting that fire may benefit the establishment or root sprouting of some hardwood species. Fourteen of the fifteen species that we sampled preserved fire scars, suggesting that the diverse suite of species in the Eastern Deciduous Forest is a viable sampling pool for examining fire history across this forest type.