Species distribution models (SDMs) assume that all ecologically relevant predictor variables are included. This assumption is frequently violated in SDMs of plant species, as soil variables are rarely included. Here, we used in‐situ, soil geochemical variables along with more commonly used topo‐climatic and remotely sensed variables to create SDMs of understorey plant species. We evaluated whether the potential importance of soil variables is greater than generally described in SDM literature, which predictors are most important, and whether a standard subset of predictors can be used to effectively model all species.

Perennial invasive plants can be controlled by damaging established vegetative individuals or by preventing establishment of new plants from seed. Less information is available about the latter. We examined how seedling establishment of glossy buckthorn (Frangula alnus), a non-native shrub that invades forests in eastern North America, is affected by four soil surface treatments - grass-dominated turf, oak leaf litter, pine leaf litter, soil compaction - relative to an untreated control (tilled soil). Data on seedling emergence, survival, growth, and reproduction were collected from 1.5 m(2) plots (six per treatment) over two years at the Kingman Research Farm, Madbury, NH, USA. Overall, buckthorn success from seed was inhibited by grass turf and facilitated by oak litter, while pine litter effects were complex and soil compaction had no effect. Specifically, relative to control, the turf treatment reduced buckthorn seedling emergence (year 2 only), increased mortality over two years, reduced density of living buckthorn, and prevented fruiting. Oak litter resulted in greater buckthorn seedling height relative to control, while pine litter, although reducing seedling emergence (year 1 only), increased both seedling height and the proportion of plants fruiting in year 2. Across all treatments and control, buckthorn seedling emergence was greatest in June, declining thereafter. Of the four treatments, only grass turf offered some promise of resisting invasion. The mechanism of resistance by turf is not known, but likely involves either more intense competition or higher levels of herbivory associated with turf. The mechanism, as well as the logistics and cost of turf establishment in logged areas, require further exploration.

Glossy buckthorn (Frangula alnus) is an invasive exotic shrub in forests of eastern North America, where it can alter the structure and function of ecosystems. Buckthorn is often abundant in eastern white pine (Pinus strobus) stands, though the specific factors that that allow invasion into these stands are not known. In an observational study, we examined the roles of tree species composition, photosynthetically active radiation (PAR, i.e., sun-light), and soil characteristics in limiting buckthorn success. Data on buckthorn biomass and forest characteristics were collected from 60 locations in closed-canopy pine and hardwood stands in southeastern New Hampshire. Using logistic regression, buckthorn presence was associated with low soil inorganic-N, high PAR, and a deep humus layer. Using generalized linear modeling, buckthorn biomass was positively associated with high PAR and negatively associated with both the basal area of trees other than white pine (non-WP BA) and sand content. The presence of reproductive buckthorn, analyzed with logistic regression, was associated with high PAR and low non-WP BA. Using discriminant analysis, locations with the oldest buckthorn were best predicted by PAR, non-WP BA, sand content, soil inorganic-N concentrations, and humus depth. White pine BA was not a predictor in any chosen model of buckthorn success. Overall, areas with high PAR and low non-WP BA were the strongest predictors of buckthorn success, and thus sites with these characteristics appear most susceptible to invasion.

Abstract Identifying the mechanisms that structure niche breadth and overlap between species is important for determining how species interact and assessing their functional role in an ecosystem. Without manipulative experiments, assessing the role of foraging ecology and interspecific competition in structuring diet is challenging. Systems with regular pulses of resources act as a natural experiment to investigate the factors that influence the dietary niches of consumers. We used natural pulses of mast‐fruiting of American beech (Fagus grandifolia) to test whether optimal foraging or competition structure the dietary niche breadth and overlap between two congener rodent species (Peromyscus leucopus and P. maniculatus), both of which are generalist consumers. We reconstructed diets seasonally over a 2‐year period using stable isotope analysis (δ13C, δ15N) of hair and of potential dietary items and measured niche dynamics using standard ellipse area calculated within a Bayesian framework. Changes in niche breadth were generally consistent with predictions of optimal foraging theory, with both species consuming more beechnuts (a high‐quality food resource) and having a narrower niche breadth during masting seasons compared to nonmasting seasons when dietary niches expanded and more fungi (a low‐quality food source) were consumed. In contrast, changes in dietary niche overlap were consistent with competition theory, with higher diet overlap during masting seasons than during nonmasting seasons. Overall, dietary niche dynamics were closely tied to beech masting, underscoring that food availability influences competition. Diet plasticity and niche partitioning between the two Peromyscus species may reflect differences in foraging strategies, thereby reducing competition when food availability is low. Such dietary shifts may have important implications for changes in ecosystem function, including the dispersal of fungal spores.

Invasive glossy buckthorn (Frangula alnus) hampers management of white pine (Pinus strobus) in the northeastern USA, especially when these species co-establish following harvest activities. Our objective was to test the effects on pine sapling growth of a simple, quick, and novel silvicultural procedure involving local buckthorn stem removal. We identified 75 five-year-old pine saplings in a Durham, NH, forest regeneration area that was clearcut in 2009 and which was heavily invaded by buckthorn. All selected pine saplings were surrounded primarily by glossy buckthorn. Around each of 50 of these pine saplings, a 1 m radius was cleared ('cut only' treatment) and for half of these there was a follow-up herbicide application ('cut + herbicide' treatment). Remaining saplings were untreated controls. After one growing season, pines responded to treatment with increased terminal leader biomass (+75%), basal stem diameter (+12%) and bark starch (+140%). Treated pines displayed even greater diameter increase (+ 29%) after two growing seasons. None of these variables differed across the two treatments. Height of treated pines did not differ from controls, even after the second growing season. When herbicide was used, there were 86% fewer buckthorn sprouts in treated areas, but pine mortality was five times greater (n = 5) than in the cut only treatment (n = 1). Our results show that, regardless of herbicide use, those pines cleared of surrounding vegetation and not subject to post-treatment mortality exhibited increased vigor and growth, suggesting a greater potential to eventually outgrow competing buckthorn and thus more rapidly reach commercial size.

Non-native glossy buckthorn (Frangula alnus Mill.) is invasive in forests of the northeastern USA but little is known of its effects on tree regeneration. We tested whether killing buckthorn stems before logging reduces its post-logging abundance and increases the density and height of eastern white pine (Pinus strobus L.) seedlings. Three 0.4 ha plots were clearcut, three were thinned, and three were left as controls. Each plot had previously been divided into three subplots that received different buckthorn treatments during the two years before logging. Buckthorn treatments were (1) stems cut at base five times; (2) stems cut once then heat killed four times; (3) untreated control. Three years post-logging, buckthorn density and stem height were unaffected by logging but equally reduced by the two buckthorn treatments. Buckthorn reduction increased density and height of pine seedlings, and seedling height also increased with logging. In the fifth year post-logging, pine height growth and biomass were greater in clearcut than in thinned treatments, greater in areas of buckthorn removal and, within treated subplots, greater in areas with low buckthorn density than in thickets of recovering buckthorn. Thus, although buckthorn inhibited regenerating pine, pre-logging destruction of buckthorn stems reduced such competition for at least four years.

We analyzed the recent (< 25 yr) spread in New Hampshire, USA, of the exotic tree Kalopanax septemlobus, native to Asia. The invasion was likely initiated by a single tree planted ca. 1972. Our objective was to assess the viability of the invasion, especially in light of the small propagule size. We tallied, mapped, aged, and measured the height and growth of K. septemlobus individuals at two sites, the University of New Hampshire campus (UC) and Thompson Farm (TF), both in Durham. We found over 3,800 plants at UC and 270 at TF in < 120 ha (296 ac) total area. Plant age ranged from 0 to 22 yr, and UC plants were as far as 775 m (2,543 ft) from the purported parent tree. Annual height growth was comparable to midtolerant native trees. Plants occurred in both open and forested habitats, and the mean level of photosynthetically active radiation incident on understory plants was 4 to 6% of full sun. The large population size, shade tolerance, rapid height growth, and ability to sprout from damaged stems suggest potential for K. septemlobus to invade and persist in forests, the most common natural ecosystem in the northeastern United States. We further suggest that small propagule size, likely a single tree, has not prevented K. septemlobus from initiating a spatially extensive and vigorous population. Kalopanax septemlobus has been planted as an ornamental in the northeastern United States, and prevention of region-wide invasion might depend on removal of these trees, even when they occur as single individuals.

In the northeastern United States, whole-tree harvesting is widely used to supply fuel to biomass energy facilities, but questions remain regarding its long-term sustainability. We have previously reported findings indicating no short-term decrease in forest productivity in whole-tree harvested sites when compared with similar conventionally (stem-only) harvested sites. Here we present additional results of the same study, but focus on the effect harvest treatment has on the species composition of the regenerating forest. Within northern hardwood forests in central New Hampshire and western Maine, regeneration surveys were conducted on four (4) small clearcuts in 2010 and twenty-nine (29) small clearcuts in 2011. The species and diameter of trees > 2 m in height were recorded within 1 m or 2 m-radius plots and used to calculate the biomass fraction of each species. The 2010 study additionally measured the density of trees 2 m in height and the diversity of understory non-tree species. Non-metric multidimensional scaling and multi-response permutation procedures were used to determine the effect of harvest treatment had on community-wide tree species composition. Potential differences were also examined on a species-by-species basis. Both analytic methods indicated no significant differences in species composition of tree species or understory communities. Within the limits of our data, we conclude that no significant effects of residue removal on species composition are observed within our sample of northern hardwood sites at this early stage of stand development.

Winter moth, Operophtera brumata L. (Lepidoptera: Geometridae), has been defoliating hardwood trees in eastern Massachusetts since the 1990s. Native to Europe, winter moth has also been detected in Rhode Island, Connecticut, eastern Long Island (NY), New Hampshire, and Maine. Individual tree impacts of winter moth defoliation in New England are currently unknown. Using dendroecological techniques, this study related annual radial growth of individual host (Quercus spp. and Acer spp.) trees to detailed defoliation estimates. Winter moth defoliation was associated with up to a 47% reduction in annual radial growth of Quercus trees. Latewood production of Quercus was reduced by up to 67% in the same year as defoliation, while earlywood production was reduced by up to 24% in the year following defoliation. Winter moth defoliation was not a strong predictor of radial growth in Acer species. This study is the first to document impacts of novel invasions of winter moth into New England.

We studied the forest structure and dynamics of the 26 ha College Woods Natural Area (CWNA), Durham, NH. The CWNA is dominated by Tsuga canadensis, but includes a remnant cohort of ca. 300 y old Pinus strobus and abundant mid-tolerant hardwoods. Our primary objectives were to: estimate the recruitment years of four mid-tolerant hardwoods, Acer rubrum, Betula lenta, Quercus rubra, and Q. velutina; relate the temporal appearance and population structure of these species to local disturbance history; and compare our results to other old forests in central New England. We hypothesized that recruitment of mid-tolerant hardwoods at the CWNA was associated with major 20th century windstorms and was limited to within 25 y post disturbance. We used plot sampling to describe densities and size structures of all tree species in the stand. Both Tsuga canadensis, the most abundant species, and Fagus grandifolia were represented in all diameter classes, whereas the mid-tolerant hardwoods were poorly represented in both the smaller and larger size classes. We took increment cores from a sample of trees of each mid-tolerant species and estimated a recruitment year for each individual. We then related recruitment years of each species to local disturbance history. Age estimates suggest that most individuals recruited after 1900 and that recruitment was associated with disturbances, including logging between 1895 and 1919, and the hurricanes of 1938 and 1954. After 1960, there was little recruitment of mid-tolerant tree species, probably due to canopy closure and lack of additional disturbance. The dynamics of mid-tolerant species in the CWNA were similar to those in an old Tsuga-Pinus stand at the Harvard Tract, 125 km to the west, as well as in other mature stands in central New England, suggesting regionally consistent responses to disturbance. Despite the current dearth of recruitment, future regeneration of these species in College Woods is likely, if not due to severe windstorms, then to the imminent loss of the Tsuga canadensis-Fagus grandifolia canopy to introduced insects and pathogens.

In the northeastern United States, many species are affiliated with early-successional forests and shrub-lands, collectively referred to as thickets. The abundance of these habitats has declined substantially in recent decades and, of those that remain, many have been colonized by exotic shrubs. We investigated how invasive shrubs may affect these habitats by focusing on possible changes to local insect communities because insects represent a diverse assemblage that is known to respond to changes in plant composition. Additionally, modifications of insect communities may affect the suitability of habitats to other organisms that prey on them. We compared insect abundance, richness, and phenology among four sites with different levels of exotic shrub cover using flight-intercept traps and beat sampling of individual shrubs. Captive lepidopteran larvae also were used to investigate preferences for foliage from native and exotic shrubs and short-term survival when larvae were exclusively fed foliage from either native or exotic shrubs. Habitats with a large proportion of cover by invasive shrubs had an abundance of generalist and pest insects, whereas sites dominated by native shrubs supported more lepidopterans, more herbivorous insects, and more rare species. Captive lepidopteran larvae avoided foliage from invasive shrubs and a majority of those provided with such a diet died. We conclude that invasive shrubs may alter local insect communities and that those modifications can reduce the suitability of thicket habitats to other organisms (e.g., nesting songbirds). The enhancement and expansion of thicket habitats has become a management priority in the region, yet activities that are applied to maintain these habitats (e.g., controlled burns, mowing, and cuts) can increase the likelihood of exotic plant invasions. We summarize guidelines that may help avoid a management dilemma when dealing with this issue. Published by Elsevier B.V.

Widespread and prolonged defoliation by the European winter moth, Operophtera brumata L., has occurred in forests of eastern Massachusetts for more than a decade and populations of winter moth continue to invade new areas of New England. This study characterized the forests of eastern Massachusetts invaded by winter moth and related the duration of winter moth defoliation estimated using dendrochronology to observed levels of tree mortality and understory woody plant density. Quercus basal area mortality in mixed Quercus and mixed Quercus—Pinus strobus forests in eastern Massachusetts ranged from 0–30%; mortality of Quercus in these forests was related to site quality and the number of winter moth defoliation events. In addition, winter moth defoliation events lead to a subsequent increase in understory woody plant density. Our results indicate that winter moth defoliation has been an important disturbance in New England forests that may have lasting impacts.

Waveform lidar imagery was acquired on September 26, 1999 over the Bartlett Experimental Forest (BEF) in New Hampshire (USA) using NASA's Laser Vegetation Imaging Sensor (LVIS). This flight occurred 20 months after an ice storm damaged millions of hectares of forestland in northeastern North America. Lidar measurements of the amplitude and intensity of ground energy returns appeared to readily detect areas of moderate to severe ice storm damage associated with the worst damage. Southern through eastern aspects on side slopes were particularly susceptible to higher levels of damage, in large part overlapping tracts of forest that had suffered the highest levels of wind damage from the 1938 hurricane and containing the highest levels of sugar maple basal area and biomass. The levels of sugar maple abundance were determined through analysis of the 1997 Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) high resolution spectral imagery and inventory of USFS Northern Research Station field plots. We found a relationship between field measurements of stem volume losses and the LVIS metric of mean canopy height (r2 = 0.66; root mean square errors = 5.7 m3/ha, p < 0.0001) in areas that had been subjected to moderate-to-severe ice storm damage, accurately documenting the short-term outcome of a single disturbance event.

Abstract In New Hampshire, the Ossipee Pine Barrens is the largest and best example of a Pinus rigida-Quercus ilicifolia dominated ecosystem remaining in the state. Because of long-term fire suppression in the 20th century, we hypothesized that undisturbed stands may be undergoing succession to more shade-tolerant Pinus strobus and hardwoods. To test this hypothesis, we sampled 41 sites within the barrens covering the range of soils, landforms, stand age, and vegetational variation present in the barrens. Current (2002) tree (≥ 10 cm dbh) and sapling (taller than 1 m, < 10 cm dbh) densities were measured by quadrat sampling. Past (1952) vegetation was reconstructed using reverse-growth equations derived from increment cores from trees alive in 2002 and forensic evidence such as stumps. Future (2052) vegetation was estimated using a simple transition model based on 1952–2002 compositional changes. Community types were classified using cluster analysis of 80 communities based on the 2002 and back-casted 1952 tree species abundances at the study sites. Cluster analysis of the 80 communities using tree relative densities produced four community types, dominated by 1) P. rigida, 2) P. rigida and Acer rubrum, 3) P. strobus and A. rubrum, and 4) A. rubrum, respectively. The frequency of the Pinus rigida community type was highest in 1952 and declined with time, with only 8% of sites predicted to support pitch pine canopies by 2052. The Pinus strobus-Acer rubrum community type increased between 1952 and 2002 as the Pinus rigida type declined, and should continue to increase in the future. The other two communities appeared to be transitional. Pinus rigida was even-aged on most sites, where forests averaged 97 ± 42 years (SD) old. Many sites will transition to P. strobus and hardwoods as canopy pitch pines die, because P. rigida recruitment was not occurring in most stands.

The extent to which forests can be invaded by exotic plants and the role of tree harvest in facilitating such invasions are important issues in invasion biology. Our objective was to determine: (a) whether a widespread exotic shrub, glossy buckthorn (Frangula alnus), can invade a common northeastern US forest type, (b) the extent to which logging facilitates buckthorn invasion, (c) whether buckthorn invades gaps through pre-disturbance (‘advance’) regeneration, (d) whether or not it forms uneven-aged populations in invaded stands. We selected nine eastern white pine – hardwoods stands in Durham, NH. Three were undisturbed, three were clear-cut, and three were partially cut. Cutting occurred ⩾6years prior to sampling. Glossy buckthorn (⩾0.5m tall) was present in all stands at the time of sampling and most buckthorn populations were all-aged, suggesting that recruitment by seed continued after initial establishment and that long-term persistence in these stands is possible. Buckthorn was present in four of six cut stands prior to cutting, indicating some advance regeneration. The results support the view that forests are not inherently resistant to invasion by exotic plants. Compared to uncut stands, however, buckthorn had higher densities in clear-cut and partially cut stands. In partially cut stands, buckthorn density was greater in canopy gaps than in adjacent uncut areas. Thus, logging facilitated buckthorn invasion. Given this result and the known negative effects of buckthorn on tree regeneration, control measures should be considered when logging stands where buckthorn invasion is likely.

We compared the distribution of migrant bird species between two islands in the Gulf of Maine to examine if differences in habitat resulted in differences in avian species composition and relative abundance during stopover. Ninety-one species were captured on both islands and those species captured on only one island were either breeding species or rare visitors to the islands. Differences in bird species distribution between islands were species-specific and consistent among sampling periods for nearly all species. Twelve species were captured more frequently on Star Island and 11 species more frequently on Appledore Island. Stopover species distribution appeared to be related to habitat structure, vegetation, diet, and habitat area. Scrub-shrub/open habitat breeding species and forest breeding species were not evenly distributed between islands. Island use was most closely associated with breeding habitat. All but two of the eight species that breed in scrub-shrub or open habitat were captured more frequently on Star Island. Ten of the species more common on Appledore Island breed in forested habitat. Nine of the 11 species more common on Appledore Island are area-sensitive in breeding areas, suggesting potential area sensitivity during migration. Differential habitat use indicates a large number of stopover sites in a wide variety of habitats are necessary to meet migration needs of passerine species. Received 17 November 2006. Accepted 22 April 2010.

The primary objective of this study was to determine whether the exotic, invasive shrub, glossy buckthorn (Frangula alnus), is more abundant in canopy gaps created by logging than in uncut forests. Secondary objectives were to determine whether buckthorn abundance in gaps is related to gap size, and whether or not buckthorn exhibits advanced regeneration. The abundance of glossy buckthorn was estimated in five patch cuts and three single-tree cuts in a 90 year old eastern hemlock–eastern white pine–sweet birch forest at the Woodman Horticultural Farm in Durham, NH, USA. Glossy buckthorn was 96 times more abundant in logged areas than in uncut control plots. The three largest but youngest gaps (>0.08 ha; 5 years old) had the greatest proportion of tall (>2 m), reproductively mature glossy buckthorn individuals, with 18.4% fruiting. The older, medium-sized gaps (ca. 0.03 ha; 10 years old) contained the highest overall densities of glossy buckthorn, but few stems were flowering (~2%) and none were fruiting at the time of sampling. Small gaps (<0.01 ha; 10 years old) appeared to be sinks for glossy buckthorn, as all individuals were <0.5 m tall and none were >4 years old. As age and size of gaps were correlated, it was difficult to determine which factor played a larger role in the establishment and persistence of glossy buckthorn. However, the greater proportion of individuals >2 m tall and greater reproductive vigor of glossy buckthorn in large gaps relative to small gaps—despite fewer years available for growth—suggest that larger disturbances lead to more resources available for buckthorn growth, survival, and reproduction. Individuals <0.5 m tall were observed in uncut control plots at low density (<30 stems/ha) and 5% of stems in large gaps were older than the gaps themselves, suggesting that gap formation released previously established glossy buckthorn individuals (i.e., advanced regeneration).

Non-native, invasive glossy buckthorn (Frangula alnus P. Mill.) threatens North American forests by inhibiting tree regeneration. While glossy buckthorn commonly invades younger, developing forests, we hypothesized that this species is competitively excluded as secondary succession proceeds. Specifically, we tested the hypothesis that glossy buckthorn mortality in New Hampshire forests is associated with low levels of photosynthetically active radiation (PAR), low levels of nutrients in the soil, and greater abundance of shade tolerant tree species. Twenty-six living and 26 dead glossy buckthorn individuals were randomly selected on three, mid-successional study sites in southeastern New Hampshire, USA. Shrub ages, indicated by wood ring counts, showed that both living and dead shrubs were members of the same cohort, roughly 16–18 years of age. Living and dead shrubs were compared as to (1) tree basal area in the surrounding forest (estimated by plot sampling), (2) light intensity in the vicinity of the buckthorn crowns (measured by Sunfleck Ceptometer), (3) canopy openness and % total transmitted PAR (estimated by hemispheric photography), and (4) concentrations of available Ca, P, Mg, and K in the B horizon. Relative to live buckthorn shrubs, dead individuals were associated with greater basal area of shade tolerant species, decreased PAR in the vicinity of shrub crown, and decreased soil concentrations of Ca, P, and Mg. The results are consistent with the hypothesis that competition for light and perhaps nutrients limits the ability of glossy buckthorn to persist in late successional stands. If these relationships are causal, active removal of glossy buckthorn might not be required to reduce its abundance in late successional stands.

Decline of Atlantic white-cedar (Chamaecyparis thyoides), an uncommon, wetland tree of the eastern coastal United States, may be due in part to successional change in which cedar is replaced by more shade-tolerant tree species. The purpose of this study was to assess population structure and natural regeneration of cedar, project future changes in stand composition, and suggest appropriate management. The research was conducted at Brown Mill Pond, an ecological reserve in Rye, New Hampshire. Age and size structure of tree species were used to infer successional trends in five plant communities: (1) mixed conifer, (2) cedar 1, (3) cedar 11, (4) cedar-red maple, and (5) pond edge. Depth to water table was measured over two field seasons. Differences in species composition and stand structure were associated with variations in water table depth. In all communities except the pond edge and small (< 0.2 ha) patch cuts, cedar was even-aged (> 90 years old) and recruitment was lacking. In three communities over the next 100 years, abundance of arboreal associates will likely increase while cedar will decline. In a previously unreported successional sequence, eastern hemlock (Tsuga canadensis) and red spruce (Picea rubens) will likely become dominant in the mixed conifer community, which had the lowest water table. In areas with an intermediate water table, such as the cedar-red maple community, red maple (Acer rubrum) will achieve co-dominance with cedar. While cedar will likely decline in the absence of disturbance, it is unlikely that cedar will be completely replaced by arboreal associates at Brown Mill Pond as cedar establishment was evident along the pond edge and in small patch cuts.