Betula Lenta Research Articles

Visible and near-infrared hyperspectral indices explain more variation in lower-crown leaf nitrogen concentrations in autumn than in summer.

Autumn canopy phenological transitions are increasing in length as a consequence of climate change. Here, we assess how well hyperspectral indices in the visible and near-infrared (NIR) wavelengths predict nitrogen (N) concentrations in lower-canopy leaves in the autumn phenological transition as they are generally understudied in leaf trait research. Using a Bayesian framework, we tested how well published indices are able to predict N concentrations in Fagus grandifolia Ehrh., Liriodendron tulipifera L., and Betula lenta L. from mid-summer through senescence, and how related the indices are to autumn phenological change. No indices were able to determine a trend in differences in N in mid-summer leaves. Indices that included wavelengths in the green and NIR ranges were the first indices able to detect a trend and had among the highest correlations with N concentration in both the last green collection and the senescing collection. Models were unique when indices were fit to data from different phenophases. Indices that focused on only the red edge (i.e., the sharp increase in reflectance between the red and NIR wavelengths) had the strongest explanatory power across the autumn phenological transition, but had less explanatory power for individual collections. These indices, as well as those that have been correlated with chlorophyll (CCI) and carotenoids (PRI), were the strongest descriptors of autumn progression. This study provides insights on challenges and capabilities to monitor a leaf's N concentration throughout and across canopy senescence.

Legacy forest structures in irregular shelterwoods differentially affect regeneration in a temperate hardwood forest

Foresters are faced with managing forests for a broad variety of societal demands such as wildlife habitat, aesthetics and site stability while still providing monetary value to landowners through timber harvest. Regeneration methods need to be developed that offer alternatives to traditional management for timber to help meet these goals. Regeneration responses in third-growth forest stands, or those following harvest of second-growth stands are not well-studied. Such forests are now widespread across temperate regions and may exhibit growth patterns different than those reported previously for regenerating second growth that originated on land abandoned from agriculture. There is a need for research that can lead to new methods or modification of existing practice. Our study examines legacy trees and the associated regeneration across a 25-year chronosequence of 34 irregular shelterwoods regenerated from second-growth forest in southern New England. We compared regeneration of the three most common regenerating tree species: red maple (Acer rubrum), black birch (Betula lenta), and red oak (Quercus rubra). We used regression analyses to examine changes through time in height growth of the tallest regeneration for each species as well as changes in total abundance. Similarly, regressions for annual height growth of regeneration in relation to legacy overstory basal area were compared for each species. Over time, self-thinning occurred in the regeneration of all focus species, but at different rates. Black birch thinned most dramatically through time, and the saplings that survived retained a high position in the canopy. Red oak self-thinned most slowly, and its tallest stems retained competitive height, although did not surpass black birch. As legacy overstory basal area increased, annual growth of red oak regeneration slowed. Stand dynamics patterns are therefore significantly different from those of second growth forests where oak is a more vigorous competitor in both number and growth as compared black birch and red maple. Our results suggest that resource managers need to both recognize these differences in stand development and consider the tradeoff between increasing legacy trees and decreases in growth rate of oak regeneration, as well as long-term effects of increased structure post-timber harvest.

Determinants of temperature sensitivity of soil respiration with the decline of a foundation species.

The eastern hemlock (Tsuga canadensis) is an important foundation species that is currently declining throughout eastern U.S. forests due to the exotic pests hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa). Hemlock is often replaced by deciduous tree species, such as black birch (Betula lenta), and has been shown to have large consequences for carbon dynamics due to a substantial loss of soil organic layer carbon storage in hemlock forests when replaced by birch and higher decomposition found in black birch stands. Soil carbon is one of the most important components of the global carbon cycle and has high potential to feedback to climate change when large portions of stored carbon are lost to the atmosphere. There is a general consensus that soil respiration increases with temperature, but there has yet to be a consensus on how temperature sensitivity of soil respiration is affected by various biotic and abiotic factors, such as soil moisture and substrate quality. In this study, the effects of soil temperature and soil moisture on soil respiration (Rs), the temperature sensitivity of soil respiration (Q10), and soil basal respiration (R10) were investigated for hemlock, young birch, and mature birch forest types annually for three years. The Rs values of the three forest types were primarily driven by soil temperature rather than by soil moisture across all years. Soil respiration data collected from hemlock, young birch, and mature birch stands were used to determine annual Q10 and R10 values. The Q10 and R10 values were not significantly different between forest stands, but they were significantly different over the three years. Determinants of Q10 and R10 differed between forest type, with soil moisture primarily influencing Q10 in hemlock and mature birch stands and soil temperature primarily influencing R10 in mature birch stands. The results suggest a complex interaction of soil moisture and soil temperature, and potentially substrate quality and quantity, as determinants of temperature sensitivities in eastern U.S. forests that have transitioned from hemlock-dominated to black birch-dominated forests.

Soil Warming Accelerates Biogeochemical Silica Cycling in a Temperate Forest.

Biological cycling of silica plays an important role in terrestrial primary production. Soil warming stemming from climate change can alter the cycling of elements, such as carbon and nitrogen, in forested ecosystems. However, the effects of soil warming on the biogeochemical cycle of silica in forested ecosystems remain unexplored. Here we examine long-term forest silica cycling under ambient and warmed conditions over a 15-year period of experimental soil warming at Harvard Forest (Petersham, MA). Specifically, we measured silica concentrations in organic and mineral soils, and in the foliage and litter of two dominant species (Acer rubrum and Quercus rubra), in a large (30 × 30 m) heated plot and an adjacent control plot (30 × 30 m). In 2016, we also examined effects of heating on dissolved silica in the soil solution, and conducted a litter decomposition experiment using four tree species (Acer rubrum, Quercus rubra, Betula lenta, Tsuga canadensis) to examine effects of warming on the release of biogenic silica (BSi) from plants to soils. We find that tree foliage maintained constant silica concentrations in the control and warmed plots, which, coupled with productivity enhancements under warming, led to an increase in total plant silica uptake. We also find that warming drove an acceleration in the release of silica from decaying litter in three of the four species we examined, and a substantial increase in the silica dissolved in soil solution. However, we observe no changes in soil BSi stocks with warming. Together, our data indicate that warming increases the magnitude of silica uptake by vegetation and accelerates the internal cycling of silica in in temperate forests, with possible, and yet unresolved, effects on the delivery of silica from terrestrial to marine systems.

Loss of a Foundation Species, Eastern Hemlock (Tsuga canadensis), May Lead to Biotic Homogenization of Fungal Communities and Altered Bacterial Abundance in the Forest Floor

Tsuga canadensis (Eastern Hemlock) is a key forest foundation species that is currently declining across the eastern US due to attack by exotic insect species, primarily Adelges tsugae (Hemlock Woolly Adelgid). In the northeastern US, declining Eastern Hemlock stands are typically replaced by fast-growing deciduous Betula lenta (Black Birch) trees, altering ecosystem processes and ecological communities. In this study, we used an approach that substituted space for time to explore how the forest floor's soil organic horizon, macrofungal communities, and bacterial abundance might be altered following Eastern Hemlock replacement by Black Birch. We compared intact, mature Eastern Hemlock forest plots at 2 sites in western Massachusetts to adjacent areas of vigorous regeneration of young Black Birch triggered by logging activity at the sites ∼25–30 years ago. Forest-floor soil organic horizons were significantly thicker under Eastern Hemlock forests and exhibited a higher carbon:nitrogen (C:N) ratio, suggesting slower decomposition and greater accumulation of organic material under Eastern Hemlock compared to deciduous Black Birch canopies. Macrofungal communities emerging from the forest floor did not differ strongly in morphospecies richness between Eastern Hemlock and Black Birch plots. However, a greater number of rare fungi taxa, defined in this study as those represented by a single observation, were detected in Eastern Hemlock plots, and the composition of Black Birch plots was more homogenized and less variable. The abundance of bacterial colony forming units (CFUs) in the soil organic horizon appeared to follow a seasonal pattern of variation between mature Eastern Hemlock versus young Black Birch plots; CFUs were most abundant in Black Birch soils in the fall, potentially tracking input of new deciduous leaf litter, whereas Eastern Hemlock plots had higher CFU counts in the summer. The results of this study suggest that forest-floor characteristics will be substantially altered by the impending loss of Eastern Hemlock, associated macrofungal communities may become simplified and homogenized, and the timing of peak bacterial abundance in the forest floor might be shifted to the fall.

Dendroecological Analysis of Xeric, Upland, Quercus-Dominated Old-Growth Forest within the Ridge and Valley Province of Maryland, USA

Mesophytic species invasion and the loss of oaks from previously oak-dominated forest communities are two well-documented changes currently affecting the deciduous forests of the Appalachian Mountains. Several previous assessments of these changes prescribe active management to maintain oak. Currently, historically white oak (Quercus alba) dominated mesic stands documented in both the Allegheny Plateau and Ridge and Valley regions show increasing dominance of mesophytic species such as red maple (Acer rubrum) and black birch (Betula lenta). We describe a unique near-xeric, 72-ha tract of old-growth forest within the Ridge and Valley Region. This upland oak-pine, formerly oak-chestnut community, has maintained oak dominance without silvicultural management, despite being greatly impacted from the loss of American chestnut (Castanea dentata), fire suppression, high deer densities, and European gypsy moth (Lymantria dispar) defoliation. A dendroecological analysis of these 200-year-old stands shows persistence of oak through centuries of documented disturbances. These unmanaged old-growth stands have resisted mesophytic species invasion and therefore may provide insight into future compositional patterns and changes of similar upland and ridgeline forests within the Ridge and Valley. The combination of low site quality of ridgelines and ecological disturbances such as defoliation events, which may act as a moderate basal area reduction, allows oaks to persist and maintain dominance without silvicultural intervention. However, fire is recommended for the maintenance of co-dominant fire-dependent species such as Table Mountain pine (Pinus pungens) and herbaceous diversity along these ridge forests.

Structural, compositional, and functional responses to tornado and salvage logging disturbance in southern New England hemlock-hardwood forests

The frequency and severity of wind storms, such as hurricanes and tornados, are expected to increase in northeastern North America under climate change. As such, salvage logging is likely to become a more frequently-used post-disturbance management strategy; however, there is concern that the compound disturbance of wind followed by salvage logging could generate negative impacts on species composition, forest structure, and ecological resilience. These impacts are variable and uncertain, posing an opportunity for further research that considers differences in forest recovery following stand-replacing wind alone versus stand-replacing wind and salvage logging. We evaluated the short-term impacts of these singular (tornado) and interactive disturbance events (tornado + salvage logging) on the structure, composition, and function of a mature hemlock-hardwood forest in south-central Massachusetts. Specifically, we were interested in quantifying the impacts of salvage logging practices on forest recovery and resilience. Our analyses consider salvage logging impacts on forest overstory in addition to the regeneration layer (defined here as tree seedlings and saplings that make up the forest understory). We found that (i) delayed overstory mortality was highest on tornado-damaged sites, contributing additional material to dead wood pools, while salvaged sites lacked much of this material and associated structural legacies; (ii) tree regeneration layer diversity, as measured by Shannon’s Index, was higher in the tornado-damaged sites than salvaged sites, but levels of sapling (≥1.4 m in height and <12.7 cm in dbh) density and richness were the same; and (iii) regeneration present on tornado-damaged sites was more functionally similar to that present on undisturbed control sites than to that on salvaged sites. Our results indicate that the compound disturbance created by salvage logging may have initially homogenized regeneration composition and pushed these areas toward disturbance-adapted species (e.g., Acer rubrum and Betula lenta) and traits (e.g., transitory on-site reproductive strategies). This shift in composition may have also been influenced by the removal of dead material and structural legacies at these sites. However, the high levels of regeneration density and richness found on both tornado-damaged and salvage-logged sites suggests that rapid forest recovery is occurring via multiple mechanisms of regeneration, such as vegetative reproduction, advance regeneration, and new seedlings. These findings highlight how post-disturbance management actions affect forest resilience and development after severe wind disturbances, and suggest that future salvage logging operations more explicitly integrate retention of structural legacies and protection of advance regeneration to enhance forest recovery.

Timing is Not Everything: Assessing the Efficacy of Pre- Versus Post-Harvest Herbicide Applications in Mitigating the Burgeoning Birch Phenomenon in Regenerating Hardwood Stands

Sweet birch (Betula lenta L.) is aggressively recruiting in temperate forest understories of the eastern United States and often dominates the post-disturbance seedling community, diminishing diversity and hindering sustainable silviculture. The type and timing of silvicultural actions affect birch recruitment via their effects on seedling recruitment, survival, and growth. Here, we examine birch regeneration under two contrasting treatment sequences: pre- versus post-shelterwood harvest herbicide application (H–S vs. S–H) in combination with white-tailed deer (Odocoileus virginianus Zimmerman) browsing (fenced vs. unfenced) at 22 sites in northwestern Pennsylvania, USA. Additionally, we examine how treatments interact with additional site factors, including potential propagule sources and site productivity (i.e., integrated moisture index). We found the S–H sequence initially reduced birch density by 71% relative to the H–S sequence; however, the magnitude of this reduction waned over five growing seasons. Furthermore, birch proliferated following the H–S sequence only where mature birch were present. Deer browsing reduced birch height by 29% relative to fenced areas protected from browsing; however, by the fifth growing season birch seedlings were over twice as tall as other hardwood species across all treatments. Finally, increasingly mesic sites enhanced birch height growth. In sum, although post-harvest herbicide (S–H) provides short-lived control over birch, land managers should also consider browse pressure, seed source, and site productivity, as these may enhance or diminish the efficacy of post-shelterwood herbicide sequence effects on birch.

Lack of forest tree seedling recruitment and enhanced tree and shrub growth characterizes post-Tsuga canadensis mortality forests in the southern Appalachians

The loss of Tsuga canadensis from invasion by hemlock woolly adelgid (Adelges tsugae, HWA) has altered ecosystem structure and function in forests across the eastern United States. In southern Appalachian forests, T. canadensis co-occurred with hardwood species and an evergreen Rhododendron maximum shrub layer in riparian and cove positions. In this region, HWA infestation was detected in 2003, with mortality reaching 97% by 2014. In this study we examined responses of light, soil moisture, tree seedling density, and overstory and understory vegetation growth from 2004 to 2014 following HWA infestation and mortality of T. canadensis. We hypothesized that seedling recruitment and vegetation growth would continue to increase over time as observed with initial trends reported through 2009, and that species that associate with ectomycorrhizal (ECM) fungi may benefit more than those that do not due to the pulse of organic material in these stands from dead T. canadensis trees. Light transmission measured at 1 m above the ground increased from 2006 to 2009, but gradually decreased from 2015 to 2017. Basal area of overstory non-Tsuga trees increased only marginally, and there was no recruitment of tree seedlings to the overstory size class, even though seedling density of deciduous species increased initially. Increased basal area and stem density of R. maximum may explain the light and seedling responses, as this species can inhibit tree seedling recruitment by limiting light and nutrients. Overstory species with the highest basal area increment (BAI) in the post-T. canadensis stands were Pinus rigida, Betula lenta and Quercus coccinea, which all associate with ECM fungi. However, not all ECM tree species grew significantly more following T. canadensis mortality compared to pre-mortality growth rates—only those ECM species that had high growth rates prior to mortality did. After a decade, growth of both overstory trees and R. maximum has not compensated for the loss of T. canadensis. Active management of R. maximum, which may involve the removal of the evergreen shrub and soil organic layer, may be required to allow for diverse tree seedling recruitment; and subsequently, restore riparian forest structure, diversity, and function.

Decline of a foundation tree species due to invasive insects will trigger net release of soil organic carbon

AbstractEastern U.S. forests are witnessing an ecologically disruptive decline in one of the region's distinctive foundation tree species, the eastern hemlock (Tsuga canadenis). The exotic insect pests hemlock woolly adelgid (Adelges tsugae, HWA) and elongate hemlock scale (Fiorinia externa) have greatly altered many forest ecosystems previously dominated by this important evergreen conifer. The consequences for ecosystem processes are far reaching because hemlock is often replaced by deciduous tree species, such as black birch (Betula lenta), which have strongly divergent effects on forest floor microenvironments and nutrient cycling. We took advantage of an accidental experiment initiated by patch‐level timber harvesting ~30 yr ago to investigate how the removal of hemlock, and its replacement by deciduous trees, has affected leaf litter characteristics, soil organic layer mass, C:N content, and soil respiration rates. We also contrasted these areas to nearby forest plots where deciduous B. lenta has been dominant for almost a century. The inclusion of healthy, intact hemlock stands in the design, and the close proximity of plots, allowed for a powerful space‐for‐time approach to detect ecosystem changes that are likely to occur across the broader landscape with HWA‐induced hemlock loss in coming years. Three years of data collection from a series of plots in hemlock, young birch, and mature birch stands revealed dramatic differences in soil carbon pools and cycling. Between forests dominated by hemlock vs. mature birch, we saw a significant decrease in soil organic layer mass and in the C:N of the remaining organic material. Although hemlock and young birch stands showed no significant differences in soil respiration rates, mature birch stands had significantly higher soil respiration rates throughout the entire growing season, regardless of wet or dry years. Our results suggest that the carbon pool in the forest floor is likely to mobilize through greater decomposition with a 6.8× decline in soil organic layer C storage as hemlocks are replaced by deciduous trees, leading to a potential net release of ~4.5 tons C per hectare. We conclude that the ramifications of this change for carbon storage could be extensive, but may take decades to manifest.

Divergent Tree Communities across Ridge, Cliff, and Talus Relate to an Association between Diaspore Weight and Micro-Topography at Mohonk Preserve, New York

Ecological study of cliff environments has steadily increased in the last three decades. However, plant communities on many cliffs have yet to be investigated, and there remains uncertainty about the mechanisms that drive vegetation patterns on cliffs. On the Trapps cliff, a renowned rock-climbing destination within Mohonk Preserve, New York, we recorded tree species and surface micro-topography (“sloping.” “level,” “incut”) along seven rappel transects. In two study areas, we also sampled the ridge and talus areas above and below the cliff transects, and in one of those areas, we included a separate lateral survey along a prominent ledge on the cliff. We used estimated diaspore (seed or fruit) weights and chi-square analyses to test for association between diaspore weight class and topographic categories across the entire study. The cliff tree communities were dominated by mature pitch pine (Pinus rigida) and more frequent but smaller-diameter sweet birch (Betula lenta). Sweet birch, a species with lightweight, wind-dispersed seeds, was disproportionately frequent on the cliff and on sloping surfaces on the cliff, while heavier, gravity-dispersed diaspore species (especially oaks) were underrepresented on the cliff in general, but disproportionately associated with level micro-topography on the cliff. Our results suggest that diaspore weight and associated dispersal mechanisms may play a role in the assembly of cliff tree communities that are divergent from the ridge above, or talus below. Management implications include protecting adjacent plant communities (ridge, talus) that are likely diaspore sources that sustain plant communities on cliffs.

Warming increases the sensitivity of seedling growth capacity to rainfall in six temperate deciduous tree species.

Predicting the effects of climate change on tree species and communities is critical for understanding the future state of our forested ecosystems. We used a fully factorial precipitation (three levels; ambient, -50 % ambient, +50 % ambient) by warming (four levels; up to +4 °C) experiment in an old-field ecosystem in the northeastern USA to study the climatic sensitivity of seedlings of six native tree species. We measured whole plant-level responses: survival, total leaf area (TLA), seedling insect herbivory damage, as well as leaf-level responses: specific leaf area (SLA), leaf-level water content (LWC), foliar nitrogen (N) concentration, foliar carbon (C) concentration and C:N ratio of each of these deciduous species in each treatment across a single growing season. We found that canopy warming dramatically increased the sensitivity of plant growth (measured as TLA) to rainfall across all species. Warm, dry conditions consistently reduced TLA and also reduced leaf C:N in four species (Acer rubrum, Betula lenta, Prunus serotina, Ulmus americana), primarily as a result of reduced foliar C, not increased foliar N. Interestingly, these conditions also harmed the other two species in different ways, increasing either mortality (Populus grandidentata) or herbivory (Quercus rubra). Specific leaf area and LWC varied across species, but did not show strong treatment responses. Our results indicate that, in the northeastern USA, dry years in a future warmer environment could have damaging effects on the growth capacity of these early secondary successional forests, through species-specific effects on leaf production (total leaves and leaf C), herbivory and mortality.

Development of cryopreservation methods for cherry birch (Betula lentaL.), an endangered tree species in Canada

Cherry birch (Betula lenta L.) is an endangered species in Canada, with only a single natural population of 18 trees found in the Niagara region of Ontario. The tree was reportedly used for medicinal purposes by First Nations and Native American peoples. The current study describes a cryopreservation method for seeds and in vitro shoot tips of B. lenta in hopes of conserving available germplasm. Cryopreservation of mature seeds was successful, with 24% of seeds germinating in the greenhouse and 12% of seeds germinating in vitro on medium supplemented with 10 μmol·L–1 thidiazuron or 6-benzylaminopurine. Postcryopreservation regrowth of in vitro shoot tips was achieved using a droplet-vitrification protocol after preculture in 0.3 mol·L–1 sucrose for 24 h followed by osmoprotection in loading solution for 20 min and treatment with vitrification solution A3 composed of glycerol, sucrose, ethylene glycol, and dimethyl sulfoxide at 0 °C for 60 min. The highest plant regeneration (52%) was obtained after unload...

In vitro propagation of cherry birch (Betula lentaL.)

An efficient procedure for the micropropagation and conservation of cherry birch (Betula lenta L.), an endangered species in Canada, is reported. The model utilizes in vitro proliferation of fresh and dormant buds from both greenhouse and mature trees. Various factors were evaluated to optimize the protocol, including plant growth regulators, type and concentration of carbohydrates, and the composition of basal salts. 6-benzylaminopurine was the most effective cytokinin for shoot multiplication, with an optimal concentration of 5 µM. Sucrose was a more effective carbohydrate source than glucose, with the highest multiplication rate occurring at 3% sucrose (w/v). Shoot multiplication was similar on Murashige and Skoog (MS) and Driver and Kuniyuki Walnut (DKW) basal salts, but significantly lower on Woody Plant medium (WPM). Culture media with half-strength DKW basal salts and 20 µM indole-3-butyric acid was found to be the best for rooting (80%). Rooted plantlets were acclimatized to the greenhouse environment with a 37% survival rate. The micropropagation technology developed in the study offers excellent opportunities and tools for rapid replenishment of cherry birch trees in their natural environment, long-term conservation, and provides a platform for further research of this nationally endangered species.

Variability in Urban Soils Influences the Health and Growth of Native Tree Seedlings

Reforesting degraded urban landscapes is important due to the many benefits urban forests provide. Urban soils are highly variable, yet little is known about how this variability in urban soils influences tree seedling performance and survival. We conducted a greenhouse study to assess health, growth, and survival of four native tree species growing in native glacial till, coal ash, urban fill, and sandy clean fill soils collected from urban forest restoration sites in New York City. Using a multifactorial design, nine replicates of silver maple (Acer saccharinum), black birch (Betula lenta), red oak (Quercus rubra), and Canadian serviceberry (Amelanchier canadensis) were planted in four urban soil types and one greenhouse mix. We hypothesized that: 1) urban soil type would influence growth, health, and survivorship; 2) each tree species would respond differentially to each soil type; and 3) seedling stress and mortality would be higher for soils with more anthropogenic disturbance. After one growing season, we found that seedlings were less healthy and grew less in soils with a history of greater anthropogenic disturbance. Seedling mortality was low (< 3% overall) except for red oak seedlings in urban fill soil from one location. These results demonstrate that urban soil conditions can impact tree growth and health while supporting high survivorship. Species × soil type interaction for height growth and stress indicate that native tree species may not respond to urban soil conditions consistently. Consequently, matching tree species to soil type could help optimize establishment and growth of urban forest restoration projects.

Decadal change of forest biomass carbon stocks and tree demography in the Delaware River Basin

Quantifying forest biomass carbon (C) stock change is important for understanding forest dynamics and their feedbacks with climate change. Forests in the northeastern U.S. have been a net carbon sink in recent decades, but C accumulation in some northern hardwood forests has been halted due to the impact of emerging stresses such as invasive pests, land use change and climate change. The Delaware River Basin (DRB), sited in the southern edge of the northern hardwood forest, features diverse forest types and land-use histories. In 2001–2003, the DRB Monitoring and Research Initiative established 61 forest plots in three research sites, using Forest Service inventory protocols and enhanced measurements. These plots were revisited and re-measured in 2012–2014. By comparing forest biomass C stocks in the two measurements, our results suggest that the biomass C stock of the DRB forest increased, and was thus a carbon sink over the past decade. The net biomass C stock change in the Neversink area in the north of the DRB was 1.94MgCha−1yr−1, smaller than the biomass C change in the French Creek area (2.52MgCha−1yr−1, southern DRB), and Delaware Water Gap Area (2.68MgCha−1yr−1, central DRB). An increase of dead biomass C accounted for 20% of the total biomass C change. The change of biomass C stocks did not correlate with any climatic or topographic factors, but decreased with increasing stand age, and with tree mortality rate. Mortality rates were highest in the smallest size class. In most of the major tree species, stem density decreased, but the loss of biomass from mortality was offset by recruitment and growth. The demographic changes differ dramatically among species. The living biomass of chestnut oak, white oak and black oak decreased because of the large mortality rate, while white pine, American beech and sweet birch increased in both biomass and stem density. Our results suggest that forests in the DRB could continue to be a carbon sink in the coming decades, because they are likely at a middle successional stage. The linkage between demography of individual trees species and biomass C change underscores the effects of species-specific disturbances such as non-native insects and pathogens on forest dynamics, and highlights the need for forest managers to anticipate these effects in their management plans.

Macroscale intraspecific variation and environmental heterogeneity: analysis of cold and warm zone abundance, mortality, and regeneration distributions of four eastern US tree species.

I test for macroscale intraspecific variation of abundance, mortality, and regeneration of four eastern US tree species (Tsuga canadensis,Betula lenta,Liriodendron tulipifera, and Quercus prinus) by splitting them into three climatic zones based on plant hardiness zones (PHZs). The primary goals of the analysis are to assess the differences in environmental heterogeneity and demographic responses among climatic zones, map regional species groups based on decision tree rules, and evaluate univariate and multivariate patterns of species demography with respect to environmental variables. I use the Forest Inventory Analysis (FIA) data to derive abundance, mortality, and regeneration indices and split the range into three climatic zones based on USDA PHZs: (1) cold adapted, leading region; (2) middle, well-adapted region; and (3) warm adapted, trailing region. I employ decision tree ensemble methods to assess the importance of environmental predictors on the abundance of the species between the cold and warm zones and map zonal variations in species groups. Multivariate regression trees are used to simultaneously explore abundance, mortality, and regeneration in tandem to assess species vulnerability. Analyses point to the relative importance of climate in the warm adapted, trailing zone (especially moisture) compared to the cold adapted, leading zone. Higher mortality and lower regeneration patterns in the warm trailing zone point to its vulnerability to growing season temperature and precipitation changes that could figure more prominently in the future. This study highlights the need to account for intraspecific variation of demography in order to understand environmental heterogeneity and differential adaptation. It provides a methodology for assessing the vulnerability of tree species by delineating climatic zones based on easily available PHZ data, and FIA derived abundance, mortality, and regeneration indices as a proxy for overall growth and fitness. Based on decision tree rules, ecologically meaningful variations in species abundance among the climatic zones can be related to environmental variability and mapped.

Can putative indicator species predict habitat quality for American ginseng?

American ginseng, Panax quinquefolius L., is a long-lived medicinal understory herb, which has been heavily harvested since the 1700s. Because of the economic value of the root, and the increasing rarity of this plant, P. quinquefolius is often reintroduced across its range. Land managers and hobby growers recommend using ‘associate species’ as a way to determine ideal site conditions for reintroduction. However, the accuracy of these putative indicator species in identifying sites that will maximize growth of this rare herb has not been tested. Using a long-term ecological dataset of 26 populations, we evaluated if 20 putative indicators (herbs, shrubs, and trees) could predict P. quinquefolius performance, as measured by the relative growth rate of the leaf area, at the population and microsite level. Of the indicators, only one tree species was able to predict positive performance. If a P. quinquefolius was within 10m of a Liriodendron tulipifera L., the plant would have increased growth, in terms of leaf area, as compared to plants that were not within 10m of this tree. Surprisingly, the presence of most putative indicator species was found to be unreliable as a site quality measure. At the population level, four putative indicators, Aralia nudicaulis L., Acer rubrum L., Betula lenta L., and Lindera benzoin (L.) Blume, were actually contra-indicators, as their presence at a site implied lower P. quinquefolius performance. If Podophyllum peltatum L. was absent from a site, but B. lenta present, P. quinquefolius had reduced growth as compared to plants present in other combinations of P. peltatum and B. lenta. The results from this study have important implications for in situ conservation strategies of this rare medicinal plant. Planting P. quinquefolius in sites that increase performance can help ensure that reintroduction projects likely have a greater chance of success, effectively reducing the waste of time, money, and resources spent on projects that have lower levels of success.

Stump sprouting of 19 upland hardwood species 1 year following initiation of a shelterwood with reserves silvicultural system in the southern Appalachian Mountains, USA

Models that quantify the probability of stump sprouting P(s) and sprout characteristics for predominant tree species in the southern Appalachian Mountains, USA are lacking. In this study, 375 plots (0.01 ha) were installed across five stands in eastern Tennessee and western North Carolina. Trees ≥3.8 cm diameter at 1.37 m above groundline (dbh) were tagged, and dbh and species recorded. Stands were regenerated using a two-aged silvicultural system (residual basal area (BA) <6.3 m2 ha−1). One growing season post-harvest, we recorded (1) sprouting (yes/no), (2) the number of sprouts per stump (sprout density), and (3) dominant (tallest) sprout height. Sprout density, sprout height, and P(s) were modeled as function of dbh, site index (SI), and BA. For white (Quercus alba L.), black (Quercus velutina Lam.), scarlet (Quercus coccinea Muenchh.), and northern red (Quercus rubra L.) oaks, and sweet birch (Betula lenta L.), yellow buckeye (Aesculus flava Aiton), and red maple (Acer rubrum L.), P(s) was inversely related to dbh. Sprout density was positively related to (1) dbh for red maple, yellow buckeye, sourwood (Oxydendrum arboreum L. (DC)), silverbell (Halesia tetraptera Ellis), and white basswood (Tilia heterophylla Vent.), and (2) SI for scarlet oak. For eight species, sprout height was influenced by dbh, SI, dbh and SI, or dbh and BA. Because stump sprouts are a primary source of regeneration, the information on stump sprouting produced for these 19 species can be used to quantify and predict early stand dynamics following regeneration harvests in these diverse southern Appalachian hardwood stands.

A similar phylogeographical structure among sympatric North American birches (Betula) is better explained by introgression than by shared biogeographical history

AbstractAimA comparative analysis of the chloroplast (cp) DNA structure of eastern North American birches (Betula) was undertaken to infer the impacts of Quaternary climate change on the phylogeographical structure of these species.LocationEastern North America.MethodsGenetic variation in chloroplast microsatellites (cpSSRs) and the psbA–trnH intergenic spacer in Betula papyrifera, Betula alleghaniensis and Betula lenta was analysed in samples from 65, 80 and 12 populations, respectively. Co‐occurring Betula uber, Betula populifolia and Betula cordifolia were also sampled to examine haplotype relationships and account for potential introgression. Haplotype networks, Bayesian analysis and comparisons of RST and GST values were used to evaluate the phylogeographical structure. Genetic diversity within and among species was compared using rarefaction analysis.ResultsThe two most widespread species, B. papyrifera and B. alleghaniensis, showed high levels of haplotype diversity, while the Appalachian endemic B. lenta possessed a single haplotype. Bayesian analysis revealed three main phylogeographical groups for B. papyrifera and four groups for B. alleghaniensis, and these two species showed extensive regional haplotype sharing and a high introgression ratio.Main conclusionsWe postulate that at least three separate refugia contributed to the recolonization of B. papyrifera and B. alleghaniensis within eastern North America, while B. lenta appears to have recolonized from a single refugium. A high haplotype diversity of B. papyrifera and B. alleghaniensis in the Great Lakes region may reflect biogeographical contact between eastern and western lineages, with the potential influence of periglacial refugia. Similar phylogeographical patterns in the distantly related B. papyrifera and B. alleghaniensis represent a geographical turnover of the same locally shared haplotypes, pointing to introgression rather than shared biogeographical history as the mechanism. Although similar phylogeographical patterns are often interpreted as evidence for common biogeographical histories, our study demonstrates that such patterns can also arise through introgression.