Establishment and Control of Hay-scented Fern: A Native Invasive Species

Hay-scented fern (Dennstaedtia punctilobula (Michx.) Moore) is a native forest understory species that behaves as an invasive plant under certain conditions. Previous work has shown that both increased understory light intensity following overstory thinning and removal of competing plants by herbivores can lead to accelerated growth of hay-scented fern, allowing it to develop dense, nearly monospecific understories that inhibit tree seedling regeneration. To study the relationship between these two factors, we sampled 28 forest stands thinned at different times and subjected to different levels of browsing by white-tailed deer (Odocoileus virginianus), and concluded that more than 15 years of intensive browsing following thinning was necessary for ferns to form closed understory canopies with densities of >90 fronds/m² and canopy heights of 60–80 cm; thinning alone or intensive browsing alone was not sufficient to cause this level of fern invasion. We applied three treatments to dense fern understories to determine the relative importance of the fern canopy and the dense mat of roots, rhizomes, and dead fronds in the inhibition of tree seedling establishment. Results after two years were: (1) complete removal of the organic mat produced a large germination response of woody and herbaceous species; (2) mixing the organic mat into the mineral soil produced an initial germination response but poor seedling survivorship, as the fern canopy regrew to near pretreatment density; (3) repeatedly clipping the ferns for two years without disturbing the organic mat resulted in a lower germination response than the removal treatment, but rapid growth of seedlings.     

Tree fern trunks facilitate seedling regeneration in a productive lowland temperate rain forest

Seedling regeneration on forest floors is often impaired by competition with established plants. In some lowland temperate rain forests, tree fern trunks provide safe sites on which tree species establish, and grow large enough to take root in the ground and persist. Here we explore the competitive and facilitative effects of two tree fern species, Cyathea smithii and Dicksonia squarrosa, on the epiphytic regeneration of tree species in nutrient-rich alluvial forests in New Zealand. The difficulties that seedlings have in establishing on vertical tree fern trunks were indicated by the following observations. First, seedling abundance was greatest on the oldest sections of tree fern trunks, near the base, suggesting that trunks gradually recruited more and more seedlings over time, but many sections of trunk were devoid of seedlings, indicating the difficulty of establishment on a vertical surface. Second, most seedlings were from small-seeded species, presumably because smaller seeds can easily lodge on tree fern trunks. Deer browsing damage was observed on 73% of epiphytic seedlings growing within 2 m of the ground, whereas few seedlings above that height were browsed. This suggests that tree ferns provide refugia from introduced deer, and may slow the decline in population size of deer-preferred species. We reasoned that tree ferns would compete with epiphytic seedlings for light, because below the tree fern canopy photosynthetically active radiation (PAR) was about 1% of above-canopy PAR. Frond removal almost tripled %PAR on the forest floor, leading to a significant increase in the height growth rate (HGR) of seedlings planted on the forest floor, but having no effects on the HGRs of epiphytic seedlings. Our study shows evidence of direct facilitative interactions by tree ferns during seedling establishment in plant communities associated with nutrient-rich soils.     

Long‐term and interactive effects of different mammalian consumers on growth,survival, and recruitment of dominant tree species

Throughout the world, numerous tree species are reported to be in decline, either due to increased mortality of established trees or reduced recruitment. The situation appears especially acute for oaks, which are dominant features of many landscapes in the northern hemisphere. Although numerous factors have been hypothesized to explain reductions in tree performance, vertebrate herbivores and granivores may serve as important drivers of these changes. Here, using data from 8‐ and 14‐year‐old exclosure experiments, we evaluated the individual and interactive effects of large and small mammalian herbivores on the performance of three widespread oak species in California—coast live oak (Quercus agrifolia), California black oak (Q. kelloggii), and Oregon white oak (Q. garryana). Although impacts varied somewhat by species and experiment, herbivory by black‐tailed deer (Odocoileus hemionus columbianus) reduced the height and survival of juvenile coast live oaks and altered their architecture, as well as reduced the abundance of black oak seedlings, the richness of woody species and the cover of nonoak woody species. Small mammals (Microtus californicus and Peromyscus maniculatus) had even more widespread effects, reducing the abundance of black oak seedlings and the height and cover of all three oak species. We also detected numerous interactions between small mammals and deer, with one herbivore having positive or negative effects on oak abundance and cover when the other herbivore was either present or absent. For example, deer often had negative effects on seedling abundance only when, or even more so when, small mammals were present. In summary, mammalian consumers play crucial roles in limiting oak recruitment by reducing seedling abundance, maintaining trees in stunted states, and preventing them from reaching sapling stages and becoming reproductive. Interactions between large and small mammals can also alter the intensity and direction of their effects on trees.     

The regeneration of pioneer tree species under browsing pressure of Sika deer in an evergreen oak forest

The effects of Sika deer (Cervus nippon) browsing on the regeneration of pioneer species were studied in relation to canopy gaps in a warm temperate evergreen oak forest in Kasugayama, Nara City. Four study sites, three in canopy gaps and one under a closed canopy, were selected and each divided into fenced and unfenced plots. Under the closed canopy, seedlings of all the pioneer species died irrespective of browsing pressure. However, in the canopy gap sites, seedlings of the pioneer species could establish and grow well. The seedling survival ratio in the fenced plots in the canopy gaps was >60% 1 year after germination. However, in the unfenced plots, only <20% of the seedlings survived 1 year, with all dying within 3 years after germination. Thus, the regeneration of pioneer trees in this forest was strongly inhibited by deer browsing. Successful regeneration of a pioneer,Zanthoxylum ailanthoides, occurred for several years even after two major wind disturbances during the past 90 years. This may be due to less browsing pressure from the deer.     

An Analysis of Vegetation Restoration on Opencast Oil Shale Mines in Estonia

We compared four types of 30‐year‐old forest stands growing on spoil of opencast oil shale mines in Estonia. The stand types were: (1) natural stands formed by spontaneous succession, and plantations of (2) Pinus sylvestris (Scots pine), (3) Betula pendula (silver birch), and (4) Alnus glutinosa (European black alder). In all stands we measured properties of the tree layer (species richness, stand density, and volume of growing stock), understory (density and species richness of shrubs and tree saplings), and ground vegetation (aboveground biomass, species richness, and species diversity). The tree layer was most diverse though sparse in the natural stands. Understory species richness per 100‐m² plot was highest in the natural stand, but total stand richness was equal in the natural and alder stands, which were higher than the birch and pine stands. The understory sapling density was lower than 50 saplings/100 m² in the plantations, while it varied between 50 and 180 saplings/100 m² in the natural stands. Growing stock volume was the least in natural stands and greatest in birch stands. The aboveground biomass of ground vegetation was highest in alder stands and lowest in the pine stands. We can conclude that spontaneous succession promotes establishment of diverse vegetation. In plantations the establishment of diverse ground vegetation depends on planted tree species.     

Herbivory on planted oak seedlings across a habitat edge created by timber harvest

Edge habitats create environmental gradients that affect plant community composition and herbivore behavior. Silvicultural disturbance creates edge habitat with direct (via changes in light) and indirect (via changes in herbivore behavior) consequences for the growth and survival of tree seedlings, and thus, the composition of the future forest stands. Herbivores, particularly ungulates, can be a major limiting factor in oak regeneration, and silvicultural disturbance may alter the abundance or behavior of herbivores following harvest. We measured the severity of herbivory on experimentally planted white (Quercus alba) and black oak (Quercus velutina) seedlings by white-tailed deer (Odocoileus virginianus) and eastern cottontail rabbits (Sylvilagus floridanus), as well as foliar damage from insects, across gradients created by clearcuts in a deciduous forest in Indiana, USA. Overall browse pressure on oaks was low in our study. Nonetheless, spatial variation in herbivory depended on herbivore taxa; herbivory by rabbits was highest inside harvest openings, whereas foliar damage by insects peaked in the forest. Intensity of deer herbivory was constant across the edge. In addition, we observed indirect interactions among herbivore species mediated by a seedling’s browsing history. Herbivore damage by deer was positively related to past browsing by rabbits, and foliar damage from insects was positively related to past browsing by both deer and rabbits. Increasing woody plant competition reduced herbivory on seedlings by both deer and rabbits. Given the lack of spatial variability in deer herbivory and low overall herbivory by rabbits, we suspect that interactions between timber harvesting and herbivory did not have a strong impact on oak seedlings at our study sites.     

Recruitment patterns and northward tree migration through gap dynamics in an old-growth white pine forest in northern Ontario

Decreases in abundances and declines in growth of eastern white pine over the past century due mainly to human activities have resulted in few large intact old-growth white pine forests in Ontario. These stands may be vulnerable to replacement by deciduous species from temperate forests further south, where recruitment in canopy gap disturbances can greatly define the regeneration process. We investigated recruitment dynamics in canopy gaps of an old-growth white pine forest of Temagami, northern Ontario, Canada, the northern limit of the temperate?Cboreal ecotone. White pine, red pine, black spruce and eastern white cedar represented 85?% of the mature canopy abundance, where trees and saplings established equally in gaps and the closed canopy. Balsam fir and paper birch were more abundant in gaps, showing increases of abundance and basal area with increases in gap size representing canopy self-replacement (balsam fir) and autogenic succession (paper birch). Red maple, at its northernmost range limit, was the only species to show linear increases of abundance and basal area with increases in gap size and gap age. This result, along with adult red maples present in gaps but absent from the closed canopy, identifies the establishment of a northward migrating species in gaps as hypothesized for pine forests at the northern limit of this broad ecotone. We discuss how migration pressures, coupled with pine recruitment limitation through reduced fire frequency by regional fire suppression and predicted future increased warming of 2?C4?°C over the next century, threatens replacement of old-growth white pine forests at this latitude with northward migrating tree species found further south.     

Opposing deer and caterpillar foraging preferences may prevent reductions in songbird prey biomass in historically overbrowsed forests

Overbrowsing by ungulates decimates plant populations and reduces diversity in a variety of ecosystems, but the mechanisms by which changes to plant community composition influence other trophic levels are poorly understood. In addition to removal of avian nesting habitat, browsing is hypothesized to reduce bird density and diversity through reduction of insect prey on browse‐tolerant hosts left behind by deer. In this study, we excluded birds from branches of six tree species to quantify differences in songbird prey removal across trees that vary in deer browse preference. Early in the breeding season, birds preyed on caterpillars at levels proportional to their abundance on each host. Combining these data with tree species composition data from stands exposed to experimentally controlled deer densities over 30 years ago, we tested whether overbrowsing by white‐tailed deer reduces prey biomass long after deer densities are reduced. Our analysis predicts total prey availability in the canopy of regenerating forests is fairly robust to historic exposure to high deer densities, though distribution of prey available from host species changes dramatically. This predicted compensatory effect was unexpected and is driven by high prey abundance on a single host tree species avoided by browsing deer, Prunus serotina. Thus, while we confirm that prey abundance on host trees can act as a reliable predictor for relative prey availability, this study shows that quantifying prey abundance across host trees is essential to understanding how changes in tree species composition interact with ungulate browse preference to determine prey availability for songbirds.     

Landscape Structural Complexity of High‐Mountain Polylepis australis Forests: A New Aspect of Restoration Goals

Forest restoration efforts should aim at creating landscapes with a balanced array of forest stands at varying successional stages, thus providing habitat for a wealth of species and multiple ecosystem services. In most high‐mountain ecosystems of South America, long‐term livestock rearing activities that include fires, browsing, and trampling have delayed or stopped forest succession resulting in simplified landscapes. To determine appropriate restoration goals for Polylepis australis mountain forests of Central Argentina, we established 146 plots of 900 m² plots throughout five river basins with different historic livestock stocking rates. In each plot, we measured tree heights, canopy cover, estimated age of oldest tree, volume of standing and fallen dead wood, fern cover, and abundance of shade tolerant Maytenus boaria trees. K‐means cluster analysis using tree heights and canopy cover as classificatory variables yielded four biologically meaningful clusters. Clusters 1, 2, 3, and 4 comprising 68, 10, 13, and 9% of the plots, respectively, showed increasing amounts of standing and fallen dead wood, fern cover, and abundance of shade tolerant M. boaria trees. Plots in clusters 1 and 2 were proportionally more abundant in basins with high human impact and at the altitudinal extremes of P. australis distribution, whereas plots in clusters 3 and 4 were relatively more abundant in well‐preserved basins and at the optimum of their altitudinal distribution. We interpret clusters 1, 2, 3, and 4 as degraded, regenerating, young, and mature forests, respectively. Restoration goals should focus on attaining an even distribution of forest types similar to that found in our best‐preserved basins.     

Facilitations between the Introduced Nitrogen-fixing Tree, Robinia pseudoacacia, and Nonnative Plant Species in the Glacial Outwash Upland Ecosystem of Cape Cod, MA

Robinia pseudoacacia, a nitrogen-fixing, clonal tree species native to the central Appalachian and Ozark Mountains, is considered to be one of the top 100 worldwide woody plant invaders. We initiated this project to determine the impact of black locust (Robinia pseudoacacia) on an upland coastal ecosystem and to estimate the spread of this species within Cape Cod National Seashore (CCNS). We censused 20 × 20 m plots for vegetation cover and environmental characteristics in the center of twenty randomly-selected Robinia pseudoacacia stands. Additionally, paired plots were surveyed under native overstory stands, comprised largely of pitch pine (Pinus rigida) and mixed pitch pine–oak (Quercus velutina and Quercus alba) communities. These native stands were located 20 m from the edge of the sampled locust stand and had similar land use histories. To determine the historical distribution of black locust in CCNS, we digitized and georeferenced historical and current aerial photographs of randomly-selected stands. Ordination analyses revealed striking community-level differences between locust and pine–oak stands in their immediate vicinity. Understory nonnative species richness and abundance values were significantly higher under Robinia stands than under the paired native stands. Additionally, animal-dispersed plant species tended to occur in closer stands, suggesting their spread between locust stands. Robinia stand area significantly decreased from the 1970’s to 2002, prompting us to recommend no management action of black locust and a monitoring program and possible removal of associated animal-dispersed species. The introduction of a novel functional type (nitrogen-fixing tree) into this xeric, nutrient-poor, upland forested ecosystem resulted in ‘islands of invasion’ within this resistant system.     

Recovery of a dwarf birch (Betula nana) population following reduction in grazing by red deer (Cervus elaphus)

Summary

In Britain Betula nana is a nationally scarce plant, its distribution being limited by climate, heather burning and grazing by deer and sheep. The recovery of a population of B. nana was monitored for several years inside a Scots pine regeneration exclosure in N.E. Scotland. Browsing pressure was reduced in the exclosure but a few red deer (amounting to 3–4 km^?2) were deliberately retained. B. nana stem density increased after red-deer density was reduced. Over the same period there was a reduction in browsing inside the exclosure. B. nana stem density was negatively related to heather height, deer presence and tree canopy cover. Comparisons of growth were made with plants outside the exclosure between 1998 and 2000, the mean annual increment of stems, allowing for browsing loss, being respectively 1.25 and 0.45 cm for inside and outside the exclosure. Most stem basal diameters inside the exclosure were smaller than outside. Reducing red deer density to 3–4 km^?2 on similar upland sites with peaty soils could lead to regeneration of B. nana.     

Mediterranean pine and oak distribution in southern Spain: Is there a mismatch between regeneration and adult distribution?

Questions: What is the current distribution of pine and oak species along environmental gradients in southern Spain? Do pine and oak regeneration niches differ from the environmental niches of adults? Is oak species regeneration favoured under the canopy of pine forests? Location: Forest areas of Andalusia (～87 600 km², southern Spain). Methods: We compiled extensive forest inventory data to explore differences in abundance (basal area, m² ha^?1) patterns of adults (dbh >7.4 cm) and regeneration (dbh ≤7.4 cm) of five pine and five oak species. Canonical correspondence analysis (CCA) and generalized linear models were applied to explore species–environment relationships along climatic, edaphic, topographic and fire‐frequency gradients. Results: Both pines and oaks segregated along complex environmental gradients, with pines generally dominating in more severe (colder and drier) environments, while oaks dominated in milder, wetter winter areas. In 40‐55% of mature pine stands there was a lack of regeneration in the understorey, while in two oak species (Q. suber and Q. canariensis) 70% of stands did not show regeneration. Pine recruits were found at a higher frequency and abundance under the canopy of their congeners, whereas some oaks (Q. ilex) had greater regeneration under mixed pine–oak canopies. Conclusions: Climatic limitations and soil properties partly explained the regional distribution of pines and oaks. We found evidence for an upward shift of Q. ilex recruits towards areas with colder conditions in pine forests, which could be explained by a possible facilitative effect of the pine canopy on seedling establishment.     

Forage availability for white-tailed deer following silvicultural treatments in hardwood forests

Closed-canopy upland hardwood stands often lack diverse understory structure and composition, limiting available nutrition for white-tailed deer (Odocoileus virginianus) as well as nesting and foraging structure for other wildlife. Various regeneration methods can positively influence understory development; however, non-commercial strategies are needed to improve available nutrition in many stands, as some contain timber that is not ready to harvest and others are owned by landowners who are not interested in harvesting timber. Applications of herbicide and prescribed fire have improved availability of food and cover for deer and other wildlife in pine (Pinus spp.) systems. However, this strategy has not been evaluated in hardwood systems. To evaluate the influence of fire and herbicide treatments on available deer forage in upland hardwood systems, we measured forage availability and calculated nutritional carrying capacity (NCC) at 14% crude protein mixed diet, following 7 silvicultural treatments, including controls, in 4 mixed upland hardwood stands July–September 2007 and 2008. We compared NCC among forest treatments and within 4 paired warm-season forage food plots to evaluate the usefulness of food plots in areas where forests are managed. Nutritional carrying capacity estimates (deer days/ha) were greatest following canopy reduction with prescribed fire treatments in both years. Understory herbicide application did not affect species composition or NCC 1 year or 2 years post-treatment. Production of forage plantings exceeded that of forest treatments both years with the exception of early-maturing soybeans and retention cut with fire 2 years post-treatment. We encourage land managers to use canopy reducing treatments and low-intensity prescribed fire to increase available nutrition and improve available cover where needed in upland hardwood systems. In areas where deer density may limit understory development, high-quality forage food plots may be used to buffer browsing while strategies to reduce deer density and stimulate the forest understory are implemented. © 2011 The Wildlife Society.     

In situ regeneration of Pinus strobus and P. resinosa in the Great Lakes forest communities of Canada

Abstract. Two extensive forest vegetation survey datasets are explored, using ordination and classification, for evidence of in situ regeneration by Pinus strobus (Eastern white pine) and P. resinosa (Red pine). Ordination of tree species contributions to total basal area in 320 upland northern hardwood- conifer stands produced distinct stand groups for P.banksiana, P. resinosa, P. strobus and mesic hardwoods in an ascending sequence along the first axis. Quercus rubra (red oak), Q. alba (white oak) and tolerant conifer groups formed segregates from the hardwood complex along the second axis. P. strobus mixes with all other forest types, but P. resinosa is restricted to its own group. Seedlings and trees of P. strobus are more abundant than saplings, which are restricted to the pine and oak forests. Therefore, seed production, dispersal and seedling establishment seem to be less of a barrier to in situ regeneration by P. strobus than subsequent survival and growth. Canonical correspondence analysis of 170 pine-dominated stands from the Canadian Shield of Ontario, in which tree species variables are segmented into height-class pseudo- species, yielded no linear relationship between environmental features or stand structure and seedling densities of P. strobus. However, total tree basal area appears to impose an upper limit to seedling density on the forest floor. Strong correlations emerged between pine seedling density and understorey vegetation. Stand classification of the understorey vegetation, using constrained indicator species analysis, yielded distinct high and low seedling groups. Low pine seedling density was associated with abundant broadleaved shrubs, herbs and seedlings as well as feathermosses and tolerant conifers. High seedling density could not be ascribed to the presence of seedbed taxa, such as Polytrichum, but is ascribed to the absence of competition and other forms of inhibition in the understorey vegetation and down through the canopy profile. In situ regeneration of P. strobus does, therefore, occur but conditions over the forest landscape are largely restrictive.     

Species shift drives decomposition rates following invasion by hemlock woolly adelgid

Insect and disease outbreak is an important cause of selective species removal and accompanying functional change in North American forests. Outbreak of hemlock woolly adelgid, Adelgies tsugae– HWA, is causing selective removal of eastern hemlock Tsuga canadensis at a regional scale. Impacts of outbreak‐caused canopy mortality and shifts in dominant species on litter decay were compared across sites that range in HWA‐caused canopy damage and subsequent canopy dominance by black birch Betula lenta. Senescent litter from eastern hemlock, black birch, and equal litter mixes were decomposed in the field for 36 months within nine sites in Connecticut and Massachusetts USA. Mass loss and % N accumulation of black birch was 65% and 52% greater compared to eastern hemlock. In contrast, outbreak related canopy damage increased litter mass loss by 11.5% in high mortality stands relative to uninfested stands but canopy damage had no impact on % N dynamics. Non‐additive effects of litter mixing influenced chemical dynamics of decaying litter; black birch accumulated less N and eastern hemlock accumulated more N compared to each species decaying alone. However, these changes offset and mixed litter bags overall showed no differences in N dynamics compared to values from each species decaying alone. In eastern hemlock stands invaded by hemlock woolly adelgid, canopy damage influences the rates and dynamics of decay but species differences between hemlock and black birch leaf litter are the dominant mechanisms of decomposition changes and a long‐lasting driver of increased N cycling rates. Species shifts may be the dominant driver of altered ecosystem processes for other insect outbreaks, particularly when replacement species have very different characteristics regulating decomposition and N cycling.     

Quercus and Pinus cover are determined by landscape structure and dynamics in peri-urban Mediterranean forest patches

Successional dynamics in Mediterranean forests have been modulated by anthropogenic disturbances during thousands of years, especially in areas densely populated since ancient times. Our objective is to determine whether pine tree cover (early-successional species) and oak tree cover (late-successional species), used as a surrogate of successional stage of peri-urban fragmented forests in the Vallès lowlands (Catalonia, NE, Spain), are primarily determined by (1) climate and topography; (2) anthropogenic disturbances; (3) patch structure; or (4) patch dynamics from 1956 to 1993. Quercus spp. and Pinus spp. tree cover were separately recorded on 252 randomly selected plots of 100 m², within forest patches ranging in size from 0.25 to 218 ha. Multiple linear regressions indicated that forest patch history is the most important variable determining oak and pine tree cover: new forest patches showed higher pine and lower oak tree cover than recently split patches (i.e. those that became fragmented from large forest areas after 1956). Patches already existing as such in 1956 (pre-existent patches) showed higher pine cover than recently split patches. Oak cover increased and pine cover decreased with increasing forest connectivity of the patch. Finally, highly frequented forests were related to high cover of pines. Climatic and topographic variables were not significant. We conclude that pine and oak cover in these peri-urban forests are mainly determined by recent patch dynamics, but also by the spatial pattern of patches. However, human-induced disturbance can modulate this as there is some evidence for pine being associated with a high human frequentation.     

Effects of introduced ungulates on forest understory communities in northern Patagonia are modified by timing and severity of stand mortality

Natural disturbances such as fires, windstorms, floods, and herbivory often act on plant communities, affecting their structure and the abundance and composition of their species. Most research has focused on the effects of single disturbances on plant communities whereas the synergistic effects of several disturbances have received less attention. In this study, we evaluated how timing and severity of tree mortality modified plant use by introduced deer and early post-mortality successional trajectories in northern Patagonian conifer forests. We sampled understory composition and deer use in Austrocedrus chilensis (ciprés de la cordillera) forest stands undergoing varying timing and severity of forest mortality as reconstructed using dendroecological techniques. In addition, we evaluated the effect of fallen logs on plant composition and deer use of plants by monitoring areas of massive dieback where fallen logs had been removed for fire hazard reduction, and nearby control areas not subjected to such removal. Stepwise regression analyses showed that history and severity of tree mortality strongly influence plant composition and deer use of plants. For deer use (with pellet counts and browsing index as response variables), results showed a positive relationship with degree of stand mortality and a negative relationship with cover of fallen logs. Similarly, cover of unpalatable shrub species was explained by canopy mortality history, whereas cover of palatable shrub species was positively associated with severity of canopy mortality. In areas where fallen logs had been removed, pellet counts were six times higher than those in control areas. Though total shrub species cover was similar between log removal and control areas, proportion of unpalatable shrubs increased in areas where fallen logs had been removed. In conclusion, deer use of plants was strongly limited by tall fallen logs, allowing palatable species to establish and grow. Fallen log removal accelerated deer entrance and changed understory composition toward more browse-resistant and unpalatable species. These results underscore the importance of considering the dynamics (timing, severity, and extent) of fallen woody debris influencing understory herbivory and post-disturbance succession. In addition, experimental results underpin the importance of maintaining snags and large woody debris in disturbed landscapes where salvage logging is a routine procedure.     

Northward migrating trees establish in treefall gaps at the northern limit of the temperate–boreal ecotone, Ontario, Canada

Climate change is expected to promote migration of species. In ecotones, areas of ecological tension, disturbances may provide opportunities for some migrating species to establish in otherwise competitive environments. The size of and time since disturbance may determine the establishment ability of these species. We investigated gap dynamics of an old-growth red pine (Pinus resinosa Sol. ex Aiton) forest in the Great Lakes–St. Lawrence forest in northern Ontario, Canada, a transition zone between temperate and boreal forest. We investigated the effects of gaps of different sizes and ages on tree species abundance and basal area. Our results show that tree species from the temperate forest further south, such as red maple (Acer rubrum L.), red oak (Quercus rubra L.), and white pine (Pinus strobus L.), establish more often in large, old gaps; however, tree species that have more northern distributions, such as black spruce (Picea mariana Mill.), paper birch (Betula papyrifera Marsh.), and red pine show no difference in establishment ability with gap size or age. These differences in composition could not be attributed to autogenic succession. We conclude that treefall gaps in this forest facilitate the establishment of northward migrating species, potentially providing a pathway for future forest migration in response to recent changes in climate.     

Method for detecting tree ring boundary in conifers and broadleaf trees using Mask R-CNN and linear interpolation

As tree rings can reveal various information regarding climate and environmental factors, increasing research is being conducted on them. Although tree ring analysis software such as Windendro has been applied, research on the development of analysis software using image preprocessing algorithms and deep learning is recently being attempted as computer vision technology. In this study, Mask R-CNN and linear interpolation were applied from images collected using a smartphone (SM-G973, Samsung, Suwon) and a scanner (CanoScan 9000F, Canon, Otaku) to propose an effective method for detecting tree ring boundaries. Pitch pine (Pinus rigida), Korean pine (Pinus koraiensis), white birch (Betula platyphylla), and cork oak (Quercus variabilis) were selected as tree species. Of the 300 images, 240 were classified as training data and 60 as validation data. As a result of learning, smartphones detected 86.0 % (381 ring boundaries) of the rings in pitch pine, 82.1 % (367 ring boundaries) in Korean pine, 84.7 % (309 ring boundaries) in white birch, and 78.7 % (318 ring boundaries) in cork oak. The scanner detected 93.2 % (413 ring boundaries) of the rings in pitch pine, 90.8 % (405 ring boundaries) in Korean pine, 88.2 % (322 ring boundaries) in white birch, and 89.4 % (361 ring boundaries) in cork oak. In particular, the smartphone showed satisfactory results of 84.7 % and 78.7 % for detecting tree ring boundaries of white birch and cork oak, where the boundaries of the rings were unclear. In the annual growth analysis results, both smartphones and scanners were statistically insignificant, and there was no difference compared with those of Windendro. Therefore, Mask R-CNN might be an effective approach for tree ring boundary detection as it showed satisfactory results, even with smartphones. In addition, although there was distortion in cases where images were acquired with a circular lens, there was no statistically significant difference from Windendro results. Thus, Mask R-CNN and linear interpolation can be used for tree ring boundary detection and growth measurement.     

Forest community structure and composition following containment treatments for the fungal pathogen oak wilt

In temperate oak forests in Ohio, USA, we examined variability in forest communities within containment treatment sites for oak wilt (Bretziella fagacearum), a fungal pathogen lethal to susceptible oak species. Containment treatments included quarantine lines in soil for limiting belowground fungal spread and sanitation cutting of 1–3 mature black oak (Quercus velutina) trees within oak wilt infection patches. At 28 sites, we compared tree structure and understory plant communities across a gradient of 1- to 6-year-old treatments and reference forest (untreated and without evidence of oak wilt). While oak seedlings were abundant, oak saplings (1–10 cm in diameter) were absent. In contrast, many native understory plant community measures were highest in oak wilt treatments. Plant species richness 100 m^?2 doubled in treatments, regardless of age, compared with reference forest. Plant cover increased with treatment age, with 6-year-old treatments exhibiting 5?×?more cover than reference forest. Non-native plants averaged only a small proportion (<?0.12) of cover across treatments and reference forest. Variability in understory communities was mostly predictable using treatment age, tree canopy cover, and geographic location, as 20 of 25 understory measures had at least 72% of their variance modeled. While oak wilt treatments did not facilitate oak regeneration nor many conservation-priority species of open savanna-woodland habitats, the treatments did diversify and increase cover of native understory communities with minimal invasion of non-native plants.