Overstory Composition Research Articles

Long-term influence of disturbance-generated microsites on forest structural and compositional development

Wind disturbance generates heterogeneous microsite structures, including downed logs, windthrow mounds, and pits. While these structures can provide opportunities for regeneration of certain tree species, the long-term influence of microsites and microsite heterogeneity on forest development has not been quantified. We used long-term measurements of a formerly old-growth Tsuga canadensis – Pinus strobus forest severely damaged by a category 3 hurricane in 1938 to quantify the impact of microsite conditions on overstory composition and structure. We asked (i) “What are the patterns in live-tree size, growth, and mortality five and seven decades after disturbance?” and (ii) “What roles do microsite heterogeneity and the presence of disturbance-generated microsites play in long-term forest development following disturbance?” We compared live-tree (>2 cm DBH) development and survival to microsite heterogeneity at the 100 m2 scale. Microsite diversity was positively related to overstory species diversity and stem density and negatively related to average tree size. We propose that plots with higher microsite diversity may have experienced more severe local disturbance, which allowed more species and individuals to establish and created varied niches that allowed these individuals to coexist and generate greater stand-level diversity. These persistent relationships highlight how microsite conditions affect forest development after severe disturbances.

Disentangling Effects of Time Since Fire, Overstory Composition and Organic Layer Thickness on Nutrient Availability in Canadian Boreal Forest

Wildfire is the primary abiotic disturbance in the boreal forest, and its long-term absence can lead to large changes in ecosystem properties, including the availability and cycling of nutrients. These effects are, however, often confounded with the effects of successional changes in vegetation toward nutrient-conservative species. We studied a system of boreal forested lake islands in eastern Canada, where time since last fire ranged from 50 to 1500 years, and where the relative abundance of the most nutrient-conservative tree species, black spruce, was largely independent of time since last fire. This allowed us to disentangle the effects of time since fire and the dominant vegetation on ecosystem properties, including nutrient stocks and concentrations. Effects of time since fire independent of vegetation composition mostly involved an increase in the thickness of the organic layer and in nitrogen concentration in both soil and leaves. Domination by black spruce had strong negative effects on nutrient concentrations and was associated with a shift toward more fungi and Gram-positive bacteria in the soil microbial community. Path modeling showed that phosphorus concentration was inversely related to organic layer thickness, which was in turn related to both time since fire and black spruce abundance, while nitrogen was more directly related to time since fire and the composition of the overstory. We conclude that discriminating between the effects of vegetation and time since fire is necessary for better understanding and predicting the long-term changes that occur in forest nutrient availability and ecosystem properties.

The influence of fire history on soil nutrients and vegetation cover in mixed-severity fire regime forests of the eastern Olympic Peninsula, Washington, USA

The rain shadow forests of the Olympic Peninsula exemplify a mixed-severity fire regime class in the midst of a highly productive landscape where spatial heterogeneity of fire severity may have significant implications for below and aboveground post-fire recovery. The purpose of this study was to quantify the impacts of wildfire on forest soil carbon (C) and nitrogen (N) pools and assess the relationship of pyrogenic carbon (PyC) to soil processes in this mixed-severity ecosystem. We established a 112-year fire chronosequence with nine similar forest stands ranging in time since lastfire (TSF) from 3 to 115 years prior to site establishment. At each site, we measured understory vegetation cover, overstory composition, physical and chemical attributes of surface mineral soils to a depth of 10 cm, and forest floor organic matter. Additionally, non-ionic resin lysimeters were buried over the winter and spring (7–8 months) at the interface of organic and mineral soil to collect O-horizon leached DOC that would potentially contact PyC particles on the forest floor. Nitrogen transformations were also monitored in laboratory soil incubations for a subset of sites. The TSF gradient was significantly correlated with PyC mass in the O-horizon (r = −0.4), O-horizon C (r = 0.4), total phenol content in both O-horizon (r = 0.4) and mineral soils (r = 0.2), and potentially mineralizable N (PMN) (r = 0.4). Recent fire sites contained higher mineral soil total N and inorganic available N, but were not correlated with TSF. Total DOC that accumulated on the non-ionic resins averaged 1.14 (SE ± 0.54) g DOC m−2 year−1 and increased with TSF (r = 0.52; p < 0.0001). Over time, soils appeared to shift toward a more phenolic-rich organic and surface mineral soil, a higher PMN index, denser moss cover, and higher cover of Mahonia nervosa and Rosa gymnocarpa. Multivariate, non-parametric analysis of soil and vegetation factors showed a significant relationship with the TSF gradient between sites (p < 0.001), but not within sites. Soil characteristics were found to be less sensitive to wildfire disturbances than aboveground vegetation composition.

Epixylic vegetation abundance, diversity, and composition vary with coarse woody debris decay class and substrate species in boreal forest

Although the importance of coarse woody debris (CWD) to understory species diversity has been recognized, the combined effects of CWD decay and substrate species on abundance and species diversity of epixylic vegetation have received little attention. We sampled a wide range of CWD substrate species and decay classes, as well as forest floors in fire-origin boreal forest stands. Percent cover, species richness, and evenness of epixylic vegetation differed significantly with both CWD decay class and substrate species. Trends in cover, species richness, and evenness differed significantly between nonvascular and vascular taxa. Cover, species richness, and species evenness of nonvascular species were higher on CWD, whereas those of vascular plants were higher on the forest floor. Epixylic species composition also varied significantly with stand ages, overstory compositions, decay classes, substrate species, and their interactions. Our findings highlight strong interactive influences of decay class and substrate species on epixylic plant communities and suggest that conservation of epixylic diversity would require forest managers to maintain a diverse range of CWD decay classes and substrate species. Because stand development and overstory compositions influence CWD decay classes and substrate species, as well as colonization time and environmental conditions in the understory, our results indicate that managed boreal landscapes should consist of a mosaic of different successional stages and a broad suite of overstory types to support diverse understory plant communities.

Lasting legacies of historical clearcutting, wind, and salvage logging on old-growth Tsuga canadensis-Pinus strobus forests

Disturbance events affect forest composition and structure across a range of spatial and temporal scales, and subsequent forest development may differ after natural, anthropogenic, or compound disturbances. Following large, natural disturbances, salvage logging is a common and often controversial management practice in many regions of the globe. Yet, while the short-term impacts of salvage logging have been studied in many systems, the long-term effects remain unclear. We capitalized on over eighty years of data following an old-growth Tsuga canadensis-Pinus strobus forest in southwestern New Hampshire, USA after the 1938 hurricane, which severely damaged forests across much of New England. To our knowledge, this study provides the longest evaluation of salvage logging impacts, and it highlights developmental trajectories for Tsuga canadensis-Pinus strobus forests under a variety of disturbance histories. Specifically, we examined development from an old-growth condition in 1930 through 2016 across three different disturbance histories: (1) clearcut logging prior to the 1938 hurricane with some subsequent damage by the hurricane (“logged”), (2) severe damage from the 1938 hurricane (“hurricane”), and (3) severe damage from the hurricane followed by salvage logging (“salvaged”). There were no differences in current overstory composition between the different disturbance histories, as most areas shifted strongly away from pre-hurricane composition through nearly complete elimination of P. strobus and corresponding increases in hardwoods (Betula and Acer spp.), while T. canadensis remained dominant. In contrast, eight decades later, structural characteristics remain distinct between logged, hurricane, and salvaged sites. Specifically, trees were larger in the logged and salvaged sites, and pit and mound structures were largest and most abundant in the hurricane site. Tree densities and coarse woody debris biomass was greater in the hurricane site than the logged sites, but not significantly different from salvaged sites. These findings underscore the long-term influence of salvage logging on forest development, indicating convergence in overstory composition over time between logged, salvaged, and non-salvaged areas, but persistent structural differences, especially in microtopographic structures and live tree development. Future salvage logging efforts should consider these impacts and provide a greater range of unsalvaged areas across the landscape to maintain important structural legacies over the long term.

Microsites Supporting Endemic Populations of Mountain Stewartia (Stewartia ovata) in East Tennessee

Mountain stewartia (Stewartia ovata) is the only member of the family Theaceae endemic to Tennessee. Apart from its physical description and rarity, little is known about this woody understory species. Accounts of stewartia populations and range descriptions are longstanding, but microsite descriptions are limited in detail. We quantified microsites supporting populations of stewartia across East Tennessee as a first step in determining whether stewartia is rare because of rare or altered habitat, limited sexual reproduction, poor dispersal, or a combination of these factors. Five populations of stewartia averaging 7.40 ± 1.08 stems per population were inventoried across four East Tennessee counties. Soils on all sites were strongly acidic, highly permeable, well-drained, cobbly loams associated with steep slopes and higher elevations and were low in phosphorus, potassium, calcium, and magnesium. A dense overstory comprised of sourwood (Oxydendrum arboreum), eastern hemlock (Tsuga canadensis), white oak (Quercus alba), eastern white pine (Pinus strobus), red maple (Acer rubrum), and mockernut hickory (Carya tomentosa) resulted in 7.05% ± 1.41% of full photosynthetically active radiation (PAR). The midstory and understory were dominated by eastern white pine, red maple, and eastern hemlock. Quantification of stand-level conditions in extant stewartia populations suggested similarities in soil pH, nutrient levels, drainage, overstory composition and structure, and PAR levels. Certain conditions in stewartia sites were unique in the region, suggesting that habitat may limit populations along with other factors. Further investigations of stewartia reproductive ecology, dispersal, and habitat requirements will be key to conserving this species.

Mapping Forest and Surrounding Landscape Changes 1949-2015 at the University of Michigan's Historic Forestry Education Properties

ABSTRACTThree forested properties owned by the University of Michigan and near to Ann Arbor were the sites of some of the earliest forestry field education in the USA. No longer managed solely for this purpose after the mid-1960s, and at the same time nested within a rapidly developing area of Michigan, current planning for the properties focuses on melding their historic legacy with renewed ecologically and sustainably sound uses. We developed new maps and knowledge of forest and land change within and surrounding the properties between 1949 and 2015. We acquired aerial photography at 5-10 year intervals, created land-cover/land-use and change data, and identified key trajectories of change. Results within Saginaw Forest (established 1904) showed a consistent amount of forest area, but transitions in some observed overstory composition from coniferous to mixed forest between 1949 and 2015. Within the present-day extent of Stinchfield Woods and the Newcomb Tract (established 1925-1955), forest area increased from 68% to 98% and 51% to 93% respectively between 1949 and 2015, as forest plantations and other regrowth replaced former cleared lands. In 0.5 km-wide buffer areas surrounding the properties, agriculture decreased, and urban uses increased dramatically between 1949 and 2015 for all three sites. Forested land cover has also increased on the surrounding landscapes, again replacing agriculture and grassland. The properties today still display the legacies of their historic forestry education and research, and are living laboratories of natural succession in planted forests. The properties now also represent some of the most protected local lands while the landscapes surrounding them continue to change.

Forest overstory composition and seedling height influence defoliation of understory regeneration by spruce budworm

Abstract Higher hardwood content in stands results in lower defoliation of overstory balsam fir (Abies balsamea (L.) Mill.) caused by spruce budworm (Choristoneura fumiferana Clem.). To determine whether higher overstory hardwood content also reduced defoliation and mortality of balsam fir regeneration of varying height classes during a spruce budworm outbreak, we sampled 36 plots representing three classes of hardwood content (0–25%, 40–65%, and 75–95%) across a gradient of fir-hardwood stands. Twenty-seven plots were sampled in nine stands near Amqui, Quebec in an early stage spruce budworm outbreak (3 years of defoliation), and nine plots were sampled in three stands in the North Shore of Quebec in a later stage budworm outbreak (7 years of defoliation). Linear mixed-effects models with repeated measures (years) were used to analyze differences in defoliation of fir regeneration as a function of hardwood content, six height classes, and three years (2013, 2014, 2015). In the Amqui plots, defoliation of fir regeneration was significantly related to all factors and interaction terms except for hardwood content, while in the North Shore plots, defoliation was significantly related to all factors and the hardwood content x height class and hardwood content x year interaction terms. Defoliation of balsam fir regeneration was 85% higher in softwood than in hardwood stands in 2013 and 2014 in the North Shore plots, when the budworm outbreak was severe. Defoliation was at least 10% higher on regeneration taller than 30 cm than on smaller regeneration in the Amqui plots in 2015 and over 15% higher in the North Shore plots. In general, balsam fir regeneration in softwood stands had higher levels of defoliation than in hardwood stands when defoliation was severe, and regeneration taller than 30 cm had higher defoliation than smaller regeneration.

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

Underplanting tree seedlings in areas where natural regeneration is limited may offer a tool by which desired overstory composition can be maintained or restored in forests. However, invasive plant species and ungulate browsing may limit the effectiveness of underplanting, and in-turn, the successful restoration of forest ecosystems. Individually, the invasive shrub Lonicera maackii and browsing by white-tailed deer (Odocoileus virginianus) have been found to negatively affect the regeneration of native tree species in the Midwestern United States, but few studies have examined their interactive or cumulative effects. Using exclosures and shrub removal at five sites, we examined the effects of white-tailed deer and L. maackii both on underplanted seedlings of Castanea dentata and Quercus rubra and on the composition, species richness and diversity of naturally regenerated native tree seedlings. Individually, both deer and L. maackii had negative effects on the survival of underplanted seedlings, but we identified no interactive effects. The presence of L. maackii or deer alone resulted in similar declines in the survivorship of Q. rubra seedlings, but the presence of deer alone resulted in lower survival of C. dentata seedlings than the presence of L. maackii alone. Lonicera maackii reduced light levels, increased seedling moisture stress and decreased relative basal diameter growth for Q. rubra seedlings. Deer reduced the relative growth in height of underplanted C. dentata and Q. rubra seedlings and increased moisture stress of C. dentata seedlings. No effects of L. maackii or deer were found on soil or foliar nitrogen or the overall abundance, species richness and diversity of naturally regenerated seedlings. However, L. maackii and white-tailed deer did affect the abundance of individual tree species, shifting composition of the regeneration layer towards shade tolerant and unpalatable and/or browse tolerant species.

The Effects of Environmental Features and Overstory Composition on the Understory Species Assemblage in Sub-Mediterranean Coppiced Woods: Implications for a Sustainable Forest Management

Understanding the relationship among environmental factors, overstory and understory is a key step for the improvement of sustainable forest management. Our aim was to understand how environmental features (topographic factors) and overstory (tree species) composition affect understory (shrub and herb species) assemblage in sub-Mediterranean coppiced woods. The study area lies in the Monti Sibillini National Park (central Italy). In 205 plots (20 × 20 m) we collected topographic features and species cover values; moreover, we defined the Social Behaviour Type (SBT — i.e. species ecological and dynamic features) of each understory species. Data were analysed using Redundancy Analysis and Generalized Linear Modeling. We found that topographic factors shaped percentage cover of different tree species and hence determined forest community type. Topography-related factors were further mediated by the tree layer composition, in filtering understory assemblage, on the basis of species SBT. We found no effect of overstory species diversity on understory species diversity. However, the presence of tree species different from the dominant ones increased understory species richness. This effect was particularly notable in evergreen woods, dominated by Quercus ilex. We conclude that, to improve the management sustainability, coppicing management should be focused on the achievement of the greater tree species diversity.

Occurrence, pattern of change, and factors associated with American beech-dominance in stands of the northeastern USA forest

American beech (Fagus grandifolia Ehrh) in the understory of tolerant hardwood stands is a major obstacle to improving the quality of forest regeneration in the northeastern USA and southeastern Canada. To better understand patterns of beech occurrence and stand conditions when it is present, we used US Forest Service Forest Inventory and Analysis (USFS-FIA) data from four northeastern USA states (Maine, New Hampshire, New York, and Vermont) across a 16-year period (1999–2015) to: (i) classify stand conditions (i.e., FIA plots) where American beech was present, (ii) identify beech-dominated stand types, (iii) assess the trend of occurrence (percentage of total forest area) of each identified stand type across the study area during the past 16years, and (iv) evaluate the relationship of each identified stand type with key biotic and abiotic factors. Based on understory, midstory, and overstory characteristics, we identified four stand types where beech was present across the region including: (i) beech-dominated, (ii) commercial hardwood-dominated, (iii) other hardwood-dominated, and (iv) softwood-dominated. Among these four stand types, the beech-dominated stand type currently occupies 27.4% of total northeastern USA forest area and has had a ∼5% increase over the past 16years with an even greater increase (>5%) across the forests of New Hampshire, New York, and Vermont. Our results showed increasing mean annual precipitation and greater overstory basal area were positively correlated with the occurrence probability of the beech-dominated stand type, but negatively correlated with the occurrence probabilities of the other identified stand types. Beech-dominated stands were generally associated with higher elevations, greater mean annual precipitation, warmer temperatures, and larger overstory basal areas. Beech dominance in the understory was associated with overstories dominated by beech, as well as overstories dominated by commercial hardwood species. Therefore, overstory harvesting in stands with beech dominant in the understory (irrespective of overstory composition) will tend to promote beech into the overstory. Our results emphasize the need for greater attention to improving regeneration composition in stands where beech is dominant to increase the long-term productivity and commercial value of northeastern forests of the USA.

Effects of Repeated Growing Season Prescribed Fire on the Structure and Composition of Pine–Hardwood Forests in the Southeastern Piedmont, USA

We examined the effects of repeated growing season prescribed fire on the structure and composition of mixed pine–hardwood forests in the southeastern Piedmont region, Georgia, USA. Plots were burned two to four times over an eight-year period with low intensity surface fires during one of four six-week long periods from early April to mid-September. Density of saplings (0.25–11.6 cm diameter at breast height) was significantly reduced after one or two fires during the first four-year period. Sapling density declined with additional burning over the next four years, but density of mesic hardwoods including sweetgum (Liquidambar styraciflua) and red maple (Acer rubrum) remained relatively high (~865 stems ha−1). Repeated burning had little effect on density or basal area of trees (≥11.7 cm dbh) and changes in overstory structure were limited to small increases in the quadratic mean diameter of all trees and pines. We found little evidence to suggest differential effects on structure or composition due to timing of burn within the growing season. Although repeated growing season burning alters midstory structure and composition, burning alone is unlikely to result in immediate shifts in overstory composition or structure in mixed pine–hardwood forests of the southeastern Piedmont region.

The Contribution of Litterfall to Net Primary Production During Secondary Succession in the Boreal Forest

Litterfall is a fundamental process in the nutrient cycle of forest ecosystems and a major component of annual net primary production (NPP). Despite its importance for understanding ecosystem energetics and carbon accounting, the dynamics of litterfall production following disturbance and throughout succession remain poorly understood in boreal forest ecosystems. Using a replicated chronosequence spanning 209 years following fire and 33 years following logging in Ontario, Canada, we examined the dynamics of litterfall production associated with stand development, overstory composition type (broadleaf, mixedwood, and conifer), and disturbance origin. We found that total annual litterfall production increased with stand age following fire and logging, plateauing in post-fire stands approximately 98 years after fire. Neither total annual litterfall production nor any of its constituents differed between young fire- or logging-originated stands. Litterfall production was generally higher in broadleaf stands compared with mixedwood and conifer stands, but varied seasonally, with foliar litterfall highest in broadleaf stands in autumn, and epiphytic lichen litterfall highest in conifer stands in spring. Contrary to previous assumptions, we found that the contribution of litterfall production to net primary production increased with stand age, highlighting the need for modeling studies of net primary productivity to account for the effects of stand age on litterfall dynamics.

Litter Species Composition and Topographic Effects on Fuels and Modeled Fire Behavior in an Oak-Hickory Forest in the Eastern USA.

Mesophytic species (esp. Acer rubrum) are increasingly replacing oaks (Quercus spp.) in fire-suppressed, deciduous oak-hickory forests of the eastern US. A pivotal hypothesis is that fuel beds derived from mesophytic litter are less likely than beds derived from oak litter to carry a fire and, if they do, are more likely to burn at lower intensities. Species effects, however, are confounded by topographic gradients that affect overstory composition and fuel bed decomposition. To examine the separate and combined effects of litter species composition and topography on surface fuel beds, we conducted a common garden experiment in oak-hickory forests of the Ohio Hills. Each common garden included beds composed of mostly oak and mostly maple litter, representative of oak- and maple-dominated stands, respectively, and a mixture of the two. Beds were replenished each fall for four years. Common gardens (N = 16) were established at four topographic positions (ridges, benches on south- and northeast-facing slopes, and stream terraces) at each of four sites. Litter source and topographic position had largely independent effects on fuel beds and modeled fire dynamics after four years of development. Loading (kg m-2) of the upper litter layer (L), the layer that primarily supports flaming spread, was least in more mesic landscape positions and for maple beds, implying greater decomposition rates for those situations. Bulk density in the L layer (kg m-3) was least for oak beds which, along with higher loading, would promote fire spread and fireline intensity. Loading and bulk density of the combined fermentation and humic (FH) layers were least on stream terrace positions but were not related to species. Litter- and FH-layer moistures during a 5-day dry-down period after a rain event were affected by time and topographic effects while litter source effects were not evident. Characteristics of flaming combustion determined with a cone calorimeter pointed to greater fireline intensity for oak fuel beds and unexpected interactions between litter source and topography. A spread index, which synthesizes a suite of fuel bed, particle, and combustion characteristics to indicate spread (vs extinction) potential, was primarily affected by litter source and, secondarily, by the low spread potentials on mesic landscape positions early in the 5-day dry-down period. A similar result was obtained for modeled fireline intensity. Our results suggest that the continuing transition from oaks to mesophytic species in the Ohio Hills will reduce fire spread potentials and fire intensities.

Targeted reforestation could reverse declines in connectivity for understory birds in a tropical habitat corridor.

Re-establishing connectivity between protected areas isolated by habitat clearing is a key conservation goal in the humid tropics. In northeastern Costa Rica, payments for environmental services (PES) and a government ban on deforestation have subsidized forest protection and reforestation in the San Juan-La Selva Biological Corridor (SJLSBC), resulting in a decline in mature forest loss and the expansion of tree plantations. We use field studies and graph models to assess how conservation efforts have altered functional connectivity over the last 25years for four species of insectivorous understory birds. Field playback studies assessed how reforestation habitat quality affected the willingness of Myrmeciza exsul, Henicorhina leucosticta, Thamnophilus atrinucha, and Glyphorynchus spirurus to travel outside forest habitat for territorial defense. Observed travel distances were greatest in nonnative and native tree plantations with high understory stem density, regardless of overstory composition. In contrast, tree plantations with low stem density had travel responses comparable to open pasture for three of the four bird species. We modeled landscape connectivity for each species using graph models based on varying possible travel distances in tree plantations, gallery forests, and pastures. From 1986 to 2011, connectivity for all species declined in the SJLSBC landscape (5825km2 ) by 14% to 21% despite only a 4.9% net loss in forest area and the rapid expansion of tree plantations over 2% of the landscape. Plantation placement in the landscape limited their potential facilitation of connectivity because they were located either far from forest cover or within already contiguous forest areas. We mapped current connectivity bottlenecks and identified priority areas for future reforestation. We estimate that reforestation of priority areas could improve connectivity by 2% with only a 1% gain in forest cover, an impressive gain given the small area reforested. Results indicate key locations where spatial targeting of PES within the SJLSBC study region would protect existing forest connectivity and enhance the connectivity benefits of reforestation.

Soil C:N:P dynamics during secondary succession following fire in the boreal forest of central Canada

Measures of soil nutrient availability such as concentrations of nitrogen and phosphorus ([N] and [P]) are important indicators of terrestrial productivity. Optimal plant growth and ecosystem functioning are also strongly correlated with nutrient ratios in soils. Long-term trends in soil [C], [N], [P], and their stoichiometric ratios during secondary succession in the fire-driven boreal forest remain unclear. We used replicated 7- to 209-year chronosequences to examine the influence of stand age and overstory composition on [C], [N], and [P] and their ratios in the forest floor, surface (0–15cm), and subsurface (15–30cm) mineral soil in the boreal forest of central Canada. In the forest floor, [C] and [N] increased rapidly during the first three decades following fire, after which they fluctuated, but remained larger than in the youngest stands. Surface soil [C] and [N] increased from young to intermediate-aged stands, but decreased in the oldest stands. Subsurface [C] and [N] followed a similar trend, but was higher in the 7-year-old stands. Forest floor [P] followed a gradual, linear increase throughout stand development but of smaller magnitude than [C] and [N]. The temporal pattern of [P] in both mineral soil layers was lower in the 33-year-old stands of all overstory types, suggesting that P resources may be outpaced by their demand during this highly competitive stage of advanced stem exclusion during forest succession. In the forest floor and surface soil, C:N differed not only with stand age but also with overstory type, due to higher C:N in intermediate-aged conifer stands. Forest floor C:P and N:P were higher in the 33- to 146-year-old stands in all overstory types and soil layers, but particularly so in the conifer stands. In the mineral layers, C:N, C:P, and N:P all followed a similar trend. Our results demonstrate the important influence of stand age, overstory composition (as influenced by succession), and soil depth on forest soil nutrient dynamics in boreal forest ecosystems.

Exploring Factors Influencing Species Natural Regeneration Response Following Harvesting in the Acadian Forests of New Brunswick

In the Acadian Forest Region of northeastern North America, forest managers are under increasing public pressure to restore the forest to a more historic, natural condition by reducing in clearcutting and promoting partial-cut treatments that more closely emulate historic, local natural disturbance regimes. However, although numerous studies on the effects of partial-cutting on forest regeneration response have been conducted in surrounding temperate and boreal forest ecosystems, there are few studies that directly explore responses to various forms of harvesting within the Acadian Forest ecosystem, with its unique mixture of northern hardwoods and boreal forest species. Here, we conducted one of the first retrospective studies on forest regeneration following a variety of harvesting methods in the Acadian Forest using univariate and multivariate regression trees to assess regeneration response in 50 naturally-regenerating, harvested forest sites in New Brunswick, Canada. Our study shows that regeneration was highly influenced by harvest type, overstory composition, and environmental conditions as reflected by ecoregion classification. Canopy opening size (as controlled by harvest method) significantly influenced the dominance of regenerating species. The presence of conspecific overstory trees increased the likelihood of their regeneration following disturbance, supporting the direct-regeneration hypothesis, especially for species with limited seed dispersal (e.g., sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.). Despite reported problems elsewhere in eastern North America, neither American beech nor balsam fir (Abies balsamea (L.) Mill.) constituted significant competition for the desired species on a broad scale, but the presence of beech was a significant deterrent for yellow birch (Betula alleghaniensis Britt.).

Short-term changes in height–diameter relation of two maple species and European cornel of understory in an oak forest in Hungary on the basis of two-parameters model

Forest understory species such as shrub and herbaceous layer, have received little attention in long-term studies. Knowledge of the diameter and the height of trees are fundamental for developing growth and yield models in forest stands. Overstory composition of the Sikfőkut Project site was dominated by sessile oak–Turkey-oak forest (Quercetum petraeae-cerris Soo 1963). Similarly to other European countries an oak decline occurred in Hungary oak woodlands at the end of 1970’s and about 63% of the oak trees perished in our site. The potential for oak species regeneration was a very low over the period of 1982-2012. Four nonlinear height-diameter functions were fitted and evaluated for Sikfőkut site based on a data set consisting of 2025 individuals for three dominant woody species (Acer campestre L., Acer tataricum L. and Cornus mas L.) and detected any short-term changes in these equations following dieback of oak canopies. These height– diameter equations increase our knowledge of the growth of these species; therefore will enable us to improve management planning in oak forests.

Fire reintroduction increased longleaf pine (Pinus palustris L.) recruitment and shifted pine demographics in a long-unburned xeric sandhill assemblage

Adaptive management methods are best for ensuring management goals are met when implementing prescribed fire to areas of fire exclusion. Prior to intense logging and subsequent fire suppression efforts of the early 1900s, longleaf pine (Pinus palustris) woodlands dominated the southeastern United States. As a pyrogenic forest type, natural wildfires occur with a 2–15year fire return interval. Remaining longleaf forests are predominantly second-growth, with current vegetation structure reflecting decades of fire exclusion resulting from continued suppression efforts. Research in longleaf savannas has demonstrated that hardwood encroachment, reduced floristic diversity, and reduced longleaf yearling establishment occurs in the absence of fire. However, few studies have examined the potential role of prescribed fire management in moderating longleaf pine regeneration in second-growth xeric sandhill assemblages. Over a seven year period of fire reintroduction, we examined the effects of prescribed fire on longleaf pine demographics and structure in a forest that experienced a significant reduction in fire frequency during the 20th century. We observed no difference in overstory composition or hardwood density between burned and adjacent unburned areas. Understory woody stem density (DBH<2cm) was dominated by juvenile longleaf plants, which likely caused greater variability in light reaching the forest floor in unburned vs. burned areas. Significant shifts in demographic structure were evident in juvenile longleaf plants that initiated height growth following the onset of prescribed fire treatments. Longleaf yearling density (<1year old) averaged 5plantsm−2 (unburned <1plantm−2) and was positively correlated with fire frequency. Greater accumulation of leaf litter in unburned (10cm) vs. burned areas (5cm) likely influenced yearling recruitment, as expected given the species’ need for contact with bare mineral soil for germination. Unlike pine savannas where reduction of hardwoods is often the target of management, intraspecific interactions (i.e. negative density dependence) likely play a greater role in successful longleaf recruitment and population demography in this sandhill assemblage. This study further highlights the utility of implementing and observing a range of fire applications when reintroducing fire to long unburned systems.

Structure and composition of an oak-hickory forest after over 60 years of repeated prescribed burning in Missouri, U.S.A

Prescribed fire is often used in upland oak forests to achieve objectives related to woodland restoration or oak regeneration. While not uncommon for prescriptions to include repeated burning at short fire return intervals, long-term frequent fire effects in hardwood forests have rarely been quantified. We describe the effects of over 60years of repeated prescribed burning on stand structure and composition in a Missouri Ozark oak-hickory forest. Data were collected in 2010 and 2013 from 40×40m plots arranged in a randomized complete block design with two blocks and three treatments: an unburned control (Control), annual prescribed fire (Annual; one-year fire return interval), and periodic prescribed fire (Periodic; four-year fire return interval). In 2013, the diameter distribution of the Control was an exponential decay, whereas those in both burn treatments were unimodal. Repeated prescribed burning, especially at four-year fire return intervals, reduced overstory density and canopy cover and shifted overstory composition from a mixture of white oak species, red oak species, and hickories to primarily white oak species. Although small-diameter stems were top-killed on Periodic plots, resprouting created a dense mid-story of small stature saplings. In contrast, Annual plots were virtually void of woody seedlings and saplings. There was no apparent tree recruitment on either Annual or Periodic plots. The abundance, richness, diversity, and evenness of the understory plant community were greater on the burned plots than on the Control plots, with forbs dominating the Annual plots and woody species dominating the Control plots. Periodic plots included a mixture of forbs and woody species, and graminoids were not common in any plots. Understory species richness per square meter was nearly three times greater on both burn treatments relative to the Control. Our results indicate that long-term, repeated prescribed burning can approximate woodland conditions. However, the lack of tree recruitment suggests that periods without fire are critical for replacing overstory trees. Moreover, additional treatments such as mechanical thinning may be important for modifying the understory environment to benefit graminoids or for reaching management objectives on desirable timescales.