Hardwood Density Research Articles

Competition and site weakly explain tree growth variability in undisturbed Central African moist forests

Abstract Identifying and quantifying factors that influence tree growth are crucial issues to ensure sustainable forest management, particularly in moist tropical forests. Tree growth depends on several factors comprising ontogenic stage, competition by neighbours and environmental conditions. Several studies have focused on one or two of them, but very few have considered all three, especially in Central Africa. We investigated the effects of diameter and competition on tree growth, in four Central African sites characterized by their soil physicochemical properties, at both tree community and population levels. We calibrated growth models using diameter data collected on 29,741 trees between 2015 and 2018, on twelve 4 or 9‐ha plots spread over the four sites. These models included diameter, wood density, competition indices and site effect as explainable variables at the community level and excluded wood density at the population level. At the community level, the best models explained 11% of growth variability with a decreasing effect of species wood density, diameter, site and competition. Our results show that even if low, site effect can result from different soil nutrients depending on both tree size and species wood density. We observed higher tree growth on sites with (i) high exchangeable K, organic C, total N and total P for low wood density species; (ii) high available P and C:N for small trees, high exchangeable Ca and Mg for medium to large trees, all belonging to medium and hard wood density species. At the population level, the best models explained between 0 to 43% of growth variability, with significant competition effect (resp. site effect) for 21 (resp. 9) of the 43 species studied. Site ranking varied greatly between the 9 species concerned, probably reflecting different sensitivities to the scarcity of particular soil nutrients. Synthesis. Our study provides original results on the factors influencing tree growth in Central Africa, showing that the potential effect of soil nutrients depends on tree size and species wood density. Remaining highly unpredictable at the population level, this effect makes it essential to increase the number of dynamics monitoring systems in logging concessions.

Effects of functional traits on the spatial distribution and hyperdominance of tree species in the Cerrado biome

The ecological influence of functional traits on species persistence as well as on their role over the organization of forest communities in the Brazilian Cerrado biome have not been fully understood yet. In this study, we assessed the effects of six functional groups, characterized by three seed dispersal syndromes (i.e., anemochory, autochory, and zoochory) and three wood density classes (i.e., hardwood, lightwood, and softwood), on tree spatial distribution patterns, habitat occupancy, and ecosystem services (biomass hyper dominance and abundance) provided by a forest community located in the “Parque do Lajeado”, state of Tocantins, Brazil. The similarity among study sites was characterized by applying the tree dominant height approach and the environmental and soil variables as input. The floristic similarity was assessed by applying the Bray-Curtis index. The zoochoric species showed more aggregated spatial pattern at local scale, which indicates that it is more sensitive to environmental gradients than other dispersal syndromes. Meanwhile, hardwood density species were more established in the community, being more persistent to environmental filters. We observed that a small number of species contributed with about 50% of the abundance and biomass of the community, whose functional traits (wood density and dispersal syndrome) indirectly affect the relationship among the community species richness and their ecosystem functions. We observed that the functional traits related to seed dispersal and wood density functional groups resulted in different spatial distribution patterns of those tree species. Therefore, functional traits and environmental factors combined have substantially affected the structure and composition of forest communities at local scale.

Intra-species variation in maximum moisture content, cell-wall density and porosity of hardwoods

Abstract Some properties of wood, such as maximum moisture content, cell-wall density and porosity, are not well known, even though they affect the performance of chemical preservatives, glues and coatings on wood. This knowledge gap was addressed in the present study by analysing these physical properties in laurel (Laurus nobilis L.) wood. Laurel is a common hardwood tree in southern Europe. Seventeen laurel trees were felled for the study, and 300 defect-free specimens were obtained from the trees for analysis. The following mean values were obtained: wood maximum moisture content, 114%; cell-wall oven-dry density, 1198 kg m−3; and oven-dry wood porosity, 45%. Significant inter- and intra-tree variations in the three properties were observed. The inter-tree variation was mainly attributed to the tree age, and the trend suggests that wood maximum moisture content and porosity are expected to be lower in older trees than those under study. The values of the three properties were slightly, but statistically significantly, lower at the highest positions in the tree. Harvesting of the basal logs of young trees is therefore advisable only if more porous wood is required, and commercial exploitation of the whole trunk of mature trees is recommended if more compact wood is required. The variation in cell-wall density was not negligible, although this variable is often assumed to be approximately constant for all wood species. Maximum moisture content and wood porosity can be estimated using bulk or apparent density as a predictor variable.

Density, extractives and decay resistance variabilities within branch wood from four agroforestry hardwood species

Agroforestry practices like pruning trees to control the light flux to crops produce every year a large volume of branches which is valorized by farmers as mulching or energy fuel. However, according to the literature, the wood of branches shows higher rates of polyphenols than stem wood and this can open some new perspectives for branch exploitation. In this study, the wood properties (density, mechanical properties, extractive content and decay resistance) were determined on branches of different sizes from oak, chestnut, poplar and walnut trees collected in two agroforestry systems. These properties were evaluated according to the wood age and the sampling position along the radial and longitudinal axes of the branch. All samples were analyzed by NIR-Spectroscopy and a predicting model aimed to assess the branch wood properties has been developed. Wood characteristics largely vary between species and do not exactly follow the same trends from one species to another. Overall, hardwood density of branches is similar to that of trunks, the content in wood extractives follows similar evolutions, and the decay resistance of branch wood does not seem to be really impacted by its position along the branch. Reliable NIRS models were built to easily predict the wood density and extractives content of agroforestry branches. The extractives content and the decay resistance of branch hardwood appear to be substantially lower than those of trunks, which suggests a non-suitability of branch wood for developing high-valued green chemistry.

Mixedwood management positively affects forest health during insect infestations in eastern North America1

Mixedwood stands are composed of hardwoods and softwoods, with neither comprising greater than 75%–80% of basal area or aboveground biomass. By conferring associational resistance and greater resilience to forests when stressed or disturbed, the more diverse composition of mixedwood stands contributes to forest health. We analyzed three examples where mixedwood stands are more resistant to insect infestations in eastern North America. In balsam fir (Abies balsamea L. Mill.) and spruce (Picea spp.) forests, susceptibility and vulnerability to spruce budworm infestations is reduced with increasing hardwood density. In mid-Atlantic oak-dominated forests, oak mortality following gypsy moth infestations was much greater in oak-dominated forests than in oak–pine mixedwoods, while pine mortality during southern pine beetle infestations was greater in pine-dominated forests than in oak–pine mixedwoods. Overall, mixedwood stands have greater resistance to infestations of defoliators and bark beetles and recover more rapidly from disturbances, reducing economic losses associated with tree mortality and mitigating short-term impacts to ecosystem functioning resulting from insect damage, especially carbon sequestration. Finally, we discuss challenges and opportunities for mixedwood management to minimize insect damage. Management strategies that incorporate mixedwood stands may provide better continuity in supply of forest products and ecosystem services in the face of projected increases in insect infestations associated with changing climate.

Validity of using Single Extruder in Wood Plastic Composite from Rice Straw and High Impact Polystyrene Wastes

This work mainly aims to study the validity of using the single extruder in achieving adhesion and compatibility between rice straw fibers and plastic wastes as an attempt for manufacturing wood plastic composite (WPC). A single extruder was used for mixing recycled high impact polystyrene (RHIPS) and Egyptian natural rice straw (RS) after being fibrated mechanically to produce an eco-friendly synthetic wood that can be named as rice straw plastic composite (RSPC). The components have passed through many operations such as drying, extrusion, shredding, etc.). To produce the final product, the flat press technique was used with a hydraulic press. Samples with 60 % mechanically fibrated rice straw (MFRS) ratio were produced. The density test was operated on the samples according to ASTM-D-792 to reveal the density of the composite. The water absorption was determined according to ASTM-D-570. Using the single extruder for blending the two components didn’t achieve high levels of compatibility. However, comparing the results with natural soft, hard wood and medium density fiberboard (MDF) synthetic wood. The prepared RSPC samples exhibited less water absorption and higher density than that of natural and MDF woods.

Microhabitat features influencing habitat use by Florida black bears

Understanding fine-scale habitat needs of species and the factors influencing heterogeneous use of habitat within home range would help identify limiting resources and inform habitat management practices. This information is especially important for large mammals living in fragmented habitats where resources may be scarcer and more patchily distributed than in contiguous habitats. Using bihourly Global Position System (GPS) location data collected from 10 individuals during 2011–2014, we investigated microhabitat features of areas within home ranges that received high vs. low intensity of use by Florida black bears (Ursus americanus floridanus) in north-central, Florida. We identified areas receiving high and low levels of use by bears based on their utilization distributions estimated with the dynamic Brownian bridge movement model, and performed vegetation sampling at bear locations within high- and low-use areas. Using univariate analyses and generalized linear mixed models, we found that (1) canopy cover, visual obstruction, and hardwood density were important in defining high-use sites; (2) the probability of high use was positively associated with principal components that represented habitat closer to creeks and with high canopy and shrub cover and higher hardwood densities, likely characteristic of forested wetlands; and (3) the probability of high use was, to a lesser extent, associated with principal components that represented habitat with high canopy cover, high pine density, and low visual obstruction and hardwood density; likely representing sand pine and pine plantations. Our results indicate that the high bear-use sites were in forested wetlands, where cover and food resources for bears are likely to occur in higher abundance. Habitat management plans whereby bears are a focal species should aim to increase the availability and quality of forested wetlands.

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.

Silvicultural treatments for converting loblolly pine to longleaf pine dominance: effects on ground layer and midstorey vegetation

AbstractQuestionsHow do management practices used to enhance longleaf pine (Pinus palustris) seedling survival and growth under a loblolly pine (Pinus taeda) canopy alter the structure of midstorey and ground layer vegetation? Do management treatments achieve general restoration targets for longleaf pine ecosystem structure?LocationMarine Corps Base Camp Lejeune, NC, USA within the Middle Atlantic Coastal Plain Ecoregion.MethodsFour levels of timber harvest were applied to loblolly pine stands: Control (uncut, basal area ~16.2 m2·ha−1), MedBA (residual basal area ~9.0 m2·ha−1), LowBA (residual basal area ~6.4 m2·ha−1) and Clearcut (residual basal area of 0 m2·ha−1). Within each canopy treatment, we applied three cultural treatments selected to facilitate longleaf pine seedling success: NT (untreated), H (chemical control of woody vegetation) and H + F (chemical control plus fertilization). Vegetation responses, including the abundance (cover) of ground layer vegetation and midstorey stem densities, were reported for three growing seasons (2008–2010) following canopy removal.ResultsThe ground layer was dominated by woody vegetation, and total vegetation cover generally increased with increasing canopy removal. Canopy treatment effects varied through time. Clearcut plots had higher total herbaceous and graminoid cover than MedBA and Control plots in 2008, while woody cover was significantly lower on Control plots than on LowBA and Clearcut plots in 2009. Clearcut plots had higher densities of loblolly pines than Control plots in 2009 and 2010. The herbicide treatment reduced hardwood densities, but increased loblolly pine densities, especially in 2010.ConclusionsSuccessful restoration prescriptions are often site‐specific because of different land‐use history, climate, site characteristics and starting conditions. To achieve the restoration objective of creating an open midstorey with an herbaceous‐dominated ground layer when converting loblolly pine stands to longleaf pine dominance on relatively productive sites with abundant hardwoods and aggressive loblolly pine natural regeneration, canopy retention can slow the rate of development of loblolly pine regeneration and herbicides reduce hardwood stem densities. Frequent, repeated burning would likely be required to further reduce woody vegetation and increase the relative abundance of herbaceous vegetation.

Effects of geometric design of forest road and roadside vegetation on traffic noise reduction

Geometric design of forest roads and design of their landscapes can reduce noise pollution and its harmful effects on human health. We investigated the effects of technical and biological parameters such as geometric road design and various roadside tree stands on reducing noise pollution according to the tree density and distance from roadway in Darabkola Forests, Sari, Iran. We recorded the noise generated by a car (Land Rover) relative to changes in longitudinal slope, horizontal curve radius and type of road pavement. We also measured noise levels according to roadside tree density and stand type (coniferous and hardwood) in 40 rectangular plots of three widths (25, 100 and 300 m) and 50 m length that were randomly demarcated along forest roads. The changes in noise level were recorded using a decibel meter with an accuracy of ±1.5 dB and resolution of 0.1 dB. Noise levels were higher alongside unpaved roads than alongside paved roads. There was an inverse relationship between the measured noise level and horizontal curve radius. The rate of noise level on horizontal curve with a radius less than 30, 30–45 m and more than 45 m were 64.8, 70.8 and 75.9 dB, respectively. The noise level increased with the increasing longitudinal slope of the road. There was a significant difference between the noise level on slopes less than 3 % (67 dB) and 3–8 % (71.2 dB) in comparison with slopes greater than 8 % (77.8 dB), (p < 0.05). Pinus brutia L. reduced the noise level more (about 6 dB) in stands of 1/3 density of mixed hardwoods within 25 m from middle of the road. Careful design of geometric properties of forest roads as well as planting coniferous trees with hardwoods is a suitable solution for reducing noise pollution.

Resource selection reflects fitness associations for an endangered bird in restored habitat

Conservation practitioners frequently have limited information on the structure and function of the ecosystems they wish to preserve, and as a result, they may use shortcuts to guide conservation actions. One such shortcut is the umbrella species approach, whereby conservation actions are geared toward one or a few key species, with the assumption that the entire community will benefit. However, fitness–habitat associations and resource use may vary across space and across management regimes, and so too may the utility of umbrella species as ecosystem surrogates. The federally endangered red-cockaded woodpecker (Picoides borealis) has been used as an umbrella species in the restoration of the longleaf pine ecosystem of the southeastern US. Restoration efforts were based on early habitat selection information in largely degraded landscapes. We examined patterns of resource selection of 97 social groups of red-cockaded woodpeckers in a restored landscape in northwest Florida. Similar to previous studies in degraded landscapes, woodpecker groups selected forest stands containing higher densities of large pines and lower densities of small pines for foraging. However, we found no evidence for another aspect of habitat selection widely documented in degraded habitat, the avoidance of areas with substantial components of hardwoods. These results align with new woodpecker fitness–habitat associations within restored landscapes and lend support to previous findings that current ecosystem restoration efforts in the study area, namely prescribed burning, may have reduced hardwood densities to below those at which they have negative impacts. The red-cockaded woodpecker has served as an effective umbrella species in degraded longleaf ecosystems by promoting management, especially prescribed burning, that benefits many other species. Whether it will continue to do so in restored habitat is not yet clear, but its tolerance of a range of hardwood conditions provides reason for optimism.

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.

Commercial thinning stimulates natural regeneration in spruce–fir stands

Understanding the response of tree regeneration following commercial thinning treatments can improve planning in managed forests dependent on natural regeneration. We used long-term commercial thinning experiments in eastern spruce–fir stands of Maine, USA, to test two hypotheses: (1) commercial thinning increases the density of tree regeneration and (2) tree regeneration density increases with increasing thinning intensity. A decade after thinning, densities of softwood and hardwood regeneration were 10 times greater in thinned stands than unthinned stands. The abundance of small softwood (0.11–0.60 m tall) was highest in lower intensity thinning treatments, whereas medium (0.61–1.40 m tall) and large (≥1.41 m tall to 8.90 cm diameter at breast height) softwoods increased proportionally with thinning intensity, a pattern related to a higher rate of recruitment in more open stands created by heavier thinning. Hardwood density generally increased with thinning intensity and developed into a significant component of the large size class. Softwood regeneration density was higher in older spruce stands than younger fir stands, which may be due to greater abundance of advance regeneration, higher residual stand mortality, and greater harvest disturbance in older spruce stands. However, acceptable softwood stocking was achieved in all replicates of thinning treatments. Therefore, in addition to providing higher individual-tree growth and merchantable yield, commercial thinning in eastern spruce–fir stands also increases regeneration density. The rate of recruitment also increased as thinning intensity increased, thus stimulating understory regeneration similar to that of a shelterwood establishment cut.

A dynamic reference model: a framework for assessing biodiversity restoration goals in a fire‐dependent ecosystem

The use of reference models as templates of historical or natural conditions to assess restoration progress is inherently logical; however, difficulties occur in application because of the need to incorporate temporal variation in ecosystems caused by disturbance and succession, as well as seasonal, interannual, or decadal variability. The landscape-scale restoration of the globally threatened and fire-dependent longleaf pine ecosystem in the southeastern United States is an example in which restoration efforts are even more complicated by the limited availability of extant reference sites. This study uses the dynamic reference conceptual framework to assess the direction and rate of recovery with respect to biodiversity restoration goals using a 15-year vegetation data set from an experimental restoration treatment in fire-excluded, hardwood-encroached longleaf pine sandhills. We compared ground-cover vegetation response to midstory hardwood removal through herbicide application, mechanical removal, and fire only. Nonmetric multidimensional scaling ordinations and proportional similarity analyses suggest that, while vegetation changed in all treatments over time, no differences in species composition or hardwood density in the ground cover were attributable to hardwood reduction treatments after 15 years with frequent prescribed fire. Furthermore, the results of this study indicate that considerable variability is associated with reference sites over time. Sites identified in 1994 as attainable restoration targets had become a moving target themselves, changing in magnitude consistent with alterations in restoration plots attributable to treatment effects and shaped by the modest increase in fire frequency imposed since 1998. In a broad restoration context, this study demonstrates a conceptual framework to better understand and integrate the range of spatial and temporal variation associated with the best available reference sites. It also illustrates a practical tool for statistically defining reference sites and for measuring restoration success in continually changing conditions that should be widely applicable to other ecosystems and restoration goals.

Influence of management intensity on the productivity of early successional Acadian stands in eastern Maine

Early successional stands composed of naturally regenerated hardwood and conifer species are abundant in the forests of northeastern North America. Substantial improvements in the composition and growth of these stands may be possible with early management intervention. Unfortunately, stand responses to early management inputs are poorly understood since many of these stands are rarely manipulated. We examined the response of early successional stands to combinations of two management intensities (with and without enrichment planting and different levels of vegetation control) and three compositional objectives (hardwood, mixedwood and conifer). The treatments were designed to represent management options available in the region, including hardwood thinning, conifer release and a combination of treatments to promote hardwood –conifer mixedwood stands. Seven years after treatment, yields of the two hardwood thinning treatments ranged from 43.4 to 56.6 Mg ha 21 , which were similar to the 52.9 Mg ha 21 yield of the untreated control but with 17 and 46% lower densities, respectively. In the conifer release treatments, the removal of hardwoods promoted conifer dominance and resulted in yields between 19.9 and 30.4 Mg ha 21 7 years after treatment. The conifer release treatments will likely be dominated by conifers in the future with varying hardwood densities due to hardwoods establishing in gaps without conifers. After 7 years, yields of the mixedwood treatments were between 19 and 47% greater than the conifer release treatments due to the retention of thinned hardwood stems and represent stands that dominate much of the forestland in the region. Results from this study demonstrated that early successional stands can be effectively managed during early stand development to improve growth and the longer term composition.

Mesoscale Variation in Snag and Hardwood Densities and Sizes in Old-Growth Forests in Western Oregon

Abstract Snags and hardwoods contribute to biological, structural, and functional diversity in old-growth forests. In the US Pacific Northwest, only general knowledge about regional patterns is available to determine target density of snags and hardwood trees. To investigate their variability at relevant scales for silviculture, we examined snag and hardwood densities and sizes in 20 old-growth units in northern and southern aspects in the Coast Range and the Willamette Valley foothills of Oregon. Snag densities varied largely between subregions and aspects, with aspect affecting densities more than subregion. In the Coast Range, snag density was 2.8 times greater on northern aspects than on southern aspects, whereas in the Willamette Valley foothills snag density was 1.4 times greater on northern aspects than on southern aspects. Density of snags larger than 101.6 cm in diameter was very low. Hardwood densities were also greater on northern aspects than on southern aspects. The negative exponential distribution of hardwood density frequency by size classes could be explained by cohort growth under a wide range of competitive pressures or repeated-recruitment events. Aspect and subregion should be taken into account when defining management targets. Allowing for flexibility at these smaller spatial scales would better reflect the variability in ecological conditions and land use history that led to the development of old-growth stands.

Effects of management, environment and landscape conditions on establishment of hardwood seedlings and saplings in central Japanese coniferous plantations

There is an increasing need to restore natural hardwood forests in landscapes dominated by monocultural conifer plantations. A convenient restoration approach is to exploit natural regeneration processes. Natural regeneration, however, is affected by diverse interacting factors, for which better understanding is required, in order to optimize restoration programs. To identify optimal management practices for improving natural regeneration of hardwood trees in coniferous plantations, we examined the effects of multiple factors on the abundance of seedlings, small saplings and large saplings (height <0.3, 0.3–1.3 and ⩾1.3 m, respectively) of hardwood tree and shrub species in both line thinned (LT) and unthinned (UT) plantations of sugi ( Cryptomeria japonica) and hardwood forests (HF) in central Japan. The effects of management practices (number of the times of weeding and cleaning, thinning method, years after thinning and forest age), environment (slope position, slope angle and canopy openness), and landscape conditions (distance from nearest hardwood forest, altitude and landuse before planting) on the number of hardwood individuals were examined by using the data obtained from the LT plantations. We also compared hardwood density between LT and UT plantations to examine the effect of line thinning. Finally, we examined species composition of LT plantations and HF to identify hardwood forest components in the thinned plantations. The effects on hardwood regeneration of environmental conditions, landscape factors and management practices applied in the plantations varied, depending on the size class and life form of the regenerating species. The abundance of large saplings of tall tree species was affected by several management factors, especially number of the times of weeding. Landscape conditions (distance from the nearest hardwood forest and altitude) affected the abundance of small saplings and seedlings of tall tree species, but not the other classes. Seedlings and small saplings of many tall tree species that contribute to hardwood forest canopies were less abundant in the LT plantations. The results show that numerous factors affect the establishment and abundance of naturally regenerating hardwood tree species, and suggest that successful establishment during early plantation stages can have long-lasting effects on natural regeneration of tall tree species.

Regeneration and Seedling-habitat Relationships of the Marginal Population of Pitch Pine (Pinus rigida) After Prescribed Burning, Eastern Ontario, Canada

Post-fire seedling establishment in relation to microsite conditions and relationships of seedlings (saplings) to older tree individuals was studied in two treatments (i.e., burned and unburned sites) in an area known as the pitch pine (Pinus rigida) ridge on Hill Island, St. Lawrence Islands National Park, Eastern Ontario. Pinus rigida is a rare tree species in Canada at the northern limit of its range. Pinus strobus (eastern white pine) and Quercus alba (white oak) are also common species of the site. The negative correlation between density of mature P. rigida trees and total canopy cover and hardwood density was con.rmed in unburned plots on the ridge. On the other hand, P. strobus density was positively correlated with those parameters. The density of P. rigida seedlings is higher (by 48%) and P. strobus seedlings lower (by 82%) in burned plots than in unburned plots. Seedling recruitment was also dependent on the occurrence of seed trees of both species. The density of P. strobus seedlings was generally higher than that of P. rigida seedlings, especially in unburned plots. The long absence of .re, high seed production of P. Strobus, and relatively low number of P. rigida seed-producing trees, which have a low amount of fertile cones, are probably the main factors in.uencing seedling recruitment on the ridge. Discriminant analysis con.rmed different seedbed requirements of both species. Pinus strobus seedlings occurred within both treatments, especially on deeper soil pro.les with thicker litter depth, although, for seed regeneration, a mineral soil seedbed or a greatly reduced organic layer was also important. Pinus rigida seedling recruitment on burned and unburned plots was comparatively higher on mineral soil, thinner litter layer, and moss and lichen cushions.

Long-term spatial and structural dynamics in Acadian mixedwood stands managed under various silvicultural systems

Using inventory data from a long-term silviculture experiment in east-central Maine, spatial models were developed to analyze 28 years (1974–2002) of stand structural dynamics. Differences in spatial pattern, species mingling, height differentiation, and relative stand complexity index (rSCI) were compared among five treatments: commercial clear-cutting, fixed diameter-limit, 5 year single-tree selection, three-stage shelterwood (both with and without precommercial thinning), and unharvested natural areas. Regardless of treatment, regeneration events (whether induced by natural breakup of the overstory or by harvesting) increased aggregation in spatial pattern and reduced species mingling, more so in the commercial clearcut and fixed diameter-limit treatments where hardwood densities were highest. Regular spatial patterns were rare. Height differentiation values for individual trees and stand-level mean rSCI were generally highest in untreated natural areas and 5 year selection treatments, intermediate in commercial clearcut and fixed diameter-limit treatments, and lowest in three-stage shelterwood treatments. After a brief adjustment period, precommercial thinning in a shelterwood treated stand generally increased species mingling, height differentiation, and rSCI. Two untreated natural areas exhibited divergent pathways of structural development. Dynamics in uneven-aged selection treatments more closely resembled that of the untreated natural areas than did the shelterwood, commercial clearcut, or fixed diameter-limit treatments.

Developing landscape habitat models for rare amphibians with small geographic ranges: a case study of Siskiyou Mountains salamanders in the western USA

To advance the development of conservation planning for rare species with small geographic ranges, we determined habitat associations of Siskiyou Mountains sala- manders (Plethodon stormi) and developed habitat suitability models at Wne (10 ha), medium (40 ha), and broad (202 ha) spatial scales using available Geographic Information Systems data and logistic regression analysis with an information theoretic approach. Across spatial scales, there was very little support for models with structural habitat fea- tures, such as tree canopy cover and conifer diameter. Model-averaged 95% conWdence intervals for regression coeYcients and associated odds ratios indicated that the occurrence of Siskiyou Mountains salamanders was positively associated with rocky soils and PaciWc madrone (Abutus menziesii) and negatively associated with elevation and white Wr (Abies concolor); these associations were consistent across 3 spatial scales. The occurrence of this species also was positively associated with hardwood density at the medium spatial scale. Odds ratios projected that a 10% decrease in white Wr abundance would increase the odds of salamander occurrence 3.02-4.47 times, depending on spatial scale. We selected the model with rocky soils, white Wr, and Oregon white oak (Quercus garryana) as the best model across 3 spatial scales and created habitat suitability maps for Siskiyou Mountains salamanders by projecting habitat suitability scores across the landscape. Our habitat suitability models and maps are applicable to selection of priority conservation areas for Siskiyou Mountains salamanders, and our approach can be easily adapted to conservation of other rare species in any geographical location.