Short-term effects of group-selection harvesting on breeding birds in a northern hardwood forest

We used a before-after, control-impact design (one year pre-harvest, two years post-harvest) and unlimited-radius point counts to study the effects of typical group-selection harvesting (0.5 gaps ha⁻¹ placed near seed trees within a standard single-tree selection harvest) and intensive group-selection harvesting (4 gaps ha⁻¹ placed on a grid with no harvesting between gaps) on the composition and abundance of breeding birds in tolerant hardwood forests in Algonquin Provincial Park, Ontario. Percent similarity between pre- and post-harvest bird communities was 5–9% lower in selection harvested stands than in reference stands. Differences in percent similarity among the three treatments were not significant, however, suggesting that the changes in the bird community in stands harvested with group selection were not substantially different than those in reference stands. Abundance of aerial foragers and tree-and-shrub nesters increased in response to typical and intensive group selection in the second year post-harvest. By contrast, bark foragers and cavity-nesters decreased in the first year post-harvest and then increased in the second year post-harvest in response to typical group selection. Abundance of 16 (73%) of 22 species was not affected by harvesting. Blue Jay (Cyanocitta cristata), Chestnut-sided Warbler (Dendroica pensylvanica), Least Flycatcher (Empidonax minimus), and White-throated Sparrow (Zonotrichia albicollis) increased in response to intensive group selection in the first or second year post-harvest, whereas Chestnut-sided Warbler, Hairy Woodpecker (Picoides villosus), and White-throated Sparrow increased in response to typical group selection in the first or second year post-harvest. Ovenbird (Seiurus aurocapilla) decreased slightly in response to typical group selection in the second year post-harvest. Our short-term data suggest that intensive, rather than typical, group-selection harvesting is preferred for maintaining densities of cavity-nesting birds and Ovenbird; whether these advantages continue through the remainder of the cutting cycle and beyond requires further investigation.     

Roost tree selection by northern myotis (Myotis septentrionalis) maternity colonies following prescribed fire in a Central Appalachian Mountains hardwood forest

Following decades of fire suppression in eastern forests, prescribed fire as a tool to restore or enhance oak (Quercus spp.)-dominated communities is gaining widespread acceptance in the Appalachian Mountains and elsewhere. However, the interactions of fire with biotic components such as wildlife that might be impacted by prescribed fire are poorly documented. For tree-roosting bats, fire can enhance roosting habitat by creating snags and increasing solar radiation at existing roosts. In 2007 and 2008, we examined roost selection of forest-interior dwelling northern myotis (Myotis septentrionalis) maternity colonies in stands treated with prescribed fire (hereafter, fire) and in unburned (hereafter, control) stands on the Fernow Experimental Forest, West Virginia. Using radio telemetry, we tracked 36 female northern myotis to 69 roost trees; 25 in the fire treatment and 44 in the control treatment. Using logistic regression and an information-theoretic model selection approach, we determined that within the fire treatment, northern myotis maternity colonies were more likely to use cavity trees that were smaller in diameter, higher in crown class, and located in stands with lower basal area, gentler slopes, and higher percentage of fire-killed stems than random trees. Moreover, roosts often were surrounded by trees that were in the upper crown classes. In the control treatment, northern myotis were more likely to roost nearer the tops of larger diameter cavity trees in early stages of decay that were surrounded by decaying trees in the upper crown classes than random trees. Roost trees in the fire treatment were associated with larger overall canopy gaps than roost trees within the control treatment. Regardless of treatment, northern myotis maternity colonies roosted in black locust (Robinia pseudoacacia) in greater proportion than its availability. Ambient temperatures recorded at a subset of roost trees in fire and control treatments indicated that daily minimum temperatures were similar, but daily mean and maximum temperatures were higher in the fire treatments, possibly due to larger canopy gaps created by the senescence and decay of the surrounding fire-killed overstory trees. Northern myotis roost-switching frequency, distance between successive roosts, and duration of individual roost tree use were similar between the fire and control treatments, suggesting similar roost tree availability despite a significantly higher proportion of potential roost trees in the fire treatment. Northern myotis readily exploited alterations to forest structure created by the reintroduction of fire, which accelerated snag creation and enlarged existing or created new canopy gaps, but it remains to be determined if these conditions translate into increased recruitment and survivorship.     

Ten-year response of the herbaceous layer to an operational herbicide-shelterwood treatment in a northern hardwood forest

Shelterwood seed cutting in conjunction with herbicide site preparation has proven effective at regenerating Allegheny hardwood forests, but the long-term impact of this silvicultural system on herbaceous vegetation has not been determined. From 1994 to 2004, we studied the impacts of operational herbicide site preparation using glyphosate plus sulfometuron methyl herbicides in the context of a shelterwood seed cut. Our study took place on 10 partially cut sites on the Allegheny National Forest in northwestern Pennsylvania. Half of each site received herbicide and half did not in a split-plot design with repeated measures. Fences were erected after year six because deer impact had increased. Resilience of individual species and the community were determined using measures of percent cover by species or species groups and indices of diversity and similarity comparing post-treatment to pre-treatment conditions and controls. In the short term, abundance of all species was reduced and there were four fewer species on average in treated areas. No species was eliminated by herbicide across all sites in the long term. Graminoids were more abundant on treated plots after year six. Targeted ferns remained less abundant on treated than control plots after 10 years. Species richness recovered within 4 years following treatment. Shannon Diversity and Shannon Evenness were greater in treated than in control plots over the full study period, but the differences were not significant in any single year. The richness-based Jaccard index of similarity did not differ between control and treatment plots after year two, while relative abundance influenced indices showed significant differences through year eight. Results suggest that herbaceous layer vegetation is resilient to the disturbance created by herbicide-shelterwood treatments.     

Predicting sapstain and degrade in fallen trees following storm damage in a Pinus radiata forest

Storm damage in production forests constitutes a major source of economic loss world wide, yet the retrieval of salvageable timber remains problematic. In particular, an inability to anticipate when sapstain and degrade will appear hampers the planning of log recovery operations. A study was conducted to monitor the deterioration of fallen trees following two winter storms causing wind and snow damage in a Pinus radiata plantation forest in the upper South Island of New Zealand. Percentage sapstain, incidence of basidiomycete decay fungi, and frequency of bark beetle infestation increased, while percentage sapwood moisture content decreased, over a period of 1 year. These changes proceeded more rapidly in fallen trees that were severed at stump height, to simulate breakage, than in those that were left partially rooted. There was little beetle activity at the time of the storms, but Arhopalus ferus (Coleoptera: Cerambycidae), and Hylastes ater, Hylurgus ligniperda and Pachycotes peregrinus (Coleoptera: Curculionidae: Scolytinae), were collected in flight traps during the following spring and summer. The predominant fungal species associated with sapstain was Diplodia pinea, while Ophiostoma piceae and Grosmannia huntii were isolated near the end of the period. The main decay fungi obtained were Phlebiopsis gigantea, Stereum sanguinolentum, and Schizophyllum commune. A generalized linear mixed model was constructed to predict the development of sapstain in fallen trees for conditions prevailing during the study after a storm at the same time of year. According to the model, a 10 m long butt log of 22 cm mid length diameter will have minimal stain (<10% of the cross sectional area affected) when cut from severed stems up to 4 months after the storm; if taken from still-rooted trees this period will extend to 1 year. However, because of large between-tree variation, economically productive log recovery will also depend on the proportion of trees that lie below an acceptable sapstain threshold. Further research is needed to determine regional and seasonal influences on the development of sapstain in fallen trees.     

Effects of vertebrate herbivores and shrub characteristics on arthropod assemblages in a northern Arizona forest ecosystem

Large herbivores have potential to affect invertebrate community structure through numerous processes, but little work has been done to evaluate the relative importance of direct and indirect factors. In this study, we measured arthropod community assemblages on Ceanothus fendleri A. Gray (Fendler's ceanothus) plants that were growing inside and outside of 4-m² exclosures. We used univariate analyses and structural equation modeling (SEM) to evaluate relationships within this herbivore–plant–arthropod system in ponderosa pine (Pinus ponderosa Laws.) forests of northern Arizona, USA. Results showed that individual arthropod abundance, family diversity, family richness, and functional group richness were significantly greater on plots where C. fendleri plants were protected from large ungulate herbivores (e.g., mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus nelsoni)) than on unprotected plots in each of the three study years. Results also indicated the following: (1) arthropod abundance was significantly greater on protected plants than unprotected plants; (2) rarefaction curves suggested arthropod family richness was similar between protected and unprotected plants in two of the three years when scaled by number of individuals but the estimated total richness was consistently higher on protected plants; (3) arthropod abundance was directly affected by protection from herbivores, plant stem length, and number of flowers; (4) arthropod family richness was related to the number of individuals collected and affected by stem length. Results from this study illustrate that arthropod communities are directly affected by foraging vertebrate herbivores as well as indirectly affected through complex plant-mediated factors in this model system. Protection of preferred forage plants such as C. fendleri from ungulate herbivores can potentially increase diversity of arthropod assemblages in these forests, help conserve biological diversity, and enhance ecosystem restoration efforts.     

Think globally,manage locally: The importance of steady-state forest features for a declining songbird

Changes in historical forest composition and structure may have cascading effects throughout the forest community. Perhaps nowhere is there a better example of current forests that carry a legacy from their past than in eastern North America. The Cerulean Warbler (Dendroica cerulea), a declining Neotropical migratory bird of high conservation concern, is one excellent example of a species that seems to be sensitive to both landscape configuration and subtle features of eastern forests of North America. We used the Cerulean Warbler as a model species to demonstrate how an appreciation of fine-scale structural attributes of forests may improve our ability to conserve late-successional forest species. To do this we evaluated the extent to which multiscale habitat features were associated with density, spatial distribution, and nesting success of Cerulean Warblers in 12 mature forest sites in southeast Ohio, 2004–2006. Results suggest that adjacency of regenerating clear-cuts did not influence density or nesting success of Cerulean Warblers in adjacent mature forest. Instead, variation in demographic parameters was best explained by local habitat features. Density and nesting success were positively associated with canopy openness, numbers of large-diameter trees, and number of grapevines—all of which are typical of heterogeneous steady-state phase forests. Thus, improved management for Cerulean Warblers may require creating features (e.g., large canopy gaps) that mimic old-growth forests. Although fragmentation and habitat loss remain important contributors to population declines of many mature forest species, our work provides evidence that subtle changes in forest structure, particularly to features associated with old forests, warrant additional attention from the conservation community.     

Forest fragmentation and duration of forest tent caterpillar (Malacosoma disstria Hübner) outbreaks in northern hardwood forests

In northern forests dominated by aspen (Populus spp.), the duration of outbreaks of forest tent caterpillar (Malacosoma disstria Hübner) has been reported to increase with forest fragmentation. This relationship has not been tested in other forest types affected by this widespread native defoliator. From 2002 to 2007, a large-scale outbreak of this insect in the northeastern United States defoliated millions of hectares, with sugar maple (Acer saccharum Marsh.) the primary host. We used digital defoliation maps generated from aerial surveys and national land cover data to assess the effect of fragmentation on outbreak duration in areas of NY, MA, VT, and NH. We found that outbreak duration increased with forest cover and decreased with the forest edge, in opposition to the pattern previously reported for aspen-dominated forests in Canada. This pattern was significant from plot sizes ranging from 100 m to 1000 m in radius. The relationship between FTC and its natural enemies, which was postulated to underlie the effect of fragmentation on outbreaks in aspen forests, may be affected differently in northern hardwood forests, or other factors may be more important in determining outbreak duration in this forest type.     

Increased mortality can promote evolutionary adaptation of forest trees to climate change

Forecasts of rapid climate change raise the question how quickly species can evolutionarily adapt to future climates. The adaptability of forest trees to environmental changes is generally promoted by high levels of genetic diversity and gene flow, but it can also be slowed down by long generation times and low mortality of established trees. Here, we investigate the adaptation of Scots pine (Pinus sylvestris) and Silver birch (Betula pendula) to climate change induced prolongation of the thermal growing season. We use quantitative genetic individual-based simulations to disentangle the relative roles of mortality, dispersal ability and maturation age for the speed of adaptation. The simulations predict that after 100 years of climate change, the genotypic growth period length of both species will lag more than 50% behind the climatically determined optimum. This lag is reduced by increased mortality of established trees, whereas earlier maturation and higher dispersal ability had comparatively minor effects. The evolutionary lag behind environmental change shown in our simulations stresses the importance of accounting for evolutionary processes in forecasts of the future dynamics and productivity of forests. Sensitivity of the adaptation speed to mortality suggests that species experiencing high mortality rates as well as populations subject to regular disturbances such as storms or fires might be the quickest to adapt to a warming climate.     

Long-term dynamics of a mixed conifer stand in Slovenia managed with a farmer selection system

The single-tree selection system is an important option for management of Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) forests because it provides continuous cover, requires low investments for tending, and promotes natural regeneration as well as high stand resistance and elasticity. It is often regarded as a very conservative system that usually results in only minor spatiotemporal changes in forest structure and composition. We studied management history, structural changes, regeneration dynamics, and light climate of a traditional single-tree farmer selection silver fir-Norway spruce forest (site typology Bazzanio-Abietetum). Stand structure was analyzed on five 0.25 ha permanent plots in 1994, 2001, and 2008. Regeneration density and height growth, forest floor vegetation, and light climate were also assessed on 1.5 × 1.5 m regeneration subplots in 2001 and 2008. Tree cores extracted from dominant trees from both species in two plots were used for reconstructing stand history and age structure of the canopy layer. We documented the forest response to three types of selection management regimes: excessive, normal, and conservative. Excessive management with harvest intensity significantly above the increment was documented until the late 1950s, including two peaks of heavy fellings (diameter limit cut) in the 1880s and 1930s, which favoured establishment of Norway spruce and released regeneration. The period that followed was characterized by normal selection management, but was nevertheless marked by a decline of silver fir as a result of air pollution and several droughts. This led to sanitary fellings that were carried out from the late 1970s to the early 1990s. In the last two decades conservative management followed, which led to suppression and decline of regeneration, especially of Norway spruce, and loss of selection structure. Although we recorded lower regeneration potential of silver fir compared with Norway spruce within the seedling category, silver fir outcompeted Norway spruce within the small-sized tree category (1 cm < dbh ? 10 cm) because of its superior height growth in low light levels (diffuse light <6%) and occupied a greater share of the canopy. Nevertheless, we anticipate that over the long-term the low light regime will also cause regeneration decline of silver fir and broadleaves. Our research revealed significant structural changes in a single-tree farmer selection forest during the last 150 years. These were a result of variable management regime and environment. A farmer single-tree selection system could better mimic the natural disturbance regime if spatiotemporal combinations of diverse felling regimes would be used.     

Invasion and management of a woody plant, Lantana camara L., alters vegetation diversity within wet sclerophyll forest in southeastern Australia

Plant invasions of natural communities are commonly associated with reduced species diversity and altered ecosystem structure and function. This study investigated the effects of invasion and management of the woody shrub Lantana camara (lantana) in wet sclerophyll forest on the south-east coast of Australia. The effects of L. camara invasion and management on resident vegetation diversity and recruitment were determined as well as if invader management initiated community recovery. Vascular plant species richness, abundance and composition were surveyed and compared across L. camara invaded, non-invaded and managed sites following L. camara removal during a previous control event by land managers. Native tree juvenile and adult densities were compared between sites to investigate the potential effects of L. camara on species recruitment. Invasion of L. camara led to a reduction in species richness and compositions that diverged from non-invaded vegetation. Species richness was lower for fern, herb, tree and vine species, highlighting the pervasive threat of L. camara. For many common tree species, juvenile densities were lower within invaded sites than non-invaded sites, yet adult densities were similar across all invasion categories. This indicates that reduced species diversity is driven in part by recruitment limitation mechanisms, which may include allelopathy and resource competition, rather than displacement of adult vegetation. Management of L. camara initiated community recovery by increasing species richness, abundance and recruitment. While community composition following L. camara management diverged from non-invaded vegetation, vigorous tree and shrub recruitment signals that long-term community reinstatement will occur. However, secondary weed invasion occurred following L. camara control. Follow-up weed control may be necessary to prevent secondary plant invasion following invader management and facilitate long-term community recovery.     

A century of logging and forestry in a reindeer herding area in northern Sweden

Boreal forest ecosystems are generally highly sensitive to logging and other forestry activities. Thus, commercial forestry has had major effects on the forests and landscape structure in northern Sweden since the middle of the 19th Century, when it rapidly extended across the region. Lichens (which constitute up to 80% of reindeer forage in winter and early spring) have often been amongst the most severely affected ecosystem components. The overall aim of the present study was to analyze how forestry has influenced the potential supply of ground-growing lichens as winter forage for the reindeer in this region over the past ca. 100 years. For this purpose, we analysed changes in forest and stand structure in Scots pine-dominated (Pinus sylvestris L.) reindeer wintering areas in the southern part of the county Norrbotten (covering ca. 58,000 ha) using detailed historical forest inventories and management plans. We found that the amount of the forest types considered potentially good pasture (mainly middle-aged and old pine forests) decreased during the first part of the 20th Century. However, the quality of grazing grounds was improved by forestry during this time mainly because selective logging made the forests more open which benefits lichen growth. During the last part of the 20th century forestry impaired the quality of grazing grounds in several ways, e.g. by clear-cutting and intensified use of various silvicultural measures. We conclude that ca. 30–50% of the winter grazing grounds have been lost in the study area because of intensive forest management during the last century. The spatially precise historical information about the affects of forestry on lichen pasture provided in this study can be used to direct forest management which will facilitate and promote reindeer herding in the future.     

Bamboo dieback and tree regeneration responses in a subtropical forest of South America

Bamboos’ vegetative growth are frequently associated to negative effects on tree recruitment and survival and despite this process, the effects of bamboo dieback after flowering events are poorly understood due the rarity of these events. 2 years after the massive flowering of the woody bamboo Merostachys multiramea in a southern South America subtropical forest, we compared changes in environmental conditions; tree species regeneration and production of new culms in canopy gaps resulted from bamboo dieback and areas of continuous canopy allowed by sparse bamboo cover. We observed sharp differences in environment conditions mainly resulted from differences in canopy openness and a NPMANOVA revealed differences among the stands regeneration directions (species composition and density). Average density, number of culms per sapling and total height of M. multiramea did not differ between stands, although slight differences were detected with increasing values toward opened sites.     

Survival and early growth of mixed forest stands installed in a Mediterranean Region: Effects of site preparation intensity

In Mediterranean environments, availability of water and nutrients are the main factors limiting the success of afforestation. As part of a wider project, an experiment was established in Northeast Portugal, aiming at testing the effect of several site preparation techniques on plant survival and growth (height and diameter) in a newly installed mixed forest stand. Results presented regard plant response during 42 months after plantation. The experimental protocol consisted in seven treatments described by mechanical operations that rank soil disturbance intensity from none to high, set in plots of 375 m², randomly distributed in three blocks, in different topographic positions (gentle slope plateau, moderate slope shoulder, and steep mid-slope). Pseudotsuga menziesii (PM) and Castanea sativa (CS) forest species were planted in a 4 m × 2 m scheme and in alternate rows with 12 plants on each row per plot, summing up 72 plant per specie and treatment at start of the experiment. The results show that: (i) the highest mortality was observed immediately after the plantation and before the dry season, on the lowest intensity treatments; (ii) after the dry season, the highest mortality was also observed in treatments with the lowest intensity of soil disturbance, while the lowest values were found on the intermediate intensity treatments; (iii) during the experimental period, the effect of treatments on plant growth (height and diameter) was statistically significant; however, experimental results do not lead yet to a clear quantitative relationship between soil disturbance intensity due to site preparation and plant response under the conditions tested.     

Catastrophic windstorm and fuel-reduction treatments alter ground beetle (Coleoptera: Carabidae) assemblages in a North American sub-boreal forest

We studied the short-term effects of a catastrophic windstorm and subsequent salvage-logging and prescribed-burning fuel-reduction treatments on ground beetle (Coleoptera: Carabidae) assemblages in a sub-boreal forest in northeastern Minnesota, USA. During 2000–2003, 29,873 ground beetles represented by 71 species were caught in unbaited and baited pitfall traps in aspen/birch/conifer (ABC) and jack pine (JP) cover types. At the family level, both land-area treatment and cover type had significant effects on ground beetle trap catches, but there were no effects of pinenes and ethanol as baits. Six times more beetles were trapped in the burned forests than in the other land-area treatments; more beetles were caught in undisturbed than in wind-disturbed sites, and one-third more beetles were caught in the ABC than in the JP cover type. Thus, the windstorm generally reduced the activity-abundance of the beetles, but prescribed-burning increased it. Both salvaged and burned forest plots (especially in the ABC cover type) had the greatest species richness, diversity, and the most unique species assemblages. There was a highly similar ground beetle species composition (nearly 100%) between the ABC and JP burned forests, indicating that burning was a more primary driver of composition than cover type. At the species level, Pterostichus melanarius, an invasive ground beetle from Europe and a cover type generalist, was the most abundant beetle in the study (one-third of the total catch), and was caught in greatest numbers in burned forests. Removal of P. melanarius from the species composition analyses altered similarities among cover types and land-area treatments. Sphaeroderus nitidicollis brevoorti and Myas cyanescens were caught exclusively in the ABC and JP cover type, respectively; two rare pyrophilous species, Sericoda obsoleta and Sericoda quadripunctata, were only caught in burned sites; three forest species, Pterostichus coracinus, P. pensylvanicus, and Sphaeroderus lecontei, were caught more often in undisturbed JP sites; and two frequently trapped, open-habitat species, Agonum cupripenne and Poecilus l. lucublandus, were nearly absent from the undisturbed and wind-disturbed sites, as salvage-logging had a significant positive effect on their activity-abundance. Most species of Amara and Harpalus were trapped only in the salvaged or burned sites, indicating invasion of these disturbed sites by open-habitat species. We conclude that both the combined effect of fuel-reduction activities subsequent to the wind event and the numerical response of the invasive P. melanarius to habitat disturbances can alter the short-term succession of ground beetle assemblages in the sub-boreal forest.     

How we improved a landscape study of species richness of beetles in woodland key habitats, and how model output can be improved

In an earlier study (Franc et al., 2007), local species richness of saproxylic oak beetles (including red-listed beetles) in forests was predicted mainly by the landscape (area of woodland key habitat within 1 km of plots). Such results are important for conservation work, but need to be backed up well, for reliable advice. We tested a two-stage method that improved our earlier models and our advice for conservation planning. We studied temperate mixed forest, rich in oaks Quercus robur/Quercus petraea, in a large landscape in Sweden. Franc et al. (2007) analysed 21 forests. Here we selected the significant explanatory variables (predictors) and other biologically relevant predictors, used the earlier 21 forests and sampled 11 new forests such that we expanded the range on the axes of the predictors. We collected in total 320 species of saproxylic oak beetles (23,137 individuals) of which 65 and 38 were red-listed (IUCN criteria, Swedish list 2000 and 2005, respectively). We partly confirmed our original results, but the results also changed in important ways: local species richness is now predicted by a combination of local, landscape and regional factors. Moreover, a local variable (dead wood) was the main predictor of saproxylic oak beetles (all species included), while for red-listed saproxylic oak beetles the landscape (woodland key habitat within 1 km of plots) was the main predictor, of local species richness. Thus, species richness of red-listed saproxylic oak beetles seems to depend mainly on landscapes factors, while total species richness of saproxylic oak beetles seems to depend more on local stand factors. We conclude that a two-stage research design can be useful in landscape and conservation studies, especially for species-rich taxa that require large samples per site.     

Growth and nutrition of Pinus radiata in response to fertilizer applied after thinning and interaction with defoliation associated with Essigella californica

Infestations of Essigella californica following the installation of post-thinning fertilizer trials in Pinus radiata plantations provided an opportunity to examine the impact of repeated defoliation over a period of 8 years (1997–2005). Replicated treatments (n = 4) of nil fertilizer (control), N (300 kg ha⁻¹) as urea, P (80 kg ha⁻¹) and S (45 kg ha⁻¹) as superphosphates were applied immediately after thinning at three sites and this was followed by a second application of NPS fertilizers 6 years later with N applied at 300 kg ha⁻¹ as urea and ammonium sulphate and P at 80 or 120 kg ha⁻¹. Defoliation of untreated P. radiata gradually increased to 50% over a period of 8 years. Basal area growth was negatively correlated with average defoliation for two consecutive post-fertilizer periods of 6 and 2 years. Growth responses to fertilizer varied considerably between sites but the largest improvement in growth was due to NPS fertilizer, this increased basal area by 30–80%. Application of N fertilizer raised total N levels in foliage and increased defoliation with a commensurate loss in growth under conditions of deficiencies of S or P. Repeated infestations gradually increased the percentage of trees with severe defoliation (>80% loss of foliage) indicating that nutrient-deficient trees have a reduced capacity for foliage recovery between episodes of peak infestation. In contrast, treatment with N fertilizer in combination with S- and P-corrected deficiencies of these nutrients, raised levels of total N in foliage and reduced defoliation to approximately 20%. Basal area growth responses to NPS fertilizers reflected improved nutrition as well as reduced insect damage. The reduction in defoliation under conditions of balanced tree nutrition was most likely due to enhanced needle retention following correction of P deficiency as well as greater availability of nutrients enabling a more vigorous recovery of P. radiata after an episode of E. californica activity. Treatment with fertilizer therefore reduced the long-term impact of aphid damage and improved growth of P. radiata.     

Structure of a Central-European mountain spruce old-growth forest with respect to historical development

This study examines the structural characteristics of the tree layer, dead wood, canopy openings, and regeneration patterns of a spruce old-growth forest in the Bohemian Forest, Czech Republic. An old-growth stand with minor human influence and a stand that was presumably logged about 200 years ago were analyzed and compared, as some forest managers considered the presumable human impact as a reason for salvage logging. Even though the stands differed in tree density, height and DBH structure, it was not possible to conclude whether it was due to management history or the environmental differences. The volume of dead wood also differed between the stands. There was about 142 and 83 m³ ha⁻¹ of dead wood in the old-growth stand and presumably logged stand, respectively. The amount of dead wood found in the old-growth stand was comparable with values reported from spruce old-growth stands across Central Europe. In both stands, many canopy trees were arranged in linear patterns, which was a result of spruce regeneration on nurse logs. This suggests that the origin and development of the stands were characterized by natural processes and during the past 200 years typical old-growth structural characteristics have already evolved.     

Understorey plant community characteristics and natural hardwood regeneration under three partial harvest treatments applied in a northern red oak (Quercus rubra L.) stand in the Great Lakes-St. Lawrence forest region of Canada

Throughout eastern North America, stands of northern red oak (Quercus rubra L.) are undergoing successional replacement by shade-tolerant competitors. In the Great Lakes-St. Lawrence (GLSL) forest region, Q. rubra approaches the northern limit of its distribution, and ecosystem-specific silvicultural directives are needed to promote regeneration. We used an inductive, ordination-based approach to explore patterns in understorey plant community composition and microenvironment under different partial harvest treatments applied in a GLSL hardwood stand, and related these to characteristics of natural seedlings of Q. rubra and its competitors Acer rubrum and Acer saccharum.Two years after harvest, we established 2 m × 2 m plots in a stratified random design under 70% (n = 20) and 50% (n = 19) crown closure uniform shelterwood, group selection (n = 15), and uncut upper slope (n = 10) and lower slope (n = 10) areas. Percent cover of understorey vascular plant species, and a suite of microclimatic and edaphic variables were measured in each plot. Density, mean diameter and mean height of seedlings in the understorey (height <1 m) were determined in each plot for Q. rubra, A. rubrum and A. saccharum.Correspondence analysis (CA) ordination extracted two major axes explaining 21.6% of the total inertia in the species cover by plot matrix. Axis one separated uncut plots from the 50% shelterwood along a gradient of canopy cover associated with partial harvest treatments. Plot scores on axis one (13.2%) reflected a shift in dominance of the understorey from shade-tolerant Acer spp. to shade-intolerant colonizers, Rubus idaeus and Carex spp. Plot scores on axis one were directly (p < 0.05) associated with total understorey plant cover, litter depth, soil temperature and pH, but not with measures of plant diversity. Axis two (8.4%) separated plots from upper slope and lower slope areas, and plot scores were inversely associated (p < 0.05) with soil pH, phosphorus and nitrogen levels. Along axis two there was a shift in dominance from competitive (e.g. A. saccharum) to stress-tolerant (e.g. A. rubrum) species as soil fertility declined. Stepwise linear regression indicated seedling diameter in Q. rubra, A. rubrum and A. saccharum was inversely related to canopy cover. This suggests all three species benefited from partial harvest, although the relationship was strongest in Q. rubra. Patterns in understorey composition, microenvironment and seedling characteristics provide the basis to identify the main competitors of Q. rubra seedlings and adjust regeneration efforts along gradients of canopy closure and soil fertility under partial harvest systems within the GLSL forest region.     

Susceptibility of ponderosa pine, Pinus ponderosa (Dougl. ex Laws.), to mountain pine beetle, Dendroctonus ponderosae Hopkins,attack in uneven-aged stands in the Black Hills of South Dakota and Wyoming USA

Mountain pine beetle, Dendroctonus ponderosae Hopkins can cause extensive tree mortality in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests in the Black Hills of South Dakota and Wyoming. Most studies that have examined stand susceptibility to mountain pine beetle have been conducted in even-aged stands. Land managers increasingly practice uneven-aged management. We established 84 clusters of four plots, one where bark beetle-caused mortality was present and three uninfested plots. For all plot trees we recorded species, tree diameter, and crown position and for ponderosa pine whether they were killed or infested by mountain pine beetle. Elevation, slope, and aspect were also recorded. We used classification trees to model the likelihood of bark beetle attack based on plot and site variables. The probability of individual tree attack within the infested plots was estimated using logistic regression. Basal area of ponderosa pine in trees ≥25.4 cm in diameter at breast height (dbh) and ponderosa pine stand density index were correlated with mountain pine beetle attack. Regression trees and linear regression indicated that the amount of observed tree mortality was associated with initial ponderosa pine basal area and ponderosa pine stand density index. Infested stands had higher total and ponderosa pine basal area, total and ponderosa pine stand density index, and ponderosa pine basal area in trees ≥25.4 cm dbh. The probability of individual tree attack within infested plots was positively correlated with tree diameter with ponderosa pine stand density index modifying the relationship. A tree of a given size was more likely to be attacked in a denser stand. We conclude that stands with higher ponderosa pine basal area in trees >25.4 cm and ponderosa pine stand density index are correlated with an increased likelihood of mountain pine beetle bark beetle attack. Information form this study will help forest managers in the identification of uneven-aged stands with a higher likelihood of bark beetle attack and expected levels of tree mortality.