Oak-dominated Stands Research Articles

Smoke Emissions and Buoyant Plumes above Prescribed Burns in the Pinelands National Reserve, New Jersey

Prescribed burning is a cost-effective method for reducing hazardous fuels in pine- and oak-dominated forests, but smoke emissions contribute to atmospheric pollutant loads, and the potential exists for exceeding federal air quality standards designed to protect human health. Fire behavior during prescribed burns influences above-canopy sensible heat flux and turbulent kinetic energy (TKE) in buoyant plumes, affecting the lofting and dispersion of smoke. A more comprehensive understanding of how enhanced energy fluxes and turbulence are related during the passage of flame fronts could improve efforts to mitigate the impacts of smoke emissions. Pre- and post-fire fuel loading measurements taken during 48 operational prescribed burns were used to estimate the combustion completeness factors (CC) and emissions of fine particulates (PM2.5), carbon dioxide (CO2), and carbon monoxide (CO) in pine- and oak-dominated stands in the Pinelands National Reserve of southern New Jersey. During 11 of the prescribed burns, sensible heat flux and turbulence statistics were measured by tower networks above the forest canopy. Fire behavior when fire fronts passed the towers ranged from low-intensity backing fires to high-intensity head fires with some crown torching. Consumption of forest-floor and understory vegetation was a near-linear function of pre-burn loading, and combustion of fine litter on the forest floor was the predominant source of emissions, even during head fires with some crowning activity. Tower measurements indicated that above-canopy sensible heat flux and TKE calculated at 1 min intervals during the passage of fire fronts were strongly influenced by fire behavior. Low-intensity backing fires, regardless of forest type, had weaker enhancement of above-canopy air temperature, vertical and horizontal wind velocities, sensible heat fluxes, and TKE compared to higher-intensity head and flanking fires. Sensible heat flux and TKE in buoyant plumes were unrelated during low-intensity burns but more tightly coupled during higher-intensity burns. The weak coupling during low-intensity backing fires resulted in reduced rates of smoke transport and dispersion, and likely in more prolonged periods of elevated surface concentrations. This research facilitates more accurate estimates of PM2.5, CO, and CO2 emissions from prescribed burns in the Pinelands, and it provides a better understanding of the relationships among fire behavior, sensible heat fluxes and turbulence, and smoke dispersion in pine- and oak-dominated forests.

Small oases below the canopy: The cooling effects of water-filled tree holes on the local microclimate in oak-dominated stands

The relevance of forests in mitigating biodiversity loss and the negative effects of climate change on the biota is largely shaped by below-canopy microclimatic conditions, which are buffered, cooler and more humid compared to adjoining open habitats. Water-filled tree holes (dendrotelms, DTs) are special tree-related microhabitats that host semi-aquatic communities and are important substrates or water sources for numerous taxa (e.g., birds, mammals, insects, fungi, bryophytes). Despite their microrefugia-role might be more pronounced under climate change-induced drought events, little is known about their microclimate and its potential drivers.In an abandoned Turkey oak-dominated coppice stand in Hungary, the microclimates of 80 paired dendrotelms and adjacent forest plots were measured in the summer of 2021. Compared to nearby open areas, under closed forests, air temperature maxima were up to 5 °C cooler, DTs had an additional negative offset of 2.5 °C and increased air humidity by 15 percentage points (5% vs. 20 %). The local microclimate of DTs and the adjacent closed forest differed significantly in means and extremes of air temperature, relative humidity and vapour pressure deficit, which was mainly driven by DT entrance area and water volume and seemed independent from local stand structure. On the contrary, nearby below-canopy microclimate was shaped by the distance from forest edge, incoming light and tree density. Water volume in DTs also influenced local forest microclimates up to 0.5–1 m from the entrances.As the frequency and severity of extreme weather events such as heatwaves are likely to intensify due to climate change, the importance of microhabitats and habitat trees for invertebrates and vertebrates will increase further, and will additionally contribute to the microclimatic refugia role of forests. Active protection of veteran trees under the scheme of continuous cover forestry or conservation-oriented management is essential facing climate change to mitigate its negative effects on forest biodiversity.

Growth response of oaks to insect defoliation: Immediate and intermediate perspectives

In this study, we investigate the immediate and short-term consequences of defoliation by the spongy moth Lymantria dispar on secondary growth of oaks (Quercus robur L. and Quercus petraea (Matt.) Liebl.), including the interplay between defoliation and water availability during the defoliation period within a large-scale field experiment in south-eastern Germany. Furthermore, the impact of defoliation on oak secondary growth is explored retrospectively based on tree core measurements.Within the large-scale filed experiment, secondary growth of 880 oaks in 44 oak-dominated stands was monitored using permanent girth tapes over a three-year period following a spongy moth outbreak. Insecticide treatments were applied to half of the plots to obtain trees without defoliation, and canopy cover dynamics were subsequently monitored ground based and from satellites in all plots.We found that moth defoliation significantly reduced oak secondary growth by 10–60% during the outbreak year, with the impact on secondary growth being directly proportional to defoliation intensity. The negative impact of defoliation on secondary growth was aggravated by increased water availability during the outbreak year.In the post-outbreak year, secondary growth of oaks that had endured mild defoliation was no longer different from that of non-defoliated oaks. In contrast, oaks that had experienced substantial defoliation still exhibited a significant 10–30% reduction in secondary growth. Regardless of defoliation intensity, no further reduction in secondary growth was detected two years after the event compared to control trees. Our complementary retrospective analysis, utilizing core samples from oaks previously subjected to a defoliation event under distinct weather conditions, disclosed a strikingly analogous recovery of secondary growth from defoliation instigated by the spongy moth. Thus, validating that our experimental findings possess broad temporal transferability.

Prescribed Fire Causes Wounding and Minor Tree Quality Degradation in Oak Forests

Despite the adaptation of many oak (Quercus) species to repeated surface fire, many public land managers in eastern North America resist using prescribed fire as a regeneration tool because of fire’s perceived negative impacts on timber values through the wounding of overstory trees. We retrospectively quantified fire-associated wounds in 139 oak-dominated stands across four national forests, each with a history of zero to six prescribed fires within the last 30 years. For trees > 25.4 cm dbh (n = 8093), fire-associated wounds within the first 3.67 m of height were categorized by type, measured for defect size and graded both accounting for and then ignoring the fire-associated wounds. Most fire-associated wounds (n = 3403) were catfaces (32.5%), seams (30.5%) or bark slough (30.1%), although catfaces had 2.1–6.4 times the average volume loss of any other wound type (9.90 ± 0.72 bd ft). Among the 2160 wounded trees sampled, 741 had multiple (≥2) wounds. Although 29.1% of all trees had at least one wound associated with prescribed fire, only 7.0% of those trees exhibited a reduction in tree grade. The likelihood of wounding was greater in stands receiving more prescribed burns, but unaffected by tree diameter for either thin- or thick-barked species. Considering both the likelihoods of wounding and grade reduction, white oak (Q. alba), chestnut oak (Q. montana), hickory (Carya sp.), shortleaf pine (Pinus echinata) and yellow-poplar (Liriodendron tulipifera) trees were more resistant to prescribed fire damage than other species. While our findings cannot be related directly to individual fire parameters, such as fireline intensity or fire duration, these results do provide estimates of the cumulative effects of multiple management-based prescribed fires that can be incorporated into fire effects models.

Modeling the Effect of Stand Characteristics on Oak Volume Increment in Poland Using Generalized Additive Models

Volume increment is one of the main concerns in forestry practice. The aim of our study was to examine the impact of factors influencing the periodic annual increment of oak. To meet our objective, we used measurement data from the national forest inventory in Poland from 2005 to 2019 for oak-dominated stands. Our study used data of 1464 sample plots with dominant oak species (Quercus sessilis Ehrh. ex Schur and Quercus robur L.) measured within the national forest inventory in Poland. We developed models explaining the dependence of the periodic annual volume increment on stand characteristics using the generalized additive model. The generalized additive model allows us to analyze each variable’s effect on the dependent variable, with all other variables fixed. We documented the effect of age, height, basal area, and relative spacing index (RSI) on the periodic annual volume increment (PAIv) of oaks in Poland. The PAIv of oaks decreased gradually as the tree aged. The dependence of the PAIv on stand density was shown through its relationship with the basal area and RSI. The developed model explained about 64.6% of the periodic annual volume increment variance.

Evaluating the impact of prescribed surface fire on seedlings in the Central Hardwood Region, USA

Abstract Oak (Quercus) is being successionally replaced by maple (Acer) across much of the eastern deciduous forest. Past research on the close relationship between oak and fire has led forest managers to use prescribed surface fires to deter this replacement. However, there has not been a comprehensive evaluation of the effectiveness of prescribed fire by managers, particularly in the Central Hardwood Region. For example, it is not known how many repeat applications of prescribed fire are needed to accumulate enough oak reproduction to successfully re-establish oak-dominated stands. Tree reproduction and midstory composition were systematically surveyed across 63 mature, oak-dominated stands ranging in prescribed fire histories and aspects on the Hoosier and Wayne National Forests in southern Indiana and Ohio, respectively. These stands represent the vast majority of stands burned to promote oak regeneration since 1990 in these two National Forests. Across all sites, seedlings in the white oak group (section Quercus) and red oak group (section Lobatae) comprised 47.8 ± 3.3 per cent and 8.2 ± 1.6 per cent (mean ± SE), respectively, of all seedlings. In comparison, common competing species (maples and American beech) comprised 5.4 ± 1.4 per cent of all seedlings. Mid- and overstory basal area, percent slope, years since last burn, and total number of burns significantly affected oak seedling density. Greater increases in taller, competitive oak seedling density occurred after sites had been burned three times and with high frequency (≤4 years between burns). However, results also suggest that if an established midstory already exists or fire has not been used on the landscape for almost a decade, repeat applications of prescribed fire will not likely increase oak regeneration in the short term without concurrent treatment of midstory stems.

Whole-Tree Harvest Effects on Macronutrients in an Oak-Dominated System after Seven Years

This study assesses the impacts of whole-tree harvesting (WTH) versus stem-only harvest (SOH) on two oak-dominated stands located in Northern Wisconsin. Specifically, our study follows up on an experiment designed to better understand the impacts of WTH and whether stands are at risk of long-term nutrient losses, which could contribute to declines in productivity. The original study assessed: (i) full biomass removal (referred to as WTH), (ii) partial biomass removal (removal to 5 cm diameter bole), (iii) a traditional SOH (removal to 10 cm bole), and (iv) no harvest (control). Our data were collected 93 months after harvest and showed significant decreases (α = 0.05) in the total (soil, woody debris, litter, and tree) Ca between WTH and SOH and for N and K from all harvest types. P and Mg were not significantly different between any of the treatment types. The woody debris was significantly decreased in the WTH in comparison to the SOH across P, K, Ca, Mg, but not N. The differences in the woody debris were initially detected, but a nutrient budget modeling exercise did not show significant declines for the ecosystem. The nutrient budget model assumptions and scale of input terms are discussed. Revisiting the sites at 93 months post-harvest versus the original 1.75 years allowed for the detection of the differences in total N, K, and Ca pool sizes.

Insect infestations and the persistence and functioning of oak-pine mixedwood forests in the mid-Atlantic region, USA.

Damage from infestations of Lymantria dispar L. in oak-dominated stands and southern pine beetle (Dendroctonus frontalis Zimmermann) in pine-dominated stands have far exceeded impacts of other disturbances in forests of the mid-Atlantic Coastal Plain over the last two decades. We used forest census data collected in undisturbed and insect-impacted stands combined with eddy covariance measurements made pre- and post-disturbance in oak-, mixed and pine-dominated stands to quantify how these infestations altered forest composition, structure and carbon dynamics in the Pinelands National Reserve of southern New Jersey. In oak-dominated stands, multi-year defoliation during L. dispar infestations resulted in > 40% mortality of oak trees and the release of pine saplings and understory vegetation, while tree mortality was minimal in mixed and pine-dominated stands. In pine-dominated stands, southern pine beetle infestations resulted in > 85% mortality of pine trees but had minimal effect on oaks in upland stands or other hardwoods in lowland stands, and only rarely infested pines in hardwood-dominated stands. Because insect-driven disturbances are both delaying and accelerating succession in stands dominated by a single genus but having less effect in mixed-composition stands, long-term disturbance dynamics are favoring the formation and persistence of uneven age oak-pine mixedwood stands. Changes in forest composition may have little impact on forest productivity and evapotranspiration; although seasonal patterns differ, with highest daily rates of net ecosystem production (NEP) during the growing season occurring in an oak-dominated stand and lowest in a pine-dominated stand, integrated annual rates of NEP are similar among oak-, mixed and pine-dominated stands. Our research documents the formation of mixedwood stands as a consequence of insect infestations in the mid-Atlantic region and suggests that managing for mixedwood stands could reduce damage to forest products and provide greater continuity in ecosystem functioning.

Feature-dependent group structures and hierarchical songbird-habitat relationships in a managed forest landscape

We examined the importance of local habitat features on forest songbird distributions using a feature-dependent group framework that organizes species in relation to variable importance of species-habitat relationships. Habitat features included vegetation structure, floristics, and environmental (i.e., topography) classes. We also examined evidence for hierarchical habitat selection by assessing feature positioning within the ensemble structural models, Random Forests. From the 44 species examined, we distinguished 14 groups, comprising two to eight species per group, and examined variation in habitat importance across the groups. Overall, floristic species turnover, shrub density, canopy height, and tree basal area were among the most important features. On average, however, no specific feature class was more important than the others across the entire collection of species. Instead, we interpreted group partitioning to occur primarily by species differentiating among specific forest types, such as bottomland riparian or oak-dominated (Quercus spp.) stands, and species responding to structural variation across successional gradients. The positioning of habitat features within individual tree models showed that for those species among specific forest types, floristics features were selected first in the models followed by environmental features. Whereas when vegetation structural features were most important, structural features were typically selected first followed by floristics. The large variability in responses likely reflects the large heterogeneity in vegetation structure and composition present in our Central Hardwood, USA, forest landscape. In such cases, avian community assembly processes incorporated the primary moisture (mesic-xeric tree species) and successional (open- to closed-canopy) vegetative gradients of these forestlands, which underscores the importance of maintaining vegetation heterogeneity under accelerating environmental change. By including diverse suites of habitat types, we demonstrate how these features vary in their importance across songbird assemblages in a diverse forestland and identify key habitat features in the conservation of these bird communities.

Metabarcoding of canopy arthropods reveals negative impacts of forestry insecticides on community structure across multiple taxa

Abstract Insecticides used to combat outbreaks of forest defoliators can adversely affect non‐target arthropods. Forestry insecticides typically suppress Lepidoptera larvae which are the cornerstone of the canopy community of deciduous oak forests. The abrupt removal of this dominant component of the food web could have far‐reaching implications for forest ecosystems, yet it is rarely investigated in practice owing to several methodological shortcomings. The taxonomic impediment and the biased nature of arthropod sampling techniques particularly impede the assessment of insecticide impacts on diverse communities. To tackle this issue, we propose an experimental approach combining sampling by pyrethrum knockdown and species determination via DNA metabarcoding, using community subsampling to derive estimates of species abundances. We applied this protocol to investigate the short‐term effects of the insecticides diflubenzuron (DFB) and Bacillus thuringiensis var. kurstaki (BTK) on canopy‐dwelling arthropod communities in German oak woodlands. Our approach allowed us to detect most of the diversity and integrate species abundances in our analyses. By classifying arthropod species into assemblages based on their expected sensitivity rather than coarse taxonomic groupings, we could unveil substantial effects of DFB across multiple taxa 5 weeks after application. Although strong effects on single species appear related to direct toxicity, substantial impacts of DFB on parasitoids and xylophagous beetles suggest that anti‐defoliator treatments can have previously unsuspected indirect effects on some components of forest arthropod communities. The impacts of BTK on community structure were consistent with that of DFB though much weaker. Synthesis and applications. Comparing diversity patterns in the arthropod communities of sprayed and unsprayed oak canopies, our results show that selective insecticides can alter species diversity in presumably non‐sensitive taxa. Even though the ecological significance of these impacts has yet to be assessed in an operational setting, their existence calls for increased regulatory scrutiny on indirect effects. As community approaches become more attainable with the rapid development of DNA metabarcoding, we suggest the inclusion of community‐level end points as regulatory requirements for the approval of forest‐use insecticides.

Beech and hornbeam dominate oak 20 years after the creation of storm-induced gaps

Oak (Quercus petraea (Matt.) Liebl. and Quercus robur L. grouped), European beech (Fagus sylvatica L.) and hornbeam (Carpinus betulus L.) are three major species of western and central European forests. When conditions are suitable for the three species, silvicultural management often favours oak because of its greater economic interest. Forest managers know that beech and hornbeam are strong competitors for oak during the regeneration phase, but the conditions that influence the relative success of the regeneration of the three species growing in mixture are still poorly characterised. The natural regeneration of the three species 20 years after canopy openings was studied based on 108 study sites established in 2001 in French forests impacted by the windstorms Lothar and Martin in 1999. In spring and summer 2018 and 2019, all saplings over 0.1 m in height were counted, species were identified and diameter at breast height (DBH) was measured for all saplings over 1.30 m. The height of the saplings with the highest and median DBH in each plot was recorded for each species. Mixed models were used to analyse the combined effects of former stand type, distance from the edge of the gap and soil conditions on species presence, sapling abundance, DBH and height. The modelling approach highlighted the preponderant role of the initial seed rain on the presence and sapling density of the three species compared to interspecific competition or distance from the edge. The two latter factors had a secondary effect on sapling DBH and height. Beech and hornbeam saplings were more abundant than oak saplings regardless of soil conditions (on average, 3097, 3063 and 344 saplings ha−1, respectively), suggesting a strong competitive ability of these two species. Oak was present on 22% (43% for hornbeam and 68% for beech) of the studied plots, at a low density but with a height and DBH similar to that of beech or hornbeam. This result highlights the high dissemination capacity of beech and hornbeam, which prevents the establishment of a stand dominated by oak. When seeking to obtain oak-dominated stands in the lowlands of Europe, the abundance of beech and hornbeam can be a limiting factor that could lead to the disappearance of oak from large areas if no silvicultural operations are performed to promote it.

Stand conditions alter seasonal microclimate and dead fuel moisture in a Northwestern California oak woodland

Fuel moisture exerts considerable influence on fire behavior and effects but varies substantially spatially and temporally. A portion of the spatial variation in dead surface fuel moisture of woodland and forest ecosystems is likely attributed to differences in stand conditions (i.e. stand density and composition). Existing evidence suggests that the role of stand conditions on dead surface fuel moisture is inconsistent across studies and more research examining the effects of stand conditions on seasonal microclimate and fuel moisture is needed. This study examined the effects of different stand conditions within Oregon white oak (Quercus garryana) woodlands and forests, including intact oak-dominated stands without Douglas-fir (Pseudotsuga menziesii), oak stands that have been invaded by Douglas-fir (encroached), and thinned stands with Douglas-fir removed within Oregon white oak ecosystems of northern California on seasonal variation of microclimate and dead surface fuel moisture. Stand condition had a strong effect on microclimate and fuel moisture over time with thinned stands consistently having warmer and drier conditions with lower fuel moisture than encroached stands in most surface fuel components. Differences in fuel moisture among stand conditions were most pronounced in the late spring and early fall. Observed fuel moisture values did not correlate well with estimates from remotely automated weather stations or process-based calculations, especially when observed fuel moisture values exceeded 20%. Collectively, these findings provide strong evidence that stand conditions can modify microclimate that contributes to variation in dead surface fuel moisture within Oregon white oak ecosystems of northern California. These differences are often not considered within commonly used fuel moisture estimates, emphasizing the need to develop better models and tools to allow managers to more accurately anticipate fuel moisture conditions in varying stands to model landscape variation in fire behavior and effects and to meet fuel reduction and restoration objectives.

Effects of forest management on bird assemblages in oak-dominated stands of the Western Carpathians – Refuges for rare species

Forest management practices have varying impacts on biodiversity because the treatments and their outcomes do not always reflect the natural processes that maintain biodiversity. These management activities can be assessed using indicator species, among which birds are most frequently used. In 2018 we compared bird assemblages in oak (Quercus spp.)-dominated forests with admixtures of European beech (Fagus sylvatica), hereafter referred to as oak-beech forests, between managed and natural forest stands on opposite sides of the Carpathian range (south-facing in Slovakia and north-facing in Poland). The aim was to quantify and model the relationships between the quantitative parameters of bird assemblages and the main habitat parameters, as influenced by differing intensities of forest management. The point-count method with limited distance was applied to census birds (N = 100). Overall forest bird assemblages were found to be similar in respect to diversity indexes in managed and protected areas, as well as between southern and northern slopes of the Western Carpathian range, but all these types of forest differed in respect to bird species composition. However, both geographic location and management intensity, altogether with forest complexity contributed the mostly in explanation of bird diversity. The greatest differences were recorded for rare species, particularly those annexed in the Birds Directive of the European Union (mainly woodpeckers and flycatchers), as these birds were found either exclusively or in much greater numbers in nature reserves. Management intensity, forest complexity, and topography best explained the diversity of rare birds. Silvicultural systems applied in management of the Carpathian oak-beech forests, particularly the shelterwood system, seem to be sufficient for the preservation of overall bird diversity. However, decreased forest fragmentation and increased deadwood amounts are necessary measures to provide more close-to-nature stand structures, which will help support higher diversity of most bird species associated with mature forests. Because the oak-beech forests comprises only about 15% of the total forest area in the Western Carpathians, creating a network of natural or close-to-nature forest patches is recommended for the conservation of forest birds (and whole forest communities), including species annexed in the Birds Directive. Conservation priorities should be focused mainly in areas of harsh topography, where reduced wood production in these forests would have a less detrimental effect on the local forestry communities. These actions should also greatly improve the nature conservation system in the Carpathians and more generally throughout Central Europe.

Effect of Prescribed Fire on Timber Volume and Grade in the Hoosier National Forest

AbstractLow-intensity surface fire is prescribed in eastern North American hardwood stands prior to overstory harvest in order to improve regeneration and recruitment of oak and other fire-tolerant and fire-adapted species. However, this use of prescribed fire potentially can reduce timber value. We inventoried overstory trees (>10 in. diameter at breast height) in 54 oak-dominated stands with varied prescribed fire histories and aspects in southern Indiana. We then documented the extent of prescribed fire damage (i.e., wounds) to overstory trees and quantified both the relative stand volume of timber loss and the proportion of trees that had tree grade reductions because of prescribed fire. Generally, as a stand received more prescribed fires, more trees were scarred, the relative volume lost increased, and a higher proportion of trees declined in grade. Overall, burned stands experienced less than 10 percent sawtimber volume loss, regardless of the number of prescribed fires and aspect. Less than 3 percent of trees, study-wide, had reduced grade because of prescribed fire. Grade and volume reductions varied by species, however. Our results suggest that prescribed fire has a minor economic impact on standing timber, particularly when timber is harvested within two decades of the first fire.

Hygrophorus yukishiro sp. nov., a new vernal edible mushroom from Nagano Prefecture, Japan

A novel basidiomycetous species, Hygrophorus yukishiro, is described from Japan. The basidiomata of this fungus have been referred to as “yuki-shiro”, “yuki-take”, and “yuki-wari”, and used as an edible mushroom in the central region of Nagano, Japan. Hygrophorus yukishiro fruits in the early spring season under oak-dominated stands. Morphological and phylogenetic analyses of the internal transcribed spacer region of the nuclear ribosomal RNA gene indicated that H. yukishiro is a sister species of H. arbustivus and belongs to section Hygrophorus, subsect. Fulventes. Hygrophorus yukishiro is similar in its external morphology and fruiting phenology to H. roseobrunneus, H. leucophaeo-ilicis, and H. roseodiscoideus, but differs in the color and texture of its pileus surface and microscopic characteristics.

Spatial modeling and inventories for prioritizing investment into oak-hickory restoration

Oak (Quercus spp.) and hickory (Carya spp.) forests in the eastern United States provide a host of ecosystem services as their mast are prized by wildlife, the timber is a valued commodity, and they are generally more tolerant of extreme weather events under a changing climate. They are, however, undergoing a severe decline in prominence throughout the region, yielding to more mesic and shade-tolerant species, largely red maple (Acer rubrum). Two decades of research in Ohio have shown that silviculture and/or natural disturbances that reduce understory shade during seedling establishment and early growth, followed by canopy opening and competition management through prescribed fire and partial cutting, can encourage oak and hickory regeneration, most successfully on drier ridges and south- and southwest-facing slopes. We employed an ecological classification and mapping approach to prioritize areas across a 17-county region (∼22,000 km2) that may be more receptive, and thus more cost effective, to successful oak regeneration following silvicultural treatment. The ecomapping effort was comprised of two parts; a GIS model of the terrain, and a stand inventory of current vegetation condition coupled with the SILVAH decision-support system to recommend needed silvicultural treatments. The GIS model is based primarily on topography as vegetation patterns in the project area are largely driven by landscape position and soil moisture regimes. It uses transformed aspect, slope angle, topographic position index, and slope position as inputs to define six classes of landtype phases: ridge, southwest upper slopes, southwest lower slopes, northeast upper slopes, northeast lower slopes, and bottomland. The first three and following two classes, respectively, were hierarchically nested to form Dry Oak Forest and Dry-mesic Mixed Oak Hardwood Forest classes at the landtype level. Dry Oak Forests require the least silvicultural intervention to sustain or restore oak, while the other two landtypes normally require serious intervention to sustain oak into the future. To determine whether sufficient stocking is present for adequate regeneration, we use forest inventory data to represent current vegetation conditions including both overstory and understory stocking. Overall, these tools allow managers to identify ‘zones of investment’, i.e., those stands with the bulk of the area in the Dry Oak Forest landtype and with some level of advance oak regeneration, which will have a greater likelihood of growing into oak-dominated stands with minimal investment of scarce funding resources.

Effect of climate and intra- and inter-specific competition on diameter increment in beech and oak stands

Differences between intra- and inter-specific competition strategies in mixed stands account for higher productivity. The mechanisms of competition as they relate to stand structure remain poorly explored. Climatic effects have also been overlooked in most approaches aimed at studying tree growth. These effects were investigated through the case study of beech-oak mixtures in France. A single-tree diameter-increment mixed model was fitted to data gathered from the Laboratoire d'Etude des Ressources Foret-Bois (LERFoB) network of permanent plots. In order to take stand structure into account, the model was able to distinguish between inter-and intra-specific competition at tree level. Differences in intra-and inter-specific competition are mainly detected in the understorey of oak-dominated stands, where suppressed beech trees performed better than suppressed oak trees. From a climatic point of view, diameter increment was sensitive to the mean temperature of the vegetative period. Concerning competition, our results demonstrate that optimal growth induced by mixtures is not only a matter of species proportion but also depends on stand structure. Regarding climatic effects, they need to be considered in growth predictions, especially given the future climatic conditions predicted for continental Europe. These findings could serve as guidelines for designing strategies to alleviate stress in oak-beech stands.

Effects of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) on understorey layer species diversity in managed forests

In total, 67 parallel plots were chosen from the database of 153 phytosociological relevés made in the Douglas-fir and parallel Norway spruce, European Beech and oak-dominated stands to find influences of this introduced tree species on the understorey layer in totally 12 localities in the whole Czech Republic territory. Douglas-fir stands influence their habitats, which was indicated by species composition changes in the ground vegetation, as well as by abundance and dominance of particular species. Douglas-fir cultivation increases species diversity of the stands, but decreases their abundance. Described differences in understorey are not so noticeable when European beech and sessile oak stands are substituted by Douglas-fir once. But even the significant phenomenon of striking nitrophilous species such as Geranium robertianum, Urtica dioica and Galium aparine occurs here. This indicates a high content of available nitrates in the humus and top-soil horizons.  

Community phylogenetic diversity and abiotic site characteristics influence abundance of the invasive plant Rhamnus cathartica L.

Aims Theory predicts that the success of introduced species is related to the diversity of native species through trait-based processes. Abiotic site characteristics may also affect a site’s susceptibility to invasion. We quantified resident plant species richness, phylogenetic diversity and several abiotic site characteristics for 24 oak forests in Minnesota, USA, to assess their impact on the abundance of a widespread, introduced terrestrial plant species, common buckthorn (Rhamnus cathartica L.). Specifically, we asked (1) whether resident species richness and phylogenetic diversity affected the abundance of R. cathartica and (2) what site characteristics explained the overall abundance of R. cathartica. Methods Our survey included 24 oak-dominated stands in Minnesota’s deciduous forests. In each stand, we identified all species in 16 plots. We also measured a series of environmental site characteristics, including canopy openness (a proxy for light availability), percent bare soil, soil pH, percent sand, an index of propagule availability, duff layer thickness (a proxy for earthworm activity), an index of insolation and slope. For all species present in at least one site, we estimated a community phylogeny. We combined all sitelevel characteristics, including phylogenetic diversity of the resident plant species, in a multiple regression model to examine site level drivers of community invasibility. Important Findings Results indicate that sites with higher overall plant phylogenetic diversity harbor less R. cathartica, even though native species richness was not significantly related to R. cathartica abundance. Regression analyses indicated that, in addition to resident species phylogenetic diversity, the most important predictors of R. cathartica abundance were canopy openness and the amount of bare soil, both positively related to the abundance of the invader. By combining the effects of abiotic site characteristics and resident species phylogenetic diversity in a model that predicted the abundance of R. cathartica, we were able to simultaneously account for a wide range of factors that might influence invasibility. Overall, our results suggest that management strategies aimed at reducing disturbances that lead to increased bare soil and light levels may be more successful if they also maximize phylogenetic diversity of the resident plant community.

Effects of timber harvest intensity on macronutrient cycling in oak-dominated stands on sandy soils of northwest Wisconsin

In Wisconsin there is concern that timber harvesting on nutrient-poor, sandy soils could lead to depletion of nutrients. This concern could become exacerbated by the increasing demand for biofuels, followed by intensified utilization practices. This project measured dry matter and macronutrient (N, P, K, Ca, and Mg) pools and major inputs (bulk precipitation, weathering+mineralization index) and outputs (leaching losses) on four treatment plots at each of five sites on sandy soils at the Governor Knowles State Forest in northwest Wisconsin: an unharvested treatment, a conventional removal of stem and branches down to a diameter of 5cm, a removal of stem and branches down to a diameter of 10cm, a removal of all aboveground biomass. All treatments were applied during the early winter, leaf-off period. Data collected over 2years (2010 and 2011) were applied to a nutrient-balance equation to determine if there were treatment-related differences in nutrient accumulation or depletion. The labile soil was the leading pre- and post-harvest pool for P, K, Ca and Mg in the ecosystem. Biomass removed during Whole-tree harvests constituted ∼50% of the ecosystem nitrogen and contributed significantly to the removal of the other macronutrients. From nutrient input–output balances, N (NH4 and NO3), K, Ca, and Mg were calculated to be accumulating on all harvest treatments. During the first year after harvest (2010), N mineralization, along with P and Ca accumulation rate, was significantly greater than unharvested treatments. Nitrogen accumulation rates, along with leaching losses of N and P, were significantly lower on all harvest treatments than on unharvested treatments. There were no significant differences in mineralization rates and leaching losses among treatments for the other macronutrients. During the second year (2011), differences in N mineralization, leaching and accumulation rates had largely disappeared. Phosphorus was the only nutrient that showed a net depletion, and this depletion was detected for all harvested treatments. However, the depletion rates were so low that it would take several rotations for any P deficiencies to become apparent. The results of this study may not apply to other sandy soils.