Pine-oak Stands Research Articles

Carbon mapping in pine-oak stands under timber management in southern Mexico.

The destructive and empirical methods commonly used to estimate carbon pools in forests managed timber are time-consuming, expensive and unfeasible at a large scale; satellite images allow evaluations at different scales, reducing time and costs. The objective of this study was to evaluate the tree biomass (TB) and carbon content (CC) through satellite images derived from Sentinel 2 in underutilized stands in southern Mexico. In 2022, 12 circular sites of 400 m2 with four silvicultural treatments (STs) were established in a targeted manner: 1st thinning (T1), free thinning (FT), regeneration cut (RC) and unmanaged area (UA). A tree inventory was carried out, and samples were obtained to determine their TB based on specific gravity and CC through the Walkey and Black method. The satellite image of the study area was downloaded from Sentinel 2 to fit a simple linear model as a function of the Normalized Difference Vegetation Index (10 m pixel-1) showing significance (p≤0.01) and a adjusted R2 = 0.92. Subsequently, the TB and CC (t ha-1) were estimated for each ST and managed area. The total managed area (3,201 ha-1) had 126 t TB ha-1 and 57 t C ha-1. Of the areas with STs, the area with FT showed the highest accumulation of TB (140 t ha-1) and C (63 t ha-1) without showing differences (p>0.05) with respect to those of the UA, which presented 129 t TB ha-1 and 58 t C ha-1. The satellite images from Sentinel 2 provide reliable estimates of the amounts of TB and CC in the managed stands. Therefore, it can be concluded that an adequate application of STs maintains a balance in the accumulation of tree C.

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.

Historical Fire Regimes and Stand Dynamics of Xerophytic Pine–Oak Stands in the Southern Appalachian Mountains, Virginia, USA

Fire-dependent yellow pine (Pinus) forests are included within the temperate deciduous forest of eastern North America. These forests, which occupy dry slopes and typically contain xerophytic oaks (Quercus), have receded under fire suppression. Understanding historical fire regimes is essential for interpreting and managing these stands. To characterize fire history and vegetation dynamics, we conducted a dendroecological study of fire-scarred trees and age structure in pine stands at four sites in the Appalachian Mountains. Fire interval estimates suggest that before fire suppression began in the early to middle 1900s, fires occurred at approximately three- to eleven-year intervals. Short intervals were probably maintained in part by large-extent fires that spread from sparse ignition points. Fire frequency showed no long-term temporal trend (e.g., no wave of fire) from the middle 1700s through early 1900s despite land–use intensification, including industrial logging and associated wildfires during the late nineteenth and early twentieth centuries. Fire occurrence was associated with drought at two sites. Age–structure analyses evoke pyrogenic pine–oak communities that predated industrial disturbances and persisted under a regime of frequent, mixed-severity fires that was likely maintained through a positive feedback with the flammable vegetation. Competing species were established under more recent fire suppression, however, and are poised to replace the pines.

Simulating the effects of thinning and species mixing on stands of oak (Quercus petraea (Matt.) Liebl./Quercus robur L.) and pine (Pinus sylvestris L.) across Europe

Tree species mixing of oak (Quercus petraea (Matt.) Liebl./Quercus robur L.) and pine (Pinus sylvestris L.) has been shown to have positive effects on ecosystem service provision. From a management perspective, however, it is still uncertain which thinning regime provides the highest possible productivity of mixed oak–pine forests in the long term. Because of a lack of empirical studies dealing with thinning and species mixing effects on oak–pine forests, we simulated forest growth in order to test which thinning type and intensity may provide the highest productivity in the long-term. To achieve this, we simulated the growth of pure and mixed stands of oak and pine for 100 years in 23 triplets located on an ecological gradient across Europe. For this purpose, we applied four different growth simulators and compared their results: the distance-independent single-tree simulator PROGNAUS, the distance-dependent single-tree simulator SILVA, the gap model ForCEEPS, and the process-based simulator 3D-CMCC-FEM. We investigated the effects of species mixing and thinning from the upper (thinning from above) and lower tail (thinning from below) of the diameter distribution by reducing the stand basal area to 50 and 80% of the maximum basal area. We compared simulated results of the relative volume productivity of mixed versus pure stands and of thinned versus unthinned stands to empirical results previously obtained on the same set of triplets. Simulated relative volume productivity ranged between 61 and 156%, although extremes of 10% and of 300% could be observed. We found the relative volume productivity to be influenced by stand age, but not by stand density, except for PROGNAUS. Relative volume productivity did not increase with the site water supply of the triplet location. Highest long-term productivity for oak, pine and oak–pine stands can be expected in consequence of thinning from above, but the effect of thinning intensity differed between simulators. Thinning effects were positively affected by stand density, but not by stand age, except for thinning from above predicted by PROGNAUS. Predicted thinning effects showed good approximation of results from thinning experiments for oak, but not for pine stands. We hypothesize the results might be caused by the insufficient simulator representation of climate and its interaction with other site variables and stand structure. Further work is needed to reduce the revealed limitations of the existing growth models, as we currently see no alternative to such kind of studies and simulators.

Ecological-coenotic features of rare flora species of pine-oak stands of Volyn Polissya

Anthropogenic influence on the natural vegetation of Volyn Polissya threatens the existence of habitats of rare and endangered species of flora. Therefore, the region, unique in botanical and geographical terms, is gradually losing its specific vegetation characteristics. Having analyzed the literature data, herbarium data and materials of our own field studies in 2016-2019, we have compiled a list of rare and endangered species of pine-oak stands. In the habitat of pine-oak stands 89 rare species were found, 29 of which are listed in the Red Data Book of Ukraine, while Silene lithuanica is included in the European Red List. 3 species (Cypripedium calceolus, Trapa natans та Caldesia parnassifolia) are included into appendices of “The Convention on International Trade in Endangered Species of Wild Fauna and Flora”. 10 species are subject to protection according to the appendix of “Convention on the Conservation of European Wildlife and Natural Habitats” 56 species are regionally rare species for the flora of the Volyn region, 4 species are rare species of pine-oak stands. In our research we have analyzed the age range, density and recovery index for the species studied. The study found that for 63 rare species the dynamics of species abundance and distribution are satisfactory. The area of distribution and the number of 7 species is increasing: Allium ursinum, Galanthus nivalis, Platanthera chlorantha, Anemone sylvestris, Campanula persicifolia, Corydalis cava, Isopyrum thalictroides In the study area 14 species grow sporadically: Juniperus communis, Potentilla alba, Digitalis grandiflora, Gymnocarpium dryoptheris, Daphne mezereum, Neottia nidus-avis, Epipactis helleborine, Scorzonera purpurea, Asparagus officinalis, Iris sibirica, Adonis vernalis, Cephalanthera damasonium, Gentiana cruciate, Gentiana pneumonanthe. Dissemination information for Caldesia parnassifolia, Succisella inflexa, Genistella sagittalis, Salix myrtilloides, Ophioglossum vulgatum is insufficient for establishing species dynamics and needs further investigation. The conservation of pine-oak stands in Volyn Polissya will help to create the conditions for the growth of rare and endangered species of flora.

Physicochemical properties of soils in the forest-park stands of Kyiv city

Physicochemical properties of soils in the forest-park stands of Kyiv city

Transgressive overyielding in mixed compared with monospecific Scots pine (Pinus sylvestris L.) and oak (Quercus robur L., Quercus petraea (Matt.) Liebl.) stands – Productivity gains increase with annual water supply

Tree species mixing has become a crucial tool in European forest management as positive interactions between species have been found to promote the provision of multiple ecosystem services, while at the same time reducing the risks associated with climate change. However, mixing effects have proven to be strongly context-dependant and some species combinations have still not been studied in detail. Here we focus on mixed forests of Scots pine and oak, which are likely to become increasingly popular for balancing wood production and other ecosystem services under climate change. Using 20-year growth data from newly established triplets in Germany and Denmark, this study investigates how mean tree and stand characteristics as well as productivity in mixed Scots pine-oak stands compare with adjacent monocultures and how stable the observed productivity relation is, considering inter-annual variations in local climate. Species mixing on average resulted in 15% higher standing volume and 14% higher volume productivity compared with the weighted mean of the adjacent monocultures. Oak profited most in mixture, showing overyielding of 19%. Overyielding on the stand and species level increased in years with higher water supply. In mixture, standing volume of Scots pine was 25% higher than in monocultures. Both species were found to modify their morphology in mixture. Oak in mixture showed a significantly higher inequality in stem volume compared with monocultures. We hypothesise that the observed overyielding of Scots pine-oak mixtures mainly results from complementary light use, where differences in shade tolerance, crown architecture and leaf phenology may be contributing factors.

Northward expansion of southern pine beetle generates significant alterations to forest structure and composition of globally rare Pinus rigida forests

Southern pine beetle (SPB; Dendroctonus frontalis Zimmerman), a native insect that has historically affected pine (Pinus spp.) ecosystems in the southeastern U.S., has recently expanded northward causing extensive tree mortality in pitch pine (P. rigida) and pitch pine-oak (Quercus spp.) forests of eastern Long Island, NY. Given the historic lack of SPB within this region, little is known regarding its potential impacts. This study examined the immediate effects of SPB-induced tree mortality and management (i.e., cut-and leave suppression) on the structure and composition of affected forest communities to inform management recommendations and projections of future forest conditions. Overstory pine basal area declined significantly following SPB infestation and management (67–100% mortality), although management partly mitigated these effects. There was no immediate impact of SPB or management on seedling and sapling density or composition, with hardwood species making up the majority of this layer and pine representing <6% of stems regardless of mortality agent. Pitch pine was less likely to be browsed by ungulates than white oak and scarlet oak. SPB infestation significantly increased snag basal area, whereas downed woody debris volumes were greatest following management. Understory community composition in pitch pine stands that had SPB or were managed had greater understory plant diversity largely through a higher abundance of disturbance-adapted species. There was less between-site variation in understory species assemblages in pine-oak forests experiencing pitch pine mortality and an increase in regeneration of pitch pine and scarlet oak in these areas. Collectively, the short-term results suggest SPB could functionally eliminate pitch pine from infested stands in the absence of additional management, and that management in pine-oak stands may exacerbate this trend, leading to increasing dominance of hardwoods species in pine barren communities. Based on our results, fuels reduction treatments combined with site-specific restoration of barrens structure and composition may be useful in maintaining stands with lower fire hazard and greater resilience to this new threat.

Mortality of eastern white pine (Pinus strobus L.) in association with a novel scale insect-pathogen complex in Virginia and West Virginia

Concerns about the health of eastern white pine (Pinus strobus L.) exist throughout its range in the eastern United States due to a variety of causal factors. In the central and southern Appalachian Mountains, a novel and poorly understood dieback phenomenon has been attributed primarily to a scale insect, Matsucoccus macrocicatrices Richards, and a putatively weak fungal pathogen, Caliciopsis pinea Peck. While the nature of this scale-pathogen complex and associated stem and branch cankers is still being explored, quantitative information on the extent of damage to the white pine resource has been lacking. Monitoring plots were established in Virginia and West Virginia beginning in 2012 to assess changes in live and dead volume of white pine. Most sites consisted of uneven aged, mixed oak-pine stands. No significant changes in stand volume were evident, likely because no large trees within the plots died during the study period. Mortality in sapling and pole-sized trees appeared elevated, however. Density dependent mortality associated with natural stand self-thinning was distinguished from density independent mortality associated with the scale-pathogen complex by establishing a baseline mortality for white pine age cohorts. Baseline mortality for each 2-cm diameter class was estimated to be approximately 12% based on the aggregate study site data, and 13–14% based on US Forest Service Forest Inventory and Analysis (FIA) data. Observed mortality within plots was then compared to baseline mortality using chi-square analysis. During the initial measurement years, observed mortality was significantly greater than baseline mortality for only the 4–6 cm diameter class. After 5 years of monitoring, observed mortality was significantly greater than baseline for five diameter classes, including 4–6, 6–8, 8–10, 14–16, and 24–26 cm. The two smallest diameter classes of these five had observed mortality over 30%, on average, while the other three classes averaged over 20% mortality. If these trends continue over time, white pine abundance or sustainability could eventually be compromised as mature trees gradually die and fewer cohorts of young trees are available to replace them.

Influence of forest tree species composition on bryophytic diversity in mixed and pure pine (Pinus sylvestris L.) and oak (Quercus petraea (Matt.) Liebl.) stands

Abstract The effects of mixed stands on biodiversity are increasingly being studied since they are supposed to offer higher habitat heterogeneity. Nevertheless, for tree-associated diversity, including epiphytes and terricolous species near tree trunks, few studies exist, and still fewer compare mixed stands with each corresponding pure tree species stand. We evaluated and quantified the influence of forest composition on tree-associated bryophyte diversity (species richness, abundance, composition) in mixed and pure oak-pine stands in a French lowland forest. The main explanatory variables for bryophyte diversity at tree-level were the identity of the phorophyte tree species and the mixture type (pure versus mixed). At the plot level, the main explanatory variable was the stand type (pure oak, pure pine and mixed). We also explored the role of other variables including the chemistry of the bryophyte substrates (soil, bark) and water supply (stemflow, throughfall), as well as stand abundance variables (basal area, interfering plant cover). We analyzed data with Generalized Linear Models under Bayesian statistics, to take into account the spatial autocorrelation between plots and any under- or over-dispersion of our data. At the tree-level, bryophyte richness and abundance were higher on oak than on pine. Pine bryophyte richness was higher in mixed compared to pure stands, whereas for oak, mixed stands did not enhance bryophyte richness. At the plot level, mixed stands hosted bryophyte communities of similar richness to those in pure oak stands, whereas pure pine stands were clearly poorer. Our exploratory models suggested strong effects of water supply chemistry (stemflow and throughfall pH or conductivity) and basal area; the latter had a strong quadratic effect on epiphytic richness at the plot level. In terms of composition, three species were more likely to be found on pine phorophytes, seven species clearly occurred more frequently on oaks. Some species were more likely to be associated to pine in mixed than in pure stands, and one species was found more often under pines in pure stands. Therefore, bryophyte diversity at the landscape level should benefit from the simultaneous presence of the three stand composition types – pure oak, pure pine and mixed stands.

Thinning enhances the species-specific radial increment response to drought in Mediterranean pine-oak stands

Radial increment analyses allow us to determine tree responses to weather and tree competition, thus enabling the development of management strategies for adapting forest stands to forecasted climate change scenarios. In this study, the responses of pine-oak mixed stands (Pinus pinaster Ait. and Quercus pyrenaica Willd.) to thinning treatments were assessed at two sites in central Spain with contrasting drought conditions. Inter- and intra-annual radial increments were recorded every two weeks from dendrometer band measurements, using a Latin square design. Each site consisted of a control (unthinned) and two thinning intensities: moderate (25% of pine basal area removed) and heavy (40% of pine basal area removed). Thinning effects were monitored over three years of different weather conditions (2010–2012), with an extreme drought event in 2012. Linear mixed models were fitted to analyze weather and thinning effects on the inter- and intra-annual radial increment rates. Additionally, the sum of two logistic functions was used to estimate cumulative radial increment patterns. Heavy thinning resulted in the greatest annual radial increment for pine, regardless of site and year, even during the 2012 drought, when compared to densely stocked forest stands. The model results indicated that heavy thinning positively affected the intra-annual pattern, increasing inflection point and spring and autumn asymptotes. Thinning also had a slight positive effect on inter- and intra-annual radial increment in oak, although this was not clear during extreme drought in 2012. The radial increment rate was related to weather variables, which reflected light (positive for solar radiation) and water availability dependence (increased with precipitation, but decreased with vapor pressure deficit) for both species. Besides water status, air humidity (positive relation with air temperature and relative humidity) also affected oak. Reducing competition by thinning stimulated radial increment in oak-pine mixed stands, which may provide an adaptive forest management tool for reducing tree vulnerability to extreme droughts, which are linked to climate change.

Do shrubs facilitate oak seedling establishment in Mediterranean pine forest understory?

Shrubs have been shown to facilitate tree seedling establishment in open Mediterranean ecosystem habitats, but their effects in forests have been much less explored. We investigated the role played by shrubs in seedling emergence, survival and growth for two co-occurring oak species – Quercusilex and Quercuspubescens – in the understory of clear Aleppo pine stands (10m2/ha). Acorns of both species were sown in two sites in South-East France that contrasted in terms of former land-use (pastoral vs agricultural), soil thickness (shallow vs deep) and type of understory (shrubs+grass vs only shrubs). Oak seedlings had a higher survival and growth on the former agricultural site with deeper soil. In general, the more stress-tolerant Q. ilex performed better than Q. pubescens. In the harsher site, seedling survival decreased with grass cover but increased with shrub cover. Shrub and grass cover decreased seedling diameter and had no effect on seedling height. In the more fertile site, shrub cover had no influence on seedling survival but had a species-specific effect on seedling growth: shrubs mostly competed with Q. ilex but ameliorated Q. pubescens growth, leading to changes in the two species performance ranking at high shrub cover. We conclude that shrubs can act as nurses for oak seedling establishment in pine forest understory, particularly in harsh conditions and for stress-intolerant species. In harsh conditions, shrub cover should be factored in as a way to promote pine forest diversification toward mixed pine–oak stands.

Carbon content of forest floor and mineral soil in Mediterranean Pinus spp. and Oak stands in acid soils in Northern Spain

Aim of study: The aim of the study was to determine the baseline carbon stock in forest floor and mineral soils in pine and oak stands in acid soils in Northern Spain.Area of study: The study area is situated in northern Spain (42° N, 4° W) on “Paramos y Valles” region of PalenciaMaterial and methods: An extensive monitoring composed of 48 plots (31 in pine and 17 in oak stands) was carried out. Litter layers and mineral soil samples, at depths of 0-30 cm and 30-60 cm, were taken in each plot. An intensive monitoring was also performed by sampling 12 of these 48 plots selected taken in account species forest composition and their stand development stage. Microbial biomass C (CMB), C mineralization (CRB), and soil organic C balance at stand level were determined in surface soil samples of intensive monitoring.Main results: No differences in soil C content were detected in the two forest ecosystems up to 60 cm depth (53.0±25.8 Mg C ha-1 in Pinus spp. plantations and 60.3±43.8 Mg C ha-1 in oak stands). However, differences in total C (CT), CMB and CRB were found in the upper 10 cm of the soils depending on the stand development stage in each species forest composition (Pinus nigra, Pinus pinaster, Pinus sylvestris and Quercus pyrenaica). Plots with high development stage exhibited significant lower metabolic quotient (qCO2), so, meant more efficient utilization of C by the microbial community. The C content in the forest floor was higher in pine stands (13.7±0.9 Mg C ha-1) than in oak stands (5.4±0.7 Mg C ha-1). A greater turnover time was found in pine ecosystems vs. oak stands. In contrast, forest floor H layer was nonexistent in oak stands.Research highlights: Results about litterfall, forest floor and mineral soil dynamics in this paper can be used strategically to reach environmental goals in new afforestation programs and sustainable forest management approaches.Keywords: C stocks; pine; Quercus pyrenaica; litter; metabolic quotient (qCO2).

Modeling of Two Different Water Uptake Approaches for Mono- and Mixed-Species Forest Stands

To assess how the effects of drought could be better captured in process-based models, this study simulated and contrasted two water uptake approaches in Scots pine and Scots pine-Sessile oak stands. The first approach consisted of an empirical function for root water uptake (WU1). The second approach was based on differences of soil water potential along a soil-plant-atmosphere continuum (WU2) with total root resistance varying at low, medium and high total root resistance levels. Three data sets on different time scales relevant for tree growth were used for model evaluation: Two short-term datasets on daily transpiration and soil water content as well as a long-term dataset on annual tree ring increments. Except WU2 with high total root resistance, all transpiration outputs exceeded observed values. The strongest correlation between simulated and observed annual tree ring width occurred with WU2 and high total root resistance. The findings highlighted the importance of severe drought as a main reason for small diameter increment. However, if all three data sets were taken into account, no approach was superior to the other. We conclude that accurate projections of future forest productivity depend largely on the realistic representation of root water uptake in forest model simulations.

Seed dispersal by small rodents favors oak over pine regeneration in the pine-oak forests of the Qinling mountains, China

Natural regeneration differences between oak and pine are common in the Qinling Mountains of central China. Thus, we examined whether this difference could be explained by seed dispersal. We investigated the seed dispersal of Quercus aliena var. acuteserrata Maxim. and Pinus tabulaeformis Carr. and the regeneration characteristics of both species were investigated in the pine-oak forest belt (oak stands, pine-oak stands, and pine stands) of Huoditang Forest in the Qinling Mountains in central China. We found that Q. aliena var. acuteserrata acorns were usually scatterhoarded, while seeds of P. tabulaeformis were generally consumed immediately. We found that 55% of the released acorns were transferred to the P. tabulaeformis stands. Moreover, Q. aliena var. acuteserrata regenerated successfully and was recruited in the three forest stands. However, the natural regeneration of P. tabulaeformis was very low in all stands because of high predation by small rodents. We propose, therefore, that the seed dispersal advantage of Q. aliena var. acuteserrata compared with P. tabulaeformis contributed greatly to the regeneration difference between these two species in the pine-oak forest belt of the Qinling Mountains in China.

Effects of vegetation type and fire regime on flammability of undisturbed litter in Southeastern France

To assess the effect of vegetation types and of fire regime on the flammability of dead fuels, samples of litter were collected undisturbed (i.e. keeping the structure of litter layers) in 29 study sites spread over the limestone-derived soils of Provence. The sampling plan comprised the most representative ecosystems of the study area: pure Pinus halepensis stands, mixed pine-oak stands and shrublands. Three classes of litter depth were studied (low, medium and high) to account for the variability existing in the field. Sampling also included the number of fires in each site since 1960 (no fire, 1 or 2 fires and ≥3 fires) and the time interval since the last fire (≤15 years, 15–45 years and >45 years). Flammability experiments were carried out in laboratory using a glowing firebrand and a 10 km h −1 wind. The main variables recorded were: ignition frequency, time-to-ignition, flaming duration, flame rate of spread, flame propagation, mean flame temperature, maximum flame height and rate of consumption. Results showed that the ignition frequency was higher in mixed stands than in pure pine stands whereas the time-to ignition, flaming duration and rate of consumption were the highest in pure pine stands. The maximum flame height and the flame propagation decreased with the increase of the number of fires and the time-to-ignition was the highest when the interval since the last fire was the shortest. Increases in litter depth resulted in increased mean flame temperature, maximum flame height and flame propagation. These results can be explained, in part, by the proportions of the different litter components.

A system for calculating the merchantable volume of oak trees in the northwest of the state of Chihuahua, Mexico

The taper functions of Kozak (1988), Bi (2000) and Fang et al. (2000) were comparatively analyzed in the present paper to develop a system for calculating the merchantable volume of oaks in the northwestern region of the state of Chihuahua (Mexico). Taper data corresponding to 298 trees were collected in mixed and uneven-aged pine-oak stands located throughout the study area, and covering the existing range of ages, stand densities and sites. Results show that the compatible segmented model developed by Fang et al. (2000) best described the experimental data and is therefore recommended for estimating tree diameter at a specific height, height to a specific diameter, merchantable volume, and total volume for oaks. The equation developed in this study is a fundamental tool for use in forest surveys in the study region and is simple enough to ensure its operational implementation. The results of the statistical analysis show that the equation can be recommended for other regions, although some local adaptations may be needed.

Fire-driven oak regeneration in French Mediterranean ecosystems

Regeneration by seeds for cork oak ( Quercus suber) and companion oaks (holm oak Quercus ilex and downy oak Quercus pubescens) is likely to be poor in the fire-prone Maures massif (southern France) but the causes are poorly known. Our objective was to assess the effective recruitment for these three oak species and their temporal pattern of recruitment, in order to determine the main limitation factors and the regeneration window of each species. We studied oak recruits (height <3 m) in naturally regenerated populations according to a gradient of fire recurrence and in five main vegetation types including shrublands and mixed mature woodlands. Fire recurrence was the main explanatory factor of oak recruitment, either directly or through vegetation type and microsite characteristics. The results indicate nil to low recruitment for holm oak and downy oak in shrublands, especially those recurrently burned and dominated by Cistus species. Cork oak recruited better than the other oaks in medium and high shrublands dominated by Erica arborea. In contrast, recruitment was high for holm and downy oak in mixed oak stands and mixed pine-oak stands that have not burned for decades. Microsite conditions such as coverage by litter and shrubs influenced oak recruitment, whereas landscape configuration and stand basal area had no influence. Our results suggest that strategic shrub-clearing, oak planting and protection of mixed oak woodlands as seed sources would help maintaining oak populations in the woodland–shrubland mosaic.

A new arenicolous &lt;I&gt;Boletus&lt;/I&gt; from the Gulf Coast of northern Florida

Boletus abruptibulbus sp. nov. is described as new to science. It inhabits old sand dunes in mixed oak-pine stands across the Gulf Coast of northern Florida.

Tree Mortality in Mixed Pine–Hardwood Stands Defoliated by the European Gypsy Moth (Lymantria dispar L.)

Abstract Defoliation by the European gypsy moth (Lymantria dispar L.) and subsequent tree mortality have been well documented in the northeastern United States. In this study we evaluate tree mortality after initial defoliation in mixed pine–hardwood stands in the southeastern United States as the range of European gypsy moth expands. In 1993, 46 mature pine–oak and pine–sweetgum stands were selected on the coastal plain in Maryland and Virginia along the advancing gypsy moth front. Initial stand conditions, defoliation, and tree mortality after a single defoliation outbreak were monitored for 4 years. Susceptible oaks and sweetgum were defoliated at the greatest intensities. After defoliation, mortality in attacked stands was 4.4 m2/ha higher in pine–oak stands and 1.7 m2/ha higher in pine–sweetgum stands, representing 13 and 3% of the total basal area, respectively. Mortality of pines was observed mainly among suppressed and intermediate trees. Logistic regressions were derived to correlate individual tree mortality to stand and tree factors associated with gypsy moth attack. On the basis of these models, susceptible understory species with degraded crowns in pine–oak stands were at the greatest risk of mortality. Dominant overstory pines in pine–hardwood stands appear to be at low risk.