Oak Density Research Articles

Effects of latitude and conspecific plant density on insect leaf herbivory in oak saplings and seedlings.

Abiotic factors and plant species traits have been shown to drive latitudinal gradients in herbivory, and yet, population-level factors have been largely overlooked within this context. One such factor is plant density, which may influence the strength of herbivory and may vary with latitude. We measured insect herbivory and conspecific plant density (CPD) of oak (Quercus robur) seedlings and saplings along a 17° latitudinal gradient (2700 km) to test whether herbivory exhibited a latitudinal gradient, whether herbivory was associated with CPD, and whether such an association changed with latitude. We found a positive but saturating association between latitude and leaf herbivory. Furthermore, we found no significant relationship between CPD and herbivory, and such lack of density effects remained consistent throughout the sampled latitudinal gradient. Despite the apparently negligible influence of plant density on herbivory for Q. robur, further research with other plant taxa and in different types of plant communities are needed to investigate density-dependent processes shaping geographical variation in plant-herbivore interactions.

Modelling potential density of natural regeneration of European oak species (Quercus robur L., Quercus petraea (Matt.) Liebl.) depending on the distance to the potential seed source: Methodological approach for modelling dispersal from inventory data at forest enterprise level

The use of natural oak regeneration from admixed oaks and neighbouring oak stands provides an interesting alternative to cost-intensive artificial oak regeneration when aiming for forest conversion of pure coniferous stands. In this study analysis of forest inventory data is done on how far and in what density natural regeneration of both Pedunculate and Sessile oak occurs in coniferous stands.In order to investigate as exclusively as possible the effect of distance to the seed source on the regeneration density of both oaks, the regeneration potential was determined by using quantile regression. By applying a .995th quantile, reducing factors on seedling density, e.g. desiccation, browsing, pathogens or limited resource availability, were excluded as much as possible. Thus, the effect of zoochorus vectors on effective dispersal could be quantified.The regeneration potential was determined based on data from the forest inventory of the Saxony state forest enterprise, Germany, including 2357 sample plots. Remote sensing data, including the location of oaks in the overstorey, were used to determine the distance to the nearest potential seed source.The results of the present study demonstrate that the highest regeneration densities are not found in the immediate vicinity of the nearest seed source, but at distances between 60 and 140 m to it, i.e. the maximum of seedling density per area unit is in some distance to the trees trunk. In the present study, dispersal distances of established regeneration up to 1565 m were detected. From a distance of 1570–2300 m on, there was no oak regeneration.The results prove that acorns are taken from the seed source and that, in addition to barochorus dispersal, the zoochorus dispersal is of great importance for the succession of coniferous stands. The position of potential seed sources is therefore an important information for silvicultural planning, in order to estimate potential oak regeneration densities.

Metapopulation dynamics over 25\xa0years of a beetle, Osmoderma eremita, inhabiting hollow oaks

Osmoderma eremita is a species of beetle that inhabits hollows in ancient trees, which is a habitat that has decreased significantly during the last century. In southeastern Sweden, we studied the metapopulation dynamics of this beetle over a 25 year period, using capture-mark-recapture. The metapopulation size had been rather stable over time, but in most of the individual trees there had been a positive or negative trend in population development. The probability of colonisation was higher in well-connected trees with characteristics reflecting earlier successional stages, and the probability of extinction higher in trees with larger diameter (i.e. in later successional stages), which is expected from a habitat-tracking metapopulation. The annual tree mortality and fall rates (1.1% and 0.4%, respectively) are lower than the colonisation and extinction rates (5–7%), indicating that some of the metapopulation dynamics are due to the habitat dynamics, but many colonisations and extinctions take place for other reasons, such as stochastic events in small populations. The studied metapopulation occurs in an area with a high density of hollow oaks and where the oak pastures are still managed by grazing. In stands with fewer than ten suitable trees, the long-term extinction risk may be considerable, since only a small proportion of all hollow trees harbours large populations, and the population size in trees may change considerably during a decade.

Formerly coppiced old growth stands act as refugia of threatened biodiversity in a managed steppic oak forest

Forest vegetation is dominated by long-lived species in the tree layer, which facilitates its relatively high inertia and ability to conserve traces of its history in its structure and species composition. Central European lowland forests have been the subject of diverse human use for millennia and some of the present stands still show remnants of historical management forms practised before the onset of modern forestry. In the past decades, biodiversity decline has become a major concern, and restoration of historical uses has been proposed as a nature-friendly alternative for forest management. We explored the consequences of the transformation of an old oak coppice, historically linked to ancient wood pasture system, to oak plantation. We focused on vascular plant species richness and differences in ecological spectra of the plant assemblages, with the goal of evaluating the consequences for biodiversity conservation and identifying possible environmental drivers behind the observed patterns. The study was performed in the best preserved complex of lowland steppic oak forests in the Czech Republic, protected as a Site of Community Importance. We fully inventoried plant species in 135 oak stands classified into three management-age classes: (1) clear-cuts, (2) young growth stands after area-wide site preparation, and (3) old growth stands. For some analyses, old growth stands were divided into those showing signs of past coppicing and the others. We found that species richness was the highest in clear-cuts, the lowest in young growth stands, and intermediate in old growth stands. Clear-cuts showed the highest uniqueness in species composition, with a high share of ruderal species. Young growth stands showed the lowest uniqueness, with a high proportion of competitive species. Old growth stands showed intermediate uniqueness and the coppiced ones had a high share of stress-tolerant species, often of high conservation value. While it is hardly surprising that the establishment of oak plantations has profound effects on biodiversity, we suggest that clear-cutting itself may not be a key issue. Destructive site preparation in clear-cuts, and competition for resources in dense young oak stands are suggested as the main factors threatening the survival of ancient biota of steppic oak forests in our study area. In contrast, continuity of site conditions in formerly coppiced old growth stands facilitates species survival. We suggest that restoration of historical management forms such as coppicing and wood pasture may support this continuity. Where oak planting is still applied, we advise minimising site preparation and applying early thinning of young growth stands.

Prescribed fire and natural canopy gap disturbances: Impacts on upland oak regeneration

Across the central and eastern U.S., decades of fire exclusion have coincided with upland oak (Quercus spp.) regeneration problems and a compositional shift toward shade-tolerant, fire-sensitive species like red maple (Acer rubrum L.) and American beech (Fagus grandifolia Ehrh.). Because oaks are fire-adapted and moderately shade-intolerant, prescribed fire is commonly used as a management tool to decrease competition, increase light, and promote oak regeneration. However, prescribed fire alone often fails to sufficiently open the canopy and improve oak competitive status, suggesting the combination of fire and canopy gaps may be necessary for oak success. To better understand the effects of single and multiple prescribed fires alone and combined with naturally-formed canopy gaps on tree regeneration, we measured tree densities (both seed and resprout origin) in five height size classes (small seedlings: ≤0.5 m, large seedlings (>0.5–1.0 m), saplings (1.1–4.0 m), midstory (4.1–7.0 m), and poles (7.1–12 m)) within gaps and non-gap areas treated with no fire, single fire, or multiple fires (2–3) across six sites within the Knobs Region of Kentucky (U.S.A.) in 2017. Oaks were common as small and large seedlings without fire, especially within gaps, but they were largely absent from larger size classes. Instead, red maples and American beech dominated sapling and midstory size classes without fire, regardless of gap treatment. Single and multiple fires reduced both absolute and relative density of American beech saplings and red oaks (Q. velutina Lam., Q. coccinea Munchh. and Q. rubra L.) of all sizes, but single fires, both within and outside of gaps, increased red maple large seedling, sapling, and midstory dominance. Multiple fires, both within and outside of gaps, reduced red maple abundance, and this coincided with increased relative density of white (Q. alba L.) and chestnut oaks (Q. montana Willd.), but not of red oaks. Red oak small and large seedlings were the only oaks where absolute density increased in the small (~300 m2), relatively old (20–30 yr), naturally-formed canopy gaps in this study. Our findings suggest that management techniques that include multiple prescribed fires and large canopy gaps (>300 m2) created relatively soon after fire will likely be necessary to reduce competing species, increase oak density, and allow oaks to reach sapling and midstory size classes.

The Banj oak Quercus leucotrichophora as a potential mitigating factor for human-langur interactions in the Garhwal Himalayas, India: People’s perceptions and ecological importance

Crop-foraging by primates is a rapidly growing concern. Effective mitigation strategies are urgently required to resolve this issue. In the Garhwal Himalayas, local people’s high dependency on forest resources is a major cause of habitat loss, which paves the way for human-primate interactions in this area. To investigate the socioeconomic factors that might explain langur crop-foraging, we conducted structured interviews among 215 households in the Garhwal Himalayas in India. We also examined langur resource use by monitoring their feeding and sleeping site activity. Less agricultural land, less agricultural production, and possession of large numbers of livestock significantly predicted villagers reporting crop-foraging events, although economic status of the correspondents did not have any effect. Perception of the villagers about reduction in forest resource was significantly affected by the amount of livestock possessed by the villagers. Our observations suggested that Banj oak Quercus leucotrichophora was the dominant species (59.2%, N = 306) in the pool of sleeping trees used by the langurs. Langurs also showed a preference in their use of sleeping sites and feeding sites, which were different from that expected by chance. Sleeping sites with high density of oak were re-used most frequently. Similarly, dense oak patches were also the preferred feeding patches. Thus, we suggest replanting of oak trees and conservation of intact oak patches, environmental education outreach, and empowerment of women in the community as potential mitigating factors to lessen the interaction between humans and langurs.

Influence of canopy openness, ungulate exclosure, and low-intensity fire for improved oak regeneration in temperate Europe.

Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGRH in burned plots became strongly negative the first year. Thereafter, RGRH was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed.

О КОНУРЕНТОСПОСОБНОСТИ ПОДРОСТА ДУБА ЧЕРЕШЧАТОГО В ШИРОКОЛИСТВЕННЫХ ЛЕСАХ ЮЖНОГО УРАЛА

The results of a comparative analysis of the height and density of pedunculate oak (Quercus robur L.) and small-leafed linden (Tilia cordata Mill.), growing in the low mountains of the western macro slope of the South Ural Mountains, are presented. The study was conducted out in a floodplain oak forest with a composition of 80 % (oak) and 20 % (linden) and a density of 0,4 in windows of the canopy. The shoots and self-seeding of both species were not revealed. The projective cover of plants in all 7 trial plots is close to 100 %. Small (up to 0,5 m) and medium (0,51–1,5 m) undergrowth prevails. The oak dominates in most cases – its share on a 10- point scale is 7,4 ± 0,5 (coefficient of variation 18,3 %), compared with linden (2,4 ± 0,6, 58,9 %). The average height of the oak undergrowth is 64,6 ± 1,2 cm with changes from 20 to 140 cm (coefficient of variation 38,7 %). The growth of linden was almost 1,5 times higher (101,6 ± 1,9 cm), but it varies less (30–175 cm and 27,7 %). Differences in height between the two species are statistically significant (p &lt; 0,001). The oak renewed more abundantly (12,4 ± 2,6 plants per square meter, 1,0 to 18,0 pcs, coefficient of variation 51,8 %) than linden (6,5 ± 1,9 cm, 0,25–13,4 pcs, 72,7 %). Plants with a developmental delay during the reversal and dying off of the main stem were not found. Smallleaved linden, which plays the role of «sod» at the first stage of his life, is currently beginning to inhibit the growth of young oak. The restoration of oak forests under these conditions is impossible without the forestry help (thinning).

Effects of extractive use on forest birds in Western Himalayas: Role of local and landscape factors

Rural populations in developing countries depend on forests for fuelwood, fodder and other non-timber forest products. Such dependence has significant effects on faunal diversity and composition, primarily due to alteration of vegetation structure. While earlier studies have assessed the consequences of extractive activities for forest fauna, very few simultaneously acknowledge the role of landscape context, which includes agricultural land-uses and managed forests. This study was carried out in oak-dominated forests located in the middle elevations of the Western Himalayas to investigate effects of extractive activities on avifaunal communities, taking into account the role of landscape composition. Birds were sampled at 74 sites, six times each, over two seasons using fixed-radius point counts. We analysed avian species richness, abundance, composition and guild abundances (based on foraging and habitat preference) as a function of vegetation structure and proportion of dense oak forest around each site. Our results suggest that extractive activities in forests can result in reduced species richness, abundance and altered composition of forest avifauna, brought about by changes in vegetation structure. We also find that these effects may be intensified by the loss of dense oak forests in the landscape. Insectivorous birds and forest specialists were most sensitive to extractive activities and landscape composition. Decreasing canopy cover and proportion of oak forest in the landscape had strong negative effects on insectivorous and forest specialist species. Other local factors such as vertical stratification and understory density also had effects on these avian guilds. Our study indicates that in order to conserve bird species in an increasingly human-dominated landscape of the Western Himalayas, it may be necessary to control extractive activities that affect forest structure as well as retain protected forest stands within a continuum of harvested forest and agricultural landscapes.

Population structure, soil characteristics and carbon stock of the regenerating banj oak forests in Almora, Central Himalaya

The present study is aimed to study regeneration status, population structure, soil characteristics and carbon stock of seven regenerating banj oak (Quercus leucotrichophora) forests in the central Himalaya. The phytosociological study was done by using ten 10 m × 10 m quadrat at each site. Biomass and carbon stock of trees were calculated by using regression equations. Soil samples were collected from three depths (0–10, 10–20 and 20–30 cm) by using soil corer. The tree density of two most dominant species of the study sites i.e. banj oak and pine (Pinus roxburghii) varied from 260–1200 trees ha−1 and 90–300 trees ha−1, respectively. Whereas, basal area of banj oak and pine varied between 5.5–21.0 m2 ha−1 and 6.4–26.0 m2 ha−1, respectively. Density-diameter curve indicated the increasing population of banj oak while declining pine in all the sites. Carbon density of the banj oak was found between 46.96–167.36 Mg ha−1 and in pine it was 17.18–72.95 Mg ha−1. Soil nutrient (especially carbon and nitrogen) improved with increase in density and basal area of forests. Additionally, substantial amount of carbon stored by these trees makes them viable for the region. Thus, identification and conservation of such forests are recommended.

White Oak (Quercus alba) Response to Thinning and Prescribed Fire in Northcentral Alabama Mixed Pine–Hardwood Forests

AbstractStrong white oak sawtimber markets, partially attributed to the stave and cooperage industries, are encouraging forest managers to re-examine silvicultural practices for white oak (Quercus alba). We examined recruitment and retention of white oak in mixed oak–pine stands on the William B. Bankhead National Forest in northcentral Alabama. Stands were subjected to three thinning levels (residual basal areas of 75 ft2/ac, 50 ft2/ac, and no thinning) and three fire frequencies (dormant season burns of none, one, three fires) in a factorial design. Both thinning treatments reduced overstory white oak tree densities, and fire had no effect on densities. For all reproduction height classes, regardless of thinning treatment, three prescribed burns increased white oak densities; thinned and burned stands had larger white oak seedling sprouts than those thinned with no burn. However, white oak reproduction height was primarily less than 2 ft tall, and seedlings larger than 4 ft tall were reduced. Thinning with one fire resulted in the highest densities of large white oak reproduction (4 ft tall up to 1.5 in. dbh). Red maple reproduction was the dominant competitor in all treatments and is positioned to dominate the reproduction cohort without additional tending treatments.

Understory Vegetation Responses to 15 Years of Repeated Fuel Reduction Treatments in the Southern Appalachian Mountains, USA

Decades of fire exclusion in the Southern Appalachian Mountains led to fuel accumulation and conversion from open oak-pine woodlands to closed-canopy mesic forests dominated by shade-tolerant hardwoods and shrubs that often do not support a diverse understory. Southern Appalachian forest managers and scientists recognize this and are implementing silvicultural treatments such as prescribed burning, mechanical treatments or a combination of these to restore forest structure. In this study, conducted at the Southern Appalachian Fire and Fire Surrogate Study site in Green River Game Land, North Carolina, we assessed the effects of four fuel reduction methods: burned 4x (B), mechanical treatment 2x (M), mechanical treatment 2x + burned 4x (MB), and control (C) on the changes in understory vegetation guilds from pretreatment to post-treatment years (2001–2016). The MB treatment was most effective at meeting the restoration objectives, as it resulted in increases in oak (ΔMB = 23,400 stems/ha) and pine (ΔMB = 900 stems/ha) stem density, importance value - calculated as the sum of relative cover and frequency - for graminoids (ΔMB = 26.0), and density of oak stems &gt;50 cm in height (ΔMB = 7133 stems/ha). The B and M treatments were generally less effective, but nonetheless met a subset of the restoration objectives. The B treatment reduced ericaceous shrub cover (ΔB = −1.2%) and increased oak stems 10–50 cm in height (ΔB = 10,017 stems/ha), while the M treatment resulted in only modest increases of mesic hardwoods, specifically for yellow-poplar (ΔM = 200 stems/ha) and blackgum (ΔM = 200 stems/ha) as compared with other treatments, but significantly increased mountain laurel and rhododendron cover (ΔM = 10.0%). Overall, these fire and fire surrogate treatments had some success in restoring understory structure, but our findings suggest a slow response in understory herbaceous vegetation.

Correlations between Oak Wood Properties

Correlations between the chemical composition and physical properties of oak wood were studied by correlation analysis. The specimens were produced from thermally treated oak wood at temperatures of 20 °C, 160 °C, 180 °C, 210 °C, and 240 °C. The physical properties were affected by the chemical composition of oak wood. The correlations of equilibrium moisture content (EMC) and oak density at EMC were similar, in accordance with the investigated properties. Oak end hardness was affected by treatment temperature. The depth of indentation significantly affected the hardness. Mass specific heat capacity and effusivity were positively correlated with EMC, sugars, holocellulose, cellulose traits, and ash and negatively affected by total extractives. Thermal diffusivity was slightly affected by treatment temperature.

Long-lasting effects of logging on beetles in hollow oaks.

There is growing evidence that biodiversity is important for ecosystem functions. Thus, identification of habitat requirements essential for current species richness and abundance to persist is crucial. Hollow oaks (Quercus spp.) are biodiversity hot spots for deadwood‐dependent insect species, and the main objective of this paper was to test the effect of habitat history and current habitat distribution at various spatial scales on the associated beetle community. We used a gradient spanning 40 km from the coast to inland areas reflecting historical logging intensity (later and lower intensities inland) through 500 years in Southern Norway, to investigate whether the historical variation in oak density is influencing the structure of beetle communities in hollow oaks today. We trapped beetles in 32 hollow oaks along this gradient in forested and seminatural landscapes over two summers. We found higher species richness and total abundance inland consistent with our expectation based on historic logging intensity. Scale‐specific environmental variables also affected the response; beetle abundances were controlled by local conditions, whereas beetle species richness responded to habitat on the landscape scale. This indicates that long time continuity as well as large areas of favorable habitat is necessary to maintain beetle species richness through time in these highly long‐lasting structures.

Propiedades físicas y dinámica de los combustibles forestales en un bosque de encino

Se evaluaron y analizaron propiedades físicas de combustibles forestales de importancia en la estimación del comportamiento del fuego y la dinámica de los combustibles durante la temporada de incendios forestales en un encinar del Edo. de México. Se estimó: i) densidad básica y humedad de los combustibles por tiempo de retardo (TR); ii) carga de combustibles leñosos por tres variantes de método; y iii) dinámica de combustibles forestales. Las densidades básicas de los materiales leñosos decrecieron a mayores tiempos de retardo: 1 h = 0.585 g cm-3, 10 h = 0.478 g cm-3 y 100 h = 0.412 g cm-3. La carga de los combustibles leñosos, estimada con densidades básicas de los materiales recolectados, fue la menor: 11.6% menos con respecto al valor obtenido usando densidades básicas de coníferas y 43% menos al usar la densidad básica de encinos referida en la bibliografía. La incorporación de materiales fue de 40.532 Mg ha-1 durante la temporada de incendios; para hojarasca correspondió 62.9% (25.491 Mg ha-1) y para leñas 18.8% (7.603 Mg ha-1). La tasa de descomposición en hojarasca fue 0.0827 y en leñas 0.0861 y 0.0404, para 1 h y 10 h TR, respectivamente. La carga acumulada al final de la temporada incrementó 205% en ramillas de 1 h y 10 h TR, mientras que la hojarasca lo hizo en 58.7%.

Linking forest successional dynamics to community dependence on provisioning ecosystem services from the Central Himalayan forests of Uttarakhand.

The study examines the relationship between Ecosystem Services (ES) supply and vegetation dynamics through a series of five vegetation types representing a hypothetical successional sequence (i.e., Grassland, Pine, Pine-Oak mix, Open Oak, Dense Oak). We quantified and compared the dependence of local livelihood on provisioning services from forests at each level of succession and the resource extraction methods used to obtain desired products through a structured social survey covering 19 villages and 702 households in Tehri Garhwal and Dehradun districts of Uttarakhand. We found that broad leaved oak forests (covering 38.5% of total 57,516 ha of the study area) were the most important vegetation formation supporting local livelihoods. Meanwhile, the extraction of services from other early successional vegetation formations was significantly lower than oak forests, both in terms of number and quantities. Notably, the highest dependence was on fuel wood, fodder, and stall inlay (animal bedding), most of which were provided by dense oak forests. The high dependence on vegetation to support household needs and subsequent resource extraction through grazing, lopping, cutting, collection, and fire, act as unsystematic management techniques in the study area, maintaining the vegetation in its present form. An understanding of ecosystem service supply from each level of succession and the resource extraction methods used to obtain desired services can assist forest managers to choose the best suited management regime depending on their aim and stakeholder demands.

Abundance-based detectability in a spatially-explicit metapopulation: a case study on a vulnerable beetle species in hollow trees

In many fragmented habitats, the detectability of a population in a habitat patch closely depends on the local abundance of individuals. However, metapopulation studies rarely connect abundance and detectability. We propose a framework for using abundance-based estimates of detectability in the analysis of a spatially-explicit stochastic patch occupancy model (SPOM). We illustrate our approach with the example of Tenebrio opacus, a beetle inhabiting hollows in old trees, and have based it on a 6-year monitoring programme of adult beetles in an area harbouring a high density of old oaks. We validated our abundance-based methodology by showing that the estimates of detectability were positively and significantly correlated with those obtained from presence/absence data (Pearson r = 0.54, p < 2E−16) in our study system. We further showed that the height of the hollow on the tree and the area of its entrance hole, the living status and girth of the host tree, and the time of survey significantly affected the detectability of beetle populations. Median detectability was 51% for one survey. The SPOM analysis revealed a high but heterogeneous extinction risk among trees, suggesting a metapopulation dynamics between the “classic” and “mainland–island” paradigms. However, it also indicated unexplained beetle colonization of trees in our study, despite the fact that we included limited detectability in our estimation procedure. This may have been due to the cryptic larval stage of T. opacus and may thus invalidate the use of a classic SPOM in our study system.

Evaluation of the corridor method for oak (Quercus sp.) cultivation using research objects in the Mircze and Kościan Forest Districts as an example

Abstract The corridor method of oak (Quercus sp) cultivation is an old, forgotten silvicultural method. It was developed around the turn of the 19th and 20th century on the south-eastern borders of Poland (Podole, Wołyń) and Russia and made use of other species such as hornbeam, linden and birch as a cover for oak, which is a tree species sensitive to frosts. The nowadays recurring phenomenon of oak disease initiated a search for silvicultural alternatives and thus the usefulness of reviving the corridor method for oak regeneration was investigated by examining existing tree stands established in this way. Our research plots were located in five young stands and two in mature as well as old stands. In the stands of the 2nd and 3rd age classes, the density of oaks was observed to be 1500–3500/ha, which accounted for 30–50%. The density of oak in old stands (7th age class) was similar to model-predicted values. Furthermore, the corridor method gave very good production results as exemplified by the oak stands growing on the fresh broadleaved site, which had a very high stand quality index. In addition, the species composition was observed to diversify throughout these oak stands’ development, thus supporting arguments for the conservation and preservation of oak-hornbeam forests. To summarise, the prerequisites for the success of the corridor method are systematic cuts of young stands (forest cultures and thickets) to inhibit the growth of accompanying undesired species and limiting the number of grazing animals.

CONDITION OF ENGLISH OAK NATURAL REGENERATION UNDER A FOREST CANOPY IN THE LEFT-BANK FOREST STEPPE

In 2010–2016 in 60 sample plots the peculiarities of forming, age and size structure of English oak natural regeneration under forest canopy was studied. It was found that undergrowth density was the highest in the fresh maple and lime oak stand (on average 3.4 thousand plants per ha), significantly increased with the age of the parent stand and decreased with the age of the renewal itself. In the age structure of English oak natural regeneration under a forest canopy, the current year plants predominated (46.1 %); the part of 2–3-year renewal was 29.8 %, the part of 4–8-year-old renewal was 22.7 %, the part of 9–15-year-old renewal was 1.4 %. As the relative density of parent stand stocking increased, the density of oak seedlings increased, the density of current year oaks increased but the density of 4–8-year-old renewal decreased as a result of insufficient illumination or competition with other plants. In the combined sample without age distribution of English oak natural renewal, the success of regeneration was good in 3,3 % of inspected plots, insufficient in 4.9 %, satisfactory in 8.2 %, unsatisfactory in 83,6 % of studied plots.

Do Torymus sinensis (Hymenoptera: Torymidae) and agroforestry system affect native parasitoids associated with the Asian chestnut gall wasp?

The Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu, is one of the most serious pests of Castanea spp. worldwide. Since local parasitoids did not effectively control this exotic pest, the Chinese parasitoid Torymus sinensis Kamijo was released into Japan and Europe resulting in a successful control of the invader. A survey of native parasitoids usually infesting oak gall wasps but associated with D. kuriphilus was carried out, sampling chestnut galls in Italy in 2013. The effect of predictive variables (years since T. sinensis release, oak occurrence, type of chestnut formation, latitude) on composition and density of native parasitoid populations was modelled with Generalized Linear Models. In total, 4410 chalcid parasitoids were recorded, and the most abundant species were T. flavipes Walker, Eupelmus spp., and Bootanomyia (= Megastigmus) dorsalis (F.). Introduction of T. sinensis and oak occurrence influenced native parasitoid richness, conversely to the latitude of the study area. In particular, every additional year of presence of T. sinensis was proved to determine the loss of about 14% of native species, and 32% of their population density. A positive correlation between the oak density occurring in the infested chestnut forests and the richness and abundance of native parasitoid species was recorded as well, highlighting how generalist parasitoids may switch hosts easily. A positive effect of increasing densities of oak trees was recorded on most of the taxa, except for T. geranii (Walker), Eupelmus spp., and Eurytoma pistaciae Rondani.Our results provide insight that both T. sinensis and oak trees affect native parasitoids, shedding light on the possible implications related to the release of exotic biological control agents on the recruitment and accumulation of native natural enemies.