Pure Oak Forests Research Articles

Evaluation of Multiple Forest Service Based on the Integration of Stand Structural Attributes in Mixed Oak Forests

In order to understand forest services at stand level through the integration of structural attributes, forest structures in three main stand types were analyzed based on various structural attributes relating to the services of habitat conservation, timber production and soil water conservation in Loess Plateau, China. Forty sample plots with similar site and environment conditions were established in three types of oak stands. Twenty-two indexes such as stand density, mean DBH, mean height, etc., were selected to analyze the relationship between structural attributes and forest service. With a core set of structural attributes selected by principal component analysis, the link between the service and structural attributes and the compatibility between each service was analyzed using correlation analysis. The results show that the oak–broadleaf mixed forest has the highest structural complexity index (SCI), indicating the best habitat conservation among others, while the oak–pine mixed forest and pure oak forest have the highest timber value in different scenarios of timber price, indicating the largest potential for timber production. Little differences were found between stand types regarding the indicators for soil water conservation. The structural attributes that had a positive correlation with habitat conservation (e.g., number of shrub species, species richness of canopy layer, the proportion of broadleaves and snag density) were identified to be negative for timber production; while the attributes that had a positive correlation with timber production (e.g., stand density and proportion of pine and oaks) were found to be negative for habitat conservation. The results of the trade-off analysis showed that timber production tends to be conflicting with the other two non-timber forest services. In order to enhance the provisioning of multiple services, it was suggested to implement the interventions that could balance these services, such as structural retention and single-tree selective logging. This study could contribute to the theoretical base for the decision making in the multi-purpose sustainable management of oak forests in China.

Detecting the oak lace bug infestation in oak forests using MODIS and meteorological data

The oak lace bug (Corythucha arcuata, Say 1832) is a new invasive sap-sucking species in the European oak forests that was first recorded in Central Europe in 2013. It invaded the region from Southeastern Europe, spreads rapidly, and shows no signs of receding after establishment. In this study, focusing on the oak forests in the transboundary area of Hungary and Croatia, we applied two novel methods for detecting and assessing the impact of the oak lace bug (OLB) during the period 2000–2019 based on MODIS NDVI measured at 250 m spatial and 8-day temporal resolution. The first detection method is based purely on NDVI and has the potential to be used in near real-time detection. The second one, based on the residual Z-score of the NDVI models using daily meteorological and soil water content data as independent variables, aims at improved OLB damage assessment by decoupling the effects of the OLB from those caused by the environmental drivers. The presented detection methods had 61.1% to 93.8% agreement with the in situ data, with a better agreement in forests with high oak share. The overall share of the false-positive OLB detections for the strictest method of model residuals was 1.8%. The results confirmed a strong and year-to-year persistent NDVI decrease (down to -14.5% in pure oak forests) during the late summer which can be attributed to the OLB. The origin of the infestation in the study area was identified to be near a resting station on the major highway from Southeastern to Western Europe, corroborating the assumptions that the OLB spread was primarily facilitated by the transport system. The detected speed of the OLB radial spread in the first 3 years of infestation was under 6 km y-1, but since then it increased to above 50 km y-1.

Effects of Pure and Mixed Pine and Oak Forest Stands on Carabid Beetles

The multiple-use approach to forestry applied in Germany aims to combine timber production and habitat management by preserving specific stand structures. We selected four forest stand types comprising (i) pure oak, (ii) equal oak–pine mixtures, (iii) single tree admixtures of oak in pine forest and (iv) pure pine. We analysed the effects of stand composition parameters on species representative of the larger carabid beetles (Carabus arvensis, C. coriaceus, C. hortensis, C. violaceus, Calosoma inquisitor). The main statistical methods used were correlation analyses and generalised linear mixed models. Cal. inquisitor was observed in pure oak forests exclusively. C. coriaceus and C. hortensis were absent from pure pine stands. High activity densities of C. arvensis and C. violaceus were observed in all four forest types. When assessed at the smaller scales of species crown cover proportions and spatial tree species effect zones, C. hortensis was found to be positively related to oak trees with a regular spatial distribution, whereas C. coriaceus preferred lower and more aggregated oak tree proportions. C. violaceus showed strong sex-specific tree species affinities. Information about preferences of carabid beetles is necessary for management activities targeting the adaptation of forest structures to habitat requirements.

Cortinarius pakistanicus and C. pseudotorvus: two new species in oak forests in the Pakistan Himalayas.

The genus of basidiomycetous fungi Cortinarius occurs worldwide, from subtropical to boreal latitudes. Although molecular systematics has triggered the study of these fungi in the Americas and Europe in the last two decades, there is still limited research on its diversity in large portions of the planet, such as the high mountain ranges of Asia. Several collections of Cortinarius were made during mycological field trips conducted between 2014 and 2018 in pure oak forests in the Pakistan Himalayas. An integrative framework combining morphological and phylogenetic data was employed for their study. As a result, the two species C. pakistanicus and C. pseudotorvus are here described as new to science. Detailed macro- and micro-morphological descriptions, including SEM images of spores, and a molecular phylogenetic reconstruction based on nrITS sequence data are provided and used to discriminate the new species from morphologically and phylogenetically close taxa. Whereas our phylogenetic tree inference gave unequivocal support for the inclusion of C. pseudotorvus within C. sect. Telamonia, the assignment of C. pakistanicus to any known sections remained elusive. These species likely establish ectomycorrhizal associations with trees in the genus Quercus, making this type of forest in the Pakistan Himalayas a promising focus for future research on the diversity of Cortinarius.

Male-skewed sex ratio in Myrica esculenta: a dioecious tree species

The population of M. esculenta tends to deviate from the equilibrium of expected 1:1 primary sex ratio predicted by Fisherian theory. Populations of dioecious plants may often exhibit biased sex ratios, which generally favour males. A study on reproductive potential, i.e., pollen production and female flower production, and reproductive success in Myricaesculenta was assessed in three diameter (diameter at breast height: dbh at 1.37 m) classes, i.e., small (10–20 cm), medium (20–30 cm), and large (30–40 cm). Population structure and sex ratio was determined in transects in four major associations of Myricaesculenta, i.e., (i) with mixed Oak-Rhododendron forest (ii) with Chir Pine–Oak forest, (iii) with pure Oak forest, and (iv) with pure Deodar forest. The sex ratio of trees was male-biased. Male frequency was higher in lower diameter classes and maximum on resource-poor site. More female individuals were recorded in higher-diameter classes and resource rich location, indicating that the total reproductive cost in M. esculenta is greater in female trees than that of the male trees. The population of M.esculenta tends to deviate from the equilibrium of expected 1:1 primary sex ratio predicted by Fisherian theory. The male trees demonstrated greater survival, especially in resource-poor conditions, which was reflected strongly biased sex ratios within the lower size classes. The study would be helpful for formulating appropriate silvicultural and genetic management strategies for this species.

Changes in litter chemistry associated with global change-driven forest succession resulted in time-decoupled responses of soil carbon and nitrogen cycles

Global change-driven forest succession may modify key soil processes with potentially important impacts over carbon (C) and nutrient cycling. We studied how changes in litter throughout the replacement of Pinus sylvestris by Quercus pyrenaica influence the structure and functioning of soil microbial communities and the capacity of soils to sequester C and retain nitrogen (N). We designed a microcosm experiment to simulate the chronological sequence from pine to oak forest conversion in Central Spain, using mixtures of senescent litter (oak leaves, pine needles and an equal mixture of needles:leaves) and soils (from pure oak, mixed and pure pine stands). We investigated changing patterns of soil C and N contents, microbial community structure (PLFA) and greenhouse gas fluxes (CO2, CH4, N2O) across the chronosequence. The succession from pine to oak forest was associated with substantial changes in microbial community structure and functioning. Soil-C sink capacity was reduced, although soil-N availability was enhanced. We further show how effects of secondary succession on the C cycle were mismatched with N dynamics in response to two chronologically decoupled facts. First, there was an acceleration in soil organic matter (SOM) turnover after microbial –especially bacterial– growth ceased to be so intensely inhibited by needle litter (ecotone soils), resulting in lower fungal to bacterial ratios; and second, N mineralization was stimulated once pine-derived SOM was no longer present in soils (pure oak forest soils), resulting in further acceleration of SOM turnover, suppression of CH4 consumption and an increase in gram-negative bacteria. Our findings suggest that different sensitivities of key mechanisms (SOM decomposition, N mineralization, CH4 consumption) to factors associated with succession (e.g. recalcitrance of pine SOM and allelopathic effects over bacteria) could have significant impacts on soil microbial ecology, C and nutrient cycling.

Bird composition and diversity in oak stands under variable coppice management in Northwestern Turkey

Abstract: Coppice management results in profound differences in forest structure and composition, which in turn can modify habitat value for bird species. We measured bird species richness and composition at 50 sample plots in pure oak forest stands in northwestern Turkey, which differed in age, cover and height in association with coppice management. We recorded a total of 38 bird species and 699 individuals across all stands. Regression-based multimodel inference showed that structural features of forest stands strongly affect bird diversity and abundance. While canopy cover and tree height affect bird diversity positively, elevation of sampling plots, tree density and tree diameter at breast height (DBH) had a negative effect. In addition, constrained ordination analyses revealed that canopy cover was the most important factor influencing bird species composition. Forest stands that have 42-85% canopy cover, i.e., a few (2009-2580 oak trees) large tall (13.36-15.78 m) trees, were the most preferred habitat by bird species. However, we also found that different bird species favor different stand structural features. Thus, variation in stand structure from maintaining some coppice management across the landscape may be beneficial for rare or endangered species and result in greater landscape level biodiversity.

Dynamics of annual falling debris decomposition and forest floor accumulation

The level of forest ecosystems’ productivity and functioning character may be to a great extent explained by its soil cover properties and carbon cycling peculiarity. The fabric and properties of forest ecosystems’ topsoil (designated in Estonia as “humus cover type”, but by Humusica as “humus form”) depends on the dynamics of annual falling debris (AFD) accumulation-decomposition in the forest floor (FF). For characterization of AFD dynamics or its flow throughout the FF into soil or atmosphere, the mean perennial graphical models were used. The comparative analysis of AFD flow and FF formation dynamics was carried out in four forest ecosystems of the temperate zone of the Atlantic-continental region. The studied forest stands were by their layers structure and interrelationships of the system “plant-soil” in stabilized stage. The used data originated from our previous researches on the dynamics of AFD by different fractions and of fractional composition of the FF. The flow of mean aboveground AFD throughout the FF depends on the quantity and dynamics of the AFD, on fractional composition of AFD and on pedo-ecological conditions of decomposition. The lowest decomposition rate was obtained in fresh moder humus cover (by Humusica Hemi- and/or Eumoder) on Glossic Retisols, but the highest, in fresh forest-mull humus cover (by Humusica Eu- and/or Mesomull) formed on Calcaric Cambisols. Due to the low decomposition rate in ecosystems formed on Glossic Retisols, only readily decomposable parts (herbs, leaves) disappear quickly from the newly formed FF. The more resistant parts of AFD accumulate for many years in a half-decomposed state on the surface of mineral soils (or on A-horizon), forming a multi-layered FF. The superficial density of phytogenic origin FF dry mass on Glossic Retisols is in limits of 21.5–24.5Mg ha−1, whereas the mean accumulation coefficient of FF formation varies from 3.35 to 3.44. The mean amount of phytogenic FF on Calcaric Cambisols with mixed spruce forest was 7.6Mg ha−1 and in the oak forest 3.2 Mg ha-1. The accumulation coefficient of FF formation in conditions of fresh forest-mull type humus cover was in the mixed spruce forest 1.50 and in the pure oak forest 0.66. The most important factors of AFD decomposition-mineralization are biological activity and agrochemical status of soil.

The influence of stand structure in submontane acidophilous oak forests on the presence of the wild service tree and sword-leaved helleborine

Abstract The objective of this work was to evaluate the occurrence of two strictly protected vascular plant species in managed stands of submontane acidophilous oak forests (Luzulo luzuloidis - Quercetum petraeae Hilitzer 1932 association) in the Sudeten foothills (Lower Silesia, Poland). During the study, the most important stand parameters influencing the occurrence of the wild service tree (Sorbus torminalis (L.) Crantz) and the orchid sword-leaved helleborine Cephalanthera longifolia (L.) Fritsch) were ascertained. The stands ranged from 50 to 130 years of age and were dominated by sessile oak (Quercus petraea (Matt.) Liebl.), which comprised 5-100% of trees. Both of the protected plant species were observed in 10% of the examined plots with the most favorable type of forest stand for sword-leaved helleborine as well as the wild service tree being clearly dominated by sessile oak (portion of oak above 80%). The analysis showed that the wild service tree was found in pure oak stands, whereas sword-leaved helleborine was also recorded in mixed stands aged 50-80 years. The increased frequency of sword-leaved helleborine was associated with a higher portion of oak in the tree layer. The results suggest that the modern silviculture practices, ‘close-to-nature’ silviculture, transform pure oak forest into mixed forest and allow for natural expansion of hornbeam (Carpinus betulus L.) as well as beech (Fagus sylvatica L.), which can induce the gradual disappearance of the orchid and the wild service tree in submontane acidophilous oak forests. Restoring semi-natural pure oak stands should play a significant role in supporting both protected species in submontane acidophilous oak forests of the Sudeten Region.

Effects of parent material, stand type and oak species on defoliation of coppice-originated oak (Quercus spp.) forests in Northern Turkish Thrace

Cases of significant defoliation in oak (Quercus spp.) forests have been reported in Turkey and throughout the world. Oak trees are important in Turkish forests and forestry and cover vast pieces of land in Thrace. In this study, in a quest to determine the general health condition of pure oak forests in Northern Turkish Thrace, the defoliation rate of tree crowns was evaluated for 8,769 trees in 336 sample plots corresponding to different geological parent materials, regions, oak species and stand types. The defoliation rates were designated and assessed based on the criteria of the European Union Forest Health Monitoring Program (UNECE-ICP Forests). The defoliation rate was, to a significant extent, affected by stand type, the geological parent material, and oak species. In general, 47 % of trees exhibited defoliation. The highest ratio of defoliation was found in Kirklareli Region, where water deficit was the highest, and the parent material was schist-calcschist. Medium diameter forests (MDF, mean dbh: 8-20 cm, ratio of defoliated trees = 65 %) among stand types, and sessile oaks (ratio of defoliated trees = 53 %) among oak species, had the highest defoliation rates. Achieved results demonstrated that the defoliation classes in observed oak stands have a significant relation with variables concerning stand types, oak species and geological parent materials.

Arthropod diversity in pure oak forests of coppice origin in northern Thrace (Turkey)

Abstract: Oak (Quercus spp.) forests are among the most important forest types in Turkey. In the past, oak forests were managed through coppice clear-cutting, but in recent decades they have mostly been converted to high forest. This study was aimed at explaining how arthropod diversity is affected during conversion from coppice to high oak forest and during the early stages of coppice succession. We tested the hypothesis that arthropod richness, abundance and diversity in coppice oak sites varied according to stand age and a number of other forest characteristics. Arthropod communities were sampled in 50 plots using four different methods: pitfall traps, sweep nets, sticky cards and cloth shaking. A total of 13 084 individuals were collected and classified into 193 Recognizable Taxonomic Units (RTUs), with the most RTUs and the greatest number of specimens captured by sweep netting. We identified 17 taxa within RTU’s with more than 1% of the captured arthropods, which constituted 75% of the total specimens. The number of RTUs varied significantly according to trap type. Arthropod richness and Shannon-Wiener biodiversity index (H′) increased with elevation and precipitation. In young (1-40 yrs-old) and middle-aged (41-80 yrs) stands, arthropod biodiversity was not significantly affected by stand type, but slightly increased with diameter at breast height and tree height. Forest characteristics, such as the litter layer, understory and crown diameter, weakly influenced arthropod richness and abundance. Cluster analysis revealed that stand types and trap types differed taxonomically. Principal component analysis showed that stand types were clearly separated by the stand parameters measured. Insect families (Formicidae, Thripidae, Lygaeidae, Dolichopodidae, Luaxanidae, Cicadellidae and Ichneumonidae) could potentially be used as indicators of coppice oak conditions. As the coppice oak changes to mature forest, further studies are needed to better assess the relation between arthropods, forest types and structural characteristics of stands.

The American forest pathogen Heterobasidion irregulare colonizes unexpected habitats after its introduction in Italy

Habitat preference of an invasive fungal tree pathogen is here compared with that of a sympatric and native closely related congener to test the hypothesis that the invasive ability of the exotic organism may be linked to its capacity to colonize substrates unavailable to the indigenous relative. We compared the distribution of infectious airspora of the North American Heterobasidion irregulare introduced into Italy with that of the native H. annosum, both regarded to be able to establish only in the presence of conifers. Geostatistical and statistical analyses were employed to test for association between both species and five Mediterranean vegetation types. Results show that H. annosum is positively associated with pines and negatively associated with deciduous oaks. The probability of finding its spores decreases to almost 0 at distances over 500 m from pines, and this species is virtually absent in pure oak forests. Spores of H. irregulare are present irrespective of vegetation type, and this species can be found not only where pines are present, but also in pure oak forests. This knowledge implies that spread of H. irregulare is not limited by the fragmented distribution of pine woodlands in central Italy and is essential to both predict and hinder its progress in Europe.