Chestnut Stands Research Articles

Molecular genetic variability of Cryphonectria hypovirus 1 associated with Cryphonectria parasitica in South Tyrol (northern Italy).

Cryphonectria hypovirus 1 (CHV-1) has been widely studied and used as a biocontrol agent because of its ability to infect the chestnut blight fungus, Cryphonectria parasitica, and to reduce its virulence. Knowledge about the hypovirus, its presence, and diversity is completely lacking in South Tyrol (northern Italy), which may obstruct biocontrol measures for chestnut blight based on CHV-1. This work aimed to study the occurrence of CHV-1 infecting C. parasitica in South Tyrol and to perform a genetic characterization of the hypovirus. In South Tyrol, CHV-1 was found to occur in 29.2% of the fungal isolates investigated, varying in frequency between different regions and chestnut stands. Twenty-three haplotypes based on partial cDNA (complementary DNA) sequences of open reading frame (ORF)-A and 30 haplotypes based on partial cDNA sequences of ORF-B were identified among 47 and 56 hypovirulent fungal isolates, respectively. Phylogenetic analysis showed that all the haplotypes belonged to the Italian subtype of CHV-1 and that they were closely related to the populations of Italy, Switzerland, Croatia and Slovenia. Evidence of recombination was not found in the sequences and point mutations were the main source of diversity. Overall, this study indicated that the prevalence of CHV-1 in South Tyrol is low compared to many other central and western European populations and determined a need to actively impose biocontrol measures. Using sequence analysis, we identified some variants of interest of CHV-1 that should be studied in detail for their potential use in biocontrol.

Potential Distribution and Suitable Habitat for Chestnut (Castanea sativa)

Chestnut, Castanea sativa Miller (Fagales: Fagaceae), is an ecologically and economically important tree species of the forest ecosystem in Southern Europe, North-Western Europe, Western Asia, North Africa, and the Caucasus. The distributional range of chestnut in Europe has been highly modified by humans since ancient times. Biotic and abiotic factors have dramatically changed its distribution. Historic anthropogenic range expansion makes it difficult to identify habitat requirements for natural stands of chestnut. In the Caucasus, natural stands of chestnut survived in glacial forest refugia and landscapes that have been difficult for humans to colonize. To identify the species reliable habitat requirements, we estimated the relationship between climatic variables and 620 occurrence locations of natural chestnut stands from the Caucasus and validated the model using GBIF data from outside the Caucasus. We found that our best model is reasonably accurate and the data from the Caucasus characterize chestnut stands throughout the species range well.

Sweet chestnut forests under black locust invasion threat and different management: An assessment of stand structure and biodiversity

Sweet chestnut forests in Europe are impacted by management abandonment, non-native species invasions and diseases, among other factors. Understanding the effects of these factors is crucial for forecasting future biodiversity changes, as well as proposing appropriate planning and management strategies. We studied sweet chestnut (Castanea sativa Mill.) and black locust (Robinia pseudoacacia L.) dominated forests within three hilly landscapes (Euganean hills, Montello, and Berici hills) of north-eastern Italy. We surveyed 25 paired sweet chestnut and black locust dominated plots of 100 m2 representing coppice or over-aged stands. We collected and analysed data related to vascular plant composition and richness, soil physical features (moisture content, shear strength and penetration resistance), ammonia-oxidising archaea in the soil, and stand structure features. Composition of vascular plants differed significantly between the two forest types, without the influence of management regime. Soil characteristics did not change comparing forest types, management regimes and their interaction, except for soil moisture that was higher in coppice forests. Ammonia-oxidising archaea abundance was lower in sweet chestnut stands. Sweet chestnut and black locust forests have a similar stand structure. The management regime played a role in determining mean diameter, number of stems and deadwood volume. We suggest adopting a heterogeneous array of silviculture practices to achieve the highest variety of forest structures and plant composition in Mediterranean hilly landscapes, coupled with management practices aimed at black locust control.

Influence of tree species richness and identity on saprophagous macroarthropod abundance and species richness in some European forest types

Impacts of tree diversity on forest soil fauna remain poorly known. Two groups of functionally similar invertebrates, millipedes (Diplopoda) and woodlice (Isopoda, Oniscidea), were sampled at 61 forest plots in four European countries (Finland, Poland, Romania, Italy) in order to (1) compare the abundance and species richness of these saprophagous macroarthropods in monospecific and mixed, three-species forest stands, and (2) determine whether the influence of tree species richness depends or not on tree identity. The results showed that, in boreal forests of Finland, regional conditions (temperature, soil) proved to be very unfavourable for millipedes and woodlice, which prevented further comparisons. In the other three regions, tree species richness had no consistent effect on macroarthropod abundance but there was a clear trend towards a higher macroarthropod species richness in mixed stands compared to monospecific stands. This resulted mainly from a significantly positive response of millipedes to tree mixtures in hemiboreal forests of Poland and mountainous forests of Romania, and from a slightly positive response of woodlice in thermophilous forests of Italy. However, not all tree mixtures were equally favourable for saprophagous macroarthropods. An examination of tree identity in mixed stands showed that mixtures including hornbeam and conifers in Poland and those including beech and spruce in Romania had significantly higher macroarthropod species richness than the other mixed stands. Moreover, macroarthropod species richness was higher in these broadleaf-conifer mixtures than in monospecific stands of either component tree species, which supports the hypothesis of a greater diversity of resources for macroarthropods in these mixed stands. This hypothesis was not supported in Italy, where macroarthropod species richness was highest in monospecific chestnut stands. The positive influence of conifer presence on the species richness of saprophagous macroarthropods in Eastern European forests contrasts with results of previous studies, which calls for further research to explain those differences.

Using inventory variables for practical biodiversity assessment in plantation stands

Aim of study: Practically and simply assessing biodiversity by using inventory variables in four types of forest plantation stands (mixed and pure) including species such are chestnut, blue gum and maritime pine.
 Area of study: Northwest Portugal in Vale do Sousa (14,840 ha), which is 97% covered with plantation forests.
 Material and methods: Simulated data, from 90-year stand-level forest management planning, were considered using three indicators: tree species (number of different species and species origin—native or exotic), mean diameter at breast height (DBH), and shrub biomass. Two shrub regeneration types (fully regenerated by seed and fully regenerated by resprouting), and three site quality conditions were also considered.
 Main results: Mean biodiversity scores varied between very low (10.13) in pure blue gum stands on lowest-quality sites with shrub regeneration by seed, and low (29.85) in mixed stands with a dominance of pine, on best-quality sites with shrub regeneration by resprouting. Site quality and shrub regeneration type significantly affected all biodiversity scores in mixed stands dominated by pine and pure chestnut stands, while less affected pure blue gum stands and mixed stands dominated by blue gum.
 Research highlights: The considered biodiversity indicators cover the major biodiversity aspects and allow biodiversity assessment over time. The findings are relevant for biodiversity conservation and fire protection management.

Mixed-effects generalized height-diameter model: A tool for forestry management of young sweet chestnut stands

Height is a key variable for forest management. However, tree height measurements are expensive and time-consuming, requiring more effort to measure in the forest than diameter breast height measurements. Indeed, height-diameter (h-d) models are increasingly used to overcome the difficulty in measuring tree heights. Therefore, more accurate h-d models are increasingly needed. The mixed-effects modeling approach is a mainstream method to estimate h-d models. This technique was used to model the h-d relationship in the first 24 years of growth of sweet chestnut (Castanea sativa Mill.) high-forest stands for timber production. A dataset of 10,868 h-d observations and 57 plots of local-inventory data were considered individually. Simple mixed-effects models considering a grouping structure in the data (plot-level) were obtained, and generalized mixed-effects models were developed by expanding the fixed structure of simple mixed-effects models with stand-level variables. Several alternative model forms were tested in terms of accuracy, applicability and measurement effort. Different alternatives for calibrated predictions of tree height at plot level were analyzed, and considerations on the trade-off between easy-to-use equations in the field practice and high-accuracy equations for forest inventory were tested. The selected Richards M1a generalized mixed-effects model simultaneously provides fixed and random parameters to estimate the chestnut tree height from tree diameter and stand-level variables using the same model. The analysis showed that the inclusion of dominant height and dominant diameter as predictors improved the accuracy of the Richards model. The Draudt method was one of the best approaches to improve tree-level height prediction accuracy using mixed-effects. The applied approach is quite feasible in 100–500 m2 plots. The use of these models and the suggested calibration process will significantly reduce the effort and costs of fieldwork teams to measure heights for forest management planning while ensuring high accuracy. This effort is greater the greater the forest density and, therefore, greater for young stands than for adult stands.

Genetic diversity of Cryphonectria parasitica causing chestnut blight in South Tyrol (northern Italy)

European chestnut (Castanea sativa) is threatened by the invasive fungus Cryphonectria parasitica, which causes chestnut blight. The virulence of the fungus can be reduced by a group of mycoviruses that can spread among vegetatively compatible strains through hyphal anastomosis. Hypovirulent isolates are used as biocontrol agents, but their efficiency can be diminished by restricted hyphal anastomosis if the variability of vegetative compatibility (vc) types in a population is high. Sexual reproduction could increase the vc type diversity and further complicate biocontrol in a region. Therefore, knowledge of genetic diversity of C. parasitica is important to assess the effectiveness of a biological control program. The present study was performed in the Autonomous Province of Bozen-Bolzano (South Tyrol) in northern Italy, where chestnut cultivation provides an additional income to farmers. The genetic characterization of C. parasitica isolates from 35 chestnut stands and one forest population in different districts of South Tyrol was performed based on the analysis of vegetative incompatibility loci, the mating type locus, and the internal transcribed spacer (ITS) region. In this study, a total of 23 different vc types were found all over South Tyrol with a Shannon diversity index of 1.86. EU-2, EU-1, and EU-13 were the most widespread vc types comprising 51%, 13%, and 9% of the fungal isolates, respectively. Both mating types were present in the region with a ratio close to 1:1. Three different haplotypes were identified based on ITS sequence analysis, which pointed to two introduction events of the fungus to the region and allowed placing C. parasitica from South Tyrol into a larger phylogeographic context.

Breeding chestnut for resistance to Phytophthora cinnamomi for improving the productivity of chestnut stands

Breeding chestnut for resistance to Phytophthora cinnamomi for improving the productivity of chestnut stands

The chestnut growing hotspot of Turkey in danger: introduction of the Asian chestnut gall wasp into Aegean region

Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae), is an important pest of Castanea species worldwide. Adults emerge in summer and lay eggs in a few days. Severe infestations may reduce chestnut and timber production. It was first recorded in Europe in 2002 from Italy. In April 2014, it was recorded in Turkey for the first time in Marmara region (Yalova, north-western Turkey). Despite quarantine measures, infected chestnut saplings were sold from this region to several growers in western Turkey (Aydın and İzmir) in 2018. Although most of these saplings were removed and burned shortly after planting, some planted saplings could not be detected and some adult emergences may have occurred before the sapling removal, we had accepted hypothetically the Asian chestnut gall wasp was introduced in the region. Confirming this hypothesis, we detected the pest in a private chestnut orchard in 2020 in İzmir. Although, to date, we have not found it in adjacent natural chestnut stands, it will most probably increase in the whole region in the near future. As the largest private chestnut orchards of Turkey occur in this region, the Asian chestnut gall wasp invasion in the region will have serious socioeconomic consequences. Accordingly, we began to inform growers and foresters in the region, and to develop pest management strategies.

Emergence and diversification of a highly invasive chestnut pathogen lineage across southeastern Europe.

Invasive microbial species constitute a major threat to biodiversity, agricultural production and human health. Invasions are often dominated by one or a small number of genotypes, yet the underlying factors driving invasions are poorly understood. The chestnut blight fungus Cryphonectria parasitica first decimated the North American chestnut, and a more recent outbreak threatens European chestnut stands. To unravel the chestnut blight invasion of southeastern Europe, we sequenced 230 genomes of predominantly European strains. Genotypes outside of the invasion zone showed high levels of diversity with evidence for frequent and ongoing recombination. The invasive lineage emerged from the highly diverse European genotype pool rather than a secondary introduction from Asia or North America. The expansion across southeastern Europe was mostly clonal and is dominated by a single mating type, suggesting a fitness advantage of asexual reproduction. Our findings show how an intermediary, highly diverse bridgehead population gave rise to an invasive, largely clonally expanding pathogen.

Strategies for the Management of Traditional Chestnut Landscapes in Pesio Valley, Italy: A Participatory Approach

Through an exploratory case study conducted in the Pesio Valley, northwest Italy, this paper proposes a framework for maintaining traditional chestnut production landscapes and addressing future development policies. The main goal was to understand how to promote a bottom-up planning approach, including stakeholder perceptions in traditional chestnut landscape management. To ensure the sustainability of the landscape, current driving forces and their landscape effects were identified by local stakeholders using a focus group technique. Population ageing, local forestry policies directed towards supporting chestnut growers’ income, social and economic needs, and land fragmentation are the main driving forces that will influence future chestnut landscapes. The focus group participants built two scenarios of possible future development of the chestnut landscape, one characterized by the disappearance and transformation of chestnut stands, the other by their permanence and maintenance. The most recommended strategies for maintaining traditional chestnut cultivation were chestnut processing, fruit designation of origin, and the cultivation of traditional varieties. This study shows that, to preserve the traditional chestnut landscape, the participation of multiple stakeholders is a useful approach in landscape planning. This methodology could guide decision-makers and planners who desire to implement a participatory approach to a sustainable development program for traditional chestnut landscapes.

Monitoring of Chestnut Trees Using Machine Learning Techniques Applied to UAV-Based Multispectral Data

Phytosanitary conditions can hamper the normal development of trees and significantly impact their yield. The phytosanitary condition of chestnut stands is usually evaluated by sampling trees followed by a statistical extrapolation process, making it a challenging task, as it is labor-intensive and requires skill. In this study, a novel methodology that enables multi-temporal analysis of chestnut stands using multispectral imagery acquired from unmanned aerial vehicles is presented. Data were collected in different flight campaigns along with field surveys to identify the phytosanitary issues affecting each tree. A random forest classifier was trained with sections of each tree crown using vegetation indices and spectral bands. These were first categorized into two classes: (i) absence or (ii) presence of phytosanitary issues. Subsequently, the class with phytosanitary issues was used to identify and classify either biotic or abiotic factors. The comparison between the classification results, obtained by the presented methodology, with ground-truth data, allowed us to conclude that phytosanitary problems were detected with an accuracy rate between 86% and 91%. As for determining the specific phytosanitary issue, rates between 80% and 85% were achieved. Higher accuracy rates were attained in the last flight campaigns, the stage when symptoms are more prevalent. The proposed methodology proved to be effective in automatically detecting and classifying phytosanitary issues in chestnut trees throughout the growing season. Moreover, it is also able to identify decline or expansion situations. It may be of help as part of decision support systems that further improve on the efficient and sustainable management practices of chestnut stands.

CHESTNUT COVER AUTOMATIC CLASSIFICATION THROUGH LIDAR AND SENTINEL-2 MULTI-TEMPORAL DATA

Abstract. Chestnut (Castanea sativa Mill.) managed forests in Galicia (Northwestern Spain) have important cultural, economic and ecosystem values. However, due to rural exodus chestnut stands are being degraded. In order to take restoration and conservation measures knowledge of these forests' location, expanse and stage is needed. The available Spanish official cartography is based on photointerpretation which is inaccurate in terms of chestnut forest location and classification. However, remote sensing has recently been proven to be an effective tool for this purpose. Sentinel 2 multi-temporal classification is recently acquiring importance as a method to classify tree species. This project intends to detect chestnut forests using LiDAR and Sentinel 2 multi-temporal data and to compare these results with those obtained using the official cartography. It also intends to assess how the use of different phenological stages could improve classification results. The results obtained provide an overall accuracy of 76% when a three-month combination is used: (March, July and September) leaf-off stage, flowering and leaf-on stage. Overlapping of the current map and the official cartography lead to an accuracy and precision increase; highlighting the utility of the presented methodology to acquire knowledge about chestnut forests location.

Conversion of Secondary Forests into Chestnut Forests Affects Soil Nutrients in Anji County, China

The maintenance of drinking water safety is a major environmental issue. It is necessary to strengthen environmental protection in water source areas and establish good vegetation coverage. This study examined the effects of secondary forests transformation on chestnut forests on soil nutrient changes in the Fuji Reservoir, Anji County, Zhejiang province, China. Plots were set up in a chestnut plantation and a nearby secondary forest to measure the nutrient contents of soil samples that were collected from different soil depths. Differences of soil nutrient content from the two stands were significant at 0–20 cm soil depth. There were no significant differences in the contents of total phosphorus and total potassium between the two forests; however, the available phosphorus content in chestnut stands was 2.73 mg/kg higher than in secondary forests. Overall, the soil nutrient contents under chestnut stands were lower than those under secondary forests. Some of the soil surface is exposed due to the low diversity of the chestnut forest. The soil nutrients in the chestnut forest are usually carried and transferred in soil particle form and they become dissolved in the runoff during rainfall and lost, which explains the lower soil nutrient contents in the chestnut forest than the secondary forest. Therefore, for economic forests, such as chestnut forests, measures should be taken to protect understory vegetation and enhance soil and water conservation capacity, which is conducive to retaining soil nutrients.

Environmental and stand conditions related to Fistulina hepatica heart rot attack on Castanea sativa

AbstractCastanea sativa forests in north‐eastern Spain have historically been healthy and have been good producers of timber and non‐wood forest products. In the last quarter of a century, Fistulina hepatica has gained relevance in this ecosystem and is believed to be responsible for Chestnut Red Stain (CRS), which inflicts heart rot in trees and causes severe economic losses. The fungus grows in the heartwood and produces no external symptoms that would enable early detection. With the objective of developing an inexpensive method to detect heart rot and to discover possible relationships between the severity of F. hepatica attack and the silvicultural management or site characteristics of chestnut stands, 38 pure C. sativa plots were selected, sampled and analysed for the presence of the fungus. DNA was extracted from the heartwood samples, and PCR was used to amplify target sequences with specific F. hepatica primers for non‐homologous ITS1 and ITS2 regions. Correlation analysis was used to inspect the multiple interactions among the environmental and management variables examined, and a predictive model was designed for forest managers to estimate the risk of infection. Both analyses revealed that stress variables were related to CRS severity. This result is especially relevant since temperatures are expected to rise in coming decades throughout the northern rim of the Mediterranean region, where chestnut is an important species. This study provides two tools for better managing chestnut forests in the coming years: an inexpensive and fast tool for diagnosis and a predictive model to estimate the risk of infection.

Role of Fresh Dead Wood in the Epidemiology and the Biological Control of the Chestnut Blight Fungus.

The invasive fungus Cryphonectria parasitica, the causal agent of chestnut blight, is able to survive and sporulate on the bark of fresh dead Castanea sativa wood for at least 2 years. Here, we experimentally investigated the role of fresh dead wood in the epidemiology of chestnut blight, specifically in the spread of the hyperparasitic virus Cryphonectria hypovirus 1, which acts as biocontrol agent of C. parasitica. A total of 152 artificially initiated, virulent bark cankers in four chestnut stands were treated with virus-infected asexual spores originating either from sporulating dead wood or from a spore suspension. Molecular markers for both the virus and the fungal carrier were used to examine the spread of the applied biocontrol virus. Fourteen months after treatment, 42 to 76% of the conidial spray-treated cankers and 50 to 60% of the cankers exposed to a sporulating dead stem had been virus infected by the applied hypovirulent conidia in all four study sites. Virus infection reduced canker expansion and promoted canker healing (callusing). Thus, fresh chestnut dead wood may play an important role in supporting the successful spread of natural hypovirulence in chestnut forests. Further, combined with the application of virus-infected conidial suspensions, it may help promote the establishment of artificially released hypoviruses in chestnut stands to control chestnut blight.

Does the persistence of sweet chestnut depend on cultural inputs? Regeneration, recruitment, and mortality in Quercus- and Castanea-dominated forests

Quercus secondary forests show a gradual transition toward mixed forests, with sweet chestnut ( Castanea sativa ) becoming increasingly abundant in the western Spanish Central System. Additionally, in chestnut-dominated stands, it shows a certain resistance to competitive displacement by Quercus pyrenaica . Our results partially refute the traditional view that C. sativa is unable to recruit in the absence of cultural inputs. Sweet chestnut, Castanea sativa, is a component of European broadleaf forests and is one of the most managed trees. Due to a reduction in cultural inputs, chestnut-dominated stands tend to be invaded by other species, and it is unclear how chestnut is able to persist in natural mixed forests. Our work aimed to identity the main factors that limit the establishment of C. sativa and to analyze the recruitment and mortality processes of C. sativa trees. The age, growth ring patterns, regeneration density, and the spatial structure of trees and saplings in 11 plots in the Spanish Central System were analyzed. Chestnut seedling density increased with C. sativa basal area, but transition toward the sapling stage appeared limited owing to light availability. In Quercus pyrenaica secondary forests, sparse canopies did not constrain chestnut regeneration, and in old chestnut stands, C. sativa showed a certain resistance to competitive displacement. By contrast, mixed young coppices showed a high mortality, most likely due to competition with other vigorous resprouters. Quercus secondary forests showed a gradual transition toward mixed forests with sweet chestnut becoming increasingly more abundant. In old stands, C. sativa is likely to persist under a gap-phase mode of regeneration. Our results partially refute the traditional view that C. sativa is unable to recruit in the absence of cultural inputs.

Allometric equations for predicting mineralomass in high-forest chestnut stands in Portugal

The assessment of nutrients in biomass tree-components is a time-consuming and expensive process, often involving tree felling, not always possible or desirable. Thus, mineralomass prediction equations are an important tool for the quantification of the nutrients exported in management and harvesting activities towards its replacement and sustainable management, as well as to evaluate the effect of other disturbances in the balance of ecosystems. Thus, given the importance of the relationship of biomass and nutrients (mineralomass) for dynamic and sustainable management of chestnut woodlands, above-ground mineralomass was studied in sweet chestnut (Castanea sativa Mill.) high-forest stands located in northern Portugal. Nutrient-specific prediction equations that allow estimating the mineralomass (N, P, K, Ca, Mg, S, B and C) stocked in the trees above the ground, considering the tree as a whole (stem + bark + branches + leaves + flowers) and seperately for each tree component: stem-wood, stem-bark, branches, leaves and flowers, based on tree dendrometric variables, DBH (diameter breast height) and total height, were developed.. Linear and non-linear regression estimation methods were used. Data analysis was based on information collected in destructive analysis of 34 felled trees, distributed by the existing diameter classes (10-65 cm) in three adult chestnut stands. Several linear and nonlinear equations were fitted by the least squares method to select models. A simultaneous fit by SUR method using iterative seemingly unrelated regression (ITSUR) was used for the final selected models. The best-fitting models are presented.

Impact of the Asian Chestnut Gall Wasp, Dryocosmus kuriphilus (Hymenoptera, Cynipidae), on the Chestnut Component of Honey in the Southern Swiss Alps.

The Asian chestnut gall wasp (ACGW; Dryocosmus kuriphilus Yasumatsu, Hymenoptera, Cynipidae) is considered as one of the most dangerous pests of the genus Castanea. In southern Switzerland, repeated heavy ACGW attacks prevented chestnut trees from vegetating normally for years before the arrival and spread of the biological control agent Torymus sinensis (Kamijo, Hymenoptera, Torymidae). This resulted in a greatly reduced green biomass and flower production. In this paper, we analyze the impact of such an ecosystem alteration of the environment on the composition of produced honey. Six beekeepers were chosen from sites with different densities of chestnut trees, each of which providing series of honey samples from 2010 to 2016. We determined the chestnut component in the honeys via a combined chemical and sensory approach, and correlated the obtained results with the degree of yearly ACGW-induced crown damage and weather conditions during the period in question in the surrounding chestnut stands. The chestnut component in the analyzed honey sample series showed a strong correlation with the degree of ACGW-induced crown damage, whereas meteorological conditions of the corresponding year had a very marginal effect. Decreases in the chestnut component of the honey were statistically significant starting from a ACGW infestation level of 30%.

Plant neighbour identity and invasive pathogen infection affect associational resistance to an invasive gall wasp

Theory predicts that mixed forests are more resistant to native pests than pure forests (i.e. associational resistance) because of reduced host accessibility and increased top-down control by natural enemies. Yet, whether the same mechanisms also apply to invasive pests remains to be verified. We tested the hypothesis of associational resistance against the invasive Asian chestnut gall wasp (ACGW, Dryocosmus kuriphilus) by comparing ACGW infestation rates on chestnuts (Castanea sativa) in stands varying in species composition (chestnut alone or associated with oaks, pines or ashes). We investigated the effects of reduced chestnut density and frequency in mixed stands, as well as the effect of biotic interactions between ACGW, its parasitoids and the chestnut blight disease (caused by Cryphonectria parasitica). ACGW infestation rates were significantly lower in chestnut–oak and chestnut–ash mixtures than in pure chestnut stands and chestnut–pine mixtures. Infestation rate decreased with decreasing chestnut relative proportion. The composition of native parasitoid communities emerged from galls significantly differed between pure and mixed chestnut stands, but not the species richness or abundance of parasitoids. The abundance of the introduced parasitoid Torymus sinensis was not correlated with ACGW infestation rates and was independent of stand composition. Blight symptoms modified ACGW infestation rates with taller trees being preferred when they were asymptomatic but avoided when they presented blight disease damage. Our results suggest that conservation biological control based on tree species mixtures could contribute to reducing the damage of invasive forest pests.