Forest Research

Expanding forest and woodland cover is a global strategy to mitigate and adapt to the climate crisis and reverse biodiversity decline. While most woodland in temperate regions is created through tree planting, natural colonisation has been advocated for as an alternative or complementary approach. However, there is limited understanding on how the structural attributes of woodlands created through these different approaches develop through time. To address this knowledge gap, we assessed a suite of structural metrics for 28 woodland sites (aged 13-43 years) that were established along a planted to natural colonisation continuum in England. We used an Uncrewed Aerial System to collect LiDAR data alongside field surveys and calculated metrics relating to above-ground biomass accumulation (canopy height and basal area) and metrics relating to structural complexity (the horizontal and vertical arrangement of canopy) as a proxy for biodiversity potential. Canopy height and basal area were higher in woodlands with larger proportions of planting. Additionally, woodlands with higher proportions of planting displayed greater vertical complexity (canopy stratification) whereas there was weak evidence that woodlands with higher proportions of natural colonisation develop greater horizontal complexity (gap fraction). This suggests that tree planting is the better option when biomass accumulation is the primary goal, whereas natural colonisation or hybrid approaches are likely to be beneficial when the focus is biodiversity or a mix of outcomes. Woodlands created through hybrid approaches that combine planting and natural colonisation offered intermediate values of biomass accumulation and structural complexity.

Nitrogen (N) is an essential element for soil microbes, and its addition to soil can have variable effects on decomposition of soil organic carbon (SOC). We sought to quantify how N addition affects soil microbial decomposition and SOC stability by examining chemically free particulate organic C (POC) and chemically bound mineral-associated organic C (MAOC). Working along a naturally occurring inorganic N deposition gradient (from 6–32 kg ha−1 yr−1) across 26 UK forest sites, we examined correlations among POC, MAOC, and inorganic N pools, comparing the responses of organo-mineral vs. mineral soils, and broadleaf vs. conifer forests. POC stocks and total microbial biomass C were not affected by N deposition in broadleaved forest soils, yet MAOC stocks increased. In conifer forest soils, MAOC decreased and POC and the microbial biomass pools were unchanged. POC and MAOC stocks were significantly greater in mineral soils than organo-mineral soils, while most inorganic N measurements did not differ by soil type. Climatic factors were found to have a weak effect on soil C pools, but POC, MAOC, DOC, and microbial biomass C all decreased with increasing stand basal area. Our results show that the effects of inorganic N addition on soil C and N cycling can depend upon local plant and soil types. Alongside N deposition, forest attributes such as stand age and forest type have a strong effect on the microbial and geochemical factors that ultimately control POC and MAOC stability.

Global forest biomes face increasing stressors and disease outbreaks that threaten ecosystem health. Tree-associated microbiota are vital for tree resilience, yet their responses to biotic and abiotic stressors in mature trees remain poorly understood. Using an experimental woodland plot of 144 Quercus petraea trees subjected to drought (rain exclusion), nutrient stress (ringbarking), and biotic treatments (bacterial pathogens and beetle larvae) to simulate acute oak decline, we tracked microbial communities in leaf, stem, and root/rhizosphere tissues across four time points over 2 years. Oak trees hosted distinct microbial communities across tissue types, which remained largely stable under stress. Rain exclusion significantly altered microbiota composition, though these changes explained less than 1% of total variance. Actinobacteriota, linked to drought tolerance, increased in the root/rhizosphere of rain-excluded trees. These findings reveal a surprising resilience of oak-associated microbial communities to environmental and biotic disturbances, highlighting their potential role in forest ecosystem stability.

Group-living primates experience the benefits and costs associated with sociality, including an elevated risk of parasite transmission. However, the relative influence of group type (i.e., social structure), group size, and habitat disturbance on parasitic infection remains unclear, particularly in Southeast Asian primates. In this study, the abundance of intestinal parasites in proboscis monkeys (Nasalis larvatus) inhabiting a riverine forest along the Menanggul River, Sabah, Malaysian Borneo, was investigated. Fecal samples (n = 160) were collected from one-male-multifemale and all-male groups in areas with varying levels of anthropogenic disturbance, with efforts made to ensure that each sample originated from a different individual. In addition, the effects of group type, group size, and sampling location on parasite abundance were evaluated using fecal egg counts and Bayesian models. Three dominant parasite species groups (Trichuris sp., Strongyloides fuelleborni, and Oesophagostomum aculeatum) with an overall infection prevalence of 81.25% were identified. Results showed that group type did not significantly affect parasite abundance. However, group size showed a positive correlation with the abundance of Trichuris sp. and a negative correlation with S. fuelleborni and O. aculeatum. In addition, our models revealed that the infection load of Trichuris sp. decreased with increasing distance from the river mouth, which was used as a proxy for a disturbance gradient, whereas O. aculeatum exhibited higher infection load at greater distances, indicating lower prevalence in more disturbed downstream areas. Thus, parasite abundance in proboscis monkeys may be shaped by social and environmental factors, with taxa-specific responses likely reflecting differences in environmental persistence and transmission ecology.

AIMS:Agricultural crop productivity and global forest biomes are coming under increasing threat from insect pests and microbial pathogens. This impact is worsened by inter-kingdom insect-microbe interactions that can increase transmission and disease severity in affected plants. While bacterial chemical cues have been shown to directly influence insect behaviour, the impact of insect-derived compounds on phytopathogens is poorly understood. Here, we investigated the chemical basis for interactions between beetle larvae and bacteria in acute oak decline (AOD), a disease characterized by inner bark necrosis of Quercus robur and Q. petraea involving a polymicrobial consortium, including Brenneria goodwinii and larval galleries of Agrilus biguttatus. METHODS AND RESULTS:We found that A. biguttatus larval extractable metabolites increase bacterial growth rate and final cell density during in vitro culture, and stimulate the differential expression of ∼600 genes, including the type III secretion system and its effectors, which are major virulence factors in plant pathogens. Chemical compounds from closely related insect species did not have this effect. CONCLUSIONS:These findings highlight the importance of inter-kingdom interactions in plant disease and suggest a role for insect-derived chemical elicitors in facilitating the virulence of phytopathogens.