•Pine-birch forests were more resistant to primary pests than pine monocultures.•Associational resistance was due to direct and indirect, growth-mediated, effects of birch.•Growth-mediated effects ...occurred independently of drought conditions.
Tree species diversity generally has positive effects on forest primary productivity and resistance to natural perturbations, but diversity-function relationships can vary with site conditions. Recently, studies in forest diversity experiments have shown that tree diversity and local climate, in particular drought intensity, interactively affect insect herbivory. On the other hand, many studies focused on the response of forests to drought in terms of tree growth but without analysing the concomitant effects on susceptibility to pests. It is of particular interest to understand the combined effects of drought and tree diversity on the growth of the host tree, since host resource concentration is a determining factor of a pest’s host choice.
We used a tree diversity experiment where tree species diversity and drought conditions were both manipulated to evaluate their interactive effects on the susceptibility of maritime pine (Pinus pinaster Aït.) forests to two primary pests (i.e. infesting healthy trees): the pine stem borer (PSB) Dioryctria sylvestrella, and the pine processionary moth (PPM; a leaf chewer), Thaumetopoea pityocampa. Using structural equation models, we investigated the direct and indirect effects (i.e. mediated by host resources) of the presence of birch and drought on the total number of attacks of PPM and PSB, in the same plots and in the same year.
We showed that pine-birch plots were more resistant to both PPM and PSB attacks than pine monocultures. Furthermore, we found that this associational resistance pattern was due to direct effects of birch trees on attacks, possibly related to disrupting non-host volatiles (NHVs), but also to indirect, resource-mediated effects whereby the presence of birch trees reduced the amount of host pine resources available to the pests. Drought conditions modulated birch mediated effects on resistance of maritime pine forests only for PSB attacks. Overall, our work improves our understanding of tree diversity-herbivory relationships and helps explain how climate might modulate such relationships.
A major conservation challenge in mosaic landscapes is to understand how trait‐specific responses to habitat edges affect bird communities, including potential cascading effects on bird functions ...providing ecosystem services to forests, such as pest control. Here, we examined how bird species richness, abundance and community composition varied from interior forest habitats and their edges into adjacent open habitats, within a multi‐regional sampling scheme. We further analyzed variations in Conservation Value Index (CVI), Community Specialization Index (CSI) and functional traits across the forest‐edge‐open habitat gradient. Bird species richness, total abundance and CVI were significantly higher at forest edges while CSI peaked at interior open habitats, i.e., furthest from forest edge. In addition, there were important variations in trait‐ and species‐specific responses to forest edges among bird communities. Positive responses to forest edges were found for several forest bird species with unfavorable conservation status. These species were in general insectivores, understorey gleaners, cavity nesters and long‐distance migrants, all traits that displayed higher abundance at forest edges than in forest interiors or adjacent open habitats. Furthermore, consistently with predictions, negative edge effects were recorded in some forest specialist birds and in most open‐habitat birds, showing increasing densities from edges to interior habitats. We thus suggest that increasing landscape‐scale habitat complexity would be beneficial to declining species living in mosaic landscapes combining small woodlands and open habitats. Edge effects between forests and adjacent open habitats may also favor bird functional guilds providing valuable ecosystem services to forests in longstanding fragmented landscapes.
This study investigates the response of bird communities to habitat edges between woodland patches and open areas in a multi‐region sampling design in French temperate mosaic landscapes. We found that forest edges exhibited higher Conservation Value Index, bird species richness and total abundance. Species sharing life‐history traits expected to be good predictors of vulnerability to global change showed as well a positive response to forest edges. Our results confirmed that forest edges are valuable for conserving and even enhancing biodiversity in managed, fragmented landscapes, by increasing local habitat heterogeneity and mitigating the effects of landscape homogenization linked to modern forestry practices.
Context
The pine wood nematode (PWN) is an invasive species which was introduced into Europe in 1999. It represents a major economic and ecological threat to European forests. In Europe, the maritime ...pine is the main host and
Monochamus galloprovinciallis
is its only vector.
Objectives
Our goal was to analyze the effect of landscape heterogeneity on the vector’s dispersal. We further aimed at developing a new method to locate the origin of insects captured in a systematic network of pheromone traps.
Methods
A mark-release-recapture experiment was carried out in a heterogeneous landscape combining maritime pine plantations, clear-cuts and isolated patches of broadleaved and mixed forests in the southwest of France. Least-cost path analysis was used to model dispersal trajectories and assign friction values to each land-use type in the landscape. We used the trap’s geographical coordinates, capture levels and mean friction values of neighbouring patches to calculate a weighed barycentre and the position of the release of marked beetles.
Results
Least Cost Path modelling revealed the vector’s tendency to avoid habitat patches such as mixed or deciduous forests and not avoid clear-cuts. The weighted barycentre method was greatly improved when the friction values of the trap’s surrounding land-uses were used.
Conclusions
Our study demonstrates the value of applying landscape ecology concepts and methods to improve our understanding and prediction of pest invasion processes. A practical application is the design of systematic grids of pheromone traps to locate the infection focus from which PWN vectors originate in a newly colonized area.
Abstract
Next‐generation biomonitoring proposes to combine machine‐learning algorithms with environmental DNA data to automate the monitoring of the Earth's major ecosystems. In the present study, we ...searched for molecular biomarkers of tree water status to develop next‐generation biomonitoring of forest ecosystems. Because phyllosphere microbial communities respond to both tree physiology and climate change, we investigated whether environmental DNA data from tree phyllosphere could be used as molecular biomarkers of tree water status in forest ecosystems. Using an amplicon sequencing approach, we analysed phyllosphere microbial communities of four tree species (
Quercus ilex
,
Quercus robur
,
Pinus pinaster
and
Betula pendula
) in a forest experiment composed of irrigated and non‐irrigated plots. We used these microbial community data to train a machine‐learning algorithm (Random Forest) to classify irrigated and non‐irrigated trees. The Random Forest algorithm detected tree water status from phyllosphere microbial community composition with more than 90% accuracy for oak species, and more than 75% for pine and birch. Phyllosphere fungal communities were more informative than phyllosphere bacterial communities in all tree species. Seven fungal amplicon sequence variants were identified as candidates for the development of molecular biomarkers of water status in oak trees. Altogether, our results show that microbial community data from tree phyllosphere provides information on tree water status in forest ecosystems and could be included in next‐generation biomonitoring programmes that would use in situ, real‐time sequencing of environmental DNA to help monitor the health of European temperate forest ecosystems.
Key message
In mixed stands of
Pinus pinaster
and
Pinus pinea
, fewer insect vectors of the pinewood nematode (PWN) were captured than in pure
P. pinaster
stands. This finding has practical ...implications for PWN disease management, including the recommendation to improve the diversity of maritime pine plantations and to conserve stone pines in infected areas.
Context
The PWN is an invasive species in European pine forests, being vectored by the longhorn beetle
Monochamus galloprovincialis
. The presence of less preferred host trees may disrupt the insect vector dispersal and slow the spread of the disease.
Aims
The aim of the study was to compare the abundance of
M. galloprovincialis
in pure stands of
Pinus pinaster
, a preferred host tree, pure
P. pinea
stands, a less preferred host, and mixtures of these two species.
Methods
We selected 20 mature pine stands varying in %
P. pinaster
and %
P. pinea
in Spain. In each stand, we installed 3 pheromone traps to catch
M. galloprovincialis
. We related trap catches to stand and landscape composition.
Results
The level of capture of
M. galloprovincialis
was highest in pure
P. pinaster
stands and decreased with increasing proportion of
P. pinea
.
Conclusions
The presence of stone pine mixed with maritime pine significantly reduces the local abundance of the PWN insect vector. The most plausible mechanism is that
P. pinea
emits odors that have a repulsive effect on dispersing beetles.
Habitat degradation and climate change are main drivers of insect species loss worldwide, raising concern about natural forest replacement by tree monocultures in a context of more frequent ...disturbances like drought. Carabid beetles are emblematic species in ecology because they are often used as indicators of biodiversity and they have important functional roles, particularly predation.
We used a tree diversity experiment with half of the plots irrigated and the other half under summer water stress to test the combined effects of tree species mixing and drought on carabid species and functional diversity.
We observed a qualitative effect of drought on carabid communities, with species turnover mainly due to predator species loss in the drier (non‐irrigated) plots.
We also found that species richness and activity density were lowest in pure pine plots and highest in mixture of pine and birch at low tree density. The likely underlying mechanism is the better provision of food and shelter resources in mixed forests.
The association of pine with birch species could compensate for the loss of carabid beetles observed between pine monocultures benefiting from the water regime of the last century and those subject to current droughts. This suggests that diversifying plantation forests is a promising way to increase their resilience to the adverse effects of climate change.
Drought in pure pine forests resulted in loss of predatory carabid beetles.
Carabid beetles were least abundant in pure pine plots and most abundant in pine‐birch mixtures under drought conditions.
Adding birch to pine may help offset drought‐induced carabid losses.
Aim The role of bird–insect interactions in shaping bird distribution patterns at the landscape scale has been seldom investigated. In mosaic landscapes, bird functional diversity is considered to be ...an important driver of avian insectivory, but depends on forest fragmentation and edge effects from adjacent, non-forest habitats. In a transcontinental experiment, we investigated edge and landscape effects on bird functional diversity and insectivory in mosaic landscapes of mixed forests and open habitats. Location New Zealand and France. Methods We paired edge and interior plots in native forest fragments in New Zealand and native plantation forests in France. We sampled bird communities using point-counts and linear transects respectively and simultaneously quantified avian insectivory as the rate of bird attacks on plasticine models mimicking tree-feeding Lepidoptera larvae. The same seven life traits and attributes were compiled for French and New Zealand birds, including biogeographic origin, body mass, mobility, foraging method, adult diet, nest location and clutch size. Bird functional diversity was quantified on this multitrait basis by four indices: functional richness, evenness, divergence and dispersion. We used mixed models to test for the effects of forest edges, study area, surrounding landscape diversity and native forest cover on bird functional diversity and insectivory. Results We found higher bird functional richness at forest edges than interiors in New Zealand and lower functional richness at edges in France. However, bird functional evenness and divergence were significantly higher at forest edges in the two countries. Functional evenness and dispersion both increased with landscape diversity and evenness increased with native forest cover. Moreover, bird insectivory increased at forest edges with functional evenness, irrespective of the study area. Main conclusions We suggest that intermediate levels of forest fragmentation and edge effects increase avian insectivory in mosaic landscapes, through enhanced functional evenness and trait complementation within predatory bird assemblages.
More diverse forests are generally more resistant to insect herbivores. This might be due to positive effects of tree diversity on predation. Although the enemies hypothesis has received conflicting ...evidence in forest ecosystems.
Carabids were sampled by pitfall trapping in a tree diversity experiment, at the centre of plots ranging from one to five tree species mixtures. The composition and vertical structure of the vegetation was assessed at three scales, in the understorey, in the canopy of the experimental plots, and in the surrounding area of each plot.
None of the tested vegetation variables had an effect on the species richness of carabids. In contrast, the vegetation compositional diversity at the understorey, canopy and surrounding scales had additive and positive effects on the activity‐density of the carabids.
Our findings indicate that more diverse forests can host a higher activity‐density of predatory carabids, as a result of the combined effect of horizontal and vertical vegetation diversity, which might increase both habitat quality and the amount of feeding resources. This highlights the relevance of manipulative tree diversity experiments to identify the ecological filters shaping local carabid communities.
Close‐up on the aerial photograph of one block of the ORPHEE experiment, where carabids were pitfall trapped at the centre of all 32 plots, ranging from one to five species mixtures.
The diversity of vegetation in the understorey, canopy and surrounding areas of the plots had additive and positive effects on the activity‐density of carabids.
Likely reasons are the improvement of habitat quality and the amount of food resources for predatory and omnivorous carabids.
Disentangling the confounded effects of edge and area in fragmented landscapes is a recurrent challenge for landscape ecologists, requiring the use of appropriate study designs. Here, we examined the ...effects of forest fragment area and plot location at forest edges versus interiors on native and exotic bird assemblages on Banks Peninsula (South Island, New Zealand). We also experimentally measured with plasticine models how forest fragment area and edge versus interior location influenced the intensity of avian insectivory. Bird assemblages were sampled by conducting 15 min point-counts at paired edge and interior plots in 13 forest fragments of increasing size (0.5–141 ha). Avian insectivory was measured as the rate of insectivorous bird attacks on plasticine models mimicking larvae of a native polyphagous moth. We found significant effects of edge, but not of forest patch area, on species richness, abundance and composition of bird assemblages. Exotic birds were more abundant at forest edges, while neither edge nor area effects were noticeable for native bird richness and abundance. Model predation rates increased with forest fragmentation, both because of higher insectivory in smaller forest patches and at forest edges. Avian predation significantly increased with insectivorous bird richness and foraging bird abundance. We suggest that the coexistence of native and exotic birds in New Zealand mosaic landscapes enhances functional diversity and trait complementation within predatory bird assemblages. This coexistence results in increased avian insectivory in small forest fragments through additive edge and area effects.
Litter decomposition is a key ecosystem function in forests and varies in response to a range of climatic, edaphic, and local stand characteristics. Disentangling the relative contribution of these ...factors is challenging, especially along large environmental gradients. In particular, knowledge of the effect of management options, such as tree planting density and species composition, on litter decomposition would be highly valuable in forestry. In this study, we made use of 15 tree diversity experiments spread over eight countries and three continents within the global TreeDivNet network. We evaluated the effects of overstory composition (tree identity, species/mixture composition and species richness), plantation conditions (density and age), and climate (temperature and precipitation) on mass loss (after 3 months and 1 year) of two standardized litters: high-quality green tea and low-quality rooibos tea. Across continents, we found that early-stage decomposition of the low-quality rooibos tea was influenced locally by overstory tree identity. Mass loss of rooibos litter was higher under young gymnosperm overstories compared to angiosperm overstories, but this trend reversed with age of the experiment. Tree species richness did not influence decomposition and explained almost no variation in our multi-continent dataset. Hence, in the young plantations of our study, overstory composition effects on decomposition were mainly driven by tree species identity on decomposer communities and forest microclimates. After 12 months of incubation, mass loss of the high-quality green tea litter was mainly influenced by temperature whereas the low-quality rooibos tea litter decomposition showed stronger relationships with overstory composition and stand age. Our findings highlight that decomposition dynamics are not only affected by climate but also by management options, via litter quality of the identity of planted trees but also by overstory composition and structure.
Display omitted
•Tree species identity and composition affected decomposition of low-quality litter.•Young gymnosperm overstories promoted decomposition.•Tree species identity effects on decomposition depended on the age of the stand.•Tree species richness explained <1 % variation in mass loss across continents.•Planting density did not impact decomposition dynamics.
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