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.
The goal of the present study is to assess how landscape configuration influenced the distribution of life-history traits across bird, carabid beetle and butterfly communities of mosaic forest ...landscapes in south-western France. A set of 12 traits was selected for each species, characterizing rarity, biogeographical distribution, body size, trophic guild, dispersal power, reproductive potential and phenology. We used a three-table ordination method, RLQ analysis, to link directly bird, beetle and butterfly traits to the same set of landscape metrics calculated in 400 m-radius buffers around sample points. RLQ analyses showed significant associations between life-history traits and landscape configuration for all three taxonomical groups. Threatened species from all groups were characterized by a combination of life traits that makes them especially sensitive to the fragmentation of herbaceous and shrub-dominated habitats at the landscape scale. These key life traits were low productivity, intermediate body mass, restricted geographic range, late phenology and ground gleaning for threatened birds, intermediate body size, spring adult activity, northern distribution and summer breeding period for threatened carabids, and restricted range, overwintering as eggs or larvae, low mobility, monophagy and short flight periods for threatened butterflies. Focusing on species life traits can provide a functional perspective, which helps to determine adequate measures for the conservation of threatened species and communities of several taxonomical groups in mosaic landscapes.
•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.
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.
According to the associational resistance hypothesis, diverse habitats provide better resistance to biological invasions than monocultures. Host‐plant abundance has been shown to affect the range ...expansion of invasive pests, but the effect of landscape diversity (i.e. density of host/non‐host patches and diversity of forest habitat patches) on invasions remains largely untested. We used boundary displacement models and boosted regression tree analyses to investigate the effects of landscape diversity on the invasion of Corsica by the maritime pine bast scale Matsucoccus feytaudi over an 18‐yr period. Taking the passive wind dispersal of the scale into account, we showed that open habitats and connectivity between host patches accelerated spread by up to 13%, whereas landscapes with high tree diversity and a high density of non‐host trees decreased scale spread by up to 14%. We suggest a new mechanism for such associational resistance to pest invasion at the landscape level, which we term ‘the pitfall effect’.
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.
Questions
Tree diversity is key to the functioning of forest ecosystems. However, which components of tree diversity are responsible for tree diversity effects on associated organisms, and in which ...context, is poorly understood.
Location
ORPHEE Experimental site, Cestas–Pierroton in the southwest of France.
Methods
We used a large‐scale tree diversity experiment in which we controlled water availability by an irrigation treatment to address tree diversity and water stress effects on the diversity and height of forest understorey vegetation. We assessed the species richness and height of understorey vegetation in irrigated and non‐irrigated 20 m × 20 m plots, either being monocultures of Pinus pinaster, Betula pendula or Quercus robur, or either mixtures of two to five species among Pinus pinaster, Betula pendula, Quercus robur, Quercus ilex and Quercus pyrenaica.
Results
Tree species composition, i.e. the proportion of birch or pine, had a significant effect on understorey plant assemblage, species richness and diversity. The proportion of the fast‐growing deciduous angiosperm Betula pendula was negatively correlated to understorey plant richness and diversity, and positively correlated with understorey vegetation height. Understorey vegetation was higher in irrigated plots than in non‐irrigated plots, but irrigation had no clear effect on the species richness, diversity or composition of understorey plant assemblages.
Conclusions
Forest tree species composition and in particular the relative proportions of different tree species had stronger effects on understorey plants than tree species richness per se. These effects were consistent across irrigation treatments. Even in young forest plantations, effects of tree mixture on understorey vegetation may be observed and seem mainly driven by the functional type of tree in the canopy and initial dynamics of plant regeneration in planted forests.
The effects of tree canopy diversity on understorey vegetation were tested by planting experimental forest stands including one to five tree species. Tree species composition rather than tree species richness affected understorey vegetation after nine years of plantation, especially the proportion of Betula pendula. Two years after starting an irrigation treatment to control water availability, drought level appeared to have a weak influence in these thermo‐Atlantic forests.
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.
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.
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