Lymantria dispar (Lepidoptera: Erebidae) is a significant defoliator both in its native and introduced regions. To better monitor and predict outbreaks for appropriate management of L. dispar, we ...estimated the defoliation distribution by L. dispar and performed nonlinear time-series forecasting of the vegetation anomaly dynamics. The Normalized Difference Vegetation Index (NDVI) obtained from Sentinel-2 was utilized to detect defoliation of the forests in the Altai Republic of Western Siberia. During the L. dispar outbreak in 2017, forest defoliation was captured by at two sites. The difference between NDVI in defoliated sites and seasonal NDVI was compared to characterize the NDVI dynamics of L. dispar defoliation. Results show that the NDVI of the two defoliated sites decreased by −0.101 and −0.087 during the season, respectively. The spatial distribution (100 m resolution) of the defoliation using NDVI showed a decreasing trend from 2017 to 2021. It showed heavy defoliation with a maximum of 10 % of the forest area from 2017 to 2018, in contrast to forest recovery in subsequent years. The defoliation was influenced by topographic factors, which occurred at relatively low elevations (916–1466 m) along roadways and open slopes. The NDVI model was built with dynamic mode decomposition (DMD) to represent the spatiotemporal dynamics of normal vegetation changes. The negative deviations between observed NDVI and the DMD-predicted NDVI then indicated anomalous vegetation changes such as defoliation by L. dispar. The study area's vegetation anomaly dynamics were forecasted using the local manifold distance-based regression (LMDr), a nonlinear forecasting technique that employs the state space reconstruction technique. The nonlinear time-series model demonstrated the best forecasting skill (ρ = 0.612) with the embedding (time-delay) dimension E = 11, suggesting the potential for anomaly detection and outbreak forecasting by the model. The study provided a good monitoring and forecasting framework for L. dispar defoliation in native ranges by combining a high-resolution imagery dataset with nonlinear anomaly detection.
•Defoliation by Lymantria dispar was detected using NDVI from Sentinel-2.•NDVI decreases in the season showed defoliation in outbreak years.•Defoliation was influenced by elevation and slope.•The vegetation anomaly was forecasted by the nonlinear time-series model.•Satellite monitoring and predictive defoliation model provide pest management tools.
•PPM showed higher incidences in stands dominated by P. pinaster and P. nigra and lower for P. sylvestris and P. pinea.•Pine stands with higher grazing pressure were more vulnerable to pine ...processionary moth.•PPM incidence is lower in structurally complex forests, with more cover of non-host trees and higher diversity of tree sizes.•Clearings occupied by bushes or rocks reduced PPM incidence, but clearings with a more simplified structure increased it.
The occurrence of the pine processionary moth (Thaumetopoea pityocampa, hereafter PPM) in Mediterranean pine forests and plantations is of increasing concern as processes such as global warming and forest cover expansion have amplified the frequency and virulence of outbreaks. This study attempts to provide as complete an overview as possible of the different factors involved in pine forest susceptibility to PPM in 98 pine stands in Central Spain. A large study area (∼3,000 km2) was considered, including three different spatial scales (<1 ha, 1 ha, 10 ha) and four different pine tree species (Pinus pinaster, P. nigra, P. sylvestris, P. pinea), monitored over a 4-year period. Models were fitted for each of the three spatial scales, as well as for a combination of them (multiscale model). Pine species had a strong influence on vulnerability to PPM, with higher incidences in stands dominated by P. pinaster and P. nigra and lower for those dominated by P. sylvestris and P. pinea. Grazing pressure, a factor thus far disregarded, was also determining, with a prominent role at both the multiscale and the stand-scale levels. Other variables were highly influential at some of the spatial scales, showing a greater resistance in pine forests or plantations with a higher diversity of pine sizes, greater tree density, and a larger cover of non-host tree species. Open habitats also played a role in PPM incidence: we detected that, both at the locality and the plot scale, the presence of clearings occupied by bushes or rocky outcrops reduced vulnerability to PPM, while the clearings with a more simplified structure produced the opposite effect. We conclude that PPM incidence is greater in structurally simple pine forests, with strong grazing pressure and abundant open spaces without woody vegetation that may favour PPM pupation. To reduce damage by PPM, pine forest and plantations should be managed to avoid oversimplified forest structures. Patches of non-host tree species should be promoted, as well as some presence of shrubs in open areas. This implies avoiding overgrazing and other management models leading to an excessive increase in bare soil. Nevertheless, it should be noted that the implementation of these recommendations should consider the remaining challenges that need to be addressed in the current context of global change, such as the increased risk of wildfires and the emergence of other pests and diseases.
•Pressure on tropical forests is significant despite better global forest management.•More planted forests are necessary but insufficient for better forest management.•Novel forest landscapes are ...important but elusive of global forest inventories.•Planted-forest expansion significantly drives transitions to net forest gain.
The Global Forest Resources Assessment 2015 shows that deforestation has slowed and afforestation has increased globally during 1990–2015. Planted forests have increasingly provided goods and services hitherto derived from natural forests, and mosaic forests in agricultural landscapes are increasing. Forest gain is occurring at higher latitudes and in richer countries whilst forest loss continues in poor countries in the tropics. Some middle income tropical countries are now also transitioning to forest gain. These transition countries are characterised by reforms to forest management and improvements in agricultural practices but also by significant expansions of planted forest, which account for ∼25–100% of gains. Forest-area estimates of the FRA align with satellite-derived estimates, with deviations of ⩽±7% globally and ⩽±17% for the tropics. Mosaics comprised of trees outside forests, remnant forest patches, and young regenerating forests constitute a modest proportion of the tropical forest estate and are seemingly well inventoried by the FRA. Extensive areas of forest experienced partial canopy cover reduction since 2000, particularly in the tropics where their area is ∼6.5 times that deforested since 1990. The likelihood of the eventual loss of these forests and a decline in their capacity to provide goods and services is a matter of concern. Demand for industrial wood and fuelwood increased 35% in the tropics since 1990, principally in poorer countries, and growth in demand will accelerate into the future, particularly in the Asia-Pacific region. Notwithstanding significant increases in forests within protected areas since 1990 to 517Mha (16.3%) globally and 379Mha (26.6%) in the tropics, increasing demands for ecological services, forest products, and climate change mitigation is likely to be met from an expanding area of planted forests more than from the declining area of natural forests, particularly in Africa. The global rate of planted-forest expansion since 1990 is close to a target rate of 2.4% per annum necessary to replace wood supplied from natural forests in the medium term, though the expansion rate has declined to 1.5% since 2005. Multiple-use forests permitting both production and conservation account for 26% of the global forest area and 17% of the tropical forest area, and have increased by 81.8Mha or 8.5% globally since 1990, with most gains in the tropics. Sustainable forest management in low-income and tropical countries remains modest, with only 37% low-income country forests covered by forest inventories. International support has proven effective at increasing this coverage since 2010.
We review and synthesize information on invasions of nonnative forest insects and diseases in the United States, including their ecological and economic impacts, pathways of arrival, distribution ...within the United States, and policy options for reducing future invasions. Nonnative insects have accumulated in United States forests at a rate of
•Management history is important for bark beetle outbreaks.•Altered tree species composition affected bark beetle outbreaks.•Interactions between drivers potentiate damage by bark beetles.•Actively ...managed stands had lower probability of bark beetle outbreaks.
Historical management practices could have a strong effect on the current status of forests and therefore affect the potential for outbreaks of forest pests. We tested whether forest management history and forest tending of Norway spruce affects the potential for bark beetle outbreaks after large disturbances. We also assessed the effect of the proportion of spruce under epidemic situations and different altitudes. For this survey we used long-term data on sanitary felling and forest inventory data. Forest management history was defined by the change in the forest compared to the natural forest composition and was divided into four classes of change in tree species composition. We compared the proportion of spruce and sanitary felling because of bark beetles with the different classes of change in tree species composition. Forest tending was analyzed by looking at how the proportion of realized cut in relation to the planned cut affected sanitary felling. The analysis was done with Bayesian modeling including both spatial autocorrelation and random effects. There was a strong association between the change in the forest tree species composition and the proportion of Norway spruce and sanitary felling because of spruce bark beetles. Interactions were observed between epidemic periods, the proportion of Norway spruce and altitude. Altitude had a negative influence and the proportion of Norway spruce had a positive influence on sanitary felling. During epidemic periods, sanitary felling was amplified at lower altitudes and in areas with a higher proportion of Norway spruce. Furthermore, there was a negative association between the proportion of realized cut in relation to the planned cut and sanitary felling in periods after abiotic stress. It is therefore suggested that monocultures of Norway spruce should be converted to mixed forests and that maintenance of the forest should be improved to increase resistance to bark beetle outbreaks.
Trees and forests provide a wide variety of ecosystem services in addition to timber, food, and other provisioning services. New approaches to pest and disease management are needed that take into ...account these multiple services and the different stakeholders they benefit, as well as the likelihood of greater threats in the future resulting from globalization and climate change. These considerations will affect priorities for both basic and applied research and how trade and phytosanitary regulations are formulated.
Abstract
Pest-specific inventories require substantial resources and are often infeasible, creating a need for alternative means of early pest detection. We examined the potential for stand ...inventories to detect forest health threats by using a unique dataset of mapped eastern spruce dwarf mistletoe (Arceuthobium pusillum Peck.) infestations in black spruce (Picea mariana Mill. B.S.P) stands of northern Minnesota, USA. We simulated stand inventories across a range of sampling intensities; that is, current standard (S) methods in Minnesota, adding one plot (S + 1), doubling the intensity (2S), and halving the intensity (S/2), using fixed-radius plots and transect buffers for detection. We categorized stands into low, moderate, and high infestation severity. We simulated detection at multiple viewing distances along S inventory transects in low severity infestation stands. Detection probability increased as sampling intensity increased. Plot-based detection averaged > 50% for moderate and high severity infestations except S/2 in moderate severity infestations. Notably, transect-based detection averaged ≥ 85% at viewing distances of 25 to 100 m. Results suggest stand inventories could provide opportunities to detect forest health threats with unique signatures when transect observations are included. Thus, forest health specialists may consider including pest-specific training for foresters in current inventory methods, requiring modest investment of time and effort.
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•A user-friendly bioassay system for oak processionary moth larvae is presented.•Spores of Bacillus strains are applied by oak bud dipping.•Bacillus thuringiensis ssp. kurstaki was ...highly efficient.•A new bacterial isolate (Bacillus wiedmannii) was not effective.•A metagenomic sequencing approach to screen for entomopathogens is presented.
The oak processionary moth (OPM) Thaumetopoea processionea is a pest of oak trees and poses health risks to humans due to the urticating setae of later instar larvae. For this reason, it is difficult to rear OPM under laboratory conditions, carry out bioassays or examine larvae for pathogens. Biological control targets the early larval instars and is based primarily on commercial preparations of Bacillus thuringiensis ssp. kurstaki (Btk). To test the entomopathogenic potential of other spore-forming bacteria, a user-friendly bioassay system was developed that (i) applies bacterial spore suspensions by oak bud dipping, (ii) targets first instar larvae through feeding exposure and (iii) takes into account their group-feeding behavior. A negligible mortality in the untreated control proved the functionality of the newly established bioassay system. Whereas the commercial Btk HD-1 strain was used as a bioassay standard and confirmed as being highly efficient, a Bacillus wiedmannii strain was ineffective in killing OPM larvae. Larvae, which died during the infection experiment, were further subjected to Nanopore sequencing for a metagenomic approach for entomopathogen detection. It further corroborated that B.wiedmannii was not able to infect and establish in OPM, but identified potential insect pathogenic species from the genera Serratia and Pseudomonas.
Classical biological control (CBC) is the introduction of a natural enemy of exotic origin to control a pest, usually also exotic, aiming at permanent control of the pest. CBC has been carried out ...widely over a variety of target organisms, but most commonly against insects, using parasitoids and predators and, occasionally, pathogens. Until 2010, 6158 introductions of parasitoids and predators were made against 588 insect pests, leading to the control of 172 pests. About 55% of these introductions were made against pests of woody plants. Establishment rates of natural enemies and success rates were higher in CBC projects targeting pests of woody plants than other pests. This review aims to answer the questions most commonly asked regarding CBC against insect pests, with particular emphasis on tree pests. The topics covered include, among others: variations in rates of successes among different systems, different target insect groups and different agents; temporal trends in CBC practices and successes; economic and environmental benefits; risks and ways to mitigate the risks; CBC against native pests; accidental successes through the adoption of the invasive pests by native natural enemies or accidentally introduced agents; and prospects and constraints for the practice of CBC in the future. Questions are answered based on the analysis of two databases, the BIOCAT2010 database of introductions of insect biological control agents for the CBC of insect pests, and a database of introductions of entomopathogens against insect pests.
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