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91 results for “defoliation”
Data from: Boreal tree growth exhibits decadal-scale ecological memory to drought and insect defoliation, but no negative response to their interaction
1. Interactions between drought and insect defoliation may dramatically alter forest function under novel climate and disturbance regimes, but remain poorly understood. We empirically tested two important hypotheses regarding tree responses to drought and insect defoliation: 1) trees exhibit delayed, persistent, and cumulative growth responses to these stressors; 2) physiological feedbacks in tree responses to these stressors exacerbate their impacts on tree growth. These hypotheses remain largely untested at a landscape scale, yet are critical for predicting forest function under novel future conditions given the connection between tree growth and demographic processes such as mortality and regeneration. 2. We developed a Bayesian hierarchical model to quantify the ecological memory of tree growth to past water deficits and insect defoliation events, derive antecedent variables reflecting the persistent and cumulative effects of these stressors on current growth, and test for their interactive effects. The model was applied to extensive tree growth, weather, and defoliation survey data from western and eastern regions of the Canadian boreal forest impacted by recent drought and defoliation events and characterized by contrasting tree compositions, climates, and insect defoliators. 3. Results revealed persistent negative tree growth responses to past water (all trees) and defoliation (host trees) stress lasting 3-6 and 10-12 years, respectively, depending on study region. Accounting for the ecological memory of tree growth to water and defoliation stress allowed for detection of interactions not previously demonstrated. Contrary to expectations, we found evidence for positive interactions among non-host trees likely due to reduced water stress following defoliation events. Regional differences in ecological memory to water stress highlight the role of climate in shaping forest responses to drought. 4. Synthesis. Study results suggest negative feedbacks in tree responses to drought and insect attack may be weaker than predicted for defoliator-dominated boreal forest systems. Instead, insect defoliation may offset the impacts of water deficit on boreal tree growth by reducing transpirational water demand. This offset mimics increased resistance to drought following forest thinning and may lessen growth and mortality losses due to increased aridity and more severe insect damage forecast for the boreal forest under global change.
Data from: Differential defoliation and mortality of white spruce and balsam fir by Eastern spruce budworm
<p>White spruce (<em>Picea glauca</em>) and Balsam fir (<em>Abies balsamea</em>) tree mortality data and tree characteristics recorded in July 2019 following an Eastern spruce budworm outbreak detected at two sites in northern Wisconsin, USA in 2014. These data were collected at the individual tree level, and include tree status, tree diameter at breast height (cm) and canopy class.</p>
Ungulate herbivores promote beta diversity and drive stochastic plant community assembly by selective defoliation and trampling: From a four-year simulation experiment
<p>Ungulate herbivores shape grassland plant communities at multiple scales, ultimately affecting ecosystem function. However, ungulates have complex effects on grasslands, including defoliation, trampling, excreta return, and their interactions. Moreover, the effects of ungulate density on grasslands are regulated by these three mechanisms. Nevertheless, how these three mechanisms affect biodiversity at multiple scales and community assembly remains poorly understood.</p> <p>Here, we conducted a 4-year novel field experiment to disentangle the effects of defoliation, trampling, and excreta return by ungulates on plant community assembly in a temperate grassland in Inner Mongolia, China. This experiment set two different scenarios: moderate ungulate density (Moderate, characterised by selective defoliation and moderate trampling) and high ungulate density (Intense, characterised by non-selective defoliation and heavy trampling), including different combinations of defoliation, trampling, and excreta return in each scenario.</p> <p>We found that defoliation and trampling increased stochasticity in community assembly and promoted alpha and beta diversity under both scenarios. Specifically, defoliation promoted the coexistence of species with multiple resource acquisition strategies (higher functional trait diversity) by reducing interspecific competition; trampling tended to facilitate random species colonisation. Conversely, excreta return favoured grasses, promoting deterministic assembly and impacting species coexistence. Notably, selective defoliation in the moderate scenario led to a dominance of stochastic processes during community assembly, whereas non-selective defoliation still did not change the dominance of deterministic processes. Further, communities subject to selective defoliation were insensitive to changes in soil properties caused by trampling and excreta return, maintaining a high-level beta diversity and the stochastic of community assembly.</p> <p><em>Synthesis:</em></p> <p>Our study provides important insights into the mechanisms by which ungulate herbivores influence plant community assembly, suggesting that defoliation and trampling have the potential to drive stochastic processes, while excreta return plays the opposite role. Our study also suggests that selective foraging by ungulates acts as stronger stochastic forces during community assembly compared to non-selective defoliation. These results imply that considering ungulate feeding preferences and foraging behaviour in grassland management will help prevent biodiversity loss and biotic homogenisation.</p>
Quantifying pine processionary moth defoliation in a pine-oak mixed forest using unmanned aerial systems and multispectral imagery (dataset, paper published in PLOS ONE)
<p>Data processed to analyze pine processionary moth defoliation.</p> <p>Digital surface model and orthomosaics derived from UAS</p>
Figure 2. A in Defoliation of the Invasive Tree Falcataria moluccana on Hawaii Island by the Native Koa Looper Moth (Geometridae: Scotorythra paludicola), and Evaluation of Five Fabaceous Trees as Larval Hostplants
Figure 2. A defoliated Falcataria moluccana
Simulated Meteorological Changes Following a Hurricane Defoliation Event
<p>Results of two simulations using the Weather Research and Forecasting model, version 3.8. The first simulation (nelson_ei_control.nc) is a hindcast of the month following Hurricane Michael's landfall (2018) in the Florida panhandle, USA. The second simulation (nelson_ei_defoliated.nc) shows the sensitivity of 3-h precipitation, 2-m air temperature, 2-m relative humidity, surface sensible heat flux, surface latent heat flux, and the ground heat flux to a dramatic reduction in vegetation along Michael's path. The data contained therein have been analyzed in "Understanding Meteorological Changes Following Severe Defoliation During a Strong Hurricane Landfall: Insights from Hurricane Michael (2018)" by Nelson and Miller published in <em>Earth Interactions</em>.</p>
Continuous remobilization from belowground provides more than half of all carbon and nitrogen in regrowing shoots after grassland defoliation
<p><span>Remobilization of carbon (C) and nitrogen (N) from roots and crowns to regrowing shoots is an important strategy for grassland plants to tolerate herbivory. While this remobilization is thought to terminate once plants have the capacity to photosynthesize again and to take up N from the soil, this has rarely been quantified.</span></p> <p><span>Here we investigated the remobilization of C and N to regrowing shoots of a perennial grassland under two defoliation frequencies (every 15 and 30 days) and two N fertilization levels (0 and 2.8 g m<sup>-2</sup>) by growing intact plant-soil cores for 60 days in a growth chamber. We measured the C remobilization from roots and crowns to regrowing shoots using a novel continuous <sup>13</sup>C labelling method, and quantified the N remobilization to regrowing shoots and plant N uptake from soil with a <sup>15</sup>N tracer method.</span></p> <p><span>Regrowing shoots relied strongly on belowground C reserves, where up to 52% of C in regrowing shoots came from belowground during the first 30 days after defoliation. Belowground C was still remobilized when plant shoots had fully regrown and retained full capacity to photosynthesize. Plants relied more on C remobilization with shorter times between defoliation events at the expense of root biomass, particularly without N fertilization. Large amounts of C remobilization were accompanied by large amounts of N remobilization (up to 89% of total shoot N) that were positively related, suggesting a coupled C and N transfer from roots and crowns to shoots.</span></p> <p><strong><em><span>Synthesis</span></em></strong><span>. The unexpectedly high dependency on C and N remobilization occurred continuously after defoliation and did not terminate once plants were fully regrown. Our results indicate that remobilization of C and N from belowground has profound effects on long-term productivity and C sequestration that needs to be considered for managing similar grasslands worldwide.</span></p>
Data from: Differential defoliation and mortality of white spruce and balsam fir by Eastern spruce budworm
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Data from: Forest defoliation by an invasive outbreak insect: Catastrophic consequences for a charismatic mega moth
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Continuous remobilization from belowground provides more than half of all carbon and nitrogen in regrowing shoots after grassland defoliation
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Data from: Boreal tree growth exhibits decadal-scale ecological memory to drought and insect defoliation, but no negative response to their interaction
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Ungulate herbivores promote beta diversity and drive stochastic plant community assembly by selective defoliation and trampling: From a four-year simulation experiment
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Tracking invasions of a destructive defoliator, the gypsy moth (Erebidae: Lymantria dispar): population structure, origin of intercepted specimens, and Asian introgression into North America
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Climate change and defoliation interact to affect root length across northern temperate grasslands
<p>1. Grassland plants, especially their root systems, are dynamic and can buffer changes resulting from exposure to multiple stressors; however, the interactive stressor effects on root dynamics and associated aboveground growth are poorly understood.</p> <p>2. Here, we examine the effects of changed precipitation and air temperature, and defoliation intensity on root length dynamics and aboveground biomass using the third year data from a multifactor experiment conducted across three northern temperate grasslands.</p> <p>3. We found that root length was more sensitive to the changes in environmental and management conditions than root mass, demonstrating the importance of root length as an indicator of rapid root system changes. Across all sites, warming, altered precipitation, and defoliation intensity interacted to affect root length while aboveground biomass was only affected by defoliation intensity, indicating that the root system was more responsive than aboveground biomass when climatic conditions change. Overall, drought reduced root length, particularly under low defoliation intensity, as well as in combination with warming and heavy defoliation, highlighting the risk of additive effects of such environmental stresses. Across unclipped plots, aboveground biomass was positively associated with total root length, the latter of which further interacted with precipitation, to affect aboveground biomass. Compared to defoliated communities, non-defoliated plant communities exhibited a greater ability to maintain aboveground biomass under drought conditions via increases in root system efficiency (the amount of aboveground biomass produced per unit of root length invested).</p> <p>4. Our results highlight the rapid change of root length in the face of interactive stressors. We postulate that the degree of stability in aboveground biomass is driven by the altered root system dynamics or species turnover. Future studies are warranted that more directly assess how root length responses under climate change impact other important plant traits in grasslands.</p>
Data from: Continent-wide population genomic structure and phylogeography of North America's most destructive conifer defoliator, the spruce budworm (Choristoneura fumiferana)
<p>The spruce budworm, <i>Choristoneura fumiferana</i>, is presumed to be panmictic across vast regions of North America. We examined the extent of panmixia by genotyping 3650 single nucleotide polymorphism (SNP) loci in 1975 individuals from 128 collections across the continent. We found three spatially structured subpopulations: Western (Alaska, Yukon), Central (southeastern Yukon to the Manitoba-Ontario border) and Eastern (Manitoba-Ontario border and Atlantic). Additionally, the most diagnostic genetic differentiation between the Central and Eastern subpopulations was chromosomally restricted to a single block of SNPs that may constitute an island of differentiation within the species. Geographic differentiation in the spruce budworm parallels that of its principal larval host, white spruce, <i>Picea glauca</i>, providing evidence that spruce trees survived in the Beringian refugium through the Last Glacial Maximum and that at least two isolated populations diverged with spruce/fir south of the ice sheets. Gene flow in the spruce budworm may also be affected by mountains in western North America, habitat isolation in West Virginia, regional adaptations, factors related to dispersal, and proximity of other species in the spruce budworm species complex. The central and eastern geographic regions contain individuals that assign to Eastern and Central subpopulations, respectively, indicating that these barriers are not complete. Our discovery of previously undetected geographic and genomic structure in the spruce budworm suggests that further population modelling of this ecologically important insect should consider regional differentiation, potentially co-adapted blocks of genes, and gene flow between subpopulations. </p>
Data from: Defoliation of a grass by reindeer is compensated by the positive effects of its soil legacy, dung deposition, and moss removal
Herbivory is one of the key drivers shaping plant community dynamics. Herbivores can strongly influence plant productivity directly through defoliation and the return of nutrients in the form of dung and urine, but also indirectly by reducing the abundance of neighbouring plants and inducing changes in soil processes. However, the relative importance of these processes is poorly understood. We, therefore, established a common garden experiment to study plant responses to defoliation, dung addition, moss cover, and the soil legacy of reindeer grazing. We used an arctic tundra grazed by reindeer as our study system, and Festuca ovina, a common grazing-tolerant grass species as the model species. The soil legacy of reindeer grazing had the strongest effect on plants, and resulted in higher growth in soils originating from previously heavily-grazed sites. Defoliation also had a strong effect and reduced shoot and root growth and nutrient uptake. Plants did not fully compensate for the tissue lost due to defoliation, even when nutrient availability was high. In contrast, defoliation enhanced plant nitrogen concentrations. Dung addition increased plant production, nitrogen concentrations and nutrient uptake, although the effect was fairly small. Mosses also had a positive effect on aboveground plant production as long as the plants were not defoliated. The presence of a thick moss layer reduced plant growth following defoliation. This study demonstrates that grasses, even though they suffer from defoliation, can tolerate high densities of herbivores when all aspects of herbivores on ecosystems are taken into account. Our results further show that the positive effect of herbivores on plant growth via changes in soil properties is essential for plants to cope with a high grazing pressure. The strong effect of the soil legacy of reindeer grazing reveals that herbivores can have long-lasting effects on plant productivity and ecosystem functioning after grazing has ceased.
Data from: Genetic structure, admixture, and invasion success in a Holarctic defoliator, the gypsy moth (Lymantria dispar, Lepidoptera: Erebidae)
Characterizing the current population structure of potentially invasive species provides a critical context for identifying source populations and for understanding why invasions are successful. Non-native populations inevitably lose genetic diversity during initial colonization events, but subsequent admixture among independently introduced lineages may increase both genetic variation and adaptive potential. Here we characterize the population structure of the gypsy moth (Lymantria dispar Linnaeus), one of the world's most destructive forest pests. Native to Eurasia and recently introduced to North America, the current distribution of gypsy moth includes forests throughout the temperate region of the northern hemisphere. Analyses of microsatellite loci and mitochondrial DNA sequences for 1738 individuals identified four genetic clusters within L. dispar. Three of these clusters correspond to the three named subspecies; North American populations represent a distinct fourth cluster, presumably a consequence of the population bottleneck and allele frequency change that accompanied introduction. We find no evidence that admixture has been an important catalyst of the successful invasion and range expansion in North America. However, we do find evidence of ongoing hybridization between subspecies and increased genetic variation in gypsy moth populations from Eastern Asia, populations that now pose a threat of further human-mediated introductions. Finally, we show that current patterns of variation can be explained in terms of climate and habitat changes during the Pleistocene, a time when temperate forests expanded and contracted. Deeply diverged matrilines in Europe imply that gypsy moths have been there for a long time and are not recent arrivals from Asia.
Data from: Combined effects of natural enemies and competition for resources on a forest defoliator: a theoretical and empirical analysis
Explanations for the dynamics of insect outbreaks often focus on natural enemies, on the grounds that parasitoid and pathogen attack rates are high during outbreaks. While natural enemy models can successfully reproduce outbreak cycles, experiments have repeatedly demonstrated the importance of resource quality and abundance. Experiments, however, are rarely invoked in modeling studies. Here we combine mechanistic models, observational data, and field experiments to quantify the roles of parasitoid attacks and resource competition on the jack pine budworm, Choristoneura pinus. By fitting models to a combination of observational and experimental data, we show that parasitoid attacks are the main source of larval budworm mortality at low and intermediate budworm densities, but that resource competition is the main source of mortality at high densities. Our results further show that the effects of resource competition become more severe with increasing host tree age, and that the effects of parasitoids are moderated by strong competition between parasitoids for hosts. Allowing for these effects in a model of insect outbreaks leads to realistic outbreak cycles, while a host-parasitoid model without resource competition produces an unrealistic stable equilibrium. The effects of resource competition are modulated by tree age, which in turn depends on fire regimes. Our model therefore suggests that increases in fire frequency due to climate change may interact in complex ways with budworm outbreaks. Our work shows that resource competition can be as important as natural enemies in modulating insect outbreaks, while demonstrating the usefulness of high-performance computing in experimental field ecology.
Data from: The dynamics of recovery and growth: how defoliation affects stored resources
Growth rate varies widely among species and the trade-off between growth rate and storage or maintenance traits is a principal axis of variation between species. Many plant species have substantial root stores, but very little is known about how growth rate modifies responses of these stores to defoliation and other stresses. Species with different growth rates are predicted to respond in distinct ways, because of variation in the pre-defoliation allocation to storage. Here, we quantified the dynamics of stored carbohydrates in seven species with varying growth rate, following defoliation in a pot experiment. For faster growing species, there was significant reduction in carbohydrate concentration following defoliation, followed by relatively fast recovery, whereas for slower growing species, carbohydrate concentration levels remained relatively invariant across treatments. Results for total carbohydrates mirrored those for concentration, but were not as significant. Our findings were consistent with the idea that faster growing species respond more rapidly than slower growers to defoliation, through changes in carbohydrate pool concentrations. Growth rate as an indicator of life-history and ecological strategy may therefore be key to understanding post-defoliation recovery and storage strategies.
Data from: Hurricane-mediated defoliation of kelp beds and pulsed delivery of kelp detritus to offshore sedimentary habitats
Severe storm events are important agents of disturbance that can transport large quantities of algal detritus from highly productive kelp beds (or forests) in shallow water to deeper, more food-limited areas. We measured canopy cover in shallow kelp beds (5 to 15 m depth) and the cover of detrital kelp in sedimentary habitats directly offshore of these beds (20 to 45 m) before and after Hurricane Earl, which struck the Atlantic coast of Nova Scotia in September 2010. The storm resulted in large losses of kelp canopy cover (from 71.0 to 38.7%, averaged across sites) and significantly increased the cover of detrital kelp deposits below the kelp beds (from 1.5 to 3.4%). Detrital deposits were more commonly found in a semi-protected bay than off an exposed headland and persisted in the bay for at least 6 wk. Sea urchins Strongylocentrotus droebachiensis were associated with detrital kelp deposits in offshore habitats. At sites with the greatest amount of detrital kelp, we estimated that sea urchins could consume this material within 2 mo, indicating that storm-generated detrital pulses may be an important form of trophic connectivity between adjacent ecosystems off this coast.
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