Deer and earthworms modify forest responses to climate change (original) (raw)
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Biological Invasions, 2013
Ahistorical drivers such as nonnative invasive earthworms and high deer densities can have substantial impacts on ecosystem processes and plant community composition in temperate and boreal forests of North America. To assess the roles of earthworm disturbance, deer, and environmental factors in the understory, we sampled 125 mixed temperate-boreal forest sites across the western Great Lakes region. We utilized structural equation modeling (SEM) to address the hypothesis that earthworm disturbance to the upper soil horizons and selective herbivory by deer are associated with depauperate understory plant communities dominated by graminoid and nonnative species. Evidence of earthworm activity was found at 93 % of our sites and 49 % had high to very high severity earthworm disturbance. The SEM fit the data well and indicated that widespread nonnative earthworm disturbance and high deer densities had similar magnitudes of impact on understory plant communities and that these impacts were partially mediated by environmental characteristics. One-third of the variation in earthworm disturbance was explained by soil pH, precipitation, and litter quality. Deer density and earthworm disturbance both increased graminoid cover while environmental variables showed direct and indirect relationships. For example, the positive relationship between temperature and graminoids was indirect through a positive temperature effect on deer density. This research characterizes an integrated set of key environmental variables driving earthworm disturbance and deer impacts on the forest understory, facilitating predictions of the locations and severity of future change in northern temperate and boreal forest ecosystems.
Non-consumptive Effects of Native Deer on Introduced Earthworm Abundance
Ecosystems, 2015
Chronic ungulate herbivory impacts are well documented, consistently showing changes in plant community dynamics. In contrast, indirect ungulate effects on soil biota and processes are less well understood and idiosyncratic. Evidence suggests that increased deer abundance in northeastern North American forests may facilitate invasions by non-native earthworms and non-native plants through indirect non-consumptive processes. We sampled earthworm abundance using paired open and fenced plots (experimentally excluding deer) from 2008 to 2011 at 12 sites at West Point, NY and in 2013 at 21 additional sites across four states that varied in exclosure size and age since establishment. Fencing decreased earthworm abundance at West Point and in regional surveys. At West Point, negative effects of fencing on earthworm abundance decreased with soil pH and were stronger at sites dominated by native than non-native understory vegetation. Sites dominated by native vegetation had more acidic soils and lower earthworm abundance compared to sites dominated by non-native vegetation. In the regional survey, negative effects of fencing on earthworm abundance increased with time since fences were established, but effects were not affected by exclosure size or site location. We show unforeseen indirect effects of deer exclusion on earthworm populations. Results illustrate the need to account for complex interactive effects among co-occurring stressors, such as deer, earthworms, and non-native plants. Failures to account for these interactions will result in hidden treatments, will complicate interpretation of ecological experiments, and will create difficulties in designing appropriate management strategies aimed at reducing stressor effects.
Assessing the Consequences of Global Change for Forest Disturbance From Herbivores and Pathogens
The Science of the Total Environment, 2000
Herbivores and pathogens impact the species composition, ecosystem function, and socioeconomic value of forests. Herbivores and pathogens are an integral part of forests, but sometimes produce undesirable effects and a degradation of forest resources. In the United States, a few species of forest pests routinely have significant impacts on up to 20 million ha of forest with economic costs that probably exceed $1 billionryear. Climatic change could Ž . alter patterns of disturbance from herbivores and pathogens through: 1 direct effects on the development and Ž . Ž . survival of herbivores and pathogens; 2 physiological changes in tree defenses; and 3 indirect effects from changes Ž . Ž in the abundance of natural enemies e.g. parasitoids of insect herbivores , mutualists e.g. insect vectors of tree . pathogens , and competitors. Because of their short life cycles, mobility, reproductive potential, and physiological sensitivity to temperature, even modest climate change will have rapid impacts on the distribution and abundance of many forest insects and pathogens. We identify 32 syndromes of biotic disturbance in North American forests that should be carefully evaluated for their responses to climate change: 15 insect herbivores, browsing mammals; 12 pathogens; 1 plant parasite; and 3 undiagnosed patterns of forest decline. It is probable that climatic effects on some herbivores and pathogens will impact on biodiversity, recreation, property value, forest industry, and even water Ž . quality. Some scenarios are beneficial e.g. decreased snow cover may increase winter mortality of some insect pests , Ž but many are detrimental e.g. warming tends to accelerate insect development rate and facilitate range expansions of pests and climate change tends to produce a mismatch between mature trees and their environment, which can . increase vulnerability to herbivores and pathogens . Changes in forest disturbance can produce feedback to climate through affects on water and carbon flux in forest ecosystems; one alarming scenario is that climate warming may increase insect outbreaks in boreal forests, which would tend to increase forest fires and exacerbate further climate warming by releasing carbon stores from boreal ecosystems. We suggest a list of research priorities that will allow us to refine these risk assessments and adopt forest management strategies that anticipate changes in biotic disturbance regimes and mitigate the ecological, social, and economic risks. ᮊ
Herbivory-mediated responses of selected boreal forests to climatic change
Climatic Change, 2001
Recent efforts to project vegetation responses to climatic warming have emphasized the tight linkages between climate and vegetation distribution. Here we provide several examples indicating that the direct effects of climatic warming on boreal vegetation can be qualitatively different than the indirect effects mediated by climatic responses of herbivores. These herbivore-mediated vegetation responses to climatic warming will likely vary regionally. In southern Fennoscandia, we project that the climatically induced changes in animal populations should enhance the density of spruce at the expense of pine and broadleafed trees. In northern Fennoscandia we project reduced herbivory on broadleafed trees and increased herbivory on pine, leading to an increase in broadleafed trees and spruce and a reduction in pine. Climatic warming in interior Alaska may reduce herbivory on broadleafed trees and increase herbivory on evergreen spruce, thus reinforcing the impact of increased fire frequency.
Canadian Journal of Forest Research, 2009
We review the observed and potential effects of climate change on native fauna of forests in northeastern North America by focusing on mammals, birds, amphibians, and insects. Our assessment is placed in the context of recent regional-scale climate projections. Climate change, particularly in recent decades, has affected the distribution and abundance of numerous wildlife species. Warming temperatures, alterations to precipitation regimes, seasonality, and climatic extremes are projected to affect species directly or indirectly in each of the focal taxa. Greatest climate change will occur during winter, and the survival of winter-active species as well as the survival, distribution, and abundance of hibernating mammals, amphibians, resident birds, and diapausing insects may be altered. Even under low emissions scenarios, effects on native fauna may be profound, affecting iconic species, endangered species, and species that provide economically valuable services, such as pollination and regulation of insect populations. However, much research that is essential to assessing the effects of climate change on the native fauna of northeastern forests remains to be done. Research that reveals causal mechanisms and relates these findings to population and community level processes will be most valuable.
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 2012
As the climate warms, boreal tree species are expected to be gradually replaced by temperate species within the southern boreal forest. Warming will be accompanied by changes in above-and belowground consumers: large moose (Alces alces) replaced by smaller deer (Odocoileus virginianus) above-ground, and small detritivores replaced by larger exotic earthworms below-ground. These shifts may induce a cascade of ecological impacts across trophic levels that could alter the boreal to temperate forest transition. Deer are more likely to browse saplings of temperate tree species, and European earthworms favour seedlings of boreal tree species more than temperate species, potentially hindering the ability of temperate tree species to expand northwards. We hypothesize that warminginduced changes in consumers will lead to novel plant communities by changing the filter on plant species success, and that above-and below-ground cascades of trophic interactions will allow boreal tree species to persist during early phases of warming, leading to an abrupt change at a later time. The synthesis of evidence suggests that consumers can modify the climate change-induced transition of ecosystems.
Climate change intensification of herbivore impacts on tree recruitment
Proceedings. Biological sciences / The Royal Society, 2012
Altered species interactions are difficult to predict and yet may drive the response of ecological communities to climate change. We show that declining snowpack strengthens the impacts of a generalist herbivore, elk (Cervus elaphus), on a common tree species. Thick snowpack substantially reduces elk visitation to sites; aspen (Populus tremuloides) shoots in these areas experience lower browsing rates, higher survival and enhanced recruitment. Aspen inside herbivore exclosures have greatly increased recruitment, particularly at sites with thick snowpack. We suggest that long-term decreases in snowpack could help explain a widespread decline of aspen through previously unconsidered relationships. More generally, reduced snowpack across the Rocky Mountains, combined with rising elk populations, may remove the conditions needed for recruitment of this ecologically important tree species. These results highlight that herbivore behavioural responses to altered abiotic conditions are crit...
Scientific Reports, 2014
Climate change causes species range shifts and potentially alters biological invasions. The invasion of European earthworm species across northern North America has severe impacts on native ecosystems. Given the long and cold winters in that region that to date supposedly have slowed earthworm invasion, future warming is hypothesized to accelerate earthworm invasions into yet non-invaded regions. Alternatively, warming-induced reductions in soil water content (SWC) can also decrease earthworm performance. We tested these hypotheses in a field warming experiment at two sites in Minnesota, USA by sampling earthworms in closed and open canopy in three temperature treatments in 2010 and 2012. Structural equation modeling revealed that detrimental warming effects on earthworm densities and biomass could indeed be partly explained by warming-induced reductions in SWC. The direction of warming effects depended on the current average SWC: warming had neutral to positive effects at high SWC, whereas the opposite was true at low SWC. Our results suggest that warming limits the invasion of earthworms in northern North America by causing less favorable soil abiotic conditions, unless warming is accompanied by increased and temporally even distributions of rainfall sufficient to offset greater water losses from higher evapotranspiration.
Forest insects and climate change: long-term trends in herbivore damage
Ecology and Evolution, 2013
Long-term data sets, covering several decades, could help to reveal the effects of observed climate change on herbivore damage to plants. However, sufficiently long time series in ecology are scarce. The research presented here analyzes a long-term data set collected by the Hungarian Forest Research Institute over the period 1961-2009. The number of hectares with visible defoliation was estimated and documented for several forest insect pest species. This resulted in a unique time series that provides us with the opportunity to compare insect damage trends with trends in weather patterns. Data were analyzed for six lepidopteran species: Thaumetopoea processionea, Tortrix viridana, Rhyacionia buoliana, Malacosoma neustria, Euproctis chrysorrhoea, and Lymantria dispar. All these species exhibit outbreak dynamics in Hungary. Five of these species prefer deciduous tree species as their host plants, whereas R. buoliana is a specialist on Pinus spp. The data were analyzed using general linear models and generalized least squares regression in relation to mean monthly temperature and precipitation. Temperature increased considerably, especially over the last 25 years (+1.6°C), whereas precipitation exhibited no trend over the period. No change in weather variability over time was observed. There was increased damage caused by two species on deciduous trees. The area of damage attributed to R. buoliana decreased over the study period. There was no evidence of increased variability in damage. We conclude that species exhibiting a trend toward outbreak-level damage over a greater geographical area may be positively affected by changes in weather conditions coinciding with important life stages. Strong associations between the geographical extent of severe damage and monthly temperature and precipitation are difficult to confirm, studying the life-history traits of species could help to increase understanding of responses to climate change.
Agriculture, Ecosystems & Environment, 2019
Anthropogenic climate change is altering the functioning of terrestrial ecosystems. Agricultural systems are particularly vulnerable to climate change as they are frequently disturbed by intensified management practices. This also threatens belowground organisms that are responsible for providing crucial ecosystem functions and services, such as nutrient cycling and plant disease suppression. Amongst these organisms, earthworms are of particular importance as they can modulate the effects of climate change on soil organisms by modifying the biotic and abiotic soil conditions. However, they are also known to decline under intensified management, justifying their use as key biotic indicators of intensified agriculture. Yet, our knowledge of the responses of belowground species to the interacting effects of warming and land-use intensification (simulated by earthworm reduction in the experimental setup) remains limited. Here, we tested the interactive effects of soil warming and reduced earthworm densities on soil protists, nematodes, meso-and macrofauna, and their diversity in a common barley system in the Hohenheim Climate Change Experiment. We found that belowground species richness was lowest at elevated temperature and reduced earthworm densities, indicating that earthworms can buffer warming effects on belowground biodiversity. Furthermore, warming increased the densities of plantfeeding nematodes, and herbivorous macrofauna benefitted from reduced earthworm densities. Our results indicate that warming and reduced earthworm densities may simultaneously modify the functioning and service provisioning of soils via shifts in diversity and density of soil biota that would likely lead to simplified belowground food webs. These findings thus highlight the importance of maintaining greater densities of ecosystem engineers like earthworms that may help buffering the detrimental effects of climate warming in agricultural systems. Kardol et al., 2010b). In Central Europe, arable lands are amongst the most important managed terrestrial ecosystems (Howden et al., 2007). They are crucial for maintaining global food security (Pachauri et al., 2014). These systems are also highly disturbed owing to management practices like tillage and heavy machine employment, which potentially convert them to low diversity ecosystems (Giller et al., 1997; Tsiafouli et al., 2015). Owing to their low numbers of component species,