Simulating the reciprocal interaction of forest landscape structure and southern pine beetle herbivory using LANDIS

The reciprocal interaction of landscape structure and ecological processes is a cornerstone of modern landscape ecology. We use a simulation model to show how landscape structure and herbivory interact to influence outbreaks of southern pine beetle (Dendroctonus frontalis Zimmermann) in a landscape representative of the southern Appalachian Mountains, USA. We use LANDIS and its biological disturbance agent module to simulate the effects of landscape composition (proportion of landscape in host area) and host aggregation on the size and severity of insect outbreaks and the persistence of the host species, Table Mountain Pine (Pinus pungens Lamb.). We find that landscape composition is less important in the modeled landscapes than host aggregation in structuring the severity of insect outbreaks. Also, simulated southern pine beetle outbreaks over time tend to decrease the aggregation of host species on the landscape by fragmenting large patches into smaller ones, thereby reducing the severity of future outbreaks. Persistence of Table Mountain pine decreases throughout all simulations regardless of landscape structure. The results of this study indicate that when considering alternative restoration strategies for insect-affected landscapes, it is necessary to consider the patterns of hosts on the landscape as well as the landscape composition.     

The long-term influence of past land use on the Walker Branch forest

Forest structure and composition influence patterns of insect outbreaks and can be explained on the Walker Branch watershed by past land use (timber harvest and agriculture), soils, aspect, and slope. In particular, pine bark beetles caused large losses of pine on sites that had been used for agriculture, on Fullerton silt loam soils, and on north-to-northeast and east-to-southeast exposures. Hickory bark beetles had a high impact on hickory biomass on Bodine soil areas that were forested in 1935 and sloped greater than 11%. Thus, prior land use can have an indirect effect on future disturbances.Because forest disturbances can affect nutrient distribution, land use can also indirectly affect nutrient availability. For example, locations of hickory bark beetle outbreaks experience a large flux of calcium from dead wood to soil because hickory accumulates large amounts of calcium in woody tissue. The research demonstrates a link between past land use, insect outbreaks, and calcium cycling.     

Spatial prediction of caterpillar (<Emphasis Type="Italic">Ormiscodes</Emphasis>) defoliation in Patagonian <Emphasis Type="Italic">Nothofagus</Emphasis> forests

In the temperate forests of the southern Andes, southern beech species (Nothofagus), the dominant tree species of the region, experience severe defoliation caused by caterpillars of the Ormiscodes genus (Lepidoptera: Saturniidae). Despite the recent increase in defoliation frequency in some areas, there is no quantitative information on the spatial extent and dynamics of these outbreaks. This study examines the spatial patterns of O. amphimone outbreaks in relation to landscape heterogeneity. We mapped defoliation events caused by O. amphimone in northern (ca. 40–41°S) and southern Patagonian (ca. 49°S) Nothofagus forests from Landsat imagery and analyzed their spatial associations with vegetation cover type, topography (elevation, slope angle, aspect) and mean annual precipitation using overlay analyses. We used these data and relationships to develop a logistic regression model in order to generate maps of predicted susceptibility to defoliation by O. amphimone for each study area. Forests of N. pumilio are typically more susceptible to O. amphimone outbreaks than lower elevation forests of other Nothofagus species (N. dombeyi and N. antarctica). Stands located at intermediate elevations and on gentle slopes (<15°) are also more susceptible to defoliation than higher and lower elevation stands located on high angle slopes. Stands in areas with intermediate to high precipitation, relative to the distribution of Nothofagus along the precipitation gradient, are more susceptible to O. amphimone attack than are drier areas. Our study represents the first mapping and spatial analysis of insect defoliator outbreaks in Nothofagus forests in South America.     

Characterizing combined fire and insect outbreak disturbance regimes in British Columbia,Canada

Context

Fires and insect outbreaks are important agents of forest landscape change, but the classification and distribution of these combined processes remain unstudied aspects of forest disturbance regimes.

Objectives

We sought to map areas of land characterized by homogenous fire regime (HFR) attributes and by distinctive combinations of fire, bark beetles and defoliating insect outbreaks, and how their distribution might change should current climatic trends continue.

Methods

We used a 41-year history of mapped fires and forest insect outbreaks to classify HFRs and combined fire and insect disturbance regimes (HDRs). Spatially constrained cluster analysis of 2524 20-km grid cells used mean annual area burned, ignition Julian date, fire size and fire frequency to delineate HFR zones. Mean annual areas burned, affected by bark beetles, and affected by defoliators were used to delineate HDR zones. Random forests classification used climate associations of HDRs to project likely changes in their distribution.

Results

Eighteen HFR zones accounted for 30% of variance, compared to 27 HDR zones accounting for 59% of variance. Fire regime designation had low predictive power in explaining 23 homogenous insect outbreak regimes or the 27 HDRs. Climate change projections indicate a northward migration of current HDR zones. Conditions suitable for defoliator outbreaks are projected to increase, resulting in a projected increase in the total rate of forest disturbance.

Conclusions

When describing forest disturbance regimes, it is important to consider the combined and possibly interacting agents of tree mortality, which can result in emergent properties not predictable from any single agent.

     

Landscape effects on the population dynamics of the fossorial form of the water vole (Arvicola terrestris sherman)

The dynamics of microtine rodents show large variations among species and even among populations of a single species. Several studies have shown that landscape structure and predation play a role in these variations. We studied the influence of landscape structure on the spatial distribution and the population dynamics of the fossorial form of the water vole (Arvicola terrestris sherman). The sampling was based on a preliminary five-year survey of a rodent cycle on a regional scale, as well as a method of abundance estimation using surface indices. This survey led to distinguishing epicentres where outbreaks started, and diffusion sections where outbreaks occurred later. Results showed differences in dynamics of spatial distribution of the vole colonies between these two types of sections. This distribution pattern is related to landscape composition and structure. Epicentres are characterized by a higher ratio of open landscape, a lower ratio of forest, and less fragmentation when compared to the diffusion sections. Therefore landscape analysis has the potential of providing a valuable framework for the designing of programs for the early control of A. terrestris populations.     

Crown rot (Phytophthora cactorum) of apple in Britain: Observations on natural outbreaks,and experiments on artificially inducing the disease in the field

Crown rot (Phytophthora cactorum) of apple came to prominence in Britain in the 1960s following the introduction of certain new types of clonal rootstock. Observations on crown rot outbreaks over the period 1976 to 1984 were as follows: only rootstocks MM.104 and MM.106 were affected; infection occurred in the bark of the rootstock axis below soil level; lesions caused girdling, and sometimes appeared above soil level and spread down the main roots to a limited extent; infection occurred during the growing season but disease development ceased with the onset of winter and did not resume the following year; trees on MM. 104 were susceptible throughout the life of the orchard while trees on MM. 106 were susceptible only during the establishment years; disease outbreaks occurred sporadically. Crown rot was induced experimentally on trees grafted on MM. 104 and on M.25 in field trials by irrigating for four to six weeks through inoculum applied to the base of the trees. No crown rot occurred on grafted MM.106 or on other grafted rootstocks in the same trials, although lesions developed above soil level on a few trees. The limited experimental data indicated that MM.104 was liable to attack throughout the growing season. The importance of environmental influences on the susceptibility of rootstocks to crown rot is discussed.     

苹果连作障碍土壤微生物的研究进展

从土壤微生物的角度，概述了苹果连作障碍发生时病原菌对再植树体的影响，并结合当前化学/生物熏蒸、拮抗微生物施用、施肥措施调整、有机改良剂添加、抗重茬砧木选择、种植制度建立等手段，概述了上述措施在缓解连作障碍过程中影响和调控土壤微生物群落结构的研究进展，对未来苹果连作障碍机理的研究及防控技术的发展方向提出了展望。     

Identifying significant scale-specific spatial boundaries using wavelets and null models: spruce budworm defoliation in Ontario,Canada as a case study

We combine wavelet analysis and multiple null models to identify significant spatial scales of pattern and spatial boundaries in historical spruce budworm defoliation in Ontario, Canada. Previous analyses of budworm defoliation in Ontario over the last two outbreaks have suggested three distinct zones of defoliation. We asked the following three questions: (1) is there statistical support for the existence of these three zones? (2) Are the locations of these boundaries consistent between outbreak periods? And (3) how does boundary identification depend on the spatial null model used? Defoliation data for the two outbreak periods (1941–1965 and 1966–2001), and the combined period (1941–2001) were analyzed using a 1D continuous wavelet transform. Boundaries were identified through comparison of wavelet power spectra of each outbreak period to reference distributions based on three different spatial null models: (1) a complete spatial randomness model, (2) an autoregressive model, and (3) a Gaussian random field model. The Gaussian random field model identified coarser scales of pattern than the autoregressive model. Locally, the Gaussian random field model found significant boundaries similar to those previously described, whereas the autoregressive model only did so for the first outbreak. These results indicate that the coarse scale spatial factors that influenced defoliation were more consistent between outbreaks relative to fine scale factors, and that previously described boundaries were strongly driven by the first outbreak. Wavelet analysis combined with spatial null models provides a powerful tool for identifying non-arbitrary scales of structure and significant spatial boundaries in non-stationary ecological data.     

Data on the inheritance of resistance to powdery mildew in the cultivated strawberry

Results are presented for levels of mildew infection in seedlings of the cultivated strawberry in years of severe outbreaks of powdery mildew. Evidence is shown for the presence of general and specific effects in mildew inheritance and of differences in breeding-value of close relatives, in this case full-sibs. The results also indicate that a maternal effect on mildew susceptibility exists, and that while ‘Cambridge Vigour’ is more susceptible than ‘Cambridge Favourite’, and gives the more susceptible progeny, there may be either a maternal effect for susceptibility transmitted through ‘Cambridge Favourite’, or an effect for resistance transmitted through ‘Cambridge Vigour’.     

Environmental factors and ecological processes controlling vegetation patterns in boreal forests

An individual tree model of forest dynamics was used to examine the environmental and ecological factors controlling forest vegetation patterns in upland boreal forests of North America. Basic life history traits that characterized the regeneration, growth, and death of individual trees were combined with species-specific responses to important environmental factors. This model simulated forest structure and vegetation patterns in conifer, hardwood, and mixed conifer-hardwood forests and woodlands in several bioclimatic sub-regions of the North American boreal forest zone. Model testing identified the processes and parameters required to understand the ecology of upland boreal forests and weaknesses in our current understanding of these processes. These factors included climate, solar radiation, soil moisture, soil temperature and permafrost, the forest floor organic layer, nutrient availability, forest fires, and insect outbreaks. Model testing also identified which of these factors were important in each bioclimatic sub-region.     

Landscape features influence genetic structure of black-tailed prairie dogs (Cynomys ludovicianus)

Black-tailed prairie dogs (Cynomys ludovicianus) currently live in metapopulations in the parts of their range where plague, caused by the bacterium Yesinia pestis, has invaded. Prairie dogs are highly susceptible to the pathogen, with most animals within towns dying during Y. pestis outbreaks. A review of population genetic studies of prairie dogs demonstrates considerable differentiation between prairie dog towns. Despite declines and fluctuations in size of prairie dog populations, they continue to harbor considerable genetic variation. This results from continual dispersal and gene flow, likely along low-lying drainages that connect towns. When combined with estimates of population size, the landscape genetic approach described here will provide precise estimates of dispersal and gene flow, in addition to evaluation of long-term stability of prairie dog metapopulations.     

A Systems-Based Approach to Safeguard the Strawberry Industry from Virus Diseases

ABSTRACT

Strawberry is susceptible to several systemic pathogens and, in particular, viruses. There are several examples of disease epidemics that resulted from virus-infected propagation material and led to losses estimated in the tens of millions of dollars. This communication focuses on actions needed to minimize the risk of similar outbreaks by developing a systems-based approach from breeding to the commercial field. This includes the development of molecular biology and bioinformatic tools that allow for the detection of all known viruses infecting strawberry but most importantly for the discovery of viruses that circulate in the system undetected and may have contributed to past epidemics. Surveys in commercial fields have yielded a map of the most prevalent viruses in strawberry production areas across the United States, knowledge that will be used in the nascent National Certification Program for Strawberry.     

A multi-scale analysis of western spruce budworm outbreak dynamics

Context

Forest insect outbreaks are influenced by ecological processes operating at multiple spatial scales, including host-insect interactions within stands and across landscapes that are modified by regional-scale variations in climate. These drivers of outbreak dynamics are not well understood for the western spruce budworm, a defoliator that is native to forests of western North America.

Objectives

Our aim was to assess how processes across multiple spatial scales drive western spruce budworm outbreak dynamics. Our objective was to assess the relative importance and influence of a set of factors covering the stand, landscape, and regional scales for explaining spatiotemporal outbreak patterns in British Columbia, Canada.

Methods

We used generalized linear mixed effect models within a multi-model interference framework to relate annual budworm infestation mapped from Landsat time series (1996–2012) to sets of stand-, landscape-, and regional-scale factors derived from forest inventory data, GIS analyses, and climate models.

Results

Outbreak patterns were explained well by our model (R ² = 93%). The most important predictors of infestation probability were the proximity to infestations in the previous year, landscape-scale host abundance, and dry autumn conditions. While stand characteristics were overall less important predictors, we did find infestations were more likely amongst pure Douglas-fir stands with low site indices and high crown closure.

Conclusions

Our findings add to growing empirical evidence that insect outbreak dynamics are driven by multi-scaled processes. Forest management planning to mitigate the impacts of budworm outbreaks should thus consider landscape- and regional-scale factors in addition to stand-scale factors.

     

Using landscape epidemiological models to understand the distribution of chronic wasting disease in the Midwestern USA

Animal movement across the landscape plays a critical role in the ecology of infectious wildlife diseases. Dispersing animals can spread pathogens between infected areas and naïve populations. While tracking free-ranging animals over the geographic scales relevant to landscape-level disease management is challenging, landscape features that influence gene flow among wildlife populations may also influence the contact rates and disease spread between populations. We used spatial diffusion and barriers to white-tailed deer gene flow, identified through landscape genetics, to model the distribution of chronic wasting disease (CWD) in the infected region of southern Wisconsin and northern Illinois, USA. Our generalized linear model showed that risk of CWD infection declined exponentially with distance from current outbreaks, and inclusion of gene flow barriers dramatically improved fit and predictive power of the model. Our results indicate that CWD is spreading across the Midwestern landscape from these two endemic foci, but spread is strongly influenced by highways and rivers that also reduce deer gene flow. We used our model to plot a risk map, providing important information for CWD management by identifying likely routes of disease spread and providing a tool for prioritizing disease monitoring and containment efforts. The current analysis may serve as a framework for modeling future disease risk drawing on genetic information to investigate barriers to spread and extending management and monitoring beyond currently affected regions.     

Fusarium avenaceum, Haupterreger der Himbeerrutenkrankheit in Norddeutschland

In 2006–2008, fungi responsible for raspberry cane blight symptoms in Northern Germany included Fusarium avenaceum, Leptosphaeria coniothyrium, Colletotrichum gloeosporioides and Botrytis cinerea (listed in order of decreasing importance). These pathogens and their symptoms are briefly described. Fusarium avenaceum has been chiefly responsible for the severe recent outbreaks of cane blight in Northern Germany, where it is ubiquitous on cultivated and wild raspberries. In 2007 infections took place during a period of wetness in mid-May and were associated with the natural formation of epidermal cracks by the expanding primocanes, but not with infestations by the gall midge (Resseliella theobaldi) which began on June 6th. In 2008, a prolonged drought throughout May and June caused a delay of F. avenaceum infections until mid-July, by which time R. theobaldi had already extensively colonised primocanes. In addition to living infected primocanes, dead above-ground cane stumps and cane fragments were the main overwintering substrates for F. avenaceum. Implications for possible crop hygiene measures against F. avenaceum are discussed.     

Disturbance and landscape dynamics in the Chequamegon National Forest Wisconsin,USA, from 1972 to 2001

Land uses, especially harvesting and road building, are considered to be the primary cause of forest fragmentation in many parts of the world. To test this perception, we (1) quantified changes and rates of change in vegetative composition and structure within the Washburn Ranger District in northern Wisconsin using Landsat images, (2) examined changes in landscape structure, (3) assessed changes within the area of road influence (ARI), and (4) investigated changes in landscape composition and structure within the context of forest management activities. Our landscape classifications included six dominant cover types: mixed hardwood (MH), jack pine (JP), red pine (RP), mixed hardwood/conifer (MHC), non-forested bare ground (NFBG), and regenerating forest or shrub (RFS). Increases in NFBG and RFS, by 196% and 28% respectively, reflect expansion of the pine-barrens. Windthrow in the mature hardwoods during the late 1970s and jack pine budworm outbreaks during the mid-1990s correlated with decreases in those classes over the corresponding intervals. A 69% decrease in mean patch size and a 60% increase in edge density reflect increased fragmentation. An inverse relationship existed between the compositional trends of forested (excluding JP) cover types and RFS and NFBG cover types. ARI covered 8% of the landscape affecting species composition within the MH, RFS, and NFBG. Results from this study are key in assessing the links between management activities and ecological consequences and thereby facilitate adaptive management.This revised version was published online in May 2005 with corrections to the Cover Date.     

The cost of gypsy moth sex in the city

Since its introduction in the 1860s, gypsy moth, Lymantria dispar (L.), has periodically defoliated large swaths of forest in the eastern United States. Prior research has suggested that the greatest costs and losses from these outbreaks accrue in residential areas, but these impacts have not been well quantified. We addressed this lacuna with a case study of Baltimore City. Using two urban tree inventories, we estimated potential costs and losses from a range of gypsy moth outbreak scenarios under different environmental and management conditions. We combined outbreak scenarios with urban forest data to model defoliation and mortality and based the costs and losses on the distribution of tree species in different size classes and land uses throughout Baltimore City. In each outbreak, we estimated the costs of public and private suppression, tree removal and replacement, and human medical treatment, as well as the losses associated with reduced pollution uptake, increased carbon emissions and foregone sequestration. Of the approximately 2.3 M trees in Baltimore City, a majority of the basal area was primary or secondary host for gypsy moth. Under the low outbreak scenario, with federal and state suppression efforts, total costs and losses were $5.540 M, much less than the $63.666 M estimated for the high outbreak scenario, in which the local public and private sectors were responsible for substantially greater tree removal and replacement costs. The framework that we created can be used to estimate the impacts of other non-native pests in urban environments.     

Landscape structure influences avian malaria ecology in the Western Cape, South Africa

A central theme in landscape ecology is that of understanding the consequences of landscape heterogeneity for ecological processes. The effects of landscape heterogeneity on parasite communities are poorly understood, although it has been shown that anthropogenic impacts may contribute to outbreaks of both parasites and pathogens. We tested for effects of landcover type, composition, configuration, and urbanisation on avian diversity and avian malaria prevalence in 26 communities of wetland-associated passerines in the Western Cape of South Africa. We predicted that avian malaria prevalence would be influenced by the pattern of farmland and urban areas in the surrounding landscapes and the sizes of the wetlands in which birds were sampled. We quantified landscape pattern using a six-class simplification of the National Landcover data set at 35 × 35 m resolution and five extents of between 1 and 20 km from each wetland. The bird community was sampled using point counts and we collected blood samples from birds at each site. We screened these for malaria using PCR and molecular techniques. Passerine species richness and infection prevalence varied significantly between different landcover types. Host richness and parasite prevalence were highest in viticultural and cropping sites respectively and lowest in urban sites. Wetlands located in indigenous vegetation had intermediate numbers of bird species and intermediate parasite prevalence. Landscape composition and habitat type surrounding wetlands emerged as useful correlates of infection prevalence. Anthropogenic landscape modification appears to have both direct and indirect effects on avian communities and their associated parasite assemblages, with attendant consequences for avian health.     

Response of mountain plovers to plague-driven dynamics of black-tailed prairie dog colonies

Sylvatic plague is a major factor influencing the dynamics of black-tailed prairie dog (Cynomys ludovicianus) colonies in the western Great Plains. We studied the nesting response of the mountain plover (Charadrius montanus), a grassland bird that nests on prairie dog colonies, to plague-driven dynamics of prairie dog colonies at three sites in the western Great Plains. First, we examined plover nest distribution on colonies that were previously affected by plague, but that had been recovering (expanding) for at least 6 years. Plovers consistently nested in both young (colonized in the past 1–2 years) and old (colonized for 6 or more years) portions of prairie dog colonies in proportion to their availability. Second, we examined changes in plover nest frequency at two sites following plague epizootics, and found that mountain plover nest numbers declined relatively rapidly (≤2 years) on plague-affected colonies. Taken together, our findings indicate that available plover nesting habitat associated with prairie dog colonies closely tracks the area actively occupied by prairie dogs each year. Given the presence of plague throughout most of the mountain plover’s breeding range in the western Great Plains, important factors affecting plover populations likely include landscape features that determine the scale of plague outbreaks, the distance that plovers move in response to changing breeding habitat conditions, and the availability and quality of alternate breeding habitat within the landscape.     

Dendroctonus micans populations on Picea pungens in the center of a non-outbreak region contain few pathogens,parasites or predators: A new threat for urban forests?

In reviewing the occurrence of the bark beetle Dendroctonus micans in the Czech Republic over the past 100 years, we found that D. micans has been detected at 80 localities with elevations ranging from 158 to 1350 m a.s.l. During 2011–2012, we recorded three local outbreaks on Picea pungens, two of which involved isolated trees in urban areas between houses (always on sites <1 ha). From these locally abundant populations, 125 adults, 5 pupae, and 73 larvae of D. micans were obtained and dissected. Among these dissected specimens, nematodes in the hemolymph were detected in only 5 adults and 11 larvae. No other parasites or pathogens were found in the D. micans specimens. Low numbers of the beetle Rhizophagus grandis, which is a specific predator of D. micans, were detected, and none contained parasites or pathogens. Locally D. micans could constitute a new limited threat to urban trees, including P. pungens, in the Czech Republic and Central Europe. Special attention should be given to solitary P. pungens trees; if D. micans is detected on these trees, defensive measures must be taken to protect uninfested trees in the vicinity.