Forests - Pests and diseases

Title

Lack of natural control mechanisms increases wildlife–forestry conflict in managed temperate European forest systems

Reference

European Journal of Forest Research
10.1007/s10342-011-0523-3

Author(s)

D. P. J. Kuijper

Study type

Peer Review Journal

Abstract

Across Europe, ungulate numbers have greatly increased over the past decades, leading to increasing concerns about the ecological and economical impacts and pleas for stronger population control. However, focussing on population control only ignores other underlying factors which may enhance the wildlife–forestry conflict. I reviewed factors which shape herbivore top-down effects in natural temperate forest systems aiming at understanding how these interactions are altered in managed forests. Carnivores are important in modifying ungulate–plant interactions. They can directly influence the numbers of ungulates, but this effect is dependent on productivity and predicted to be smallest in highly productive temperate forest. Indirectly, they modify herbivore top-down effects by creating a landscape of fear. Despite the abundance of knowledge from American systems, there is a lack of knowledge on how this process might work in European systems. Next to carnivores, abiotic conditions interact with herbivory by influencing forage quality and availability. Forest gaps lead to concentration of ungulates and their effects, due to increased forage supply. Abiotic conditions also influence the response of plants following herbivory, which can be tolerated by showing increased regrowth or resistance due to chemical or physical defence. In typical managed forest systems, carnivores and abiotic conditions which shape ungulate top-down effects in natural forests are altered or absent. Human hunting might replace the direct effects of carnivores, but does not replace their indirect effects. Forestry practices also have modified herbivore–plant interactions in several ways, creating a forest with lower ungulate carrying capacity and higher sensitivity for ungulate browsing. These changes logically increase the strength of herbivore top-down effects in managed forests and increase the wildlife–forestry conflict. To reduce this conflict, aiming only at reducing wildlife numbers is predicted to have little effects when they do not coincide with habitat ameliorations. Forestry practices may therefore greatly enhance the conflict that exists between wildlife and forestry but can also be an important tool to reduce this conflict by adapting management practices that allow more natural functioning of forests systems.

Policy theme(s)

Biodiversity >> Threats to biodiversity >> Human impacts
Forests >> Forest protection >> Forest biodiversity

Keywords

Ungulates; Browsing; Damage; Red deer; Roe deer; Carnivores; Top-down effects

Entry Source:

Selected for Science for Environment Policy News Alert

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http://www.springerlink.com/content/l36851555w005684

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Contact the study author at:

dkuijper@zbs.bialowieza.pl

Title

Reference

Forests 2011, 2(2), 486-504; doi:10.3390/f2020486
Part EU-funded

Author(s)

Jan Stenlid, Jonàs Oliva, Johanna B. Boberg and Anna J.M. Hopkins

Study type

Peer Review Journal

Abstract

New diseases in forest ecosystems have been reported at an increasing rate over the last century. Some reasons for this include the increased disturbance by humans to forest ecosystems, changed climatic conditions and intensified international trade. Although many of the contributing factors to the changed disease scenarios are anthropogenic, there has been a reluctance to control them by legislation, other forms of government authority or through public involvement. Some of the primary obstacles relate to problems in communicating biological understanding of concepts to the political sphere of society. Relevant response to new disease scenarios is very often associated with a proper understanding of intraspecific variation in the challenging pathogen. Other factors could be technical, based on a lack of understanding of possible countermeasures. There are also philosophical reasons, such as the view that forests are part of the natural ecosystems and should not be managed for natural disturbances such as disease outbreaks. Finally, some of the reasons are economic or political, such as a belief in free trade or reluctance to acknowledge supranational intervention control. Our possibilities to act in response to new disease threats are critically dependent on the timing of efforts. A common recognition of the nature of the problem and adapting vocabulary that describe relevant biological entities would help to facilitate timely and adequate responses in society to emerging diseases in forests.

Policy theme(s)

Biodiversity >> Threats to biodiversity >> Invasive species
Forests >> Forest protection >> Forest pests and diseases

Keywords

biosecurity; communicating biological concepts; forest health; global change; invasive pathogens; legislation; pathway analysis; species concepts

Entry Source:

Selected for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.mdpi.com/1999-4907/2/2/486/
This study is free to view

Contact the study author at:

jan.stenlid@slu.se

Title

Reference

Journal of Vegetation Science
DOI: 10.1111/j.1654-1103.2011.01340.x

Author(s)

Benjamin S. Ramage, Alison B. Forrestel, Max A. Moritz, Kevin L. O'Hara

Study type

Peer Review Journal

Abstract

Questions
How is sudden oak death disease progression affected by forest type? Which specific factors influence mortality rates and patterns? How do these trends vary across spatial scales?
Location
Point Reyes National Seashore, California, USA.
Methods
Sudden oak death, caused by the exotic pathogen Phytophthora ramorum, is affecting forests throughout coastal California. We investigated disease progression in tanoak (Notholithocarpus densiflorus syn. Lithocarpus densiflorus), the most susceptible species, in two distinct forest types: coast redwood (Sequoia sempervirens) and Douglas-fir (Pseudotsuga menziesii var. menziesii). Within each forest type, we used a variant of a split-plot design to sample proximate areas at two different stages of disease progression (relatively unaffected vs severely impacted), and used generalized linear mixed effects models to analyse these data.
Results
Annual mortality rates were much higher in Douglas-fir (10.1–26.2%) than in redwood (3.2–8.2%) forest, and data suggested that similarly divergent rates will continue into the future (proportions of surviving trees with disease symptoms remained constant from the beginning to the end of the study period). Across both forest types, survival probabilities were lower for tanoaks with larger diameters and tanoaks in plots (1/20 ha) and neighbourhoods (3-m radius) with greater basal area of previously killed tanoak. All variables were significant when included in the same model, suggesting that disease spread is occurring simultaneously at two local spatial scales. Several other biotic and abiotic variables were unrelated to tanoak survival probability.
Conclusions
We detected mortality rates that exceed any rates previously associated with sudden oak death, while demonstrating that these rates can vary substantially between adjacent forest types. However, because the Douglas-fir forests of our study area are adjacent to the ocean, which is somewhat uncommon for this forest type, our findings do not necessarily indicate that all Douglas-fir forests with a substantial tanoak component are at risk of similar impacts. Our data also suggest that, in both forest types, local patchiness in disease presence/severity is an ephemeral condition resulting primarily from stochastic processes (e.g. long-distance dispersal events), while intra-plot spread around infected trees is deterministic and probably inevitable. Our findings should inform scientists and managers throughout the world attempting to understand disease progression in regions recently invaded by P. ramorum (e.g. Europe) and/or affected by other exotic forest pathogens.

Policy theme(s)

Biodiversity >> Threats to biodiversity >> Invasive species
Forests >> Forest protection >> Forest pests and diseases

Keywords

Disease ecology; Douglas-fir; Exotic pathogen; Forest disease; Lithocarpus densiflorus; Mortality rate; Notholithocarpus densiflorus; Phytophthora ramorum;
Pseudotsuga menziesii; Redwood; Sequoia sempervirens; Tanoak

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://onlinelibrary.wiley.com/doi/10.1111/j.1654-1103.2011.01340.x/full
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Contact the study author at:

bsramage@berkeley.edu

Title

Reference

Ecology Letters
Volume 14, Issue 11, pages 1108–1116, November 2011

Author(s)

Sarah E. Haas, Mevin B. Hooten, David M. Rizzo, Ross K. Meentemeyer

Study type

Peer Review Journal

Abstract

Empirical evidence suggests that biodiversity loss can increase disease transmission, yet our understanding of the 'diversity-disease hypothesis' for generalist pathogens in natural ecosystems is limited. We used a landscape epidemiological approach to examine two scenarios regarding diversity effects on the emerging plant pathogen Phytophthora ramorum across a broad, heterogeneous ecoregion: (1) an amplification effect exists where disease risk is greater in areas with higher plant diversity due to the pathogen's wide host range, or (2) a dilution effect where risk is reduced with increasing diversity due to lower competency of alternative hosts. We found evidence for pathogen dilution, whereby disease risk was lower in sites with higher species diversity, after accounting for potentially confounding effects of host density and landscape heterogeneity. Our results suggest that although nearly all plants in the ecosystem are hosts, alternative hosts may dilute disease transmission by competent hosts, thereby buffering forest health from infectious disease.

Policy theme(s)

Biodiversity >> Threats to biodiversity >> Invasive species
Forests >> Forest protection >> Forest pests and diseases

Keywords

Bayesian hierarchical model; emerging infectious disease; forest ecosystem; landscape epidemiology; Phytophthora ramorum; spatial autocorrelation; species diversity; sudden oak death; zero-inflation

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2011.01679.x/abstract
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shaas1@uncc.edu

Title

Is insecticide spraying a viable and cost-efficient management practice to control pine processionary moth in Mediterranean woodlands?

Reference

Forest Ecology and Management
Volume 261, Issue 11, 1 June 2011, Pages 1732-1737

Author(s)

Luis Cayuela, José Antonio Hódar and Regino Zamora

Study type

Peer Review Journal

Abstract

Insect pests are a major threat to many forests worldwide, from boreal to tropical forest ecosystems. Some pests exhibit periodical outbreaks, after which their populations often crash as a result of natural biological control. To offset such outbreaks, several management techniques are used, including aerial spraying of insecticides. The question remains whether pest decline following an outbreak is the result of management practices or a natural consequence of the insect's population cycle. In this study, we assessed the performance of aerial spraying of insecticides on pine woodland stands to control pine processionary moth Thaumetopoea pityocampa (PPM) outbreaks in southern Spain. To achieve this, we compared the degree to which a forest stand recovers from defoliation from one year of severe damage by PPM to the following year (infestation index) in stands that were treated (i.e. subjected to aerial spraying) and untreated using a 4-years database from the Regional Environmental Council. The results revealed a significant similar recovery from infestation after a PPM outbreak of both sprayed and non sprayed pine woodland stands, for the four most representative pine species (black, Aleppo, maritime, and stone pine). It is concluded that insecticide spraying cannot be considered a prevention for outbreaks if it is applied once the outbreak explodes. Management practices that can help control PPM outbreaks include promoting spatial heterogeneity at the landscape level, fostering biodiversity in pine plantations, and reinforcing parasitoid insect and predatory bird populations that negatively affect the PPM. This study illustrates how simple sampling designs and statistical tests can be useful decision-making tools and can help improve the environmental viability and cost-efficiency of forest management practices.

Policy theme(s)

Forests >> Forest protection >> Forest pests and diseases

Keywords

Aerial spraying, Defoliation, Insect outbreak, Pine processionary moth, Population cycle,  Thaumetopoea pityocampa

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.sciencedirect.com/science/article/pii/S0378112711000545
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Contact the study author at:

luis.cayuela@urjc.es

Title

A case of habitat complementation in forest pests: Pine processionary moth pupae survive better in open areas

Reference

Forest Ecology and Management
Volume 261, Issue 6, 15 March 2011, Pages 1069-1076

Author(s)

A.-M. Dulaurent, A.J. Porté, I. van Halder, F. Vétillard, P. Menassieu and H. Jactel

Study type

Peer Review Journal

Abstract

Little attention has been given to the relevance of habitat complementation concept to the population dynamics of insect herbivores. Late instar larvae of the pine processionary moth (PPM) Thaumetopoea pityocampa move in late winter from pine stands, their feeding habitat, to neighbouring habitats where they pupate until next summer. They search for sunny exposed soil which they can find in open areas. We investigated the effect of both forest cover and soil origin, with three matching types (pine stand, broadleaved stand and open area) on the survival of PPM pupae. The microclimatic soil variables which significantly differentiated cover types and soil origins were the maximum temperature and the mean relative humidity in spring, soon after pupation has occurred. A significant effect of the cover type, but not of the soil origin, was detected on the proportion of dead, emerged or diapausing pupae. Open areas were more suitable for pupae survival than forest covers (pine or broadleaved stands), due to warmer and more humid soil conditions. In this study, we provide one of the first examples of habitat complementation for an insect herbivore, as PPM population can benefit from the combination of pine habitats for the feeding of larvae with open habitats for pupation. The presence of broadleaved stands next to pine stands might also represent an ecological trap for PPM pupae, as broadleaved habitats may turn to be less suitable for pupae survival in spring when the apparition of leaves creates cooler conditions.

Policy theme(s)

Forests >> Forest protection >> Forest pests and diseases

Keywords

Soil, Insect, Conifer, Broadleaved tree

Entry Source:

Selected for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.sciencedirect.com/science/article/pii/S0378112710007322
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Contact the study author at:

dulaurent@pierroton.inra.fr