The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Stefan Vidal - One of the best experts on this subject based on the ideXlab platform.
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shade tree diversity cocoa Pest Damage yield compensating inputs and farmers net returns in west africa
PLOS ONE, 2013Co-Authors: Herve Bertin Daghela Bisseleua, Daniel Fotio, Alain Didier Missoup, Stefan VidalAbstract:Cocoa agroforests can significantly support biodiversity, yet intensification of farming practices is degrading agroforestry habitats and compromising ecosystem services such as biological Pest control. Effective conservation strategies depend on the type of relationship between agricultural matrix, biodiversity and ecosystem services, but to date the shape of this relationship is unknown. We linked shade index calculated from eight vegetation variables, with insect Pests and beneficial insects (ants, wasps and spiders) in 20 cocoa agroforests differing in woody and herbaceous vegetation diversity. We measured herbivory and predatory rates, and quantified resulting increases in cocoa yield and net returns. We found that number of spider webs and wasp nests significantly decreased with increasing density of exotic shade tree species. Greater species richness of native shade tree species was associated with a higher number of wasp nests and spider webs while species richness of understory plants did not have a strong impact on these beneficial species. Species richness of ants, wasp nests and spider webs peaked at higher levels of plant species richness. The number of herbivore species (mirid bugs and cocoa pod borers) and the rate of herbivory on cocoa pods decreased with increasing shade index. Shade index was negatively related to yield, with yield significantly higher at shade and herb covers<50%. However, higher inputs in the cocoa farms do not necessarily result in a higher net return. In conclusion, our study shows the importance of a diverse shade canopy in reducing Damage caused by cocoa Pests. It also highlights the importance of conservation initiatives in tropical agroforestry landscapes.
Emmanuel Opunifrimpong - One of the best experts on this subject based on the ideXlab platform.
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silvicultural systems for plantation mahogany in africa influences of canopy shade on tree growth and Pest Damage
Forest Ecology and Management, 2008Co-Authors: Emmanuel Opunifrimpong, D F Karnosky, Andrew J Storer, Joseph R CobbinahAbstract:Overexploitation of the African mahoganies, Khaya anthotheca and K. ivorensis, could lead to their commercial extinction in the near future. Efforts to establish plantations to sustain supply have been discouraged by the shoot borer Hypsipyla robusta Moore. We hypothesized that there is a shade level at which Hypsipyla attack and branching are reduced, but height growth is adequate. We report on the growth of these African mahoganies and Hypsipyla attack under three different forest canopy shade levels: open (55% open sky), medium shade (26% open), and deep shade (11% open). Hypsipyla attack on K. anthotheca was 85%, 11%, and 0% attack in the open, medium, and deep shade treatments, respectively. However, growth in medium and deep shade was slow. Mean tree height for K. anthotheca was 413.8, 126.2, and 54.5 cm in the open, medium and deep shade treatments, respectively. K. ivorensis showed similar trends. The reduced growth under these shade levels limit the use of this strategy for controlling Hypsipyla attack.
Herve Jactel - One of the best experts on this subject based on the ideXlab platform.
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Pest Damage in mixed forests disentangling the effects of neighbor identity host density and host apparency at different spatial scales
Forest Ecology and Management, 2016Co-Authors: Herve Jactel, Maxime Damien, Celine Meredieu, Margot Regolini, Inge Van Halder, Bastien CastagneyrolAbstract:Mixed forests are thought to be less prone to Pest insect Damage than monocultures. This may result from reduced host availability (i.e., density effect) or from non-host trees reducing the physical or chemical apparency of host trees (i.e., associational resistance, AR). However, associational and density effects are often confounded in mixed forests. We aimed to disentangle their relative contribution to attacks of pine trees by a specialist Pest, the pine processionary moth (PPM, Thaumetopoea pityocampa). We assessed pine infestation by PPM by counting the number of winter nests during three consecutive years along an experimental gradient of pine density in presence or absence of a fast growing species, namely birch. The total number of PPM nests per plot increased with pine density (maximum in high density monocultures), while the proportion of attacked pine trees decreased along the same gradient. Birch provided associational resistance via reduced pine apparency due to their greatest higher. This mechanism occurred at two spatial scales, whenever birch was planted within pine plots or in adjacent plots. Associational resistance was stronger in dense stands, probably due to reduced distance between pines and neighboring birches. But AR faded with time, pines becoming taller than birches, making density effects preeminent over apparency effects. Our findings suggest that mixing tree species to trigger resistance to Pest insects requires taking into account the relative growth rate of associated species together with the relative proportion of associated species, both within and between stands.
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tree diversity reduces Pest Damage in mature forests across europe
Biology Letters, 2016Co-Authors: Virginie Guyot, Bastien Castagneyrol, Aude Vialatte, Marc Deconchat, Herve JactelAbstract:Forest Pest Damage is expected to increase with global change. Tree diversity could mitigate this impact, but unambiguous demonstration of the diversity–resistance relationship is lacking in semi-natural mature forests. We used a network of 208 forest plots sampled along two orthogonal gradients of increasing tree species richness and latitudes to assess total tree defoliation in Europe. We found a positive relationship between tree species richness and resistance to insect herbivores: overall Damage to broadleaved species significantly decreased with the number of tree species in mature forests. This pattern of associational resistance was frequently observed across tree species and countries, irrespective of their climate. These findings confirm the greater potential of mixed forests to face future biotic disturbances in a changing world.
Yann Clough - One of the best experts on this subject based on the ideXlab platform.
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interaction complexity matters disentangling services and disservices of ant communities driving yield in tropical agroecosystems
Proceedings of The Royal Society B: Biological Sciences, 2014Co-Authors: Arno Wielgoss, Alfianus Rumede, Hannes Seidel, Saleh Shahabuddin, Teja Tscharntke, Yann Clough, Brigitte FialaAbstract:Owing to complex direct and indirect effects, impacts of higher trophic levels on plants is poorly understood. In tropical agroecosystems, ants interact with crop mutualists and antagonists, but little is known about how this integrates into the final ecosystem service, crop yield. We combined ant exclusion and introduction of invasive and native-dominant species in cacao agroecosystems to test whether (i) ant exclusion reduces yield, (ii) dominant species maximize certain intermediate ecosystem services (e.g. control of specific Pests) rather than yield, which depends on several, cascading intermediate services and (iii) even, species-rich ant communities result in highest yields. Ants provided services, including reduced leaf herbivory and fruit Pest Damage and indirect pollination facilitation, but also disservices, such as increased mealybug density, phytopathogen dissemination and indirect Pest Damage enhancement. Yields were highest with unmanipulated, species-rich, even communities, whereas ant exclusion decreased yield by 27%. Introduction of an invasive-dominant ant decreased species density and evenness and resulted in 34% lower yields, whereas introduction of a non-invasive-dominant species resulted in similar species density and yields as in the unmanipulated control. Species traits and ant community structure affect services and disservices for agriculture in surprisingly complex ways, with species-rich and even communities promoting highest yield.
Virginie Guyot - One of the best experts on this subject based on the ideXlab platform.
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tree diversity reduces Pest Damage in mature forests across europe
Biology Letters, 2016Co-Authors: Virginie Guyot, Bastien Castagneyrol, Aude Vialatte, Marc Deconchat, Herve JactelAbstract:Forest Pest Damage is expected to increase with global change. Tree diversity could mitigate this impact, but unambiguous demonstration of the diversity–resistance relationship is lacking in semi-natural mature forests. We used a network of 208 forest plots sampled along two orthogonal gradients of increasing tree species richness and latitudes to assess total tree defoliation in Europe. We found a positive relationship between tree species richness and resistance to insect herbivores: overall Damage to broadleaved species significantly decreased with the number of tree species in mature forests. This pattern of associational resistance was frequently observed across tree species and countries, irrespective of their climate. These findings confirm the greater potential of mixed forests to face future biotic disturbances in a changing world.
