Tree species composition rather than diversity triggers associational resistance to the pine processionary moth

TitleTree species composition rather than diversity triggers associational resistance to the pine processionary moth
Publication TypeJournal Article
Year of Publication2014
AuthorsCastagneyrol B, Régolini M, Jactel H
Pagination516 - 523
Date Published2014/9//
ISBN Number1439-1791
KeywordsAssociational resistance, biodiversity, Forest, Herbivory, ORPHEE, Thaumetopoea pityocampa, Tree apparency, Tree height

The reduction of insect herbivory is one of the services provided by tree diversity in forest ecosystems. While it is increasingly acknowledged that the compositional characteristics of tree species assemblages play a major role in triggering associational resistance to herbivores, underlying mechanisms are less well known. We addressed this question in the ORPHEE experiment by assessing pine processionary moth infestations (Thaumetopoea pityocampa) across a tree diversity gradient from pine monocultures to five species mixtures. We showed that tree species richness per se had no effect on the probability of attack by this pest. By contrast, the infestation rate was strongly dependent on plot composition. Mixtures of pines (Pinus pinaster) and birches (Betula pendula) were less prone to T. pityocampa infestations, whereas mixtures of pines and oaks (Quercus spp.) were more often attacked than pine monocultures. By taking into account the relative height of pines and associated broadleaved species, this effect could be explained by pine apparency. Pines were on average 343 ± 5 cm height. Birches, as fast growing trees, were slightly taller than pines (363 ± 6 cm), while oak trees were significantly smaller (74 ± 1 cm). Host trees of T. pityocampa were then partly hidden in mixtures of pines and birches but more apparent in mixtures with oaks. We suggest that reduced pine apparency disrupted visual cues used by female moths to select host trees prior to oviposition. This study highlights the need to take into account tree traits such as growth rate when selecting the tree species that have to be associated in order to improve forest resistance to pest insects.

A measure for the amount of tree species mixed on a given site or stand. Can be measured in various forms (e.g. Shannon Index, tree species richness).
The capacity of an ecosystem to withstand the impacts of drivers without displacement from its present state. ( MA 2003)
a woody perennial plant, typically large and with a well-defined stem or stems carrying a more or less definite crown — note sometimes defined as attaining a minimum diameter of 5 in (12.7 cm) and a minimum height of 15 ft (4.6 m) at maturity, with no branches within 3 ft (1 m) of the ground.
The rate at which the number of individuals in a population increases in a given time period as a fraction of the initial population. wiki
Short TitleBasic and Applied Ecology

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