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Assessment of pest and pathogen attack on trees in more or less diverse stands

Book Contribution - Book Abstract Conference Contribution

Pests and pathogens attacking trees are common disturbances in European forests. Increasing the diversity of trees in forest stands may have an effect to counter this problem. Several researches showed reduced levels of herbivory in mixed tree stands, as well as an increased resistance to pest and diseases. In more diverse tree communities, individual tree species are less obvious to find by the herbivore (resource concentration hypothesis). More complex communities also provide more favourable conditions enhancing the control of natural enemies (shelter for birds, supplementary food for parasitoids). The objective of this research is to observe patterns of damage caused by pest and pathogen attacks in forest plots with increasing tree diversity in a recently established, large-scaled biodiversity experiment (FORBIO) in Belgium (http://forbio.biodiversity.be/). The research was conducted by assessing selected trees for damage using a scoring system, and by assessing arthropod diversity with the vacuum sampling method. In total 2,816 trees were assessed for three damage symptoms (defoliation, discoloration, and shoot damage) during early autumn 2012. While the arthropod samples were collected from a subset of 216 trees in spring 2012. From the total 2,816 trees inspected, 75.89% suffered from defoliation, 52.49% suffered from discoloration, and 4.13% lost part of their shoots. Different tree species in different stand diversity showed different damage patterns. Betula pendula (birch) showed rather similar damage degrees caused by defoliation, discoloration, and shoot dieback in more or less diverse stands. While Fagus sylvatica (beech) showed reduced degrees of defoliation and discoloration in more diverse stands. In case of defoliation, there were more birch trees (96.07% from 510 trees observed) showing damage symptoms than beech trees (89.87% from 523 trees observed). However, the mean damage was more severe in beech (67.49±29.24%) than in birch (9.86±4.96%). From the 216 trees sampled, 10,087 individuals from 12 different orders were identified. Arthropod abundance in birch trees showed a similar trend in more or less diverse stand (107-123 arthropods per tree). Arthropod abundance in beech monoculture (42 arthropods per tree) was lower than in the most diverse stand (102 individual/trees). Shannon-Wienner diversity indices showed that arthropod found in birch monoculture stands (0.31) were less diverse than in beech monoculture stands (1.40). In more diverse stands, diversity indices of birch did not increase, but they did increase for beech. However, in the most diverse stands, diversity index was increased in birch (0.82) and decreased in beech (0.85). These preliminary results show that there are different pattern of pest and disease attack between species and in more or less diverse stands. An important result is that pest and pathogen attack was reduced in more diverse stands of beech. More of the results will be presented during the talk.
Book: Starters in het Natuur- en Bosonderzoek, Abstracts
Number of pages: 1