Читать книгу North American Agroforestry - Группа авторов - Страница 90

Variations in tree–crop combinations and spatial arrangements in agroforestry have been shown to have an effect on insect population density and species diversity (Altieri, 1991; Pardon et al., 2019). Agroforestry helps reduce pest problems because tree–crop combinations provide greater niche diversity and complexity than monoculture systems of annual crops (Martin‐Chave, Béral, & Capowiez, 2019). This effect may be explained in one or more of the following ways: (a) wide spacing of host plants in the intercropping scheme may make the plants more difficult for herbivores to find; (b) one plant species may serve as a trap crop to detour herbivores from finding the other crop; (c) one plant species may serve as a repellent to the pest; (d) one plant species may serve to disrupt the ability of the pest to efficiently attack its intended host; and (e) the intercropping situation may attract more predators and parasites than monocultures, thus reducing pest density through predation and parasitism (Root, 1973; Jose et al., 2004).

Reports of agroforestry practices enhancing beneficial insects are limited in the temperate agroforestry literature. Studies with pecan, for example, have looked at the influence of ground covers on arthropod densities in tree–crop systems (Bugg, Sarrantonio, Dutcher, & Phatak, 1991; Smith et al., 1996). Bugg et al. (1991) observed that cover crops (e.g., annual legumes and grasses) sustained lady beetles (Coleoptera: Coccinellidae) and other arthropods that may be useful in the biological control of pests in pecan (Bugg et al., 1991; Garrett et al., 2009). However, Smith et al. (1996) found that ground cover had little influence on the type or density of arthropods present in pecan. Brandle et al. (2004) summarized the beneficial effects of windbreaks on natural enemies of crop pests. According to them, windbreaks influence the distributions of both predator and prey. Greater diversity of the edges provides numerous microhabitats for life‐cycle activities and a variety of hosts, prey, pollen, and nectar sources. As windbreak structure becomes more complex, various microhabitats are created and insect populations increase in both number and diversity.

Fig. 4–7. Effect of trees on air and soil temperature of holm oak dehesas: (a) air temperature as a function of distance from the tree, and (b) soil temperature (ST) with respect to the air temperature both beneath and beyond the tree canopy

(adapted from Moreno Marcos et al., 2007).