Do birds help trees grow? An experimental study of the effects of land-use intensification on avian trophic cascades.

Autor: Harris SH; Department of Forest Ecosystems & Society, Forest Biodiversity Research Network, Oregon State University, Corvallis, Oregon, 97331, USA., Kormann UG; Swiss Ornithological Institute, Seerose 1, CH-6204, Sempach, Switzerland., Stokely TD; Department of Forest Ecosystems & Society, Forest Biodiversity Research Network, Oregon State University, Corvallis, Oregon, 97331, USA., Verschuyl J; National Council for Air & Stream Improvement, Anacortes, Washington, 98221, USA., Kroll AJ; Weyerhaeuser, 785 N 42nd Street, Springfield, Oregon, 97478, USA., Betts MG; Department of Forest Ecosystems & Society, Forest Biodiversity Research Network, Oregon State University, Corvallis, Oregon, 97331, USA.
Jazyk: angličtina
Zdroj: Ecology [Ecology] 2020 Jun; Vol. 101 (6), pp. e03018. Date of Electronic Publication: 2020 May 07.
DOI: 10.1002/ecy.3018
Abstrakt: By regulating populations of herbivores, predators can indirectly influence plant production. However, the factors influencing the strength of this type of trophic cascade are still unclear. We hypothesized that changes to plant community structure would affect the number of avian predators, thereby mediating cascade strength. Using a 4-yr, blocked, split-plot experiment, we independently manipulated both predators (birds) and plants in an early seral managed forest system in western Oregon, USA, and measured abundance across three trophic levels. We applied herbicides, as a surrogate for land-use intensification, to recently clear-cut stands to establish an experimental gradient in plant abundance and species richness, and excluded birds using 28, 225 m 2 exclosures. In total, we counted and identified 94,738 arthropods of 141 families in paired control and bird exclosure plots. On average, insectivorous birds reduced arthropod abundance by 16% and plant damage by 14%, and some well-known pests (e.g., Adelges cooleyi) of crop trees (mostly Pseudotsuga menziesii) in our system were reduced by as much as 30%. However, this effect did not translate into a trophic cascade that increased crop-tree growth in the presence of birds. We experimentally reduced plant abundance and diversity by 67% and 55%, respectively, in the most intensive herbicide treatment in relation to untreated controls, but reduced vegetative resources did not change the strength of the direct effect of birds on arthropods or the indirect effect of birds on plants.
(© 2020 by the Ecological Society of America.)
Databáze: MEDLINE
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