Agricultural landscapes with prevailing grassland can mitigate the population densities of tree-demaging alien species
Abstract
Alien organisms can seriously damage plants that are important to humans. Because such pests are often managed at the site scale, our understanding of how factors on broader spatial scales affect their numbers remains poor.
To understand how factors relevant to larger spatial scales affect alien numbers, we used the horse-chestnut leaf miner (Cameraria ohridella) as a model organism. We studied how its site-based population density was related to six kinds of land use in independent landscapes (ranging from 2 to 64 km2) that surrounded each study site in the Czech Republic.
For each landscape, we quantified the area occupied by coniferous forests, deciduous forests, crop fields, grasslands, parks and urban areas, and linear vegetation. Data were collected from 30 sites in 2002 and from 35 different sites in 2014.
The abundance of alien pest was most closely associated with the landscape occupied by grassland. This relationship was negative, and its strength increased with spatial scale in 2002 but decreased in 2014.
Grassland area was negatively correlated with crop field area, and we infer that grasslands help to control alien pest abundance while crop fields should have the opposite effect. We suggest that increasing the percentage of the landscape patches planted with grassland is one of the possibilities that could help control alien and perhaps other pests of trees.
Furthermore, increasing the area of grasslands might hinder the spread of invasive organisms and facilitate pest management. Moreover, landscape-based management might be directly or indirectly influenced by agricultural subsidies.