From the abstract: "We find that agricultural intensification, in particular pesticides and fertiliser use, is the main pressure for most bird population declines, especially for invertebrate feeders. Responses to changes in forest cover, urbanisation and temperature are more species-specific. Specifically, forest cover is associated with a positive effect and growing urbanisation with a negative effect on population dynamics, while temperature change has an effect on the dynamics of a large number of bird populations, the magnitude and direction of which depend on species' thermal preferences."
Here forests and trees in general are all cut so the farmers can do farming. Considering the amount of land that is changing into a deserts (which negatively affects the farmers too), it's a bit strange they keep cutting forest cover instead of subsidising maintaining and replanting.
