Forest-grown yerba mate: implications for the birds of Paraguay´s Atlantic interior forest

COCKLE, KRISTINA; LEONARD, MARTY

New Orleans, USA

Congreso; III North American Ornithological Conference; 2002

The Atlantic forest of Paraguay, Brazil, and Argentina is one of the world’s most diverse and threatened ecosystems. It is being cleared rapidly to make way for export crops and cattle. If the region's birds are to be maintained, we must explore alternative forms of agriculture that conserve some aspects of the forest. An alternative to clearing the native forest completely is to remove only the understory, then plant crops such as yerba mate (Ilex paraguariensis) under the forest trees. Although feasible, it is not known how well this approach maintains Atlantic forest bird communities. In other regions, the shade-grown crops most often used by forest birds have diverse tree species, high canopy cover, adjacent forest, and low input of agrochemicals. In this study, I describe the bird community of a shade-grown yerba mate plantation with these characteristics, and compare it to that of nearby Atlantic forest. I used spot-mapping and encounter rates to compare the diversity and abundance of birds in a plantation of shade-grown yerba mate to that in the surrounding forest. Of 145 species that regularly used the forest, 96 (66%) also used the plantation. As expected, the plantation contained many species associated with forest edge or man-made habitat, but few species of the forest floor and understory. Midstory birds entered the plantation occasionally, but most did not use it regularly. The forest birds best represented in the plantation were those that feed in the forest canopy (including mixed species canopy flocks) and insectivores that feed on tree trunks. The plantation supported various species that are sensitive to fragmentation and logging elsewhere in the Atlantic forest region, including five of the seven globally-threatened species encountered in the forest at my site. To determine whether a higher density of subcanopy trees and higher canopy cover would allow more forest birds to use the plantation, I also compared the abundance of birds between two areas within the plantation that differed in tree density, canopy cover, and the amount of contact with native forest. In the area of high tree density and canopy cover (also the area most surrounded by native forest) we encountered twice as many birds of the forest understory and midstory than in the area of low tree density. However, most of these birds were only occasional; they did not use any part of the plantation regularly. The area of low tree density attracted more edge-adapted birds and more forest canopy frugivores than the area of high tree density, although the frugivores may have responded to an abundance of fruiting trees rather than to the low stem density. For some bird species, the shade-grown yerba worked effectively as a buffer to the adjacent forest reserve. However, only a portion of the forest bird community was preserved in the plantation, despite a diverse and connected canopy, adjacent natural forest, and the absence of agrochemicals. In the end, no agroecosystem can substitute for natural forest, and Atlantic forest birds will not be conserved unless large tracts of intact Atlantic forest are also protected. Shade-grown yerba should only be promoted in cases where forest would otherwise be cleared, or has already been cleared, for conventional agriculture or livestock. In the latter case, new habitat could be created for some forest birds by planting yerba mate and Atlantic forest tree seedlings.