Bird species diversity in riparian buffers, row crop fields, and grazed pastures within agriculturally dominated watersheds

Abstract

In response to concern about the loss of ecosystem services once provided by natural riparian systems, state and federal agencies have established incentive programs for landowners to convert sensitive lands from agricultural to conservation uses. Enhancement of wildlife habitat, while identified as a function of such systems, has often been of secondary importance to soil conservation and water quality objectives. Though greatly important, little consideration has been given to how specific species will respond to the design and management of riparian buffers or other conservation lands. This study compared avian communities within a chronosequence of riparian buffers established on previously cropped or pastured land with those of the nearby matrix land cover types (row crop fields and an intensively grazed pasture). The riparian buffers consisted of native grasses, forbs, and woody vegetation established at three different times (2, 9, and 14? years prior to survey). At each site, 10 min point counts for breeding birds were conducted using 50 m fixed radius plots, which were visited eight times between May 15 and July 10, 2008. A total of 54 bird species were observed over all of the study sites. The re-established riparian buffers in this study had higher bird abundance, richness, and diversity than the crop and pasture sites. These results suggest that re-establishing native riparian vegetation in areas of intensive agriculture will provide habitat for a broad suite of bird species, but that specific species will reflect successional stage, horizontal and vertical vegetative structure, and compositional diversity of the buffer vegetation. These results emphasize the importance of matching buffer design and management to species requirements if the objectives are to attract specific target species or species groups.

Planting grass filter strips: Does it influence the structure and function of riparian habitats of agricultural headwater streams?

“…These results are consistent with others [5,7,[34][35][36] who have quantified the impacts of agriculture on riparian habitats. Berges et al [36] observed greater tree density, greater percentage trees and shrubs, and greater maximum canopy height in planted forested riparian habitats compared to row crop and pasture within an agricultural watershed in Iowa. Kyriakeas and Watzin [35] documented that forested riparian habitats in Vermont CPOM input within riparian habitats.…”

“…Others [36,[45][46][47][48][49] have suggested that it will take at least 10 years for grass filter strips and other types of vegetative conservation practices to fully establish. The development of woody vegetation structure may require longer time periods depending on the tree growth rates following planting.…”

“…Riparian restoration projects that plant fast growing tree species and protect the newly planted trees from herbivory and competition could achieve restoration within 15 years, while projects that plant slower growing species and choose not to use protective measures might require as long as 35 years for restoration of forested riparian habitats [45]. Within an agricultural watershed in Iowa planted forested riparian habitats that were at least 14 years old had greater vertical structure and greater variety of tree and shrub sizes than nine year old and two year old planted forested riparian habitats that were still dominated by herbaceous vegetation [36]. While planted forested riparian habitats protected from cattle by fencing exhibited greater woody vegetation species richness compared to unprotected riparian habitats, these planted forested riparian habitats still exhibited less woody vegetation species richness and abundance than unimpacted forested riparian habitats ten years after planting within an agricultural watershed in Scotland [49].…”

Using biodiversity to link agricultural productivity with environmental quality: Results from three field experiments in Iowa

“…In contrast, native tallgrass prairie communities are typically dominated by stiff-stemmed warm season grasses, such as Indiangrass (Sorghastrum nutans), big bluestem (Andropogon gerardii) and switchgrass (Panicum virgatum), and a wide range of erect forbs, including species in the genera Solidago, Aster, Rudbeckia, Ratibida, Silphium, Helianthus and Monarda 55 , which are less prone to collapse under heavy rain, and which are more effective in providing resistance to water flow and sediment movement 56,57 . In addition to reducing water runoff and soil erosion from crop fields, strips and patches of perennial native plants in and around agricultural areas can provide habitat to support native animal populations, including species of conservation concern [58][59][60][61][62][63] . Many bird species respond positively to agricultural conservation practices such as grassed waterways 64,65 , field borders 66,67 , and riparian buffer strips 62,68 ; the general trend among these studies is increased bird presence, abundance and richness where those small habitats are present adjacent to row crops.…”

“…In addition to reducing water runoff and soil erosion from crop fields, strips and patches of perennial native plants in and around agricultural areas can provide habitat to support native animal populations, including species of conservation concern [58][59][60][61][62][63] . Many bird species respond positively to agricultural conservation practices such as grassed waterways 64,65 , field borders 66,67 , and riparian buffer strips 62,68 ; the general trend among these studies is increased bird presence, abundance and richness where those small habitats are present adjacent to row crops. Compared with monocultures of cool-season grasses, diverse prairie communities are expected to provide higher quality bird habitat and harbor more bird species 65,69,70 .…”