Joseph P. Colletti

Riparian forest buffers in agroecosystems – lessons learned from the Bear Creek Watershed, central Iowa, USA

Intensive agriculture can result in increased runoff of sediment and agricultural chemicals that pollute streams. Consensus is emerging that, despite our best efforts, it is unlikely that significant reductions in nutrient loading to surface waters will be achieved through traditional, in-field management alone. Riparian forest buffers can play an important role in the movement of water and NPS (non-point source) pollutants to surface water bodies and ground water. Riparian buffers are linear in nature and because of their position in the landscape provide effective connections between the upland and aquatic ecosystems. Present designs tend to use one model with a zone of unmanaged trees nearest the stream followed by a zone of managed trees with a zone of grasses adjacent to the crop field. Numerous variations of that design using trees, shrubs, native grasses and forbs or nonnative cool-season grasses may provide better function for riparian forest buffers in specific settings. Properly designed riparian buffers have been shown to effectively reduce surface NPS pollutant movement to streams and under the right geological riparian setting can also remove them from the groundwater. Flexibility in design can also be used to produce various market and nonmarket goods. Design flexibility should become more widely practiced in the application of this agroforestry practice.

Agroforestry and forestry-related practices in the Midwestern United States

A survey, conducted in 1990–1991 on agroforestry and forestry-related systems in eight Midwestern states, showed that three traditional and three nontraditional agroforestry systems are practiced in the region. Of 46 traditional systems reported, most common was agrisilviculture (28), then silvipasture (12) and agrisilvipasture (6). These systems often involved corn, soybeans, and hay planted with tree species for nut, timber, or Christmas tree production, and cattle. Non-traditional agroforestry systems were field windbreaks/shelterbelts (29), treeshrub intercropping systems (21), and boundary plantings (11). These systems involved a variety of northern hardwood species evergreens, and shrubs. There was also a preponderance of specialized systems (97) of growing trees with the production of mushrooms, nuts, syrup, wildlife, and other nonwood products. The survey is exploratory in nature and, although the results may not represent a complete count of people involved with agroforestry in the region, the numbers reported may indicate where a practice may be prevalent. The results reflect the fact that much work still needs to be done by agroforesters in this region. They also provide some basis for further research on more suitable systems, and for identifying other researchable questions on agroforestry for the region. The methodology also made possible a bigger nucleus for networking of agroforesters and other interested people in the Midwest. Finally, although not normally considered as agroforestry, the significance of the other specialized systems reported in this survey is that they offer varied ways of connecting forestry with other activities in a largely agricultural landscape, and that they may even be seen as opportunities for easier transition into agroforestry.