No abstract

Encroachment by woody vegetation is a major threat to tallgrass prairie streams, and converts them from open-to closed-canopy systems. This change presumably shifts the relative importance of basal resources from autochthonous to allochthonous and may alter functional feeding group composition and production of consumers. Riparian trees were removed from 2 headwater stream reaches on the Konza Prairie Biological Station to examine effects of forest encroachment and removal. Removal reaches were compared to reaches with naturally open and closed canopies before and after manipulation. Benthic organic matter and macroinvertebrates were sampled monthly for 1 y before (year 1) and after (year 2) riparian forest removal. Total secondary production in removal reaches ranged from 8.9 to 10.2 g ash-free dry mass (AFDM) m −2 y −1 in year 1, and increased significantly to 13.4 to 14.5 g AFDM m −2 y −1 in year 2. Scraper production in removal reaches was 2.8 to 3.9 g AFDM m −2 y −1 in year 1, and increased significantly to 6.0 to 8.7 g AFDM m −2 y −1 in year 2. Shredders did not respond negatively to the removal, but scrapers dominated production (45-60% of total) in open and removal reaches after manipulation. Total production in naturally open reaches was 7.6 to 12.6 g AFDM m −2 y −1 in year 1 and decreased to 6.5 to 9.8 g AFDM m −2 y −1 in year 2. Riparian forest removal altered macroinvertebrate production and functional structure, but higher production in removal reaches than in open reaches after manipulation suggested that natural conditions were not restored 1 y after removal. However, ordinations indicated communities in open and removal reaches became more similar after manipulation. Forest encroachment alters prairie stream structure and function, and riparian forest removal may be an effective restoration and management practice for remaining prairie streams.Prairie habitats once covered ∼162 million ha of North America, but most were significantly altered for agriculture, resulting in <5% of intact prairie remaining (Samson and Knopf 1994). Reduced native ungulate grazing and decreases in fire frequency and intensity in the last century have resulted in the encroachment of native woody species on the few remaining prairie remnants, particularly along riparian corridors. In some regions, fire suppression has resulted in complete conversion to closed-canopy forest in as little as 35 y (Hoch and Briggs 1999). These changes in riparian vegetation ultimately result in a shift from open-to closed-canopy conditions. Riparian vegetation strongly influences the chemical and physical attributes of streams, ultimately affecting ecosystem structure and function (Vannote et al. 1980, Gregory et al. 1991. Historically, because of the frequency of wildfires, ungulate grazing, and hydrological patterns, headwater tallgrass prairie streams were bordered by relatively short riparian prairie vegetation (e.g., grasses, forbs, and shrubs) and characterized as open-canopy systems Dodds 1998, Dodds et al. 2004). These conditions res...

Conversion to agriculture, habitat fragmentation, and the loss of native grazers have made tallgrass prairie one of the most endangered ecosystems. One management option for the remaining prairie parcels, patch-burn grazing (PBG), applies a controlled burn to a portion of the prairie to attract cattle, creating a mosaic of more- and less-grazed patches. Although beneficial to cattle and grassland birds, the potential impacts of PBG on streams have not been studied, and a holistic approach is needed to ensure against adverse effects. We used a Before-After-Control-Impact design to assess potential impacts of PBG with and without riparian protection on tallgrass prairie headwater streams. We sampled stream macroinvertebrates and benthic organic matter 2 yr before and 2 yr during PBG treatments on two grazed watersheds with riparian fencing (fenced), two unfenced grazed watersheds (unfenced), and two ungrazed (control) watersheds. Very fine benthic organic matter increased significantly (51%) in unfenced streams compared with controls ( < 0.007), and fine particulate organic matter (<1 mm and >250 µm) increased 3-fold in the unfenced streams compared with controls ( = 0.008). The contribution of fine inorganic sediments to total substrata increased 28% in unfenced streams during PBG, which was significantly different from controls ( = 0.03). Additionally, the abundance of Ephemeroptera, Plecoptera, and Trichoptera taxa decreased from 7635 to 687 individuals m in unfenced streams, which was significantly lower than in control streams ( = 0.008). Our results indicate that PBG adversely influences prairie streams through sediment inputs and reductions in sensitive invertebrate taxa, but riparian fencing can alleviate these impacts.