Grazing intensity and ecosystem processes in a northern mixed-grass prairie, USA
Biondini ME and Patton BD. 1998. Grazing intensity and ecosystem processes in a northern mixed-grass prairie, USA. Ecological Applications. 8(2):469-479
The objective of this study was to evaluate for an 8-yr period the ecosystem-level impacts of no grazing vs. sustained moderate and heavy cattle grazing in terms of: (1) plant species basal cover, density, and composition; (2) aboveground net primary production (ANPP), N content of ANPP (ANPP-N), belowground net primary production (BNPP), and N content of BNPP (BNPP-N); (3) litter and root decomposition and N loss; and (4) soil C, total soil N, and net in situ soil N mineralization. Moderate and heavy grazing treatments were designed to achieve an end-of-the-grazing-season residual vegetation of 50respectively, of the long-term average ANPP of comparable ungrazed sites. The main factor affecting the vegetation response was the increase in precipitation after the drought of 1988; few differences were due to grazing intensity. The total absolute basal cover of grasses increased steadily in all treatments, from an average of 4and diversity increased from 51 plants/m2 and 14 species in 1988 to 412 plants/m2 and 36 species in 1995. Grazing, however, increased the relative composition of Poa pratensis and Achillea millefolium, but reduced the relative composition of Bouteloua gracilis and Aster ericoides. ANPP and ANPP-N were correlated with rainfall, but not with grazing intensity. Heavy grazing led to declines in standing dead biomass, litter, peak root biomass and biomass-N, root N concentrations, and in situ net soil N mineralization. There was an increase in root decomposition and N loss with grazing. From this study, we reached the following conclusions about the northern mixed-grass prairie: (1) climatic variations, in particular droughts, control major trends in plant species composition and production, with grazing playing a secondary role; (2) heavy grazing leads to declines in standing dead biomass and biomass-N, litter biomass and biomass-N, peak root biomass and biomass-N, and in situ net soil N mineralization, which may have a significant long-term impact on range condition; and (3) grazing pressures that lead to a removal of 50maintenance of range condition.
- Type
- Journal Article
- Authors
- Biondini, Mario; Patton, Bob
- Units
- SODN
- Keywords
- climatic vatiation, grazing pressure, litter and root decomosition, net primary production, net soil N mineralization, nitrogen loss, North Dakota, northern mixed-grass prairie, soil C and N, species compostition