Publication Date
1993
Description
It is widely recognised that many grassland communities are stable,though the mechanisms that maintain this stability are only poorly understood. We identify and discuss processes that contribute to stability at three levels of grassland organisation: 1) the individual plant, 2) the population, and 3) the community. At the level of the individual plant, the classical theory of apical dominance does not consistently explain the response of tiller recruitment to defoliation. At the level of the population, conclusions regarding tiller recruitment in response to radiation quality in the competitive neighbourhood and the contribution of dormant axillary buds to annual tiller recruitment are both inconclusive and require further study. Competition, as it influences resource availability at the plant, population and community levels of grassland organisation, appears to exert the greatest regulation on tiller populations. However, the relative contribution of competitive interactions at these various levels has yet to be established and it is uncertain whether competition regulates tiller recruitment by directly affecting axillary bud availability and activity or whether regulation occurs as one component of an overall affect on plant growth. At the community level, grazing frequently modifies the balance of competitive interactions in favour of the smaller-statured, early and mld-seral species that effectively avoid grazing by the possession of decumbent canopy architectures. Consequently, these species partially or totally replace the larger-statured, competitive, late-seral species within the community. We suggest that these compositional shifts in response 10 grazing are best understood through the underlying population processes. Late-seral dominants frequently exhibit a decrease in basal area and tiller density per plant and per unit area while the more leniently grazed early or mid-seral species exhibit an increase in these population parameters. This shift in population structure enables the more grazing-resistant early and midseral species to acquire a greater proportion of the available resources and eventually dominate the community as long as intensive grazing continues. Greater insight into the demographic changes that accompany community degradation will provide a more predictive model for the assessment of ecological disturbances and a potentially effective procedure for monitoring grassland responses to disturbance.
Citation
Briske, David D. and Silvertown, Jonathan W., "Plant Demography and Grassland Community Balance: The Contribution of Population Regulation Mechanisms" (2024). IGC Proceedings (1993-2023). 42.
https://uknowledge.uky.edu/igc/1993/session11/42
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Plant Demography and Grassland Community Balance: The Contribution of Population Regulation Mechanisms
It is widely recognised that many grassland communities are stable,though the mechanisms that maintain this stability are only poorly understood. We identify and discuss processes that contribute to stability at three levels of grassland organisation: 1) the individual plant, 2) the population, and 3) the community. At the level of the individual plant, the classical theory of apical dominance does not consistently explain the response of tiller recruitment to defoliation. At the level of the population, conclusions regarding tiller recruitment in response to radiation quality in the competitive neighbourhood and the contribution of dormant axillary buds to annual tiller recruitment are both inconclusive and require further study. Competition, as it influences resource availability at the plant, population and community levels of grassland organisation, appears to exert the greatest regulation on tiller populations. However, the relative contribution of competitive interactions at these various levels has yet to be established and it is uncertain whether competition regulates tiller recruitment by directly affecting axillary bud availability and activity or whether regulation occurs as one component of an overall affect on plant growth. At the community level, grazing frequently modifies the balance of competitive interactions in favour of the smaller-statured, early and mld-seral species that effectively avoid grazing by the possession of decumbent canopy architectures. Consequently, these species partially or totally replace the larger-statured, competitive, late-seral species within the community. We suggest that these compositional shifts in response 10 grazing are best understood through the underlying population processes. Late-seral dominants frequently exhibit a decrease in basal area and tiller density per plant and per unit area while the more leniently grazed early or mid-seral species exhibit an increase in these population parameters. This shift in population structure enables the more grazing-resistant early and midseral species to acquire a greater proportion of the available resources and eventually dominate the community as long as intensive grazing continues. Greater insight into the demographic changes that accompany community degradation will provide a more predictive model for the assessment of ecological disturbances and a potentially effective procedure for monitoring grassland responses to disturbance.
