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Incorporating Plant Mortality and Recruitment Into Rangeland Management and Assessment
- Tony. Svejcar, Jeremy. James, Stuart. Hardegree, Roger. Sheley
- Rangeland ecology & management 2014 v.67 no.6 pp. 603-613
- range management, risk, grasses, community structure, plant communities, rangelands, seedlings, niches, ecological succession, plant density, vegetation cover, mortality, prediction
- Rangeland management is largely focused on managing vegetation change. Objectives may include managing against change if the desired vegetation is in place, or attempting to create a shift in vegetation if the desired plant community is not present. There is a rich body of research documenting influences of disturbance and management on rangeland vegetation. However, in many cases the information is largely observational and does not identify mechanisms driving change. We propose using the regeneration niche concept to more effectively predict when vegetation change is possible and to suggest successional direction. Simply stated, as plants die and leave gaps in the community, recruitment of new individuals will dictate successional direction. Recruitment requires that propagules are present, that the propagules find safe sites in which to establish, and that the seedlings and young plants are able to compete with existing vegetation and survive. In many rangeland communities, perennial bunchgrasses are a key to stability and invasion resistance. Existing literature shows that most rangeland bunchgrasses have average life spans of 10 yr or less, so periodic recruitment is necessary to maintain communities in which they are a major component. Disturbance can influence plant population dynamics, and we suggest classifying disturbances based on how they influence mortality and recruitment. We also suggest that more emphasis be placed on the concept of critical transitions and less on the degree of disturbance per se. In other words, a small disturbance at the wrong point in community composition (low plant density and high gap size for example) can cause a transition, whereas major disturbance in a high condition community may yield little risk of transition. We suggest that a focus on mortality and recruitment will provide a mechanistic approach for predicting vegetation change and making management decisions. We refer to this approach as recruitment-based management.