Across the GP, grassland managers are diligently working to maintain acceptable levels of shrub cover. Restorations are especially prone to explosions of sumac, dogwood, and a variety of other shrubs. A new study from researchers at Kansas State University synthesized the mechanisms for woody encroachment as they are currently understood.
Download the paper here: Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors.
This paper discussed grassland, shrubland, and woodland transitions in the central grasslands of the U.S. Authors noted that shrubs are highly successful at acquiring and using deep water sources in deep soils. In shallower soils, shrubs must compete directly with the fine root systems of grassland plants and may not be as successful. These differences in how plants acquire water can help us understand shrub transitions and fire effects.
The authors noted the importance of fire return intervals for maintaining grassland and the difficulty of returning to the grassland state once shrubland and woodland thresholds have been crossed. They found that 2 year fire return intervals are likely to maintain grasslands successfully, while 3 year intervals are less predictable. Precipitation, fire intensity, and a number of factors can also influence the rate of transition to shrubland or woodland. Previous work has described a transition from grassland to juniper woodland in about 40 years without fire, but the authors suggest a much quicker transition to the woodland state is possible. Grazing may moderate longer fire return intervals, but much more needs to be learned about the mechanisms and relationships of grazing to fire and grassland stability.
Ratajczak, Z., J. B. Nippert, J. M. Briggs and J. M. Blair. 2014. Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors in the Central Great Plains of North America. Journal of Ecology 2014, 102, 1374–1385 doi: 10.1111/1365-2745.12311