COLLABORATIVE RESEARCH: Woody Encroachment into Desert Grassland: Experimental Asessment of the Critical Seedling Establishment Phase

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The proliferation of shrubs and trees in arid/semiarid grasslands and savannas in recent decades has been widely documented. This worldwide phenomenon threatens the livelihood of rural economies through adverse impacts on livestock production. It is also thought to have had a significant impact on the terrestrial carbon cycle in North and South America, Australia and Africa. The ability of woody plants to encroach into grasslands varies widely among species. Why are some so successful and others not? The study will address this question by determining how woody plants gain their foothold in grasslands during the critical establishment phase. By comparing the survivorship and growth of more and less successful woody encroachers under a range of climatic conditions and disturbances (defoliation), the study will determine a) which root and shoot growth characteristics, of the many that seem plausible, are reliably associated with encroachment potential; and b) how soil properties (such at clay content) may amplify or mitigate environmental factors influencing encroachment potential. The goals are two-fold: (1) to develop guidelines that can be used to identify potential problem species and characterize the conditions under which they are likely to establish so that appropriate management actions can be taken to minimize their invasion into grassland; and (2) to generate information needed to parameterize simulation models that can be used to forecast when and where woody plant invasions are likely to occur, thus giving land managers time to develop and implement appropriate preventative measures. Outreach activities will be an integral part of this work.