Driving Factors and Key Contexts for Emergence of Woody Plant Encroachment in Rangeland Ecosystem

The phenomenon of woody plant encroachment (WPE) has been recognized as a global example of the transition and change in vegetation composition, which occurs in grasslands and rangeland ecosystems around the world. Considering the scope of this phenomenon and its impacts on the ecological services and the livelihood of millions of local people, it is necessary to investigate the factors and contexts of the phenomenon emergence. By reviewing related studies of the phenomenon in natural ecosystems, this paper examines and recognizes the factors and effective areas and contexts of its emergence. In general, the summary of the research showed that long-term factors such as climate, soil and human management and short-term factors including climate fluctuations and human activities affect WPE, the dynamics of woody plants and the species composition of each region. In addition, at the local level, changes in the amount and type of precipitation, herbivory, types of fires, and soil characteristics affect the probability of the abundance of woody plants and the WPE phenomenon. This research suggests that future research should examine and identify a combination of traits of woody plants needed to cross all obstacles and stages of WPE, this will help to explain the WPE phenomenon in the past and its prediction in the future.

This study, by reviewing the findings related to this phenomenon in natural ecosystems, investigates and recognizes the effective factors and contexts of emergence, has dealt with this phenomenon.

The causes and factors of the WPE are still something like a puzzle, and several stimuli may interact and intensify the occurrence of this phenomenon. Therefore, understanding the phenomenon of WPE requires considering multiple interactions between stimulating and limiting factors and their changes over time in a specific location. There is uncertainty in quantifying the importance of these stimuli and understanding their interaction with each other. In general, the WPE is affected by long-term (such as climate and carbon dioxide concentration) and short-term (such as fire and herbivory) driving factors that affect the dynamics of woody plant cover and the