My dissertation focuses on major concerns of oak-dominated ecosystems. This includes both oak ecosystems in the western US and eastern and Midwestern regions. Specifically, I examine functional connectivity and barriers to gene flow in valley oak populations in California and address threats to forest diversity and resilience such as fire suppression, biotic invasion. In addition, I examine the effect of management and restoration practices on forest communities, especially red and white oaks in the Chicago metropolitan area. The summary of chapters is provided in chapter one.

In the second chapter, I examined whether certain landscape features such as topography and land cover are barriers to gene flow among valley oak populations, a threatened species in California, U.S.A. Using mathematical equations and GIS, I created landscape resistace surfaces. In addition, I measured recent migration rates among populations to examine the direction of gene flow. The results showed elevation played a greater role in inhibiting gene flow whereas there was no relationship between genetic distances and land cover. I concluded that valley oak restoration and protecting the gene donor populations are crucial for the species conservation.

In the third chapter, I studied woody species community change, non-native species richness over time, and biotic homogenization in urban forests in DuPage County, Illinois. Also, I examined the role of fire, clearing, and deer control management on non-native and shadetolerant species. The results showed change in the woody species communities over 35 years but no evidence of homogenization. Non-native species richness increased over time, although it was lower in the managed plots. I found that deer control was associated with lower non-native species abundance and richness in year 2014 and suggest that fire prescription and clearing may be more effective in controlling no-native species when applied regularly.

In the last chapter, I projected the effect of different management scenarios including deer control, fire prescription, fire and deer control coupled, and no management on oak density and dominance over 100 years. I also used simulations to find expected change in structure and composition of oak dominated forest. The results showed that the importance value of red and white oak will not differ under different management scenarios. Nevertheless, importance value of oaks are related to their longevity and not successful recruitment. Thinning and clearing along with prescribed fire and deer control may be more effective in oak restoration in the Midwest. [link to publication]