Hastings Natural History Reservation

14 May, 02 AM - 18 May, 05 AM

Among ecosystems invaded by exotic species, California?s 17.5 million acres of grasslands and savannas are unique in their nearly universal ecological conversion from perennial to annual-dominated communities. Many factors contribute to invasions in a particular location; the most significant ofteninclude disturbances leading to increased nutrient levels or alterations in water availability. These disturbances are frequently attributed to anthropogenic influences such as fertilization, nitrogen deposition, overgrazing and eutrophication. Once dominated by an exotic, however, natural resource heterogeneity in the landscape may contribute to persistence of non-native species.Understanding the distribution and effect of heterogeneity is central to a clear mechanistic understandingof the impact of an experimental treatment or land management choice such as grazing. Woody savanna species are one natural source of heterogeneity in grassland ecosystems and while the impact of some tree species on soil and understory composition has been studied, variation in the impact of different types of trees within multiple savanna settings has not been studied. Additionally, previous studies have not included sites with different rainfall and climate patterns, and can not comment on larger, regional patterns. My objective in this project is to examine the effects of oak canopies on understory vegetation across a regional precipitation and climate gradient. My previous work at Sedgwick Reserve has explored the effects of these important rangeland trees at a single location, but the generality of the patterns for other areas in the state remains unknown. In particular I am interested in the observed patterns of increased species diversity in open grassland relative to below-canopy habitats and the higher species richness in the near vicinity of evergreen oak species. To further explore these patterns, I will be visiting several different reserves this spring and early summer. The selected reserves span southern and northern California and annually differ in precipitation as well as temperature. Previous authors have suggested that the effect ofan oak tree on the productivity of the herbaceous layer may vary according to annual rainfall amounts, or with the abundance of fine oak roots in the upper layers of soil. To examine the support for these patterns, I will investigate the following questions (1) How do oaks impact surrounding vegetation and soil properties in sites with different mean annual precipitation? (2) Do these impacts differ between evergreen and deciduous oak species? and (3) Is the effect of oaks on species diversity of the understory related to the presence of fine oak roots in the upper layers of soil? Primarily I will only be surveying understory vegetation beneath evergreen and deciduous species of oaks in savanna settings. In addition to recording species cover, light and soil moisture during these surveys I would also like to take a series of soil cores at each tree along a transect from full canopy cover to open grassland. The soil cores will be taken of only the upper 15 cm of soil, and I will bring these back to Santa Barbara with me for analysis on fine root distributions and nutrient content. There will be no other manipulations or disturbance associated with this project. My primary purpose is observational.

Visit #21292 @Hastings Natural History Reservation

Approved

Under Project # 21541 | Research

Islands of invasion - regional patterns in the effect of oak trees on California grasslands

faculty - University of California, Santa Barbara

Reservation Members(s)

Karen Stahlheber May 14 - 18, 2010 (5 days)

Reserve Resources(s) | Create Invoice

Bunk House Cottage 1 May 14 - 18, 2010