Developing an Understanding of Vegetation Change and Carbon Budjets in Semi-Arid Environments
Objective 1: Compare and contrast ecosystem structure and function over both grass-to-creosotebush and grass-topiñon-juniper transitions.
By expanding beyond a one site, one view, perspective this study aims to address both key vegetation transitions occurring in the Sevilleta LTER, within a common methodological framework. A key conclusion from previous studies over both transitions is that they result in an increased heterogeneity of resources, reinforced by a series of feedbacks, particularly, increased bare inter-plant areas and an increased vulnerability to runoff and erosion. However, the different vegetation types present over the Sevilleta ecotones can result in different ecohydrological interactions, as a result of their physiological characteristics and physical scale. This study will characterize the changes in both vegetation and soil properties for both the dominant transitions, followed by monitoring of the temporal and spatial variation in fluxes as a result of monsoon rainfall events.
Objective 2: Use carbon isotope ratios/plant biomarker techniques to develop an understanding of vegetation change and sediment (particularly associated carbon) dynamics in response to rainfall events.
The technique ofusing δ13C signatures of bulk SOM for understanding semi-arid erosion dynamics, carbon dynamics and long-term vegetation change, needs refining due to the complexities of these environments where soils are not in a steady state. This will be addressed by fraction specific analysis of samples. Specifically this will involve the extraction of n-alkane lipid fractions, which have been chosen due to their ease of extraction, resistance to degradation and due to the body of research suggesting C3 woody species and C4 grass species produce distinctive n-alkane signatures (i.e. Zech et al, 2008).