Woody Encroachment of a Riparian Corridor in a Tallgrass Prairie: Dendrochronological Evidence from Kansas

The density of forested cover in grassland regions has been increasing globally during the past several decades. Although there is some evidence to suggest that climate change is playing a role in this woody encroachment, there is a lack of consensus on both the causes and consequences of this land cover change. To examine the role of climate on tree establishment and growth at a very large spatial scale, we used dendrochronological techniques coupled with spatial analyses of the effects of climate drivers on biotic responses such as establishment and growth. We sampled ring widths of selected large trees and collected establishment dates of trees for four deciduous tree species in the riparian zone of a 119 ha experimental watershed at the Kansas Konza Prairie Biological Station, near the current prairie–forest boundary of North America. Annual tree-ring width is positively correlated with the Palmer Drought Severity Index and growing season precipitation, although winter climate variables also affect deciduous tree growth. A pulse in tree establishment occurred shortly after a shift in management in the 1980s, including bison grazing and biennial burning treatments. Spatial patterns of woody vegetation expansion in this watershed indicate that recruitment is increasing at higher elevations in the riparian corridor.