Woody encroachment decreases diversity across North American grasslands and savannas.
Woody encroachment is a widespread and acute phenomenon affecting grasslands and savannas worldwide. We performed a meta-analysis of 29 studies from 13 different grassland/savanna communities in North America to determine the consequences of woody encroachment on plant species richness. In all 13 communities, species richness declined with woody plant encroachment (average decline = 45%). Species richness declined more in communities with higher precipitation (r2 = 0.81) and where encroachment was associated with a greater change in annual net primary productivity (ANPP; r2 = 0.69). Based on the strong positive correlation between precipitation and ANPP following encroachment (r2 = 0.87), we hypothesize that these relationships occur because water-limited woody plants experience a greater physiological and demographic release as precipitation increases. The observed relationship between species richness and ANPP provides support for the theoretical expectation that a trade-off occurs between richness and productivity in herbaceous communities. We conclude that woody plant encroachment leads to significant declines in species richness in North American grassland/savanna communities.
Division of Biology, Kansas State University, Manhattan, Kansas 66502, USA. zarata@ksu.edu
Zakary
Z
Ratajczak
Jesse B
JB
Nippert
Scott L
SL
Collins
D044822:Biodiversity; D005075:Biological Evolution; D003247:Conservation of Natural Resources; D003710:Demography; D009656:North America; D010944:Plants / Q000145:classification*; D011891:Rain