01717nas a2200145   4500008004100000245008900041210006900130300001300199490000700212520121200219100001801431700002301449700002401472856007501496       2012                        eng d00aWoody encroachment decreases diversity across North American grasslands and savannas0 aWoody encroachment decreases diversity across North American gra  a697 -7030 v933 a<p>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.</p>1 aRatajczak, Z.1 aNippert, Jesse, B.1 aCollins, Scott., L.  uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/11-1199.1