Decreased root heterogeneity and increased root length following grassland invasion

1. Plant invasions can be promoted by environmental heterogeneity, but the opposite effect, the impact of plant invasion on heterogeneity, has received little attention. Grassland invasions might contribute to decreased spatial heterogeneity because invaders tend to be larger than native vegetation. Lowered heterogeneity may contribute to the low diversity of invaded communities, as well as to the persistence of invasive populations. 2. We compared the spatial heterogeneity of roots and resources in uninvaded native grassland and in stands invaded by a relatively large exotic grass (Agropyron cristatum), in four combinations of mowing and nitrogen (N) addition. We focused on roots because they account for the majority of primary production in grasslands. 3. The spatial heterogeneity of root length (m root / m2 rhizotron image) and root production was significantly lower beneath A. cristatum than uninvaded grassland. This result was consistent in all combinations of mowing and N addition...