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Elevated nitrogen effects on B romus tectorum dominance and native plant diversity in an arid montane ecosystem
Author(s) -
Concilio Amy L.,
Loik Michael E.
Publication year - 2013
Publication title -
applied vegetation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.096
H-Index - 64
eISSN - 1654-109X
pISSN - 1402-2001
DOI - 10.1111/avsc.12029
Subject(s) - bromus tectorum , dominance (genetics) , species richness , ecology , ecosystem , species evenness , biology , forb , grassland , perennial plant , biochemistry , gene
Questions Dominance of the widespread fire‐altering invasive grass, B romus tectorum, is markedly reduced at upper elevations in the G reat B asin D esert. Here, we evaluated whether increased anthropogenic nitrogen ( N ) deposition would have an effect on species composition and ecosystem invasibility by B . tectorum at high elevations, and whether B . tectorum cover was associated with decreased native plant diversity. Location Sagebrush steppe of the eastern S ierra N evada, CA , US , at the western edge of the G reat B asin D esert. Methods We set up 54 paired plots, half of which were exposed to elevated N deposition (50 kg·ha −1 ·yr −1 at the time of snowmelt for 4 yr) and half acted as controls, in areas differing in disturbance history (grazed, burned and grazed–burned). We monitored species composition each summer from 2008 to 2011 and then compared species richness, S hannon's diversity ( H '), S impson's dominance ( D '), S impson's evenness ( E 1/D ), B . tectorum dominance and community similarity (with ANOSIM and SIMPER analyses) by N treatment and disturbance history. Results Species composition differed by disturbance history in all years ( ANOSIM , P < 0.05), and the grazed–burned plots consistently had the highest levels of B . tectorum dominance ( P ≤ 0.0003) and cover ( P ≤ 0.0001). B romus tectorum cover was inversely related to native forb species richness ( r = −0.44, P < 0.0001), H '( r s = −0.73, P < 0.0001), ‐ln( D ') ( r s = −0.75, P < 0.0001) and E 1/D '( r s = −0.49, P < 0.0001). We found no evidence that increased N deposition would affect native plant diversity after 4 yr in this arid montane ecosystem, but the possibility of longer‐term effects cannot be eliminated. Conclusions Results suggest that high‐elevation plant communities are already experiencing invasion impacts even though changes to the fire cycle have not yet occurred. In the most disturbed areas, B . tectorum cover is approaching the threshold for increased fire risk, which could result in more severe impacts at high elevations.