Table 1. Environmental and soil characteristics of the upper and lower sites on Rattlesnake Mountain, Washington, USA.

Environmental data include long-term mean annual temperature (MAT) and precipitation (MAP) based on both older [63] and recent (unpublished weather station data) sources; this climatic regime has been broadly stable for the last 3000–5000 years [64]. Soil values are 0–5 cm means±s.d. of the ‘native’ cores sampled from upper and lower sites (N = 24). Bulk density, carbon and nitrogen, particulate organic matter (POM) C, and POM N all differed significantly (P<0.001) between the lower and upper sites. Soil cores were taken from areas of the two sites dominated by Poa spp.

	Upper site	Lower site
Altitude (m a.s.l.)	844	310
MAT (°C)	23.5	28.5
MAP (mm)	272	224
Plant species	Poa secunda, Pseudoroegneria spicata	P. spicata, P. secunda, Artmesia tripartita
Soils	Silt loams (coarse-silty, mixed, mesic Xerollic Camborthids)
Bulk density (g cm-3)	1.42±0.07	1.51±0.08
Carbon (0–5 cm, %)	2.04±0.81	0.95±0.32
Nitrogen (0–5 cm, %)	0.19±0.08	0.09±0.03
POM C (%)	0.27±0.09	0.07±0.03
POM N (%)	3.00±1.02	0.89±0.35
C:N (0–5 cm)	10.5	10.1