Table S1.

Soil and plant community variables (means ± SE) illustrating differences among harsh, lush, and nonserpentine grassland habitats

Variable	Mean ± SE			F	P
	Harsh serpentine	Lush serpentine	Nonserpentine
Ca/Mg ratio	0.41 ± 0.04	0.37 ± 0.01	2.06 ± 0.08	41.42,129	<0.001
NH4+ (ppm)	1.33 ± 0.07	2.65 ± 0.11	2.74 ± 0.10	80.82,126	<0.001
OM (%)	2.18 ± 0.08	4.07 ± 0.12	3.81 ± 0.13	102.02,129	<0.001
pH	7.21 ± 0.04	7.06 ± 0.03	6.10 ± 0.04	279.72,129	<0.001
Moisture retention capacity (%)	21.32 ± 0.69	32.11 ± 0.60	26.75 ± 0.52	77.312,126	<0.001
Total biomass (g/0.0625 m2)	8.64 ± 1.21	38.32 ± 2.47	38.37 ± 3.59	66.72,63	<0.001
Species richness (number/1 m2)	14.91 ± 0.90	12.50 ± 0.74	9.81 ± 0.88	9.02,64	<0.001
Exotic cover (%)	2.86 ± 1.14	59.26 ± 4.49	91.53 ± 2.70	188.72,64	<0.001
Native cover (%)	73.47 ± 4.82	26.79 ± 5.63	2.87 ± 0.76	62.72,64	<0.001

Differences between the habitats were tested using ANOVA. The soil samples were collected in early April 2010, just before the first treatment application. Plant biomass samples (including live biomass and litter) were collected and species richness and percentage covers of exotic and native species were estimated at the end of May 2010, using only untreated plots. Biomass and NH₄⁺ concentration were square root-transformed, and Ca/Mg ratio and organic matter (OM) content were log-transformed for the analyses. Soil moisture retention capacity was measured under a constant 0.3 ATM pressure potential. The analyses were performed at A&L Western Laboratory (Ca/Mg ratio, OM, and pH) and at the University of California, Davis Analytical Laboratory (NH₄⁺ and moisture-retention capacity).