^3 INTRODUCED GRASSES 



I 1 NATIVES 



KS COLONIZERS 



NO NO NO 



FERTILIZER FERTILIZER FERTILIZER FERTILIZER FERTILIZER FERTILIZER 



NATIVES ONLY 



NATIVES + LOW GRASS NATIVES + HIGH GRASS 



Figure 1 — Total density of introduced grasses, 

 natives, and colonizers for 1985 in research 

 plots that were seeded with natives and a zero, 

 low, or high level of introduced grasses and 

 then either fertilized or not fertilized. Values 

 are mean ± S.E., n is variable. 



introduced grasses and native species (both p < 0.001). 

 But there were still no statistical differences attributable 

 to fertilizer. The two seeding treatments that included 

 introduced grasses had higher combined densities of in- 

 troduced grasses and natives than the natives-only treat- 

 ment (p < 0.05). Because of the residual introduced 

 grasses on the study area, there were no differences be- 

 tween native species and introduced grass densities in the 

 natives-only treatment. However, introduced grass densi- 

 ties were higher than those of native species in the high 

 and low grass density treatments (p < 0.05), but not dif- 

 ferent between the latter two treatments (p < 0.05). 



Standing Crop Biomass and Individual 

 Species Responses 



Figure 2 and table 2 detail the highly significant differ- 

 ences in standing crop biomass among species categories 

 (p < 0.01), between fertilizer treatments (p < 0.001), and 

 among years (p < 0.001). Few significant effects were 

 attributable to grass seeding density. In contrast to the 

 density results, introduced grass standing crop biomass 

 increased with each increase in grass seeding density 

 (p < 0.05). Native species showed no differences in stand- 

 ing crop among the three seeding densities and colonizer 

 standing crop decreased with each increase in seeding 

 density (p < 0.05). 



Total standing crop biomass decreased significantly 

 over time (p < 0.001) primarily due to a decline in colo- 

 nizer species productivity from year 1 through year 3. 

 The effects of fertilizer were not consistent among species 

 categories or over time. Introduced grasses, native spe- 

 cies and colonizers had significantly higher standing crop 

 in fertilized than in unfertilized treatments in year 1 

 (p < 0.05). However, by year 3 there were no differences 

 between fertilized and unfertilized treatments for any of 

 the species categories (p < 0.05). For introduced grasses 



5 6 



2 4- 



^3 INTRODUCED GRASSES 



I 1 NATIVES 



Ig^l COLONIZERS 



ill 



=1 Li E5 



NO NO NO 



FERTILIZER FERTILIZER FERTILIZER FERTILIZER FERTILIZER FERTILIZER 



NATIVES ONLY 



NATIVES + LOW GRASS NATIVES + HIGH GRASS 



Figure 2— Dry weight biomass of introduced 

 grasses, natives, and colonizers for 1985, 1986, 

 and 1987 in research plots that were seeded with 

 natives and a zero, low, or high level of introduced 

 grasses and then either fertilized or not fertilized. 

 Values are mean ± S.E., n is variable. 



standing crop decreased between years 1 and 3 in fertil- 

 ized treatments, but increased in unfertilized treatments 

 (p < 0.05). Standing crop of native species did not change 

 over time in fertilized treatments, but increased between 

 years 1 and 3 in unfertilized treatments (p < 0.05). Colo- 

 nizer standing crop decreased significantly over time in 

 both fertilized and unfertilized treatments. 



Table 2 shows that first and third year standing crop 

 biomass of intermediate wheatgrass, smooth brome, and 

 orchardgrass were higher than those of meadow foxtail 

 and Timothy. This may be attributable to differences in 

 the initial densities of residual individuals of these spe- 

 cies. By year 3 standing crop biomass of slender 

 wheatgrass greatly exceeded that of the other native 



4 



