Results

At the Rio Quebrada Grande site, the largest stones had the highest percent coverage with moss (95-98%). (see Figure 1) Respectively, at the Rio Negro site the largest patches had the highest percentage of biomass (70%). (see Figure 2) The t-test showed that the perceived differences were statistically significant, i.e. P=0.01.

Figure1. Rio Q.Grande.Bryophyte richness vs. size of substrate.

Figure 2. Rio Negro. Bryophyte richness vs. size of patch.

The river velocity at the Rio Negro site was significanly higher (0.84 m/s) than at the Rio Grande site (1.27 m/s). (see Figure 3) The t-test showed that this difference may not be statistically significant, i.e. P=0.057 which is slightly more than the required 0.05.

Figure 3. Bryophyte richness as a function of river velocity. Both sites are shown.

The streams sites varied in the degree to which vegetation shaded the channel. At the Rio Grande site the canopy cover was significantly denser (86 %) than at Rio Negro where it is relatively open (40.5%). (see Figure 4) The t-test for this factor showed that these differences are statistically significant, i.e. P=0.008.

Figure 4. Bryophyte richness as a function of canopy cover. Both sites are shown.