Discussion

Generally, bryophytes are more abundant on large rocks than on small. This pattern is found around the world and is thought to be driven by the facts that large rocks are less likely to be turned over or buried and more likely to project from the water's surface thus creating habitat for bryophytes. In addition, small and medium sized rocks tend to have higher ranges of disturbances like river fluctuations. My results confirm the trend that larger rocks have higher total percentage cover with bryophytes. The best explanation for the reason why there is a higher total percentage cover in larger patches is the texture of the rock in the Rio Negro site. It was obvious that moss tended to grow in the crevices of the rock than on smooth surfaces. This may be because water from rainfall and splash from the stream stays longer in the crevices than on the smooth surface of the rock where it runs off back into the river.

Hydraulic drag forces have an effect on bryophytes growth and distribution. Drag forces caused by river velocity tend to dislodge bryophytes from the substrate. The results of this study show that river velocity may have an effect on bryophytes growth and distribution. The site at Rio Negro had a significantly higher river velocity and lower total percentage of bryophytes than the Rio Quebrada Grande site.

There are differences in light among the sites of the two streams caused by varying canopy cover. Light conditions are an important factor for growth of bryophyte communities. More light is correlated with less growth of bryophytes. The results of this study confirm this trend. The site at Rio Negro was considerably dryer because the canopy cover was relatively open. There were also less bryophytes to be found at this site. The Rio Q. Grande site, in comparison, was shadier and had a higher total percentage cover of bryophytes.