If you need an accessible version of this item please contact JSTOR User Support

Ecological Importance of Snowbrush Ceanothus Velutinus in the Oregon Cascades

J. Zavitkovski and M. Newton
Ecology
Vol. 49, No. 6 (Nov., 1968), pp. 1134-1145
DOI: 10.2307/1934497
Stable URL: http://www.jstor.org/stable/1934497
Page Count: 12
  • Download PDF
  • Cite this Item

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support
Ecological Importance of Snowbrush Ceanothus Velutinus in the Oregon Cascades
Preview not available

Abstract

Twelve stands of snowbrush were selected for a biomass study to estimate nitrogen fixation under field conditions west of the summit of the Oregon Cascades. Total nitrogen in the upper 2 ft of soil was higher under snowbrush than in the open, but the difference may have been caused by loss of nitrogen from open areas rather than by nitrogen fixation. Total nitrogen in the upper 15 cm of soil under snowbrush did not differ from that found under nonfixing shrub species. Various shrub species may increase the total soil nitrogen under their canopies, however, if only by accumulation from sites that lack vegetation. More nitrogen may be tied up in the biomass of mature snowbrush stands than in stands of other shrubs. The difference could be explained by nitrogen fixation, which may range from zero to about 20 kg/ha per year under conditions of this study. Nodulated snowbrush seedlings produced 2.5 times the dry weight that non-nodulated seedlings produced in a nitrogen deficient soil. Sixty-one per cent of the nitrogen in nodulated greenhouse seedlings was fixed. Such fixation rates may be reached on infertile soils in the field, but they seem unlikely on soils of medium or better fertility. This point seems to be substantiated by delay in nodulation of snowbrush in soils with increased levels of organic matter. Bioassay tests using Douglas fir seeds and hemlock seedlings showed that snowbrush did not add to the soil any significant amount of nitrogen by nitrogen fixation. The species contributes to the formation of a new organic layer, however, through large amounts of nitrogen-rich litter.

Page Thumbnails

  • Thumbnail: Page 
1134
    1134
  • Thumbnail: Page 
1135
    1135
  • Thumbnail: Page 
1136
    1136
  • Thumbnail: Page 
1137
    1137
  • Thumbnail: Page 
1138
    1138
  • Thumbnail: Page 
1139
    1139
  • Thumbnail: Page 
1140
    1140
  • Thumbnail: Page 
1141
    1141
  • Thumbnail: Page 
1142
    1142
  • Thumbnail: Page 
1143
    1143
  • Thumbnail: Page 
1144
    1144
  • Thumbnail: Page 
1145
    1145