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PB

Philip Burton

University of Northern BC
The Nisga'a Lava Beds of the Nass Valley resulted from the eruption of the Tseax Volcano approximately 250 years ago. Important to the history and culture of the Nisga'a First Nation, the lava beds are one of the most recent and most accessible volcanic surfaces in Canada, but have been surprisingly little studied. We set out to quantitatively describe the dominant vegetation found on the 25 km2 lava plain, and to update floristic inventories conducted in the 1970s. While the vascular flora showed few surprises, 125 specimens of mosses and lichens were forwarded for expert identification. We hoped to identify cohorts of trees associated with the occasional years in which weather was suitable for establishment in is harsh environment, and thereby extrapolate their likely frequency in the future. In sampling 66 random locations, however, it became apparent that substrate differences, forest edge effects, and episodes of favourable weather are not as impo  rtant as recent disturbance history. Many areas dominated by mature tree cover have a history of flooding and sediment deposition. Large expanses still dominated by Stereocaulon lichen or Racomitrium moss have experienced multiple wildfires that set succession back to bare rock. In other locations, more than 100 different species of herbs, shrubs and trees are established in lava cracks or hollows and are gradually extending their influence outwards. The future vegetation of the lava beds may be more directly influenced by climatic effects on the disturbance regime than by direct suitability for the growth of different species.