Sunday, July 27, 1997 Mark Johnston wrote: >However, the attempt to mimic broad spatial patterns does not address the stand-level functional >impacts of fires. The most important ways in which fire differs from timber harvesting are nutrient >cycling and the ways fire interacts with the plant's regeneration mechanisms. Nutrients are rapidly >made available following fire by means of the ash created by combustion of biomass, which has high >levels of important plant nutrients - this does not happen following timber harvest. Other changes to the >soil environment following fire are also often beneficial to microbes that affect nutrient availability, >especially nitrogen. In addition, fire affects regeneration mechanisms differently than does harvesting, in >particular plants that reproduce from seed buried in the upper soil layers. Finally, community level >characteristics such as species diversity and biomass accumulation are different between sites >experiencing fire and harvesting. I think it is important not to idealize the differences between fire and logging. Hot fires often burn the soil so deep that most of the seeds are killed and the organics are oxidized and lost to the atmosphere. The ash from the fire can provide a "nutrient flush" but they can also be washed away to rivers by rain. Fire can be far more destructive, i.e. result in much slower forest recovery, than logging and fire can also be less destructive if it doesn't crown or burn the soil. It is also important to consider the role of fire in site disturbance, that is in burning off the organic layer and exposing the mineral soil. Many pines, spruce, larch etc. do much better at regeneration on mineral soil than on humus. Logging does not produce this effect unless it is followed by slash burning or by mechanical disturbance such as disc plowing. The seeds don't really care how the mineral soil is exposed, so long as it is. When comparing "natural" disturbance with "human" disturbance it is important to remain extremely objective with regard to structure, function, ecological succession, nutrient cycling, etc. Cheers Patrick Moore, GREENSPIRIT 4068 West 32nd Avenue Vancouver BC, CANADA V6S 1Z6 (604) 221-1990 phone/fax e-mail pmoore@rogers.wave.ca Internet http://www.greenspirit.com May the Forest be With You ---------- From:<johnston@larix.derm.gov.sk.ca> To: Multiple recipients of list FOREST <FOREST@LISTSERV.FUNET.FI> Subject: Do forest practices emulate natural disturbance? Date: 11:17 AM Forest list members: Alan Shanfield wonders about forest practices emulating natural disturbance. I and a number of other forest ecologists are actively investigating this question in a number of studies across Canada, especially with respect to the role of fire in boreal forests. It is important to ask this question at several spatial scales. At the landscape scale, there are many cases across Canada in which patterns created by fire have been analyzed and are being used as a model for harvest planning. Analyses include size class distributions, perimeter to area ratios, the amount of residual remaining inside burned areas, and many other aspects of the spatial distribution of fire-created patches on the landscape. The idea is that eventually the patterns of cuts will come to resemble those created by fire. Perhaps one of the leading examples is the work being done by ALPAC in NE Alberta, but many other companies and government agencies are also adopting this approach. This addresses one aspect of disturbance, that is the patterns created at broad spatial scales, and is important especially to large mammals (e.g., moose) that make use of large areas for home range. . It is essential that ecosystem management recognize the effects of fire at a range of spatial scales and incorporate this knowledge in designing sustainable forest management models. Thoughts, anyone? Cheers. -- Dr. Mark Johnston Forest Ecosystem Science Saskatchewan Environment and Resource Management Box 3003, Prince Albert, SK, Canada S6V 1G6 tel 306.953.2491 fax: 306.953.2360 email: johnston@derm.gov.sk.ca ----------
Mail converted by
MHonArc 1.1.0