Forest Investment Account (FIA) - Forest Science Program
FIA Project Y081114

    Effects of wildfire severity and harvesting on natural regeneration potential of Douglas-fir in the dry Interior Douglas-fir forests
 
Project lead: Simard, Suzanne (University of British Columbia)
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
Rationale: After the wildfires in interior BC in 2003, the need for research on forest recovery and regeneration after fire has become more apparent. The McLure fire affected 26,420 hectares of mature interior Douglas-fir forests just south of Barriere, BC (Ministry of Forests, 2003). In the past, fire was the dominant disturbance in Douglas-fir forests, but it is unclear what level of fire severity provides the optimal conditions for regeneration. A major aim of this project is to provide information to forest mangers on designing silvicultural systems that emulate natural disturbances, and also for managing natural disturbances, in order to promote successful regeneration. BC forests are commonly characterized by a mixed fire regime, which includes areas of high severity fire resulting in total mortality of overstory vegetation to areas of low severity fire causing little overstory mortality, thereby creating residual stands of variable complexity and regeneration potential. Forest managers are attempting to emulate these natural disturbances using partial retention cuts and site preparation methods, so it is important to understand how managed and natural disturbances affect resource availability and soil processes (e.g., mycorrhization for nutrient and water uptake) important to natural regeneration). Related research work: The proposed project is a continuation of a large-scale experiment examining Douglas-fir natural regeneration potential after the McLure fire. The project has been funded for three years by an NSERC Special Research Opportunities grant to Drs. M.D. Jones (PI) from May 1, 2004, to May 1, 2007; this NSERC funding allowed the establishment of the experiment, three years of seedling and environment monitoring in the field, and several complementary laboratory studies. It provided stipend and research support for Simard’s PhD student, Jason Barker, complete this work. The three years of funding will cease May 1, 2007, one year prior to completion of the primary research. Hence, this proposal requests one year funding to support PhD candidate, Jason Barker, to complete his experiments, write his thesis, publish the results in leading forest science journals, and extend the results to foresters and scientists at local, provincial and national levels. This project is also related to a CFS Mountain Pine Beetle Initiative project lead by Dr. Keith Egger at UNBC entitled “Assessment of post-beetle impacts on natural regeneration of lodgepole pine”. Objectives: This project is examining the effects of clearcutting and fire severity on the forest canopy and soils, and their effects on the survival, growth, and mycorrhizal status of regenerating Douglas-fir seedlings. Mycorrhizal colonization links together a number of changes, such as alterations in nutrient cycling, which can occur in soil ecosystems after a disturbance because of their important role in obtaining soil resources. The specific hypotheses being tested are: 1. Growth and survival of natural Douglas-fir regeneration is enhanced with increasing disturbance severity and decreasing residual stand complexity because of greater light, nutrient and water availability; 2. High severity burns are more favorable than clearcuts for survival and growth of natural Douglas-fir regeneration because of greater soil nutrient and water availability; 3. High severity disturbances reduce mycorrhizal inoculum and colonization but do not affect seedling growth; 4. Low severity disturbances hinder natural regeneration potential of Douglas-fir. Methodology: To meet objectives 1-4, we compared five treatments representing different levels of wildfire and forest harvest severity: high severity fire, low severity fire, clearcut with no site preparation, clearcut with screefing, and undisturbed forest. In May 2004, four replicate sites of each treatment were sown with 1000 Douglas-fir seeds each. From May 2004 to Sept. 2006, seedlings were monitored for germination, mycorrhizal colonization, growth, survival, physiology, and foliar nutrients. Soil characteristics that can influence tree growth, such as nitrogen and phosphorus availability, were also measured. Mycorrhizal fungi were identified using morphological and molecular characteristics. Stable isotopes were used to evaluate seedling physiology and nutrient availability. Additionally, two lab experiments will be initiated in Sept 2006 to determine a) the effect of timing of mycorrhizal colonization on regeneration potential and N uptake; and b) the effect of increasing N levels on B nutrition, which can be an important limitation to regeneration in these forests. Delayed or reduced mycorrhization caused by destruction of inoculum by severe disturbance can lead to regeneration failure. At the same time, wildfire can increase short-term N availability, but increased N can also stimulate B deficiencies in interior BC. Both N and B levels affect root development and hence seedling productivity. To test the effects of delayed mycorrhizal inoculation, seedlings in a growth chamber will be subjected to two inoculation times (12, 16 wks) using native mycorrhizal species and compared against a non-inoculated control. N uptake potential will be assessed using 15N labeled fertilizer. To test the effect of N-induced B deficiencies, Douglas-fir seedlings will be grown in field soil for 20 wks in a greenhouse and subject to 3 fully crossed levels of B and N. Seedling growth, foliar nutrients, and mycorrhizal colonization will be measured. Using the funding proposed here, these experiments will be completed and the data analyzed in 2007/08. Preliminary findings: Early field results indicate that high severity fires and clearcuts (with or without screefing) are favorable environments for regeneration, but over the longer term, survival in the clearcuts has been greater. Colonization and diversity of mycorrhizae in the high severity burns has remained low, probably because inoculation from residual trees and forest floor has been dramatically reduced. This suggests reduced mycorrhization by fire does not reduce growth but may cause greater mortality of poor performers. Our preliminary results suggest that high severity fires may be at risk for future regeneration problems, and that benefits from forest floor and residual tree complexity can be incorporated into partial retention harvest and site preparation designs to create favorable regeneration environments.
Contact: Simard, Suzanne, (604) 822-1955, suzanne.simard@ubc.ca

    Deliverables:

Executive summary (20Kb)

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Updated August 16, 2010 

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