Download presentation
Presentation is loading. Please wait.
Published byKerrie Bennett Modified over 9 years ago
1
Fuel treatment effects on forest carbon and wildfire Malcolm North, Sierra Nevada Research Center, mpnorth@ucdavis.edu
2
Wildfires: A Large Source of Emissions (Wiedinmyer and Neff 2007) By one estimate annual forest growth can offset 6-10% of anthropogenic CO 2 But these gains can be offset by emissions in fire-prone forests
3
Premises: In California’s fire-dependent forests, significant C can be released during wildfire The amount of that release increases with fire severity and size General objective: If possible increase C storage, reduce the risk of C loss due to wildfire and in the process minimize C emissions Forests need to be managed for more than just carbon sequestration Fortunately, forest restoration and C management share a common long- term objective: Redirect ecosystem C away from unstable (the growth of numerous, small trees) to stable pools ( the growth of fewer, large-size trees which are fire-resistance [i.e., pines]) The question is how to get there and what are the tradeoffs between different means to that end
4
Conceptual Model of Tradeoffs in Fire-Dependent Forests Effect % * * If Ladder AND Surface fuels are removed What we know: The general shape of these curves What we don’t know: The slope and inflection points How these vary by forest type, productivity, etc. Desired direction ‘Risk’High Low ‘Benefits’ Present Future
5
Total Live Tree Carbon Stocks: 1865: 346 Mg C/ha Current Forest: 249 Mg C/ha Potential for Increasing Forest C Storage Less carbon in modern fire-suppressed forests than active-fire (1865) forests due to loss of large trees The plus is forests have potential to sequester a lot more carbon >
6
Model estimate of wildfire emission is 38 Mg C/ha Bonnicksen estimated 156 Mg C/ha average for CA wildfires (FCEM Report #2) A forest structure (1865) of a low density of large pines has lowest wildfire and prescribed fire emissions
7
Untreated Thinned and Prescribe Burned Fire Direction
10
a) control b) burn only c) understory thin d) understory thin/burn e) overstory thin f) overstory thin/burn > > > > > > 1865 Control Pre-treat Post-treat Pre-treat Post-treat Pre-treat Post-treat Pre-treat Post-treat Pre-treat Post-treat Live tree C and diameter distribution by species before and after 6 treatments Desired: higher C stocks, greater density and a higher % of pine in the large dbh classes
11
1865 Control Burn only Understory thin Understory thin/burn Overstory thin Overstory thin/burn
12
Summary: What we may know and what we clearly don’t know Fuels treatments: Reducing ladder AND surface fuels reduces fire severity. Reducing surface fuels is key to restoring many ecosystem processes Thinning overstory trees (reducing crown bulk density) has a limited effect on reducing fire severity. Simulations (field data is absent) suggest treating 20-30% of a landscape can significantly reduce fire severity and extent Don’t know: How long fuel treatments remain effective How treatments affect residual tree growth (rate of C sequestration) When reducing crown fire risk, how resistant should the forest be made? (i.e. what percentile weather conditions should be targeted? Impacts of climate change?)
13
Carbon Dynamics: Within the limits of current measurements: 60-70% of ecosystem C is above ground, with about 80% of that in live trees. In uncut forests, trees 5-25 cm dbh and 25-50 cm generally will contain about 5% and 15-20%, respectively of total live tree C. Fuels treatments reduce forest C, losses increase exponentially with tree size In most fuels treatments, fossil fuel use is a small % of C loss. C losses from milling waste and prescribed burn vary but are probably in the range of 5-20% of aboveground C Estimates of prescribed fire emissions (15-25 Mg C/ha) are probably within the actual ‘ballpark’ but wildfire emissions (25-45 Mg C/ha), while improving, are still very rough. Estimates of fire CO 2 emissions are hampered by our lack of knowledge about C deposition, rates of atmospheric vs. soil incorporation of dead wood C, ‘real’ soil C loss, etc. Summary: What we may know and what we clearly don’t know
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.