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Tree Size and Species Influence Snag Retention Following Severe Wildfire In Extending forest restoration to post-fire management: opportunities and challenges Dave W. Peterson USDA Forest Service Pacific Northwest Research Station Wenatchee, WA [email protected] Most of the discussion about dry forest restoration goes like… Decades of fire exclusion and forest management have changed forest structure, fuels, and fire We need widespread forest restoration to make forests more resilient to fire and other disturbances Thinning and prescribed fire are the primary tools Hard to treat and maintain enough dry forests Forest restoration objectives Create forest landscapes in which fire can occur without devastating consequences (Reinhardt et al. 2008) – Create and maintain fuel beds that support wildfires consistent with natural fire regime – Manage fire intensity and severity (impacts), not frequency, size, or ease of suppression Restore diverse landscapes that are resistant and resilient to current and future stressors (Hessburg et al. (2016) Principles for restoring fire- resistant (resilient) forests Reduce surface fuels Increase height to live crown Decrease crown density Keep big trees of Source: Agee and Skinner, 2005 fire-resistant species But what happens when bad things happen to good forests… Large wildfires don’t always wait for restoration treatments to be completed And sometime weather trumps restoration! We end up with lots of dead trees, burned soils, altered wildlife habitat, and unused planning documents What do we do now? Declare victory and go home. – Fire has reintroduced itself to the ecosystem. – Repair fire suppression damage and walk away. – Let Nature take care of things. Accept defeat and move on to greener forests. – Fire destroyed the forest we wanted to save. – Do emergency post-fire rehabilitation work. – Focus on restoring and protecting the remaining green forests. Start planning for the next fire. How much restoration work is needed/possible after wildfires? Does fire restore diverse landscapes that are resistant and resilient to current and future stressors Wildfires can increase or reduce landscape diversity Large fires also create a wide range of post-fire forest & fuel conditions Fire Environment Fire environmental Topography, weather, triangle and fuels combine to influence fire behavior These elements vary in space and time Fuels are the most easily managed, so are often a focus area in forest restoration Fire Why not after wildfire? What happens to all those dead trees after stand-replacing fire? Post-fire snag dynamics study How long do snags persist after wildfire? How is snag decay linked to wildlife usage and fuel deposition? Surveyed snags and fuels on 159 plots within 55 wildfires in eastern Oregon and Washington – Fires burned 1970-2007 – Survey 1-39 years after fire – Ponderosa pine/Douglas-fir – Expected fire return < 40 yr Changes in snag condition over time (standing/fallen, whole/broken) Most snags break off or fall 5-15 years after fire Ponderosa pines fall faster than Douglas- firs or true firs Small diameter snags fall faster than large diameter snags Fall rates appear to taper off after snags develop broken tops Changes in snag decay class with increasing time since fire Most branches and tops fall in first 10-15 years Soft snags start to develop 10-20 years after fire; dominate by 30 years after fire Changes in log decay classes Downed logs become soft logs fairly quickly (10- 15 years) Logs are coming from ponderosa pines and smaller trees When are snags being used by cavity-nesters? Only one-third of sites visited had any standing cavity snags Most cavities were found 10-20 years after fire Most were in medium to large diameter snags (30-60 cm dbh) Surface woody fuels As snags break and fall, surface woody fuels increase Average fuel loads increase for 15-20 years after fire, and then stabilize or decline Rotten large fuels increase for 40 years or more Fuels deposited are proportional to basal area killed (restoration effect!) Can post-fire logging can be used to reduce future woody fuel loads? Post-fire logging does significantly alter surface fuels through time Initial pulse of higher fuels on logged sites Extended period of reduced woody fuels Biggest difference is in the large fuel classes Rotten large fuels diverge after 20 years (reburn window opens) How much does it reduce fire severity? Could post-fire logging be a useful tool in forest restoration? Post-fire logging reduces woody fuels – Are the reductions big enough to modify fire behavior? Facilitates future prescribed fire use in regenerating forest – Broader range of potential burn prescriptions Facilitate regeneration with species resilient to fire and climate Questions about ecological impacts and when/where to apply treatment What are the alternatives? Leave burned forests alone and wait for the next fire to clean up the fuels (along with the forest and fuels) Use repeated Rx fires to consume fuel as it is deposited and rots, without killing too many young trees How about also doing restoration in young regenerating forests? Modify future fire behavior on landscape, forest response to climate change Regeneration objective is to promote early seral species resilient to fire and climate Use prescribed fire to modify surface and canopy fuels, and favor fire resistant species Have to keep costs low Find the right timing Modified principles for restoration in forests after stand-replacing fire Mature forests Regenerating forests – Reduce surface fuels – Reduce surface fuels – Increase height to – Increase height to live crown live crown – Reduce crown density – Reduce crown density – Keep large trees of – Promote development resistant species of large trees of resistant species Adapted from Agee and Skinner, 2005. Forest Ecology and Management Preston Creek Prescribed Fire Study Entiat River Basin, north-central Washington Dry forests – ponderosa pine, Douglas-fir, and grand fir History of stand-replacing fires in Entiat Basin – Wolverine (2015) – ~65,000 acres – Duncan (2014) – ~ 40,000 acres – Tyee Fire (1994) – 95,000 acres – Dinkelman Fire (1988) – 51,000 acres – Entiat Fire (1970) – 61,000 acres Preston-Fox Management Area Management area is within a 34,000 acre contiguous block of the 1970 Entiat fire. Contains the Entiat Experimental Forest Structurally and compositionally homogeneous stands Window for effective thinning still open, but not for long Landscape patterns driven mostly by geology/soils, with few relict forest stands Spatial variability in fire effects Established 264 Fire heterogeneity monitoring plots within prescribed fire perimeter. Assessed percentage of surface area burned Complete (118) Grouped plots by area burned Partial (72) None (74) Burn variability related to local surface fuels Changes in tree size distributions Prescribed fire killed Partial fire (5-95%) 100 mostly smaller trees Alive after fire 80 Almost dead (less than 4” dbh) Dead after fire 60 Resulting distribution is 40 unimodal with mean of Tree density (stems/acre) 20 4-5” dbh 0 Fire is basically Complete fire (100%) thinning from below 100 80 and favoring large 60 trees over small trees. 40 Note higher mortality Tree density (stems/acre) 20 in larger size classes on 0 0 1 2 3 4 5 6 7 8 9 10 11 12 complete burn plots Tree size class (inches) Changes in height to live crown Height to live crown increased by an 16 14 average of over 5 Prefire 2004 12 feet on partially Postfire 2005 burned plots. 10 8 Height to live crown 6 increased by an 4 average of over 8 2 Height to Live Crown (ft) Height to Live Crown feet on completely 0 burned plots No Fire Partial Complete Fire Class Back to basics… How did we do? Reduce surface fuels – Yes. Additional fires used to further reduce fuels. Increase canopy base height (live crown) – Yes, in many places. Decrease crown density – Yes, but not enough Promote development of large trees – Yes, so far. Thank you. Questions? .
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