Analysis of 15 Years of Data from the California State Parks Prescribed Fire Effects Monitoring Program
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Analysis of 15 Years of Data From the California State Parks Prescribed Fire Effects Monitoring Program R7 SNPLMA Project # 6A07 Prepared by: Alison E. Stanton and Bruce M. Pavlik BMP Ecosciences 3170 Highway 50 Suite #7 South Lake Tahoe, CA 96150 Prepared for: California State Parks, Sierra District P.O. Box 16 Tahoe City, CA 96145 This research was supported through a grant with the USDA Forest Service Pacific Southwest Research Station and using funds provided by the Bureau of Land Management through the sale of public lands as authorized by the Southern Nevada Public Land Management Act. http://www.fs.fed.us/psw/partnerships/tahoescience/ The views in this report are those of the authors and do not necessary reflect those of the USDA Forest Service Pacific Southwest Research Station or the USDI Bureau of Land Management. 1 Table of Contents Key Findings ................................................................................................................................... 3 Introduction ..................................................................................................................................... 5 Methods ........................................................................................................................................... 7 Monitoring Program .................................................................................................................... 7 Site Description ........................................................................................................................... 8 Prescribed fire treatment ............................................................................................................. 8 Vegetation measurements ......................................................................................................... 10 Surface and ground fuel measurements .................................................................................... 11 Plot Selection............................................................................................................................. 11 Data Analysis ............................................................................................................................ 13 Results ........................................................................................................................................... 13 Forest Structure and Composition ............................................................................................. 13 Fuel Loading ............................................................................................................................. 18 Understory Vegetation .............................................................................................................. 23 Discussion ..................................................................................................................................... 29 Monitoring Recommendations ...................................................................................................... 31 State Parks outside of the Lake Tahoe basin ............................................................................. 32 State Parks in the Lake Tahoe basin.......................................................................................... 39 Unburned conditions in four CA State Parks ........................................................................ 43 2010 Re-sample effort ............................................................................................................... 47 References ..................................................................................................................................... 50 2 Key Findings Forest Structure and Composition • Prescribed fire reduced the density of live trees (>2.5 cm DBH) an average of 46% in the year following fire. By ten years, the density was 65% lower. • Significant tree mortality occurred only in pole-size (15-30 cm DBH) and sapling (2.5- 15 cm DBH) sapling size classes. • On average, 73% of tagged trees pre-burn were white fir <30cm DBH. • Reduced tree density after fire did not shift the proportion of white fir, which still accounted for 75% of all trees ten years post-fire. • Average tree size significantly increased by about five cm (QMD) the year after fire. • Snag density increased significantly in the first five years following fire, but returned to pre-fire levels by ten years post-fire. • Average basal area (BA) and seedling density did not change in response to fire. Fuel Accumulation • The pre-treatment surface and ground fuel load was significantly reduced an average 67% by prescribed fire. • With an average rate of accumulation of 0.542 kg/m 2 for all fuel components combined, the surface and ground fuel load would be expected to equal the pre-fire fuel load by 2010. • Prescribed fire significantly reduced fine surface fuels (FWD) and the subsequent rate of accumulation was nearly zero. • Prescribed fire significantly reduced the rotten component of coarse surface fuels (CWD) but did not reduce the sound component which accumulated to nearly three times pre-fire levels within ten years. • The duff layer comprised the largest portion of the total pre-treatment fuel load and showed the largest response to prescribed fire with the greatest reduction in average loads following fire and the greatest accumulate rate in subsequent years. Understory Vegetation Response • Pre-fire understory vegetation was sparsely distributed on the landscape with an average cover of only 16%. • Prescribed fire significantly reduced understory cover by an average of 58% the year following fire, mainly due to a decline in shrub cover. 3 • Understory percent cover recovered to pre-fire levels by ten years post-burn, likely due to a significant increase in the nitrogen fixing shrub whitethorn ( Ceanothus cordulatus ). • Sub-shrub percent cover appears to have been significantly reduced in all years by fire, but forb cover did not show any response. • Species richness did not decline in the year following fire, but was significantly greater five and ten years later, when sample plots had on average three to four more species than before the burn. Monitoring Recommendations Malakoff Diggins SP • Average surface fuel load was moderately reduced by prescribed fire, but overstory stand characteristics and understory vegetation cover did not change, possibly due to very low severity of the 2006 prescribed fire. A new monitoring plan is warranted over additional post-treatment sampling of the existing FMH plots. Plumas-Eureka SP • No prescribed fire has been applied to the FMH plots installed in 2000, but 2010 presents an opportunity to conduct sampling using modified protocols in order to 1) evaluate change in the overstory and fuel loads and 2) develop an effective treatment prescription and 3) inform the scheduling of subsequent treatments. Lake Tahoe Basin State Parks • A limited comparison indicates that unburned forest and fuel conditions in Burton Creek and Emerald Bay SPs may be comparable to Sugar Pine SP, especially if the plot data for the two other parks are combined. • It was not possible to include D.L Bliss SP in the comparison because of insufficient data. If any treatments are planned in the future in D.L. Bliss a new monitoring plan should be developed. • Conduct a re-sampling effort in 2010 as follows: o Streamline sampling protocol and limit data collection to those variables that yield statistically robust results. o Add collection of tree height, live crown base height, and canopy cover to determine current crown fire potential. o Limit re-sampling of treatment plots in 2010 to the 15 FMH plots burned in the 1995-1996 prescribed fires in Sugar Pine Point. o Re-sample 10 control plots in Sugar Pine and 2 control plots in Emerald Bay in 2010. 4 Introduction A significant portion of the Lake Tahoe basin is considered a high-risk environment for severe wildfires (Murphy et al 2006). The elevated threat originates from human land use practices over the last 150 years, beginning with Comstock era logging in the 1860’s and continuing because of effective fire suppression. By the turn of the 20 th century, nearly two-thirds of the lower elevation pine forest was clear-cut (Murphy and Knopp 2000). Recovery of the forest over the last 100 years was irreversibly altered by management focused on fire suppression. Prior to European settlement, frequent, low intensity fires shaped forest structure, composition, and resilience (Martin and Rice 1990). Fire return intervals ranged from 5 to 18 years at the lowest elevations around the lake and from this it is estimated that approximately 850 -3,237 ha (2,100 to 8,000 ac) burned each year in the Tahoe Basin because of human and natural ignitions, compared to fewer than 200 ha (500 ac) burned per year today through prescribed fire and wildfire (Manley et al. 2000). Modern forests that developed under fire suppression after extensive logging are overly dense and crowded with small trees and extraordinary accumulations of fuels (Barbour et al 2002, Taylor 2004). A large body of scientific evidence supports the utility of prescribed fire in reducing crown- fire potential or improving the resilience of forest stands to wildfire, but these studies are largely based on informal observations (Brown 2002; Carey and Schumann 2003), post-fire inference (Omi and Kalabokidis 1991; Pollet and Omi 2002) and modeling (Finney 2001; Stephens 1998; Agee and Skinner