Jeffrey Pine-Mixed Conifer Forests in Northwestern Mexico. Scott Stephens Department of Environmental Science, Policy, and Management UC Berkeley

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1 Jeffrey Pine-Mixed Conifer Forests in Northwestern Mexico Scott Stephens Department of Environmental Science, Policy, and Management UC Berkeley

2 Sierra San Pedro Martir Mountains Northern Baja California Mediterranean climate (more summer precipitation than most of CA.) Annual precipitation averages 24 in (61 cm) limited precipitation record Granitic parent material common Area has been grazed by livestock 200 years, varying intensities

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4 Forests in Northwestern Mexico Sierra San Pedro Martir (SSPM) Within the California floristic province unique to Northern Baja California Forested area approximately 100,000 ac. Elevation upper plateau 8800 feet 3 large plateaus, peninsular mountains Jeffrey pine-mixed conifer forests Similar to forests in southern California and eastern Sierra Nevada Fire suppression begins in 1970, no harvesting

5 Image 1: Aerial

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8 FH Mission

9 FRI 10%

10 Fire History Frequency similar to Jeffrey pine dominated forests in the eastern Sierra Nevada and Lake Tahoe Interval between fires 8-15 years Seasonality of past fires is different than Sierra Most fires in earlywood, June and July Few in dormant period Stephens et al. 2003

11 Forest Structure Sampling Jeffrey pine-mixed conifer forest 7 x 7 grid (200 m between plots) Area sampled 512 acres (1.44 km 2 ) Grid densification in random area Spatial statistics being done Similar aspect, soils, slope, vegetation Live tree plots 0.25 acre Snag plots 1.0 acre

12 Forest Composition Jeffrey pine-mixed conifer forest (percent basal area by species) 66.3% Jeffrey pine (Pinus jeffreyi) 23.1% white fir (Abies concolor) 8.4% sugar pine (Pinus lambertiana) 1.4% lodgepole pine (Pinus contorta) 0.8 % quaking aspen (Populus tremuloides) Average basal area 86 ft 2 /acre (20 m 2 /ha) range ft 2 /acre ( m 2 /ha)

13 Forest Structure Live trees (above 1 inch DBH) Average 60 trees/acre (149 trees/ha) Range trees/acre Structural classification of forest (hierarchical cluster analysis ) 33% old forest, single stratum 24% young forest, multi-strata 43% old forest, spatially distinct multi-strata Large amount of variability Stephens and Gill 2005

14 Regeneration in the SSPM Regeneration in distinct patches What are the size and shapes of the patches? What percentage of this forest is currently in patches?

15 Patch Definition All areas with at least 3 trees cm DBH within a 7m x 7m area (22.5 ft x 22.5 ft.) Used information from 4 ha stem map Line intercept method (random start) Total distance 8.4 km (5.22 miles) If patch intercepted then data taken

16 Patch Results Number of patches: 54 Average patch size acres (0.01ha) Range acres ( ha) Average tree height in patch 19 ft (5.8 m) Average tree height adjacent to patch 75.1 ft (22.9 m) Percent of area in patches: 3.8% Patch abundance (number/ha): 8.5 Stephens and Fry (J. Veg Sci 2005)

17 Tree Ages Mapped x and y location of every tree and seedling in two 10 acre areas Cored every tree above 1 inch DBH Cores taken approximately 6 inches above ground level All corers crossdated Pattern (spatial statistics) being investigated

18 Tree Age in 10 acre Stem Map 180 (678 total) Number of Trees Year

19 Snag Density Snags (2001 and before) average 1.7 snags/ac (4.2 snags/ha) 0-9 snags/ acre ( snags/ha) Snags (2002) (added 22 more) average 2.1 snags/acre (5.3 snags/ha) 0-9 snags/ acre ( snags/ha) Drought last 4 years, more mortality in 2003 Stephens 2004, Stephens et al. 2007

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23 How Common are Average Snag Densities in the SSPM? 0 snags on 26% of plots Less than average density on 65% of plots Greater than 4 snags/ac (10 snags/ha) in 14% of plots Conclusion average densities are rare occur in approximately 12% of plots

24 Surface and Ground Fuel Loads 3 fuel inventory transects at each plot (147 transects) Used van Wagtendonk s data (1996, 1998) Average surface fuel load 6.6 tons/acre (15.2 metric tons/ha) Average ground fuel load 3.5 tons/acre (8 metric tons/ha) All fuels are at very low loads, USA commonly 3-7 times larger Stephens 2004

25 How Common are Average Fuel Loads? Less than average load of 6.6 tons/acre (15.2 metric tons/ha) on 73% of plots Greater than 8 tons/acre (18 metric tons/ha) on 24% of plots Greater than 16 tons/acre (36.8 metric tons/ha) on 8% of plots Conclusion average fuel loads are rare (14% of plots) high loads in small areas, low hazard

26 Wildfire July 4, 2003 Started in chaparral below forest In SSPM lightning ignited fires suppressed by 8 person hand crew Very low hazards, suppression efficient Fire burned approximately 1500 acres Largest fire in 20 years Occurred at end of severe drought Same drought as in Southern California

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30 Wildfire Impacts Wildfire Impacts Approximately 20% of trees killed 50% of the smallest and largest trees killed Fire was very patchy directly linked to heterogeneity of forest structure and fuels Fire maintained or increased spatial heterogeneity produces fire with diverse effects continues high spatial heterogeneity bark beetles killing a few trees Mortality very low even after 4 year drought and wildfire

31 Forest Restoration in Similar Forests High amount of spatial variability desired, probably was the pre-historic landscape can live with some areas with high fuel hazards, high snag densities Contrast: Large continues forested areas with high fire hazards very susceptible to high severity fires Must develop methods to measure, quantify, and communicate spatial variability Currently rare in US forest management most standards and guides as for average conditions replicated at the stand level over large areas

32 Carl Skinner Acknowledgements USFS PSW Research Station Samantha Gill Cal Poly State University Ernesto Franco Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, (CICESE), B.C., Mexico