Eastern Oak Silviculture The role of prescribed fire Dan Dey U.S. Forest Service, Northern Research Station Columbia, MO
6-20 yrs New Jerse Fire Frequency 1650-1850 Guyette et al. 2012
Tallgrass Prairie Distribution Transeau 1935
Historic Distribution of Savannas and Woodlands? Modern Oak Forests Oak Savannas McPherson 1997 Million Acres Oak-Hickory 130 Oak-Pine 34 Oak-Gum-Cypress 30 Savannas in the Midwest 30 million acres Nuzzo 1986 51% of forests are oaks Smith et al. 2001
Historic fire frequency 1650-1850 MFI 30-100 MFI 20-30 MFI 6-20 MFI 6-20 Interactions between fire and topography, soils, climate effects vegetation composition & structure
Oak Adaptations to Fire 183 to 698 ºF @ 10 41 to 45 ºF @ 0.5 Brose et al. 2014 Death @ 140 ºF for 1 minute 1. Oaks are masting species 2. Acorns are buried in soil by animals Seed moisture Soil poor conductor of heat Location of root collar buds 3. Oaks preferentially store carbohydrates in roots
Oak seedlings & saplings have increasing capacity to sprout after fire topkill Low intensity fires can reliably topkill trees up to 4 dbh Oaks are favored by frequent burning
Bark protects trees from heat Time to reach 140 o F (a lethal temperature at one minute of exposure) Hare 1965
Overstory trees & Low intensity fires Mortality Topkill Slash Concentration 20 dbh Red Oak 5% loss of basal area 18 dbh Red Oak
Compartmentalization a boundary setting process a response to wounding Oaks are better than many species 1. Resists loss of normal function -- conductance of water, minerals and carbohydrates 2. Resists spread of fungal infection
Decay Resistance of the Heartwood FPL 1967 Resistant or very resistant Moderately resistant Slightly or nonresistant Bur oak Swamp chestnut oak Hickories Chestnut oak Baldcypress (young growth) Maples Post oak Honey locust Red & black oak White oak Longleaf pine Other pines Osage-orange Slash pine Yellow-poplar Black locust Sassafras Sweetgum Cottonwood
The Era of Fire Suppression Increasing Forest Density Fire Suppression * States from Minnesota to Louisiana eastward.
Fire Regime Condition Class https://www.frames.gov/partner-sites/frcc/frcc-home/ Class I = Low departure from historic pre-euro veg. Class II = Moderate Class III = High Based on Changes in: Species composition Structural stage Canopy closure
Changes in Land use history & the forests of today
Oak Regeneration Success & Browsing Deer Density (per mi 2 ) Dk Brn = > 45 Tan = 30-45 Yellow = 15-30 Green = < 15 Low deer food: uncut mature forests Medium deer food: range of forest seral stages High deer food: forest interspersed with farmland 6 12 20 36
Mean Annual Change Importance Value 1980-2008 Fei et al. 2011
Common Status of Oak Forests Overstory oaks mature 80 to 120+ yrs No oak in the midstory Oak advance reproduction is absent or small Abundant shade tolerant species Less than 5% of full sunlight on dry-mesic / mesic / hydric sites
Initial Floristics Determines Future Forest Composition In Eastern Hardwood Forests Overstory Composition and Size Structure: Seed production Seed bank reserves Stump sprouting capacity Midstory Composition and Size Structure: Sprouting Capacity Continued recruitment into the overstory Understory Composition and Size Structure: Sprouting capacity Continued recruitment into the overstory
Sound acorns per tree Red Oak Seed Production Oak seedlings establish in years of mast production Dominant and Codominant oaks are the seed producers Without Oak seed producers regeneration is by artificial methods seedling planting direct seeding Or succession toward non-oaks Sound acorns per tree 1800 1600 1400 1200 1000 800 600 400 200 0 0 20 40 60 80 100 DBH (cm) Diameter breast height (cm) Downs 1944
Survival Probability Survival of Red Oak Seedlings in the forest understory 1.0 0.8 0.6 0.4 0.2 0.0 Years since germination fully stocked 0 2 4 6 8 10 12 Mesic Forests: S. Appalachians NE Wisconsin Beck 1970 Loftis 1988 Crow 1992 Less than 5 % of full sunlight common
Sources of Oak Regeneration Seedlings Slow juvenile shoot growth 1 yr Preferential allocation of biomass to roots Seedling Sprouts 3 yr Exponential increase in sprouting ability with increasing diameter
Key to Oak Regeneration Success Abundant and Large Advance Reproduction Dominance probability 1.0 0.8 0.6 0.4 0.2 0.0 0 0.4 1 0.8 2 1.2 3 1.6 4 2.0 5 2.4 6 Initial basal diameter (cm) (in) Probability of an oak being free-to-grow at age 8 yrs. S. Appalachian Clearcuts Site Index 21 69 mft Site Index 24 79 m ft Site Index 27 89 mft (Loftis 1990)
Stump Sprouts Sprouts arising from cut stems > 2 in dbh Fastest growing source of reproduction Stocking insufficient to maintain composition 45 to 75% of dominant oak reproduction from stump sprouts Morrissey et al. 2008 Gould et al. 2002 Swaim et al. 2012
Not All Oaks Produce Stump Sprouts Probability of live sprout year 1 1.0 0.8 0.6 0.4 0.2 0.0 Age 50 y Northern Red Oak SI = 75 ft SI = 60 ft Age 110 y 0 10 4 20 8 30 12 16 40 50 20 24 60 70 28 80 Parent tree DBH (cm) (in) Southern Indiana clearcut Weigel and Johnson 1998
The Key to Sustaining Oak Stocking is Adequate Large Advance Reproduction Oak seedings have good growth 30 to 50% of full sunlight Maximum growth occurs between 50 to 100% full sunlight White oak Intermediate Scarlet oak Intolerant
How do we develop larger oak advance reproduction? Net photosynthesis (mg CO 2 /gm dry wt/ hour) 3 2 1 0-1 saturation point compensation point NET CARBON GAIN NET CARBON LOSS (dark respiration) 0 500 1000 1500 2000 Northern Red Oak Light Compensation 2 to 5% f.s. Light Saturation 20 to 40% f.s. Increasing height growth 50 to 70% f.s. Light intensity (ue m -2 s -1 )
Percent Structure and light Oak seedlings have good growth 30 to 50% of full sunlight PAR and canopy closure as a function of stocking Maximum growth occurs between 50 to 100% full sunlight 100 90 canopy closure 80 70 60 50 40 30 20 10 0 0 20 40 60 80 100 Stocking(%) photosynthetically active radiation Upland oak stands in Missouri Ozarks Blizzard et al. 2013
Stand Density & Oak Growth 60 ft 2 per acre or more: reduces survival of oak stumps reduces growth of oak stump sprouts Dey et al. 2008 reduces oak advance reproduction growth and survival, and hence, density of large oak seedlings Larsen et al. 1997 Green 2008 Kabrick et al. 2008 discriminates against red oak species causing shifts to white oaks or other shade tolerant species Kabrick et al. 2008 Arthur et al. 1998 Oaks need 30 to 50% f.s. but competitors must be controlled
Fire in the Life Cycle of Oak Arthur et al. 2012
A leaf covering helps maintain acorn moisture content Leaf litter > 2 deep is a barrier to acorn germination Equilibrium in leaf litter accumulation in 12-14 yrs Leaf litter recovers to 75% of equilibrium in 4 yrs after fire Fire before acorn drop Fire after acorn drop Fire kills 70% of acorns in Pennsylvania Auchmoody & Smith 1993 58% mortality in 1-yr-old northern red oak Johnson 1974
Advance Repro Survival & Fire Oaks are favored by frequent burning Dey and Hartman 2005
Frequent Fire & Stand Structure in an Ozark Forest 79 ft 2 /ac basal area 69% stocking After 10 years -- <5% reduction in overstory basal area Midstory removal can increase light to 10 to 20 % of full sunlight Depending on forest cover type and ecosystem
Combining Fire with Group Openings Can Promote Oak Regeneration 3 or 5 fires begun 7 years before gap formation and ending 1 to 2 years after promoted the development of large white oak advance repro Hutchinson et al. 2012
Scenario #1: Mature forest no oak advance reproduction It may take 10 to 30 yrs to get a good acorn crop and develop large oak advance reproduction Site preparation burning to reduce leaf litter, reduce competing advance reproduction & midstory, destroy seed in forest floor, and xerify the seedbed to inhibit mesic species germination That is enough time for advanced decay to develop, but larger trees are more resistant to scarring in low intensity burns
Scenario #2: Mature forest with abundant small oak advance reproduction Shelterwood harvest removing 50% basal area or to B-level stocking Release burning with low intensity dormant season burn in ±3 years Remove shelterwood, burn in ±3 years If oak seedlings 0.75 basal diameter consider moderate to higher intensity fire in late spring early leaf out Risks advance decay in any overstory trees that will be retained for the long-term, especially with higher intensity burns
Scenario #3: After final shelterwood removal, or clearcutting Before crown closure and stem exclusion stage of stand development If competing stems are <4 to 5 dbh, especially with low intensity fires Release burning with low to high intensity fires every 3-5 years as needed to develop competitive oaks If oak reproduction is large enough (e.g., 0.75 basal diameter) go with higher intensity burns in early leaf out to summer season
Scenario #4: Crown closure, stem exclusion stage Release burning inhibits continued recruitment into the overstory and is a clumsy, indiscriminant way to control stand density and composition Risk of bole wounding and advanced decay in sapling & polewood crop trees is high Mechanical/chemical release is a better alternative
Scenario #5: Uneven-aged management Not appropriate for oaks on mesic & hydric sites Regeneration and overstory recruitment occur simultaneously Fire would set back to seedling stage stems meant for overstory recruitment Midstory stems are dominated by shade tolerant, fire sensitive species Risk of bole wounding and advanced decay in sapling, polewood and small sawtimber trees is high Hard to burn small group openings in a matrix of uncut or single-tree harvest
Scenario #6: Savanna & woodland management To reduce density in a mature forest requires moderate to high intensity fires that would cause large bole wounds to residual trees Similar to the fire regimes in the early 1900s that led to so much decay, and volume and value loss The longevity of wounded and decayed trees is reduced due to windthrow and stem breakage It would be better to harvest the overstory to desired stand stocking & use low intensity fires to achieve other ecological objectives and control small hardwood sprouts
Dbh age 10 (inches) Oak overstory recruitment: Requires a fire-free period Vigorous oak saplings grow 1.6 in in dbh in 10 years site index 65 ft in Missouri 3.5 Oak stump sprouts grow initially faster in the open Stump Sprout DBH 10 years after Harvest 3 2.5 2 1.5 1 0.5 0 Clearcut Group Single-tree White oak Scarlet oak Black oak
Recruitment to Dominance needs to be managed Hilt 1985 Morrissey et al. 2008 Zenner et al. 2012 Ward and Stephens 1994 Ward 2009 Only dominant oaks remained at end of stem exclusion Those were largely stump sprouts Oaks were more competitive on xeric & lower quality sites Recommend oak release thinning at crown closure Only oaks that are dominant at end of crown closure are likely to remain dominant/codominant at maturity
Crop Tree Release Stand age 10 to 20 years Canopy closure 50 to 75 crop trees per acre 4-sided crown touching method
Homogenization of the forest landscape & the need for active forest management to promote oak ecosystems and diversify the landscape 60 to 70% of eastern forests are 40 to 100 years old Shifley et al. 2012 With developing shade tolerant understories Dominated by woody species and shade tolerant forbs in the understory