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Forest Site Classification 2007 Upland Hardwood Silviculture Training
Bent Creek Experimental Forest
Henry McNab
Research Forester
Lesson Plan (23 July 2007, 1350-1415)
• Class discussions – 15 min.– Review importance of site classification in
silviculture and methods.
• Field demonstration – 10 min– Examine species composition method of
classifying moisture regimes.
• Field trip: Blue Ridge Pkwy– 2 hr.– Species composition approach to site
classification, American chestnut, and ?
Forest Site Quotations
• “Perhaps the single most important decision a forester can make is to manage for the right species on the right site. (Anon.)
• “No valid silvicultural decision can be made without reference to site quality... (Daniel, Helms, and Baker, Principles of Silviculture)
Site Classification: Definition
• Site:The continuously varying non-living (atmosphere and soil) components of forest ecosystems that make up the physical environment, or site.
• Classification: The arranging of complex relationships into fewer, simpler groups to facilitate understanding, communication, and application.
Site components• Components that are
relatively stable on a site and affect species composition:– Temperature (elev.)– Moisture (landform)– Fertility (geology, soil)
• Light – ~constant at top of canopy– Variable on forest floor
depending on disturbance
• Disturbances vary by time of occurrence and level of intensity and primarily affect the density of a species:– Fire– Climate (ice, wind)– Insects (pine beetle)– Disease (chestnut)– Silviculture
Why classify sites?
• Silvicultural reasons– Species composition– Thinning response– Regeneration success– Biomass production– Sawlog grade– ?
• (David M. Smith, The Practice of Silviculture)
• Other forestry reasons– Hazard rating (ice)– Equipment
limitations– Taxes– Wildlife habitat– Recreation potential– ?
Methods of site classification
• DIRECT – measure of actual crop production on a site:– Agricultural crops:
bushels of wheat from a field.
– Forest crops: cu ft of wood from a stand.
– Not practical.
• INDIRECT - measure of something related to crop production:– Soil moisture– Growing season– Precipitation– Species– Site index
Site index definition & concept
• The average height of the dominant and codominant trees in a stand at a reference age, usually 50 years in eastern hardwoods.
• Assumptions (height is independent of stocking, fully stocked stands, free to grow, no previous damage, species native to site, and even-aged stand).
• Tree is phytometer of site components.
Site index curves
• Site index curves at an index age 50 years for yellow-poplar in the S. Appalachian Mtns.
• Sample 25 trees/ac!!• Accuracy – a 10-ft
site class.
Site Index - Evaluation
• Advantages– Widely used– Quick and easy(?)– Directly related to
growth and yield– Works well for some
species: conifers, yellow-poplar
• Problems– Multi-species stands– Multi-aged stands– Missing species– Previous damage– Inaccurate curves– Samples needed– Past suppression– Coring problems– Height measurement
Site Index - Problems• Single stemmed
species– Yel.-pop. (excurrent)
• Multi-stemmed species– Oaks (decurrent)
Site index method: guide curve vs stem analysis
• Schnur’s 1937 SI by guide curve method
• Carmean’s 1972 SE by stem analysis
• Note difference at older ages.
B.C. Site classification work
• Site index (oaks, yellow-poplar, E. white pine)• Soil-site (scarlet oak, black oak, yel.-poplar)• Ecological modeling (quantify site variables
that affect composition and distribution of species-moisture, temperature, fertility)
• Species composition (quantify species on a site as an indication of environmental conditions)
Soil-site relationships: Scarlet Oak and Black Oak
• Developed by Doolittle 1957.
• Block diagram for site index of scarlet and black oak as related to depth of A horizon, position on slope, and sand in A horizon.
SI of SO and BO by aspect; BCEF
Aspect class (Doolittle ’57) No. plots Avg. SI
N and NE 17 68.6
E and SE 37 67.1
S and SW 49 60.4
W and NW 7 58.6
N, NE, E, and SE 54 67.5
S, SW, W, and NW 56 60.2
Soil-site relationships: white oak
• In the Boston Mtns of Arkansas, site index of white oak varies with aspect and slope shape / position. (1 = ridge, 5 = cove)
Species composition method
• Advantages– Intuitive for managers– Easy to apply/modify– Cost and time
effective– Consistent among
users– Computer can do it
from inventory plots– Forest Vegetation
Simulator (FVS)
• Problems– Must have field data– Can’t use with GIS– Not for planted
stands– Must know
dendrology– Lack of S.I. number
Species composition (species list)
• Method not new – Cajander (1926) forest site types in Finland.
• Physiological characteristics of species present on the site indicate the predominant environmental gradients:– Moisture regime (wet/dry)– Fertility regime (rich/poor)– Temperature regime (hot/cold)
• Almost any species can occur on almost any site, but only those species well adapted will be common (not rare) in the stand.
Site classification literature
• Barnes, B.V., et al. 1982. Ecological forest site classification. J. For. 80:493-498.
• Carmean, W.H. 1975. Forest site quality evaluation in the U.S. Adv. Agron. 27:209-269.
• Jones, J.R. 1969. Review and comparison of site evaluation techniques. Res. Pap. RM-51, 26 pp.
• Tesch, S.D. 1981. The evolution of forest yield determination and site classification. Forest Eco. & Man. 3(1980/1981):169-182.
Components of site productivity
SITE
QUALITY
Climate (Disturbance)
Topography
MANAGEMENT (Planned disturbance)
Productivity
Characteristic vegetation
Geology / soil
Light (top of canopy)
More disturbances
Productivity
Mos
tly f
ixed
(The one site component you can change using silviculture is…?)
(Bugs, fire, disease)
Light (in canopy)
Summary
• Why classify forest sites?– Subdivide the landscape for management purposes
• Environmental components of site quality– Moisture, fertility, temperature regimes
• Species composition method– Integrate environmental components
• Land owner recommendations– Management species
• Field trip – Moisture/fertility/species relationships in mid-elevation zone along Blue Ridge Parkway.