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.

Site index conversion curves

Central States S. Appal. Mtns

YP site index and soil series

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)

Moisture regime indicator species: trees

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.

Moisture regime index and oak S.I.

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.