Single-cohort Mixed Species Deciduous Stands Exhibiting Multi-cohort

Attributes in the Southeastern United States

Wayne K. ClatterbuckSilviculture & Forest Management

Forestry, Wildlife & FisheriesUniversity of Tennessee, Knoxville

wclatterbuck@utk.edu

Overview

1. Examine stand structure in four stands within east TN with seemingly multi-cohort attributes

2. Hypothesize why stands are actually single-cohort

3. Are multi-cohort stands feasible in these forests?

Study Area Selection• Second Growth Stands

from a Stand Initiation Disturbance

• Age > 100 years, no major disturbances during period

• Multiple Canopy Layers

• At least 20 ha in size

• Government-owned – state or federal

Four Study Areas• Cumberland Mountains

(East Tennessee)

• Cumberland Plateau (East Tennessee)

• Smoky Mts National Park (East TN)

• Pisgah National Forest (Western North Carolina)

Site Characteristics• Productive Cove Hardwood

Forest Types, SI = 28 m at 50 years, mesic sites

• 65 inches or 160 cm annually

• Composed of more than 25 species

• Located in concave areas that escaped weather events that are frequent

Species• Shade Intolerants --- Yellow-

poplar, black cherry, black walnut, sweetgum, sycamore, cottonwood

• Intermediates --- white oaks, red oaks, hickories, ash

• Shade Tolerants --- red maple, hornbeam, sourwood, dogwood, buckeye, elm

Species• Though sugar maple and

American beech are present, they are on outskirts of range and are not prominent

• Assumption: too warm and humid for these species

• No commercially available shade-tolerant specie present, making multi-cohort management problematic

Diameter Distribution

1 hectare = 2.4 acres 1 inch = 2.5 centimeters

Diameter Distribution

1 hectare = 2.4 acres 1 inch = 2.5 centimeters

All 4 Study Areas had similar diameter distributions

Structure• Negative exponitial (reverse J-shaped)

diameter curves

• Multi-species with different shade tolerances

• All within the same age range (+ or - 10 years), EVEN-Aged or single-cohort

Diameter Distribution

1 hectare = 2.4 acres 1 inch = 2.5 centimeters

Composed of shade-tolerant, non-commercial species --- (Cornus, Oxydendron, Nyssa, Acer rubrum, Sassafras, Ulmus)

Why Single-Cohort and Differing Diameters?

1. Mixed Species2. Stand-Initiating Disturbances

Mixed Species

• Different species grow at different rates (tolerances)

• Different regeneration mechanisms• Different rates to maturity by species• Different responses to disturbance

Different ???

Disturbance

• Disturbance is rampant on the landscape• Varies by frequency and intensity• Natural and anthropogenic

1. Frequent stand initiating disturbance

– Windstorms ---- tornados, hurricanes, storms

– Fire --- formerly more prevalent– Insects/Disease outbreaks

Difficulties with Multi-Cohorts

Average Number of days with thunderstorm events each year

Source: Kim Coder, University of Georgia

Source: National Geographic

Source: National Weather Service

Insects & Disease

Invasives•Emerald Ash Borer•Thousand Cankers Disease of Walnut•Hemlock Woolly Adelgid•Gypsy Moth•Southern Pine Beetle•Oak Decline

2. Ecology of the various species present

– No commercially available shade-tolerant species – Aggressive Liriodendron (yellow-poplar) --- a

pioneer and late successional species– Do not know species composing late-successional

complex because of frequent disturbance– Thus, must pay attention to regeneration to be

sustainable

Difficulties with Multi-Cohorts

3. Short ownership intervals

– 85% of forest land (4.6 million ha) in Tennessee are in private woodland ownership

– According to last Woodland Owners Survey, average forest tenure is 12 to 15 years

Difficult to maintain multi-cohort stands with constant turnover

Difficulties with Multi-Cohorts

4. Surrogate of using diameter rather than age in representing multi-cohort stands

– Large diameter trees are not necessarily old– Small diameter trees are not necessarily

young– Wide variation in development of multi-

species stands

Difficulties with Multi-Cohorts

Bottomline

Question:Do we desire multi-cohort stands in mixed mesophytic forests?

We already have the structure w/o much effort, although single-cohort

Bottomline

Stands are:• Complex / Variable / Heterogenous•Functionally Resilient•Flexible/Adaptable•Challenging because of frequency of change

Bottomline

The challenge for multi-cohort stands is:• Regenerating acceptable species (primarily intolerants and intermediates) in the shade of the overstory when desirable shade tolerants are not part of the system

Bottomline• Even with the rapidity of

major disturbances, we can create even more variability, if desired, through incomplete disturbances, more than likely on an area basis (groups and small patches)

• Challenge is still regeneration of favored species

Bottomline• Sustainability in these

frequently disturbed systems is an open question because of the difficulties in regeneration

• But still many opportunities !!!

Next• Creating and maintaining stable, mixed

hardwood-pine stands (oak-pine) when each component is favored at different successional stages and with varying longevities

• Stay Tuned

Questions?