Single-cohort Mixed Species Deciduous Stands Exhibiting Multi-cohort Attributes in the Southeastern...
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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
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?