Yellow-Poplar
Yellow-Poplar — How Fast Can It Grow?

Historically, yellow-poplar has been an important species in the central and southern Appalachian forest. Recent market developments and inventory information indicate that its importance as a raw material will probably increase in the future. The variety of new uses and markets causes concerned citizens to ask if there will be adequate resource to meet the increasing demand for high-quality, high-value timber.

Whenever new markets for small-size/low-value material develop, there is legitimate concern about how these markets will influence harvesting practices. Will the opportunity to remove smaller-size trees result in lowering the diameter-limit for widespread diameter-limit cutting? Or, might the forestry community be able to influence harvesting so small, low-quality trees are used to make products that do not require large, high-quality trees? The removal of those trees actually contributes to the management of high-quality trees by providing additional growing space. The latter scenario could be referred to as having your cake and eating it too.

Concern is especially great on the non-industrial private forest where all too frequently harvesting is done without the supervision of a professional forester. The challenge before the forestry community in West Virginia is to see if we really can have our cake and eat it too. We are fortunate to have the silvicultural knowledge that enables us to manage yellow-poplar to grow high-value product while harvesting low-quality material. The question is: "Do we have the ability and will to act as a forest community in a way that will cause this economically desirable outcome to become a reality? It is my hope and belief that we do and we will.

This released yellow-poplar crop tree has a crown that is both wide and deep, which gives it good potential for rapid growth.

How fast can yellow-poplar grow? It depends on site, stand history, age, and the free-to-grow rating of the trees. This article focuses on the growth of individual yellow-poplar crop trees, providing advice on how to manage them to accelerate the growth of the trees with the greatest potential to produce high-value timber products.

Some of the most thorough research on individual tree growth was done on yellow-poplar at West Virginia University by Torkel Holsoe in the late 1940's and early 1950's. His work was enhanced by growth and tree quality studies conducted by Dick Trimble, Clay Smith, Neil Lamson, and now Gary Miller at the Fernow Experimental Forest. Some additional information has been collected in recent years from crop tree demonstration areas at Coopers Rock and Camp Creek State Forests in West Virginia, and Raystown Lake and my own Perkey Tree Farm in Pennsylvania. While we certainly don't have all the answers regarding growth of yellow-poplar, we do know enough to make some firm recommendations.

COOPERS ROCK CROP TREE DEMONSTRATION AREA

The crop tree demonstration area at Coopers Rock State Forest has seven monitored growing seasons. Yellow-poplar is growing in association with red oak in sufficient numbers to make some comparison between the growth rates of the two species.

Rodger Ozburn, West Virginia Division of Forestry, discusses growth of crop trees with landowners at Coopers Rock Crop Tree Demonstration Area.

The following charts illustrate the difference in growth between the yellow-poplar and the red oak.

   

Here are some observations:

• Yellow-poplar crop tree growth varies more from year-to-year than red oak, possibly reflecting a greater sensitivity to annual precipitation.

• Red oak out-performed yellow-poplar every year but one.

The following table shows that the yellow-poplar trees that received a crop tree management release grew almost an inch more in diameter over the seven growing seasons than the yellow-poplar control trees.

Coopers Rock Crop Tree Demonstration Area
Yellow-Poplar Growth
 
Location
1998
drh
1995
dbh
Growth Rate
(Inches/Decade)
CT Release Treatment
Area-Wide Thinning
Control
15.4
15.6
15.3
17.3
16.9
16.3
2.7
2.0
1.5

Visitors to the Coopers Rock Crop Tree Demonstration Area have frequently expressed concern about the area-wide growth parameters in the most intensively cut crop tree management treatment areas. Permanently located 10 BAF variable radius plots were established and measured prior to treatment, immediately after treatment, and six years following treatment. Remeasuring these plots has provided information about growth of basal area, relative stand density, and board foot volume following treatment. Although the measurement of these parameters is not essential to the application of crop tree management, they do provide a valid measure of how these widely accepted parameters change following a treatment.

Coopers Rock Crop Tree Demonstration Area
Basal Area
 
CTM Objective(s)
Pre-Treatment
Fall, 1998
Post Treatment
Spring, 1989
 
1994
Timber, Wildlife, Aesthetic

Timber, Wildlife

Timber

148

132

130

83

60

43

115

98

70

The growth in basal area and relative density is striking. For example, on the intensively cut plot where timber was the only objective, the basal area changed from 43 to 70 square feet (all trees 1-inch dbh and larger). Of the 27 sq. ft. of growth, 7 feet was on regeneration established after the treatment. Twenty square feet was on residual trees. It is critical to recognize that this growth can only be expected when the crop trees have healthy, vigorous crowns that are capable of accelerating growth in response to the increase of site resources made available to them. A diameter-limit cut to a similar basal area that removes most of the stand's best performers cannot be expected to give the same results.

CAMP CREEK CROP TREE DEMONSTRATION AREA

The Camp Creek Crop Tree Demonstration Area is located on a site that is not productive for yellow-poplar. However, the comparison of growth rates between crop trees and control trees reveals a very dramatic response to release. Control trees grew 1.3 inches/decade, and released crop trees grew 3.0 inches/decade.

Camp Creek Crop Tree Demonstration Area
Growth (Inches/Decade)
Species Control Crop Trees
Yellow-Poplar
Chestnut Oak
Black Oak
White Oak
1.3
1.8
1.7
1.5
3.0
2.5
2.2
2.2

Comparing control and crop tree growth rates among species (yellow-poplar, chestnut oak, black oak, and white oak) reveals how responsive to release yellow-poplar is on this site. Yellow-poplar is the slowest growing tree in the controls, but it is the fastest growing released crop tree.

The following area-wide statistics for the crop tree management plots at Camp Creek reflect the difference the growth potential of the residual trees can have on the basal area growth of the plot. The post-treatment basal area of all three crop tree management plots was about equal. In the plot where timber was the only objective, more of the residual trees had characteristics that would enable them to respond to the increase in growing space. Where wildlife and aesthetics were also important objectives, crop trees included large, old, hollow black gum trees that met the plot objectives, but were unable to grow rapidly following release. This difference in the growth of individual crop trees is reflected in the reduced basal area growth rate for the plot.

Camp Creek Crop Tree Demonstation Area
Basal Area
 
CTM Objective(s)
Pre-Treatement
Fall, 1989
Post Treatement
Spring, 1990
 
1995
Timber, Wildlife, Aesthetic

Timber, Wildlife

Timber

137

150

153

62

63

63

78

77

92

RAYSTOWN LAKE CROP TREE DEMONSTRATION AREA

The growth rate of both control and crop trees at Raystown Lake indicates that the site productivity is significantly greater than at either Coopers Rock or Camp Creek. The yellow-poplar control trees at Raystown Lake are growing approximately at the same rate as the released crop trees at Coopers Rock. While there are other variables, such as the age and size of the crop trees, the primary reason for the growth difference is probably site related. The released yellow-poplar crop trees at Raystown Lake are growing approximately twice as fast as the released yellow-poplar crop trees at both Coopers Rock and Camp Creek.

   

In contrast to Coopers Rock, the yellow-poplar at Raystown Lake is growing faster than the red oak. This growth rate relationship may change later in the life of the stand.

FISH TROUGH DEFERMENT AT THE FERNOW EXPERIMENTAL FOREST

At the Fernow Experimental Forest near Parsons, West Virginia, a deferment cutting was installed in 1980. Approximately thirteen healthy, high-quality trees per acre were left standing in what would otherwise have been a silvicultural clearcut to 2-inches dbh. The primary purpose of keeping these large trees was to explore the mitigating effect the residual trees had on the aesthetic appearance of the treatment.

The growth of these fully released trees has been monitored over a fifteen-year period, providing good data for seventy-five-year-old yellow-poplar on a good site. Prior to release, the stand had not been managed, so the crowns weren't quite the width and depth recommended by Torkel Holsoe. However, these trees can be used to provide a basis for a conservative estimate of physical growth rates of relatively large (16- to 24-inch dbh) yellow-poplars. These rates can be combined with relevant stumpage values to estimate real rate-of-return (ROR) and income per tree. This information provides a gauge that can be used to help managers decide how large they want to grow released crop trees before they are regarded as being financially mature.

With the stumpage price assumptions used for this calculation, both the real rate-of-return and income per tree are declining after the trees reach 22 inches dbh. Changing stumpage prices and value thresholds associated with increases in diameter can have dramatic effects on both rate-of-return and tree income per year. When establishing financial maturity, both of these parameters are important to consider because:

Fernow Experimental Forest
Fish Trough Deferment
 
DBH Class
Growth
(In./Dec.)
ROR
(%)
Income
($/Tree/Year)
16
18
20
22
24
3.1
3.5
3.3
3.3
3.5
6.9
8.7
6.7
5.4
3.7
$1.83
$3.15
$3.64
$3.76
$3.23

The combination of these two financial parameters provides an indication of how the investment is performing relative to the amount of capital obligated at the beginning of the period (rate-of-return). It also gives an indication of the consequence of that investment (income per tree per year).

It is easy to translate income per tree per year to income per acre per year. Again, using the example from the Fish Trough Deferment Cut at the Fernow, if there are ten 16-inch trees per acre, they yield an annual produced income of $18.30/acre. If there are ten 24-inch trees per acre, they yield an annual produced income of $32.30 — almost twice as much. As the number of high-quality, rapidly growing trees per acre increases, so does the resulting income per acre.

SELECTING YELLOW-POPLAR CROP TREES WITH THE BEST FINANCIAL POTENTIAL

Size of Crown — To produce a good rate-of-return and income, a tree must have a healthy crown that is not only wide, but deep, as well. In many previously unmanaged stands, the most vigorous dominant and codominant trees have live crown ratios of about 20 percent. To achieve good growth rates, it is desirable to have live crown ratios of 40-50 percent. This higher ratio is easier to develop in young stands that have not yet achieved a significant percentage of their full height growth. In middle-aged yellow-poplar stands (50-60 years old), opportunities for increasing crown size still exist, but are limited by the slower height growth. Working in young stands that are between 25- and 60-feet tall may be difficult because the work must often be done precommercially. However, trees in these stands have the potential to develop the deep crowns needed to sustain excellent growth rates, dependent on the site, throughout their lifespan.

In the early 1950's Torkel Holsoe recommended releasing individual trees to maintain live-crown ratios close to 50 percent. He diagrammed crowns and boles of trees to graphically show how much additional clear wood is produced when crowns are released and deep crowns are maintained. The released trees have rapid growth rates that result in larger boles with more clear wood on the lower two logs than can be obtained from smaller diameter trees with lower crown ratios. If this recommendation would have been applied on a widespread basis, we would have a very impressive high-quality yellow-poplar resource to harvest today.

Clear Wood Volume Comparisons


100-year-old yellow-poplar. Knotty cores shaded black.

Although it is unlikely we could financially afford to grow crop trees to the diameters indicated in the preceding graphic, the principal is valid for trees grown to diameters we accept as being financially mature today (20 to 26 inches dbh). Using 1950's vintage stumpage prices, Torkel showed that released 2-log trees with deep crowns could reach approximately the same value in 70 years that 3-log trees could reach in 100 years. Diameters (dbh) at these two respective ages were approximately the same — 23.5 inches.

Epicormic Branches — With yellow-poplar, what you see is what you get. That is, if the potential crop tree has existing epicormic branches or visible dormant buds, they will persist and grow following a crown-touching release. However, the species has little tendency to produce additional epicormic branches. Consequently, there is seldom a decrease in log grade because of the release. The following graphic compares this tendency with red and white oak.

Crown Configuration — Yellow-poplar crowns are very subject to breakage in wind, ice, and wet snow storms. To reduce the probability of crown damage, it is advisable to avoid selecting crop trees that have major V-shaped forks, especially if there is a visible seam below the fork. Branches that are smaller and join nearly perpendicular to the main stem are preferable. Discriminate against selecting crop trees that have major crooks on the main stem; crooks are a vulnerable point of breakage. As with any species of timber crop tree, it is desirable to have a crown that has live branches on all four sides of the main stem so the weight of the crown is balanced around the bole.

Windfirmness — Windthrow has not been a problem with yellow-poplar in the previously mentioned crop tree management demonstration areas or the research treatment areas established on the Fernow Experimental Forest. However, on sites with shallow soils on exposed ridges, caution may be appropriate. When tip-overs are observed in the woods, frequently people assume it is because of windthrow. Although wind may be a factor in the event, often ice, wet snow, and saturated soil are also major contributors. In my opinion, there is much greater risk for damage to yellow-poplar from crown breakage than from windthrow.

WHAT DOES IT ALL MEAN?

Yellow-poplar has the potential to be a premier tree in the central Appalachians. With adequate release, it can grow at the rate of 3 to 5 inches per decade on acceptable sites. With those growth rates, harvestable-size sawtimber trees are possible in 50 to 60 years. Although we still may not match southern pine volume per acre growth rates, good yellow-poplar sites can produce pretty impressive volumes of potentially high-value product.


This released yellow-poplar crop tree is growing well at the Perkey Tree Farm and Stewardship Forest in southwestern PA.

If we apply a crown-touching release to the most desirable timber crop trees at a relatively young age, good naturally regenerated stands may have 35 crop trees per acre that can be retained to a mature diameter at breast height of about 20-22 inches. The butt logs of these trees will contain about 200 board feet, with an additional 100 board feet in the second log. That equates to about 7,000 board feet of high-value product and 3,500 board feet of lower value product. If that volume is grown in 50 to 60 years, we have a rotation length that may approach competitiveness with other wood-producing regions of the country.

In the past we have not made widespread, large-scale investments in yellow-poplar stands. Considering its potential growth rate on good sites, and the ease with which it is regenerated naturally (in the absence of an excessively high deer population), perhaps the time has come to change our investment strategy in this country. We need to direct financial and human resources to the development of this excellent investment opportunity in the central Appalachian hardwood region. The Stewardship Program (a public initiative) and the Sustainable Forestry Initiative (a private endeavor) have names that indicate a commitment to the management and wise use of our forest resource. The new markets for yellow-poplar give the forestry community an excellent opportunity to act on this commitment to the stewardship of a sustainable forest resource. Let's do it.

•AWP•