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Timber Density and Quail
While maximizing timber and bobwhite on the same area is impossible, the relationship between timber and bobwhite numbers has yet to be adequately quantified. Therefore, for 3 years we monitored bobwhite populations on 6 sites across the Red Hills using covey call point counts and relating this index of bobwhite abundance to timber density. To do so, we related timber basal area over 200 acre plots surrounding the point count. We obtain multiple counts from each point and take the most coveys heard at that point.
What is basal area? It is the cross-sectional area of a tree trunk at 4.5 ft above the ground or measured at breast height. A tree with a diameter of 14” at 4.5 feet has about 1 square foot of basal area. Therefore a stand with 40 of these 14” DBH trees on an acre would have a basal area of 40 square feet per acre. Basal areas provides a great index to the amount of canopy closure created by a stand of trees regardless of the age of the trees.
Mature Pine Stands with 15 to 80 square feet of basal area
15 Square Feet Basal Area
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40 Square Feet Basal Area |
80 Square Feet Basal Area
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Figure 1: Relationship between pine basal area and bobwhite abundance in October on 6 plantations in the Red Hills
Figure 2: Bobwhite abundance compared across stands with low and high basal areas
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We found bobwhite abundance was inversely related to timber volume (r = -0.61, p = 0.002). Adjusted covey counts averaged 11.3 coveys below, and 6.4 coveys above 40 ft2/ac of basal area (F1, 21 = 19.4, P < 0.001). Where maintaining high densities of bobwhites is a priority, we recommend pine basal areas be < 40 ft2/ac. However our data also suggests that bobwhites can be maintained at about “a bird per acre” at basal areas up to 60 ft2/ac, assuming sound management is applied. Our experience suggests that more longleaf pine can be carried per acre than old field pines; however this is just speculation at this point. More information on timber management and bobwhite can be found in our new “Red Hills Forestry Stewardship Guide” available from Tall Timbers.
We also recommend reducing off-site hardwoods such as sweetgum, water oak, hickory, live and laurel oaks, that have encroached into upland pine forests. For bobwhite management, maintaining about 1-2 ft2/ac of hardwoods adapted to upland pine forests (such as southern red oak, black cherry, post oak) will provide maximum habitat for bobwhites and other early successional species.
We also compared bobwhite numbers to timber density for 2002, a good production year for bobwhite, and 2003, a poor production year for bobwhite. Timber density had more of a negative relationship during 2003, the wet cool summer, than 2002. That is, during good years, all stands produce birds relatively equally, but during poor years, lighter timber maintains bobwhite numbers better than heavily timbered stands. Therefore, maintaining the correct timber density on a property managed for bobwhite may reduce the variation in bobwhite numbers from year to year.
Why does timber density matter? Bobwhites thrive from a healthy groundstory of sun-loving plants, such as grasses and annual weeds. As timber density increases, the timber shades out important plants that provide food and cover for bobwhites. Also, as timber density increases, the predator community and micro-climate of the stand become less favorable for bobwhites. |
