Masters Theses

Date of Award

8-1988

Degree Type

Thesis

Degree Name

Master of Science

Major

Forestry

Major Professor

Edward R. Buckner

Committee Members

Glendon Smalley, John Graveel, Richard Evans

Abstract

Two south-facing slope positions were planted with sweetgum (Liquidambar styraciflua L.), yellow-poplar (Liriodendron tulipifera L.), loblolly pine (Pinus taeda L.), and northern red oak (Quercus rubra L.). The upper slope position was originally an undisturbed oak-hickory forest; the lower slope position was an old field with a 20-year-old stand of shortleaf and Virginia pines. Soils in the area are Typic Paleudults. Four treatments were tested on each of the four species as follows: 1) fertilizer applied at planting time, 2) irrigation applied the first 7 years after planting, 3) the combination of fertilization and irrigation, and 4) control.

At age 7, yellow-poplar appeared to be highly sensitive to treatments on both slope positions. Fertilized trees were taller on both slope positions while irrigated trees were taller only on the upper slope. The tallest trees in the study were in fertilized and irrigated plots on the upper slope. After 22 years, trees receiving fertilization and/or irrigation were still taller and relative plot volume was greater than untreated trees. The relative height advantage was much less at age 22 than at age 7.

Sweetgum appeared to be somewhat less responsive than yellow poplar to treatments. At age 7, fertilized trees were taller on both slope positions. Irrigation had little apparent influence on height growth of sweetgum. At age 22, irrigated trees were shorter than non-irrigated trees and the height of fertilized and unfertilized trees was essentially equal. Fertilization and irrigation had little apparent influence on relative plot volume at age 22.

There were no apparent treatment or planting site effects on the survival and height growth of northern red oak. Both survival and height growth were the poorest of the four test species. For this reason, it was not included in further analysis.

At age 7 loblolly pine was the tallest of the four species for all site and treatment conditions except yellow-poplar growing on the upper slope with fertilization and irrigation. Unlike yellow poplar or sweetgum, the best growth was on the lower slope. Apparently loblolly pine was less sensitive to soil/site conditions than either of the hardwoods.

While initial survival and height growth of loblolly pine were adequate, by age 22, mortality of the pine had increased in some plots to such an extent that there were not enough trees present for statistical analyses. It was no longer included as a test species in the study.

Changes in growing conditions following the cessation of irrigation treatments and the small quantity of fertilizer applied seemed to have had adverse effects on height growth during the second growth interval during which the best growth of sweetgum and yellow poplar was better on untreated plots. A trend that appeared to be consistent was the more intensive the treatment applied during the first growth interval, the worse the growth during the second growth interval.

The reason for this anomaly was not clear. It may have been related to changes in the soil environment which affected the concentration and distribution of tree roots and micro-organisms once the fertilizer was utilized and irrigation was discontinued.

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