Bilan, M. Victor

Korstian, C.F.

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Stephen F. Austin State UniversitySFA ScholarWorksFaculty Publications Forestry1957Some Further Evidence of Competition BetweenLoblolly Pine and Associated HardwoodsC.F. KorstianM. Victor BilanArthur Temple College of Forestry and Agriculture, Stephen F. Austin State UniversityFollow this and additional works at: http://scholarworks.sfasu.edu/forestryPart of the Forest Sciences CommonsTell us how this article helped you.This Article is brought to you for free and open access by the Forestry at SFA ScholarWorks. It has been accepted for inclusion in Faculty Publicationsby an authorized administrator of SFA ScholarWorks. For more information, please contact cdsscholarworks@sfasu.edu.Recommended CitationKorstian, C.F. and Bilan, M. Victor, "Some Further Evidence of Competition Between Loblolly Pine and Associated Hardwoods"(1957). Faculty Publications. Paper 367.http://scholarworks.sfasu.edu/forestry/367Some Further Evidence of Competition Between Loblolly Pine and Associated Hardwoods C. F. Korstian and NI. Victor Bilan School of Forestry, Duke University, Durham, l•orth Carolina COMPETITION results when the com- bined demands of plants for the essentials for growth are greater than the available supply. Com- petition in forests occurs whenever plants grow so close together as to result in a struggle for light above ground and for moisture and soil nutrients below ground. It causes the overtopping, suppressing, and crowding out of the weaker indi- viduals by more vigorous and more aggressive trees. Differences between individuals within a species in their response to competition results in an expres- sion of dominance by the more ag- gressive trees. In mixed stands the most aggressive species usually be- come dominant. When they are able to maintain their competitive advantage and reproduce success- fully they are usually considered as being relatively more tolerant than their associates. This gives rise to the concept that tolerance is "the capacity of a tree to de- velop and grow in the shade of and in competition with other trees. "2 It is "a general term for the rela- tive ability of a species to survive a deficiency of an essential growth requirement, such as light, mois- ture, or nutrient supply." The relative tolerance of the dif- ferent species when in intense com- petition is very important in deter- mining their respective roles in the natural succession of forest com- munities toward the climax type for a given climatic area. Studies were begun at Duke Uni- versity in 1932 to obtain additional evidence on the part played by the •Presented at 12th Congress, Interna- tlonal Union of l•orest Research Organ- izations, Oxford, England, July 1956. •Forestry Terminology. p. 85. Society of American l•oresters. Washington, D.C. 1950. interacting factors of light and soil moisture in the competition, the expression of dominance, and the relative tolerance of loblolly pine (Pinus taeda L.) and its com- monly associated species of angio- sperms. Comparative studies were made of soil moisture and light in- tensity on seven sets of trenched and untrenched plots in loblolly pine, shortleaf pine, post oak- blackjack oak, white oak-black oak-red oak and red gum-yellow- poplar forest types. 3 The results showed that in closed stands in which light intensity was essential- ly the same a deficiency of soil moisture during the growing sea- son was 'responsible for the death of pine seedlings one to two years old on the untrenched plots. The angiosperms, commonly present in the understory or sometimes newly germinated, usually persisted, al- though they sometimes died back and sprouted out again. Trenching was followed by in- creases in the number of all species and in general luxuriance of the vegetation. Subsequent observa- tions, however, indicated that after six to ten years the pine trees on the trenched plots became un- thrifty and began to die. After a lapse of 10 to 15 years nearly all of the pines had died indicating that, apparently because of the relative intolerance of the pine trees to the shade of the overstory, a deficiency of light may have caused their ultimate death. This conclusion is supported by the re- sults of a recent experiment sug- gesting that reduced light intensity is an important factor in the poor survival of pine seedlings under SKorstian, C. 1•., and T. S. Coile. Plant competition in forest stands. Duke School Forestry Bul. 3. 125 pp. 1938. 821 forest stands. 4 These results are in accord with earlier research• whieh showed that at reduced light intensities hardwoods are photosynthetically more efficient than pines. This fact suggested that the lesser growth and smaller root systems of pine seedlings grown in the shade are likely to result in inadequate photosynthesis. Although under adequate light intensity pines can grow where moisture conditions are equal to or less than the needs of hardwoods, it appears that in shade they are unable to grow and develop successfully. In other words the survival and growth of pines require a light intensity high enough for them to produce suf- ficient food to develop root systems capable of absorbing the necessary water. These considerations emphasize the interrelationship of the com- plex factors involved in competi- tion and that not only the environ- mental factors of light intensity, soil moisture, and dissolved nu- trients but also the relative photo- synthetic efficiency and root habit and development are involved in relative tolerance. In an effort to obtain additional evidence on the interactions and relative importance of these en- vironmental factors another study was initiated in the Duke Forest in 1951. Sixty loblolly pine seed- lings seven years old were selected from an even-aged stand of loblolly 'Kramer, P. J., I-I. J. Oos•ing, and C. 1•. Korstian. Survival of pine and hard- wood seedlings in forest and open. Ecol- ogy 33:427-430. 1952. 'Kramer, P. J., and J.P. Decker. Re- lation between light intensity and rate of photosynthesis of loblolly pine and certain hardwoods. Plant Physiol. 19: 350-358. 1944. 822 pine and hardwoods. The hard- woods included a variety of species indigenous to roesic upland sites of the North Carolina Piedmont Plateau. The experimental area represented a high quality site as indicated by an abundance of yellow-poplar ( Lirgodendron tulip- ifera L.). Twenty pines were randomly selected for each of the following treatments: 1. Both crown and root com- petition was greatly reduced by killing all woody plants within 33 inches of the pines with Atomate (ammonium sulfamate). 2. Crown competition was greatly reduced by tying back all woody plants capable of shading the pines, leaving root co•npetition undisturbed. 3. The pines in this group were allowed to compete with the as- sociated species above and below ground. They served as the con- trol for treatments 1 and 2. Height and diameter growth was recorded for four succeeding growing seasons. Growth analyses for the first two growing seasons indicated that the unreleased ,con- trol pines grew significantly less than those in treatments 1 and 2. There was, however, no significant difference between the growth of the pines under treatments 1 and 2. At that time treatment 1 was modified by poisoning' all woody plants within 12.5 feet of the pines. The accompanying table includes the .adjusted treatment means of height and diameter growth for the four years. Adjusted means in- dicate the treatment means wl,ich would have been obtained had the group means been the same at the beginning of the experiment. Because of the high site quality of the area which probably had an adequate amount of mineral nu- trients required for the growth of forest trees, the root competition in this experiment represents JOURNAL OF FO,RESTI•Y TABLE 1.--ADJUSTED TREATMENT MEAATS OF I•IEIGItT AND •)IAMETER (•RO%VTIt FO• FOUR YEARS Treatmen• Adjusted mean growth Height Dia•nctcr Adjusted Average difference mean growth Average difference between adjusted I inch above between adjusted treatme•t means ground treatment means Inches 1. Hardwoods poisoned 98.7 2. Hardwoods tied back 84.5 3. Control 60.9 Inch es Inches Inches Treatment 1 minus Treatment 1 minus Treatment 2 Treatment 2 14.2 • 2.34 0.67 • Treatment 1 minus Treatment 1 minus Treatment 3 Treatment 3 37.8 *• 1.67 1.40 • Treatment 2 minus Treatment 2 minus Treatment 3 Treatment 3 23.6 • 0.94 0.73 • •Significant at 5 percent level. •Significant at 1 percent level. mainly that for available soil •noisture. Average light intensity available to the crowns of the experimenfal pines was measured on a clear day between 10:30 A.M. and 3:00 P.M. It was expressed as a percentage of the light intensity measured in an open field during the same per- iod. The calculated values for treatments I and 2 were the same; namely, 73 percent of full sunlight and that for the untreated control was 35 percent. Since there was no significant difference in the inten- sity of light available to the pines in groups I and 2, the differences in average growth of the treatment groups can be attributed to differ- ences in available soil moisttire. Thus the trees in group I grew significantly more than those in group 2 because they had access to more available soil moisture during the growing' season. The difference in light intensity apparently accounts for the varia- tion in growth of groups 2 and 3. The pines within group 2 were ex- posed to twice the intensity of light available to those in the con- trol. The combined effect of deficient light and soil moisture is reflected in the growth and general appear- ance of the treated and control pines. Most of the treated pines ap- peared healthy and vigorous. They 'had well developed leaders and long crowns composed of first to fourth order branches. The dark green needles pointed upward, forming an acute angle with the stems. Most of the control pines had an unthrifty chlorotic appearance. Many of them were completely overtopped by competing hard- woods. Three control pines died during the last growing season. It is interesting to note that all three dead pines had been exposed to the lowest light intensity within the control group. The present experiment further emphasizes the importance of both light and soil moisture as vital factors in the growth and develop- ment of loblolly pine when in com- petition with hardwoods. Either deficient soil •noisture or inade- quate light intensity can become alimiting factor and the interacting combination of both usually pre- vents the survival of this species under such conditions. Thus the death of the intolerant pine per- mits the more tolerant and com- monly slower growing hardwoods ultimately to dominate the stand and ,become the climax in the natural succession. 

Some Further Evidence of Competition Between Loblolly Pine and Associated Hardwoods

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Some Further Evidence of Competition Between Loblolly Pine and Associated Hardwoods

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