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Reprinted from Weed Science, Vol. 24, January 1976, pages 144-145

Douglas Fir Release from Tanoak and Pacific Madrone Competition 1

S. R. RADOSEVICH, P. C. PASSOF, and 0. A. LEONARD2

Abstract. Broadleaf species such as tanoak [Lithocarpus den­ to small Douglas fir were treated by the cut-surface method in siflorus (Hook. & Arn.) Rehd.] and pacific madrone (Arbutus April, 1964. Herbicides used were the amines of 2,4-0 and menziezii Pursh) reduced conifer growth on previously logged 2,4,5-T and the potassium salt of picloram. The amine formu­ or burned areas of the northern California and southwest Ore­ lations of 2,4-0 and 2,4,5-T contained 0.48 kg ae/L. Picloram gon coast range. Cut-surface applications of 2,4-D [ (2,4-di­ contained 0.24 kg ae/L. chlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophe­ noxy)acetic acid], and picloram (4-amino-3,5,6-trichloropico­ Hatchet cuts wer.e made through the bark into the wood at linic acid) into tanoak and pacific madrone growing as over­ the base of 7 .6 to 10.2 cm stems of tanoak and madrone such story to Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] that all the bark was severed around the tree. No attem~t was were found to provide acceptable control for 10 years follow­ made, to have separate cuts connected since the objective was ing application. Increment cores obtained from Douglas fir in to sever vertical lines of flow of both water and carbohydrates. treated and non-treated plots revealed substantial stem enlarge­ Cuts were made horizontal to the ground so the herbicide ment as a result of tanoak and pacific madrone control. would not run out once placed in the cut. Each cut received approximately 2 ml of either undiluted 2,4-0, 2,4,5-T, or INTRODUCTION picloram. Treatments consisted of 232 m2 areas in which all A recent estimate indicates almost 2.5 x 106 ha of potentially tanoak and madrone were cut-surfaced. A non-treated area wa~ productive redwood [Sequoia sempervirens (D.Don) Endl.] also included for comparative purposes. The experiment was and Douglas fir timberland in northern California and south­ conducted as a completely randomized design with a single west Oregon are occupied by evergreen broadleaf trees (1). replication but multiple observations eer treatment. These areas are infested by such species as tanoak and pacific In August 1974 stems of surviving and dead tanoak, pacific madrone. madrone, and Douglas fir were counted. In addition radial Substantial increases of Douglas fir growth can be demon­ cores at breast height were obtained with an increment borer strated by controlling competing species with herbicides (2, 5). from all living Douglas fir. Tree age and inside bark basal area The control of trees by injecting herbicides into their vascular growth was then determined. Growth differences between systems through axe cuts through the bark (cut-surface appli­ trees in treated and non treated plots were subjected to at-test cation) has been demonstrated as an effective means to remove for statistical analysis. undesirable tree species (3, 4, 6, 7). Recent interest in the cut-surface method of injecting herbicides for hardwood tree RESULTS and DISCUSSION control in forests can be attributed to several factors. One In the untreated area 76 live stems of broadleaf trees (3273 important reason is the relatively poor control of resprouting stems/ha) were found. Since these. trees exist as overstory to species from herbicide application by aircraft. Often only in­ Douglas fir, a high degree of interspecific competition oc­ complete control of tanoak is observed even after yearly appli­ curred. Satisfactory control of both hardwood tree species was cation for 3 yr. Also, the cut-surface method allows the user to achieved by cut-surface application of any herbicide tested control only trees which he desires. Thus, only trees of one (Table 1). However, some tanoak survival due to stem recovery species or size need to be treated. This necessarily increases the rather than seedling establishment was observed with each her­ herbicide selectivity to desirable trees in the area since desir­ bicide. Three Douglas fir died in the picloram treated area. able conifer trees can be injured by aerial applications of her­ bicide. Cut-surface applications offer a further advantage in that the herbicide is confined to the treated tree. This study was initiated to determine the effects of tanoak and pacific madrone control by the cut-surface method on Douglas fir Table I. Control after 10 yr of tanoak and pacific madrone stems by stem growth. cut-surface injection of several herbicides. Tanoak and madrone stems/232 m 2 MATERIALS and METHODS Alive Dead Control The study was located about 13 km west of Ukiah, California. Treatment (no.) (no.) (%) The stems of tanoak and pacific madrone growing as overstory Control 76 0 0 2,4-D 13 84 86.6 1 Received for publication June 9, 1975. 2,4,5-T 24 88 78.6 2 ,~ Asst. Prof. and Asst. Bot., Dep. of Bot., Univ. of California, Davis Picloram 7 112 94.1 ' : 95616; Forest Advisor Coop. Ext., Ukiah, CA; and Bot. Emerit., Dep. LSD.OS 69.7 -J of Bot., Univ. of California, Davis, CA.

144 Volume 24, Issue I (January), 1976 'I

RADOSEVICH ET AL : DOUGLAS FIR RELEASE

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\ 2, 4-0

Figure 1. Radial cores from Douglas-fir at 2, 4, 5-T breast height taken 10 yr after tanoak and madrone PlCLORAM overstory control by 2,4-D, 2,4,5-T, picloram, and control treatments, . CONTROL respectively.

o· 1 2 3 4· 5 6 7 8 9' ·Cffl

Picloram release into soil from teachings of decomposed leaf remove tan oak and pacific ma drone overstory. Intraspecies and root material or root leakage and subsequent uptake by competition among the Douglas fir themselves explains the the Douglas fir could account for the observed mortality. observed growth differences between the 2,4-D and other her Comparisons of tree basal areas were made for only Douglas bicide treatments. Hardwood tree control with proper Douglas0 fir 15 years or older (Table 2 and Figure 1). Trees less than 15 fir thinning as suggested by Newton (6) may realize even great- years old were excluded because at the time of treatment they er production increases than are suggested by this study. were either nonexistent or very small and were subjected to It is apparent that tanoak and pacific madrone growing in competition from larger trees of the same species. The mean association with Douglas fir can seriously reduce the growth of basal growth of Douglas fir not receiving tanoak and pacific that timber species. Since both broadleaf species existed as an 2 madrone overstory control was 7.2 cm • Douglas fir receiving overstory, shade removal can account for increased Douglas fir the benefit of overstory tree control Were found to have signif­ growth in treated plots. Furthermore, increased moisture or icantly larger basal areas. It was determined that basal area nutrient availability as a result of broadleaf tree control is also growth was increased by 260, 451, and 405 percent 10 yr after possible. treatment with 2,4-D, 2,4,5-T, and picloram, respectively, to LITERATURE CITED 1. Gratkowski, H., D. Hopkins, and P. Lauterbach. 1973. The Pacific coast and northern Rocky Mountain region. J. Forest. 71:138-143. Table 2. Comparison 10 yr after treatment of inside bark basal area 2. Gratkowski, H.D. and P. Lauterbach. 1974. Releasing Douglas-fir at breast height of at least 15 yr old Douglas fir. from varnishleaf ceanothus. J. Forest. 72: 150-152. Basal Areaa Basal Growtha 3. Johnson, W., C.M. McKell, R.A. Evans, and L.J. Berry. 1959. Yield 2 and quality of annual range forage following 2,4-D application in Treatment (cm ) (% of control) blue oak trees. J. Range Manage. 12: 18-20. Control 7.2 100 4. Leonard, O.A. 1957. Effect of phenoxy herbicide concentrates ap­ 2,4-D 18.7** 260** plied to cuts of resprouting tree species. Weeds 5:291-303. 2,4,5-T 32.5** 451** 5. Newton, M. 1963. Success in Douglas-fir plantations as related to site and method of removal of bigleaf maple overstory. West. Picloram 29.2* 405* Weed Contr. Conf. Res. Prog. Rep. pp. 17-18. aMean values of 15 observations for control, 14 observations for 6. Newton, M. 1965. Injector treatments for pre-commercial thinning 2,4-D and 3 observations for 2,4,5-T and picloram. of Douglas-fir. West. Weed Contr. Conf. Res. Prag. Rep. p. 42. • = significantly different from control treatment at to. I and 7. Sterrett, J.P. 1969. Injection of hardwoods with dicamba, picloram •• = significantly different from control treatment at t.os- and 2,4-D. J. Forest. 71 :820-821.

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