( , About This File: . . ' ' lication .. sc nning the printed pub This file was created bV corrected; the software have been Misscans Identified by . es may remain. . however, some mistak EFFECTS OF FERT IL IZAT ION ON MORTAL ITY IN WESTERN HEMLOCK AND DOUGLAS-F IR STANDS Richard E. Miller Overstocking in hemlock and/or Douglas-fir stands is often associated with low site productivity. Although stocking control or precommercial thinning Is desirable In such stands to concentrate growth on fewer trees, costs are high and benefits may be low. Fertilizing can be a tool for thinning pure stands and/or weeding mixed stands if fer­ tilization enhances site productivity and induces faster suppression or loss of noncrop trees. Overstocking In hemlock and/or Douglas-fir stands is often associated with low site productivity. Although stocking control or precommerclal thinning is desirable in such stands to concentrate growth on fewer trees, costs are high and benefits may be low. Fertilizing could be a tool for thinning pure stands and/or weeding mixed stands if ferti­ lizing would enhance site productivity and induce faster suppression or loss of noncrop trees. To explore this alternative or supplemental tool for thinning overstocked stands, I reviewed published and unpublished data seeking answers to two questions: Several studies in pure hemlock and Douglas­ fir stands indicate that fertilizing with nitrogen at dosages up to about 400 pounds per acre generally stimulates diameter growth of upper crown class trees more than lower. Although there Is a general trend for tree losses in fertilized plots initially to exceed those of unfertilized, differences are usually small and not statistically signifi­ cant. Besides changing the relative competitive status of upper and lower crown classes, fertilizing Douglas-fir with 200 to 400 pounds of N per acre at several locations increased crown breakage and tree mortality from winter damage. Mortality was generally in smaller-than-average trees. In an overstocked mixed stand of Douglas-fir and hemlock, fertilization stimulated basal area growth of dominant Douglas-fir and significantly (p < 0.09) increased rate of mortality during a 6-year period after treatment. Net reductions In live stems averaged 2 percent on control plots compared to 12 and 24 percent for the two fertilizer treatments, 600N and 300N + 150P + lOOK + 50S. Fertilized plots averaged signifi­ cantly (p < 0.08) greater mortality In smaller diameter classes, which were primari­ ly hemlock. Despite these initial and prob­ ably continued reductions In stand density following fertilizing, these mixed stands will probably remain overstocked for effici­ ent production of sawtimber. If increased pulpwood or fiber production through fertili­ zation is not an acceptable option for gros­ sly overstocked, pure, or mixed stands, then increased investments In mechanical thinning, preferably early and In combination with fertilizing, or even stand replacement should be considered. I. Can fertilizer serve as a thinning tool in pure stands of hemlock or Douglas­ fir? 2. Can fertilizer serve as a selective weeding tool in mixed stands of these two species? Results and Discussion IntuitiVe bases A review of knowledge about stand growth and mortality is desirable before considering empirical evidence from fertilizer trials In western hemlock and Douglas-fir. Stand density and site index In pure, even-aged, normally stocked stands of Douglas-fir and western hemlock, there are generally fewer trees present at a given stand age on high-quality sites than on low­ quality sites (McArdle et al. 1961; Barnes 1949). These general relations between stand density and site quality integrate differ­ ences in (1) seedfall, (2) germination and seedling survival, and (3) subsequent rates of growth and mortality. Unquestionably, faster rates of stand growth on high-quality sites lead to faster reductions in stem numbers. RICRA U h LLER USFS Forestry Science Laborator. ruy ia ! 253 ' Based on these trends in natural stands. we can expect increased rates of mortality In overstocked stands wherever fertilizer In­ creases rate of growth ( I.e., temporarily increases site productivity). Although extremely large fertilizer dosages, espec­ ially on soils of low buffering capacity, could cause direct and rapid increases in mortality due to toxicity, moderate ferti­ lizer dosages that enhance growth will prob­ ably cause slow changes in mortality rates by increasing competition among trees. Landing, basal area growth of Intermediate and suppressed trees during the 3-year period after treatment was apparently increased by the 400- but not· the 200-pound N dosage (Table I). Basal area growth of dominant and codominant trees was Increased at both dosage levels. As indicated by ratios of growth, the competitive position of the upper canopy classes was improved by fertilization. In a less excessively stocked stand at Port Renfrew, however, 3-year basal area growth of intermediate and suppressed trees was in­ creased by both N dosages and the relative competitive position of dominants and co­ dominants was not improved (Table I). Although initial differences in stocking and diameter distribution among plots at both areas may be masking true treatment effects, it is more likely that fertilizer will induce mortality in lower crown classes at Jeune Landing than at Port Renfrew in the future. Relative response by tree size When fertilizer is applied to unthinned stands, not all trees respond equally. Thus, the relative competitive position of some trees will be improved to the disadvantage of others. For example, nitrogen fertilizer applied in dense Douglas-fir stands usually stimulates diameter growth of large more than of small trees (Gessel et al. 1965; Gessel et a1. 1969; Miller and Pienaar 1973). These results in western hemlock and Douglas­ fir suggest that upper crown classes in overstocked stands generally respond more to fertilization than do lower crown classes. Such differential response should accelerate losses in lower crown classes by making them less competitive for light, moisture, and nutrients. In two 32-year-old hemlock stands, DeBell et al. (1975) also found that upper crown clas­ ses responded much more to nitrogen ferti­ 1 izer than did lower crown classes. Initial results, however, in one of two sapling hemlock stands on Vancouver Island (Lee 1972) were not consistent with this generalization. In an excessively stocked stand at Jeune Average basal area growth of hemlock by crown class and N Table 1. 1 dosage, 3-year perio Crown classll N dosage S + 1 (pounds per acre) CD Quotient11 Initial stand + D ---Number---- --Square feetJeune Landing (11 lears old) 0 0.008 0.018 2.25 13,700 200 .008 .026 3.25 17,630 400 .013 .032 2.46 12,770 Port Renfrew (13 lears old) 0 .006 .028 4.67 6,370 200 .010 .028 2.80 9.870 400 .009 .041 4.56 7,280 11 Source: 11 S m Lee (1972). suppressed, I 11 Quotient - m Three plota per treatment. intermediate, CD growth of CD + D t S + I. 254 q codominant, and D m dominant. Relative response by tree species In the 35-year-old site V plantation In southwestern Washington, nitrogen dosages of 280 and 420 pounds per acre increased tree losses by twofold and fourfold, respectively, during the 7 years after treatment (Table 2). Lighter dosages of 140 pounds per acre did not increase tree losses. Mortality was mostly related to winter damage and largely confined to smaller trees; 60 percent were in the lower third of the diameter range whereas only 5 percent Were in the upper third. However, a higher proportion of larger trees was affected at the largest dosage. Tree species vary in their tolerance and response to fertilization; thus, fertilizing mixed stands may Increase growth of some species to the detriment of others. Stand composition will probably shift to spec Ies benefiting most from treatment. Changes in susceptibility to climate or biotic agents So far we have considered effects of ferti­ Ilzation in changing the relative competit Ive position among trees which Initially d Iffer In size or species. Fert IlIzation may also affect tree mortality by changIng tree re­ sistance to climatlc damage or biotic attack. Direct Evidence: Tool Mortality data from field trials provide direct evidence about fertilizer as a thin­ ning tool. In assessing the effects of fertilization on mortality, we shOUld con­ sider losses in number of trees by diameter class. Stem volume is a less reliable para­ meter because larger volume of mortality on fertilized plots could indicate that more trees died and/or that the same number of trees died, but the volume of the Indlvidu ' trees was greater. One might assume that If fertilizer Improves nutrition and general vigor of trees, then tree resistance to climatic damage or biotic attack should be increased. We have much to learn about the effects of improved, or overly improved, nutrition on susceptibility of Douglas-fir and western hemlock to climatic extremes and attacks from disease and insects. There Is, however, one recurring observation about Douglas-fir that is pertinent; fertilization with moderate to heavy dosages of nitrogen can increase winter damage and mortality. This was ·flrst noted in a fertilizer trial in southwestern Wash­ ington by Reukema (1968) and later confirmed by Miller and Pienaar (1973). Increased winter damage and mortality has also been observed in two locations of the cooperat Ive Regional Forest Nutrition Research Project administered by the University of Washington (Atkinson, personal communication). Table 2. Fertilizer as a Thinning Effect of fertilization on mortality rates in Douglas-fir Although pub I ished information suggests that addition of nitrogen to dense juvenile stands of Douglas-fir accelerated competition and mortality (Crossin et al. 1966; Gessel and Shareeff 1957), these conclusions were based on unreplicated plots. This lack of replication coupled with initial differences in diameter distribution between fert Ilized and control plots constrain conclusions about fertilizer effects. Average lOBS of trees after seven growing seasons by treatment and cause, per acre basi N dosage (pounds per acre) Live Total dead 1963 1963-70 -� -- --- Winter breakage Breakage mortality Total mortali ty Total -Percent- Died ---�--- -Percent-11 ---Percent-- 0 600 93 16 113 73 65 78 140 573 67 12 107 53 50 79 280 627 193 31 220 167 76 87 420 620 227 37 260 200 77 88 1/ Source: 11 Percent of damaged trees. Miller and Pienaar (1973). II Three plots per treatment. 255 lng, In Itial stems averaged 14, 700 per acre. Dur Ing the 3-year period after fertil Iz Ing, the basal area growth of upper crown class trees was stimulated more than lower (Table I). Concurrent tree losses on plots treated with 200 and 400 pounds N per acre averaged 4 and 17 percent greater than losses on the control plots.3 These differences, however, were not statistically significant (p < 0. 95) after plots were adjusted for Initial diff­ erences In tree numbers by covariance analy­ sis. A reanalysIs of a repl Icated ser Ies of plots near Darrington, Washington, showed that fertilizing this 15-year-old stand (I) In­ creased basal area growth during the next 22 years and (2) accelerated Ingrowth Into merchantable diameter classes, but probably failed to Increase rates of mortalIty (Table 3).2 Fertilizing with heavy dosages of NPS clearly Increased growth. The CaMg treatment may have slightly Increased growth. The Initial variability of this stand In diameter distributions precludes further conclusions. Additional data for reanalysis provided by Dr. Stanley P. Gessel, Professor, Universi of Washinqton. on June 1. 1976. Effect of fertilization on mortality rates in hemlock 11 As previously mentioned, Lee (1972) examIned effects of various nitrogen dosages up to 400 pounds per acre In young, overstocked hemlock stands on Vancouver Island. At Jeune Land­ Table 3. Additional data for reanalysis provided by Dr. Y. Lee, Research Hensuratlonist, Canadian Forestry Service, Victoria, British ColUmbia, on April 22, 1976. A 10 percent probability of making a Type I error (p < 0.10) was accepted in this paper as being statistically significant. Average stand conditions and changes during a 22-year period after treatment of a 15-year-01d stand near Darrington, Washington, per acre basis 11 Repeated applications of various fertilizers provided specified approximate elemental dosages (pounds per acre) of 700N, 385P. 700S, 950Ca., and 100Mg. See Gessel et a1. 256 (1965) for more details. Initial stand density at the second locaton near Port Renfrew was also excessive (7,840 stems per acre). Although th Is density was about half that at Jeune Landing, mortality was about twice as much. . An average of 34 percent of the original trees on the control plots died during the 3-year period. After adjustment for initial differences In stand density, losses on plots treated with 200 and 400 pounds N per acre averaged 13 percent less and 33 percent greater than the control plots. Again, these differences were not statistically significant (p < 0. 30). In summary, short term evidence from both areas suggests that the 400-pound-N dosage per acre could have increased the rate of natural thinning. The large with-treatment variation in initial stand density and tree losses precludes more definite conclusions at this time. In conclusion, these data from replicated plots of pure Douglas-fir or hemlock stands fail to support firm conclusions about the ultimate effect of moderate dosages of N on rates of mortality. After adjusting mor­ tality losses for initial differences in number of trees, differences in mortality between fertilized and control plots were small and not statistically significant. In most cases, however, mortality on fertilized plots exceeded that on untreated plots, suggesting a contributory benefit from fer­ tilizing these overstocked stands. It seems unlikely that measurable effects on mortality can be expected without a strong positive or negative effect on tree growth. Direct Evidence: Weeding Tool Most conifer stands in the Pacific Northwest are composed of more than one species. Mixtures with hemlock are prevalent, presum­ ably because hemlock Is a prolific seeder and shade-tolerant. Depending on relative stum­ page values and projected rates of growth, program to reduce stocking will attempt to weed the least desirable species. Data from replicated plots In two pole-sized stands in northwestern Oregon also showed that a conventional 200-pound-N per-acre dosage had only a slight effect on tree growth and rate of tree mortality. During a 12-year period following fertilization of a 30-year-old heavily stocked hemlock stand, about 12 percent more stems died on plots fertil ized with 200 pounds of N as urea than on untreated plots (Table 4). 5 This increase in mortality was small and did not differ significantly from that lost on control plots (p < 0. 20). A closer examination of the mortality trends within the 12-year period showed that 92 percent of this mortality occurred during the first 7 years on the fertilized plots compared to 69 percent on the control plots (Table 4). This suggests that fertilization accelerated rate of mor­ tality and normal trends toward fewer trees. . These slight effects on mortality trends are understandable since fertilizing had l Ittle affect on net or gross basal area growth (Table 4). In 1969 we began comparing various treatments for increasing merchantable yields In two grossly overstocked, mixed conifer stands on the Quilcene Ranger District of the Olympic National Forest (Table 6). Our study at Gold Creek and Deadfall Creek followed an earlier one by the Ranger District in which 3-year diameter growth of dominant trees at Gold Creek was increased sevenfold by fert Ilizing, slightly by heavy thinning, and increased 3. 5 times by combining thinning and fertilizing (Beamer 1967). In each area we compared eight treatments with a control. Three treatments Included thinning and N dosages of 0, 300, and 600 pounds per acre. The remaining five treat­ ments were In unthlnned plots. We again compared nitrogen dosages of 300 and 600 pounds; moreover, we combined N at the 300­ pound dosage with P, P + S, or P, K, S in three additional treatments. We appl ied both thinning and fertilizing treatments to 1/20-acre plots centering on codominant Douglas-fir nominally spaced on a I-chain grid. In a second well-stocked stand of hemlock in northwestern Oregon, diameter growth of dominant trees was reduced by about 20 per­ cent duri g the first 2 years after ferti­ 1ization with 200 pounds of nitrogen per acre as urea (DeBell et al. 1975). During the 4-year period after treatment, tree losses in the fertllized plots averaged 15 percent of the initial stand compared to 12 percent for the control. In a 9-year period prior to fertilization the reverse was true; mortality in the same plots was greater on the control plots (Table 5). 6 This reversal illustrates the general irregular pattern of mortality and the uncertainty in ascribing small changes In tree growth or mortality to fertilizing or other treatments. 2! Y Unpubl ished data supplied by Bruce Rottlnk, Research Plant Physiologist, Crown Zellerbach Corporation, Camas, Washington, on April 24, 1976. Ibid. Fertilizer as a Selective 257 We periodically measured diameter and height of subject trees and tallied 1ive trees larger than 0. 5 Inches d. b. h. initially and after 6 years on at least two quadrants. The differences between tallies represents the net change In number of stems. We cannot determine actual losses from the initial stand because our direct tally of dead trees after 6 years was unreliable. Notches cut Into the dead trees In the initial tally were no longer visible after 6 years. Thus, we Table 4. Average loss of trees during a l2-year period after fertilizing 1 a 30-year-old hemlock stand, per acre basi&-1 N dosage in pounds Item o 200 1,413 1,260 92 92 6 5 253 236 Hemlock - percent 81 86 Douglas-fir - percent 17 15 Initial stand Stems Hemlock - percent Douglas-fir - percent Basal area 5.7 D.b.h. - inches 5.9 Growth in basal area 63 58 101 110 Years 1-7 413 620 Years 8-12 183 50 Years 1-12 596 671 96 96 Net - square feet Gross - square feet Losses Stems - numbeJ-1 Hemlock - percent of total 11 Source: per treatment. Bruce Rottink, Crown Zellerbach Corporation. Three plots Trees 1.5 inches d.b.h. and larger. I Adjusted for initial differences in total stems. cannot distinguish between dead trees ini­ tially present in the stand and those which died after treatment. Results at Gold Creek During the 6 years after treatment, net losses of stems averaged about 20 percent. At less excessive stand densities there were few trees under the I-Inch diameter class, so the net reduction was essentially In trees lost from the originally tallied stand. At more excessive Initial densities, Ingrowth Into the I-Inch class partially offset losses. In the six control plots, tree losses were positively and nearly perfectly correlated with initial number ( r 0. 99). The greater the number of initial stems, the greater net loss during the intervening 6 years. = 258 In contrast, tree losses In fertilized plots were variable and poorly correlated with Initial number of trees. Bartlett's test of homogeneity of variance substantiated that variation in tree losses among fertilizer and control treatments was unequal. The fertl­ Ilzer treatments were obviously causing the difference. This Implies that the fertilizer treatments In the unthinned stand Increased variation In mortality, among plots, poss­ ibly because the effect of fertilizer de­ pended on initial site and stand conditions at each plot. An alternative interpretation 15 based on the fact that a greater propor­ tion of the fertilized plots was Initially more heavily stocked ( Figure I) . Therefore, net losses of trees on fertilized plots were not likely affected by variation In amount of Ingrowth Into the I-Inch diameter class. Table 5. Average trends of mortality before and after fertilizing a 42-year-old hemlock stand, per acre basis !! Year (and age). N dosage in pounds 1971 (42) 1974 (46) 650 430 380 640 470 400 1962 (33) Live stems o 200 Loss - numbers o 200 50 170 70 Loss - percent o 200 1/ 220 Source: 34 12 27 15 Bruce Rottink, Crown Zellerbach Corporation. Two p lots per treatment. Table 6. Initial stand statistics Gold Creek Item Deadfall Creek Dominant age - years 70 - 80 30 - 40 Site IV - IV - V V- Stems per acre 5,200 7,800 Douglas-fir - percent 28 9 Western hemlock - percent 67 72 5 19 All - number Western redcedar - percent ' Itio , and d. b. h. distribution ( Figure 2). Tests of homogeneity of variance showed that only two of the five fertilizer treatments sampled conditions comparable to those on the control plots. Subsequent statistical analyses of mortality were restricted to treatments 4 (600 pounds of nitrogen as urea) and 7 (300N + 150P + lOOK + 50S). In conclusion, fertilization probably In­ creased among-plot variation In tree losses. This finding hinders a generalization about the effect of fertilization on rate of tree loss and necessitates further effort to explain this Interaction between fertiliza­ tion and the site and stand conditions at Gold Creek. Results at Deadfall Creek Despite random allocation of the six repli­ cations of each treatment at Deadfall Creek, treatments did not equally sample the Initial variation in tree numbers, species compos- 259 In the 6 years after fertilizing, net losses of trees on the control plots averaged 2 percent compared to 12 and 24 percent on plots treated with 600N and 300N + PKS, respectively ( Table 7). Losses on fertilized Figure I. Net change in stem numbers durIng a 6-year perIod after fertilizing, per acre basis, Gold Creek. Treatment means are circled. a -2 -Lt -Ei -8 ., ." <l ... ." <l .a ., ... III <l <l 00 <l '" .a u ... '" <l >. '" -Ia -12 - I Lt -lEi - 18 -2 -22 20 Gold Creek -2Lt Pounds/acre -2Ei -28 1 3 -3kl 5 -32 N S:z:mbo1 P 0 0 3 0 6 0 3 1.5 3 1.5 3 1.5 4 7 6 fa X K s 0 0 0 0 0 1 0 0 0 .5 .5 .5 := Table 7. 100 :3 30 Initial stems - thousands Lt Ei 7 8 9 Ikl Average net change in live tree number and basal area 6 years after fertilizing ( Deadfall Treatment Creek ) Net change by d.b.h. clas ell (pounds of Basal area Live stems element per acre) All 1-3 inches 4+ inches All 1-3 inches 4+ inches ----------------------Percent----------------------- o 600N 300N + 11 PKS 4 25 6 -22 36 9 -26 43 - 2 - 2 14 12 -12 -18 24 -24 -35 34 Treatment means adj usted for initial differences in stems and· bssal area. 260 3 II 12 Net change in stem numbers during a 6-year period after fertilizing, per acre basis, Deadfall Creek. Treatment means are clr€led. Figure 2. -2 -Y -6 -8 -I ru § 3 -12 -IY s ru - 16 ru -18 ro ru -20 ro u -22 Gold Creek -2Y S mbol -26 -28 1 3 -3 5 4 6 7 -32 20 Pounds/acre X P N 0 3 6 3 3 3 0 0 0 1.5 1.5 1.5 I 2 100 K s 0 0 0 0 0 .5 .5 0 0 0 1 I 3 . 5 3 30 I Y E 7 B 9 I II 12 Initial stems - thoussnds plots averaged significantly greater than those on control plots (p < 0.09), but the effects of the two fertll izer treatments did not differ significantly from each other (p < 0.24). Net Increases In live stand basal area averaged slightly greater on the control plots but did not differ signifi­ cantly from increases on fertilized plots. Net losses of trees and basal area in the '1- to 3-inch d.b.h. classes were signifi­ cantly increased after fertilization (p < 0.08). Losses of smaller stems--nearly all hemlock in the initial stand--averaged 2 percent on the control plots compared to 18 and 35 percent on those treated with 600N and NPKS (Table 7). Total basal area in smaller trees increased by 4 percent In the control plots, and decreased by 22 and 26 percent in the fertilized plots (Table 7). It is Important to note that these net losses In the 1- to 3-inch diameter classes resulted from (I) mortality among the original trees, (2) growth into the 4-inch class, and (3) ingrowth into the I-inch class which offset losses. Net changes among larger trees (4-lnch class and above) resulted from (I) Ingrowth from the 1- to 3-lnch class, (2) growth of the original trees, and (3) any mortality that offset gains. During the 6 years after treatment, control and fertillzed plots Increased In number of trees and basal area In the 4-inch and larger classes. These Increases were consistently greater for the two fertilizer treatments, but differences were not statistically sIgnifi­ cant (p < 0. 35). 261 Basal area growth of dominant subject trees (one per 1/20-acre plot) increased after fertilization, but these gains were not statistically significant (p < 0.25). Re­ lative to the average growth of untreated dominants, 6-year growth after 600N and 300N + PKS averaged 20 and 12 percent greater. The NPKS fertilization stimulated growth of the 20 largest trees per acre less than the N fertil ization, and reduced numbers of smaller trees more than the N fertilization. One explanation is that the complete treat­ ment probably increased salt concentration in the soi 1 more than did the 600-pound N treat­ ment with urea. This increased salt concen­ tration could have reduced growth improvement of dominant trees and increased mortality in smaller trees through a direct toxic effect as well as by decreasing availability of soil moisture. I conclude that fertilizing at Deadfall Creek reduced overall stand density and especially that in smaller trees. Species composition was also shifted because most of the smaller trees were hemlock. Net losses in hemlock trees averaged 0 percent on the control plots compared to 20 and 40 percent on the 600N and 300N + PKS. Fertilizer probably caused a greater net shift of trees and basal area into the 4-inch and larger diameter classes and increased growth of the 20 largest stems per acre. Figure 3. This 75-year-old hemlock/Douglas-fir stand averaged 5,200 stems per acre. efficient sawtimber or even pulpwood or fiber production is the land manager's objective, then some investment in mechanical stocking­ control and/or fertilizing appears necessary. The lack of increased diameter growth by the 20 largest trees per acre during the 6-year period after thinning is disappointing but not unusual for low-quality sites. Increased growth of these largest trees after fertili­ zing is encouraging, but the response was less than that measured in a nearby prelimi­ nary trial by the ranger district. Costs and Benefits of Treatments Despite increased rates of mortality at Deadfall Creek during the 6 years following treatment, current stocking remains excessive for efficient production of sawtimber. Although greater and quicker reductions in stand density could be obtained using another tool, the power saw, costs of mechanically thinning this stand are high. For example, in thinning our thirty-six 1/20-acre plots (nearly 2 acres), experienced operators needed between 80 and 90 hours per acre (Figure 3). On an operational basis at least 50 hours per acre is a 1ikely expenditure of manpower. This equals $300 per acre thinning costs, assuming a $6-per-hour cost for labor These estimates are probablY and equipment. conservative because 2 years earlier district foresters estimated costs of $400 to $450 per acre to thin the Gold Creek stand to about the same spacing. By far the best treatment was the combination of thinning and fertilizing, but it was also the most expensive. Response to all treat­ ments was probably slowed by poor crowns after initial overstocking. For example) crown expansion after fertilizing was notice­ able only in the fourth year after treatment. Undoubtedly, additional benefits will accrue to all treatments in the future. A fifth treatment option is also available for grossly overstocked stands, particularly those with some merchantable volume or little 1 ikelihood for adequate response to thinning or fertilizing. Such stands could be harves­ ted or destroyed, then replaced with neW stands scheduled for early control of growing stock. The Quilcene Ranger District is selectively using this option. Although stocking control or precommercial thinning is particularly necessary in exces­ sively overstocked stands to concentrate growth on fewer trees, costs are high and benefits may be low because of the inherently Thus, managers of low site productivity. such overstocked, low qual ity sites have difficult decisions. For example, in the 40-year-old stand at Deadfall Creek we examined costs and shori term benefits of four options (Figure 4). If Th inning with a powe r sm. to about 400 stems per acre required 50 manhours per acre. 262 The land manager should have sufficient funds and manpower to reduce stocking to desired levels on all stands within a short period of time. If this is not the case, a priority system is necessary. Early stocking control to concentrate growth on potential crop trees is most desirable for increasing usable yields and reducing initial thinning costs. For example, power saw thinning the 40-year­ old stand at Deadfall Creek from about Figure 4. Costs and effects of four silvicultural options in a 35-year-old, overstocked stand, per acre basis. 26k1 F 21-1Vj <. '" . 220 . . o . . am IBt?J +J Q) Q) .... 160 Q) g 0' CIl '" Q) 11-1121 '" 12VJ ...... '" CIl '" .0 nm Q) :> ''; H 80 T Deadfall Creek 6-year change - percent 6P.l Treatment Cost Stems B.A. growth (dams) -Do11ars- LiLa F T T + F 0 150 300 450 0 20 - 2 -18 -95 -95 100 121 78 198 0 fl 3 s: Lf Live stems . - thou s an ds E 7 a 8,000 stems per acre to 500, cost a conserva­ tive $300 per acre ( approximately 50 man­ In contrast, It cost $90 per acre to hours ) . reduce stocking from 30,000 to 500 stems per acre in a nearby, 12-year-old plantation ( Figure 5) having much natural fill-in ( Vag­ Ie, personal communication ) . Although we have no measure of tree response following thinning in this younger stand, a quicker and greater response to thinning is Iikely be­ cause the trees had better crowns and a shorter period of competition. Conclusions for Land Managers Analysis of a portion of data available from existing field trials in pure hemlock and Douglas-fir shows a general trend for tree losses in fertilized plots initially to exceed those of unfertilized. Although these differences were statistically nonsignifi­ cant, I conclude that where fertilizing improves tree growth in overstocked stands, it probably will also increase rates of 263 This 10-year-old, site V Douglas-fir plantation with natural fill-in averaged 30,000 stems per acre. With conventional dosages of N (100-400 pounds per acre), reductions In overstocking will probably be slow--certalnly much slower and In most cases less beneficial than those from a chain saw. If Increased pulpwood or fiber production through fertilization is not an acceptable option for overstocked stands of hemlock and/or Douglas-fir, then Increased investments in mechanical thinning, prefera­ bIy early and combined with fertil izing, or even stand replacement should be considered. natural thinning. With llght-to-moderate dosages of nitrogen (100-400 pounds per acre), release will be slower and much less than that from a chain saw. With Increasing dosage, faster and greater release Is likely because the fertilizer could have a toxic effect or temporarily reduce available soil moisture. Moreover, moderate-to-heavy dosages of nit­ rogen to Douglas-fir will I ikely Increase winter damage and mortality (Miller and Plenaar 1973). The main potential benefit from conventional fertilizer dosages is Increased stand growth. The acceleration of competition or rate of suppression mortality which Is likely to accompany growth Increases is a contributory benefit. Conclusions for Researchers Analysis of these field experiments demon­ strates the uncertainty in ascribing changes in tree mortality or growth to fertllization or other treatments. Effects of treatment are frequently influenced and masked by Interacting stand and site factors. To improve sensitivity and discriminating power of field experiements, we need to identify factors which interact with treatment causing erratic responses. Knowing these factors, we can reduce their influence by stratifying experimental designs. These refinements are necessary for improving our ability to pre­ dict where fertilizers will be most and least effective. In a 40-year-old overstocked hemlock/Douglas­ fir stand of low site quality, fertilizer increased basal area growth of the dominant Douglas-fir and markedly increased losses of 1- to 3-inch 6iameter trees. Most of the small trees in this stand were hemlock, so these increased losses cannot be considered as selective weeding. REFERENCES Atkinson, William A. 1975. Personal commu­ nication. College of Forest Resources, University of Washington, Seattle. August 19. Gessel, S. P. and Abdulla Shareeff. 1957. Response of 30-ye r-old Douglas-fir to fertllization. Soil Science Soci­ ety of America Proceedings 21(2):236­ 239. Barnes, George H. 1949. Yield of even-aged stands of western hemlock. U.S.D.A. Forest Service Technical Bulletin No. 1273, 52 pp., Washington, D.C. Gessel, S. P., T. N. Stoate, and K. H. Turn­ bull. 1965. The growth behavior of Douglas-fir with nitrogenous fertilizer in western Washington. A first report. College of Forestry, Institute of For­ est Products, University of Washington Research Bulletin No. 1, 204 pp. Seattle, Washington. Beamer, Haroid. 1967. The Gold Creek-Dead­ fall Creek fertilizatIon project. Un­ published report. U.S. Forest Service, Quilcene Ranger District. Copy on file at Olympic National Forest, Olympia, Washington. Gessel, S. P., T. N. Stoate, and K. J. Turn­ bull. 1969. The growth behavior of Douglas-fir with nitrogenous fertilizer In western Washington. The second report. 119 pp. InstItute of Forest Products, University of Washington, Seattle. Crossin, E. C., J. A. Marlow, and C. L. Alnscough. 1966. A progress report on forest nutrition studies on Vancou­ ver Island. Forestry Chronicle 42(3): 265-284. DeBell, D. S., E. H. Mallonee, J. Y. Lin, and R. F. Strand. 1975. Fertilization of western hemlock: A summary of exist­ Ing knowledge. Crown Zellerbach Corp­ oration, Central Research Forest Re­ search Note No. 5, 15 pp. Camas, Wash­ Ington. Lee, Y. 1972. Report on fertilization of dense Juvenile western hemlock. Unpub­ lished Internal Report BC-31, 11 pp. Canadian Forestry Service, Victoria, British Columbia. 264 McArdle, Richard E., Walter H. Meyer, and Donald Bruce. 1961. The yield of Doug­ las-fir In the Pacific Northwest. U.S.D.A. Forest Service Technical Bulletin No. 201, 74 pp. Washington, D.C. Reukema, Donald L. 1968. Growth response of 35-year-old, Site V Douglas-fir to nitrogen fertilizer. U.S.D.A. Forest Service Research Note PNW-86, 9 pp. Pacific Northwest Forest and Range Experiment Station, Portland, Oregon. Miller, R. E. and L. V. Plenaar. 1973. Seven-year response of 35-year-Old Doug­ las-fir to nitrogen fertilizer. U.S.D.A. Forest Service Research Paper PNW-165, 24 pp. Pacific Northwest Forest and Range Experiment Station, . Portland, Oregon. Vagle, Nick. 1976. Personal communication. Quilcene Ranger District, Olympic National Forest. Quilcene, Washing­ ton. Reproduced from Proceedings of Western Hem10ck Management Conference, of Forest Resources, University of Washington, U.S. Department of Agriculture, May 1976, for official use. 265 College by the Forest Service,