A permanent study was established in 1970 and 1971 to measure the impact, spread, and intensification of dwarf mistletoe on precommercially thinned Douglas-fir and lodgepole pine in Montana. Mean diameter growth on all plots was reduced 21 percent in Douglas-fir, but the reduction is only significant at the 0.15 level. No diameter growth reduction occurred in the lodgepole pine. Height growth was not affected in either species. Infected trees, as a percent of the total number of trees in the study, increased from 3.4 percent in 1970 to 9.2 percent in 1983 in Douglas-fir, and from 1.8 percent in 1971 to 7.4 percent in 1984 in lodgepole pine. Dwarf mistletoe rating, a measure of infection intensity, increased in some trees, decreased in some, and did not change in others. There was no effect of thinning at this young age and low dwarf mistletoe intensity. Dwarf mistletoe intensity and impact may increase as the stands mature

Dooling, Oscar J.

Eder, Robert G.

Johnson, Ralph R.

United States. Forest Service. Northern Region

Undetermined

ScholarsArchive@OSU

•4• •••GROWTH IMPACT, SPREAD, AND INTENSIFICATION OF DWARF MISTLETOEIN DOUGLAS-FIR AND LODGEPOLE PINE IN MONTANAbyOscar J. Dooling, Ralph R. Johnson, Robert G. Eder'ABSTRACTA permanent study was established in 1970 and 1971 to measure the impact,spread, and intensification of dwarf mistletoe on precommercially thinnedDouglas-fir and lodgepole pine in Montana. Mean diameter growth on all plotswas reduced 21 percent in Douglas-fir, but the reduction is only significant atthe 0.15 level. No diameter growth reduction occurred in the lodgepole pine.Height growth was not affected in either species. Infected trees, as a percentof the total number of trees in the study, increased from 3.4 percent in 1970to 9.2 percent in 1983 in Douglas-fir, and from 1.8 percent in 1971 to 7.4percent in 1984 in lodgepole pine. Dwarf mistletoe rating, a measure ofinfection intensity, increased in some trees, decreased in some, and did notchange in others.There was no effect of thinning at this young age and low dwarf mistletoeintensity. Dwarf mistletoe intensity and impact may increase as the standsmature.1Plant Pathologist, Cooperative Forestry and Pest Management;41	 Biometrician, Fort Collins Computer Center; and Computer Analyst, CooperativeForestry and Pest Management, respectively.      United States	 Forest	 NorthernDepartment of	 Service	 Region• AgricultureP.O. Box 7669Missoula, Montana59807••INTRODUCTION•• •Dwarf mistletoes (Arceuthobium spp.) are parasitic seed plants dependent uponconifer hosts. The dwarf mistletoes and western conifers have probably evolvedtogether since the Miocene period, or about 25 million years (Hawksworth1978a). Dwarf mistletoes may affect their hosts in several ways:1. They cause a reduction of height and diameter growth, with acorresponding reduction in volume growth.2. They can kill trees directly.3. Heavily infected trees produce fewer seeds and seeds of lower viability(Korstian and Long 1922, Munns 1919).4. Wood in bole infections is altered. Affected wood has shorter anddistorted tracheids and a greater proportion of ray tissues (Piirto and others1974, Hunt 1971).5. Infection weakens trees and makes them more susceptible to insects,especially bark beetles.6. They may cause ecological effects by altering species compositionthrough tree mortality or by increasing fire hazard (Hawksworth 1978a, Wicker1978).These effects create problems in some areas because of the demands we place onthe forests for goods and services, but we can alleviate them to a degreethrough silvicultural practices.We can decrease losses by reducing the dwarf mistletoes below the economicthreshold. The study we report on here was designed to help us determine whatthat threshold is.THE STUDYDouglas-fir (Pseudotsuga menziesii (Mirb.) Franco) (DF) plots were establishedon the Lolo National Forest in 1970 and lodgepole pine (Pinus contorta Dougl.)(LP) plots on the Gallatin National Forest in 1971. Plots were marked forpermanent location with steel fence posts at each corner, and plots wereremeasured 3 years after establishment to determine amount of latent infection(DF 1973, LP 1974) and at 5-year intervals thereafter (DF 1978, 1983; LP 1979,1984). In addition to collecting the usual mensurational data (diameter,height, crown ratio), each tree was rated for dwarf mistletoe infection usingthe 6-Class dwarf mistletoe rating (DMR) system (Hawksworth 1977).Objectives of the study were to determine effects of precommercial thinning fordwarf mistletoe control on growth impact, associated mortality, and spread andintensification of dwarf mistletoe.••••••••-2-	 •• •••••••Four plots (DF 1.73 acres, LP 2.77 acres) with a one-half chain buffer stripwere established for each replicate. Three square subplots (DF 0.25 acre, LP0.5 acre) with a one-half chain buffer strip were superimposed upon each plot.All subplots were to have been 0.5 acre, but because of a shortage of suitablestands, the DF subplots were reduced to 0.25 acre.Treatment variables were precommercial thinning and dwarf mistletoe removal.Thinning treatments were applied at the plot level; subplots received differentlevels of dwarf mistletoe removal. The subplots were the basic treatment unitand received the combined silvicultural and dwarf mistletoe treatments.Four silvicultural treatments were applied to plots and buffer strips:1. Check (no thinning).2. Crop trees (681 trees/acre) spaced 8 X 8 feet, all others removed .3. Crop trees (222 trees/acre) spaced 14 X 14 feet, all others removed .4. Crop trees (109 trees/acre) spaced 20 X 20 feet, all others removed .Three dwarf mistletoe treatments were applied to subplots and buffer strips:1. Check (no dwarf mistletoe removal).2. Partial high: Only dominants and codominants which fit potential croptree criteria and were free of or lightly infected with dwarf mistletoe wereleft. Trees were pruned to light infection (DMR 1) if necessary to achieve astocking level.3. Partial low: Only dominants and codominants which fit potential croptree criteria and were free of, lightly, or moderately infected (up to DMR 3)with dwarf mistletoe were left.There were two Douglas-fir replicates, or 24 one-fourth acre sub-plots,2and three lodgepole pine replicates, or 36 one-half acre subplots.Additional details of the study are covered in an unpublished study plan datedJuly 1970 on file in the Northern Region office.••2There are actually 25. One of the check/check plots was thinned by1111	 mistake to 14 x 14 feet, and a substitute was established in 1971.• -3-DATA ANALYSISWe compared actual growth with predicted growth using a diameter growth modelsimilar to the one used in the Prognosis Model for stand development (Wykoffand others 1982), which uses the individual tree as the basic unit of growthprojection. By using tree data from the study and keeping the site variablesconstant, we found the variables that had an effect on growth were:1. Position of tree in the basal area (BA) distribution.2. BA of stand.3. Size of tree.4. Grouped DMR's equal to or greater than 3.5. Crown ratio.We did an analysis of variance by multiple regression on the resulting growthcalculations.RESULTS Growth Impact Diameter--The analysis of variance for the Douglas-fir plots is shown in table1. Variables are defined as:LNDDS = Log (change in diameter squared)LNDBH = Log (diameter breast height)BBAL = Basal area of larger trees at beginning of 10-year periodMISTDUM1 = Grouped DMR's less than 3CR = Crown ratioMISTDUM2 = Grouped DMR's equal to or greater than 3BALLND = Basal area of larger trees Log (1 + diameter breast height)The effect of DMR's less than 3 is not significant, and DMR's equal to orgreater than 3 have an effect on diameter growth that is significant at the0.15 level. The multiplier for the dwarf mistletoe effect on Douglas-fir is0.79, or a reduction in diameter growth of about 21 percent.The analysis of variance for the lodgepole pine plots is shown in table 2.MISTDUM1 in this case is all DMR's combined. They were combined because only afew trees had DMR's equal to or greater than 3. The effect of dwarf mistletoeis not significant.n• •••••0 •••••-4-Variables in the EquationT SIG T	42.907	 .0000	13.191	 .0000	.343	 .7316	17.770	 .0000	10.800	 .0000	2.708	 .0068BETA.77789-.157594.0821E-03.25605.22022SE B.02257.01288.052258.89660E-045.43693E-04.11114••Table 1.--Analysis of the effect of dwarf mistletoe on Douglas-fir••	growth predictions.Multiple R .62245 Analysis of varianceR Square .38745 DF Sum of squares Mean squareAdjusted R Square .38299 Regression	 6 184.01627 30.66938Standard Error .59419 Residual	 824 29C.92716 .35307•••• •F = 86.86542	 SIGNIF F = C.0Variables in the EquationVariable	 BWith Two MIST DUNSSE B BETA T SIG TLNDBH .63699 .03715 .71025 17.145 .0000BBAL -.06582 6 .60301E-03 -.32147 -9.968 .0000MISTDUN1 -8.778878-03 .09071 -2.735E-03 -.097 .9229CR .11066 .02697 .12490 4.103 .0000MISTDUM2 -.23705 .15892 -.04585 -1.492 .1362BALLND 4.361720E-03 7 .10191E-04 .2562g 6.142 .0000CON TANT 1 244 1••Table 2.--Analysis of the effect of dwarf mistletoe on lodgepole pinegrowth predictions.Multiple R	 .76223 Analysis of varianceR Square	 .58099	 DF Sum of squares Mean squareAdjusted R Square .58029 Regression	 5	 1228.04883	 245.60977Standard Error	 .54343 Residual	 2999	 885.65745	 .29532F = 831.68012	 SIGNIF F = 0.0Variable BLNDBH .96846CR -.16997MISTDUM1 .01792BAL -.01581BALLND 5.871697E-03(CONSTANT) .30100•alk••• -5-••••••Beight--Dwarf mistletoe had no discernible effect on height growth in eitherDouglas-fir or lodgepole pine.Spread and IntensirsationBetween tree--In the Douglas-fir plots, number of infected trees increased from42 in 1970 to 115 in 1983 (table 3).Table 3.--Dwarf mistletoe-infected Douglas-fir by thinning levels by year.ThinningTotal No.trees in1970 1973 1978 1983No.	 % of No.	 % of No.	 % of No.	 % of1	 1 td -	 -	 ; - - t •	 : • .1 -	 -Check 271 25 9.2 29 10.7 38 14.0 46 17.08 X 8 584 9 1.5 24 4.1 38 6.5 49 8.414 X 14 266 7 2.6 11 4.1 18 6.8 20 7.520 X 20 122 1 0.8 0 0 0 0 0 0•In the lodgepole pine plots, number of infected trees increased from 88 in 1971	 • •to 370 in 1984 (table 4).•Table 4.--Dwarf mistletoe-infected lodgepole pine by thinning levels by year.Total No.	 1971	 1974	 1979	 1984Thinningleveltrees instudyNo.trees% oftotalNo.trppn% oftntalNo.trPPn% oftntelNo.trppn% oftotalCheck 1,020 24 2.4 33 3.2 45 4.4 80 7.88 X 8 2,486 22 0.9 30 1.2 87 3.5 138 5.614 X 14 1,072 14 1.3 21 2.0 27 2.5 94 9.020 X 20 429 28 6.5 36 8.4 41 9.6 58 13.5All 5.007 88 1.8 120 2.4 200 4.0 370 7.4Within tree--In the Douglas-fir plots, 42 trees were infected in 1970. The DMRincreased on 14 trees, remained the same on 18 trees, and decreased on 10 trees(table 5).-6-•••••••a• •••4• • Table 5.--Within tree intensification of dwarf mistletoe in Douglas-fir. Thinning	 DMR increase or decreaselevel	 +2	 +1	 0	 -1	 -2 • - - - - No. Trees - - - -Check	 4	 8 12	 1	 08 X 8	 0	 0	 4	 4	 114 X 14	 1	 1	 2	 1	 220 X 20	 0 _Q _Q.	 1 _Q  Total	 5	 9	 18	 7	 3 In the lodgepole pine plots, 88 trees were infected in 1971. The DMR increasedon 21 trees, remained the same on 33 trees, and decreased on 34 trees (table6).Table 6. Within tree intensification of dwarf mistletoe in lodgepole pine.Thinning	 DMR increase or decreaselevel	 +3	 +2	 +1	 0	 -1	 -2	 -3	 -4	  No. Trees 	Check	 1	 1	 2	 12	 7	 1	 0	 08 X 8	 0	 1	 3	 7	 10	 0	 0	 114 X 14	 0	 0	 6	 7	 1	 0	 0	 020 X 20	 A.	 2	 0	 _/	 12	 2	 0	 _QTotal	 1	 4	 16	 33	 30	 3	 0	 1klortality In the Douglas-fir plots, 28 trees died in 13 years. In the lodgepole pineplots, 114 trees died in 13 years.DISCUSSION•Growth Impact.Significant impacts of dwarf mistletoe on growth of Douglas-fir and lodgepolepine were not discernible. Several factors, either singly or in combination,4	 could be involved.••• -7-••••Both the Douglas-fir and lodgepole pine stands were only lightly affected. Theaverage stand DMR was less than 1 for both species when the study wasinitiated. During the first three plot measurements, many new infections werepruned, or trees were cut, unless infections occurred in the dwarf mistletoecheck plots. Some trees were pruned each time the plots were measured. In1983 and 1984, no pruning was done, and by the next scheduled remeasurements(1988 and 1989), a better indication of infection levels and their impact maybe available. Reducing dwarf mistletoe impact by pruning was not an objectiveof the study, but pruning likely reduced both infection levels and impact.Stocking density may be more important in determining growth than lightinfection of dwarf mistletoe, at least during early stages of standdevelopment.Stand age was also apparently important. All the trees except those on oneDouglas-fir plot are less than 30 years old. Stands less than 30 years old donot normally show much of an effect from dwarf mistletoe infestations, butolder stands respond in a measurable way to different infestation levels.There was no effect of dwarf mistletoe on lodgepole pine growth, probablybecasue there were too few trees with dwarf mistletoe ratings of 3 and greaterto test effects of high ratings. Also, there may be more of a host response tosystemic infection (Douglas-fir) than to local infection (lodgepole pine)(Rawksworth and Wiens 1972).Live crown ratio (LCR) is correlated with tree growth. A tree with a 90percent LCR would normally be growing much faster than one with a 20 percentLCR. There may also be a dwarf mistletoe connection here; it is reasonable toexpect that a DMR of 3 would have much more of an impact on a tree with a 20percent LCR than one with a 90 percent LCR. It would probably take severeinfection levels (very high DMR's) to overcome a tree with such a large crown.There was no effect of thinning on dwarf mistletoe. This is likely due to theyoung stand age and low dwarf mistletoe intensity. Thinning effects will beexamined following future exams.Spread and IntensificationBetween tree--Given the low number of infected trees at the beginning of thestudy, th5 spread to uninfected trees was about what would have beenexpected.	 Overall, the increase in infected Douglas-fir was from 3.4 to 9.2percent of the total number of Douglas-fir in the study, not quite threefold.The increase in infected lodgepole pine was greater, 1.8 to 7.4 percent, orabout fourfold.For the study as a whole, the small number of infected trees both at the startand after 13 years helps explain the lack of growth impact, but on atree-by-tree analysis, this is not so. A 9 percent infection level can beequated to an average stand DMR of much less than 1 (Rawksworth 1977, 1978b).3Personal communication from F. G. Rawksworth.-8-• ••••n••••••• •••4Within tree--In the Douglas-fir plots, slightly more trees (14) showed anincrease in DMR than a decrease (10), but more (18) remained the same. In thelodgepole pine plots, however, fewer trees showed an increase (21) than thosethat showed a decrease (34). A like number (33) showed no change.With trees as young as the ones in the study, this tendency for DMR to remainthe same or decrease is not uncommon. The trees are growing rapidly, and they• are either keeping up with or actually outgrowing the dwarf mistletoe. Forexample, a tree with a DMR of 2 may have light infection in both the lower andmiddle thirds. If this tree puts on enough height growth between plot readingsto increase crown length enough that all infection is confined to the lowerthird, the tree then by definition has a DMR of 1. This can also happen with aheavy infection in the lower third and a light infection in the middle third (aDMR of 3). If the tree grows enough to where all the infection is confined tothe lower third, then the DMR is decreased from a 3 to a 2. Decreases of twoor more DMR classes occur, but most are probably caused by differences in theway the trees were rated by different persons in subsequent plot readings.These slow rates of spread and intensification of dwarf mistletoe in both• Douglas-fir and lodgepole pine are similar to those in red and white firs inCalifornia (Scharpf and Parmeter 1976).MortalityNone of the mortality in either species could be attributed to dwarf mistletoe.Some of the mortality in the Douglas-fir plots was caused by root disease(Armillaria ostgyae) (Romagn.) Herink, but more trees were missing than dead.Most of the missing trees were removed when a road was rebuilt through two ofthe plots; the remainder were apparently cut for Christmas trees.Most of the mortality in the lodgepole pine plots was caused by breakage,either from heavy snow or by the breakup of the old dead overstory trees thatwere girdled in 1971.RECOMMENDATIONSBased on the study so far, we make these recommendations:1. Continue the study. Some trends are developing in growth impact,spread, and intensification, but additional time is needed to elucidate overalleffects.2. Do no more pruning. This modifies the original study, but it willbetter define spread and intensification.• •••••411•••••••3. Continue the Douglas-fir measurement interval at 5 years (next readingin 1988). Growth impact should become more significant in another 5 years.4. Change the lodgepole pine measurement interval to 10 years (nextreading in 1994). No impact is yet evident, but probably will become so inanother 10 years.5. Continue with current management recommendations. DMR levels of 2 orless appear to be below the economic threshold. For precammercial standsrecommendations include:--Remove infested overstory trees by felling or girdling.--When precommercially thinning infested stands, leave only crop trees thatare uninfected or free of infections in the upper two-thirds of the crown (DMRof 2 or less).LITERATURE CITED Hawksworth, F. G.1977. The 6-class dwarf mistletoe rating system. USDA Forest Service,Gen. Tech. Rep. RM-48, 7 p.Hawksworth, F. G.1978a. Biological factors of dwarf mistletoe in relation to control. In:Dwarf mistletoe control through forest management. Symp. Proc., R. F.Scharpf and J. R. Parmeter, Jr., tech. coords. USDA Forest Service, Gen.Tech. Rep. PSW-31:5-15.Hawksworth, F. G.1978b. Intermediate cuttings in mistletoe-infested lodgepole pine andsouthwestern ponderosa pine stands. In: Dwarf mistletoe control throughforest management. Symp. Proc., R. F. Scharpf and J. R. Parmeter, Jr.,tech. coords. USDA Forest Service, Gen. Tech. Rep. PSW-31:86-92.Hawksworth, F. G., and D. Wiens.1972. Biology and classification of dwarf mistletoes (Arceuthobium). USDAForest Service, Agricultural Handbook No. 401, 234 p.Hunt, K.1971. A comparison of Kraft pulping of sound and dwarf mistletoe-infectedwestern hemlock wood. Can. Dep. Fish. and For., For. Products Lab.,Vancouver, BC. Inf. Rep. VP-X-78, 7 p.Korstian, C. F., and W. R. Long.1922. The western yellow pine mistletoe: effect on growth and suggestionsfor control. USDA Bull. 1112, 35 p.Munns, E. N.1919. Effect of fertilization on the seed of Jeffrey pine. Plant World	 •22:138-144.411-10-	 •Piirto, D. D., D. L. Crews, and H. E. Troxell.1974. The effects of dwarf mistletoes on the wood properties of lodgepolepine. Wood and Fiber 6:26-35.Scharpf, R. F., and J. R. Parmeter, Jr.1976. Population buildup and vertical spread of dwarf mistletoe on youngred and white firs in California. USDA Forest Service, Research Paper•	 PSW-122, 9 p.Wicker, E. F.1978. Refinement and quantification of data for regulating dwarf mistletoepopulations: an ecosystems approach. In: Dwarf mistletoe control throughforest management. Symp. Proc., R. F. Scharpf and J. R. Parmeter, Jr.,•	 tech. coords. USDA Forest Service, Gen. Tech. Rep. PSW-31:137-142.Wykoff, W. R., N. L. Crookston, and A. R. Stage.1982. User's guide to the Stand Prognosis Model. USDA Forest Service,Gen. Tech. Rep. INT-133, 112 p.•••

Growth impact, spread, and intensification of dwarf mistletoe in Douglas-fir and lodgepole pine in Montana

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Growth impact, spread, and intensification of dwarf mistletoe in Douglas-fir and lodgepole pine in Montana

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