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Home , Taxus, Taxus brevifolia

Responseof Pacific Yew ( brevifolia) to Partial Removal of the Overstory

J.D. Bailey, Schoolof Forestry, Northern Arizona University,Flagstaff, AZ 86011-5018, and L.H. Liegel, USDA Forest Service,Pacific NorthwestResearch Station, Corvallis, OR 97331. Downloaded from https://academic.oup.com/wjaf/article/12/2/41/4741186 by guest on 29 September 2021

ABSTRACT. Growthresponse of Pacificyew (Taxusbrevifolia) to canopydisturbance or partial removal is undocumented.Ten year radial incrementgrowth was determined from coresof yewstems in adjacentintact andpartially harvestedstands of Douglas-(Pseudotsuga menziesii) in the centralOregon Cascades. The harvestedstand had approximately half of itsoverstory removed in 1978.In theintact stand, 10 yr growth incrementafter 1978 averaged 0.9 mmless than the pre-1978 increment; in thepartially harvested stand, the post-1978! 0 yr incrementaveraged4.7 mm more than the earlier one. This case study in theresponse of Pacific yew growthrate to partial overstoryremoval suggests that managerscan preferentially retain thesetrees in selectareas to encourageoMer forest characteristicsor suppliesfor medicinalproducts. West. J. Appl.For. 12(2):41-43.

Pacificyew () isa taxad (member of young and old stands. family ) occurring from southeastAlaska to Full or partial removal of forest overstoryvegetation northern as well as in interior areas of , typically stimulatesgrowth of understoryshrubs and Montana, and British Columbia. In the early 1990s, bark (Smith 1986). However, the magnitudeof that harvestedfrom natural standsof yew was the sole source responseremains undocumentedfor Pacific yew trees, of taxol, a drug successfullyused to treat severalforms of which are extremely slow growing. Minore et al. (1993) cancer tumors (Wani et al. 1971, Rowinsky et al. 1990). identified canopydensity as an importantfactor affecting Before nonbark sources of taxol were found, environmen- the responseof yew growth to scarring. The increased talists were concernedthat increasingharvest of yew bark radial growth in responseto overstory removal may in- from old-growth standswould decreasegenetic and bio- creasethe supplyof yew bark for taxol productionbecause logical diversity for Pacific yew. The USDA Forest Ser- of the development of larger stems and thicker bark, as vice (1992) therefore issued interim management guide- demonstratedby Kelsey and Vance (1992). Partial over- hnes to conservethe regional yew resourceand initiated storyremoval would rarely be justified as an independent studies on ecology and population dynamics of Pacific silviculturaloperation specifically for yew, but increased yew (Busing and Spies 1995, Bailey and Liegel, in prep.). yew growth would be an interestingsecondary benefit of Being extremely shade-tolerant,Pacific yew typically any forestoperation that reducesoverstory density. In this grows under an overstory of large trees in older forests study,we comparedthe effect of releaseon radial growth (Minore 1979, Bolsingerand Jaramillo 1990). Spies(1991) of yew trees in an intact control stand and an adjacent reported that most Pacific yew in unmanaged federal partially harvestedstand. forestsgrew in stands->195 yr old, and hence they can be considered one of the few consistent "indicators" of old- Methods and Materials growth stands of Douglas-fir (Pseudotsugamenziesii). However, Zaerr et al. (1990) viewed yew occurrence Studyplots were locatedin two Douglas-fir dominated stands near Santiam Pass in the central Cascade Mountains simply as the result of episodicdisturbances that occurin (Willamette National Forest) at 975 m (3200 ft) elevation. Stands were adjacent to one another on a west-facing NOTE: This is Paper3149 of theForest Research Laboratory, Oregon State hillside with a 25 % slope.The intact standwas 5 ha (13 ac) University,Corvallis. and the harvested stand, which had been partially har-

WJAF12(2) 1997 41 vested in 1978, was ! I ha (28 ac). A 2 ha (5 ac) plot was Intactold-growth stand: establishedin each standfor use in mappingthe location of individual ye• stems>7.5 cm (3 in.) dbh via a !lIIIqc tally along a grid (Bailey and Liegel. in prep.}. Plots were establishedwith a randomly located corner referencedto a predeterminedstand entry point: plots were orientedto stay 75 m from any standedge. This effort produceda yew stem diameter distribution for each stand that was used to Partially~harvestedstand: stratify individual tree sampling.Within the grid. we also established four 0.05 ha circular plots to characterize overstoryand understoryvegetation and soils (Table I ). We then measured 22 (intact stand) and 23 (harvested stand)randomly selectedyew trees representativeof the stands' diameter distributions. For each tree. we collected Downloaded from https://academic.oup.com/wjaf/article/12/2/41/4741186 by guest on 29 September 2021 incrementcores from just above the stemcollar in each of the four cardinal directions(Figure ! }. Cores were stored in paperstraws and later mountedand sanded according to proceduresadapted from Swetnamet al (1985). Ten year Figure 1. Increment cores extracted from Pacific yew trees in an growth incrementsfor the periods 1967-1977 and 1982- intact old-growth stand of Douglas-fir and a stand partially 1992 were determinedfrom eachcore by usinga binocular harvested in 1978. Note incremental growth increases in the latter. Marks indicate 1978 annual rings. microscopeand ruler (+0.2 mm). We avoided the years immediatelyfollowing 1978 to allow for developmentol Results the responseand error in aging cores. Data entry was verified and validated b3 a 100ck recheck of recorded Our assumptionthat these standswere originally simi- increments. lar in terms of yeu distribution and growth appearscor- We analyzed the data for differences in incremental rect. Ten year radial tncrementsfor the period 1967-1977 growth before and after 1978 in both standsby using a are not significantlydifferent (P = 0.74) for the two stands standardt-test at the tree andplot level (SAS Institute.Inc. (Table I. Figure I ), and yew trees do not currently have 1988). Comparisonsat the tree level are basedon up to 4 significantly different age. height. crown, or diameter cores per tree; at the plot level, 70 and 84 cores per plot. distributions(P > 0.2). Soils and understoryvegetation blocked by tree, were analyzed from the intact and har- were similar, although the intact stand had greater herb vestedstands, respectively. densities.litter accumulations.and apparentsoil moisture Table 1. Mean stand and yew tree characteristics (1992) in the that year (Bailey and Liegel, in prep.). intact Douglas-fir stand partially harvested in 1978 in the central Yeu trees are currently growing. however, under sig- Oregon Cascades. Canopy density and total tree density and nificantly different overstories(Table ! }. The intact stand basal area are based on n = 4. Yew density and basal area are based on a 100% tally. Yew tree variables and growth increments averages70ok canopy coverage of large Douglas-fir. west- are based on n = 22 for intact stands and n = 23 for harvested ern hemlock (Tsttga heterophylla), and western redcedar stands. (Tltuja plicata). The harvested stand includes the same species, but averages only 34c/c canop5 closure: both Intact Harvested standshave scatteredwindthrow. Pacific yew was inten- Stand variables tionally preserved in the harvestedstand, although it was Canopydensity (%) 70"o 34% sometimes damaged by logging activity; this perhaps Totaltrees per hectare (per ac) 85 (210) 38 (93) explainsa slight reductionin density,basal area, and total Yew n'eesper hectare(per ac) 19 (47) 12 (29) height of yew (Table ! ). TotalYews: basalpercent area (m of 2/ha} total(ft stems 2/ac} 12522%(308} 31øo85 (209) The direction of changein 10 yr incrementsbefore and alter 1978 differed between the two stands. In the intact Yew basalarea {m -'ha} (ft -'/ac} 2.1 {91 1.4 •6) Yews:percent of totalbasal area 3% 3% stand. the 1982-1992 growth incrementis significantly Yew tree x ariables less (0.9 ram: P = 0.07) than that for 1967- ! 977 (Table I ). Numberof yexx,s measured This pattern is consistentwith growth processesin which intensivelyIn) 22 23 a steady fiber volume is accrued on an increasing bole Mean yew age(yr) 138 133 diameter over time. At the individual tree level, 3 of 22 Mean yew dbh(cm) 15.0 15.0 Mean yew total height(m} 6.2 5.3 yew trees show a significant growth decrease(P _<0.10) Mean yew crownwidth (m) 2.2 2.3 after 1978. The remainder of the trees show no significant Yew growthincrements change in radial growth rate. I 0 yr growth 1967-1977 (mm) 7. I 7.9 In contrast. the postharvest 10 yr increment in the l0 yr growth 1982 1992(ram} 6.0 12.6 harvestedstand is significantly greater14.7 ram; P < (1.01) DiffErenceafter 1978 harxest (mm) 0.9 *4.7 P-value,testing difference from 0 0.07 <0.01 than that prior to harvest. A strong growth release fol- lowed partial overstory removal in this stand. At the

42 WJAF 12(2) 1997 individual-treelevel, 10 of 23 yew treesshow a stgmflcant clearcuts)as possibleor desiredm a particularlandscape. increasein incrementalgrowth (P _<0.10) following har- Suchretention and accelerated growth will aid the recovery vest, 11 shownonsignificant differences, and 2 individu- of yew treepopulations in PacificNorthwest forests. als show a significantdecrease. These latter individuals arenot particularlyold or young,large or small,or located Literature Cited under a denserpart of the stand. BAILEY,J.D., ANDL. LIEGEL.Pacific yew (Taxusbrevijblia Nutt.) growthand Discussion sitefactors in westernOregon. (In prep.). BOLSiNGER,C.L., ANDA. JARAMILLO.1990. Taxus brevtfolia Nutt. Pacificyew. Partial removal of an overstory canopy at this site P. 573-579 in Silvics of . Vol. 1. . Bums, R.M., andB.H. Honkala (tech.coords.). USDA For. Serv. Agric. Handb.654. causeda strongresponse in incrementalgrowth of yew. BUSING,R.T., ANDT.A. SPinS.1995. Modeling the populationdynamics of Indeed, this analysis was prompted by the striking in- Pacificyew. USDA For. Serv.Res. Note PNW-RN-515. 13 p. creasein incrementalgrowth found in most cores taken KELSE¾,R.G., ANDN.C. VANCE.1992. Taxol andcephalomannine concentra- tionsin the foliageand bark of shade-grownand sun-exposedTaxus from the harvested plot for another study. This work brevifoliatrees. J. Nat. Prod.55:912-917. confirms that yew, like most shade-tolerantunderstory MINORE,D. 1979.Comparative autecological characteristics of northwestern Downloaded from https://academic.oup.com/wjaf/article/12/2/41/4741186 by guest on 29 September 2021 trees, can respondto partial canopy removal. tree species--aliterature review. USDA For. Serv. Gen. Tech. Rep. PNW-87.72 p. This increasedincremental growth is important given MINORE,D., S. MITCHELL,JR., B. O'RIORDAN,AND H.G. WEATHERLY.1993. the potential for any new demandfor yew bark for medici- Effectsof partialbark removalon the growthof Pacificyew (Taxus nal products. However, our ability to boost natural taxol brevifoliaNutt0. Unpublished. ROWlNSKY.E.K., L.A. C^ZENAVE,^NO R.C. DONEHOWER.1990. Taxol: A novel productionis uncertain.Kelsey and Vance (1992) demon- investigationalantimicrotubule agent. J. Nat. Cancer Inst. 82:1247-1259. stratedthat yew trees growing in full sun following total SAS INSTITUTE,INC. 1988. SAS/STAT user'sguide, release 6.03 ed. SAS canopyremoval had 60% thicker bark than shade-grown INSTITUTE,INC., Cmy, NC. 1028p. SMITH,D.M. 1986. The practiceof silviculture.Ed. 8. Wiley, New York. yews; however, sun-grown tree bark had a 45% lower 527 p. concentrationof taxol. If the effects of partial canopy SPIES,T.A. 1991. species diversity and occurrence in young,mature, and removal are assumed to be intermediate to those of full old-growthDouglas-fir stands in western Oregon and Washington. P. 111- 121in Wildlife and vegetation ofunmanaged Douglas-fir forests. Ruggiero, removal,then increasingstem diameters would producea L.F., et al. (coords.).USDA For. Serv.Gen. Tech. Rep. PNW-285. net gain in taxol yield. However, further study of bark SWETNAM,T.W., M.A. THOMPSON,AND E.K. SUTHERLAND. 1985. Using dendro- thickness and taxol concentrations at various levels of chronologyto measureradial growthof defoliatedtrees. USDA For. Serv., Coop. StateRes. Serv., Agric. Handb.639. 39 p. canopy removal would be neededto confirm this projec- USDA FORESTSERVICE. 1992. An interim guide to the conservationand tion. managementof Pacific yew. Tech. Rep. Pac. NorthwestRes. Stn., The growth responseof Pacific yew is also important Portland,OR. 72 p. WANI,M.C., H.L. TAYLOR,AND M.E. WALt..1971. Plant antitumor agents. V1. given concernsfor yew populationstability over time, and The isolation and structureof taxol, a novel antileukemic and antitumor society'spreference for usingalternatives to clearcuttingfor agentfrom Taxusbrevlfolia. J. Am. Chem.Soc. 93:2325-2327. supplyingwood fiber. Knowing that Pacific yew survives ZAERR,J.B., D. MINORE,M.A. RADWAN,AND C. BOLSINGER.1990. Factors relatedto taxolcontent ofTaxus brevil'blia. Unpublished paper and grant andactually responds to canopyrelease, land managerscan submittedto the NationalCancer Institute, Washington, D.C. Collegeof justify retainingas much of it in harvestunits (including Forestry,Oregon State University, Corvallis, OR. 34 p.

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