Authors DON MINORE was a plant ecologist (now retired) and HOWARD G. WEATHERLY

is a forestry technician, Forestry Sciences Laboratory, 3200 S.W. Jefferson Way,

Corvallis, OR 97331.
Abstract Minore, Don; Weatherly, Howard G. 1996. Stump sprouting of Pacific yew. Gen.

Tech. Rep. PNW-GTR-378. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station. 6 p.

Large numbers of Pacific yew (Taxus brevifolia Nutt.) trees have been cut to supply

bark for taxol production, and replacement of those trees may depend on their ability

to sprout from the stump. Stump characteristics were related to the initiation and

survival of epicormic branches (sprouts) on 100 yew stumps in each of 11 recently

harvested stands during 1992. Half of the stumps were artificially shaded, and all

were remeasured in 1993. The number of living stumps in each stand was positively

correlated with average stump height and average percentage of bark retained.

Postharvest sprouting was most abundant on stumps with established sprouts or live

branches. For individual stumps, the number and length of preharvest sprouts were

the only variables consistently related to number of postharvest sprouts. Artificial

shading did not promote sprouting.

Keywords: Regeneration, growth, survival, height, bark, Taxus brevifolia.
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Introduction Pacific yew (Taxus brevifolia Nutt.) often sprouts from the stump after the crown

has been killed or cut (Bolsinger and Jaramillo 1990). Those stump sprouts may

survive and grow in the shaded understories of undisturbed stands, and they may

be a critical element in the preservation of yew gene pools when overstory removal

or other major disturbance damages or destroys existing yew crowns. Stump sprouts

also may be an important source of winter food for browsing ungulates and other

animals.

Stump sprouting is particularly important now that large numbers of mature yew

trees have been cut to supply the bark needed for taxol production. Maintenance of

Pacific yew in harvested stands, preservation of local gene pools, and a continuing

supply of browse may depend on the ability of this species to sprout from the stump.

Sprouting from the stump is common in several other tree species, where it tends

to increase with stump height and decrease with stump age (Dutt and Urmila 1987,

Johansson 1987, Khan and Tripathi 1986). Successful sprouting often declines with

increasing stump diameter (Johannson 1992, Khan and Tripathi 1986, Neal 1967),

and small-diameter stumps of Pacific yew in Idaho were observed to sprout more

successfully than larger stumps.1 Nevertheless, Cabanettes and Pagès (1992) found

that large stump diameters benefit the height growth of stump sprouts in chestnut

(Castanea sativa Miller). Sprouting sometimes declines with stump age (Kauppi and

others 1988, Lynch and Bassett 1987, Neal 1967), It also declines with shading in

some species (Finney 1993; Johansson 1987, 1991), but the partial shade afforded

by an overstory canopy has been thought to favor adventitious bud development

and sprout survival on yew stumps (USDA Forest Service 1992).

The prevalence of successful stump sprouting in Pacific yew and the factors that

affect rates of success are unknown. Our study was designed to provide that information by relating environmental factors and stump characteristics to the percentage

of live stumps in harvested areas, to the number of sprouts per stump in those areas,

and to the effects of shading on sprout survival and growth.

Methods Sale areas where at least 100 yew stumps had been cut during a short time were

located and examined in the Rogue River and Willamette National Forests of western Oregon. Cutting dates differed among the sale areas. At each area, 100 eligible

stumps were numbered, measured, and mapped as they were encountered. Eligible

stumps retained at least 50 percent of their bark. They were located and first measured in 1992, then relocated and remeasured 1 year later, in 1993. The following

variables were measured at each stump:

• Stump height (cm)

• Stump diameter (cm)

• Stump age (age of tree at time of cutting)

• Bark retained (percent)

1 Green, Pat; Ward, Roger. 1991. Yew sprout assessment, Nez

Perce National Forest, Idaho. 1 p. Unpublished report. On file

with: Yew Technical Committee, USDA Forest Service, Pacific

Northwest Region, P.O. Box 3623, Portland, OR 97230.

1
• Number of preharvest sprouts

• Number of postharvest sprouts

• Length of longest preharvest sprout (cm)

• Length of longest postharvest sprout (cm)

• Total overstory canopy density (percent)

• Radiation index

• Soil moisture (percent) at 0 to 30 centimeters

Preharvest sprouts were distinguished from postharvest sprouts by counting internodes—a method confirmed through the presence of tree-marking paint on some

preharvest sprouts. Canopy density was measured at each stump with a spherical

densiometer (Lemmon 1957). Radiation index is a measure of potential solar insolation derived from slope, aspect, and the tables of Frank and Lee (1966). Soil moisture was measured on the north side of each stump by time domain reflectometry

(Topp and Davis 1985). Half of the eligible stumps in every sale area were randomly

chosen and artificially shaded by piling bark, slash, and other readily available debris

against their south and west sides.

Averaged sale-area variables (stump height, percent bark retained, and overstory

canopy density) were related to the number of stumps that survived in those sale

areas with a stepwise multiple regression (n = the number of sale areas, α = 0.01).

Individual stump variables (height, diameter, age, percent bark retained, overstory

canopy density, soil moisture, number of preharvest sprouts, and length of preharvest sprouts) were related to the number of postharvest sprouts on those stumps in

separate regressions for each sale area (n = 100, α = 0.05). The effects of artificial

shading were examined in analyses of variance that included all the sale areas as

experimental blocks.

Results Eleven sale areas (1,100 stumps) were measured in 1992 and remeasured in 1993.

Harvest dates ranged from June 1991 through July 1992, but stump sprouting was

not correlated with season or year of cutting. Sprouting was erratic, and the number

of postharvest sprouts per stump ranged from 0 to over 500. Those sprouts developed on the sides of the stump and not on the root collar. Sixty-seven percent (739)

of the stumps were alive (had living preharvest or postharvest sprouts) in 1993, but

only 28 percent (311) of the 1,100 stumps measured had living postharvest sprouts.

Stump survival in the individual sale areas ranged from 13 to 94 percent (table 1)

and was significantly (P < 0.01) related to the average stump heights and average

percentages of bark retained in those sale areas:

Live stumps (percent) = 0.90(stump height) + 2.33(percent bark) – 163.98 ,

where

R2 = 0.93,

Syx = 8.23, and

n = 11.

2
The number of postharvest sprouts on any given stump usually was related to the

number and length of preharvest sprouts on that stump, but other within-sale

variables were not consistently related to sprout abundance (table 2). Artificial

shading did not benefit sprout development or survival, but shading did increase

the length of postharvest sprouts (table 3).

Discussion and

Conclusions

Widely differing numbers of sprouts tended to obscure the correlation of stump characteristics or environmental factors with sprout production on individual stumps in a

sale area. The stumps within a given sale area differed in size, age, bark retained,

and overstory canopy density; and the number of sprouts occurring on those stumps

often ranged from zero to several hundred. We tried to record all the measurable

variables present after yew harvest and hoped to find environmental variables

associated with this enormous variation in number of sprouts. That attempt failed.

Unmeasured, preharvest factors (for example, stump gender or genotype) may be

responsible for the number and length of preharvest sprouts, and those preharvest

sprouts are the best indicators of postharvest sprout abundance. They may provide

the photosynthesis needed to maintain a stump in vigorous sprouting condition.

Alternatively, the presence of preharvest sprouts may be just an indication of tree

vigor and the ability to sprout.

Shading stumps by piling slash, bark, and debris against their south and west sides

did not benefit the initiation and survival of sprouts. Indeed, the physical damage

associated with occasional collapse of the piled material may have been detrimental

to existing sprouts. Surviving sprouts tended to become longer when shaded in this

way, however, and that additional growth may be important in the future.

Table 1—Sale area characteristics and variables

Sale

area Elevation

Radiation

indexa Cuttingdate

Average

stump

heightb

Average

stump

diameterb

Average

stump

ageb

Average

bark

retainedb

Average

canopy

densityb

Live

stumps

in 1993c

Meters – – Centimeters – – Years ––––– Percent–––––

A 750 0.42 5/92 30.0 18.6 120 81 31 68

B 1375 .44 7/92 49.8 33.0 151 91 63 94

C 1125 .41 6/92 43.3 13.0 106 92 33 90

D 1200 .42 4/92 40.1 18.2 158 96 90 93

E 875 .46 5/91 15.1 21.1 145 88 84 46

F 1425 .48 5/91 22.9 29.1 143 72 16 19

G 975 .41 10/91 18.5 29.1 179 70 85 13

H 975 .35 7/91 36.0 12.6 91 87 44 80

I 1375 .47 7/91 43.6 43.8 248 88 55 75

J 1450 .48 6/91 66.9 23.4 141 85 27 88

K 1375 .47 6/91 43.3 27.5 170 84 43 74

a A measure of potential solar insolation derived from slope, aspect, and the tables of Frank and Lee (1966). b Based on 100 measurements in a given sale area. c Stumps having at least 1 live sprout in 1993.

3
Pacific yew tends to grow in the understory, and exposure tends to dry out both

stumps and sprouts, so the absence of any correlation of sprouting with overstory

canopy was surprising. Although postharvest canopy densities ranged from 0 to

97 percent, the shade provided by overstory trees did not significantly affect sprout

initiation, sprout growth, or stump survival. Preharvest canopy densities may have

been important influences on the development of preharvest sprouts, however, and

overstory canopy should not be completely discounted as a factor in the sprouting

of yew stumps.

The number of stumps that retained or developed sprouts, and thus remained alive

in 1993 in any given sale area, was positively related to average stump height and

average percentage of residual bark. That relation is logical, because those two

factors also tend to be associated with the presence and survival of existing preharvest sprouts, and stumps with preharvest sprouts tend to be more vigorous than

stumps without them.

Tall yew stumps and stumps with intact bark have a better chance of sprouting and

surviving for 2 years than short stumps or stumps with damaged bark. Similar 2-year

results for the survival of birch (Betula pendula Roth) stumps were also true after

5 years (Johansson 1992), even when many sprouts died on the tallest stumps

(Kvaalen 1989). Future harvesting of Pacific yew probably should employ maximal

stump height and minimal stump-bark removal when sprouting is to be maximized.

Stump sprouting of Pacific yew is erratic, however, and it should not be relied on

to regenerate harvested yew trees or stands.

Table 2—Correlationsa of postharvest sprout abundanceb with other local variables, by sale area

Sale

area

Stump

height

Stump

diameter

Stump

age

Bark

retained

Overstory

canopy

Soil

moisture

Number of

preharvest

sprouts

Length of

longest

preharvest

sprout

A 0.222 0.274 0.255

B .588

C 0.276 .648 .263

D -0.271 .396

E 0.242 .673 .352

F .286 .406

G -0.245 .216

H .351 .731 .255

I .632 .520

J .432

K .376 .275

a Significant (P < 0.05) correlation coefficients. b Log10(number of postharvest sprouts alive in 1993).

4
Acknowledgments Financial support for this work was provided by the Bristol-Myers Squibb Company,

which provided funds to the USDA Forest Service for conservation biology research

on Pacific yew.

Literature Cited Bolsinger, Charles L.; Jaramillo, Annabelle E. 1990. Taxus brevifolia Nutt. Pacific

yew. In: Burns, R.M.; Honkala, B.H., coords. Silvics of North America. Volume 1:

Conifers. [Place of publication unknown]: U.S. Department of Agriculture, Forest

Service: 573-579.

Cabanettes, Alain; Pagès, Loïc. 1992. Effet des techniques de coupe et des

variations du milieu sur la croissance en hauteur des cépées dans un taillis

de châtaignier (Castanea sativa). Canadian Journal of Forest Research.

22: 1694-1700.

Dutt, A.K.; Urmila, J. 1987. Effects of coppicing at different heights on wood

production in leucaena. Leucaena Research Reports. 8: 27-28.

Finney, Mark A. 1993. Effects of thermal wounding, shading and exogenous auxin

on some sprouting responses of coast redwood seedlings. Tree Physiology.

12: 301-309.

Frank, Ernest C.; Lee, Richard. 1966. Potential solar beam irradiation on slopes:

tables for 30o to 50o latitude. Res. Pap. RM-18. [Fort Collins, CO]: U.S. Department of Agriculture, Forest Service, [Rocky Mountain Forest and Range Experiment Station]. 116 p.

Table 3—Effects of artificial shadinga on mean development, survival, and

growth of stump sproutsb

Stump

treatment

Number of living

sprouts/stump in

1992c

Number of living

sprouts/stump

in 1993d Live stumps

in 1993

Length of

longest

postharvest

sprout in 1993

Percent Centimeters

Shadede 14.2a 18.0a 67.6a 7.2a

Unshadede 14.2a 24.2a 67.1a 5.8b

Standard errorf 4.2 6.9 5.9 1.0

a The piling of slash and bark against the south and west sides of shaded stumps. b Means in the same column that are followed by the same letter are not significantly different (P < 0.05). c At time of shading. d 1 year after shading. e N = 11 sale means. The mean for each sale was based on 50 stumps. f Standard error of the mean.

5
Johansson, Tord. 1987. Development of stump suckers by Betula pubescens at

different light intensities. Scandinavian Journal of Forest Research. 2: 77-83.

Johannsson, Tord. 1991. Sprouting ability of two-year-old Betula pendula stumps

exposed to different light intensities during five years. Scandinavian Journal of

Forest Research. 6: 509-518.

Johannsson, Tord. 1992. Sprouting of 2- to 5-year-old birches (Betula pubescens

Ehrh. and Betula pendula Roth) in relation to stump height and felling time. Forest

Ecology and Management. 53: 263-281.

Kauppi, Anneli; Rinne, Päivi; Ferm, Ari. 1988. Sprouting ability and significance

for coppicing of dormant buds on Betula pubescens Ehrh. stumps. Scandinavian

Journal of Forest Research. 3: 343-354.

Khan, M.L.; Tripathi, R.S. 1986. Tree regeneration in a disturbed sub-tropical wet

hill forest of north-east India: effect of stump diameter and height on sprouting of

four tree species. Forest Ecology and Management. 17: 2-3, 199-209.

Kvaalen, H. 1989. Virkning av forskjellig stubbehøyde på skuddskyting,

stubbeoverlevelse og vekst av stubbeskudd etter host av seks år gammel

hengebjørk (Betula pendula Roth). Rapport 5. [Place of publication unknown]:

Norsk Institutt Skogforskning. 11 p. [Forestry Abstracts 1990:V 51-1281].

Lemmon, Paul E. 1957. A new instrument for measuring forest overstory density.

Journal of Forestry. 55: 667-669.

Lynch, Ann M.; Bassett, John R. 1987. Oak stump sprouting on dry sites in

northern lower Michigan. Northern Journal of Applied Forestry. 4: 142-145.

Neal, Robert L., Jr. 1967. Sprouting of old-growth redwood stumps...first year after

logging. Res. Note PSW-137. [Berkeley, CA]: U.S. Department of Agriculture,

Forest Service, [Pacific Southwest Forest and Range Experiment Station]. 8 p.

Topp, G.C.; Davis, J.L. 1985. Measurement of soil water content using time-domain

reflectometry (TDR): a field evaluation. Soil Science Society of America Journal.

49: 19-24.

U.S. Department of Agriculture, Forest Service. 1992. An interim guide to the

conservation and management of Pacific yew. Portland, OR: Pacific Northwest

Region. 72 p.

6
Minore, Don; Weatherly, Howard G. 1996. Stump sprouting of Pacific yew. Gen.

Tech. Rep. PNW-GTR-378. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station. 6 p.

Large numbers of Pacific yew (Taxus brevifolia Nutt.) trees have been cut to supply

bark for taxol production, and replacement of those trees may depend on their ability

to sprout from the stump. Stump characteristics were related to the initiation and

survival of epicormic branches (sprouts) on 100 yew stumps in each of 11 recently

harvested stands during 1992. Half of the stumps were artificially shaded, and all were

remeasured in 1993. The number of living stumps in each stand was positively

correlated with average stump height and average percentage of bark retained.

Postharvest sprouting was most abundant on stumps with established sprouts or live

branches. For individual stumps, the number and length of preharvest sprouts were

the only variables consistently related to number of postharvest sprouts. Artificial

shading did not promote sprouting.

Keywords: Regeneration, growth, survival, height, bark, Taxus brevifolia.

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