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Wildlife, Animals, and Plants
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Introductory
SPECIES: Taxus brevifolia | Pacific Yew
ABBREVIATION :
TAXBRE
SYNONYMS :
Taxus baccata var. brevifolia
Taxus baccata ssp. brevifolia
Taxus boursieri
Taxus lindleyana
SCS PLANT CODE :
TABR2
COMMON NAMES :
Pacific yew
western yew
yew brush
yew
mountain mahogany
TAXONOMY :
The currently accepted scientific name of Pacific yew is Taxus
brevifolia Nutt. [36]. Pacific yew is a member of the family Taxaceae
[29].
LIFE FORM :
Tree, Shrub
FEDERAL LEGAL STATUS :
No special status
OTHER STATUS :
NO-ENTRY
COMPILED BY AND DATE :
D. Tirmenstein December, 1990.
LAST REVISED BY AND DATE :
NO-ENTRY
AUTHORSHIP AND CITATION :
Tirmenstein, D. A. 1990. Taxus brevifolia. In: Remainder of Citation
DISTRIBUTION AND OCCURRENCE
SPECIES: Taxus brevifolia | Pacific Yew
GENERAL DISTRIBUTION :
Pacific yew grows along the Pacific Coast of southeastern Alaska
southward through western British Columbia to central California
[46,55]. In the Rocky Mountain region, it occurs from southeastern
British Columbia through northwestern Montana and northern Idaho into
eastern Washington and Oregon [46].
Dense stands of shrubby Pacific yew dominate approximately 40,000 acres
(16,000 ha) in the South Fork of the Clearwater Drainage of
north-central Idaho [14]. This plant has been essentially eliminated
from another 9,880 acres (4,000 ha) by timber harvest [14].
ECOSYSTEMS :
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir - spruce
FRES24 Hemlock - Sitka spruce
FRES25 Larch
FRES27 Redwood
STATES :
AK CA ID MT OR WA BC
ADMINISTRATIVE UNITS :
CODA CRLA GLAC LAVO MORA NOCA
OLYM PORE REDW SAJH WHIS YOSE
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
4 Sierra Mountains
8 Northern Rocky Mountains
KUCHLER PLANT ASSOCIATIONS :
K001 Spruce - cedar - hemlock forest
K002 Cedar - hemlock - Douglas-fir forest
K003 Silver fir - Douglas-fir forest
K005 Mixed conifer forest
K006 Redwood forest
K007 Red fir forest
K012 Douglas-fir forest
K013 Cedar - hemlock - pine forest
K014 Grand fir - Douglas-fir forest
K015 Western spruce - fir forest
K029 California mixed evergreen forest
SAF COVER TYPES :
206 Engelmann spruce - subalpine fir
207 Red fir
211 White fir
212 Western larch
213 Grand fir
215 Western white pine
SRM (RANGELAND) COVER TYPES :
NO-ENTRY
HABITAT TYPES AND PLANT COMMUNITIES :
Pacific yew grows as an understory dominant or codominant in a number of
coniferous forests of the Pacific Northwest and northern Rocky
Mountains. Overstory dominants include grand fir (Abies grandis), white
fir (Abies concolor), and western hemlock (Tsuga heterophylla). Vine
maple (Acer circinatum), queencup beadlily (Clintonia uniflora), and
wild ginger (Asarum caudatum) are common codominants. In parts of
northern Idaho, Pacific yew grows as a climax dominant which forms a
nearly contiguous shrublike overstory. It is listed as an indicator or
dominant in the following habitat type (hts), community type (cts), and
plant association (pas) classification schemes:
Area Classification Authority
CA mixed evergreen cts Sawyer and others 1977
CA, OR: Siskiyou Mtn. forest pas Atzet and Wheeler 1984
Province
CA, OR: e Siskiyous forest cts Waring 1969
n ID forest cts, hts Cooper and others 1987
OR: Abott Creek RNA forest cts Mitchell and Moir 1976
s OR: Cascade Mtns. forest pas Atzet and McCrimmon 1990
OR, ID: Wallowa- general veg. pas Johnson and Simon 1987
Whitman NF
n Rocky Mountains Pacific yew cts Crawford and Johnson 1985
VALUE AND USE
SPECIES: Taxus brevifolia | Pacific Yew
WOOD PRODUCTS VALUE :
The nonresinous wood of Pacific yew is fine grained, heavy, hard, and
very strong [5,32,55,62]. It is elastic but very durable, and resists
decay [5,32]. The sapwood is light yellow and thin, and the heartwood
is bright orange or rose red [5]. The wood responds well to finishing
and turns well on lathes [5,30]. This attractive wood has been used to
make canoe paddles, tool handles, poles, and fence posts [32,62]. It is
sometimes used in carving, cabinet-making, and for turned articles
[5,65] but has little or no commercial importance [30,32].
Native Americans traditionally used Pacific yew for constructing
harpoons, spear handles, eating utensils, wedges, paddles, and clubs
used in battle and for hunting seals [5]. Pacific yew is renowned for
its value in making bows and was formerly referred to as "bow plant" by
the Salish people [75]. Bows made from Pacific yew tended to be broad,
short, and flat [80]. Pacific yew is still used to craft some of the
finest archery bows. The best bows are made from wood which has been
cured for several decades [5] and are, not surprisingly, quite costly.
IMPORTANCE TO LIVESTOCK AND WILDLIFE :
Pacific yew provides important food and cover for many wildlife species
[34,68]. Old-growth grand fir/Pacific yew forests are often considered
critical moose winter habitat [61].
Browse: Many wild ungulates feed on Pacific yew including deer, elk,
and moose [14,21,49]. In parts of northern Idaho, it is a preferred
winter moose browse [14]. Although Pacific yew browse may be eaten
during all seasons, use is particularly heavy in fall, winter, and
spring [14,60,61]. In winter, moose eat available forage and bark which
they strip from trees [14]. Plants may be severely hedged in some areas
[60]. Use is typically greatest when other forage is buried by snow
[60]. Moose utilization by season has been documented as follows [60]:
percent aggregate use
May - July 3
July- September 0
October - November 42
December - April 41
In a winter study at a Connecticut nursery, as much as 77.1 percent of
all Pacific yew shoots were browsed by white-tailed deer [12]. Rabbits
and other small herbivores may also browse Pacific yew in many areas
[21].
Pacific yew is reportedly toxic to domestic livestock [65,77], but
conclusive evidence of toxicity is lacking [15,37]. The closely related
English yew (Taxus baccata) is poisonous to cattle, horses, sheep,
rabbits, and man [66]. Some researchers report that Pacific yew is
similarly toxic, particularly when cut, piled, and allowed to rot [32].
However, in many areas livestock appear to browse branches "with
impunity" [70]. Livestock use is generally limited to the winter months
or periods of food scarcity [15].
Fruit: Fruit of Pacific yew is sweet but reportedly poisonous to some
species [70]. It is readily eaten by many species of songbirds
including the Townsend's solitaire, varied thrush, and hermit thrush
[34]. The ring-tailed cat also feeds on the fruit of Pacific yew [77].
Foraging sites: Pacific yew snags may be used by foraging woodpeckers
[48].
PALATABILITY :
Foliage of Pacific yew is at least somewhat palatable to many large
ungulates and is highly palatable to moose, particularly during the fall
and winter [14,60]. Fruit is highly palatable to many species of small
birds and mammals [5,77].
NUTRITIONAL VALUE :
NO-ENTRY
COVER VALUE :
Pacific yew commonly forms a dense subcanopy which provides excellent
hiding and thermal cover for large ungulates and other wildlife species
[34,68]. On riparian sites, it provides shade which maintains cool
water temperatures for salmonids and other anadromous fish [68].
VALUE FOR REHABILITATION OF DISTURBED SITES :
Potential rehabilitation value of Pacific yew is unknown. However,
plants can be easily propagated from cuttings [5,42] or seed [65].
Cleaned seed averages approximately 17,600 per pound (39/g) [65].
Techniques for propagation from seed have been examined in detail
[21,28,65].
The fibrous root system of Pacific yew can aid in stabilizing stream
channels [68].
OTHER USES AND VALUES :
Pacific yew is an attractive ornamental which is frequently used as a
hedge plant [65]. It was first cultivated in 1854 [65]. According to
Kruckeberg [42], only the best foliage forms of Pacific yew can compare
with the much more widely planted English yew. A shrubby form of
Pacific yew, often associated with serpentine soils, is generally
considered the most desirable ornamental form [42]. Once established in
the garden, Pacific yew grows well in partial shade or full sun [42].
Some Native American peoples traditionally associated Pacific yew with
death and bereavement [32,75]. The fragrant foliage was used as a
deodorant and cleaning agent [75]. Tonics made from Pacific yew were
used medicinally by many peoples of the Pacific Northwest [75].
Although seeds are poisonous, the fleshy portions surrounding them were
sometimes eaten [75]. The supple, stringy underbark was sometimes used
for braiding and weaving various items [32].
Taxol, a substance obtained from the bark of Pacific yew [33], has
inhibited the growth of various types of cancer cells in experimental
tests [1,44]. Clinical trials indicate that taxol produces a definite
but limited activity against metastatic melanoma and some types of
leukemia [44]. It may also be useful in treating ovarian cancer and in
inhibiting the growth of carcinosarcoma cells [11,44,38]. Taxol
inhibits the replication of Trypanosoma cruzi, a pathogenic protozoan
which causes Chagas disease [11], as well as the disease-causing
flagellate Trichomonas vaginalis [35].
Researchers are currently working on methods to synthesize taxol in the
laboratory, but efforts to date have been only partially successful
[39]. Pacific yew yields more taxol than any other species of yew
(Taxus spp.) and remains the primary source of this substance [11].
Recent experiments suggest that it may soon be possible to obtain taxol
from the leaves rather than from the bark [39].
MANAGEMENT CONSIDERATIONS :
Timber harvest: Pacific yew is uncommon on most recently harvested
sites [81]. It is sensitive to drastic changes in light and temperature
and can be severely harmed by increasing exposure to heat after tree
canopy removal [34]. Sensitivity to frost may also cause decreases in
yew after overstory removal [11]. Plants commonly turn orange or brown,
and the foliage dies back after clearcutting [5,11,49]. However,
Pacific yew often adapts to unshaded conditions through changes in twig
distribution and leaf morphology [11]. In a northern Idaho study,
approximately 78 percent of individual plants survived overstory removal
[11].
Reductions in the cover of Pacific yew are often dramatic. Antos [2]
reported 1.4 percent cover after grand fir types were clearcut in
western Montana. Prior to timber harvest, Pacific yew represented
nearly 20 percent cover. The effects of timber harvest have been
examined in a number of studies [4,18,19]. Uneven-aged individual tree
removal or group selection is much less damaging to yew than
clearcutting [34]. Broadcast burning also greatly reduces the cover of
Pacific yew [61].
Wildlife: In parts of northern Idaho, moose browse Pacific yew heavily
during winter. Browse in clearcuts is generally covered by deep snow
and inaccessible to moose. However, plants within the understory of
old-growth forests are readily accessible and heavily utilized [60].
Clearcutting in these areas does not favor moose. For best moose
habitat, timber harvest should be avoided in old-growth grand
fir/Pacific yew communities [61]. To protect Pacific yew and maintain
adequate moose browse, whole tree removal should be used where possible
to lessen the need for slash disposal [61]. Slash should be piled and
then burned rather than broadcast burned. Natural grand fir and
Engelmann spruce (Picea engelmannii) regeneration can be supplemented by
planting Douglas-fir (Pseudotsuga menziesii) in small clearings [61].
Damage: Pacific yew may be severely damaged by rabbits and deer [21].
Moose occasionally kill trees by girdling the trunk [14]. In some
locations ungulates can hedge or even remove Pacific yew from springs
and seeps [14]. In parts of northern Idaho, heavy moose browsing can
prevent Pacific yew dominance on ridges and south aspects [14]. In some
areas, yew regeneration can be significantly impacted by moose [14].
Pacific yew is resistant to damage from sulfur dioxide pollution [11]
and is resistant to insects and disease [50].
Allelopathy: Seedlings of other species are rarely found beneath yews
[49]. Pacific yew has exhibited inhibition both in laboratory
experiments and in the field [16,64]. Allelopathic compounds may be
concentrated in senescent leaves and leached into the litter [64].
Bark collection: Approximately 20,000 pounds (9,080 kg) of bark is
required to produce 2.2 pounds (1 kg) of taxol [1]. In some locations,
populations of Pacific yew are threatened by collectors gathering bark
for its anticancer properties [68]. If this demand continues, this
important species could become scarce in many areas [11].
Old growth indicator: Scher and Jimerson [68] noted that long-lived
temperature-sensitive species such as Pacific yew may serve as useful
indicators of old-growth forests.
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Taxus brevifolia | Pacific Yew
GENERAL BOTANICAL CHARACTERISTICS :
Pacific yew is a slow-growing evergreen shrub or tree which commonly
reaches 20 to 40 feet (6-12 m) at maturity [65,68]. On favorable
coastal lowland sites, scattered individuals can grow to 60 feet (18 m)
in height and have diameters of 2 to 3 feet or more (0l6-0.9 m) [5]. On
poor sites, such as those at higher elevations, Pacific yew grows as a
large sprawling shrub [62]. This large shrub or tree can reach maturity
at 250 to 350 years of age [62] and often survives for several centuries
[5].
Pacific yew is characterized by a conical crown and slender, drooping
horizontal branchlets [32,55]. The trunk is limby and often contorted
or malformed [29,32,62]. Twigs are slender, hairless and green, but
become dark reddish brown in the second growing season [32]. Bark is
very thin (approximately 0.25 inch [64 mm]), scaly, with purplish outer
scales covering newly formed reddish or purplish inner bark [30,32,62].
The root system is fibrous [68].
The sharp-pointed leaves are linear to lanceolate, 0.5 to 1 inch (1-3
cm) long, and spirally arranged [32,55,62]. Leaves are dark
yellow-green above and paler beneath [30,55]. Leaves persist for at
least 5 to 6 years [30,62].
Pacific yew is dioecious [30]. Globose, yellowish staminate cones
approximately 0.12 inch (3mm) in length are produced in abundance on
male plants [11,30]. Single, greenish, ovulate cones are borne on the
lower sides of branches [30,62]. Fruit is a red, fleshy, ovoid,
berrylike aril [30,55]. Each fruit is approximately 0.4 inch (1 cm) in
length and matures in one season [62]. The cup-shaped fruit surrounds a
large single, naked seed [30,70]. The seed is reddish, obvoid-oblong,
with a hard bony shell exposed at the apex [29,62].
RAUNKIAER LIFE FORM :
Phanerophyte
REGENERATION PROCESSES :
Pacific yew can establish beneath a closed forest canopy by seed or by
vegetative means [49]. In many areas, layering is the primary mode of
reproduction, but seedlings are also common on some sites [2].
Seed: Most species of yew (Taxus spp.) produce at least some seed
annually [65]. Seeds can remain viable for 5 or 6 years if properly
stored [65]. Conclusive evidence is lacking, but some researchers have
suggested that seed may be stored in the soil [31]. Seed is commonly
dispersed by birds, and some long-distance transport is possible [50].
Passage through avian digestive tracts may affect seed dormancy [11].
Germination: Seeds of Pacific yew have a "strong but variable" dormancy
[65] and generally require stratification before germination can begin
[53]. In laboratory experiments, seeds germinated well after prolonged
warm and cold stratification [65]. Seed can be planted 0.4 to 0.5 inch
(10-13 mm) in depth and subjected to alternating day (86 degrees
Fahrenheit [30 deg C]) and night (68 degrees Fahrenheit [20 deg C])
temperatures for at least 28 days. However, even when properly treated,
some seed may not germinate until the second spring. Results of an
experimental test were as follows [65]:
stratification temp. duration germ. capacity
warm cold day night (days) (avg. %) (range)
--- --- 86 F 68 F 60 55 50-99
In other laboratory tests, average germination ranged from 50 to 60
percent [77]. Under natural conditions, germination may not take place
until the second year [65].
Seedling establishment: Seedling establishment is generally more
favorable beneath a canopy than in canopy gaps [14]. Means [52]
observed seedling densities of 0.4 per acre (1/ha) in gaps but noted 47
per acre (115/ha) beneath a canopy in the western Cascades of Oregon.
Seedlings are reportedly uncommon in undisturbed situations but are
often abundant in partially cut areas where yew is present [11].
Vegetative regeneration: Branches and stems of Pacific yew commonly
root when in contact with the soil [14,49]. Plants are generally
unharmed after being flattened by large conifers during canopy break-up
[14,49]. Crushed yews often form a series of layered branches that give
rise to numerous individual plants [14,49]. Regeneration of Pacific yew
is favored by falling debris [49]. Layering enables Pacific yew to
quickly expand into gaps created as senescent conifers fall. Sprouts
generally develop from cut or broken stumps [14]; epicormic branching is
also common [11].
SITE CHARACTERISTICS :
Pacific yew grows in a variety of cool and moist shaded habitats in
coastal lowlands and mountains [5,30,32]. It occurs in canyon bottoms,
on moist forested flats near streams, and scattered at various upland
sites [14,30,32]. At middle elevations in northern Idaho, it forms a
dense tangle of shrubs approximately 10 to 15 feet (3-5 m) in height.
Elsewhere, small groups or scattered individuals are more common [5,11].
Pacific yew grows on dry, rocky sites and in avalanche chutes west of
the Cascades [5]. However, it is commonly found in warm, humid
concavities [82]. Pacific yew is the most shade tolerant tree in the
Pacific Northwest [62]. In less humid climates, it may actually require
shade [41].
Plant communities: Pacific yew commonly grows beneath the dense shade
of western hemlock, Douglas-fir, and Pacific silver fir (Abies amabilis)
forests [5,68]. Although most often associated with relatively moist
plant associations dominated by western hemlock, Sitka spruce (Picea
sitchensis), and Pacific silver fir, it also occurs in relatively moist
microsites beneath species more typically associated with drier sites
such as ponderosa pine (Pinus ponderosa), incense cedar (Libocedrus
decurrens), Oregon white oak (Quercus garryana), Jeffrey pine (Pinus
jeffreyi), and knobcone pine (P. attenuata) [11,55,68]. In parts of
eastern Oregon and California, Pacific yew is a prominent component of
white fir forests [11,54]. In northern California and southwestern
Oregon, it is common in mixed evergreen forests dominated by white fir,
Douglas-fir, canyon live oak (Quercus chrysolepis), chinkapin
(Castanopsis chrysophylla), and Pacific madrone (Arbutus menziesii)
[6,7,55,82]. At the extreme southern edge of its range, Pacific yew
grows beneath sequoia (Sequoia sempervirens) [11,27]. In the northern
Rockies, it is associated with grand fir and western redcedar forests
[11,56]. Pacific yew also occasionally grows in warmer subalpine fir
(Abies lasiocarpa)-Engelmann spruce communities [11].
Plant associates: Common plant associates in coniferous forests of the
northern Rocky Mountains include pachistima (Pachistima myrsinites),
northern twinflower (Linnaea borealis), menziesia (Menziesia
ferruginea), Rocky Mountain maple (Acer glabrum), blue huckleberry
(Vaccinium membranaceum), wild ginger, queencup beadlily, one-sided
wintergreen (Pyrola secunda), western rattlesnake plantain (Goodyera
oblongifolia), oneleaf foamflower (Tiarella unifoliata), and bunchberry
(Cornus canadensis) [6,13,25,81]. In southwestern Oregon and
California, vine maple (Acer circinatum), dwarf Oregon grape (Mahonia
nervosa), northern twinflower, salal (Gaultheria shallon), and hazel
(Corylus cornuta) grow with Pacific yew [6,67,82]. Elsewhere in the
Northwest, Pacific rhododendron (Rhododendron macrophyllum), vine maple,
salal, western swordfern (Polystichum munitum), Oregon oxalis (Oxalis
oregana), Pacific dogwood (Cornus nuttallii), and oceanspray (Holodiscus
discolor) are common associates [11].
Climate: Pacific yew grows in cool temperate and mesothermal climates
[40,41]. Abundance increases with increasing precipitation and
decreases with greater elevation and latitude [40]. Average annual
precipitation ranges from 18 to 116 inches (47-294 cm) [11]. Sites are
generally characterized by mild wet winters and warm dry summers [14].
Pacific yew is moderately tolerant of frost, but the protection offered
by a layer of snow is necessary in continental climates [41]. This
plant is resistant to flooding and survives temporary inundation [41].
Soils: Western yew commonly grows on deep, moist, well-drained soils
[62,77] and is well adapted to acidic conditions [41]. In British
Columbia, it tends to be most productive in alluvial habitats where
soils are nutrient-rich [41]. A study conducted in the Bitterroot
Mountains of Montana and Idaho indicated that sites dominated by Pacific
yew have high levels of nitrogen [51]. Pacific yew grows on soils
derived from a variety of parent materials including granite, diorite,
gabbro, serpentine, pre-Cambrian metasediments, schists, and gneiss
[14,42,67,79].
Elevation: Pacific yew grows at elevations ranging from 2,000 to 8,000
feet (610-2,438 m) [62]. In Oregon, it occurs at low to middle
elevations [74], and in British Columbia, it occurs from submontane to
subalpine habitats [41]. Elevational ranges by geographic location have
been reported as follows:
Reference
from 3,200 to 7,000 feet (975-2,134 m) in MT [17]
350 to 4,350 feet (104-1,329 m) in CA [11]
< 7,000 feet (2,134 m) in CA [55]
200 to 4,450 feet (60-1,350 m) in OR & WA [11]
SUCCESSIONAL STATUS :
Pacific yew is present in many climax or near climax communities of the
Pacific Northwest and northern Rocky Mountains [9,51,59,81]. It is a
particularly common component of old-growth grand fir, western redcedar,
and Douglas-fir-western hemlock communities [23,49,51,68]. Pacific yew
increases in cover up to a stand age of at least 500 years in
northwestern old growth Douglas-fir forests which are characterized by
long fire-free intervals [68]. This fire-sensitive species is absent
from areas characterized by high fire frequencies.
Pacific yew does occur on disturbed sites, including previously logged
stands [11], but reaches greatest abundance in undisturbed areas
[19,68]. Plants often grow as suppressed individuals in undisturbed
stands [26]. After timber harvest, this residual species expands as the
overstory develops [5], but where residual plants have been removed,
such as by broadcast burning, plants do not generally develop until a
protective overstory canopy has formed [50].
Pacific yew was common in mature stands 230 years or older but was
absent in second-growth communities (50- to 80-year-old stands) in
Washington [57]. Similarly, it represented 15 to 20 percent cover in
various old-growth stands in the northern Rocky Mountains but was rare
(1.4 to 2 percent cover) in immature stands (7 to 16 years old and 30 to
90 years old) [2,3,4]. Percent cover of Pacific yew in different aged
stands in western hemlock-Douglas-fir forests of the western Cascades
was documented as follows [69]:
stand age
(years) 2 5 10 15 20 30 40 undist. old growth
% cover 0.05 0.18 0.16 1.51 0.66 2.26 0.49 9.56
Mesic old-growth forests in canyons of the Bitterroot Mountains in Idaho
and Montana are commonly dominated by Pacific yew, western redcedar,
and/or grand fir [49]. Pacific yew typically establishes after the
initial colonization period, and is described as the only "relay"
species not colonizing these sites in early seral stages [49]. The
ultimate composition of these forests (dominance by Pacific yew, grand
fir, or western redcedar) is largely attributable to random events which
occur during stand establishment rather than to a sequential replacement
process [49,50].
In parts of the northern Rocky Mountains, the short tree, Pacific yew,
"expresses climax sociological dominance over tall conifers" such as
grand fir [14]. This situation differs from the classical pattern in
which progressively taller taxa gradually assume dominance over shorter
forms [14]. The successional role of Pacific yew in these forests has
been subject to a number of interpretations. However, Pacific yew is
generally considered the climax dominant because, in the absence of
disturbance, it successfully replaces itself "to the near exclusion of
tall conifers" [14]. Evidence suggests that grand fir may be slowly
eliminated where Pacific yew is replacing itself successfully [14,34].
"At climax, other tree species occur primarily as a result of gap-phase
replacement in the yew canopy and definitely do not have as great an
influence on the community as [Pacific yew]" [14]. Gap phase
replacement or microsuccession prevents the development of an exclusive
canopy of Pacific yew because other conifer seedlings tend to outcompete
yew in the canopy openings. Elsewhere, grand fir and other conifer
seedlings may be eliminated by dense yew competition [68]. However, on
sites where Pacific yew occurs only sporadically, grand fir often
reproduces more successfully.
SEASONAL DEVELOPMENT :
Fruit of Pacific yew matures in a single season. Seeds ripen in
September and October [30], and the fruit generally falls from the plant
in October [77]. Flowering and fruiting has been documented as follows:
Location Flowering Fruit ripens Reference
CA April-May ---- [55]
n ID ---- August-October [58]
WA June August-October [65]
Pacific Northwest April-June ---- [30]
FIRE ECOLOGY
SPECIES: Taxus brevifolia | Pacific Yew
FIRE ECOLOGY OR ADAPTATIONS :
Pacific yew is susceptible to heat damage and is most often associated
with forests characterized by long fire-free intervals. Fire is rare in
many old-growth forests of the Pacific Northwest [68]. Fire intervals
in forests containing Pacific yew have been estimated as follows:
Location Fire interval Reference
Bitterroot Mtns. ID, MT 60 years [50]
c Western Cascades, OR 100 years [52]
Siskiyous, OR 20 years [7]
nw CA - low elev. 500-600 years [68]
nw CA - mid elev. 150-200 years [68]
Mature moist-site stands in which Pacific yew grows as scattered
individuals are often considered relics from past fires [34]. In parts
of the Northwest, stand age ranges from 80 to 250 years where fire
intervals average 70 to 120 years [14]. Similarly, in parts of western
Montana, the age of Pacific yew averages approximately 210 years where
fire replacement cycles are estimated at 150 years [14]. This suggests
that the association of Pacific yew with moist microsites conveys some
protection from fire.
After fire, Pacific yew slowly reestablishes by means of bird-dispersed
seed as the overstory canopy develops.
POSTFIRE REGENERATION STRATEGY :
Secondary colonizer - offsite seed
FIRE EFFECTS
SPECIES: Taxus brevifolia | Pacific Yew
IMMEDIATE FIRE EFFECT ON PLANT :
Pacific yew has thin bark and is sensitive to heat damage [14,68].
Plants are generally killed by even light ground fires [49], and this
species is almost always eliminated from burned stands [14,50]. In
western Montana, Stickney [73] observed that all plants were eliminated
from burned stands. An abundance of Pacific yew can be equated with an
absence of fire [14].
Plants which occasionally survive fire do so because they occur in the
wettest concavities which are relatively unaffected by fire [7].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT :
NO-ENTRY
PLANT RESPONSE TO FIRE :
Pacific yew reoccupies burned areas through bird-dispersed off-site
seed. Although vegetative regeneration is possible after mechanical
disturbance, Pacific yew's susceptibility to heat damage makes postfire
sprouting unlikely or impossible.
This plant may require shelter provided by other species for
reestablishment [50] and typically recovers slowly. Hofman [31]
observed that seedling germination was delayed for at least 6 years
after a hot slash burn in northern Idaho. Pacific yew is rare on
recently burned sites, even where it was a common component of preburn
communities [18,20,71]. In a northern Idaho study, Pacific yew was
present on 80 percent of the preburn plots but was absent from all plots
during the first years after fire [72,73]. In parts of the northern
Rocky Mountains, it is described as the "only principal residual species
eliminated by fire" [73].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE :
NO-ENTRY
FIRE MANAGEMENT CONSIDERATIONS :
Fire history: Because of its sensitivity to fire, the age of Pacific
yew can be used to estimate minimum stand age [49]. However, because it
establishes after initial colonization, the oldest stem is often
significantly younger than the age of the stand itself [49].
Prescribed fire: Johnson and Simon [34] recommend against prescribed
fire in Pacific yew types. Although a light underburn will not damage
the duff layer, yew may be adversely affected. Scher and Jimerson [68]
note that "although prescribed burning reduces the probability of
catastrophic wildfires, precautions must be exercised to maintain
biodiversity by protecting temperature-sensitive species" such as
Pacific yew. In some areas, prescribed and/or wildfires can contribute
to the depletion of yew populations [68]. Broadcast burning after
clearcutting has virtually eliminated yew in some areas [61,68].
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SPECIES: Taxus brevifolia | Pacific Yew
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Index
Related categories for Species: Taxus brevifolia
| Pacific Yew
|
 |
