BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Taxus candensis | Canada Yew 



GENERAL BOTANICAL CHARACTERISTICS : 
Canada yew is a native, evergreen, coniferous shrub.  It grows from 1 to
3 feet (0.3-0.9 m) and occasionally up to 6 feet (2.8 m) tall.  It is
rarely arborescent [5,9].  The dense, spreading branches can grow up to
6.6 feet (2 m) long, spreading from the base for about one-third of
their length.  The bark is nearly smooth.  The fruit is a fleshy,
cuplike aril surrounding a single seed [35].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Canada yew is monoecious, producing a single seed per female strobilus
[44], but under certain conditions it is dioecious.  Size appears to
influence sex expression.  Small Canada yews tend to be male, but if
monoecious, they tend to have more female strobili than male stroboli.
Large Canada yews are typically monoecious but with male-biased
strobilus ratios.  Stresses such as browsing increase the proportion of
individual males in the population; however, the number of female
strobili in the population is greater than that of male strobili.  The
adaptive significance of this differential sex expression is unclear
[2].

Most yews produce some seed almost every year.  The seeds are
disseminated by birds.  Natural germination usually does not take place
until the second year.  The seeds exhibit a strong but variable dormancy
that can be broken by combined warm and cold stratification [35].

Canada yew commonly reproduces by layering, forming a continuous
population of genetically identical plants.  The connections between
genets usually rot [2].


SITE CHARACTERISTICS : 
Canada yew occurs in humid, continental climates.  It grows on moist,
poszolic, or leached loam soils; growth is best on well-drained silt
loams of pH 5.0 to 7.5 [5,13,25,40].  Canada yew occurs in cool, rich,
damp woods and wooded swamps; on banks; along bog margins; and ravines
[34,44,45].  Elevational range of Canada yew in the Adirondack Mountains
of New York is from 100 to 2,300 (30-700 m) [19].
 


SUCCESSIONAL STATUS : 
Obligate Climax Species

Canada yew does not occur in early seral of mid-seral communities.  It
is a slow-growing, shade-tolerant species that grows best in the stable
environmental conditions of climax forests [25,33].  Growth is best in
at least partial shade [25].  Canada yew appears to have a competitive
advantage over intolerant species only under a well-developed canopy
[33].  On Isle Royale, Michigan, Canada yew occurred in moderate shade,
densely populating some sites, but it did not occur under the very dense
shade of balsam fir.  Balsam fir, in turn, does not reproduce where
Canada yew forms dense ground layers.  Canada yew populations migrate;
they increase in size by layering, and die back in older portions of the
genet, which then allows other plants to come in [6,13,34,43].
Disturbances tend to exclude Canada yew.  In the early part of this
century, a virgin forest in Connecticut that had reamined free of fire
for more than 300 years had a well-established population of Canada yew.
Second-growth forests in the same area had no Canada yew in their
understory [27].


SEASONAL DEVELOPMENT : 
Male and female strobili open from April to May in the upper midwestern
states.  The aril ripens the same year from July through September [35].

Related categories for Species: Taxus candensis | Canada Yew