BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Toxicodendron rydbergii | Western Poison-Ivy 



GENERAL BOTANICAL CHARACTERISTICS : 
Western poison-ivy is a native, rhizomatous, low shrub [9,21].
Throughout much of its distribution, western poison-ivy assumes a
subshrub growth form, typically less than 3 feet (0.9 m) tall [7].  In
Utah, plants are rarely more than 12 inches (30 cm) in height [21].
However, under favorable site conditions where plants have remained
relatively undisturbed for several decades, individuals sometimes reach
heights of 10 feet (3 m) or more [7].  This species exhibits a
nonclimbing habit, differentiating it from eastern poison-ivy
(Toxicodendron radicans), which produces arerial roots [7].  Stems are
somewhat woody, simple or sparsely branched, arising from much branched
rhizomes.  Long-stalked leaves are borne alternately near the summit of
the stem and are divided into three coarse-toothed leaftlets [7].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Western poison-ivy regenerates both sexually and vegetatively [7,20].

Sexual reproduction:  Numerous, monecious flowers are produced in small,
rather dense axillary clusters.  Birds and mammals disperse the fruits.
Unconsumed fruits are retained on the plant through winter and are
deposited beneath parent plant in spring [22].  Since plants readily
invade disturbed areas [7], bare mineral soil appears to be conducive to
germination and establishment.

Vegetative reproduction:  Vegetative expansion via rhizome initiation is
a major mode of reproduction in established plants [7].  Leafy shoots
are produced via basal stem nodes located along much branched rhizomes;
on some sites, rhizomes may extend up to 7 feet (several meters) beyond
the parent plant [19].  As a result of this extensive network of
rhizomes, western poison-ivy frequently forms thickets under favorable
site conditions.  These thickets may represent a single clone or several
individuals [7]. 


SITE CHARACTERISTICS : 
Western poison-ivy exhibits a wide ecological amplitude and occurs on a
variety of habitats ranging from riverbottoms to subalpine sites [7,20].
Western poison-ivy is considered a ubiquitous weed throughout much of
its distribution and easily invades disturbed areas such as roadsides,
talus slopes, lakeshores, floodplains, fencerows, logging units, sand
dunes, and railroad rights-of-way [7,16,22].  Plants rarely dominate
large areas but may become locally abundant in mesic sites with moderate
amounts of sunlight such as rills, ravines, edges of waterfalls,
creekbanks, streambottoms, river terraces, and floodplains [20,21].  It
occurs on a variety of soils.  Plants are frequently found on alluvial
deposits of floodplains and river terraces [7]; this species has also
been reported growing in both sandy and calcareous soils in the Great
Plains [9].

Throughout the western portion of its distribution, western poison-ivy
is usually associated with riparian communities [9,21].  In the northern
Great Plains it is a common understory component of gallery forests and
floodplain communities along the Little Missouri River and its major
tributaries [8,16].  Plants occur to a lesser extent on forested upland
sites throughout this region [10,11,18].  Tree associates in the Great
Plains include water birch (Betula occidentalis), paper birch (B.
papyrifera), quaking aspen (Populus tremuloides), eastern cottonwood
(Populus deltoides), eastern hophornbeam (Ostyra virginiana), green ash,
American elm, ponderosa pine, and common juniper.  Shrub associates
include western snowberry (Symphoricarpos occidentalis), chokecherry
(Prunus virginana), bur oak, Oregon-grape (Mahonia repens), western
hazelnut (Corylus cornuta), fragrant sumac (Rhus aromatica), and Wood's
rose (Rosa woodsii).  Herbaceous associates include Canada wildrye
(Elymus canadensis) and wild sarsaparilla (Aralia nudicaulis).  Ranging
from the foothills through the ponderosa pine belt in the Rocky
Mountains, this species is also able to occupy more xeric sites
including orchards, open woods, dry rocky hillsides, and canyon bottoms
[12,20].

In the eastern United States plants usually inhabit more open areas
within hardwood forests where sugar maple (Acer saccharum), yellow birch
(Betula alligheniensis), beech (Fagus grandifolia), basswood (Tilia
americana), and hop hornbeam (Ostyra spp.) comprise the overstory.
Other overstory dominates on many sites in the Northeast include hemlock
(Tsuga canadensis), eastern white pine (Pinus strobus), balsam fir
(Abies balsamea), and red spruce (Picea rubens).  In the East western
poison-ivy typically occupies mesic sites but is also commonly found on
rocky fields, pastures, talus slopes, precipices, gypsum cliffs, and
slatey ledges [7].

Elevational ranges for several western states are as follows
[4,10,11,12,21]:

    from 4,500 to 8,500 feet (1,372-2,591 m) in CO
         2,000 to 4,000 feet (610-1,220 m) in MT
         1,968 to 2,722 feet (600-830 m) in ND
         3,500 to 6,525 feet (1,067-1,989 m) in SD
         3,690 to 7,413 feet (1,125-2,260 m) in UT
         3,700 to 7,200 feet (974-2,195 m) in WY.


SUCCESSIONAL STATUS : 
Facultative Seral Species

Western poison ivy is a ruderal species and is a common early seral
component of numerous riparian communities throughout its widespread
distribution [7].  Plants rapidly invade disturbed sites where
competition has been reduced.  They are well adapted to the continued
disturbances characteristic of floodplains and lakeshores [8].  Although
this species establishes during early seral stages, its persistence on a
site is somewhat unclear.  On floodplain sites along the Little Missouri
River in North Dakota, highest cover (18%) of western poison-ivy
occurred on the most recent alluvial deposits.  Within these cottonwood
(Populus deltoides) communties, western poison-ivy cover gradually
declined as the overstory canopy began to close; on climax sites
described as a green ash/western snowberry habitat type, it was still
present but cover was substantially reduced (4.4%) [8].


SEASONAL DEVELOPMENT : 
Detailed information concerning the seasonal development of western
poison-ivy is not available.  On the Great Plains plants sometimes bloom
twice within one season; first in May or June and again in August or
September [9].  Fruits are usually well developed by fall and often
persist on the plant through the winter [20].  Dittberner and Olson [4]
list the following anthesis data for several western states:

State           Earliest flowering         Latest flowering

CO                   May                         June
ND                   May                         July
UT                   June                        July
WY                   June                        September.

Related categories for Species: Toxicodendron rydbergii | Western Poison-Ivy