BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Rubus parviflorus | Thimbleberry 



GENERAL BOTANICAL CHARACTERISTICS : 
Thimbleberry is a low, scrambling or erect, unarmed deciduous shrub
which grows from 1.6 to 8.2 feet (0.5-2.5 m) in height
[15,17,45,103,133].  The perennial stems are few, erect, and simple
[75,128].

The perennial stems, or canes, typically live for 2 to 3 years [15].
Sterile first-year stems, known as primocanes, develop from buds at or
below the ground surface and generally bear only leaves.  During the
second year, lateral branches, or floricanes, develop in the axils of
the primocanes produce flowers and fruit [45].  Growth is rapid under
favorable growing conditions.  Plants may reach heights of 6.6 to 8.2
feet (2 to 2.5 m) within 10 years.  Maximum rates of height growth often
occur during the second and third years after establishment [15].

Twigs are greenish and finely hairy [128].  Grayish bark becomes flaky
or shreddy with age [103].  Large, simple, palmately-lobed leaves are
green above but pale beneath [133].  Leaves are unequally serrate [103]
and turn brilliant orange to maroon in fall [8].  Showy white or,
rarely, pink flowers occur in clusters of two to seven [133].  Loosely
cymose, perfect flowers are borne in a flat-topped terminal panicle or
corymb [45,64].  The fruit of thimbleberry is made up of a "thimblelike"
aggregate of numerous hairy, red or scarlet drupelets [45,103,128,133].
These drupelets are nearly dry at maturity and fall apart readily when
picked [133].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Thimbleberry reproduces through seed but also regenerates vegetatively,
even in the absence of disturbance.  It is capable of forming dense
thickets through vegetative sprouting [112].  Establishment from seed
appears to be the primary mode of colonization in newly disturbed areas
[15].  Abundant seedling establishment typically occurs during the first
year after disturbance [78].

Vegetative regeneration:  Thimbleberry, a strongly rhizomatous shrub
[52,105,131], is also capable of vigorous sprouting from rootcrowns
[105] and roots [17,118].  A single thimbleberry seedling can spread and
occupy a relatively large area as rhizomes develop and spread [80].
Most local expansion of this shrub is attributable to rhizome sprouting
[123].

Seed:  Most species within the genus Rubus produce good seed crops
nearly every year [11].  However, thimbleberry seed production can be
limited at higher elevations.  Thimbleberry fruits, or "berries," are
made up of an aggregate of numerous small red drupelets [128,133] which
fall to the ground when ripe [15].  Fruit is almost dry at maturity and
readily breaks apart when picked [133].  Seed averages 0.8 inches (2
mm) in length [80].

Germination:  Thimbleberry seeds have a hard, impermeable endocarp and
dormant embryo [80].  Consequently, germination is often slow [105].
Seed has exhibited moderate viability in germination tests, with maximum
germination estimated at 62 percent [15].  Specific germination
requirements have not been documented for thimbleberry, but both warm
and cold stratification are probably required [105].  Most Rubus seeds
require, as a minimum, warm stratification at 68 to 86 degrees F (20 to
30 degrees C) for 90 days, followed by cold stratification at 36 to 41
degrees F (2 to 5 degrees C) for an additional 90 days.  These
conditions are frequently encountered naturally as seeds mature in
summer and remain in the soil throughout the cold winter months.
Laboratory tests indicate that exposure to sulfuric acid solutions or
sodium hyperchlorite prior to cold stratification can enhance
germination [11].  Allelopathic compounds produced by bracken (Pteridium
aquilinum) can apparently inhibit germination and subsequent growth of
thimbleberry [15].

Seedbanking:  Thimbleberry seed is noted for its ability to remain
viable for long periods of time [105,116].  Seedbanking is believed to
represent an important postdisturbance regenerative strategy in this
species [77,80,98,116].  Kramer [80] observed buried thimbleberry seed
in 50 percent of all plots examined in several Douglas-fir and grand fir
habitat types of central Idaho.  Kramer and Johnson [82] observed
maximum seed densities of 17.6 per foot square (189/m sq) in central
Idaho.  Approximately 91 percent of the thimbleberry seed was found
buried at a depth of 0 to 2 inches (0-5 cm), with 9 percent at 2 to 4
inches (5-10 cm) [82].  Kramer [80] found that 22 percent of all seeds
were buried at depths of 2 to 4 inches (5 to 10 cm).  Approximately 14
percent of all buried seed was viable, although the total number of
viable seeds from lower soil layers (2 to 4 inches [5-10 cm]) was less
than one half of that of the more shallowly buried seed [80].

Seed dispersal:  Thimbleberry seed is readily dispersed by birds and
mammals [1,52,80].  Groups of seedlings occasionally germinate from
rodent caches.  However, small mammals generally play only a local role
in thimbleberry seed dispersal [98].  Birds often effect wider dispersal
[15].  Gravity may also aid in seed dispersal [105].


SITE CHARACTERISTICS : 
Thimbleberry occurs in a variety of moist-to-dry and wooded-to-open
sites [64].  It commonly grows on open, wooded hillsides, in subalpine
meadows, along streambanks and canyons, on borders, and roadsides, and
on dry exposed sites at higher elevations [17,39,45,60,128,130].
Thimbleberry is often well represented in areas of snow creep, such as
in avalanche chutes or on steep slopes [29,48].  It is particularly
common on cool moist sites and predominates on north aspects throughout
much of northern Idaho [69].  Thimbleberry frequently occurs as
scattered individuals, but in some areas occurs in dense contiguous
patches [15].

This moderately shade-tolerant shrub [76,116] is occasionally found at
low light levels but is typically most abundant at 60 to 100 percent of
full sunlight in Oregon forests [116].  In some areas, thimbleberry can
survive within the understory of forests receiving only 3.5 percent of
full sunlight [15].  Although it persists in closed stands, it is
typically most abundant on disturbed sites within the forest canopy,
such as cutover or windthrown areas [16,30,80,87,100].

Soil:  Species within the genus Rubus grow well on a variety of barren
infertile soil types [11].  These shrubs tolerate a wide range of soil
temperature and pH but do require adequate soil moisture for good growth
[18].  Thimbleberry grows well on dry, rocky soil and deep well-drained
loam [29,68].  Growth of thimbleberry is reported as "good" on loam or
clay-loam, "fair-to-good" on sandy loams, but only "fair to poor" on
gravel, sand, or clay [28].  Thimbleberry grows well on soils derived
from a variety of parent materials [15].

Elevation:  Thimbleberry grows across a wide elevational gradient from
sea level to subalpine zones [55,64].  Generalized elevational ranges by
state are as follows [28,73,103,133]:

            from 8,000 to 9,500 feet (2,438 to 2,896 m) in AZ 
               < 8,000 feet (2,438 m) in CA
            from 7,000 to 10,000 feet (2,134 to 3,048 m) in CO
                 3,500 to 8,000 feet (1,067 to 2,438 m) in MT
                 4,691 to 9,004 feet (1,435-2,745 m) in UT
                 6,700 to 7,900 feet (2,042-2,408 m) in WY


SUCCESSIONAL STATUS : 
Thimbleberry is a persistent seral species which frequently dominates
the understory during the first several decades after disturbance
[89,116,123].  It readily invades disturbed sites through rhizomes or
seedling establishment [15].  Thimbleberry quickly established on
mudflows and other harsh microsites after the eruption of Mount St.
Helens [54].  This shrub is an important seral species in many
cedar-hemlock, western hemlock, grand fir, Douglas-fir, redwood, and
other coniferous forests of the West [25,39,59,116,140].  This shrub
generally occurs in greatest abundance in seral stands throughout its
range [59] but can persist in trace amounts in many climax forests
[13,80,135].  In many mature forest stands, thimbleberry may be
restricted to disturbed sites such as clearings or areas of windthrow
[30].  On certain disturbed sites perpetuated by snow creep,
thimbleberry is functionally both a pioneer and climax species [29].
Thimbleberry is a nitrogen-demanding species and in some areas, begins
to decline within 2 to 5 years after timber harvesting as soil nutrient
levels decrease [79].  Plant vigor and canopy cover generally decline as
tree cover increases [69,100].

Douglas-fir:  Thimbleberry is an important seral species in Douglas-fir
forests of the Pacific Northwest and Rocky Mountain regions
[25,51,52,53].  During the first few years after disturbance, weedy
annual colonizers become dominant but are soon replaced by perennial
invaders such as thimbleberry [51].  This shrub reaches peak abundance
more than 10 years after disturbance in Douglas-fir forests of Oregon's
western Cascades [52].  However, it reportedly becomes dominant as soon
as 5 years after logging and slash disposal in northwestern Douglas-fir
forests [96] and assumes prominence during the first 3 years after
disturbance in northwestern Montana [21].

Grand fir:  Thimbleberry is also a major seral species in grand fir
habitat types of Idaho where it quickly increases following reduction of
the overstory [116,139].  This shrub remained dominant in grand
fir/pachistima (Pachistima myrsinites) stands which had been clearcut
and burned 12 years earlier [139].  In northern Idaho it is particularly
abundant after timber harvest on sites which were severely burned by
wildfires 40 to 60 years earlier and frequently persists for relatively
long periods of time.  Consequently, some researchers note that the
relative successional amplitude of thimbleberry in grand fir types of
northern Idaho is uncertain [116].  In some grand fir-Sitka
spruce-Douglas-fir forests of northern California, thimbleberry is
abundant 5 to 10 years after disturbance.  Thimbleberry is overtopped at
approximately 30 years in redwood (Sequoia sempervirens)-grand fir
forests but generally persists in reduced abundance [140].

Cedar-hemlock:  Thimbleberry occurs in cedar-hemlock communities from
newly disturbed sites to stands of 400 years or older [47] but is much
more prevalent in younger stands [47].  In cedar-hemlock forests of
northern Idaho, thimbleberry is an initial increaser after logging but
begins to decrease by approximately 25 years after disturbance [135].
It has reached maximum cover in western redcedar/queencup beadlily
(Clintonia uniflora) habitat types by 3 to 5 years after fire [98].


SEASONAL DEVELOPMENT : 
Phenological development of thimbleberry varies according to elevation
and weather conditions [15].  It generally leafs out in mid to late
spring.  However, buds may become active by late February in parts of
Oregon and Washington [119].  Leaves begin to fall in late summer to
autumn [114].  Leaf fall may be early in dry years.  In Oregon, leaves
were shed by late August in particularly dry years [61].  Phenological
development of thimbleberry foliage in the northern Rocky Mountains is
detailed below [114]:

            leaf buds   leaves full   leaves start  leaves begin  leaves 
            burst       grown         to color      to fall       fallen

earliest    April 5     May 12        August 1      August 21     August 28
latest      June 3      July 20       Sept. 30      October 1     October 23 

Similar phenological development has been reported from the central
coast of British Columbia [15].  Generalized fruiting and flowering
dates by location are as follows [15,28,73,87,104,128]:

location            flowering dates            fruiting dates

   AK               June - July                August - September
   AZ               July - September                ----
   BC                    ----                  early June to September
   CA               March - August                  ----
   CO               June - August              August - later
Great Plains        May - July                      ----
   MT               June - August                   ----
n ID, w MT          May - August               late June - September
   UT               May - July                      ----
   WY               June - August                   ----
 
In northern Idaho and western Montana, seed dispersal generally begins
in July or August [114].

Related categories for Species: Rubus parviflorus | Thimbleberry