BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Rubus idaeus | Red Raspberry 



GENERAL BOTANICAL CHARACTERISTICS : 
Red raspberry is a deciduous, erect or arching, thicket-forming shrub
which grows from 1.6 to 9.8 feet (0.5-3 m) in height [36,80,86,93].  The
total height and extent of growth is largely attributable to climatic
factors [101].  Woody stems are bristly or prickly with shreddy,
exfoliating yellow-brown bark [36,93].  Leaves are alternate and
pinnately compound in leaflets of three to five [86,93].  Leaves are
green and glabrous to hairy above but white or gray, hairy to glabrate
and greenish beneath [98].  Small showy perfect white flowers are
borne in clusters of one to four in a compound cyme [36,55,80,93].
Fruit of the red raspberry is made up of many to several, red or
pinkish-purple drupelets [80,98].  Aggregates of drupelets are commonly
referred to as a "berry."

Red raspberry is made up of mostly biennial canes (stems) on a
long-lived perennial rootstock [45,99].  This rootstock initially forms
from seedling establishment or the production of root suckers [99],
which gradually separate from parent plants as the connecting root
tissue dies [45].  Sterile first-year stems, or primocanes, develop from
buds at or below the ground surface and generally bear only leaves
[36,99].  During the second year, lateral branches, known as floricanes,
develop in the axils of the primocanes which produce both leaves and
fruit [36,100].  A "typical" raspberry rootstock system is made up of at
least one floricane and several primocanes [99].  It should be noted
that some commercially grown strains of red raspberry are
primocane-fruiting; that is, they are capable of bearing fruit during
the fall of the first year of development [21,92].  Primocane-fruiting
appears to be absent entirely or represents an atypical situation in
native-growing populations of red raspberry.


RAUNKIAER LIFE FORM : 
   Hemicryptophyte


REGENERATION PROCESSES : 
Red raspberry reproduces through seed and also regenerates vegetatively.
It is capable of forming dense thickets through sprouting.  Reproductive
versatility is well represented in the Rubus genus, with sexual
reproduction, parthenogenesis (development of the egg without
fertilization), pseudogamy (a form of apomixis in which pollination is
required), and parthenocarpy (production of fruit without fertilization)
occurring widely [17].  The following types of reproduction have been
documented within the genus:  (1) sexual reproduction, (2) nonreduction
at meiosis on the female, male, or both sides, (3) apomixis with
segregation, (4) apomixis without segregation, and (5) haploid
parthenogenesis [17].  These modes of asexual reproduction are important
because they help contribute to the vigorous, aggressive spread of red
raspberry.

Red raspberry is capable of vigorous sprouting after disturbance [18]
but also expands in clonal area through vegetative regeneration
[95,100].  Natural vegetative regeneration occurs through root sprouts
or "suckers" [95,100,101], "stolons" [95], "rhizomes" [39,52], and basal
stem buds or rootcrowns [45,95,101].  The precise mode of vegetative
regeneration depends on the type and severity of disturbance.  Dense
raspberry thickets form from the roots or stems of parent plants which
separate to form individual plants with the deterioration of connecting
tissue [45].  Red raspberry allocates most energy to vegetative
regeneration on recently disturbed sites with favorable growing
conditions [99].  With time, initially elevated nutrient levels decline,
and shading increases.  As growing conditions deteriorate, red raspberry
shifts its reproductive effort to the production of large numbers of
seed [39,100].

Red raspberry sprouts readily from portions of aboveground stems which
survive disturbance [52].  Many raspberry species are capable of rooting
from the stem nodes, and layering has been widely reported in the red
raspberry [95].  This shrub is also capable of sprouting from axillary
buds located "well above the ground level" [45].  Rootcrown or stembase
sprouting is an important regenerative mode, which in the raspberry
gives rise to biennial stems even in the absence of disturbance [36,45].
Red raspberry typically sprouts from the rootcrown if aerial foliage is
cut late in the growing season [95].  In related species such as
salmonberry (R. spectabilis), apical dominance exerted by extant
rootcrowns inhibits sprouting from belowground structures such as roots
or rhizomes [106].

Root "suckering" is a normal, on-going process in red raspberry stands
[45,101].  However, particularly vigorous root suckering is often
observed after the aboveground vegetation is damaged or destroyed.  This
shrub regenerates from buds located on the larger main roots as well as
those present on lateral roots which are often located fairly close to
the soil surface [52,101].  The mean depth of these underground
regenerative structures (root buds) was estimated at 2.4 inches (6 cm)
in a New Brunswick study [28].  During the first 2 to 3 years after
establishment, root suckers fill in spatial gaps in the clone [100].
Root sucker mortality is generally high during the third and fourth
years because of intense intraspecific competition for sunlight, space,
and nutrients which result in "self thinning" of stands [45,100].
Suckering ability declines with age, with production decreasing from an
average of 1.5 per square foot (16.0/sq m) in 3-year-old stands to 0.77
per square foot (8.25/sq m) in 4-year-old stands [100].  Although
relatively few root suckers actually reach the canopy, survival rates of
those that do is high [100].  Most root suckers live for only 1 or 2
months [100].  Several researchers report that red raspberry is capable
of sprouting from rhizomes after fire or other disturbance [39,52].
However, others have observed that red raspberry lacks rhizomes with any
regenerative capability [28].  The term "rhizome" may have been loosely
applied to rhizomelike roots which do possess the ability to sprout.
Geographic or genetic differences in red raspberry morphology and
physiology are also possible.

Seed:  Immature fruit, commonly referred to as "berries," are pink and
hard [10].  Ripe fruit is generally red, but less commonly white or
yellow [43].  Several to many small individual drupelets form an
aggregate fruit [10,98].  Fruit size appears to be related to soil
moisture [72], although significant genotypic variation has also been
noted in the size and number of fruits produced annually [22].
Decreased stored nutrient availability and water stress can influence
overall fruit production [16].  It is estimated that 70 to 90 percent of
red raspberry flowers eventually mature into fruit which results in an
abundance of seed [99].  Whitney [100] observed that 77 percent of all
plants flowered, with 85 percent of those flowering producing seed.
Most species of raspberry produce good seed crops nearly every year
[10], but seed production does vary annually in the red raspberry
according to climatic factors and the age of the cane.  Whitney [100]
observed average seed production of 65 seeds per square foot (700 seeds/
sq m) in 2-year-old canes, with maximum production of 1,301 seeds per
square foot (14,000 seeds/sq m) in 4-year-old canes.  Annual seed
production averaged 604 seeds per square foot (6,500 seeds/sq m) over a
4-year period [100].

Pollination:  Red raspberry is primarily pollinated by bees, although
flies and beetles also pollinate some flowers [40].  Under natural
conditions, it is almost exclusively self-incompatible [55] which
contributes to morphological variability.

Germination:  Seed of the red raspberry is relatively large [31], with
viabilty averaging up to 92 to 99 percent in laboratory tests [95].  Red
raspberry seeds have a hard, thick, impermeable coat and dormant embryo
[10].  Seeds have the ability to become dormant a second time in
response to environmental factors [50].  Consequently, germination is
often slow.  Most raspberry 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 [10].  Cold stratification alone is
insufficient to induce germination in red raspberry [59].  Laboratory
tests indicate that exposure to sulfuric acid solutions or sodium
hyperchlorite prior to cold stratification can improve germination
[10,43,50,95].  Evidence suggests that the digestive enzymes of mammals
can also enhance germination, with seeds eaten by chipmunks and deer
mice exhibiting better germination than untreated seeds [59].  Sowing
seeds at greater depths with subsequent exposure to light can produce
better germination than shallow plantings, presumably because of greater
soil moisture [50].  Results of specific germination tests have been
documented in a number of studies [10,50,59].

Seedbanking:  Red raspberry amasses large numbers of seed which persist
in the soil until favorable germination conditions are encountered
[31,35,100].  Often, many seeds remain buried in the soil of stands
which lack any sign of the parent plants [31].  Red raspberry seed can
remain viable for 60 to 100 years or more [62,73,100].  Seeds are less
likely to germinate when fresh [50,62], and may reach maximum viability
at 50 to 100 years of age [34].  In a New Hampshire study, approximately
90 percent of Rubus (R. idaeus and R. allegheniensis) seed germinated
during the first summer after disturbance in 38-, 95-, and >
200-year-old stands, whereas only 60 percent of those in 5-year-old
stands germinated [34].  More than 4,048,583 Rubus seeds per acre (10
million/ha) have been found in the soil of 5-year-old beech (Fagus
spp.)-birch (Betula spp.)-maple (Acer spp.) stands [34].  Numbers
declined to 48,588 per acre (120,000/ha) in 200-year-old stands [34].
Annual reductions in stored seed have been attributed to: (1)
degeneration resulting in death, (2) fungi or animal predation, and (3)
annual germination of some seeds.  Fyles [31] reported 237 to 1,883
seeds per foot square (22-175/m sq) in organic soil and 0 to 2,582 per
foot square (0-240 m sq) in mineral soil of upland coniferous forests of
central Alberta.  Distribution of germinating seeds by stand age in
beech-birch-maple forests of New Hampshire were as follows [34]:

                           stand age in years 

                          5       38        95        200 +
#seeds/m sq.            1,016    286        68        12

Seed dispersal:  Red raspberry seed is readily dispersed by birds and
mammals [87,100].  After they mature, the highly sought-after fruit
rarely remains on the plants for long [10].  Birds have been observed to
deposit 2,429 to 2,834 viable seeds per acre (6,000 to 7,000/ha)
annually in beech-birch-maple forests of New Hampshire [34].  Mammals
such as mice and chipmunks may be important dispersal agents in some
areas [59].

Seedling establishment:  Most seedlings germinate during the first year
after disturbance [99,100] and produce stands which are primarily
even aged.  In many instances, as much as 70 to 90 percent of all
individuals establish during the first year after disturbance [100].
Researchers have observed minimal recruitment in the second, third, and
fourth years after fire [100].  Little seedling establishment occurs
beneath the shade of a closed forest canopy [100].


SITE CHARACTERISTICS : 
Red raspberry grows across a wide range of sites throughout most of the
world's temperate regions [20].  It commonly occurs in clearings or
borders in boreal forests, in ravines, on bluffs and streambanks of
prairie regions, and on talus or scree above timberline [39,86,93,95].

Soil:  Raspberries are tolerant of a wide range of soil pH and texture
but do require adequate soil moisture [14].  Red raspberry grows on
imperfectly to well-drained sandy loam to silty clay loam, but best
growth occurs on moderately well-drained soils [95].  Although red
raspberry grows well on barren and infertile soils, it reportedly has a
relatively high demand for soil nutrients and is most abundant on
nutrient-rich soils [39].  This shrub is moderately tolerant of acidic
soils [95].

Elevation:  Generalized elevational ranges for selected locations are as
follows [23,98]:

               from 6,500 to 11,700 feet (1,981 to 3,569 m) in CO
                    2,400 to 7,000 feet (732 to 2,134 m) in MT
                    5,500 to 9,600 feet (1,676 to 3,420 m) in UT
                    6,500 to 11,000 feet (1,981 to 3,355 m) in WY 


SUCCESSIONAL STATUS : 
Red raspberry vigorously invades and colonizes many types of disturbed
sites [62,95,100].  It is generally considered a pioneer or early seral
species [35] which flourishes and completes its life cycle during the
first years after disturbance [100].  This shade-intolerant species
often dominates sites during early successional stages but decreases as
the canopy closes [62,100].  Although the plants themselves remain
prominent for only a relatively brief period, viable seeds can persist
for 60 years or more in the soil or duff [73].  Widespread germination
after disturbance frequently leads to the development of even-aged
stands [100].  In many areas, red raspberry is absent beneath the canopy
of mature forests but persists in forest openings [39].  Whitney [99]
reports that few stands of red raspberry persist for longer than 5 to 12
years.

Red raspberry invades black and white spruce stands in Alaska during the
first years after disturbance but declines as taller shrubs and trees
become established [29,39].  In many northern black spruce forests, red
raspberry is present only in early successional stages [29].  On mesic
and submesic sites in sub-boreal forests of British Columbia it
typically increases during the first 10 years after timber harvest or
fire but is virtually eliminated within 14 years because of rapid
increases in shade [39].  Red raspberry often dominates jack pine stands
of Minnesota within 5 years after disturbance [2,39] and subsequently
declines as the canopy develops.  In parts of western Montana, red
raspberry initially grows rapidly but begins to decline within 3 to 4
years after disturbance as nutrient levels decrease [18].  Red raspberry
can persist for up to 4 or 5 years in northern hardwood forests as long
as stands remain relatively open [47,73].  In birch-maple forests of New
Hampshire, red raspberry reaches peak abundance in the second through
fourth years after disturbance [100].  However, it rarely persists for
more than 10 years [100].  Red raspberry is subsequently replaced by
species such as aspen, chokecherry (Prunus spp.), and birch [100].


SEASONAL DEVELOPMENT : 
Red raspberry is typically biennial, with each shoot passing through
well-defined phenological stages during its 2-year lifespan [45].
Vegetative shoots develop from the roots or stems of parent plants, or
as seedlings, during the first year [45,99,100,101].  Lateral flowering
stalks (floricanes) are produced during the second year [22,99,100].
Floricanes leaf out early and exhibit rapid growth [99].  After
producing fruit in late summer, the leaves of floricanes senesce and the
cane gradually dies [99].  Stages of the 2-year growth cycle of red
raspberry are detailed below [45]:

                        
                            YEAR 1
       Phases               

phase 1:  initiation of root buds                  
phase 2:  subterranean suckering           
phase 3:  emergent suckers; elongation slows or stops
          as sucker reaches surface; leaves form a rosette
          at or above the soil surface.
phase 4:  1st winter dormancy-most leaves shed     

                            YEAR 2

phase 5:  elongating shoot; rapid elongation.      
phase 6:  initiation of flower buds; shoot stops   
          elongation at end of growing season.  
          secondary rosettes form; axillary meristems
          initiate flower primordia; dormant fruit buds;
          leaves become senescent and fall. 
phase 7:  breaking dormancy of flower buds; require 
          cold to break dormancy; buds grow in spring
          (some cultivars produce fruit before dormancy).
phase 8:  flowering and fruiting; basal buds elongate
          into a vegetative replacement shoot which
          repeats the biennial cycle.
phase 9:  senescence and death.  (after fruiting the
          shoot dies back "to the position from which
          a replacement shoot has grown").

Flowering:  Flowerbud initiation is influenced by temperature, genetics
(cultivar), and geographic location [21,48,69,92].  Flowering is also
related to the age and vigor of the plant and the date at which
vegetative growth terminates [16,67].  Flowerbud initiation is triggered
by low temperatures and short days and generally begins in late summer
or autumn [16,21].  Flowerbud initiation can be induced by exposure to
temperatures of 55 degrees F (12.8 degrees C) at 9 hour days or 50
degrees F (10.0 degrees C) at 16 hour days [21].  Although flowerbud
initiation occurs over winter in most red raspberries, initiation in
primocane-fruiting cultivars begins in summer [92].  Bud break typically
occurs in early spring [16].  Evidence suggests that higher spring
temperatures may promote earlier and more rapid flowering [67].

Fruiting:  Fruit maturation begins soon after flowering [88].  Timing of
flowerbud initiation largely determines fruiting season [21], although
fruiting dates also vary according to cultivar and geographic location
[21].  Annual variation in fruit ripening has also been reported [21].
Both flowering and fruiting proceeds from the top of the floricane
downward [22].  After maturation, fruit spoils rapidly [88].
Generalized fruiting and flowering dates by geographic location are as
follows [21,23,36,54,80,84,86,88,93]:

     location        flowering             fruiting

       AK            June-July             July-September
       AZ            June-July             -----
       BC            -----                 July-August
       CO            June-July             -----
     East            -----                 July-October
 Great Plains        May-July              -----
       MT            June-August           -----
    NC, SC           June-August           July-August (or later)
       ND            June                  -----
  New England        ----                  late June-August
  nc Plains          June-July             July-August
       UT            May-July              -----
       WY            June-August           -----

Related categories for Species: Rubus idaeus | Red Raspberry