More info for the terms:
apomixis,
competition,
forest,
fresh,
fruit,
layering,
natural,
root crown,
root sucker,
seed,
severity,
shrub,
stratificationRed 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 root crowns [
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]. Root crown 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 root crown if aerial foliage is
cut late in the growing season [
95]. In related species such as
salmonberry (R. spectabilis), apical dominance exerted by extant
root crowns 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
viability 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].
Seed banking: 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. alleghaniensis) 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].
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Halved raspberry 
