More info for the terms: apomixis, duff
Trailing blackberry exhibits vigorous vegetative regeneration but also
commonly reproduces through seed. Reproductive versatility is common 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 fruits
without fertilization) occurring widely. The following types of
reproduction have been documented in blackberries: (1) sexual
reproduction, (2) nonreduction at meiosis on the female, male, or both
sides, (3) apomixis (seed contains embryo of maternal rather than sexual
origin) with segregation, (4) apomixis without segregation, and (5)
haploid parthenogenesis [11]. These modes of asexual reproduction
contribute to the aggressive, vigorous spread of blackberries.
Vegetative regeneration: Most species within the Rubus genus are
capable of vigorous sprouting from root or stem suckers, or rooting stem
tips [24]. Trailing blackberry sprouts readily from "suckers"
(presumably root suckers), or "nonrhizomatous sprouts" after fire or
mechanical disturbance [9,52,61]. It is also capable of spreading
rapidly from trailing stems which root at the nodes [37,65]. These
modes of vegetative spread occur even in the absence of disturbance.
Seed production: Most blackberries produce good seed crops nearly every
year [6]. During the first year of development, blackberries grow from
perennial rootstocks or creeping stems and produce sterile vegetative
shoots known as primocanes [24]. Lateral branches which produce both
leaves and flowers (floricanes) develop in the axils during the second
year [24]. Black shiny drupelets are produced on the floricanes of
trailing blackberry [6]. Fruit is oblong to conical, and up to 0.8
inches (2 cm) in length [55]. 384,000 per pound (845,814/kg) [6].
Germination: Blackberry seeds have a hard, impermeable coat and dormant
embryo; consequently, germination is often slow. Most blackberries
require, as a minimum, warm stratification at 86 to 68 degrees F (30 to
20 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 [6]. 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 [3].
Seed dispersal: Fruit of the trailing blackberry is readily dispersed
by many small birds and mammals [27]. After they mature, the sweet,
succulent berries rarely remain on the plant for long [6].
Seedbanking: The seeds of most blackberries remain viable for at least
several years after being buried in the soil or duff [6]. Although the
precise length of viability has not been determined for the trailing
blackberry, Morgan and Neuenschwander [52] regard it as a species which
relies heavily on seedbanking for postfire regeneration. Average seed
densities of 290 per foot square (27 per m sq) have been reported in
western redcedar (Thuja plicata)/pachistima and western redcedar/
queencup beadlily (Clintonia uniflora) habitat types in coniferous
forests of northern Idaho [55].