Re: Greasewood
- To: ,
- Subject: Re: Greasewood
- From: J*
- Date: Thu, 21 Sep 2000 07:06:41 -0700
The following information is from the Fire Effects Information System,
available on the web. Chamise is another common name for Adenostoma
fasciculatum. You'd have to go back to the FEIS for the references that are
in brackets.
REGENERATION PROCESSES :
Chamise reproduces sexually and vegetatively. Since chamise seed
germinates at high rates only after fire, seedling recruitment and
population expansion are fire dependent [68,69]. Canopy rejuvenation
through the production of new basal sprouts occurs with or without the
influence of fire [68,70].
Reproduction by seed: Onset of seed production occurs early in chamise,
often by 3 years of age [27]. Seed production does not appear to
decrease with age. Ninety-year-old shrubs generally produce
substantially greater quantities of seed than those 20 years of age
[66]. Seeds are dispersed during the summer [69]. Because the small
achenes are not highly specialized for wind disperal, most seeds fall
near the parent plant [69]. Although the seed crop is abundant, the
majority of seeds are not filled and viability is quite low, in some
cases 0 to 4 percent [38,69,88,126]. Maximum seed production occurs
following winters with above-average rainfall [3,38].
Chamise produces a dimorphic seed population composed of dormant as well
as readily germinable seeds [16,126]. Dormancy is imposed by a more or
less impermeable seedcoat. Heat from fire scarifies the seedcoat and
stimulates germination [16,69,126]. Christensen and Muller [16] found
that germination was enhanced when seeds were exposed to temperatures of
160 to 180 degrees Fahrenheit (71-82 deg C) for 15 minutes. Keeley [69]
suggested that heat shock from fire and the presence of charate (charred
wood) may act synergistically to stimulate germination. In laboratory
studies, Keeley found that addition of charate significantly increased
germination (11%) relative to controls (4%). Maximum germination (18%),
however, occurred when heat-treated seeds were incubated in the presence
of charred wood [69]. Black sage (Salvia mellifera) apparently inhibits
chamise germination [131].
Under natural conditions, dormant seeds accumulate in the soil until
stimulated by fire to germinate [66,126]. Chamise seeds are unpalatable
and seedbanks apparently are not subject to heavy predation [111].
Consequently, chamise seed densities increase over time [133]. Seed
density in the seedbank beneath 9-year-old stands was estimated at 2,000
seeds per square meter while in 85-year-old stands, seed density was
approximately 21,000 seeds per square meter [132]. Abundant germination
from soil-stored seed occurs during the first rainy season after fire;
germination during the second year is uncommon [54,67,111]. Although
emergent seedling populations are quite high [45], mortality is
substantial during the first several years [39,54,120]. On sites in
southern California, approximately 90 percent of the seedlings that
germinated during March and April died within the first year [80].
Drought stress during late spring and summer is a major cause of
first-year seedling mortality [59,86]. By the end of the second growing
season, drought-induced mortality decreases as seedlings develop
sufficient root biomass [87]. Taproots of newly germinated seedlings
are barely 2 inches (5 cm) long by July, whereas taproots of 2-year-old
seedlings range between 8 and 12 inches (20-30 cm) [80]. Small mammal
herbivory contributes significantly to mortality [17], particularly in
the fall [85]. First-year mortality due to rabbits may be as high as 25
percent [85]. Failure to establish may also be due to lack of suitable
microsites and competitive interference [43,86]. On southern California
burns, survival of first-year seedlings was not affected by the presence
of residual shrubs or herbaceous perennials; annuals, however,
significantly reduced seedling growth [80].
Many chamise plants die during subsequent years [48,120], but some
survive [48,54]. Twenty-five years after a fire in central California,
chamise resulting from seed were still growing and had reached an
average height of 31.9 inches (80 cm) [54].
A portion of chamise seed germinates without fire scarification under
favorable moisture and temperature conditions [126,133]. A study of the
seedbank beneath an 85-year-old stand of chamise indicated that 20
percent of the chamise seedbank (density averaged 9,500 chamise seeds/sq
m) was readily germinable [133]. Although initial establishment
sometimes occurs without the influence of fire [35,54,101], seedling
survival beyond the first year is extremely low and usually limited to
areas recovering from human disturbance or overgrazing [135]. In mature
chaparral, seedlings occasionally establish in canopy gaps, but
successful establishment almost never occurs directly beneath the canopy
[17,38,69,70,72,134].
Vegetative regeneration: Chamise rejuvenates its crown by continually
producing new sprouts from an established lignotuber [48,69,70].
Following disturbances such as fire or cutting, chamise sprouts
vigorously from surviving adventitious buds on the lignotuber [57,120].
-----Original Message-----
From: Patti <mtpander@earthlink.net>
To: medit-plants@ucdavis.edu <medit-plants@ucdavis.edu>
Date: Tuesday, September 19, 2000 9:34 PM
Subject: Greasewood
>Hi,
>
>Just a quick question. My son has a science question of which I'm not
>sure the answer. Can anyone help? What does Adenostoma ( Chamise,
>greasewood) need to reproduce? Western Garden Book doesn't say, nor do
>any of the websites we've checked. Any help would be greatly
>appreciated!
>
>Thanks,
>Patti
