blooming pattern: another variable?

Kenneth Hixson
Sat, 05 Nov 2005 19:31:39 PST
>Jim M, responding to Paul's post, said:
>I my earlier post I largely ignored the role of pollinators. But the more I
>think about it, the more important the role of pollinators seems to be.
>         Ummm, I am reluctant to disagree with either Paul or Jim M., but
it appears to me that something isn't being considered--pollenation is a
two way street, with the pollenated (the plant) deriving benefit, but the
pollenator (bee, moth, hummingbird, whatever) also getting something
from the act.  The pollenator may well cease to exist within a very short
time, while the pollenated (plant) continues to exist.  I still remember
seeing pictures of someone hanging from a rope over the side of a cliff
in Hawaii, hand pollenating plants whose pollenator had apparently
ceased to function, and without which the plants were unable to set
seed.  I even have similiar plants in my own garden--they're called Yucca.
My yucca had several hundred flowers this summer, and set no seed
pods, even though I hand pollenated some flowers.  Although the
proper pollenator isn't present, the yucca is.  I have seen a few seed
pods on yuccas in this area, so something occasionally does pollenate
yucca flowers, even if the cornuba moth doesn't exist here.
         It is my belief that the available plants affect the population of
pollenators even more than the pollenators affect the reproduction of
plants.  Plants can continue to exist and propagate, without seed
production, but pollenators will cease to exist within a very short period
of time without plants.

>Harold pointed out two advantages of autumn bloom: less competition for
>pollinators and a reduced likelihood of rain damaging the pollen.
         There is a camellia nursery in North Carolina which touts the
advantages of fall blooming camellias, specifically, by flowering in fall, the
flowers are not damaged by winter freezes (though seed production may
be affected) and by flowering in the fall, camellia flowers are unaffected
by a fungus disease called camellia petal blight which occurs in the spring.
         These two reasons are equally applicable to bulbs--or any other
plant for that matter.  The problem with less competition for pollenators
is that many pollenators have attuned their life cycles to specific periods
of time.  In my area, and many others as well, there are solitary bees
which only are active for a very short period of time.  Orchard Mason Bees,
for instance, hatch about the time apple trees flower, mate within a week,
pollenate fruit trees, lay eggs, and die within a month or six weeks.
They are very efficient pollenators of fruit trees at a time when common
honey bees are inactive (it's too cold for honeybees) but it is hard to
build up a large population to pollenate apple orchards, and they don't
pollenate much other than fruit trees.  They wouldn't do much for flowers
at any other time of year.  In fact, they probably do not pollenate much
other than fruit trees, even if other things are flowering when they are
active.  As pollenators, the are fairly restricted in what they will pollenate.

>Alberto pointed out that autumn flowering positions
>the ripening seed to take advantage of the long growing season ahead. Again,
>this undoubted advantage would work to favor plants which are already by
>nature autumn blooming.
         But so does summer flowering.  Western american lilies flower in
June or July when the weather is great for pollenators.  The seed ripens
relatively slowly--not until August, September, even October.  It falls to the
ground, gets exposed to cool moist conditions (a prerequisite for many
western american seeds) and germinates.  I've seen lily seed germinating
before Thanksgiving/late November, with the full effect of winter still to
come.  Other western american bulbs follow a similar pattern, though often
not ripening as slowly.  It is quite common for native bulbs to ripen seeds
on a stalk of a plant that has already died to the ground, with only a bare
seed stalk and seedpods remaining.  Obviously, winter is less of a danger
than the hot, dry summer.

>Paul focused on the significance of the seasonal activity of pollinators,
>and really hit the nail on the head: his explanation accounts for the very
>existence of seasonal flowering in some plants.
>Paul's explanation makes sense in a climate where pollinators and plants are
>active throughout a long season. Paul said that if an ancestral plant
>population were active all year, but its pollinator came to be active only
>part of the year, eventually the plant flowering season would shift to
>reflect the period of activity of the pollinator. If the pollinator's major
>season of activity were autumn, then you would get autumn blooming plants.
>         If the pollenator were the Orchard Mason Bee, and the plant were
a  fall flowering camellia, the camellia would continue to exist--but the
Bee would be extinct.  Pollenator and pollenated is a two way street--both
affect the other to some extent, but they are not the only, and probably
not the most important reason for why plants do what they do.
  Imagine an oak tree--not insect pollenated, but it produces thousands
perhaps millions of seeds (acorns) in the course of its' existance.
Only one is needed to continue the existance of the oak tree.  Producing
thickets of competing seedlings is actually detrimental to the continued
existance of the parent plant.

>Pollinators are probably the major cause of fall blooming plants.
>         I believe it more likely that environmental conditions--favorable
growth conditions for seedlings/small plants without much nutrient
reserves, are far more important, and pollenators have managed to
evolve to take advantage of a nutrient source.

>Let's take it a step further. Paul's scenario would account for the
>emergence of a seasonal flowering flora anywhere.
         Ummm, I can't agree.

>Because plants which bloom in the spring provide pollen and nutriment to
>pollinators, it makes sense that the competition of pollinators for the
>earliest pollen sources would cause the plant populations they pollinate to
>become progressively earlier in their flowering time. The pollinators select
>plants for early bloom, and they thus cause plant populations to bloom
>         Only if you ignore the effects of environmental conditions such as
frost, rain, fungus diseases, grazing by herbivores, etc  The first flower to
bloom may well be the one that gets grazed, whether pollenated or not,
while one of hundreds in flower at the same time may be ignored.  If you
look at what actually happens, plants flower at a specific time, which can
be predicted fairly accurately for most plants.  The presence or absence
of pollenators probably doesn't affect the flowering date.  Actually, being
selected by a gardener for earlier or later flowering is a more likely result
than the actions of pollenators.

>Many bulbous taxa seem to have been pushed to three extremes: fall blooming
>at the beginning of a fall-winter-spring growing cycle, late-winter/early
>spring bloom in areas with severe winters,  and summer blooming at the end
>of the growing season (the themidaceous/Calochortus cycle) in some dry
>summer areas. Each provides advantages to the taxa in question: reduced
>competition for pollinators, specialized pollinator relationships and
>enhanced seedling survival.
         To me, it appears that enhanced seedling survival is more important
than all other factors combined--at least, on western american bulbs/plants.
This isn't necessarily true for all climates or all plants, but in my area 
it does
seem true.

Ken     Zone 7? westen america 

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