Very interesting thread. From an economical perspective, the issue of alternate bearing is indeed
important to fruit farmers, as it seems that all trees of the same variety in a certain area will follow
the same pattern seasonally. In my experience, avocados (Hass) typically have "on" and
"off" years which is represented regionally, and this trend can affect market price
significantly. An "on" year creates a glut and low market prices, as everyone has a bumper crop
that year. (this trend is more complicated now with the importation of foreign fruit) Alternate bearing
can be pretty extreme with avos, with harvests ranging from 15,000 lbs/acre to 2,000 lbs/acre.
However, if you had Hass avocado trees (the variety is important in a commodity market)
that were unaffected by alternate bearing, you would be a happy farmer. You would have
above average harvests during "off" years and your crop would demand a higher
price, as a result of limited supply. I imagine plant breeders have tried to get
around this one, but I am not sure (anyone know?).
The process of "thinning"- removing small fruit- is very common with most
stone and pomme fruits, mainly because if you remove 1/2 to 2/3 of the fruit you will
get larger fruit (and we all know that bigger is better :) Thinning is not feasible
with avocados as the trees are usually too tall, and they tend to drop excess fruit
during the year on their own accord. I have never heard that thinning was an attempt
to disrupt alternate bearing. Also, in my experience thinning is mainly practiced on
deciduous trees.
>From and evolutionary biology perspective, I am not too convinced of the predator
satiation hypothesis- this appears to be a Darwinian approach based on competition. I
agree that the more fruit a tree produces the more the animals will plant it (not just
squirrels but birds), and it would be a "reproductive advantage" to have more
fruit every year.
I think alternate bearing (in some trees at least) is based more on weather
(and possibly that the tree simply needs rest after a big year). Here in
Southern California we can tell if we are going to have good winter rains if
the coast live oaks set lots of acorns. The trees seem to know that there
will be good conditions for their fruit to grow into new trees and they pump
them out.
Loren Luyendyk
805-452-8249
Permaculture Design and Education
ISA Certified Arborist #WE-7805A
www.sborganics.com
www.globalpermaculture.com
www.surferswithoutborders.com
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