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Conservation in the tropics and
Prosopis: The allpurpose tree
Paul R. Earl
Save the planet!
OUR PLANET seems to be drying out, and
water wars not so far off. The primary selection
factor may become humidity. The planetary
extremes have always been ice and sand, and
resistance to desiccation is likely to soon involve
the genetics of crop plants. Although the fight
for food is perhaps more obvious than the one
for water, both exhibit the Mathusian notion
that geometrically increasing demand exceeds
arithmetically increasing supply. Thus,
overpopulation is accelerating.
Sensitive actions like deforestation are
rapid and highly evident now, because of
human overpopulation. The Brazilian
disaster was forest fire for the benefit of
the cattle industry. Almost everybody
knows these things and does little about
them, because they are not empowered to
act positively. But also, the public likely
does not understand the fragility of the
ecology involved and even contributes to
green groups embezzling money.
Education and public health and add
development may well be poorly financed
just because they are not given priority.
This is true of research and also
conservation.
As we do not have the direct power to
make changes, we shall suggest tropical
legumes mainly for abandoned lands.
Peter Felker of Texas demonstrated the
applicability of mesquites to the lands
they are found on.
How does Prosopis (mesquite)
fit into rural development?
The use of trees as windbreakers in arid
lands is sufficient reason for promoting
them. Mesquites sometimes grow where
nothing else except cactuses can. However,
the days when they formed productive
hardwood forests are over. By
desertification kindled by man, the days of
trees over 100 years old are over, mostly.
The range for growth is governed
by the relative humidity and
temperature. When the air is dry,
the stomata of the leaves close and
photosynthesis stops. Then individual
biomasses and new tree establishment
are reduced. When the air is moist,
other species of shrubs and trees will
display successful plant composition.
“The rebellious sands are subdued and the
inhospitable soils are colonized. The dreary scene of
dry districts is changed to that of green belts. The
bleak treeless landscape is painted with splashes of
brown, green and yellow. The monotony is broken
for the traveler and the sheep and goats munch and
crunch happily on the proteinous pods. The rural
folk, whose lands were getting buried under drifting
sands are grateful to the Forester and Prosopis, and
the poor folk who had no fuel to burn in their
hearths now have Prosopis. They collect the fuel in
their leisure and sell in towns for a descent price.”
The pod crop, browsing leaves and
gathering fuel have been mentioned.
Charcoal for cooking and fence posts and
living fences along with fine furniture
including rich parquet floors are
attractive products. However, vegetation
to stabilize landscapes might be the most
important role for mesquites. The pod
harvest might be better appreciated, and
timber in all forms conserved and
protected.
Foliar morphology.
By eye, mesquites can only be told apart by
their foliar morphometrics. Prosopis has
species only in taxonomic dreams, since all or
most cross.
The illustration of the mesquite Prosopis
glandulosa is for the description by John
Torrey in 1828. Influourescences of over 200
individual flowers and pods are shown. The
flowering parts of all mesquites are similar.
Torrey’s mesquite is from Col. Long’s creek,
Union County, New Mexico, USA
The biological species concept
depends upon crossability.
Regardless at present, the taxonomic
species is more popular.
This means that about 80 taxonomic
species are taken as real,
although 2-3 or even only one
biological species exists (P. africana).
The 5 measures of the leaves are
a) LL length of leaflet,
b) LR length of rachis,
c) PL number of pairs of leaflets,
d) PR number of pairs of raches, and
e) LP length of the petiole.
LL, LR & LP are in mm, whereas PL & PR
are counts. Either 1 or 2 PR are common,
and the range is 1-4 PR. Four different
races are shown in the illustration. Other
morphological characters like has-or-hasnot spines are almost worthless.
If and only if different mesquites are grown
in a common garden can phenotypes and
genotypes be distinguished.
Mesquites have not been categorized into
satisfactory species by any means including
the polymerized chain reaction of DNA.
Most of the mesquites of the Americas cross.
Convergence is a large unresolved issue.
When a niche in Chile is the same as one in
Venezuela and another in Mexico, expect to
find the same leaf design. Favored hybrids
including mutants are fixed by the niche.
Some crosses of New World mesquites
demonstrating the high crossability among
Prosopis. Tiny is a new race from Sonora,
Mexico.
Similar leaf designs found far apart are
fixed by their niches that are perhaps
identical and do not necessarily have genes
acquired from common descent. Does this
sound like a Lamarckian argument?
Plantations like natural woods can slow
down soil erosion.
An ounce of prevention is worth a
pound of cure. This will not hold when
the damage is inevitable. Does this
slogan relate to sustainability?
Sustainability only applies to opulent
countries. The harsh nature of the
future ecology is being vastly
underestimated. Removal of woods
changes green to brown.
Then a mesquite plantation while approved
as a step in the right direction may
somewhat alleviate aridity but not cure it.
The redistribution of water through
evapotranspiration by shrubs and trees is
an enormous benefit of this cover. The
cover is sometimes accused of using up
water that it is actually redistributed.
Dimwitted people may believe that
mesquite-occupied areas are adversely
using all the water when the problem can
be human population/water.
Prosopis microphylla,
15 m high,
at Zumpango,
Guerrera, Mexico
beside a seasonally
dry arroyo (stream).
Maximum height of
mesquite at Lago
Chapala, Jalisco,
Mexico is 22 m.
Summary.
Standard commercial forestry does not
consider mesquites since generally
mesquite woods are exhaused by overuse.
They, in Felker’s words, “just hold the
world together.” Mesquites represent a
vital part of the tropical world, because of
their freatic ability to gather water through
times of drought and store it. Storage
means the shutdown of biomass
production.
Summary (cont).
They can grow a meter in height per
year if they get the water. They provide
browse, pod harvest and household fuel
wood. Vast arid territories support
silvopastoral systems. These lands cannot
sensibly be converted to crop lands,
and must produce at low levels.
Although mesquite plantations may not
be truely profitable, their value as
windbreakers is high.
Summary (cont).
A great problem is enormous destruction
by bulldozer landclearing and fires. The
common basis of desertification is the futile
attempt to grow crops when the native
vegetation cannot prosper. The final
problem is how to give higher values to arid
lands, while knowing that subsidies fail.
Perhaps mesquite product development can
extend beyond poverty, and improve the
quality of life.