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These notes are my personal notes. The course instructor or TAs have
no responsibility for the contents or any discrepancies between the materials
presented in the classroom and these notes. You cannot use or refer to these
notes to support or defend your answers on your exams. I suggest you use these
notes to complement your own notes, and not to solely rely on. I would
appreciate your feedback on any part of these notes that I may be
misunderstanding.
Ø None.
1.
Tropical Ecosystems (section 2)
About the talk
by Don Montan (?), the Director of Macroeconomics and Biodiversity Protection
program at WWF, and one of Dr. Hall’s graduate students.
·
When there
are some kinds of impact on organisms, proximate causes of the impact are
deforestation, pollution. Then ultimate reasons are population growth, economic
growth, corruption, and whole suite of reasons. Mostly people look at immediate
reasons for the destruction of ecosystems they wish to conserve, but in fact we
have almost no success stories with that resulted in the protection of
organisms. Therefore with this new program, WWF is trying to look at the
connection between macroeconomic policy and how impacts wildlife.
·
What’s our
perception of wildlife is doing here? – Game animals are more abundant than
before due to successful wildlife management of game animals. We have been
remarkably successfully for some species. Other species that used to be
abundant game species are grouses, ring-neck pheasants (imported). They are not
abundant anymore because of succession. The woods are older now and more
amenable for turkeys than for grouses.
·
There’s no
sense of anything that is completely human-domination of these tropical areas
(Bolivia and Madagascar). Instead of continual shifting cultivation, people put
cow and after a while, soil is washed away and the land is worth nothing.
People go on to the next spot. We are losing the tropical forests.
·
Forests in
New York are coming back. But that is only because we don’t have solar-based
economy but an industrial-based economy.
·
If you want to
go to ecosystems, the frontiers for what we need to do and know and understand
is at the interface of environment and, in some sense, economics. We need to
generate some kind of new economics. It’s not good enough to be a good
biologist any more. If you want to be a biologist, you need a new kind of
biology that link up with the social sciences. Example:
·
People in
Madagascar cut the forest that is surrounding agricultural valleys, drought
that used to come 1 in 8 or 9 years now come 3 to 4 year. Because forest allow
water to come slowly down into the valley through ground recharge and help
maintain agriculture when it doesn’t rain much in a particular year. People are
not going to protect ecosystems because they want to ecosystems. There are
economic reasons to protect the ecosystems.
How would you use
the word “efficiency” to judge whether a tropical forest is efficient or not?
Is Tropical forest efficient in nutrient uptake? Output = plant uptake, input =
nutrients from rain, decomposition, etc. To answer the question, we have to
compare the ratios of plant uptake to nutrients available between tropical
forests and Hubbard Brook or deserts. TRFs capture roughly the same amount of
incoming solar radiation as most other ecosystems do, in some cases a little
higher, in some cases a little lower. Tree uptake is high percentage, but also
lots of nutrient loss.
Tropical
ecosystems are old. “Old” means it has been a long time since the last
significant disturbance. Forests in northern U.S. are new (<10,000 years
old) because the land has been covered with glaciers until recently. Even below
the glaciers – Pennsylvania, Maryland – might be old because climate is
completely different now it was not too long ago.
In old
ecosystems, soils are red with iron or aluminum oxides. High rainfall = all
soluble nutrients are washed out. What their soils don’t have – N, P, Ca, Mg.
Why Fe, Al are left behind? – They are insoluble.
But not
everywhere in tropics have such soils – around volcano, (ex. banana soil in
Costa Rica), riparian, or swamps (Histosols – rich thick organic soil. On
average, soils in tropics are much poor in nutrient. Central Africa,
Adirondacks are very old portion of the earth. In these areas it is hard to
make living because soil nutrients are washed out. For example, the amount of K
around here is 60 times more than that in the middle Africa.
There are large
stocks in tropical forest. Large biomass is not necessarily indicative of high
productivity. It may increment very very slowly. People are fooled by lushness.
There are also very rich soils. It’s not correct to say all tropical soils are
poor. They are iron- and aluminum-rich. But iron and aluminum are not
nutrients.
Are tropical
forests efficient in their use of nutrients? We don’t know. In a sense they are
inefficient since nutrients are leached. You might say tropical forests are
good at retaining those nutrients that remain. There are two mechanisms:
·
Some plants
grow its root into leaf litters to directly suck up the nutrients.
·
Some plants
put roots grow up to a tree’s armpits for N released from trapped and dead
insects.
The big
four-year tree in Costa Rica we saw in Dr. Hall’s slides is growing on a rich
Andisol. Trees in tropics tend to grow very well if soil is good. Example, a
Finland’s well-managed forest produces 3 m3/ha/yr, whereas such
forest in Malaysia can produce 20 m3/ha/yr. Why should trees in tropics grow better? –
Because of long growing season. On the other hand, agricultural crops, ex.
corn, don’t grow well in tropics.
H.T. Odum, “I
don’t believe that any undisturbed forest is nutrient limited.” How can we say
that? Natural forests accumulate what they need. The stock of the forest has
all the inventory of what they need. When a tree fall and decay, the released
nutrients are picked up by roots of surrounding trees. K is critical in Puerto
Rico. If that’s the case, he also will say if a forest needs N, there will be a
feedback process that will encourage N fixers. He believes a natural forest has
all kinds of quite complex mechanisms for maintaining its own structure and
function so that it continues of producing over time. Self-organization.
Examples:
·
There are
bats in Puerto Rico that eats Cecropia fruits. There are never found except
where there was a relatively recent disturbance. Bats roost upside down on Cecropia
trees near clearings. Bats eat Cecropia fruits. At 6:00pm so, which is their
morning, they wake up and fly around over the clearing for warm-up before they
leave for searching food into the forest. As they fly, they poop, which become
fertilizer for the new growth in the clearing, i.e., the early success ional
spots. H. Odum argues there’s a co-evolution between Cecropia and bats that
maintain forest structure and function. It’s a coevolved relation that will
produce many more Cecropia that will lead to the forest growing back more
rapidly and hence less loss of nutrients. There’re whole co-evolved systems
here of maintaining the forest structure and function in which the bat is a
component that has been selected for as an agent. And bats are reward by getting
more Cecropia fruit and higher energy gain in its life and would work to propel
its gene into the future.
·
Ants and acacia.
Acacia provide ants with swollen thorn as shelter and Beltian body for food.
Ants provide with protection from herbivores and competitors.
·
Soil
samples collected from a Costa Rican tropical rain forest were all low in N
except from one location, which was happened to be an old leaf-cutter ant’s
nest. Leaf-cutter ants chew leaves and grow bacteria and eat the bacteria which
are N-fixers. Leaf-cutter ants are considered to be bad for trees. But in
ecosystem perspective, these old leaf-cutter ant’s nests are source of the
whole ecosystem. Even roots 400m away grow into the nest and take takes up N
from the old nest.
These are three examples
of co-evolved relations of tropical ecosystems which are more characteristic in
tropical ecosystems than in any other ecosystems. Why should co-evolved
mechanisms more characteristic in tropical ecosystems? – Because they are old.
Things about tropical
ecosystems – which are true?
1) Higher diversity
2) Most of nutrients are stored in
vegetation
3) Year-round sun light
4) Narrow range of temperature
5) Poor soil fertility
6) High rain fall
7) Rapid decomposition
8) Open and closed
9) Daily fluctuation of temperature > annual
fluctuation
1) Trees – yes, birds – yes, Lizards – no.
Bird diversity – here: 80 to 90, tropics around 500. Why? – Migration.
2) Lugo says wrong. No example shows
nutrients are more abundant in the vegetation of the tropics than in the soil.
Correctly, nutrients in tropical soils are often less than in temperate soils.
But rarely are more nutrients in the vegetation than in the soil (???).
3) Yes, but correct to say more intense
sunlight. Tropics are cloudier.
4) No. For example, top of Mount Kenya near
equator has wide range of temperature.
5) Depends.
6) Depends. Yes on equator. Not inland,
rainshadow, cold upwelling spots.
7) True in rain forest.
8) ?
9) + or - correct.
·
Luquillo
Experimental Forest (LEF): trail.
·
Higher
elevation in LEF: Completely different type of trees. Colorado trees, also
found in Florida and N. Carolina. This forest is very much dominated by one
species. We must be careful about diversity. 100 tree species if you sample
10ha of this vicinity, or 200 species on the whole mountain. Similar places in
Costa Rica have 2000 species. Characteristics of islands.
·
After
disturbance: tree fall due to hurricane. Disturbances are normal part of this
ecosystem.
·
Upper
forest: plantains (banana family). Continuously bathed in mist – little
transpiration.
·
Trees in
upper forest are only 20 feet tall and don’t grow tall. Soil water is
saturated. Another theory is that transpiration is low because the air is
saturated and molecules don’t’ leave stomates.
·
Land
slides: soil is saturated and slides down. Roads themselves generate
landslides.
·
Hurricane:
November. No leaves were left on trees.
·
Ridges are
protecting the vegetation of the other side of the mountain from hurricane
damage.
·
Human
disturbance: within 20 miles of San Juan.
Last modified:
April 22, 2001.
Any comments?
E-mail to akogawa@syr.edu