On 17 July, Alexander Friend wrote:
>Is anyone else bothered by the mis-use of the photosynthetic gas exchange
>phenomenon to imply that deforestation will threaten our oxygen supply? If
>so, have you seen or written anything accessible to college sophomores on
>the subject?
I understand your objection and agree that deforestation will have little
direct effect on atmospheric oxygen. But the greater impacts of rampant
deforestation must not be lost in the shuffle. You are correct in your
apprehensions about the misuse and misstatements concerning the direct
effects of deforestation on atmospheric oxygen, but the greater
miscalculation is the assumption that trees are a renewable resource.
With this error there is some logic to suspect indirect damage to
photosynthetic oxygen production could be significant.
The ecological and sociological consequences of uncontrolled clearing and
excessive harvesting must be considered alarming. Temperate and tropical
deforestation may have dramatic effects on climate, nutrient cycling, and
both bio productivity and species diversity. Human activities ever
increasingly affect well established modes of bio productivity. Some
estimates in the mid-80's suggested that more than 40% of earth's bio
productivity was influenced by human endeavors causing habitat disruptions:
farming, mining, fishing, housing, transportation, aerosols, pollution,
and xenic species introductions. The list is endless and our populations
grow. As habitat degrades, the sociological impact of these activities
stagger the imagination and amplify the damage.
Forestry science needs to continually press for stronger ecological models
for harvesting timber and for the political/economic understanding that
management of forests is on a centuries, not a fiscal year, time scale.
When a tree is removed from an ecological community, non renewable
nutrients are removed AND the fundamental dynamics of the community are
altered. Two examples:
Pennsylvania has a wonderful commitment to maintaining forested lands.
Their state forestry program is one of the best. Yet, in Pennsylvania,
native forests are essentially gone and have been gone for more than a
century. The mix of tree species has been altered forever and in many
areas "suboptimal" species flourish. As you walk the forests you can find
signs of massive die-offs of these suboptimal species and of displaced
native species. Many of these disrupted communities are potential
reservoirs of disease/disease vectors and compete for limited nutrients
with the few remaining native species. The entire system is potentially
instable and susceptible to massive disruptions. So there is damage to the
productivity of those areas that lingers HUNDREDS of years after the
forests were initially harvested.
In the tropics, immediacy of need (political, economic, social, etc.)
continue the ravage of the only ecologically viable entity in those
regions...the rain forests. Farming and housing are not compatible with
the soil and climate of the region. The result of this havoc has been
increasing soil erosion and nutrient loss. During the rainy season, the
sediment plume from the Amazon can occasionally be seen hundreds of miles
off shore. Sediment and particulates are major impediments to aquatic
photosynthetic activity. Continental shelves comprise perhaps 5 percent
of the oceans surface area but are major spawning grounds for most marine
animals and major nutrient exchangers. If the primary producers in shallow
waters suffer, the resultant hypoxia will disrupt the entire marine food
chain.
Clearly these two examples appear to be extremes, but while the situation
in Pennsylvania is not nearly as threatening as that of Africa or South
America, it is just as real. The bioproductivity of the Delaware and
Chesapeake Bays have degraded significantly over the centuries in part
because of increased run off. The strength of our "American" economy has
mitigated sociological impacts and we have consequently ignored the
ecological impacts of our past misuse of these resources. In the tropics,
the ecological and sociological impacts will likely be more extreme. The
population pressures are greater, the ecosystem more fragile, and their
economic resources are meager...eventually their problem will be our
problem.
Perhaps this string on the oxygen myth will expand into an exploration of
the myraid issues related to ecological models for resource utilization and
address the political issues attendant to implementing management
techniques based on those models.
rlh
Richard Hall
Comparative Animal Physiologist
University of the Virgin Islands
