With aknowledgement to Wayne Tyson for his comment regarding the
importance of a theoretical foundation and practical research before
acceptance of such statements as those Sr. de Alba Avila questions,
doesn't it defy the laws of chemistry, physics, and common sense to say
that rapidly growing trees are putting more carbon into the atmosphere
than they store? Excuse me, but do the proposers of this idea think that
the rapidly growing trees are CREATING the carbon atoms that they are
using to build tree tissues, and that they are respiring. Perhaps they
have not heard of photosynthesis. It is true that the trees are being
built largely out of thin air, but the carbon being added to tree trunks
is carbon that is being REMOVED from the atmosphere. Certainly some
carbon goes back into the atmosphere as a result of respiration needed
to convert the simple sugars created by photosynthesis into more complex
cellular materials and into the woody xylem that represents long-term
carbon storage, but the sum total of carbon ending up in those two
compartments: carbon stored in wood and carbon respired back into the
atmosphere, must be equal to the amount of carbon originally withdrawn
from the atmosphere. Ecological studies report that carbon storage is
greatest, rather than least, in rapidly growing young stands of trees.
His other quoted statement: "it is argued that the root loss due to
grazing can increase the net C content in the soil" is equally difficult
to understand. In grassland soils, carbon captured (again, FROM THE
ATMOSPHERE) through photosynthesis in the aboveground grass blades is
stored in roots as starch, xylem and as other plant tissues. Thus root
loss implies loss of carbon from the soil, not a gain, as grasses use
stored carbon (in starches and sugars) to build structures aboveground
which can capture solar energy. Thus stressing a grassland ecosystem by
heavy grazing will increase the rate of withdrawal of carbon from the
soil, as plants seek to replace lost foliage, thereby causing loss of
root mass and loss of carbon from the soil.
In both cases, it is important to understand that the source of all the
carbon in the system is the atmosphere, and subsequent disposition of
the carbon needs to be accounted for, as Odum does so well for energy in
his energy flow diagrams.
mike
