Chemistry Reference
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age of 2-8 years with stomatal conductance and transpiration by the method of sap flow in
Australia. These authors observed an increase in transpiration of the stand from 2 to 5 years
of age, where it reached to the peak in rates of exchange with subsequent decline thereafter.
This decrease was related to the decline of leaf area index, with the result in annual growth
rates and efficiency of water use. Although in our study, transpiration and stomatal
conductance have been obtained at leaf scale by porometry, these variables had the same
behavior found by them, i.e., the major tendencies of transpiration rates were observed in
the plot and watershed scales, where individuals were more developed. We should also
remember that the measurements, at whatever age (pot, plot or watershed scales), were
always performed only in fully expanded leaves at the top of the canopy directly exposed to
solar radiation. The difference between our study and [10] is that the evaluations performed
by the method of sap flow are closely related to the total leaf area of the crown, without the
need to quantify the leaves that consist it, nor the diversity in the degree of development of
each one of them. The leaf area index is generally considered the most important
determinant of differences in transpiration between different forest stands [13, 28].
Generally, young forests have a higher concentration of leaf area in a single layer of canopy,
while as the tree grows, the leaves are more uniformly distributed in generating various
vertical profiles of leaf area [29] and these changes in the distribution of stem and leaves can
have pervasive effects on canopy transpiration.
The justification of this work for having higher gas exchange tendencies, at the leaf level , in
the plot and watershed scales may be explained by the fact that individuals did not reach
their peak of development, as justified by [10]. Thus, the physiological activities continue to
"full steam" favoring the growth of biomass. So that, in terms of forest production, in the
decision making about the best time for cutting the planted forest (
Eucalyptus
sp), it is
studied the balance of production curves and mean and yearly increments, with the aim of
identifying the maximum mean rate of increase in production. When this point is reached, it
is said that this is the peak production of the forest, that is, when it reaches its greatest
efficiency in production (technical age for cut-off). After this peak, there is a decline in the
production curve, and economically speaking it is not feasible to keep the tree standing.
The scaling up of information held on a lower scale to a higher scale is more problematic for
several reasons. The transpiration of most plant species, including eucalyptus, is determined
by several factors that vary continuously. In addition to age, among them are climatic
demand (solar radiation and vapor pressure deficit of the atmosphere, temperature and
wind speed), the physiological mechanisms related to the stomatal response to
environmental factors, water availability and soil nutrients [6, 20]. Another issue addressed
by [12] which is normal to expect that the rate of perspiration varies from species to species,
as well as vegetative growth.
Since transpiration is related to the development of leaf area in plantations of short duration
such as eucalyptus, which have high rates of initial growth, can also happen fast
maximization of water use by these crops, which ultimately generate implications for the
prediction of its water needs and impacts on watershed hydrology.
