Section 5.2: Background
79
5.2 Background
The annual growth of a tree is the net result of many complex and interrelated
biochemical processes. Trees interact directly with the microenvironment of
many leaf and root surfaces. The fact that there is a relationship between
these extremely localized conditions and larger scale climate parameters oifers
the potential for extracting some measure of the overall infiuence of climate
on growth from year to year.
Growth may be aifected by many aspects of the microclimate: for exampIe, sunshine amounts, precipitation, temperature, wind speed and humidity.
There are other non-climate factors that may exert an infiuence, such as
competition, defoliators and soil nutrient status. Nevertheless, wherever tree
growth can be dated absolutely and is limited directly or indirectly by some
climate variable, dendroclimatology can be used to reconstruct some information about past environment al conditions.
The general approach taken in dendroclimatic reconstruction work is:
• to collect (sampie) data from a set of trees which have been selected
on the basis of si te and phytosociological characteristics so that climate
should be the major growth-limiting factor;
• to assemble the data from individual trees into a composite site chronology by cross-dating and averaging the individual series after the removal
of age eifects (standardization);
• to build up a network of site chronologies for a region;
• to identify statistical relationships between the chronology time series
and instrumental climate data for the re cent period (the calibration period);
• to test, or verify, the resulting reconstruction against independent dataj
and
• finally, to use these relationships to reconstruct climate information from
an earlier period (the reconstruction period) covered by the tree-ring
data.
5.3 Site Selection and Dating
Not all trees are suitable for dendroclimatology. It is axiomatic that the rings
be dated absolutely. In general, dendroclimatology is difficult to apply in
the tropics where seasonal growth cycles tend not to occur (or not to occur
with any consistency). There is rarely a marked seasonal cycle in climate
conditions in the tropics. Plants without radial cambium, such as palms, do
not produce annual rings and cannot be used.
79
5.2 Background
The annual growth of a tree is the net result of many complex and interrelated
biochemical processes. Trees interact directly with the microenvironment of
many leaf and root surfaces. The fact that there is a relationship between
these extremely localized conditions and larger scale climate parameters oifers
the potential for extracting some measure of the overall infiuence of climate
on growth from year to year.
Growth may be aifected by many aspects of the microclimate: for exampIe, sunshine amounts, precipitation, temperature, wind speed and humidity.
There are other non-climate factors that may exert an infiuence, such as
competition, defoliators and soil nutrient status. Nevertheless, wherever tree
growth can be dated absolutely and is limited directly or indirectly by some
climate variable, dendroclimatology can be used to reconstruct some information about past environment al conditions.
The general approach taken in dendroclimatic reconstruction work is:
• to collect (sampie) data from a set of trees which have been selected
on the basis of si te and phytosociological characteristics so that climate
should be the major growth-limiting factor;
• to assemble the data from individual trees into a composite site chronology by cross-dating and averaging the individual series after the removal
of age eifects (standardization);
• to build up a network of site chronologies for a region;
• to identify statistical relationships between the chronology time series
and instrumental climate data for the re cent period (the calibration period);
• to test, or verify, the resulting reconstruction against independent dataj
and
• finally, to use these relationships to reconstruct climate information from
an earlier period (the reconstruction period) covered by the tree-ring
data.
5.3 Site Selection and Dating
Not all trees are suitable for dendroclimatology. It is axiomatic that the rings
be dated absolutely. In general, dendroclimatology is difficult to apply in
the tropics where seasonal growth cycles tend not to occur (or not to occur
with any consistency). There is rarely a marked seasonal cycle in climate
conditions in the tropics. Plants without radial cambium, such as palms, do
not produce annual rings and cannot be used.