Geoscience Reference
In-Depth Information
In Nevado de Colima, a 3900 m elevation site in central western México,
we have been co-monitoring stem growth and weather on two plots of
Pinus
hartwegii
. The monitoring network consists of a meteorological station and
two sets of dendrometers installed on pure stands of
P. hartwegii
located
~100 m below tree line. This species has previously shown promise for pale-
oclimate analysis because of sensitivity to the North American Monsoon.
Co-measuring tree growth and climate over a 3-year period has allowed a
better understanding of the complex response of this species to changing envi-
ronmental conditions. Box Figure
7.18
shows that the onset of spring growth
is coincident with soil temperatures higher than a threshold of around 3.6ºC.
Summer growth, however, is dependent on monsoon precipitation, with high
correlations to precipitation and relative humidity. The pattern of growth mir-
rors the lull in the monsoon in late summer. We also have confirmed the
cessation of growth and shutdown of cambial activity in the winter months at
this high-elevation tropical site. Long-term ecological monitoring has allowed
direct correlation at daily and monthly timescales between tree growth and
weather. It is desirable that the monitoring previously described be continued
over long time periods to better understand the radial growth behaviors.
—F. Roig, P. Hartsough, G Massacchesi, F. Biondi, and G. Martinez Pastur
In South America, the only chronologies that presently extend into the mid-
Holocene are for
Fitzroya cupressoides
from southern Chile. The Volcan Apagado
(41º35
S, 72º30
W) chronology is now the longest continuous chronology in the
However, much more work is needed to develop multimillennial length chronolo-
gies encompassing most of the Holocene and employing other species in more arid
regions of South America.
As in other areas of the world, it is also possible that anthropogenic activities
may be subtly changing climate-growth relationships in these trees, compounding
the difficulties of isolating a clear climate signal in these records. The recent high
growth rates of
Nothofagus
at the upper tree line across Patagonia provide a major
piece of evidence to assemble a case for anomalous regional warming in response
to be a valid interpretation of the data, changes in the efficiency with which water is
used in relation to increased atmospheric CO
2
content (fertilization), may also exert
some influences on tree growth.
7.5 Discussion and Conclusions
Precisely dated, annually resolved tree-ring records from numerous sites through-
out the Americas provide the basis to evaluate the changing signatures of tropical
and high-latitude modes of climate variability, their time-evolving patterns, and their
