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Daily Weather and Tree Growth at the Tropical Treeline of North America
Franco Biondi (*), Peter C. Hartsough (*), Gregory D. McCurdy (**), and Scotty Strachan (*)
(*) Department of Geography, University of Nevada, Reno, NV 89557, USA
(**) Western Regional Climate Center, Desert Research Institute, Reno, NV 89512, USA
Abstract
We present here the 2001-2003 results of intensive monitoring studies aimed at quantifying tropical treeline climate and
radial increment of Pinus hartwegii Lindl. trees on Nevado de Colima, in the middle of the North American Monsoon region.
An automated weather station was installed at 3760 m elevation, 19˚34.778' N latitude, 103˚37.180' W longitude, within a
forest where multi-century tree-ring records had been previously developed. At the same time, automated electronic
sensors for recording tree growth at half-hour intervals were set up at two sites located within a 1-km radius from the
weather station. Meteorological observations recorded every half-hour were summarized on a daily basis. Time-series
patterns are reported for atmospheric pressure, precipitation, incoming solar radiation, air and soil temperature, relative
humidity, soil moisture, wind speed and direction. Of particular interest is the sudden decrease in air temperature after the
onset of the monsoon season, which determines very high relative humidity over the summer and results in air
temperature having a spring maximum. Dendrometer data show that the timberline growing season begins in March-April
and ends in October-November. As an unexpected result, it was also possible to measure the progressive decline of
Pinus hartwegii stem increment in response to an outbreak of roundheaded pine beetle (Dendroctonus adjunctus
Blandford), which ultimately killed most trees at one of our two experimental sites.
N
V
Elevation (m):
50˚N
The station was deployed in an area that is relatively accessible with a four-wheel drive vehicle,
and that is actively being protected for conservation and research purposes by ‘El Patronato del
Nevado de Colima y Cuencas Adyacentes, A.C.'.Permission to install the equipment was obtained
from the local authorities with the help of Prof. Ignacio Galindo, Director of the ‘Centro Universitario
de Investigaciones on Ciencias del Ambiente' at the Universidad de Colima, Colima, Mexico.
0.7
J F M A M J J A S O
J F M A M J J A S O
Jan 14
Oct 25
Total Precipitation (mm)
Oct 25
Mean Soil Water Volume (%)
J F M A M J J A S O
Mean
Standard
Deviation
Minimum
Maximum
5.03
654.54
10.2
1.3
9.0
11.2
8.3
2.9
30.35
4
90
47
43
31.1
6.6
121.2
36.8
1.95
1.42
2.7
2.2
2.6
3.4
3.0
1.2
3.41
12
16
28
22
10.7
2.8
106.2
6.8
0.41
646.10
-0.9
-7.7
1.5
1.1
0.9
0.1
20.80
0
9
0
0
13.2
2.7
0.0
0.5
9.01
657.70
18.2
7.5
15.6
18.8
16.3
9.7
44.30
164
100
100
95
80.0
29.5
359.9
61.2
Table 2. Features of Pinus hartwegii trees outfitted with point and band dendrometers on
Nevado de Colima, Mexico.
Easting 1 (m) Northing 2 (m) DBH 3 (cm)
Missing data from 1:00 pm on March 31st, 2002 until 2:30 pm on June 6th, 2002.
2
Missing data from 6:30 am on November 16th, 2002 until 4:00 pm on March 16th, 2003.
3
Missing or off-range observations from 7:00 pm on May 28th, 2003.
4
Missing data from 5:30 am on December 8th, 2002 until 4:00 pm on March 16th, 2003.
5
Missing or off-range observations from 12:30 pm on July 20th, 2003.
22.972
20.400
19.129
31.426
16.741
12.450
0.000
55.5
49.1
63.4
56.2
51.9
71.1
37.9
18.0
PD
15.6
PD
24.0 PD, PDN, PDB, BD
22.5
PD, PDN, BD
19.2
PD
20.8
PD, PDN, BD
14.4
PD
tree 1
tree 2
tree 3
tree 4
tree 5
tree 6
tree 7
tree 8
-26.097
-21.418
-24.148
-9.141
12.790
15.498
12.832
9.841
-4.602
1.874
6.470
-8.230
5.694
0.271
-8.333
-11.321
35.1
68.1
55.8
43.0
99.5
59.5
54.6
66.7
15.4
21.0
18.9
12.0
22.5
15.9
18.0
21.0
PD, PDH, BD
PD, PDH
PD, BD
PD
PD
PD
PD, BD
PD, PDB
X-coordinate measured from the underground field computer
Y-coordinate measured from the underground field computer
3
Stem diameter at breast height (1.3-1.5 m above ground)
4
PD = point dendrometer; PDN = point dendrometer on north side of the stem; PDB = point
dendrometer outside bark; PDH = point dendrometer higher along the stem; BD = band dendrometer
PD tree 1
PD tree 2
PD tree 3
PD tree 3N
PD tree 4
PD tree 4N
BD tree 4
PD tree 6
PD tree 7
Cumulative Stem Increment (mm)
8.5
8.0
7.5
7.0
6.5
6.0
5.5
A complete representation of seasonal growth
patterns is given by point dendrometers at site
5.0
4/4/02
4/14/02
4/24/02
5/4/02
5/14/02
5/24/02
6/3/02
1 (figure below). From these measurements, it is
Calendar Day
clear that diurnal cycles unrelated to wood growth
are smoothed out and irrelevant when records are plotted over several months. It is also evident that wood formation
begins in March-April and continues until October-November, and that a definite dormant period occurs between
growing seasons. Considering the patterns observed for weather variables, one can say
that tree growth begins in response to increasing spring temperatures, and then continues
because of summer precipitation. The graphical relationship between stem size and
precipitation also reveals that occasional winter storms can create a temporary swelling
of the trunk, which gradually returns to its previous size when water evaporates. This
‘hydration’ noise is much larger for point dendrometers that measure radial changes
outside bark (not shown). It has also been possible to monitor "in real time" the effect of a
bark beetle infestation (clearly marked on the bark by yellowish resin mixed with boring dust).
In 2002, trees 2 and 5 (the
11.0
infested ones) display stem
precipitation
sizes that are either flat or
10.0
tree 1
tree 2
declining, whereas trees 1
tree 5
9.0
and 7 (spared by the insect
tree 7
outbreak) are growing just
8.0
like in the previous year.
15
7.0
10
6.0
5
Calendar Day
9/17/02
8/8/02
6/29/02
5/20/02
4/10/02
3/1/02
0
1/20/02
12/11/01
11/1/01
9/22/01
7/4/01
4.0
8/13/01
5.0
5/25/01
Oct 25
Jan 12-13
-13.803
0.000
5.485
13.992
17.336
25.526
9.000
2
Precipitation (mm)
The impact of tropical depression Kenna is clearly visible on Oct 25th, 2002. However, a few other storms had a greater
impact than Kenna. In particular, on Jan 13th, 2002, the atmospheric pressure dropped to 645 mb, almost 6 standard
deviations below the long-term mean of 654.5 mb, and 5 mb less than usual minima. Air temperature was extremely
low, with the maximum falling below 0˚C (only on this day), to -0.85˚C, and the minimum reaching -7.47˚C (and -7.66˚C
the day after), 3˚C less than any other minima recorded at the site. Furthermore, Jan 12th was extremely cloudy, as
shown by the very low value for incoming short-wave radiation. On Jan 13th the mean 30-minute standard deviation
of the wind vector direction was only 0.5˚, much lower than usual. Winds were therefore constantly from the south
(171˚), and extremely strong. In fact, both wind speed and wind gust were initially considered missing for that day
(because the sonic wind sensor showed values of 1000 mph), but they very likely exceeded 160 km/h.
tree 1
tree 2
tree 3
tree 4
tree 5
tree 6
tree 7
1
1
Cumulative Stem Increment (mm)
Max Relative Humidity (%)
N D J F M A M J J A S O
Min Relative Humidity (%)
J F M A M J J A S O
Sensors 4
Site 2
J F M A M J J A S O
Jan 22
M J J A S O N D
Height (m)
Site 1
Time-series plot of stem size during two months
in 2002 can be used for comparing growth
patterns measured by different sensors.
Measurements are taken at half-hour intervals
by band (BD) and point (PD) dendrometers
mounted on six trees at site 2.
Jan 21
Max Soil Temperature (%)
N
9.0
M J J A S O N D J F M A M J J A S O N D
M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O
In May 2001 we also installed automated point and band
dendrometers (Keeland and Sharitz, 1993) to measure
stem increment of Pinus hartwegii at half-hour intervals
at two locations within a 1-km radius from the weather
station.
Table 1. Summary of daily weather observations recorded at Nevado de Colima, Mexico, from
May 22nd, 2001, to October 31st, 2003.
Total Incoming Short-wave Radiation (kJ m-2)
893
Mean Barometric Pressure (mb) 1
827
Maximum Air Temperature (°C)
893
Minimum Air Temperature (°C)
893
Air Temperature Range (°C)
893
2
Maximum Soil Temperature (°C)
774
Minimum Soil Temperature (°C) 2
774
2
Soil Temperature Range (°C)
774
Mean Soil Water Volume (%) 3
775
Total Precipitation (mm) 4
796
5
Maximum Relative Humidity (%)
874
Minimum Relative Humidity (%) 5
874
874
Relative Humidity Range (%) 5
-1
892
Maximum Wind Gust (km h )
Mean Wind Speed (km h-1)
892
Mean Wind Direction (°)
893
Mean 30-min Stand. Dev. of Wind Direction (°)
893
M J J A S O N D J F M A M J J A S O N D
J F M A M J J A S O
M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O
A summary of weather variables is given below,
and details are included in a manuscript currently
under reviews (copies are available from F. Biondi).
M J J A S O N D J F M A M J J A S O N D
J F M A M J J A S O
Min Soil Temperature (˚C)
M J J A S O N D J F M A M J J A S O N D
Soil Temperature Range (˚C)
M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O
Variable
M J J A S O N D J F M A M J J A S O N D
M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O
Mean Wind Speed (km h-1)
0.6
M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O
Max. Wind Gust (km h-1)
0.5
Jan 13
Mean Barometric Pressure (mb)
Jan 13-14
0.4
M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O
M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O
Air Temperature Range (˚C)
0.3
Oct 25
Jan 13
J F M A M J J A S O
Min Air Temperature (˚C)
M J J A S O N D J F M A M J J A S O N D
0.2
M J J A S O N D J F M A M J J A S O N D
Jan 12
J F M A M J J A S O
Oct 25
Max Air Temperature (˚C)
M J J A S O N D J F M A M J J A S O N D
Total Incoming Short-wave Radiation (kJ m-²)
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2
88˚W
72˚W
Jan 13
96˚W
80˚W
Mean Wind Vector Direction (˚)
104˚W
64˚W
Mean 30-min St. Dev. Wind Vector Direc. (˚)
The strategic location of Nevado de Colima within the North American
45˚N
Monsoon system can be shown by the correlation (r) from 1915 to 1997
40˚N
between the Nevado de Colima tree-ring chronology (green star) and
35˚N
summer (June through August) Palmer Drought Severity Index over
30˚N
US climate divisions (Biondi 2001). Notice the relationship with the
25˚N
Midwest plains, which is consistent with the findings of Higgins et
= -0.22
= 0.37
20˚N
al. 1997. Symbol size for point correlations is directly proportional
to the absolute r value, as shown for the highest positive (blue
128
˚W
120˚W
upward triangles) and lowest negative (red downward triangles)
112˚W
point correlations. Contour intervals were objectively determined
(Smith and Wessel 1990).