Infrared Camera Measurements Reveal Diurnal Variation in the Effect of Mechanically Induced Internal Voids on Stem Temperatures of Small Trees Passively Heated by the Sun

Daniel C. Burcham; Eng-Choon Leong; Yok-King Fong; Puay-Yok Tan

doi:10.48044/jauf.2013.006

Article Figures & Data

Figures

Tables

Download figure
Open in new tab
Download powerpoint
Figure 1.
Commercial growing media was removed from the root systems of Dracaena fragrans (a, b) and Syzygium grande (c, d) to access the bottom of the stem, and longitudinal voids were subsequently introduced using wood auger drill bits. Inadvertent root damage was avoided insofar as possible during the void introduction process.
Download figure
Open in new tab
Download powerpoint
Figure 2.
The mechanically induced voids ranged in size from 1.3 to 3.8 cm diameter in both Dracaena fragrans (a) and Syzygium grande (b). The voids were oriented axially along the stem center (pith in S. grande) and extended between 5 and 35 cm above the root flare.
Download figure
Open in new tab
Download powerpoint
Figure 3.
Temperature data were extracted from longitudinal rectangular transects positioned horizontally and central across the stem surface overlying the internal voids (left) and three evenly distributed lines longitudinally oriented along the stem surface (right).
Download figure
Open in new tab
Download powerpoint
Figure 4.
Average diurnal variation in temperature (°C) and relative humidity (%) during the two experimental periods, lasting four days each, was typical for equatorial climatic conditions in Singapore. Experiment one was conducted between June 15–18 and experiment two between August 10–13, 2011. Note: error bars (± SD) illustrate the observed variability in environmental parameters at regular intervals.
Download figure
Open in new tab
Download powerpoint
Figure 5.
IR images taken in the morning revealed homogenous stem temperature distributions among all plants in both experiments; this was corroborated by the relatively uniform linear temperature trends for each treatment plotted in the coordinate plane. In the line graph, each treatment’s values were offset consistently by +1°C greater than the preceding treatment’s to avoid overlapping lines in the coordinate plane. Note: The dashed horizontal reference lines show the modified treatment mean surface-air temperature differential, vertical reference line denotes the purposefully selected reference point, solid zero line represents the point at which unmodified treatment surface temperatures and ambient temperatures are identical, and the error bars (± SD) illustrate the observed variability in surface temperature at regular intervals.
Download figure
Open in new tab
Download powerpoint
Figure 6.
IR images taken in the evening revealed abnormal temperature reductions near the 3.8 cm internal void position in both experiments. Basal temperature gradients of progressively cooler temperatures were observed on all plants except one, the non-irrigated control, which presented a comparably cool, vertically homogenous temperature distribution. These observations were supported by a sharp deviation in the linear temperature trend near the 3.8 cm voids and the relatively flat trend line for the non-irrigated control, respectively. In the line graph, each treatment’s values were offset consistently by +1°C greater than the preceding treatment’s to avoid overlapping lines in the coordinate plane. Note: The dashed horizontal reference lines show the modified treatment mean surface- air temperature differential, vertical reference line denotes the purposefully selected reference point, solid zero line represents the point at which unmodified treatment surface temperatures and ambient temperatures are identical, and the error bars (± SD) illustrate the observed variability in surface temperature at regular intervals.

Tables

Figures

View popup

Table 1.

Physical characteristics of mechanically induced voids in Dracaena fragrans and Syzygium grande stems.

Experiment	Treatment	Characteristics of void
Experiment	Treatment	Diameter (cm)	Height above soil (cm)	Relative cross-sectional area (%)	Volume (cm³)
Set 1	1	0.0	0.0	0.0	0.0
D. fragrans	2	0.0	0.0	0.0	0.0
	3	1.2	30.0	25	33.9
	4	2.5	25.0	50	122.7
	5	2.5	30.0	50	147.3
	6	2.5	35.0	50	171.8
	7	3.8	30.0	76	340.2
Set 2	1	0.0	0.0	0.0	0.0
S. grande	2	0.0	0.0	0.0	0.0
	3	1.2	15.0	25	17.0
	4	2.5	15.0	50	73.6
	5	3.2	5.0	65	40.2
	6	3.2	10.0	65	80.4
	7	3.2	15.0	65	120.6
	8	3.8	15.0	76	170.0

View popup

Table 2.

Localized stem temperature deviation from the mean surface temperature in linear temperature plots.

	Set 1: Dracaena fragrans^{^z}				Set 2: Syzygium grande^{^z}
	Time				Time
	0830h		1830h		0830h		1830h
Treatment	Deviation from linear trend (°C)				Deviation from linear trend (°C)
	Mean ± SD	P-value	Mean ± SD	P-value	Mean ± SD	P-value	Mean ± SD	P-value
1	0.11 ± 0.07	0.361	0.17 ± 0.07	0.588	0.14 ± 0.09	0.389	0.03 ± 0.11	0.851
2	0.06 ± 0.09	−	0.21 ± 0.04	−	0.09 ± 0.08	−	0.04 ± 0.06	−
3	0.05 ± 0.07	0.908	0.15 ± 0.02	0.751	0.10 ± 0.09	0.878	−0.01 ± 0.01	0.551
4	0.04 ± 0.06	0.728	0.28 ± 0.04	0.162	0.12 ± 0.08	0.575	0.08 ± 0.13	0.736
5	0.05 ± 0.10	0.908	0.19 ± 0.07	0.821	0.08 ± 0.09	0.918	−0.04 ± 0.17	0.355
6	0.04 ± 0.01	0.728	0.27 ± 0.15	0.188	0.14 ± 0.02	0.446	0.05 ± 0.03	1.000
7	0.00 ± 0.07	0.306	0.51 ± 0.14	0.001^{^y}	0.10 ± 0.08	0.878	0.14 ± 0.04	0.337
8	−	−	−	−	0.12 ± 0.09	0.646	0.34 ± 0.16	0.004^{^y}

↵^zNumber of repeated measures (n = 12).
↵^yRepresents a significant difference (P < 0.05) from Treatment 2, the irrigated control.

Set 1: Dracaena fragrans^{^z}
	Time				Time
	0830h		1830h		0830h		1830h
Treatment	Surface-air temperature differential (°C)				Standard deviation (°C)
	Mean ± SD	P-value	Mean ± SD	P-value	Mean ± SD	P-value	Mean ± SD	P-value
1	−0.35 ± 0.07	0.253	−1.64 ± 0.29	0.821	0.24 ± 0.13	0.514	0.23 ± 0.03	0.061
2	−0.23 ± 0.08	−	−1.58 ± 0.22	−	0.20 ± 0.07	−	0.29 ± 0.05	−
3	−0.19 ± 0.06	0.728	−1.41 ± 0.22	0.466	0.16 ± 0.06	0.615	0.24 ± 0.04	0.112
4	−0.19 ± 0.06	0.752	−1.49 ± 0.24	0.693	0.16 ± 0.05	0.547	0.27 ± 0.05	0.509
5	−0.11 ± 0.10	0.278	−1.33 ± 0.30	0.286	0.14 ± 0.01	0.370	0.22 ± 0.03	0.032^{^y}
6	−0.13 ± 0.09	0.382	−1.50 ± 0.26	0.714	0.25 ± 0.13	0.453	0.23 ± 0.04	0.050^{^y}
7	−0.13 ± 0.27	0.382	−1.62 ± 0.41	0.888	0.14 ± 0.02	0.424	0.17 ± 0.02	0.001^{^y}

	Mean temperature (°C)				Skewness (sk)
1	25.60 ± 1.72	0.931	30.16 ± 0.93	0.942	1.79 ± 1.23	0.810	−0.86 ± 0.02	0.001^{^y}
2	25.73 ± 1.74	−	30.21 ± 0.91	−	1.58 ± 1.38	−	−0.23 ± 0.21	−
3	25.76 ± 1.72	0.980	30.39 ± 0.91	0.814	0.70 ± 1.15	0.322	−0.26 ± 0.08	0.854
4	25.76 ± 1.74	0.981	30.31 ± 0.88	0.899	0.58 ± 0.94	0.260	−0.14 ± 0.14	0.507
5	25.84 ± 1.76	0.935	30.47 ± 0.87	0.728	0.44 ± 0.36	0.203	−0.25 ± 0.14	0.890
6	25.82 ± 1.69	0.948	30.30 ± 0.89	0.906	2.02 ± 1.35	0.618	−0.26 ± 0.34	0.836
7	25.82 ± 1.70	0.948	30.18 ± 0.82	0.964	0.21 ± 0.38	0.131	0.06 ± 0.10	0.058

Set 2: Syzygium grande^{^z}
Treatment	Surface-air temperature differential (°C)				Standard deviation (°C)
1	−0.61 ± 0.22	0.147	−0.92 ± 0.42	0.258	0.17 ± 0.02	0.327	0.26 ± 0.07	0.311
2	−0.78 ± 0.07	−	−0.32 ± 0.51	−	0.22 ± 0.06	−	0.22 ± 0.01	−
3	−0.61 ± 0.15	0.147	−0.25 ± 0.66	0.893	0.21 ± 0.04	0.818	0.16 ± 0.03	0.078
4	−0.76 ± 0.09	0.881	−0.51 ± 0.89	0.720	0.19 ± 0.05	0.594	0.24 ± 0.01	0.608
5	−0.65 ± 0.10	0.252	−0.05 ± 0.34	0.605	0.19 ± 0.07	0.594	0.29 ± 0.06	0.053
6	−0.61 ± 0.11	0.133	−0.22 ± 0.68	0.843	0.20 ± 0.07	0.702	0.27 ± 0.03	0.193
7	−0.64 ± 0.06	0.219	−0.19 ± 0.55	0.803	0.20 ± 0.04	0.760	0.22 ± 0.02	1.000
8	−0.58 ± 0.19	0.082	−0.81 ± 0.78	0.353	0.19 ± 0.06	0.494	0.30 ± 0.04	0.023^{^y}

	Mean temperature (°C)				Skewness (sk)
1	25.47 ± 1.76	0.907	28.85 ± 0.65	0.260	−0.12 ± 0.43	0.543	−0.75 ± 0.20	0.046^{^y}
2	25.30 ± 1.73	−	29.45 ± 0.71	−	0.20 ± 0.87	−	−1.32 ± 0.38	−
3	25.47 ± 1.67	0.907	29.52 ± 0.55	0.893	0.66 ± 1.24	0.374	−0.28 ± 0.10	0.001^{^y}
4	25.32 ± 1.72	0.991	29.26 ± 0.13	0.721	−0.29 ± 0.21	0.351	−0.93 ± 0.37	0.156
5	25.43 ± 1.69	0.927	29.72 ± 0.68	0.607	−0.25 ± 0.22	0.397	−1.14 ± 0.64	0.509
6	25.48 ± 1.76	0.903	29.55 ± 0.82	0.843	−0.39 ± 0.47	0.269	−0.39 ± 0.03	0.003^{^y}
7	25.44 ± 1.78	0.922	29.58 ± 0.82	0.804	−0.27 ± 0.28	0.374	−0.38 ± 0.23	0.003^{^y}
8	25.51 ± 1.61	0.886	28.96 ± 0.35	0.355	0.12 ± 0.50	0.887	0.05 ± 0.24	0.000^{^y}