Light in the Daintree Rainforest, Northern Queensland, Australia - 16°10' S 145°25' E
Recordings made on 8th October 2006 by Frances Baines

Fig. 1 : Thornton Peak from Cooper Creek, Daintree

Daintree National Park, north of the Daintree River 110km north of Cairns, is a stretch of ancient tropical lowland rainforest. It is one of the oldest rainforests on the planet, more than 135 million years old, and covering approx. 1,200 sq. km.

These recordings and photographs were taken in the Cooper Creek area at the foot of Thornton Peak (fig.1) on a fine day in early October - at the very end of the dry season.

The rainforest hardwoods and fan palms cover the slopes of the mountains to the sea and to the riverbanks, which are lined with mangroves. In March 2006, cyclone Larry damaged the forest and there are new clearings in some areas where trees have fallen, although the canopy has grown back well. Sunbeams reach the forest floor in many places creating a mosaic of light and shade.

The recordings were made using the following equipment:

  • Solarmeter 6.2 UVB meter (W/cm)
  • Solarmeter 6.5 meter (UV Index)
  • SkyTronic LX101 model 600.620 digital lux meter
  • Electronic Temperature Instruments Ltd. model TN1 infra-red non-contact thermometer
  • Unbranded battery-operated digital "patio" thermometer/hygrometer with probe

We were lucky enough to be escorted around the Cooper Creek Wilderness Reserve by the land manager herself, Mrs. Prue Hewett, who shared her deep knowledge and love of this amazing place with us and showed us many of its secrets - including the fan palms, tree ferns, a pair of Southern Cassowary birds (Casuarius casuarius) and four beautiful Boyd's Forest Dragons (Hypsilurus boydii) (fig.2). We were able to quietly approach these arboreal lizards quite closely; they were perched in areas of dappled light and shade and did not seem to be basking. Prue said that they do appear to thermoregulate to some extent by moving up and down the tree, in and out of deeper shade.

Figs. 3 and 4: the UVB in the vicinity of a Boyd's Forest Dragon at mid-afternoon

 

As can be seen from figs. 3 and 4, the amount of UVB available to the dragon depends upon his exact position on the tree trunk. 25W/cm was the highest reading I could obtain close to him; however there were shafts of direct sunlight on adjacent trees, giving readings up to 238W/cm (at 3.00pm). The UV Index graduated from 0.1 in the shade to 4.8 in the sunlight.

Overall light levels were surprisingly high - at 3.00pm, just before taking these photographs, I recorded 2,000 lux in the shade and 90,000 lux in the sunlit area (global readings). The direct solar reading was 130,900 lux.

The full set of recordings are given in the table below. Direct recordings refer to those made with the meter sensor aimed at the sun; global readings are taken with the sensor aimed directly upwards. "Maximum basking temperatures" refer to the highest surface temperature located at the site (eg. on a rock, log or bare ground) exposed to the sun, measured with the infra-red non-contact thermometer.

 

 

Fig. 2: One of four beautiful Boyd's Forest Dragons (Hypsilurus boydii) we encountered at Cooper Creek

Fig. 5: Cooper Creek
Cooper Creek, Daintree, Queensland. 16°10' S 145°25'E
Recordings of UVB, visible light, temperature and humidity for 8th October 2006
Time
Situation
UVB direct (W/cm)
UVB global (W/cm)
UVI direct
UVI global
Lux x100 direct
Lux x100 global
Ambient (air) temp.F
Max basking temp.F
Humidity %
06:30 after dawn on beach
9
8
0
0
588
120
75.9
78.1
62
09:00 sun patch in forest
150
100
2.9
2
1164
850
77.3
104.1
72
09:00 forest shade
 
4
 
0
 
9
73.1
75.9
68
10:00 fully sunlit clearing
351
305
8.4
7.5
1333
1100
93.5
132.6
46
10:30 fully sunlit clearing
362
325
9.5
8.5
1318
1200
96.6
135.3
61
10:30 sun patch in forest
263
237
6.8
6.2
1238
1200
93.0
108.1
48
10:30 forest shade
 
6
 
0.1
 
17
92.4
92.1
48
11:00 fully sunlit clearing
323
305
8.4
8.0
1256
1200
94.2
121.8
45
13:00 fully sunlit clearing
353
315
9.0
8.9
1314
1250
94.2
148.6
47
13:00 forest shade
 
6
 
0.1
 
14
 
78.6
66
13:30 fully sunlit clearing
302
275
7.5
6.8
1269
1150
87.9
149.9
61
13:30 sun patch in forest
98
 
2.4
 
 
 
81.5
 
 
13:30 forest shade
 
4
 
0.1
 
 
78.6
 
66
15:00 fully sunlit clearing
238
164
4.8
3.6
1309
900
92.3
123.6
55
15:00 forest shade
 
4
 
0.1
 
20
90.1
 
 

These recordings are just a simple "snapshot" of the conditions found on one fine day at the end of the dry season. In no way do they give a full picture of the microhabitat of this remarkable rainforest.

It is interesting to note the wide range of temperatures, light levels and UVB light levels available on the forest floor - all within feet of each other, and constantly changing as the sunlight moves through the canopy above.

Below are some more photographs of the rainforest and of some of the meter readings taken on a walk through the rainforest at about half past eight in the morning on that day.

It was a great privilege and a wonderful experience to visit this beautiful and special place.

 

2007 Frances Baines

Reproduced here with permission


Fig. 6: sunlight may even reach the
buttress roots in the rainforest
Fig. 7: light through
the canopy

Figs. 8 and 9: 112W/cm (fig. 8) and 151W/cm (fig.9) in sunlight
on the forest floor between 8.32 - 8.36 am on Oct.8th 2006.

Fig. 10: The fan palm canopy at Cooper Creek.


Fig. 11: UV Index of 3.0 in dappled sunlight on forest floor, 8.35 am.

Fig. 12: The Southern Cassowary (Casuarius casuarius) which just walked up to us out of the forest, gazed at us demurely and walked on by....

Fig. 13: just after dawn in Cow Bay, Daintree, 6.30am