The mean Tf for the site across all 11 events was 425.5 mm. Nine of the 22 gauges that had a complete rain record over the entire study period show a cumulative deviation below the site mean. Of these, gauge 19 shows the most deviation in either direction at 265 mm below the site mean. Gauge 17 is the closest gauge to the site mean, with a cumulative deviation only two mm above the site mean, while gauges 16 and 25 show the most deviation above the site mean (Table 4.3).
The CPC above each rain gauge ranged from 87% at gauge 8 to 95.7% at gauge 15, with a mean of 91.8% across the site, while the mean CAI was 3.1 (Table 4.3). The mean basal area for the site was 116.8 m2/ha. The mean number of trees in the 5 m radius around each rain gauge was
66 Table 4.3 Spatial variation of throughfall and canopy characteristics for the funnel rain gauges. CPC = canopy projective cover; CAI = Canopy Area Index; BA = basal area.
Gauge Cumulative throughfall (mm) Cumulative deviation around site mean (mm) Standard deviation (%) CPC
(%) Mean CAI BA (m2/ha)
Distance to nearest stem (cm) No. of trees* 1 365.5 -60 5.9 92.3 2.73 121.8 130 15 2 485 59.5 7.5 88.7 2.16 187.9 110 11
3 N/A N/A N/A 87.2 2.18 240.2 115 7
4 501.5 76 8.8 94.9 3.54 361 130 8
5 404 -21.5 5.7 93.7 7.05 47.3 40 4
6 N/A N/A N/A 90.2 2.5 64.4 70 13
7 438.5 13 6.9 89.5 2.24 219.5 90 6
8 478.5 53 7.3 87 2 55.9 50 13
9 322 -103.5 4.1 90.6 2.9 373 180 7
10 459 33.5 7.3 93.6 3.15 68 42 16
11 N/A N/A N/A 88.9 2.46 166.8 290 10
12 462 36.5 8.1 89.3 2.28 35.4 212 11 13 386.5 -39 6.6 90.9 2.35 56.7 90 18 14 374.5 -51 5.5 89.8 3.38 17.2 120 3 15 330.5 -95 5 95.7 4.72 16.3 7 7 16 567 141.5 7.8 90 2.55 12.3 95 9 17 427.5 2 6.9 91.5 2.92 240 120 15 18 476.5 51 8 93.2 2.86 85 160 12 19 160.5 -265 3.1 92.8 2.77 163.1 110 10 20 437.5 12 6.7 91.7 2.97 49 176 6 21 489.5 64 7.4 92.6 2.87 46.5 118 11 22 461.5 36 7.7 95.1 3.45 99.3 84 10 23 373.5 -52 4.9 96 4.01 15.7 99 8 24 392.5 -33 6.1 96.5 3.59 137.7 98 6 25 567.5 142 10.9 93 3.88 40.5 120 8 Mean 425.5 0 6.74 91.8 3.1 116.8 114.2 9.8 * Values taken for a 5 m radius around each gauge.
There were no significant relationships between the canopy characteristics and Tf distribution within the forest. There were also no significant relationships between the standardised I and CPC in the arc around the mean wind direction for each event. Therefore, the hemispherical canopy images taken at each rain gauge location (Figures 4.5 – 4.6) were examined visually to determine whether there were any obvious reasons why the distribution of rainfall around the site mean varied so greatly between the gauges.
Figure 4.5 Hemispherical canopy images taken at the site of each funnel rain gauge for gauges 1-12. Top markers represent magnetic north, with east to the left of
the image and west to the right of the image. Image date: 25/3/2011.
Figure 4.6 Hemispherical canopy images taken at the site of each funnel rain gauge for gauges 13-25. Top markers represent magnetic north with east to the left of the image and west to the right of the image. Image date: 25/3/2011.
69 It can be seen from the images that gauge 9, which recorded more than 100 mm below the site mean, has a lot of tree cover to the south-west, which would possibly block some of the rain from the prevailing weather direction. There is a large open section of the canopy towards the centre of the image, which would reduce the CPC, although not necessarily the rainfall (Figure 4.5). Gauge 16 recorded more than 140 mm of rain above the site mean. The image shows an open canopy, with small trees to the south-west that may be letting rainfall through (Figure 4.6). Gauge 17 was the gauge most similar to the site mean. The image shows a relatively open canopy in all directions, with a very even distribution of vegetation. There are also no large tree trunks in the image (Figure 4.6). The CPC and CAI values for gauge 17 are also very similar to the site means for these values (Table 4.3). Gauge 19 recorded the greatest deficit in rainfall around the site mean, at 265 mm below. The image shows a lot of tree trunks and thick cover, particularly within the southern quadrant of the photograph (Figure 4.6). Gauge 25 recorded more than 140 mm of rain above the site mean. The distribution of vegetation within the image looks
reasonably even, and the CPC is close to the site mean. However, the image shows a low branch directly over the rain gauge, which could be responsible for funnelling rain through drip points directly into the gauge (Figure 4.6).
The distribution of species and basal diameter for all trees within a 5 m radius of each of the 25 rain gauges are shown in Figure 4.7. Nothofagus cunninghamii was evenly distributed around the site, with a number of larger sized trees. Atherosperma moschatum also has a strong presence, with a cluster of the species occurring exclusively around gauges 20, 24 and 25. In terms of basal area and number of individuals, A. moschatum is the dominant tree. Eucryphia lucida appears in clusters at about three of the mapped locations, while a handful of Orites diversifolius and Anodopetalum biglandulosum individuals occur within the mapped area of the site. Individual occurrences of
70 Figure 4.7 Map of the 25 rain gauges at Site Call with the location, species and diameter at breast height (DBH) in cm of all trees and tall shrubs in a 5 m radius of each rain gauge. Note: the apparent gaps in the above plan do not necessarily represent an absence of trees, rather they fall outside of the mapped area.
71