74 
D. R. MELICK 
ing topography; the degrees of shading were 
determined using a contour map constructed 
from stereoscopic photographs. 
At the end of the drought of 1983, the dawn 
water potentials of plant samples collected from 
various heights on the slope of the Woolshed 
Creek gully were measured in the field. Samples 
were stored in airtight plastic bags and water 
potentials were measured on a pressure bomb 
within 30 minutes of collection. During this 
drought the average visible crown damage to 
major species was visually estimated for the 
major species in the Woolshed Creek area. 
Fifteen individuals of each species were re¬ 
corded and the average results tabulated. 
Soil sampling and analysis. Surface soil samples 
(from 0-0.1 m deep) were collected at each 
quadrat site. Soil pH was measured on air-dried 
soil (< 10 mm) by glass electrode in a soil-water 
slurry having a weight : volume ratio of 1 : 5. 
Particle size analysis was performed by the 
pipette and sieve method (Coventry & Fett 
1979). Soil textures were categorized according 
to Leeper (1964) and soil colours were deter¬ 
mined using a Munsell soil colour chart. 
Prior to chemical analyses, samples were air- 
dried and sifted (<2 mm). Acid soluble and 
“adsorbed" phosphorus was extracted from 
soils by shaking samples in 0.1 A r HCl and 0.03 N 
NH 4 F for 40 seconds, as described for the Bray 
and Kurtz No. 2 phosphorus extraction (Jackson 
1958). Phosphorus levels were then measured 
colorimetrically on a Technicon auto analyser. 
Exchangeable calcium was determined on air- 
dried soil (<2 mm) by ammonium saturation 
using 1 mol/L ammonium acetate at pH 7.0. Cal¬ 
cium levels within each leachate were analysed 
by atomic absorption spectrophotometry. 
Because the analysis of calcium by this method 
is subject to interference by anions, lanthanum 
(3000 ppm La in 0.8 A r H 2 S0 4 ) was added to each 
digest, to give a concentration of at least 1500 
ppm La within each sample; this suppressed any 
interference by anions in the analysis. 
RESULTS AND DISCUSSION 
Environmental parameters 
Insolation. The potential insolation over the 
area shows a wide range from 250-775 
kJ/cm 2 /yr on the north and south facing slopes 
respectively of Woolshed Creek. There is only 
minor variation on the plateau areas, from about 
630-700 kJ/cm 2 /yr. These data suggest that 
moisture relations will be profoundly affected in 
sites where topography is complex. 
Moisture. There was a progressive decrease in 
the relative water potentials of plants with 
increasing distance up the side of the gully at 
Woolshed Creek (Table 1), indicating the pres¬ 
ence of a soil moisture gradient. Of the tree spe¬ 
cies present at Woolshed Creek, the greatest 
drought damage to foliage was observed in 
Rapanea howittiana and Tristaniopsis laurim 
(Table 2). 
Soil. The results of the soil survey indicate that 
most of the area is covered with a top soil of 
sandy loam texture. Significant areas adjacent to 
Woolshed and Bull Creeks support sandy loams, 
and probably reflect the presence of shaly parent 
material. Some of the smaller areas of sands 
along parts of the stream courses appear to be 
related to depositional features. 
The pH of surface soils shows considerable 
variat ion from acid (pH 4.2) to near neutral (pH 
7.1) (Table 3). A large proportion of the area has 
soils with pH values from 5.0 to 5.9 but there are 
small areas, particularly in the upstream section 
of Woolshed Creek, where the pH is low (4.2- 
4.9). Neutral to slightly acid soils almost cer¬ 
tainly reflect the proximity of calcareous beds, 
either in situ or upslope, and this is illustrated by 
Dawn water potential (MPa) 
Gully 
Mid 
Top of 
Species 
floor 
slope 
slope 
Acmena smithii 
-1.13 
-1.95 
-222 
Pellaea falcata 
-0.38 
-0.52 
-6.58 
Pittosporum undulatum 
— 
-1.76 
-2.32 
Table 1. Dawn water potentials of plants in the field on 
the northern aspect of 1 
the Woolshed Creek gully in 
February 1983. 
Species 
% of foliage showing 
drought damage 
Acacia mearnsii 
12.5 
Acmena smithii 
17.0 
Acronynichia oblongifolia 
9.5 
Kunzea ericoides 
6.0 
Pittosporum undulatum 
9.5 
Rapanea howittiana 
35.5 
Tristaniopsis laurina 
29.5 
Table 2. Estimated average drought damage to the 
crowns of mature trees in the Woolshed Creek gully in 
February 1983. Each value represents the average of 
ten observations. 
