Journal of the Royal Society of Western Australia, 86:31^0, 2003 
Groundwater-dependency and water relations of four Myrtaceae shrub 
species during a prolonged summer drought 
P K Groom 
Centre for Ecosystem Management, School of Natural Sciences, Edith Cowan University, 
100 Joondalup Drive, Joondalup, WA 6027: current address. Centre for Horticulture and Plant Sciences, 
University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797 0 p.groom@uws.edu.au 
(Manuscript received August 2002; accepted March 2003) 
Abstract 
Seasonal water relations and water source (5 2 H analysis) data were examined for four Myrtaceae 
shrub species inhabiting a winter-wet depression (dampland) and surrounding landscape on 
Perth's coastal sandplain. Data were collected during an exceptionally dry spring-autumn period 
in 2000/2001. The two species occurring within the dampland, Astartea fascicularis and Pericalymma 
ellipticum, were probably accessing shallow soil moisture or groundwater (at a depth of 0.35 m) 
during October 2000 (spring), but were not accessing groundwater (at a depth of 1.45 m) during 
the summer drought (March 2001). Species occurring on the dampland embankment (Hypocalymma 
angustifolium, Eremaea pauciflora) and at a site further upslope (E. pauciflora only) had a significant 
reduction in predawn xylem water potential and morning stomatal conductance in response to the 
summer drought, with neither species accessing groundwater during summer. The dampland 
species were able to maintain summer morning stomatal conductances similar or greater than the 
conductance measured during the previous spring, implying that shallow soil moisture 
(gravimetric content of 10-20%) was sufficient to sustain their summer water-use requirements. 
5 2 H data suggests that P. ellipticum may have been utilising groundwater in early winter (July 
2001), implying that the minimum accessible groundwater depth for this species at the study 
dampland is approximately 1.4 m. 
Keywords: dampland, groundwater, sandplain, seasonal water relations, summer drought, 
winter-wet depression, Myrtaceae 
Introduction 
Plants occurring above a shallow aquifer may be 
dependent on groundwater as a regular source of 
moisture, with the degree of dependency depending on 
seasonal groundwater and depth, and the species' 
rooting pattern. Some species only occur where 
groundwater is at a particular depth, with their loss or 
decline indicative of an altered hydrological regime 
caused by a natural decline in water table levels or 
groundwater extraction (Stromberg el al. 1996; Wierda et 
al. 1997). The capacity to exploit an underground water 
source, or soil moisture at depth, makes it possible for 
some species to survive long periods without rain 
(Cramer et al. 1999; Williams & Ehleringer 2000). 
Perth is on the northern section of a coastal sandplain, 
under which lies a large, shallow unconfined aquifer 
(total superficial aquifer groundwater storage of 18 700 x 
10 6 m 3 ; Davidson 1995). This coastal plain consists of 
urban development, extensive areas of native Banksia and 
other woodlands, introduced pine plantations, and 
numerous wetlands. Over 50% of the latter have been 
lost to landfill or drainage (Arnold & Sanders 1981). 
Shrub species from the family Myrtaceae are a major 
component of the coastal plain vegetation. The many 
winter-wet depressions are often dominated by a shrub 
stratum of shallow-rooted Astartea fascicularis (Labill) DC 
and Pericalymma ellipticum (Endl) Schauer. Species such 
© Royal Society of Western Australia 2003 
as Hypocalymma angustifolium (Endl) Schauer are 
dominant along the upper edges of these depressions 
where the soil is rarely waterlogged (Muir 1983; 
Farrington et al. 1990). In more elevated positions deeper- 
rooted species, e.g. Eremaea pauciflora (Endl) Druce, are 
common. 
Populations of myrtaceous shrub species inhabiting 
low-lying, winter-wet depressions on Perth's sandplains 
have declined in size since 1966 (Groom et al. 2000a). This 
has been attributed to the gradual decline in 
groundwater and soil moisture levels in most areas of 
this aquifer since the 1970s (Heddle 1980; Davidson 1995), 
resulting from the combined effects of below average 
rainfall (the sole source of groundwater recharge on the 
sandplain) and increased regional groundwater 
abstraction. 
Perth experienced its driest spring to autumn period 
between September 2000 and April 2001 (Bureau of 
Meteorology, Perth, WA). During this period, the 
seasonal water relations and groundwater-dependency 
(by 5 2 H analysis) of the abovementioned myrtaceous 
shrub species were monitored at sites within and 
adjacent to a winter-wet depression (part of the Lexia 
wetlands) on the eastern edge of the coastal plain. This 
study examines how species from different topographical 
positions within a sandplain landscape sustain their 
water requirements during periods of drought. It is 
expected that during times of drought, plants overlying 
shallow aquifers may rely more on groundwater 
resources (i.e. less on soil moisture reserves) or may be 
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