Journal of the Royal Society of Western Australia, 87:115-121, 2004 
Seedling growth and physiological responses of two sandplain 
Banksia species differing in flood tolerance 
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 
3 p.groom@uws.edu.au 
(Manuscript received: March 2004; accepted February 2005) 
Abstract 
Banksia littoralis (Proteaceae) inhabits winter-wet locations and wetland fringes that are prone to 
seasonal flooding events on the Swan Coastal Plain. To survive in these locations, B. littoralis 
seedlings must be able to tolerate periods of flooding or complete submergence if establishment is 
to be successful. Flood tolerance was assessed in seedlings of B. littoralis subjected to 104 days of 
continual soil waterlogging by comparing changes in seedling growth and leaf ecophysiology with 
those of well-watered plants. Flood tolerance was also assessed in seedlings of Banksia prionotes, a 
species that grows in drier locations on the Swan Coastal Plain. As expected, B. prionotes was 
unable to survive long periods of soil waterlogging or submergence (97% mortality after 72 days of 
flooding). Both species responded to flooding by closing their stomates and reducing 
photosynthetic capacity, although B. littoralis was able to recover lost photosynthetic potential 
when flooded conditions subsided. After 72 days of flooding, there was a substantial decrease in 
relative growth rate in flooded B. prionotes seedlings, compared to that of well-watered plants, 
although this was not associated with significant differences in biomass allocation. Flood-affected 
B. littoralis seedlings were significantly smaller than well-watered seedlings after 72 days of 
flooding, but were the same size after 104 days. Flood tolerance enables B. littoralis seedlings to 
survive exceptionally wet winter-spring months when flooding events are more likely to occur, 
although surviving the annual summer drought may be more important to sustain seedling 
establishment. 
Keywords: Banksia littoralis , Banksia prionotes , flooding, photosynthetic capacity, stomatal 
conductance, submergence 
Introduction 
Species confined to wetland fringes and winter-wet 
depressions are being lost from Perth's Swan Coastal 
Plain as a result of declining groundwater levels and 
poor groundwater recharge, due to local and regional 
abstraction, and successive years of below average 
rainfall (Aplin 1976; Groom et al. 2000, 2001). The loss of 
Swamp Banksia ( Banksia littoralis R.Br.; Proteaceae) trees 
and its replacement by more xeric Banksia species has 
occurred over the past 40 years (Groom et al 2001) as 
winter-wet swamps become filled with sand from the 
surrounding dunes (Heddle 1980; Muir 1983). This may 
have been because B. littoralis trees were unable to access 
sufficient moisture to meet their summer water-use 
requirements as soil moisture content and groundwater 
levels declined (Groom et al. 2001; Groom 2002; Zencich 
2003). 
Decreasing occurrence of flooding events may be an 
alternative explanation for the loss of tree species from 
wetland fringes, as it directly impacts seedling 
recruitment and establishment. Flooding is not 
necessarily required to sustain the recruitment and 
survival of wetland tree seedlings (Froend et al 1993) but 
© Royal Society of Western Australia 2004 
may provide sufficient soil moisture for seedlings to 
survive post-winter and subsequent dry summers. 
During flooding events, seedlings of wetland species 
must either be flood-tolerant or tolerate periods of 
submergence if seedling establishment is to be successful. 
The ability of seedlings to tolerate flooding or 
submergence may be an important contributor to a 
species' ecological distribution. 
This paper compares the seedling flood response 
strategies of Banksia littoralis , a tree species known to 
tolerate flooding events, and a congener from the Swan 
Coastal Plain that typically grows in drier locations (B. 
prionotes Lindl.) (Groom 2004). Differences in flood 
responses and ability to tolerate complete submergence 
are measured in terms of changes in growth and leaf 
ecophysiology. 
Methods 
Setup and Design 
Banksia seeds were obtained from Nindethana Seed 
Supply (Albany, WA). Seeds were imbibed in tap water 
for 30 min before being placed in plastic petri dishes 
lined with moist filter paper, and germinated at 15°C, the 
optimal germination temperature for other southwest 
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