Water relations of the canopy species in a Banksia woodland, Swan Coastal Plain, Western Australia

Abstract

Diurnal and seasonal water relations were measured in selected species of a Banksia woodland at a site with groundwater at a depth of 6–7 m. The canopy co‐dominants Banksia attenuata and Banksia menziesii exhibited similar patterns of variation in water relations, both diurnally and seasonally. Stomatal conductance was usually 0.4–0.5 cm s−1 diurnally and seasonally and, generally, did not respond to water deficit and other factors. Transpiration was correlated positively with factors indicative of atmospheric evaporative demand, especially total global radiation and pan evaporation, and was highest in summer when canopy water use reached 2.1 mm d−1. Xylem pressure potential at dawn averaged −0.25 MPa in both species throughout the year. Minimum xylem pressure potential varied seasonally and was negatively correlated with transpiration. Seasonal means of minimum xylem pressure potential varied from −1.0 MPa in winter to −1.5 MPa in early summer. Both Banksia species appeared to function as phreatophytes, utilizing groundwater which enabled them to maintain high rates of water use in late summer. Water use over a 12 month period totalled 635 mm, of which the canopy and understorey contributed 61% and 39%, respectively. Water use in the woodland was dominated by the canopy in late summer and the understorey at other times.

Influence of groundwater depth on the seasonal sources of water accessed by Banksia tree species on a shallow, sandy coastal aquifer

“…However, B. prionotes utilised a larger proportion of groundwater at all times (range in groundwater use of 20-100%) perhaps due to its fastgrowing habit, root distribution, or the results are an artefact of differences in the mixing model used to infer dependence. Groundwater use by the lower and upper slope trees is consistent with observations reported for B. attenuata and B. menziesii trees overlying a similar depth to groundwater of 6-7 m (Dodd and Bell 1993). Based on shoot water potential analysis alone, it was concluded that these species were able to access and utilise groundwater in late summer.…”

“…To address this issue, the present study investigated the water sources used by B. ilicifolia, which is limited in its distribution to lowlying areas of the landscape and therefore shallow depths to groundwater, and more drought-tolerant species, such as B. attenuata (Dodd and Bell 1993), which occurs across a broad range of topography.…”

“…and B. menziesii R.Br. were examined by Dodd and Bell (1993) based on shoot water potentials and it was reported that these species appeared to function as phreatophytes (groundwater-using plants) in late summer. To date, studies such as these have concentrated on only one depth to groundwater.…”

Long term trends of stand transpiration in a remnant forest during wet and dry years

“…Large differences in rainfall between the two years examined (522 mm cf 1062 mm) led to a greater proportion of rainfall being transpired in 2003 than 2004 (61% vs. 42% estimated using the E sv method and 71% vs. 37% estimated using the E PM method). These estimates of the proportion of rainfall lost as transpiration are in agreement with those for a Banksia woodland in Western Australia (Dodd and Bell, 1993) and an open wet schlerophyll forest in the Australian Capital Territory (Leuning et al, 2005). Despite the reduction in the proportion of rainfall used in transpiration when more rain occurred, the volume transpired increased with increasing rainfall (317 mm vs. 443 mm estimated using the E sv method and 371 mm vs. 398 mm estimated using the E PM method).…”

Pathogen driven change in species-diverse woodlands of the Southwest Australian Floristic Region: a hybrid ecosystem in a Global Biodiversity Hotspot

“…Redistribution of ground water over summer is an important function of deep-rooted species due to the extremely low water holding capacity of Banksia woodland soils (Dodd & Bell 1993, Pate & Bell 1999. Hydraulic lift facilitates survival of shallower rooted understorey species (roots < 2 m) by providing sustained moisture over the dry summer months (Caldwell et al 1998, Groom 2004).…”