Estimating the Water Requirements for Plants of Floodplain Wetlands

and this can affect how summary statistics such as mean are calculatedand used, especially in multivariate analyses. The index in common use(Grimes index; Note 26) is specific to eucalypts, and assumes epicormicregrowth. This index would need to be modified for use with otherspecies, such as Casuarina and Melaleuca. Even within eucalypts,species differ in form and shape. A new reference set covering the fullcondition range will be needed when applying a condition index to aspecies not previously assessed in this way. Modifications made byindividual workers mean that inter-species comparisons are not valid,and possibly even intra-species, if from different sites.Standard physiological techniques for measuring water stress, such asxylem pressure potential, are more useful as a research or monitoringtool when undertaking a time series in relation to soil water.Other than treesFor many emergent macrophytes, the perennial part of the plant (therhizome, the tubers etc.) is underground and the canopy is the only partof the plant that is visible. In these cases, there is an overlap withabundance measures; condition can be size and colour of the canopy,estimated directly as biomass, leaf number, LAI or recorded indirectlyusing height or shoot density.Condition options are very limited for leafless plants such as manyemergent macrophytes (eg. Eleocharis, Juncus, Schoenoplectus etc.)which have a photosynthetic culm, and for leafless twiggy shrubs suchas lignum Muehlenbeckia florulenta, and grasses such as canegrassEragrostis australasica. Suitable measures are estimates of size, such asheight, diameter, cover or (select species only) stem density (Figure 17).With lignum, as with other leafy shrubs, size can be estimated fromaerial photography.Figure 17. Vigour in leafless speciesLignum Muehlenbeckia florulenta under dry conditions but showing thedifference in height, twig density and overall habit between well-watered(left) and infrequently-flooded areas (right).Spatial issuesBroad-scale and fine-scaleThe basic approach to building an empirical vegetation–hydrologyrelationship (Section 4) is to link spatially-defined vegetation data withspatially-defined hydrology data.Section 5: Obtaining Vegetation Data 59