Estimating the Water Requirements for Plants of Floodplain Wetlands

and their interaction, were chosen as experimental factors because ofobservations that submergence was likely to be limiting recruitment.Recording survival and growth, not just immediately after submergencebut also at the end of a post-submergence recovery period, showed theimportance of including delayed responses when making assessments(Denton and Ganf 1994).Tree seedlings + depth and duration: ‘Mesocosms’ (similar to largepots, with drain-holes to manipulate water levels) and smaller pots wereused in an outdoor experiment to test the effects of water depth andflood duration on saplings and seedlings of Melaleuca quinquernervia.This tree is a pest in Florida but is a native and valued species onfloodplains in tropical Australia.Comparative studiesComparative studies extend the single-species approach by subjectingtwo or more species to the same experimental treatments. From theresults of such studies it is possible to make an informed guess as towhich species would be favoured by a particular water regime.Examples of multi-species studies done in the field are: the effect ofchanging water levels and depth on Baumea arthrophylla andTriglochin procerum (Rea and Ganf 1994); and water regime (mainlydepth and duration) and eutrophication effects on Baumea articulataand Typha orientalis (Froend and McComb 1994).Note 29Remote sensing: thefutureResearch is currently underway todetermine spectral characteristicsassociated with leaf senescence andleaf water stress, using a test site witha number of young trees, planted in areplicated experimental lay-out, onwell-fertilised and nutrient stressedsites crossed with varying degrees ofwater stress. The target species isEucalyptus camaldulensis. Spectralreflectance differences have beenalready detected for other eucalyptspecies (Laurie Chisholm, pers.comm., 1999).Regeneration and maintenance: Three macrophyte species werecompared in a series of experiments investigating their regenerationfrom fragments, seasonal growth patterns, and survival and growth inwater depths ranging from 10 to 100 cm. The species, Marsilea mutica,Ludwigia peploides and Myriophyllum aquaticum, all occurred atBushell’s Lagoon, west of Sydney. The study concluded that the twonative species were better adapted to fluctuating water levels, whilestable water levels suited the introduced milfoil (Yen and Myerscough1989).Comparative studies need not be limited to species, but could includeseedbanks. For example, the viability of different parts of a floodplainwetland could be tested to determine which areas might needsupplementary planting.Competition studiesCompetition experiments are important because it is very difficult toaccurately predict interactions between species based on currentknowledge. Water may be a resource or a stress, or both: thus, changingwater regime will affect the vigour of species differently. If theircompetitive interactions change, then species composition will change,boundaries may alter and the abundance of target species, whethernuisance or exotic or rare plants, may be affected. Competition studiesexplore how two species affect each other’s growth under specifiedconditions.A standard design is to grow each species separately (a ‘monoculture’ asa control) and together, in varying densities, and under a range ofconditions. Competition experiments done in the laboratory tend to belarge, and involve very many pots; they require strengths inexperimental design, planning, and analysis.Section 5: Obtaining Vegetation Data 63