Estimating the Water Requirements for Plants of Floodplain Wetlands

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identical conditions. PFTs differ from growth-form in that they focus onassumed or observed responses.PFTs can be used in models of vegetation change. This is an attractiveapproach because it is a way of reducing the enormous complexity ofmodelling species individually to a few recurrent patterns. PFTs haveyet to be used in modelling dynamics of floodplain vegetation. This willrequire putting species into functional groups based on their responsesto flooding and drying, and to changes in water regime. The system ofPFTs developed for wetland plants (Figure 10 and Note 12) is relevant,at least to part of floodplain wetlands; no PFTs have yet been workedout that include both floodplain and wetland species.Figure 10. Wetland plant functional typesSeven plant functional types identified from 60 wetland plant species, onlagoons on the New England Tablelands (diagram supplied byM. Brock, 1999).WETLAND PLANTSresponse to water presence or absenceTerrestrialDoes not tolerate floodingAmphibiousTolerates flooding and dryingSubmergedDoes not tolerate dryingAmphibious:Fluctuation-toleratorsAmphibious:Fluctuation-respondersTerrestriale.g. Cirsium sp.emergent vines low growing treese.g. Eleocharis spp.e.g. Hydrocotyle sp.morphologicallyplastice.g. Myriophyllum sp.floatinge.g.Nymphoides sp.Submergede.g. Vallisneria sp.Plant water regimeThe water regime of a floodplain wetland is its characteristic pattern offlooding, drying or water-level changes. These changes can bedescribed in terms of when water level changes occur, how much, howfast and for how long (Figure 5). For plants, water regime is also thepattern of flooding, drying or water-level changes but it refers to thespecific patterns needed to ensure species maintenance andregeneration.• A maintenance water regime, as used here, is the water regimeneeded by an established mature plant to survive in the long-term;that is to grow and to periodically flower, and also to set seed atintervals that ensure the population seedbank or propagule bankis maintained.28 Estimating the Water Requirements for Plants of Floodplain Wetlands
• A regeneration water regime is one that ensures periodicestablishment or re-establishment of plants, whether from seed orfrom other propagules. If from seed, then the regeneration waterregime must satisfy conditions for seed germination followed bysuccessful seedling establishment; if from propagules, then thereare similar requirements for initial or follow-on conditions,although these may be subtly different.Maintenance and regeneration requirements are usually quite different.The environmental conditions required for germination, or for survivalof a seedling, are not the same as those required by the adult plant. Forexample, many emergent macrophytes germinate on wet muds,comparable to drawdown conditions; only some have seedlings that cantolerate submergence. Shallow water is likely to be detrimental, at leastuntil the plant reaches a critical stage: in contrast, adult plants cantolerate water depths ranging from 0 to about 1.5 metres.Components of plant water regimeWater regime refers to the hydrograph shape and size, and the patternof hydrographs through time. Size and shape characteristics arecorrelated under natural conditions, but this can change once a river isregulated or its flow regime modified. Describing a hydrograph shapeand the pattern of hydrographs through time in terms of its componentsis useful, in terms of clarifying plant responses. Seven components canbe recognised (see below): of these, the most frequently studied aredepth and frequency.Depth: The importance of depth and the effects of changing depth arevery much dependent on species growth-form and size. Plants withrigid or erect aerial leaves, such as emergent macrophytes, seedlings andtussock grasses, can grow in water to a certain depth, depending ontheir height or size. Equally, they can tolerate an increase in waterdepth, provided a reasonable proportion of the canopy or stem is notsubmerged, otherwise they become stressed or may even die (Note 13).Thus, although depth is measured in absolute terms, in millimetres ormetres, the ecological effect on these plants depends on the size of thespecies in question. Floating-leafed plants with flexible petioles cangrow in water up to two metres deep, depending on how effectively therhizome is ventilated from the leaf, and can tolerate fluctuations inwater level, roughly of 10–20 cm, such as caused by wind-inducedwaves. Free-floating and submerged forms are not greatly affected byincreases in depth, unless this causes a reduction in light.Note 12PFTs on TablelandlagoonsThe first Australian study of wetlandPFTs was done on isolated lagoonson the New England Tablelands.Seven PFTs were defined in terms oftheir response to water regime(Brock and Casanova 1997).These seven PFTs were empiricallydetermined by a combination ofexperiment and observation of 60wetland plants. The lagoons havevariable water levels and anintermittent water regime, and thelittoral zone, being periodicallyexposed and submerged, meansthese lagoons are a variable andunpredictable environment in whichto grow and the complete plant lifecycle.Several of the 60 species used in thisstudy are also found on inlandfloodplains, but dominant floodplainspecies are not included.An alternative system of wetland PFTshas been developed in North Americabut not yet applied in Australia. Thisrecognises three main plant types:ruderal, matrix, and interstitial: it isuseful for disturbance rather thanwater regime (Boutin and Keddy1993).Duration of inundation: Duration refers to the time that surfacewater is present, measured in weeks or months. Duration is importantfor obligate aquatics as it defines the potential growing period for adults,including flowering and seed-set or storage, or the time frame forgermination and seed-set if an annual. For facultative aquatics or thosetolerant of mud-flats, conditions may be favourable for growth even afterthere is no more surface water, for as long as the soils remainwaterlogged or moist. For floodplain species, duration of floodingdefines the period when soil water is recharged by infiltration.Season of flooding: Season, or timing, here refers to when floodingbegins. Season is significant because it is a short-hand way to refer to acombination of climatic factors that affects plants: temperature, daylength,and whether day-length is increasing or decreasing. Temperaturedetermines the rate of physiological processes, evident as growth;Section 2: Introducing the Vegetation 29
Page 1 and 2: Estimating the WaterRequirements fo
Page 3 and 4: ContentsPreface 7Acknowledgments 8G
Page 5: List of Tables1 Spatial variability
Page 8 and 9: Note that the guide is concerned pr
Page 10 and 11: ecomes a matter of how to use what
Page 12 and 13: Figure 1. Floodplain featuresThe fl
Page 14 and 15: Figure 4.Wanganella Swamps, souther
Page 16 and 17: Floodplain wetlands, being a mosaic
Page 18 and 19: Section 2:Introducing theVegetation
Page 20 and 21: size and vigour rarely reach their
Page 22 and 23: floodplains survive there because t
Page 24 and 25: The lagoon floor is then colonised
Page 26 and 27: Note 11Growth-formsField guides to
Page 30 and 31: Note 13Changes in depthSome herbace
Page 32 and 33: Focusing on depthWater regime analy
Page 34 and 35: Note 15Internet dataEnvironmental d
Page 36 and 37: Step 3: Vegetation-hydrologyrelatio
Page 38 and 39: Note 19Modelling and time-stepsIn s
Page 40 and 41: Section 4: Old andNew DataOne of th
Page 42 and 43: see Figure 15), despite a three-fol
Page 44 and 45: frequency. This is rather limiting,
Page 46 and 47: Figure 13. Lippia, a floodplain wee
Page 48 and 49: single measure of the vegetation to
Page 50 and 51: Section 5:ObtainingVegetation DataW
Page 52 and 53: However, if the chosen species has
Page 54 and 55: Figure 15. Range of tree condition
Page 56 and 57: Figure 16. Spatial-temporal sequenc
Page 58 and 59: Note 26Canopy condition indexA visu
Page 60 and 61: Note 27Mapping floodplainwetland ve
Page 62 and 63: Shape of species responseThe shape
Page 64 and 65: Figure 18. Heat pulse sensorHeat pu
Page 66 and 67: section, using storage volume and i
Page 68 and 69: Figure 20. Crack volume and drying
Page 70 and 71: Figure 21. The relationshipbetween
Page 72 and 73: epresentative, there should be no m
Page 74 and 75: All of the curves are described by
Page 76 and 77: monitoring, precision levels, scali
Page 78 and 79:
sites of significant recharge and d
Page 80 and 81:
Figure 24. Degraded channelPart of
Page 82 and 83:
and so depth estimates are inaccura
Page 84 and 85:
Section 7:PredictingVegetationRespo
Page 86 and 87:
AEAM and the Macquarie Marshes. An
Page 88 and 89:
Category 3: hydraulic/empiricalAppr
Page 90 and 91:
For example, changes in surface and
Page 92 and 93:
ReferencesPrefaceArthington AH and
Page 94 and 95:
Section 3Roberts J and Marston F (1
Page 96 and 97:
Kunin WE and Gaston KG (1993). The
Page 98 and 99:
Singh VP (1995).“Computer models
Page 100 and 101:
Web ListingsNote 40Data on the WebM
Page 102 and 103:
flood. This has not been attempted,
Page 104 and 105:
Seven points over the flow range is
Page 106 and 107:
used as exclusions; or can be quant
Page 108 and 109:
Table A1 - 4. A flooding overlay ch
Page 110:
Table A2 - 1.(cont’d) K c and K s
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Estimating the Water Requirements for Plants of Floodplain Wetlands

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