How do Water Regime and Grazing Alter the Reproductive Capacity of Aquatic Plants?

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Dr Margaret A. Brock
Botany, Rural Science and Natural Resources, University of New England
Environment Australia, 2000

1. Research Findings (continued)

d) Results and interpretations (organized by objectives)

Objective 1. Determine the effects of timing, duration, and depth of flooding on the growth of a range of wetland plants with differing reproductive and growth strategies

I Does water regime influence plant community establishment and water quality in the UNE Experimental Wetlands?

The five water regimes imposed in the UNE Experimental wetlands have been maintained from 1997 to 2000 (Figure 1). The permanent and mimic regimes have two replicate ponds and the Spring Fill, Autumn Fill and Twice Annual Fill regimes have four replicate ponds. The mimic regime simulated water level changes at the time in Llangothin Lagoon during the study. The water levels within Llangothlin Lagoon and 3 other New England wetlands are shown in Figure 2. New England wetlands have water regimes that vary from season to season and year to year in an unpredictable way depending on local rainfall patterns.

In the five water regimes in the UNE experimental wetlands we have shown experimentally that:

  • Plant community composition is influenced by water regime in the experimental wetlands (see Figures 3-7 and Figure 8 for functional group types). In autumn 2000 after 30 months of establishment under experimental water regime treatments:
    • the Permanently flooded ponds showed well developed submerged plant communities (not well developed in ponds with fluctuating water regime) with a narrow band of amphibious species at the shallow depths,
    • Spring fill ponds had both submerged species (established in the previous 6 months since the last dry phase) and good representation of amphibious-tolerator and amphibious-responder species,
    • Autumn fill and Twice annual fill (autumn and spring) ponds were about to fill after a summer dry and had no submerged species but amphibious-tolerators, amphibious-responders and terrestrial species were well represented,
    • The Llangothlin mimic ponds filled in mid 1998 and maintained a fluctuating water level around the pond mid point through to autumn 2000, allowing a narrow band of submerged species and broad areas of amphibious-tolerator and amphibious-responder species together with some terrestrials.
  • Photographic representation of the sequential development of vegetation for each of the five water regime shows (in Figures 3- 7):
    • the water regime changes from 1997-2000,
    • year to year changes: summer vegetation and water regime, January 1998, January 1999, January 2000,
    • seasonal changes in 1999: summer, autumn, winter, spring.
  • The immediate water conditions present at a particular time had a marked influence on plant species composition. For example in April 2000 (after 30 months experimental water regime treatment) the species growing at any position in a pond reflected whether conditions were dry, damp or flooded, and falling or increasing at that point in the preceding weeks, irrespective of the total water regime in each pond.
  • There were no major variations in water quality parameters (conductivity, pH, turbidity, temperature, dissolved oxygen and biologically available nitrogen and phosphorous) between water regimes, within water regimes or between the ponds and Duval Creek, upstream and downstream of the wetlands (Attachment e).

II Does the dominant vegetation under different water regimes in the UNE Experimental Wetlands change with year and season?

Figures 3-7 show changes in vegetation within the 5 water regimes imposed at the UNE wetlands. Between year and between season changes are described in terms of the species and functional groups of plants (Figure 8) present in each year and season.

Autumn Fill (Pond number 9, Figure 3)

Between years: Autumn Fill wetlands were empty in summer. In summer 1998, little colonization took place on the planted seed bank strips, but some terrestrial species (mainly grasses) colonized the dry slope. In subsequent years (summer 99 and 00), terrestrial species still dominated the dry wetland, but some amphibious species (Centipeda minima, Eleocharis pusilla, Myriophyllum variifolium, Isotoma fluviatilis and Crassula helmsii) were also present. These individuals were stressed and in low abundance due to the lack of water and hot summer temperatures.

Between seasons: Autumn Fill wetlands were dominated in summer and autumn 99 by terrestrial species, with few amphibious and no submerged species (see "Between years"). With the increasing water levels in autumn, there was a slight increase in the abundance of amphibious species, although in winter 99, most of these species died off due to cold temperatures and frosts. Only Eleocharis acuta and M. variifolium survived in low numbers which consequently resulted in little vegetation present. In spring 99, amphibious species germinated in damp areas of the wetland, although at this time the water level was decreasing, leaving these species stranded under increasingly dry conditions.

Spring Fill (Pond number 14, Figure 4)

Between years: Spring Fill wetlands were full in summer. In summer 1998, colonization was restricted to the planted seed bank strips, with amphibious species growing at the water's edge and submerged species (Vallisneria gigantea) underwater. In subsequent years (summer 99 and 00), aquatic vegetation had spread throughout the wetland, with increased diversity in both the submerged (Chara spp., Nitella spp., and V. gigantea) and amphibious (Myriophyllum variifolium, Eleocharis spp., Hydrocotyle tripartita, Marsilea mutica and Nymphoides geminata) functional groups.

Between seasons: Spring Fill wetlands were dominated in summer and autumn 99 by many amphibious species (see "Between years"), with submerged species underwater. In winter 99, most species died off due to low water levels, cold temperatures and frosts, with only Eleocharis pusilla, E. acuta and M. variifolium surviving in low numbers. In spring 99, there was not much vegetation, but amphibious species were beginning to re-colonize as the water levels increased.

Twice Annual Fill (Pond number 16, Figure 5)

Between years: Twice Annual Fill wetlands were damp to one third full in summer. In summer 1998, colonization was restricted to the planted seed bank strips, with amphibious species growing at the water's edge and terrestrial species in the dry areas. In subsequent years (summer 99 and 00), the amphibious community in the damper areas had diversified to include mainly amphibious fluctuation-tolerator species (Centipeda minima, Agrostis avenacea, Cyperus sanguinolentus, Eleocharis spp., Isotoma fluviatilis, and Lythrum salicaria) with some Amphibious fluctuation-responder species (Myriophyllum variifolium and Marsilea mutica). Terrestrial species (mainly grasses) still dominated the drier part of the wetland slope. In summer 00, Typha orientalis had invaded the wetland.

Between seasons: Twice Annual Fill wetlands were dominated in summer and autumn 99 by many amphibious species (see "Between years"), with terrestrial species above the water's edge. In winter 99, most species died off due to low water levels, cold temperatures and frosts, with only Eleocharis pusilla, Isotoma fluviatilis and M. variifolium surviving in low numbers. In spring 99, there was not much vegetation, but amphibious species were beginning to re-colonize as the water levels increased.

Mimic (Pond number 5, Figure 6)

Between years: Mimic wetlands have water levels which do not fluctuates on a annual cycle. Summer depths were 20cm (1998), 40cm (1999) and 80cm (2000). In summer 1998, colonization was restricted to amphibious species on the planted seed bank strips, with terrestrial species elsewhere in dry areas of the wetland. In subsequent years (summer 99 and 00), aquatic vegetation had spread throughout the wetland, with increased diversity in amphibious species (Myriophyllum variifolium, Eleocharis spp., Isotoma fluviatilis, Marsilea mutica and Nymphoides geminata). In summer 2000 with increased water levels, submerged species (Nitella spp.) had colonized underwater areas.

Between seasons: Mimic wetlands were dominated in summer and autumn 99 by a diverse community of amphibious species (see "Between years"), with some terrestrial species (Panicum gilvum, Paspalum sp.) in drier areas. In winter 99, the water level increased and most species died off due to either flooding (terrestrial species) or cold temperatures and frosts (some amphibious species). Only Eleocharis acuta, Marsilea mutica and M. variifolium survived during winter. In spring 99, the vegetation increased rapidly in species diversity and abundance, mainly due to many amphibious species growing throughout the wetland, and also submerged species (Nitella spp.) underwater, and terrestrial grasses in dry areas.

Permanent Flood (Pond number 8, Figure 7)

Between years: Permanent wetlands were always full . In 1998, the permanent wetland was very turbid, although in 1999-2000 water clarity increased greatly due to stable water levels. In summer 1998, colonization was restricted to the submerged species Vallisneria gigantea underwater on the planted seed bank strips. Some terrestrial and amphibious species colonized the edge zone. In subsequent years (summer 99 and 00), the submerged aquatic vegetation (Chara spp., Nitella spp., and V. gigantea) had spread throughout the wetland, with an increase in amphibious species (Myriophyllum variifolium, Eleocharis spp., and Typha orientalis) in the edge zone.

Between seasons: Permanent wetlands were dominated in all seasons of 1999 by the amphibious species T. orientalis and large numbers of the submerged species Nitella spp., Chara spp., and V. gigantea. In the edge zone, a narrow strip of amphibious species (Potamageton tricarinatus, Eleocharis acuta and Myriophyllum variifolium) established and remained for most of the year. The only variation to the vegetation in this wetland occurred during winter, when many species in the edge zone died due to the cold temperatures and frosts.

III How do timing, duration and depth of flooding influence growth and reproduction of a range of wetland plants in the UNE Experimental Wetlands?

In the period from December 1997- April 2000 in the UNE Experimental Wetlands at Newholme:

  • Over 100 species of vascular plants grew in the experimental wetlands. Species could come from the donor wetland seed bank, from dispersal into the wetland ponds by wind of water from the surrounding pasture or from Duval Creek (the water source). We assume that aquatic species came from the donor seed bank and many of the terrestrial species from the surrounding pasture. Between 68-92 species grew in each regime (Figure 9). There are no significant differences between numbers of species in each regime. As both Permanent and Mimic regimes had only two replicate ponds in contrast to four ponds for each of the Autumn, Spring and Twice Annual fill regimes it is to be expected that slightly lower total species numbers were recorded in Permanent and Mimic ponds.
  • Within each water regime all functional groups of species were well represented (Figure 10). It is noteworthy that all the aquatic groups of plants, "submerged", "amphibious tolerators", "amphibious responders" and "terrestrial-damp" are equally well represented in all water regimes. The "terrestrial -dry" group is smaller in the permanent regime which provides only a narrow band of habitat for these species that do not tolerate flooding. This suggests that from a mixed seed bank water regime does not select particular functional groups differentially.
  • The number of water regimes in which each species (or functional group) occurred could tell us whether some species were specific to particular water regimes (Figure 11a). However our results show that 50% of species occurred in all five water regimes and a further 20% in four regimes. All functional groups of plants were represented. Less than 10% of species occurred in only one water regime and the majority of these were not aquatic plants but terrestrial colonizers. Thus water regime does not select for particular species from a mixed seed bank.
  • In contrast the majority of species did not reproduce in all water regimes: 30% of species didn't reproduce in any regime and a further 30% of species reproduced in only one or two water regimes (Figure 11b). Hence water regime may select which plants can reproduce.

Figure 10. Total species richness of functional groups (FG SR) for each water regime in the UNE Experimental Wetlands between December 1997 and April 2000.

Figure 10. Total species richness of functional groups (FG SR) for each water regime in the UNE Experimental Wetlands between December 1997 and April 2000.

Water regimes: AF=Autumn Fill, M=Mimic, P=Permanent, SF=Spring Fill, TF=Twice Annual Fill
Functional groups: TDR=Terrestrial-dry, TDA=Terrestrial-damp, AT=Amphibious fluctuation-tolerator AR=Amphibious fluctuation-responder, S=Submerged.

Figure 11. Number of water regimes in which species occur.

Figure 11. Number of water regimes in which species occur.

Number of species in different functional groups (a) present, and (b) reproducing in 1 to 5 water regimes. For (b), zero (0) water regimes indicates species present but not reproducing in any regime. Functional groups are: TDR: Terrestrial-dry, TDA: Terrestrial-damp, AT: Amphibious fluctuation-tolerator, AR: Amphibious fluctuation-responder, S: submerged

  • Plant community development over time was shown to have patterns related to water regime. Multivariate analysis of vegetation data over three years for each of two seasons summer (Figure 12) and autumn (Figure 13) in the middle of each pond (5m distance from deepest point) is presented to represent species patterns within each pond. Patterns of vegetation in quadrats at 3m and 7m distance from the deepest point were compared with the 5m results and were found to be consistently more closely related to 'flooded' and 'terrestrial' vegetation respectively in each regime. Hence 5m quadrat data are interpreted. Patterns (Figures 12 and 13) show:
    • 1997 , the year of establishment was different from other years,
    • In 1998-1999 and 1999 -2000 water regime determined patterns based on species presence and abundance in both autumn and summer analyses,
    • Permanent ponds were different from other ponds,
    • In general Autumn fill and Twice annual fill ponds grouped together,
    • Spring fill was most likely to group with the mimic ponds when water levels were similar (summer),
    • The sequential development of this vegetation in each pond both within and between years is shown in pictorial form in Figures 3-7 for each water regime.

IV How does season of planting influence plant establishment and reproduction under different water regimes in the UNE Experimental Wetlands?

Donor seed banks material were introduced to the wetlands in strips in two seasons, spring 1997 and autumn 1998. Season of planting does influence plant reproduction (Figure 14, Appendix f). The results show:

  • In initial plant community establishment, season and length of time since planting did not affect the number of species present under any water regime.
  • Conversely, reproductive maturity of species (both species number and number of individuals) was influenced by season and time since planting.
  • Thus the timing of planting donor seed banks in wetlands potentially influences which species add seeds to the soil seed bank in the first year of establishment. To maximize the number of species being added to the seed bank within the first year of revegetating a wetland, donor seed banks should be planted in spring so that most species have reached reproductive maturity by summer and autumn, and have seeded before winter.

V Do water regime and season influence plant reproduction?

Reproduction of species is influenced by both season and water regime (Figure 15, Attachments i, j). Results show:

  • Autumn is the season in which most species reproduce in all water regimes (Figure 15b).
  • 60% of species recorded in each water regime were reproductive in autumn 1999, and autumn 2000, 18 and 30 months after the wetlands were planted with seed bank material and water regimes were imposed (Figure 15a,b).

Figure 15. Number of plant species (a) present and (b) reproducing under different water regimes over time in the UNE Experimental Wetlands.

Figure 15. Number of plant species (a) present and (b) reproducing under different water regimes over time in the UNE Experimental Wetlands.

Regimes: AF = Autumn Fill, M = Mimic, P = Permanent Flood, SF = Spring Fill, TF = Twice Annual Fill

  • Although it appears that the Spring and Autumn fill and the Twice annual fill regimes had more species reproducing and a higher total number of species (Figure 15) this is probably not significant because of the influence of the greater number of replicate ponds in these treatments.
  • Some terrestrial species are rare in the ponds and only reproduce occasionally in dry conditions.
  • Submerged species only reproduced in water regimes which were flooded for long enough for growth and reproduction between spring to autumn (Permanent, Mimic and Spring Fill, Figure 15, Attachment i). Submerged species grew in Autumn and Twice-annual fill but did not flower in these regimes.

VI How does water regime influence plant establishment from seed bank and vegetative material in the UNE Experimental Wetlands?

Establishment from vegetative and seed bank material were compared in an honours project (Attachment k). Major findings included:

  • Plant establishment from sexual (seed bank) and vegetative propagules (vegetative blocks) gives different plant community composition.
  • Water regime may influence this. The same species, or functional group of species, can respond differently to a particular water regime depending on its life cycle stage. For example, amphibious-tolerator species (e.g. Cyperus sanguinolentus), can tolerate flooding in the vegetative phase but will not germinate and establish under flooded conditions.
  • Prolonged flooding or drought may reduce the number of functional groups of species present by selecting for vegetative growth (rather than germination) of species within particular functional groups (e.g. submerged and terrestrial respectively). A full range of functional groups including amphibious-tolerator and amphibious-responder groups (Figure 8) can return to the plant community by germination from the seed bank after the return of flooding and drying cycles.

VII How does water regime influence other components of the biota in the UNE Experimental Wetlands: frogs and invertebrates?

  1. Pilot study on the influence of water regime on macroinvertebrate species richness ( Attachment g, S Botting UNE) The UNE Experimental Wetlands contain wetland vegetation with different water regimes imposed. This provided a variety of habitats for aquatic macroinvertebrate communities. In autumn (April) 2000:
    • Aquatic macroinvertebrate communities were lower in number of taxa in Autumn fill regime which was just filling at the time, indicating a colonization phase. Slightly higher numbers of taxa were present in the Spring fill regime which may indicate a better developed community when ponds had been full for the preceding several months.
    • High numbers of damselflies, backswimmers and mosquito larvae were present in all regimes.
    • In general numbers of taxa were consistent between ponds in a water regime.
  2. Pilot study on the influence of water regime on frog species richness, abundance and reproduction (Attachment h, M. Healey, DLWC).
    • A total of eight frog species from two families were recorded at the UNE Experimental Wetlands. The species richness of calling frogs in Autumn fill and Spring fill and Twice annual fill treatments increased when ponds were filling and decreased as they dried. More frog species were calling in Permanent and Mimic water regimes, which may be related to their flooded state. Abundance of frogs showed the same trends as for species richness.
    • There were differences between the floating and submerged egg masses being deposited in particular water regime treatments. Floating egg masses (associated with the Family Myobatrachidae) were found in all water regimes whereas submerged egg masses (associated with the Family Hylidae) were only detected in Spring and Twice annual fill treatments during the early to mid filling phase.
    • These trends indicate that frogs are responding differentially to water regime. This warrants confirmation as it may give important cues to management of biota under different water regimes.

VIII How do timing, depth and duration of flooding influence plant growth and reproduction under experimental tank conditions?

Outdoor tank experiments have been used to elucidate the influence of duration, depth and timing of flooding on aquatic plant establishment and reproduction. If a plant does not establish it does not have a chance to reproduce either vegetatively or sexually. Therefore we report on establishment and the chances of converting establishment to vegetative or sexual reproduction under different water regimes from a series of tank trials. The work of Casanova and Brock (2000)(Attachment a) studied how water regime influences germination and establishment whereas that of Warwick and Brock (Attachment i) and Crossle and Brock (Attachment j) explores how water regime influences reproduction. The main findings were:

  • Depth, duration and frequency of inundation influenced plant community composition but depth was least important (Casanova and Brock, 2000)
  • The duration of individual flooding events was important in segregating plant communities: shorter floods (less than two weeks encouraged higher species richness and biomass. (Casanova and Brock , 2000).
  • The ability of species to tolerate or respond to fluctuations in flooding and drying was important (Casanova and Brock ,2000).
  • · The highest biomass and species richness developed where the seed bank was kept damp without flooding or dying. This community was dominated by terrestrial species. The lowest biomass and species richness developed in pots that were continuously flooded (Casanova and Brock, 2000).
  • Short, frequent floods promoted high species richness and biomass particularly of amphibious species that tolerate or respond to fluctuations. Amphibious-responder species dominated the biomass in depths over 20cm whereas amphibious-tolerator species dominated in shallower depths had the greatest biomass. Terrestrial species were able to establish during dry phases between short floods (Casanova and Brock, 2000).
  • A large proportion of the terrestrial species establishing were exotics.
  • Longer floods lowered species richness and biomass of terrestrial species.
  • The majority of species germinating and establishing in a summer experiment were able to flower and set seed. In contrast autumn establishing species did not flower in the experimental time frame (Attachment i).
  • Flooding duration is most important for submerged aquatics as they need flooding for long enough for reproduction, whereas amphibious species can reproduce when flooded or damp (Attachments i, j).

Objective 2. Investigate the effect of grazing and the interaction of grazing with water regime on production of reproductive units by aquatic plants

How do water regime and grazing interact to affect plant germination, establishment and reproduction?

An outdoor tank trial was designed to test the interaction of clipping and water regime on plant community establishment and reproduction (Attachment j). This 4 months trial was harvested in autumn 1999. Water regimes were altered weekly by changing the suspension levels of pots in outdoor tanks. Each tank contained pots with each of six water regimes and two clipping treatments (clipped and unclipped). Six replicate tanks of seed bank and established plant material were used. Six water regimes simulated aspects of the water regimes in the UNE Experimental Wetlands (Figure 16). Results (Figure 17) suggest that:

  • Water regime influenced both species presence or absence and the mode of reproduction as evidenced by:
    • The number of species reproducing sexually was greater when vegetation was exposed (i.e. not flooded),
    • Species were just as likely to reproduce vegetatively when flooded as when damp.
  • Within a water regime clipping influenced mode of reproduction as evidenced by:
    • Species in clipped treatments reproduced both sexually and vegetatively when damp, not flooded,
    • Species in unclipped treatments reproduces both sexually and vegetatively under all regimes, both damp and flooded,
    • In the permanently flooded regime, clipped vegetation reproduced vegetatively or not at all, in contrast to unclipped vegetation which had some species reproducing sexually and some both sexually and vegetatively
    • Vegetation which was submerged but had a fluctuating water regime reproduced sexually in both clipped and unclipped treatments.
  • Water regime influences whether species reproduce sexually or not: the number of species reproducing sexually is greater in damp than flooded communities.
  • For flooded vegetation clipping further reduces the number of species reproducing sexually.
  • For exposed (damp) vegetation, clipping does not reduce the number of species reproducing sexually.

Objective 3. Determine the effects of water regime on the allocation of plant biomass to different reproductive modes

How does water regime and clipping influence the allocation of biomass to reproduction?

Target species from aquatic functional groups were followed to assess how water regime and clipping influenced allocation of biomass to reproduction (Attachment j). The following species were selected: Submerged: Vallisneria gigantea, Amphibious- responders: Myriophyllum variifolium, Limosella australis, Amphibious-tolerators: Centipeda minima, Cyperus sanguinolentus, Isotoma fluviatilis and Lythrum salicaria. The study showed that:

  • For amphibious species, water regimes incorporating damp conditions were best for establishing vegetation (ie biomass) and reproducing:
    • water regime that changed from flooded to damp favored establishment and reproduction in the amphibious -responder species, Limosella and Myriophyllum and the amphibious- tolerator species Lythrum. Clipping further increased the biomass and reproductive output of Lythrum and Limosella, but not Myriophyllum under this water regime,
    • In contrast, permanently damp conditions favored growth and reproduction the amphibious -tolerator species Centipeda and Cyperus. These species reproduced only when kept permanently damp. Clipping did not influence the number of reproductive units.
  • For the submerged species (Vallisneria) flooded conditions were required for growth and reproduction:
    • water regimes suitable for submerged species must provide flooding for long enough for reproduction and seed set ( Attachments i,j),
    • Clipping reduced both the amount of biomass and the number of reproductive units produced for this submerged species.

Objective 4. Validation of selected response patterns by studying wetland plants in temporary wetlands under a range of natural flooding and drying regimes.

Do plant perform similarly under experimental and natural conditions?

Species selected to represent various aquatic plant functional groups (Figure 8, Attachment j) were monitored in the field as well as in outdoor tank trials and in the University of New England experimental wetlands. Four sites on the New England Tablelands were monitored for level and vegetation change with season (Figure 1, Figure 18). Figure 18 compares the plant community composition of Llangothlin Lagoon, with the Permanent and Mimic regimes in the UNE Experimental wetlands. The Mimic regime has been modeled on water level changes at Llangothin lagoon during the study period. Llangothlin Lagoon has both permanent areas and an edge zone in which water levels fluctuate within and between seasons.

Figure 18. Total species richness of functional groups at Llangothlin Lagoon (LL), and the Mimic (M) and Permanent Flood (P) water regimes at the UNE Experimental Wetlands, in autumn (Aut98) and spring (Spr98) 1998.

Figure 18. Total species richness of functional groups at Llangothlin Lagoon (LL), and the Mimic (M) and Permanent Flood (P) water regimes at the UNE Experimental Wetlands, in autumn (Aut98) and spring (Spr98) 1998.

Functional groups: TDR=Terrestrial-dry, TDA=Terrestrial-damp, AT=Amphibious fluctuation-tolerator AR=Amphibious fluctuation-responder, S=Submerged.

Our studies show:

  • There are similarities in species composition and abundance in field sites and the University of New England experimental mimic ponds in areas where comparable water levels are found.
  • Functional groups are present in field sites in relation to water regime. Amphibious groups dominate zones where water level fluctuations are extensive. Submerged plants dominate the areas of wetlands where water is persistent.

Observations of plant performance in relation to water regime have made at other wetlands including Gingham-Gwydir wetlands, Murrumbidgee wetlands at Wagga and Leeton, coastal wetlands on the mid north coast, and the Macquarie Marshes. Our publications on aquatic plant management (Attachments l and m) are based on extrapolations from findings in our research wetlands to a wide range of wetlands. Some generalizations for most wetlands include (see attachment m):

  • Shallow habitats with amphibious plants change as water levels rise and fall.
  • Many plant species tolerate or respond quickly to water level changes.
  • Permanently flooded habitats tend to have submerged plants that do not tolerate drying.
  • Terrestrial edge habitats tend to have weedy plants which do not tolerate flooding.
  • A mosaic of habitats provides a diverse set of conditions for organisms in a wetland.
  • Fast lowering or raising of water levels may leave edge habitats bare of aquatic plants,.
  • Steep sided wetlands won't have wide zones of aquatic plants stimulated by water level fluctuations.

Objective 5. Model the responses of the different reproductive types under different water and grazing regimes from an 18-30 month data set

To model the response of plant reproductive types under different water regimes we have examined how a new seed bank develops as an indicator of wetland sustainability through reproduction. If a wetland is to become sustainable it must develop a seed bank from which plants can germinate after a drying event. Plants must germinate, establish, flower, set seed and leave viable seed in the seed bank. Alternatively plants may reproduce vegetatively while conditions are good for growth.

As explained in section c) above we have not been able to include grazing regime in our field experimentation within the timeframe of the project.

How does water regime influence the development of seed banks over time?

In the five water regimes in the UNE Experimental Wetlands we have examined how a new seed bank has developed in 18 and 24 months since the ponds were first filled.

In autumn 1999 and spring 1999 sediments from each pond were sampled and germinated to determine whether seed banks were developing in each wetland pond. Samples for germination were taken from the opposite side of the ponds from where the donor seed bank was introduced. Seeds germinating from these samples have a) been produced in the ponds from flowering plants or b) dispersed to the sediment from outside the ponds (wind, birds etc) or c) movement from the introduced seed bank strips within the pond. We are assuming that flowering and seeding within each pond will be the major source. Sand samples and initial donor seed bank samples were included in the experiments as references . Results show that:

  • Seed banks were present in both autumn and spring 1999 in each water regime. In autumn 1999 between 15-20 species were present in each water regime and in spring 1999 between 20 and 30 species were present in each water regime. All functional groups germinated from each of the five water regimes. (Figures, 19, 20, 21). We cannot assume that the increase in number of species from autumn to spring reflects an increase in species in the seed bank as the reference seed bank also had increased spring numbers. There were no differences in species number between water regimes (Figure 19).
  • However there were differences in abundance of individuals between water regimes (Figure 20). As shown graphically Autumn-fill had more seedlings in both autumn and spring than the other regimes and the permanent ponds in autumn had fewer seedlings. The dendrogram (Figure 22) show a similarity in Autumn-fill and Twice annual-fill regimes which is consistent with the vegetation patterns shown in the developing vegetation (Figure 12 and 13). Similarly Spring-fill and Permanent ponds group together which is consistent with the reproductive and vegetation patterns shown after a spring and summer with flooding in the ponds (Figure 22 and 12). The Mimic ponds separated alone and may reflect water regime which is fluctuating more slowly.
  • Abundance of individuals showed patterns within functional groups. Submerged species only had substantial seed banks from Permanent, Spring-fill and Mimic regimes - those regimes which have been wet for long enough in spring to autumn for species to flower, set and drop seed. Amphibious-responder species were well represented in all regimes. Amphibious-tolerators were best represented in Twice annual-fill and Autumn-fill regimes , those regimes which were not flooded for long during the reproductive season. Terrestrial species had small numbers in all regimes.
  • Each water regime had 4-6 dominant species (Figure 23). In general these dominants differed from the species that dominated the extant vegetation at the same time. Exceptions were the submerged species and a few amphibious- tolerator species present in both extant vegetation and the seed bank.
  • The set of dominants differed with water regime. The submerged species Nitella sp, Chara sp and Vallisneria gigantea dominated the flooded conditions of the Permanent and Spring-fill wetlands but no other regimes.
  • The amphibious-responder species Elatine gratioloides and Limosella australis were the only two species that were dominant in seed banks of most water regimes.
  • This suggests that a substantial seed bank (in total numbers and in species richness) can develop within 18 months of plants establishment from seed bank in a wetland. This new seed bank will develop in species richness with further time.
  • We believe that the development of a species-rich seed bank is a significant indicator of the development of a sustainable wetland.

Figure 19. Average species richness (+/- SE) of the newly developed seed bank, from sediment from different water regimes in two seasons (Autumn and Spring 1999) in the UNE Experimental Wetlands.

Figure 19

Sediment sources: AF=Autumn Fill, M=Mimic, P=Permanent, SF=Spring Fill, TF=Twice Annual Fill, SA=Sand, SB= original donor seed bank.

Figure 20. Average number of seedlings germinating from newly developed seed banks from different water regimes in the UNE Experimental Wetlands, split by functional group and season.

Figure 20

Sediment sources: AF=Autumn Fill, M=Mimic, P=Permanent, SF=Spring Fill, TF=Twice Annual Fill SA=Sand, Seed bank= original donor seed bank Functional groups: TDR=Terrestrial-dry, TDA=Terrestrial-damp, AT=Amphibious fluctuation-tolerator AR=Amphibious fluctuation-responder, S=Submerged.

Figure 21. Seed bank development: total number of species in each sediment source, split by functional group and season.

Figure 21

Sediment sources: AF=Autumn Fill, M=Mimic, P=Permanent, SF=Spring Fill, TF=Twice Annual Fill SA=Sand, Seed bank= original donor seed bank Functional groups: TDR=Terrestrial-dry, TDA=Terrestrial-damp, AT=Amphibious fluctuation-tolerator AR=Amphibious fluctuation-responder, S=Submerged.

Figure 22. Dendrogram showing separation of newly developed seed banks from sediment from different water regimes in the UNE Experimental Wetlands and in different seasons, based on species presence and number.

Figure 22

Codes are as follows: Sediment sources: AF=Autumn Fill, M=Mimic, P=Permanent Flood, SF=Spring Fill, TF=Twice Annual Fill, Sa=Sand, SB=original donor seed bank. Number 1-4 indicates replicate number. Au=Sediment collected in Autumn 1999, Sp=Sediment collected in Spring 1999.

Figure 23. Dominant species in the extant vegetation and new seed banks for the five water regimes in the UNE Experimental Wetlands, in Autumn 1999 (Aut) and Spring 1999 (Spr).
  Autumn Fill Spring Fill Twice Annual Fill Mimic Permanent Flood
Extant Veg Seed bank Extant Veg Seed bank Extant Veg Seed bank Extant Veg Seed bank Extant Veg Seed bank
Aut Spr Aut Spr Aut Spr Aut Spr Aut Spr Aut Spr Aut Spr Aut Spr Aut Spr Aut Spr
S Chara spp.         X     X               X X      
Nitella spp.             X X           X   X   X X X
Vallisneria gigantea             X                   X X X X
AR Crassula helmsii         X X     X X                    
Elatine gratioloides     X X     X X     X X     X X     X X
Glossostigma sp.         X                     X        
Limosella australis     X X     X X   X X X     X X        
Marsilea mutica X X     X X     X X     X X            
Myriophyllum variifolium X X     X X     X X     X X     X X    
Nymphoides geminata         X       X       X              
Otellia ovalifolia         X                              
Potamageton tricarinatus   X                       X     X X    
AT Centipeda minima X X   X         X X       X   X        
Cyperus sanguinolentus                 X                      
Eleocharis spp. X X     X X     X X     X X     X X    
Isotoma fluviatilis X       X       X X     X X            
Juncus 'pinrush'                 X                      
Lythrum salicaria X   X X       X     X X                
Typha orientalis                                 X X    
TDA Juncus bufonius X           X X X             X     X X
Persicaria spp. X                 X                    
Conyza bonariensis             X       X                  
TDR Polygonum spp. X X X               X                      
Terrestrial grasses X X X X X X X X X X X X X X X X       X

Species are split by functional group: S=Submerged, AR=Amphibious fluctuation-responder, AT=Amphibious fluctuation-tolerator, TDA=Terrestrial-damp, TDR=Terrestrial-dry.

How can responses of plant types under different water regimes over time be extrapolated to other systems.

Results are being extrapolated to other systems both within Australia and on other continents by:

  • Comparing wetland plant seed characteristics by contrasting NSW upland temporary wetlands (with unpredictable water regimes) with New Jersey (USA) freshwater tidal marshes (with predictable water regimes) ( Leck and Brock, in press). This paper was developed as an invited paper on the "Comparative Ecology of Wetland Seeds" in a symposium on Evolution of Dormancy and Germination at the 1999 International Botanical Conference in St Louis Missouri.
  • Suggesting that the zone subject to water level fluctuation in a wetland, the amphibious zone, is the major place in which selection takes place for species adapted to aquatic habitats. The major selective force is hydrological regime (Leck and Brock, in press).
  • A paper showing how water regime differentiates plant communities will be presented at the INTECOL Wetlands Meeting in Quebec in August 2000. This paper extrapolates from this research to interpretations in other wetlands including the Macquarie Marshes, Gingham-Gwydir wetlands, Kakadu wetlands (all Ramsar sites) and Tasmanian wetlands and South African floodplain wetlands.

Objective 6. Present findings in a way that can be used by water managers to aid in the planning of flooding and drying regimes in temporary wetlands

Opportunities to extend these field trials into other wetlands and wetland systems in which flooding and drying regimes are important include communication through face to face interactions, and development of publications on techniques for wetland management which are targeted at wetland users and mangers, both private and government.

I Development and delivery of a) two wetland management technique booklets, b) a textbook for wetland managers and c) papers for the management literature.

  1. Our major efforts at delivery "in writing" have focussed on the development of two booklets on wetland plant management:
    • "Are there plants in your wetland? Revegetating wetlands" (Brock and Casanova, 2000, Attachment l).
    • "Does your wetland flood and dry? Water regime and wetland plants". (Brock, Casanova and Berridge, in press due for publication September 2000, Draft as Attachment m).

    These booklets follow the format of a booklet from a previous project (LWRRDC) Are there seeds in your wetland? Assessing wetland vegetation (Brock 1997), (7000 copies distributed and the booklet reprinted through the Wetland R & D Program). The new booklets have been developed as two more in the same series and will be advertised widely as a set of guides for wetland plant management. A draft brochure which will be used to advertise these booklets in Rip Rap, CRCFE newsletter etc is in draft (Attachment n). We are planning ongoing activities to assess the uptake of the ideas in these booklets.

    Publication and distribution plans for the wetland plant management booklets are:
    • "Are there plants in your wetland? Revegetating wetlands" was published in June 2000, (10,000 copies).
    • "Does your wetland flood and dry? Water regime and wetland plants" due for publication September 2000 (10,000 copies, delays due to computer virus).
    • We have arranged for both booklets to be distributed together as follows:
    • mailed with "Rivers for the Future"(LWRRDC) -2500 copies,
    • mailed through Wetland Link -1000 copies,
    • mailed through Greening Australia -500 copies,
    • for distribution to managers NSW Department of Land and Water Conservation -2000 copies,
    • AFFA shop front for orders -2000,
    • Advertising flyer (Attachment n) being developed for publication in newsletters (ASL, CRCFE, Rivers Symposium etc),
    • copies available for EA, UNE, Wetland Care Australia, schools, workshops as required.
  2. Findings from this research have been incorporated in a textbook for students, scientists and managers.
    • Specific discussions of water regime and wetlands with management implications have been included as a major theme in the textbook, Australian Freshwater Ecology: processes and management. (Boulton and Brock 1999, see Attachment o). Research from this project has been used to inform the science and management discussed this book.
  3. Interpretations for the management literature are also being made.
    • Several papers addressing how water regime in temporary wetlands has been changed and how it influences wetlands and their management in an agricultural landscape have been presented at conferences and or published. See Brock, Smith and Jarman (1999), Brock and Jarman (in press) and invited Wetland Lecture at Australian Society for Limnology conference 1998 and at Australian Wetland Conference (Wetland Care Australia) 1999.

II Face to face communication activities

Many activities both at the UNE Experimental wetlands, and in field situations have enabled discussion of the role of water regime on wetland plant establishment and reproduction with wetland managers, school, and university students, politicians, farmers and other members of community. Activities are ongoing and have included:

  • The opening of the UNE Experimental Wetlands by the NSW Minister for Land and Water Conservation, Hon. Richard Amery in March1999. This was attended by Natural Resource Management Agencies, High School teachers and students, UNE staff and students, local farmers, council members and politicians.
  • Field days in New England region for wetland users and managers and Landcare groups.
  • UNE Undergraduate students in Science and Natural Resources classes at the UNE experimental wetlands.
  • workshops with Department of Land and Water Conservation in wetland monitoring for regional staff in July 1999 and visits in 2000.
  • National and international wetland scientists and managers visiting the project and site (e.g. Prof M Leck, USA, Dr M Finlayson, NT, Dr S. Blanch, Inland Rivers Network).
  • A group of visiting Indian Wildlife and Park Management Scientists NSW DLWC regional staff advice.
  • Discussions and presentation at Wetland Care Australia Wetlands Meeting 1999

Communication at local, regional and national and international levels will continue to be ongoing as will longer term research in the UNE experimental wetland facility.