School of Agriculture, Food and Ecosystem Sciences - Research Publications

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    Plastic weed matting is better than jute or woodchips for controlling the invasive wetland grass Phalaris arundinacea, but not Phragmites australis.
    Greet, J ; King, E ; Stewart-Howie, M (Polymeria Publishing, 2016)
    Woven polypropylene (plastic) weed matting, jute and eucalypt woodchips were trialled for controlling reed canary grass (Phalaris arundinacea L.) and common reed (Phragmites australis (Cav.) Trin. ex Steud.). At two sites, one dominated by reed canary grass and the other by common reed, 50 m x 20 m was mowed and sprayed and ten (10 m x 10 m) plots established, eight of which were fenced. Plots were covered with either plastic weed matting, jute or eucalypt woodchips, or were controls. All plots were planted with native trees and shrubs and understorey plants. Plastic weed matting was the most effective at reducing regrowth of reed canary grass (<5% cover after one year) and promoting the growth of native plantings (>60% cover). Both plastic weed and jute matting were similarly effective at reducing its regrowth (to 10%), but both matting types were compromised by common reed regrowth. While trees and shrubs grew well across all fenced treatments ( 100% survival), understorey plants only established and grew where weed regrowth was controlled. Unfenced unguarded trees and shrubs were virtually eliminated by browsing. Plastic weed matting (combined with other control measures, and protection from browsers where necessary) may provide the best opportunity to control reed canary grass and facilitate wetland restoration.
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    Counting the cost of revegetation: is direct seeding cheaper than planting tube-stock?
    Ede, F ; Greet, J ; Dabal, R ; Robertson, D ; Smith, R (University of New England, Armidale, 2018)
    Direct seeding is often assumed to be cheaper than planting tube–stock, but limited data exist to compare the relative costs of the two techniques. At four riparian sites in Victoria, we assessed the number of plants established over time in the months after direct seeding or planting. The costs of surviving plants and of weed management were calculated. Plants were 11 times cheaper when established by seeding ($1.88/plant) than when planted ($21.03/plant). Incorporating weed management costs, direct seeding was 1.3–2.4 times more cost–effective than planting tube–stock, although costs were high for both techniques.
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    The flooding tolerance of two critical habitat-forming wetland shrubs, Leptospermum lanigerum and Melaleuca squarrosa, at different life history stages
    Zacks, G ; Greet, J ; Walsh, CJ ; Raulings, E (CSIRO PUBLISHING, 2018)
    Understanding the effect of water regime on the different life history stages of woody wetland plants is essential to managing their persistence. The common and widespread myrtaceous shrub species, Melaleuca squarrosa Donn. ex Sm. and Leptospermum lanigerum (Aiton) Sm., provide habitat for two critically endangered fauna within the Yellingbo Nature Conservation Reserve (south-eastern Australia), but are in decline putatively because of the altered flooding regimes. We, thus, tested the effects of flooding depth and duration on their seed germination and seedling establishment, and seedling growth and survival in two separate glasshouse experiments. We also compared the condition of mature plants of both species at an intermittently flooded (reference) site, and two near permanently flooded (impact) sites. Seeds of both species were able to germinate underwater, but early flooding reduced seedling establishment. Seedling growth of both species was greater in waterlogged than in well drained or inundated conditions, whereas no seedlings of either species survived >8 weeks of submergence. Leptospermum lanigerum seedlings were generally more flood tolerant than were M. squarrosa seedlings. Correspondingly, crown condition of mature M. squarrosa, but not L. lanigerum, was poorer at impact than reference sites. Prolonged flooding in swamp forests is likely to (1) limit woody plant recruitment, because flooding reduces seedling establishment, growth and survival, and (2) be deleterious to the maintenance of less flood-tolerant species (e.g. M. squarrosa). Moist exposed substrate is likely to be best for promoting the recruitment of both study species, and intermittent flooding for maintaining adult M. squarrosa plants.
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    Unpalatable neighbours reduce browsing on woody seedlings
    Moser, S ; Greet, J (ELSEVIER SCIENCE BV, 2018-04-15)
    High levels of browsing by mammalian herbivores can negatively affect the survival and growth of seedlings, and consequently revegetation and forest regeneration outcomes. Typical forms of protection (e.g. tree guards and fencing) are costly, particularly when used in large-scale projects, therefore, low-cost alternatives are needed. Based on associational refuge theory, we assessed the revegetation technique ‘cryptic planting’, whereby woody seedlings are planted within the foliage of unpalatable plants to deter browsing. We established a trial where 432 six-month-old tubestock of three woody species (Eucalyptus camphora, Melaleuca squarrosa and Leptospermum lanigerum) were cryptically (within the foliage perimeter of unpalatable plants) or non-cryptically planted across three wetland forest sites. The plants were left for four weeks before being scored for browsing damage based on an estimate of biomass removed. To further assess cryptic planting, we surveyed 352 plants of the same three woody species two years after they were planted cryptically or non-cryptically at the same three sites, and surveyed each plant for browsing damage. Overall, cryptic planting reduced browsing damage from 37% to 22%, and from 51% to 23%, in the trial and survey, respectively. E. camphora plants were particularly susceptible to browsing. These results suggest that cryptic planting provides an alternative to costly tree guards and fencing and can be used to reduce browsing on woody seedlings.
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    Slashing Phragmites (Phragmites australis) prior to planting does not promote native vegetation establishment
    Greet, J ; King, E (WILEY, 2019-05)
    Summary Phragmites or Common Reed (Phragmites australis) is a tall rhizomatous cosmopolitan grass. While native to Australia, it can be invasive in wetlands, forming dense monocultures and reducing their ecological integrity. We assessed the potential for the cutting of Phragmites reeds prior to planting to promote the establishment of indigenous shrubs that might ultimately outcompete Phragmites. We established ten 5 m × 5 m quadrats in an area dominated by Phragmites, brush‐cut the reeds to ground level in five of them and left five uncut as controls. Within each quadrat, we planted 20 plants (~40 cm tall) of each of five indigenous shrub species, unguarded (4 plants/m2). We surveyed the plants one month after planting and annually for the following four years for survival, height and browsing damage. Browsing damage to plants was common (>50%) and unaffected by cutting. After four years, overall plant survival rates were ~25% and mean plant heights for the five shrub species ranged between 120 and 174 cm. Cutting of Phragmites had no positive effect on plant survival or height. In fact, two Melaleuca species grew taller in the uncut quadrats. Cutting of Phragmites reed beds prior to planting is unlikely to promote the establishment of woody plantings. However, planting within established Phragmites with or without prior brush‐cutting is worthy of further trialling as a potential tool for reinstating native diversity at Phragmites‐dominated sites.
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    Managed flooding can augment the benefits of natural flooding for native wetland vegetation
    Duong, A ; Greet, J ; Walsh, CJ ; Sammonds, MJ (WILEY, 2019-01)
    Managed flooding is increasingly being used to maintain and restore the ecological values of floodplain wetlands. However, evidence for its effectiveness is sometimes inconsistent and water available for environmental purposes often limited. We experimentally inundated a floodplain wetland (or “billabong”) in late spring by pumping water from its adjacent creek, aiming to promote the native wetland flora and suppress terrestrial exotics. Vegetation was surveyed before (spring) and after (late summer) the managed flood in the experimental billabong and in three control billabongs. Floodplain water levels were continuously monitored. Wet conditions caused two of the control billabongs to also flood, but to a lesser extent than the experimental billabong. We therefore assessed vegetation changes relative to flooding duration. With increasing flooding duration, the cover of wetland vegetation (amphibious and aquatic species) increased and the cover of terrestrial and exotic vegetation decreased, with these effects largest in the deliberately flooded billabong. Flooding durations greater than 20 days generally resulted in increased cover of wetland plants and restricted the growth of terrestrial plants. Reinstatement of more appropriate flooding regimes can thus promote native wetland plants, while suppressing terrestrial exotic species. Our study also provides evidence for the use of modest water allocations to augment the benefits of natural flooding in the maintenance and restoration of native wetland plant communities.
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    Seasonal timing of inundation affects riparian plant growth and flowering: implications for riparian vegetation composition
    Greet, J ; Cousens, RD ; Webb, JA (SPRINGER, 2013-01)
    Changes to the timing of peak river flows caused by flow regulation affect riparian vegetation composition, but the mechanisms driving such vegetation changes are not well understood. We investigated experimentally the effects of timing of inundation on riparian plant growth and flowering. We collected 168 sods from 14 sites across five lowland rivers in south-eastern Australia. Plant cover and flowering within the sods were surveyed each season for a year. During this period, sods were inundated for 6 weeks in either early spring or in summer. Terrestrial plant taxa (which included most exotic species) senesced in response to inundation, regardless of its timing. In contrast, native amphibious species (particularly amphibious forbs) responded favourably to inundation in spring, but were unaffected by inundation in summer. Native and exotic emergent macrophytes responded favourably to inundation regardless of timing, and flowered frequently in both the spring- and the summer-inundation treatments. In contrast, many native annuals flowered only in the spring-inundation treatment, while more exotic grasses flowered in the summer-inundation treatment. In temperate climates, inundation in early spring followed by non-flooded conditions is likely to be important for promoting the growth of amphibious forbs and the recruitment and flowering of riparian annuals. Without inundation in spring, many terrestrial exotic weeds may flourish and set seed prior to any subsequent inundation (e.g. in summer). We contend that natural seasonal timing (i.e. winter-early spring) of flow peaks is important for the maintenance of native riverbank vegetation and reducing the extent of terrestrial exotic species within the riparian zone.
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