Literature review: Impact of Chilean needle grass ... - Weeds Australia

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ecorded in them. Lowland grassland and grassy woodland were ranked highest with 344 taxa of which 87 were considered very serious. Between one quarter and one third of the flora in each of the main grassland regions consists of exotics (Kirkpatrick et al. 1995). Weed invasion is a major problem for survival of the native flora. Dicotyledonous herbs are the most threatened group (Groves 2004). Weed diversity and dominance at grassland sites is often high. For example McIntyre (1993) found that 97% of samples in New England tablelands native grasslands in 1990-91contained exotic species. Trémont (1994) found that secondary grasslands in that area were composed of 27% exotics in areas ungrazed for 16 years and 32% in grazed areas, with exotics comprising 50% and 43% of the grasses in the two treatments respectively. In the Monaro region exotics accounted for an average of 35% of species, and sites on the Southern Tablelands generally had >20% exotic cover in spring (Sharp 1997). According to Kirkpatrick et al. (1995), the high invasibility of grasslands is probably related to their high soil fertility. McIntyre and Lavorel (1994a 1994b) reported declines in native species richness and increases in exotic richness on sites of increasing natural substrate fertility (granite < sediment < basalt) on the New England Tablelands and a similar trend for water enrichment. Exotic invasion occurred simultaneously with the introduction of livestock and resulted from the carriage of seed in their coats or digestive tracts, or by movement of fodder, and the superior adaptations for survival that these plants possessed under the new grazing regimes (Kirkpatrick et al. 1995). Invasions may have been facilitated by the disappearance or dysfunction of the C 4 grass, the C 3 grasses, or the intertussock forbs (Groves and Whalley 2002) resulting from various forms of disturbance. Soil disturbance that raised the level of available nutrients in situ has had particularly insidious effects (Wijesuriya and Hocking 1999). Extraneous nutrient addition also commonly results in damage. Roadside grasslands in western Victoria were rapidly invaded by Holcus lanatus in 1983 after nutrient rich soil drifted from drought-affected agricultural land, a number of significant remnants being destroyed (Kirkpatrick et al. 1995). Competition from annual grasses may significantly impact on native forbs with similar cool season growth patterns (Morgan 1994) but invasion by perennial grasses including N. neesiana has resulted in much greater community change (Hocking 1998, Lunt and Morgan 2000). In the New England grasslands low native diversity occurred in areas with greater frequency of soil disturbance and water enrichment, and was associated with thick litter cover and >5% bare ground (McIntyre 1993). Exotic species were rarely dominant, but Hypochoeris spp., Plantago lanceolata L., Vulpia spp., Trifolium arvense L., Bromus spp. and Paspalum dilatatum were dominants in a small number of 30 m 2 quadrats. The six sites with the lowest richness all had high soil disturbance and litter >5 cm deep, and were dominated by perennial exotic grasses. Severe soil disturbance in these grasslands eliminated a large number of native taxa, which were replaced largely by exotic species (McIntyre and Lavorel 1994a 1994b). The disturbance-intolerant species included many rare taxa which apparently were unable to recolonise disturbed ground or were uncompetitive in situations of high productivity (McIntyre and Lavorel 1994a). A group of disturbance-tolerant species were found over the range of disturbance states and included natives such as Acaena spp. and Asperula conferta Hook. f. and the exotics Hypochaeris radicata L. and Centaurium erythraea Rafn. A further group of “disturbance specialists” exploited areas that had been heavily grazed or where the soil had been disturbed, and were mainly exotics, including Paspalum dilatatum and Plantago lanceolata L., but included a few native herbs. Disturbance specialists tended to dominate the sward where disturbance was intense (McIntyre and Lavorel 1994a). T. triandra grasslands of the Victorian volcanic plains in general have a large exotic vascular plant component, even those that have been minimally disturbed and are rich in native species (Morgan 1998c 1998d). For example 41% of the 102 species found in quadrats at Evans Street, Sunbury grassland in 1993-4 were exotics, 52% being annuals, and 77% of them having
Opinions differ on the nature and intensity of disturbance required for weed invasion. Patton (1935 p. 175) considered intact grasslands on the Victorian basalt plains to be highly resistant: “So long as the natural vegetation covering, open though it be, is maintained, entrance to new-comers is denied.” Lunt (1990a) found that areas of Derrimut Grassland ploughed during the 19th century were amongst the most diverse, with an average of 17 native and 13 exotic vascular plant species per 15 m 2 , probably illustrating one of the dilemmas of native grassland management, that certain types of disturbance favour both weeds and the native flora (Trémont and McIntyre 1994). Some exotics allegedly invade without major prior disturbance, by virtue of their superior competive abilities (Carr 1993), but prior disturbance may often be difficult to detect, and effects of historical disturbance may resonate long into the future. Disturbance that destroys native species certainly facilitates invasion by weeds both in terms of species and population sizes, and their occupation reduces recolonisation by natives. Nutrient and water enrichment often favours the exotics (McIntyre 1993). Soil disturbance was found to be the most important factor determining variation in plant species composition in grasslands of the New England Tablelands, more important than altitude, topographic position, lithology or water enrichment, but the greatest floristic effects resulted from soil disturbance accompanied by grazing (McIntyre and Lavorel 1994a). Dorrough et al. (2004) found that the intensity of grazing explained significant increases in the exotic richness of Monaro Tablelands grasslands, but that exotic status itself did not significantly explain plant responses in matched areas with contrasting grazing history. Exotic plant diversity was high even at the lowest grazing frequency. In many areas the local species pool is more likely to contain exotics that are well adapted to wetter conditions than natives (Kirkpatrick et al. 1995). The annual grass Bromus hordeaceus can be abundant where fire has been absent for a long period but is quickly eliminated by burning (Kirkpatrick et al. 1995). The consensus position of most grassland specialists appears to be well represented by McIntyre and Lavorel (1994a p. 381): “With little exogenous disturbance, the native grassland consists of a matrix of dominant perennial tussock grasses (e.g. Poa, Themeda) as well as smaller statured interstitial species that form the bulk of of species richness... including some exotic ‘tolerant’ species. With increasing disturbance, the tolerant species will persist and many ‘intolerant’ species will decline, to be partially replaced by disturbance specialists. At the highest levels of disturbance, the matrix of native perennial grasses is usually replaced by large statured exotic grasses or forbs ... species richness is very low and a only a few tolerant native species persist.” The presence of weeds in native grasslands may impact on native plants not only through direct competition, but also by ramifiying effects through the food chain. Foraging by cockatoos for the bulbs of Romulea has been recognised as a theat to the integrity of one northern Victorian grassland (Kirkpatrick et al. 1995). Prevention of exotic weed invasion in grasslands has two main components, minimisation of disturbance to maintain an intact ground vegetation stratum, and hygiene measures to prevent entry of propagules (Davies 1997). Edges of grassland remnants tend to be the most highly invaded e.g. at Evans St. the road edges have significantly greater exotic plant richness and significantly lower native plant cover and richness than in core areas (Morgan and Rollason 1995, Morgan 1998d). Morgan (1998d) found no correlation between exotic plant richness and the amount of ‘bare’ (cryptogam encrusted) ground, a weak negative correlation with T. triandra cover and a stronger negative correlation with native plant richness. Grasslands that are floristically rich with native species are considered of high quality and have high diversity of forbs, an open structure with a high proportion of intertussock space, few weed species and management regimes involving regular biomass reduction by grazing or burning (Henderson 1999). Floristically poor (low quality) grasslands have low forb diversity, a canopy of dominant grasses that is often closed, abundant weeds and often a management regime lacking regular biomass reduction (Henderson 1999). Rare and endangered plants “The most imminent threat to the biological diversity of grassland is the extinction of rare and threatened species and genotypes. These cannot be resurrected once lost, whereas the grassland communities could conceivably be re-established ...” (Kirkpatrick et al. 1995 p. 87). A large number of rare and threatened plant species occur in native temperate grasslands of south-eastern Australia (Tables 6 and 7). Robinson (2005) stated that approximately 200 native forb species that occur in these grasslands are rare and endangered, many of which were formerly common and widespread. Scarlett et al. (1992) provided lists of depleted, rare, vulnerable, endangered and presumed extinct grassland plants in Victoria. Scarlett and Parsons (1993) compared the numbers of threatened vascular plants across major landscape types in Victoria, including a category consisting of grasslands, grassy woodlands and fertile lowland open forests (Table 6). The highest concentration of endangered species occurred in this ‘grassy’category, whether assessed in the Victorian context or in terms of species populations throughout Australia. There was no doubt that undescribed taxa were under threat including species in Senecio, Craspedia, Podolepis, Leptorhynchos and Microseris (all Asteraceae), although some have subsequently been described. Herbs and low semi-shrubs comprised the majority of rare and threatened taxa. Kirkpatrick et al. (1995) listed 24 lowland temperate grassland taxa considered to be nationally rare or threatened, and calculated that 11% (79 species) of the total lowland grassland flora was rare or threatened. These data can now be considered to be poor indicators of current circumstances: “Even the most common species of lowland grassland forbs are now comparatively rare ...” (Robinson 2005). Table 6. The number of extinct, endangered, vulnerable, rare and insufficiently known vascular plant taxa of Victorian grasslands, grassy woodlands and fertile lowland open forests in 1993. Source: Scarlett and Parsons (1993). ConservationStatus Extinct Endangered Vulnerable Rare Insufficiently known Total Australia-wide 3 16 19 5 5 48 Victoria 9 33 54 43 3 142 105
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Literature review: Impact of Chilea
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Fire 49 Other disturbances 50 Shade
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Conventions and standards Botanical
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neesiana appears to be a habitat ge
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population densities of existing sp
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elated plants have similar defences
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For invasion to occur there must be
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As yet there appears to be no evide
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experimental manipulation of specie
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species tend to be those which tran
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Taxonomy and nomenclature Stipeae N
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Vernacular names ‘Needlegrass’
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to Bouchenak-Khelladi et al. 2009).
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1 m (Walsh 1994), ca. 90 cm (Verloo
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Figure 2. Anatomy of the seed of N.
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are the seeds larger/smaller, longe
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also based on a misunderstanding of
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Table 2. Modified Feekes Scale for
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Argentina, in the provinces of Chac
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Figure 3. Recorded distribution of
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1994). Only 3 of 186 exotic grasses
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According to Morfe et al. (2003) th
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populations have been found in the
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(Honaine et al. 2006). The flechill
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In Australia the altitudinal range
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Proximity to urban development appe
Page 53 and 54: In the southern Brazilian campos of
Page 55 and 56: arundinacea (Gardener et al. 2005).
Page 57 and 58: al. 2008). Cues for masting may be
Page 59 and 60: Approximately 200 alien grass speci
Page 61 and 62: Dispersal of seed in contaminated s
Page 63 and 64: In New Zealand, Hurrell et al. (199
Page 65 and 66: No emergence was observed in undist
Page 67 and 68: and high impact (“ability to caus
Page 69 and 70: also noted that despite a wide rang
Page 71 and 72: a small reduction in seedhead produ
Page 73 and 74: Slashing and mowing Slashing can re
Page 75 and 76: Themeda re-establishment McDougall
Page 77 and 78: species (Lawton and Schroder 1977 p
Page 79 and 80: y increased importance of ant grani
Page 81 and 82: BIODIVERSITY “Biodiversity ... on
Page 83 and 84: According to Woods (1997 p. 61) “
Page 85 and 86: 2004, Richardson and van Wilgen 200
Page 87 and 88: negative depending on the particula
Page 89 and 90: Competition with native plants Comp
Page 91 and 92: asexual seed production, so local f
Page 93 and 94: GRASSLANDS Grasses: “... the most
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Page 97 and 98: Floristic composition, vegetation s
Page 99 and 100: proportion of the flora then presen
Page 101 and 102: tussock space (Stuwe and Parsons 19
Page 103: Like vascular plant diversity, comm
Page 107 and 108: Species Common Name Family Aust ACT
Page 109 and 110: in shifting the distribution, exten
Page 111 and 112: of these systems is largely explain
Page 113 and 114: pasture. The least understood trans
Page 115 and 116: tend to benefit more from relaxed c
Page 117 and 118: Bovids crop their food between the
Page 119 and 120: are therefore less likely to distur
Page 121 and 122: esult in a “short-term flush” o
Page 123 and 124: Fire effects on weeds Moore (1993 p
Page 125 and 126: Table 8. Typical nutrient levels in
Page 127 and 128: grasses produced sigificantly more
Page 129 and 130: Fossorial vertebrates are or were o
Page 131 and 132: (Rosengren 1999). Approximately one
Page 133 and 134: Table 12. Areal extent and conserva
Page 135 and 136: Foreman (1997) investigated the eff
Page 137 and 138: Willis (1964) considered that the f
Page 139 and 140: Austrostipa-Enneapogon) from around
Page 141 and 142: Woodlands and New England Grassy Wo
Page 143 and 144: Thylogale billardierii), Peramelida
Page 145 and 146: Its original habitat on the mainlan
Page 147 and 148: Table 17. Endangered reptile specie
Page 149 and 150: equirement, but unlike plants and v
Page 151 and 152: e assigned the same biodiversity sc
Page 153 and 154: Nematodes are mostly minute animals
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found in all mainland states, O. co
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Keyacris scurra, Melbourne (1993) o
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was once widespread in south- easte
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eing sluggish and wingless, and exi
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estoration and, if Australia follow
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close to the plant are able to bury
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Species *Chirothrips mexicanus Craw
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Table A2.1 (continued) Species Life
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Table A2.1 (continued) Species *Het
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Nematodes of grasses and grasslands
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REFERENCES Aceñolaza, F.G. (2004)
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Benson, D. and McDougall, L. (2005)
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Chan, C.W. (1980) Natural grassland
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DNRE (Department of Natural Resourc
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Fuhrer, B. (1993) A Field Companion
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Groves, R.H. and Whalley, R.D.B. (2
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Iaconis, L. (2004) Chilean needle g
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Levine, J.M., Adler, P.B. and Yelen
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McDougall, K.L. (1987) Sites of Bot
Page 197 and 198:
Morfe, T.A., McLaren, D.A. and Weis
Page 199 and 200:
Perelman, S.B., León, R.J.C. and O
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Saunders, D.A. (1999) Biodiversity
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Thellung, A. (1912) La flore advent
Page 205 and 206:
Weiss, J. and McLaren, D. (2002) Vi
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