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

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5°C warmer than under the canopy and much larger differences occurred in summer. Such contrasts will substantially affect the behaviour and activity levels of invertebrates. Farrow (1999) found no clear differences in the diversity of canopy-living insects in small burnt patches and unburnt areas in ACT grasslands and suggested that recolonisation occurred within 6 months of fire. Nearly twice as many individual insects were present in summer in areas burnt 6 months prior to sampling than in unburnt areas, and more than three times as many in the following spring. Species that benefit from more open ground, like many ants, probably commonly proliferate. Maintenance or periodic refreshment of plant diversity by fire will benefit a wide range of herbivorous taxa with particular food plants, and maintenance of the forb components will benefit nectar and pollen feeders. Maintenance or enhancement of animal diversity at the primary consumer level will flow on to higher tropic levels, benefitting the diverse array of predators and parasitoids. Greenslade (1994) found litter removal by fire was likely to markedly reduce Collembola diversity for at least two years. Other detritivores dependant on plant litter would be expected to be similarly disadvantaged. Any beneficial effects on fire on plant diversity may or may not flow on to invertebrates, depending, in part on whether source populations of new and recolonising species exist (Tscharntke and Greiler 1995). Driscoll (1994) concluded that some species may be completely intolerant of fire, while others may require it for survival. Any species that spend part of their lifecycle underground are probably relatively resistant to fire, while those that do not are likely to be more highly vagile and have an ability to recolonise from unburnt areas. Sedentary, non-subterranean species are probably most vulnerable to extinction, but there are unlikely to many of them in fire adapted vegetation. As with vascular plants (Stuwe 1994) and bryophytes (Morgan 2004), the indigenous invertebrate flora of grasslands that have been subject to periodical fire over many thousands of years must consist largely of fire-adapted species, whether or not they are fire survivors or recolonisers. Fire regime management in Victoria now incorporates the goal of providing the conditions necessary for the persistence of the indigenous biota (Mansergh et al. 2006b) but implementation of this idealfor the various biotic elements, including animals, is difficult and is bound to produce contradictory results because different valuable elements of the biota may be advantaged or harmed by the same fire cycle. The difficulty for managers is to evaluate and juggle the often contrary needs and tolerances of the various components in each grassland remnant. Nutrients and soil factors Lowland native grassland in Australia is found on relatively fertile, organic-rich, cracking clay soils on substrates of volcanic rocks (basalt and dolerite), fine-grained sedimentary rocks (including limestone) or recent alluvium (Kirkpatrick et al. 1995). In the past, temperate grasslands have erroneously been characterised as low in nutrients, based on analysis of soils. Mott and Groves (1994 p. 376) state that “Australian grassland soils are of very low fertility, particularly of nitrogen and phosphorus, by comparison with those of grasslands elesewhere”. Sharp (1997) lists low soil nutrient content as one important factor determining the distribution of native grassland in the ACT. Australian soils have in general been considered to be nutrient deficient (e.g. Roberts et al. 2006). However, like tropical rainforest, much of the system nutrients are held in the plants. Above- and below-ground biomass In temperate herbaceous communities 60-80% of vascular plant biomass is underground (see Reynolds 2006 p. 57). In grasslands up to 90% is below-ground (Wijesuriya and Hocking 1999) and it is usual for a high proportion of total plant biomass to be represented by roots and buried crowns. More of the energy captured in photosynthesis in grasslands is directed to below-ground parts than those above-ground and most of the nutrient circulation occurs below ground (Soriano et al. 1992). In Australian grasslands most of the biomass is contained in the dominant grasses (Groves 1965). T. triandra- and Poa-dominated communities are more productive (i.e. produce more biomass) than the Austrodanthonia and Austrostipa grasslands that predominate in drier areas (Lunt and Morgan 2002). The mean root: shoot ratios in North American grasslands varies from 13 to 2, being higher in cooler climates (Tscharntke and Greiler 1995). Cooler and drier grasslands generally have ratios between 13 and 6, while warmer, more humid grasslands have ratios between 6 and 2 (Soriano et al. 1992). A ratio of 2.6 was calculated for one Argentinean pampas grassland (Soriano et al. 1992). Rodríguez et al. (1995) measured below-ground biomass down to 10 cm depth in five grazed grassland communities in Spain and found that 61-68% of the total biomass was below ground, of which 49-68% was in crowns and the remainder below 1 cm depth. Groves (1965) found that the root:shoot ratio of a T. triandra grassland had very high seasonable variability but that root biomass was generally 2 to 4 times that of above-ground parts, i.e. 66-80% of the biomass of the overwhelming dominant grass was below ground. In one Pampas grassland 65% of the underground biomass was located above 10 cm, 85% above 30 cm and 100% above 70 cm, a similar distribution to most temperate, subhumid grasslands (Soriano et al. 1992). Underground net primary productivity in one Pampas grassland was estimated to be about 5000 kg ha -1 yr -1 , just 17% less than productivity above ground, with a below-ground: above-ground productivity ratio of 0.9 (Soriano et al. 1992). Soil nutrient levels The soils of Australian native grasslands usually have low nutrient levels (Table 8), and a high organic matter content with organically bound N and P (Wijesuriya and Hocking 1999). However most of the nutrients in the system are locked up in the biomass of the grasses. In the Victorian basalt plains, soils derived from sediments have higher nutrient levels than those derived from basalt, and soils on stony rises have the highest fertility (Williams 2007). 124
Table 8. Typical nutrient levels in Australian grassland soils. Source: McIntyre and Lavorel (2007). Vegetation N P (mg kg -1 ha -1 ) Natural grasslands low 1-3 (low) Native pasture medium 1-3 (low) Fertilised (improved) pasture high 20 (high) Sown pasture high 20 (high) Enriched grassland medium medium Moore (1973) suggested that nitrate levels in the surface soils rarely exceeded a few parts per million at any time of year. In grasslands in general a “small active fraction” of soil organic matter dominates both C respiration and N mineralisation (microbial conversion of N into the plant-available nitrate and ammonium forms) (Wedin 1999 p. 194). Roberts et al. (2006 p. 148) stated that pasture productivity may be limited when P falls below 25 mg/kg (Colwell), but that “native pastures ... tend to be more tolerant of lower P levels than those dominated by introduced species”. Weed invasion and nutrient enrichment Nutrient enrichment by legumes, application of fertiliser, runoff, deposition of atmospheric pollution etc. is a major cause of alien grass invasion worldwide (Milton 2004) and experimental addition of nutrients often rapidly leads to weed invasion (Carr 1993). Eutrophication, particular with N and P, is a major cause of plant diversity decline in terrestrial ecosystems (Hobbs and Heunneke 1992, Hautier et al. 2009). Grasses tend to be particularly favoured by nutrient inputs, and biodiversity losses are usually associated with their increasing productivity and dominance (Hobbs and Heunneke 1992). Australian soils have generally been characterised as nutrient impoverished, particularly in relation to phosphorus, but also in nitrogen, minor nutrients and organic matter (Leeper 1970). Because most Australian native plants are adapted to these low nutrient levels, nutrient enrichment favours the establishment of exotic weeds that are better adapted to high levels of fertility (Brereton and Backhouse 2003). Cale and Hobbs (1991) found a strong positive correlation of nutrient gradients across roadsides with exotic plant diversity and suggested that nutrient enrichment may increase their competitiveness. Cover of exotics increased from
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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
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In the southern Brazilian campos of
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arundinacea (Gardener et al. 2005).
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al. 2008). Cues for masting may be
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Approximately 200 alien grass speci
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Dispersal of seed in contaminated s
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In New Zealand, Hurrell et al. (199
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No emergence was observed in undist
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and high impact (“ability to caus
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also noted that despite a wide rang
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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
Page 95 and 96: susceptible to N. neesiana invasion
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 and 104: Like vascular plant diversity, comm
Page 105 and 106: Opinions differ on the nature and i
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: Fire effects on weeds Moore (1993 p
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
Page 155 and 156: found in all mainland states, O. co
Page 157 and 158: Keyacris scurra, Melbourne (1993) o
Page 159 and 160: was once widespread in south- easte
Page 161 and 162: eing sluggish and wingless, and exi
Page 163 and 164: estoration and, if Australia follow
Page 165 and 166: close to the plant are able to bury
Page 167 and 168: Species *Chirothrips mexicanus Craw
Page 169 and 170: Table A2.1 (continued) Species Life
Page 171 and 172: Table A2.1 (continued) Species *Het
Page 173 and 174: Table A2.1 (continued) Species Life
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Table A2.1 (continued) Species Life
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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
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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
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Weiss, J. and McLaren, D. (2002) Vi
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