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

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‘abandonment’ of foliage. Senescence dieback of T. triandra swards after extended periods of biomass accumulation might possibly be the result of altered water relations, rather than the postulated ‘self-shading’: the underlying mechanisms require further investigation. But like other dominant C 4 grasses worldwide, accumulation of large quantitites of dead biomass by T. triandra is apparently an adapted strategy that enables it to perpetuate its dominance by providing appropriate conditions for frequent burning (Hocking and Mason 2001). The high C:N ratio of C 4 grass foliage means the leaves have low nutritional quality and limited palatability to herbivores (Moore 1993, Moretto and Distel 2002) so a higher proportion die without being eaten than leaves of C 3 grasses, and the litter is more resistant to microbial breakdown than that of non-C 4 plants (Wedin 1999, Groves and Whalley 2002) so more of it can accumulate. Senescence dieback of T. triandra increases the soil available nutrients, probably as a result of increased rates of decay of both above and below ground vegetation, due to increased moisture and temperature under the thatch of dead leaves, and by reduced nutrient uptake by living biomass (Hocking and Mason 2001). However utilisation of the nutrient pulse by other plants is not possible until the high cover of dead grass decays or or is removed by fire or other biomass reduction. When this occurs major weed growth usually follows (Hocking and Mason 2001). Effects of T. triandra biomass accumulation on other species Commonly, in the absence of of regular biomass reduction by fire, grazing or mowing, litter accumulation by exotic or native perennial grasses results in the suppression of the smaller intertussock native vascular plant species (McIntyre 1993, Kirkpatrick et al. 1995, Morgan 1998e). Entire populations of perennial forbs can disappear within a short period in the absence of fire (Morgan 1998e). In T. triandra grassland unburnt for >5 years the cryptogam crust also degenerates due to litter accumulation, shading and increased earthworm activity (Scarlett 1994). However bryophyte diversity in areas burnt at 1-2 year intervals is reduced compared to longer unburnt areas (Morgan 2004). Periodic biomass reduction is required to maintain the vascular flora, a large proportion of which have soil seed banks which disappear after 1 year (Lunt 1990c 1995a, McIntyre 1993, Stuwe 1994). Morgan (1995b) for example found that 90% of Rutidosis leptorhynchoides seed germinated within a few weeks of autumn rains. Endangered species that are threatened when fire frequency in T. triandra grasslands is too low include Senecio macrocarpus (Hills and Boekel 1996) and Rutidosis leptorrhynchoides (Morgan 1995a, Humphries and Webster 2003). Sharp (1997) experimentally confirmed the hypothesis that litter removal is required to facilitate establishment and reduce suppression of the smaller native grasses and the low-growing and small forb components in ACT grasslands. Lack of fire or some other management regime with similar effects is therefore a threat to the continued existence of the more mesic, T. triandra dominated grasslands, both in terms of the keystone species (T. triandra) and most of the other plant components. Suppression of other native species by the dominant grasses is not generally a problem in grasslands on shallow rocky soils and the more xeric inland plains, and fire is not necessary to maintain their indigenous vascular plant diversity (Kirkpatrick et al. 1995). Effects of fire on Themeda triandra T. triandra is well adapted to survive fire but mortality nevertheless occurs. Stafford (1991) reported that very few four-year-old T. triandra plants survived an intense wildfire in Cleland Conservation Park, South Australia, and a fire at Organ Pipes National Park, Victoria, in April 1997 before a severe drought resulted in substantial mortality and a dramatic cover decline (McDougall and Morgan 2005). However biennial autumn burning at Organ Pipes usually did not inhibit an already established trend of increased T. triandra frequency and cover (McDougall and Morgan 2005). Burning generally does not kill T. triandra tussocks (Henderson 1999) nor the very high proportion of other grassland plants which are fire-adapted hemicryptophytes, geophytes etc., i.e. perennial plants with perennating buds protected underground (Morgan 1996, Lunt 1990a 1990c.). T. triandra usually regains high cover quickly, returning to pre-fire biomass levels in 2-4 years (Morgan 1994). At Evans St., Sunbury, cover reached 43% after 9 months and was predicted to reach 100% after 2-3 years (Morgan and Rollason 1995). Creation of bare ground along with an ash bed probably enhances seedling establishment for most native species (Stuwe and Parsons 1977), but these are favourable conditions for most exotic vascular plants as well. In South African grassland Uys et al. (2004) recorded declines of T. triandra related to longer fire frequency but continued persistence at a semi-arid (550 mm per annum) site 26 years post fire. Fire also enables T. triandra regeneration from seed. In T. triandra establishment experiments, Stafford (1991) found that burning of areas to which a close thatch of whole T. triandra culms had been applied resulted in immediate seed germination, with an estimated seedling density of c. 1000 m -2 . Areas thatched in December and burnt 10 months later produced seedlings at the end of October, the most suscessful of which produced seed the following February. However fire kills T. triandra seeds that have not worked their way into the soil (Hocking pers. comm.). Effects of fire on other vascular plants Particular forb species may be negatively effected by regular burning during a particular season. The late-flowering native pea Glycine labrobeana (Meisn.) Benth. is very susceptible to regular fires in late spring-early summer, which destroy its flowers and seeds (Scarlett and Parsons 1993). Cullen spp., also late flowering peas, may be rare in rail reserves for the same reason (Morgan 1994). Thesium australe, once widespread in native temperate T. triandra grasslands, is short-lived and highly dependent on annual seedling recruitment, is probably eliminated by annual burning (Scarlett and Parsons 1993), apparently germinates well without fire and after fire, but seems to require open conditions for growth (Scarlett et al. 2003). As previously noted, Morgan (2004) found that more frequent fires reduced bryophyte diversity in Victorian basalt plains grasslands by loss of species, mostly mosses, although none of the 150 m 2 quadrats he surveyed had a richer moss and liverwort flora than the total of 990 m 2 surveyed at the frequently burnt Evans St. Sunbury site by Morgan and Rollason (1995). Presumably the greater exposure and dessication resulting from frequent fire destroys mosses and removes suitable habitat, including the shade and increased humidity of dense cover provided by T. triandra. Slow recovery and recolonisation of mosses post-fire has been widely reported in other ecosystems, and, as for vascular plants, frequent burning of native grasslands through ecological time has probably eliminated the most fire-sensitive species long ago (Morgan 2004). Fire damage to soil cryptogam crusts can also facilitate grass invasion (Milton 2004). 122
Fire effects on weeds Moore (1993 p. 351) argued that Themeda grasslands remained “remarkably stable” under regimes of marsupial grazing and periodic burning, and if otherwise undisturbed were “not invaded by introduced species”. Fire results in temporary increases in nutrient availability and this fluctuation of resources may enhance invasion by exotic plants (Hobbs 1989). In general burning of south-eastern Australian native grasslands promotes post-fire colonising plants, most of which are exotic annuals that recruit from a large soil seed bank (Lunt 1990b, Lunt and Morgan 2002). However Stuwe and Parsons (1977) found a smaller proportion of the vascular flora consisted of alien species at regularly burnt (railway) sites than in grazed or unmanaged T. triandra grasslands, while Dodd et al. (2007) found that sites burnt less frequently had higher exotic seed banks, and considered regular burning to be detrimental to the exotics. Burning of some degraded T. triandra grasslands has been reported to lead to major increases in cover and density of exotic annuals, which then slowly decline (Lunt 1990b 1990c, Morgan 1998d). Scarlett’s (1994) view was that regular burning of sites with a long history of grazing and trampling rarely has any major impact on exotic annuals, an effect he linked to the poor re-establishment of the cryptogam crust. Fire is often considered to provide advantages in reducing weed populations, but may promote or inhibit particular weed species or functional groups. Fire is demonstrably an effective tool to greatly reduce the cover of exotic invasive grasses when the invasives are not fire adapted, and to restore native plant cover (e.g. MacDougall and Turkington 2007). In temperate Australian grasslands spring fires might reduce or prevent seed set in exotic annual grasses (Stuwe 1986) but late autumn burning promotes their regeneration along with Romulea rosea (L.) Eckl. (Iridaceae) (Lunt 1990c). Burning can reduce the density of the exotic grasses Briza maxima, Cynosurus echinatus L., Lolium rigidum Gaudin, L. perenne and Bromus hordeaceus in T. triandra grasslands but promotes a range of others including Aira and Vulpia spp. (Lunt 1990c, McDougall 1989, Adair 1995). As with the native plants, seasonality of the fire may determine the effect on particular exotics (see Morgan 1996), while the impacts on propagule production and seed bank levels are obviously important factors. According to Adair (1995) no clear evidence was then available that the season of burning has a significant effect on introduced grasses and forbs. Exotics are likely to be advantaged if they account for a high proportion of the soil seed bank, which is generally the case (Kirkpatrick et al. 1995, Morgan 1998c, Dodd et al. 2007). Robertson (1985) found similar densities of exotic annuals after autumn and spring burns at Gellibrand Hill. Stuwe (1994) among others argued that biomass-reduction burning now facilitates the growth of both native and exotic plants, while Lunt (1990b), based on seed bank studies at Derrimut, argued that burning is likely to promote exotics more, or at least as much as natives. Dodd et al. (2007) argued that exotic dominance of the seed bank is partly due to removal of fire, which along with exotic dominance in the surrounding landscape matrix, is likely to result in increased weediness of remnants. Decisions about the desirability of burning need to be based on an understanding of the contents of the soil seed bank and the phenology of the above ground cover at each site in order to predict whether a burn would be beneficial for the flora. Determining an appropriate fire regime even at a single small site can thus becomes prohibitively difficult. Most native grasslands contain a mix of weeds with different life strategies, so fire cannot be used as a general tool to favour the native species (Lunt 1990c). Stuwe (1994) warned that burning of areas with a N. neesiana seed bank should not be undertaken unless follow up herbicide treatment could be undertaken. However there appear to have been no studies on the specific effects of fire timing and intensity on N. neesiana populations in native grasslands. No information appears to be available about the comparable fuel loads of grasslands with and without N. neeesiana, so it is difficult to speculate about whether N. neesiana infestations increase or decrease the frequency and intensity of fires. In relation to vascular plants of native grasslands, there is a general consensus that the interaction between fire and grazing is the major factor involved in the abundance of most native species, including threatened taxa, and that low fire frequency is detrimental to most species (Scarlett and Parsons 1993). Frequent burning (a fire every 2-5 years) is necessary to maintain grasslands dominated by T. triandra, but other Victorian grassy ecosystems (E. camaldulensis and E. melliodora grassy woodlands in the Grampians and Sandplain Grassland in the Mallee) appear not to require burning to maintain their vascular plant diversity (Lunt 1991). In T. triandra grasslands, long intervals between fires results in loss of forb diversity (Stuwe and Parsons 1977, Lunt 1990c, Lunt and Morgan 1999). Morgan (1998c) found no correlation between seed bank species richness and fire history for five grasslands in the Victorian volcanic plains. However fires do not generally lead to significant seedling recruitment of native plants (Henderson 1999, Lunt and Morgan 2002), possibly because of severe depletion of the seed bank resulting from prior affects of long-term livestock grazing on seed production (Lunt 1990b 1990c). T. triandra is more sensitive to grazing shortly after fire (Groves and Whalley 2002). Effects of fire on animals Combinations of positive and negative effects of fire also occur with other organisms. Fire can change the abundance, range (spatial and temporal), fecundity and dietary choice of other organisms by altering the provision of food, shelter and habitat (Low 2002). Fire directly results in the elimination of many animal populations, although many sedentary species survive underground. According to Yen (1995 1999) the effects of fire on temperate Australian grassland invertebrates were unknown, while Driscoll (1994) noted that they were ‘yet to be investigated’. Studies from other ecosystems tend to be equivocal, with few lessons for grasslands (Driscoll 1994). Edwards (1994) argued that fire often causes local extinction, but recolonisation from unburnt areas is usual, so in a situation where an invertebate is dependent on a community that is scarce and highly fragmented, recolonisation is often impossible. This appears to be the case with Synemon spp. (Edwards 1994) and with xanthorhoine moths (McQuillan 1999), although with organisms like Synemon that spend a major part of their lifecycle underground, the precise timing of the fire with respect to the above-ground stages would appear to be critical. Removal of dense cover by fire and the creation of open ground will radically alter temperatures at the ground surface. Lunt (1995a) quantified temperature differences between the canopy surface in T. triandra grassland, the ground surface temperature and soil temperatures at 3 cm depth, in areas where the canopy was closed and in open gaps from July to April. The canopy provided excellent insulation with temperatures on the surface similar to those in the soil. Temperatures in gaps were generally 123
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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
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
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: esult in a “short-term flush” o
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
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
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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
Page 185 and 186:
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
Page 191 and 192:
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
Page 203 and 204:
Thellung, A. (1912) La flore advent
Page 205 and 206:
Weiss, J. and McLaren, D. (2002) Vi
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