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

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whole, gene flow via pollen is estimated to be on average an order of magnitude greater than gene flow via seeds, and most long distance gene flow is via pollen (Petit 2004). Anthesis in grass species occurs at particular times of day, often in the morning or the afternoon (Connor 1986). Release of pollen occurs at times of high temperatures and low humidity.There appear to be few records of stipoid anthesis times. Piptatherum holciforme flowers at night and P. virescens early in the morning (Connor 1986). Ramasamy (2008) observed most Nassella trichotoma anthesis in the morning (7-11 am) with some later in the day. The structure of grass inflorescences and flowers influence their pollen dispersal and trapping characteristics (Connor 1986). Wind is the main dispersal agent for grass pollen, but insects may play some small role (Connor 1986). Rates of spread Few published records exist of the rate of change in the dimensions of N. neesiana infestations and the rates at which the plant spreads (Table 5). In New Zealand the maximum rate of dispersal on a linear front from known sources was 8 km over 59 years at Marlborough and 3.5 km over 30 years at Waipawa (Connor et al. 1993). Comparable Australian data does not appear to be available. N. neesiana was rated by Platt et al. (2005) as having a rapid, rather than moderate or slow rate of dispersal. The ACT Weeds Working Group (2002 p. 4) stated that the “rate of spread and establishment is unknown, but believed to be rapid”. However perceptions of rapid spread in Australia may be partly false, due to recognition failures (Walsh 1998). Table 5. Measured and inferred rates of spread of N. neesiana. Locality Distance Period Rate Notes Reference (m) (y) (m y -1 ) Marlborouegh, NZ 8000 59 136 District infestation expansion Connor et al. 1993 Waipawa, NZ 3500 30 117 District infestation expansion Connor et al. 1993 New Zealand 120-140 With no active management Slay 2002c Hawke’s Bay NZ 3-10 5 0.6-2 Patch expansion Slay 2002c Areas (ha) Period (y) Rate (ha y -1 ) Marlborough, NZ 1555-3000 14-15 101-103 District expansion Slay 2002a, 2002c (3071) hypothetical 1 5 100 Expansion at 100 m per year Slay 2002a hypothetical 1 10 350 Expansion at 100 m per year Slay 2002a Rare long-distance dispersal events (e.g. by water or human transport) are thought to contribute to accelerating rates of spread that have been recorded as plant invasions proceed (Mack and Lonsdale 2001). This is because the likelihood of successful dispersal increases in proportion to the size of the propagule pool. This factor may also be contributing to the Australian perception. Invasion patterns Trengrove (1997) observed that N. neesiana dispersed along roadsides by slashers then invades into adjoining paddocks “in a front”. The pattern in the ACT is of movement outwards from a central Canberra source population along urban and periurban roadsides mainly via mowing and slashing, with spread outward from the linear corridors, often by the same means (ACT Weeds Working Group 2002). Slay (2002c) listed a range of situations where infestations occur in New Zealand that are indicative of seed dispersal patterns: “paddocks sown with uncertified seed between 1950 and 1980 ... holding paddocks close to the road ... the edges of farm tracks ... 1-3 m away from power poles, along fence lines or other places where stock ‘rub’ ... river banks ... around hay barns ... sheep yards”. Soil seed bank The soil seed bank may be thought of as the consequence of four different processes: dropping of individual panicle seeds, the shedding of inter-twined seed masses, the release of stem cleistogenes when the culm decays and the release of basal cleistogenes when stem bases decay. Cleistogenes enter the seed bank as the culms decompose or after fire (Groves and Whalley 2002). Culms deteriorate slowly through summer and autumn and the leaf sheaths rupture in autumn or winter, releasing stem cleistogenes (Slay 2002c). Basal cleistogenes are released after the tiller or parent plant dies and decomposes, possibly 12-18 months after mortality (Slay 2002c). Testing of panicle seeds of N. neesiana with triphenyl tetrazolium chloride (tetrazolium) reported by Puhar and Hocking (1996) indicated 80-95% viability. The seeds in general are reportedly viable for more than 12 years (Benson and McDougall 2005), “many years” (Quattrocchi 2006) or “in excess of three years” in the soil (Snell et al. 2007p. 4). Bourdôt and Ryde (1986) stated that both panicle and stem seeds have >90% viability and survive for “several years” in the soil. The soil seed bank was large and persistent in heavily infested sites investigated by Gardener on the Northern Tablelands of NSW in the 1990s (Gardener et al. 2003b). Assessments of the seed bank in seven populations in the Argentinian pampas showed it be close to zero (Gardener et al. 1996b, Gardener et al. 1997). Possible reasons for this include high levels of seed predation by ants, attack by a seed pathogen after seed shed, or rapid microbial decomposition in the soil, however the closely related Nassella clarazii (Ball) Barkworth was found to have aseed bank of c. 1200 m -2 (Gardener et al. 1996b). 62
In New Zealand, Hurrell et al. (1994) measured a soil seed bank (to about 10 cm depth) under old established stands of 2,600- 35,000 seeds m -2 , with an average density of 10,500 seeds m -2 , of which approximately 70% were cleistogenes, with few or no aerial seeds in some samples. Tetrazolium testing showed 58% viability of cleistogenes and 86% of aerial seeds, with a total average viability of 67%. In pastures at Waipawa, New Zealand, the seed bank was composed almost entirely of cleistogenes (Slay 2002c), with a mean of 6437 ±3437 viable cleistogenes and 660 ±1289 viable panicle seeds m -2 (Slay 2001). Bourdôt and Hurrell (1992) found 4000-18,000 viable seeds m -2 under pasture, 99% in the top 25 mm and 0% below 100 mm, on a silt loam at Marlborough. Viability (as determined by tetrazolium treatment) of seed buried in polyproylene mesh bags for 6 years in this soil increased with increasing depth of burial, 24% of seed remaining viable at 25 cm depth, 17% at 5 cm, 5% at 2.5 cm and 0.1% for soil at the surface (Bourdôt and Hurrell 1992). Analysis of decay data suggested that an increaing proportion of buried seed survived at increasing depth indefinitely in a state of dormancy, whereas no surface seed was viable after 1 year (Bourdôt and Hurrell 1992). However there are doubts about the reliability of tetrazolium tests for determination of seed viability (Puhar and Hocking 1996). Seeds that are hard when pressed between the thumb nail and forefinger are “almost certainly viable” (Bourdôt 1988). In pastures in New Zealand in the absence of seed input, annual depletion rates of the soil seed bank were 38% when “regularly” mown to prevent panicle seeding, 61% with repeated glyphosate applications, and between 66% and 77% for single to repeated annual cultivations (Bourdôt and Hurrell 1992). Smaller seed banks have been described in New England Tablelands pastures by Gardener (1998) who made direct counts of loose seeds in the soil to 4 cm depth, with all seeds considered to be of panicle origin (Gardener et al. 2003b p. 622). Under dense infestations 681-11,307 viable seeds m -2 were found. If basal cleistogenes, contained in tiller bases and not loose in the soil, are included, the estimated total seed numbers were increased by 35.5% (Gardener and Sindel 1998) or 20% (Gardener et al. 2003b). Within N. neesiana tussocks 44.1% of seeds were panicle seeds and 55.9% basal cleistogenes (Gardener et al. 2003b). In native grasslands and grassy woodlands in the Melbourne area the viable seed bank appears to be substantially smaller. Seed banks at Iramoo Wildlife Reserve determined by Bram Mason (unpublished) were up to 7000 m -2 (Robinson 2003 2005). Beames et al. (2005) assessed panicle seed banks in areas of high quality native grassland at Laverton and Grey Box woodland at Melbourne Airport that had been subject to a range of different management regimes to control N. neesiana. They separated the seeds into four categories: filled, unfilled (caryopsis absent), successful germinants (germinating at the time of sampling) and unsuccessful germinants. At Laverton a maximum seed bank (seed of all categories) of ca. 2200 m -2 was found, however unfilled and unsucessfully germinating seed accounted for ca. 90% of seed. In areas subject to N. neesiana management, seed bank numbers did not exceed 1000 m -2 , with similar proportions in each seed category, except for filled seed, which comprised a much smaller proportion in two of the managed areas. At Melbourne Airport the maximum seed bank exceeded 7000 m -2. The unburnt, unsprayed treatement had a significantly smaller seed bank than most of the managed areas. Significantly more filled seed was found outside managed areas, which in most cases had zero filled seed. One major conclusion was that most of these differences were the result of reduced seed input due to ongoing herbicide treatment, which possibly reduces the proportion of viable seed produced and seed persistence. The study indicates that the seed bank in non-agricultural areas is much less persistent and easier to deplete than had previously been assumed. Hocking (2005b) reported even lower levels in infestations subject to herbicidal control in southern Victora: 80% unviable seed. He suggested that the size of the seed bank may be widely variable on a regional basis and between sites managed for agriculture and conservation, and that agents in the soil at some sites may be destroying a high proportion of seed. Hocking (in Iaconis 2006b) reported no differences in the soil seed banks of agricultural and natural areas, but high variability between sites, and >50% of the seeds unfilled. In New England pastures, dramatically better fruiting in wetter years (Gardener et al. 1996a) led to major addition to the seed bank (e.g. 41.6% of seeds incorporated in 1996), but in drier years input was only sufficient to maintain existing seed bank numbers or inadquate to maintain pre-existing levels (Gardener et al. 2003b). Rates of decline of the seed bank determined for New England pastures without input after 3 y, were 4676 to 1323 seeds m -2 in bare plots and 4585 to 1507 seeds m -2 in vegetated plots, with no significant effect of ground cover on decline, and a predicted decline without input (based on a fitted exponential decay curve) to 10 seeds m -2 after 12.4 y (Gardener et al. 1999, Gardener et al. 2003b). The seed bank longevity was found to be >6 y (Gardener and Sindel 1998) and half-life 1.3 y (Gardener et al. 2003b). There is anecdotal evidence of gemination from continuously bared ground after 6 y (Gardener and Sindel 1998). Where soil cracking occurs in summer, as in the clays of the Victorian basalt plains, seed dropped in late spring and early summer will certainly move into the soil to greater depths than was sampled in the two Australian studies, which both assumed a similar depth profile of the seed bank to that found on a silt loam in New Zealand by Bourdôt and Hurrell (1992). This may be especially significant since viability of seed increases with depth of burial (Bourdôt and Hurrell 1992). Grasses that produce relatively few large seeds “often emerge from seed located deeper in the soil …where … water is available for a longer time … and many have high seedling growth rates” (Groves and Whalley 2002). Germination and seedling recruitment Seed dormancy The panicle seed have dormancy - the tight lemma may provide a barrier to water and gas exchange and mechanically constrain the embryo (Gardener and Sindel 1998) - and appear to have an after-ripening requirement after falling from the plant of between 3 and 12 months for maximum germination (Gardener et al. 1999, Gardener et al. 2003b). The overlapping margins of the lemma and its toughness make it difficult to break open to expose the caryopsis, a feature also of Austrostipa spp. (Barkworth 2006). Puhar (1996) found by staining with tetrazolium chloride that 93.5% of N. neesiana seeds collected in the previous summer were viable, but in laboratory tests less than 2% germinated under a day/night cycle of 30/20ºC and 14/10 hr light. Removal of the lemma enabled 100% germination within three days under the same conditions. 63
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Literature review: Impact of Chilea
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Fire 49 Other disturbances 50 Shade
Page 5 and 6:
Conventions and standards Botanical
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neesiana appears to be a habitat ge
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population densities of existing sp
Page 11 and 12: elated plants have similar defences
Page 13 and 14: For invasion to occur there must be
Page 15 and 16: As yet there appears to be no evide
Page 17 and 18: experimental manipulation of specie
Page 19 and 20: species tend to be those which tran
Page 21 and 22: Taxonomy and nomenclature Stipeae N
Page 23 and 24: Vernacular names ‘Needlegrass’
Page 25 and 26: to Bouchenak-Khelladi et al. 2009).
Page 27 and 28: 1 m (Walsh 1994), ca. 90 cm (Verloo
Page 29 and 30: Figure 2. Anatomy of the seed of N.
Page 31 and 32: are the seeds larger/smaller, longe
Page 33 and 34: also based on a misunderstanding of
Page 35 and 36: Table 2. Modified Feekes Scale for
Page 37 and 38: Argentina, in the provinces of Chac
Page 39 and 40: Figure 3. Recorded distribution of
Page 41 and 42: 1994). Only 3 of 186 exotic grasses
Page 43 and 44: According to Morfe et al. (2003) th
Page 45 and 46: populations have been found in the
Page 47 and 48: (Honaine et al. 2006). The flechill
Page 49 and 50: In Australia the altitudinal range
Page 51 and 52: 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: Dispersal of seed in contaminated s
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
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
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pasture. The least understood trans
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tend to benefit more from relaxed c
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Bovids crop their food between the
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are therefore less likely to distur
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esult in a “short-term flush” o
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Fire effects on weeds Moore (1993 p
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Table 8. Typical nutrient levels in
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grasses produced sigificantly more
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Fossorial vertebrates are or were o
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(Rosengren 1999). Approximately one
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Table 12. Areal extent and conserva
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Foreman (1997) investigated the eff
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Willis (1964) considered that the f
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Austrostipa-Enneapogon) from around
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Woodlands and New England Grassy Wo
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Thylogale billardierii), Peramelida
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Its original habitat on the mainlan
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Table 17. Endangered reptile specie
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equirement, but unlike plants and v
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e assigned the same biodiversity sc
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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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Page 175 and 176:
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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
Page 187 and 188:
Fuhrer, B. (1993) A Field Companion
Page 189 and 190:
Groves, R.H. and Whalley, R.D.B. (2
Page 191 and 192:
Iaconis, L. (2004) Chilean needle g
Page 193 and 194:
Levine, J.M., Adler, P.B. and Yelen
Page 195 and 196:
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
Page 201 and 202:
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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