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

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Disturbance, defined as any process that creates open ground, changed habitat or altered resource availability (Hobbs 1989 1991, Mack and D’Antonio 1998, Lockwood et al. 2007) is universal at a range of spatial and temporal scales, so gaps in vegetation and fluctuating resource pools are always available. Under this definition, disturbance includes reduction or lack of normal disturbance to which the community is adapted, e.g. reduced fire frequency, removal of grazing, or loss of burrowing mammals, can provide fluctuating resources, as native plants senesce or seed banks decay without replacement. Elimination of perturbation in disturbance-dependent systems is one of the most serious ‘disturbances’ they can suffer (MacDougall and Turkington 2007). Many plant communities and species require disturbance, particularly for regeneration (Hobbs and Huenneke 1992). Whether or not the gaps or unused resources created by disturbance can be taken up by an exotic species therefore depends on their size, their spatial and temporal availability, the pool of available species and the requirements of the particular species (Prieur-Richard and Lavorel 2000). Whether or not a particular species invades is dependent on the disturbance characteristics: its mgnitude and severity,duration, predictability,distribution in space and time and synergistic effects on other disturbances (Lockwood et al. 2007). When the parameters of the disturbance are suitable, exotic species that possess resource utilisation traits not present in the native flora often seize the advantage (McIntyre et al. 1995). Invasions of exotic plants can be greatly increased by combinations of disturbance such as nutrient addition and soil disturbance (Cale and Hobbs 1991). Early successional stages have greater pools of unused resources and less competition, so are more susceptible to invasion (Davis et al. 2000). Resource poor environments are not invaded by many exotic species (Cox 2004). Greater species diversity generally corresponds with more complete resource usage, so diversity theoretically confers invasion resistance by limiting resource fluctuation. Weed invasions are commonly associated with extreme resource fluctuations. One example is the invasion of Buffel Grass Cenchrus ciliaris L. in arid Australia. Prior to 1974 it was apparently naturalised in a few small areas in the semi-arid inland, but in the unusually wet season of 1974-5 it spread along flood plains and “run-on areas” across large areas of the arid zone (Moore 1993 p. 316). Nutrient enrichment is often a significant contributory cause of invasions (Milton 2004). For example, King and Buckney (2002) compared total N and P, and concentration of Na, K, Ca and Mg cations in soils of 16 urban bushlands and 8 national parks in Sydney and the proportion of exotic plant species present in the vegetation. All soil nutrients were significantly higher in urban areas, and gradients from low to high invasion, and low to high concentrations, were correlated. The correlations were best explained by a combination of nutrients rather than any single nutrient. Direct manipulative studies have demonstrated that nutrient addition without other disturbance can cause weed invasion. Other studies show that both nutrient enrichment and other disturbance are required to alter community composition. Hobbs (1989) experimented in a range of heathland, shrublands and woodlands by digging the soil, adding fertiliser, both digging and fertilising, and adding seeds of Avena fatua L. and Ursinia anthemoides (L.) Poir. Very similar results were obtained in all communities. Avena responded to digging with little fertiliser effect. Ursinia showed little response to any treatment. Digging or fertiliser alone had little effect on resultant weed biomass, but a strong effect together. These results were attributed to better seed survival and more safe germination sites in the dug areas, a probable small increase in nutrient availability in dug treatments and extreme nutrient limitation for the weeds. Hobbs (1989) therefore argued that certain types of disturbance do not significantly increase resource availability and do not make a community more invasible. In a long-running experiment Davis et al. (2000) demonstrated a strong relationship between the levels of disturbance and nutrient enrichment and the mean aggregate cover of 54 plant species deliberately sown into a Derbyshire, UK, grassland. Fluctuating resources theory posits that resource removal or impoverishment will not cause an invasion. This was tested by Kreyling et al. (2008) who examined the effects of drought and heavy rainfall on simple experimental plant communities by counting individual plants that invaded from the matrix vegetation. Heavy rainfall increased invasibility while drought decreased invasibility. Higher diversity in the experimental plots (4 spp. vs. 2 spp.) decreased invasibility, and the two effects acted independently and were additive. Furthermore, several species that invaded were dependent on the functional groups present in the artificial communities or the nature of the particular weather event. Thus the predictions of both niche theory and fluctuating resources theory were supported. Enrichment or limitation of any resource including available space, soil nutrients, water and light may facilitate invasion. However the basic ecological processes that enable invasion are no different to those that enable native plants to regenerate or occupy new areas (Davis et al. 2000). In ecological time, an organism that is unable to change its distribution in response to environmental change must either evolve or become extinct. The theory of fluctuating resources predits that greater susceptibility to invasion occurs: 1. immediately after resource enrichment or following a decline in rate of resoure usage; 2. when a disturbance increases resource supply or reduces resident vegetation sequestration of resources; 3. when the interval between resource enrichment and resident vegetation sequestration is long; 4. when grazing is introduced, paticularly in high-nutrient areas; 5. that there is no necessary relationship between community plant diversity and invasion resistance and 6. that there is no general relationship between average community productivity and invasion resistance (Davis et al. 2000). In temperate Australian native grasslands the theory therefore predicts that: 1. areas subject to more intense or frequent resource enrichment are more prone to invasion (e.g. areas with soil disturbance, areas where the existing vegetation has died or been killed, floodplain areas, areas subject to fertiliser drift, areas more subject to anthropogenic N enrichment such as roadsides, urban areas, etc.); 2. fires in autumn create greater susceptibility to invasion than fires in spring, since autumn fires mean a longer interval between the growth period of the dominant grass Themeda triandra and the resource enrichment, providing the opportunity for winter growing N. neesiana to sequester more nutrients, light and space; 3. more intense fires intensify invasion because they create a greater increase in nutrient supply and a longer period of reduced resource capture by native plants; 4. drought will facilitate invasion, especially if it breaks in the period preceding the main N. neesiana seedling establishment and growth periods; 5. grazing of long-ungrazed areas will facilitate invasion since it makes available nutrients that were previously locked up by the native plants, and 6. grasslands with greater native species richness will be more resistant to invasion only if they are characterised by more complete and total resource utilisation. 12
For invasion to occur there must be not only fluctuating resources or resource enrichment, but propagule pressure (Davis et al. 2000). Disturbance (including the absence of particular disturbances), resource enrichment and propagule dispersal events are often correlated and can occur as part of the same event (e.g. intensive grazing by a flock of sheep contaminated with N. neesiana seed). Determining the proximate cause of invasions is thus complicated, but it is necessary to investigate the contribution of each of these factors to succesful invasions in order to devise optimal management practices. Propagule pressure Propagule pressure is the number of propagules dispersed into a given area and may be more important than any other factor in determining the success of a potential invader (Williamson and Fitter 1996, Lonsdale 1999, Levin 2006). Propagule pressure is equivalent to the factorial combination of the number of introduction events and the number of individuals per event (Lockwood et al. 2009). Where the availability of propagules is low, recruitment is always limited (Levin 2006) and when populations are small, there is a reduced likelihood that they will survive (Lockwood et al. 2009). Rejmánek (2000 p. 498) examined various proxy measures for propagule pressure and concluded that, as a general rule, initial population size and the number of introduction attempts determined the success of an invasion: the “most robust but ... trivial, generalization in invasion ecology”. However a recent metaanalysis (Hayes and Barry 2008) found a significant association between the number of released or arriving individuals or the number of release/arrival attempts and establishment success only for animals, and considered the proposition to be ‘untested’ for plants. Propagule pressure is a complex function, based on fecudity, dependent on propagule dispersal mechanisms and the availability and incidence of dispersal agents, and ultimately determined by the ability of the propagules to find suitable habitat and establish new populations (Williamson and Fitter 1996). In situations where an invasive species is already present and reproducing, use of the term “propagule rain” may be preferable (Lockwood et al. 2009). Where more than one potential invader is being considered, e.g. with community-level processes, the combination of propagule pressures is better termed ‘colonisation pressure’ (Lockwood et al. 2009). Plant taxa that achieved successful ancient long distance (transcontinental) dispersal have similar characteristics to modern invasive plants: high propagule dispersability, large propagule production by multiple, large populations, wide geographical range and major presence in their communities (Levin 2006). Species with large native ranges tend to be more abundant and produce more propagules per unit area so have a greater chance of becoming invasive elsewhere, purely based on the propagule pressure they exert (Levin 2006). Substantial propagule pressure is required to overcome the genetic and demographic liabilities of small populations (Levin 2006). Vacant niches and competitive exclusion Under the theory of competitive exclusion and niche displacement, a more competitive invader can occupy the niche previously occupied by a native species, and an empty niche is open to invasion. The theoretical underpinnings of this approach are derived from community assembly theory, based on island biogeography (Woods 1997, Seabloom et al. 2003, Cox 2004). Shea and Chesson (2002) reframed the theory in the context of community ecology. Niche theory and dispersal assembly theories may be contrasted with ‘neutral community assembly’, which predicts that the characteristics of a potential entrant to a community have a neutral effect on the possibility of it becoming a part of that community, in particular, each species is equally likely to reproduce (Leigh 2007). The ‘storage effect’ is a related concept that incorporates the temporal and spatial variation of niche elements. “The invader must be able to take advantage of times or locations in the landscape where the environment favours its population growth over that of the resident species, and store those gains in time or space in such a way that they are not eroded too much in unfavourable times or locations” (Melbourne et al. 2007 p. 84). ‘Storage’ can consist of a seed bank, a population of adult plants or a dormant tuber. Richer communities supposedly have more niches, both filled and vacant (Prieur-Richard and Lavorel 2000). Resources that are unsequestered by existing native species represent elements that could contribute to an ‘empty niche’. An invader might use resources in a different way to the native species or at different times, without interfering with other species, and so could theoretically occupy a previously empty niche. Or it might, through competitve processes, sequester resources that would otherwise by used by the resident species. Species that are ecologically similar to an invader are often lacking in successfully invaded communities (Mooney and Drake 1989, Systad 2000), suggesting that vacant niches are often present and that competitive exclusion often repels invasions. However various authors have argued that there is little evidence for the existence of vacant niches (Newsome and Noble 1986, Prieur-Richard and Lavorel 2000) and that the competitive superiority of plant invaders to native species has “rarely been tested experimentally” (Seabloom et al. 2003 p. 13384). Invasive plants that establish in dense populations must displace other plants and alter community composition, unless they occupy an unfilled niche, but if the niche was unfilled there should be no displacement, the invader is not a problem, and it successfully integrates into the existing community. The invasive species may displace another plant with a similar niche, or may be widely competitive and have the potential to completely restructure or replace a community, alter its successional dynamics or directly interact with disturbance regimes (Woods 1997, Mack and D’Antonio 1998), and thus alter the niche space of many community components. A community or one of its members may repel even a superior invasive competitor “because of the priority effect that established residents have over invaders” (Systad 2000 citing Case 1990 1991). Alternatively a native species may persist on sites where they have unusual competitive advantages, e.g. native grasses persist on sites with serpentine soils, but have been largely replaced by exotic grasses in California (Melbourne et al. 2007 citing Harrison 1999). Other author have argued that the niche concept itself is “a circular argument empty of mechanism and process” (Wedin 1999 p. 193). Niche theory is largely contradictory, since niches are multidimensional hyperspaces defined by their occupation by a species population in relationship with all the other organisms in the community (Herbold and Moyle 1986, my emphasis). A 13
Page 1 and 2: Literature review: Impact of Chilea
Page 3 and 4: Fire 49 Other disturbances 50 Shade
Page 5 and 6: Conventions and standards Botanical
Page 7 and 8: neesiana appears to be a habitat ge
Page 9 and 10: population densities of existing sp
Page 11: elated plants have similar defences
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 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
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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
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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
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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
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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
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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
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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:
Page 175 and 176:
Page 177 and 178:
Nematodes of grasses and grasslands
Page 179 and 180:
REFERENCES Aceñolaza, F.G. (2004)
Page 181 and 182:
Benson, D. and McDougall, L. (2005)
Page 183 and 184:
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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