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Montserrat Vilà - One of the best experts on this subject based on the ideXlab platform.
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Landscape-scale positive feedbacks between fire and expansion of the large Tussock Grass, Ampelodesmos mauritanica in Catalan shrublands
Global Change Biology, 2005Co-Authors: Karl Grigulis, Francisco Lloret, Sandra Lavorel, Ian D. Davies, Anabelle Dossantos, Montserrat VilàAbstract:In the northern Mediterranean Basin, agricultural land abandonment over the last century has resulted in increasing frequencies of very large, intense fires. In Catalonia (NE Spain) some fires have been locally associated with the expansion of the large, evergreen, resprouting Tussock Grass Ampelodesmos mauritanica. We tested the hypothesis of a positive feedback between the abundance of A. mauritanica and changing fire regimes. We used permanent plots distributed across a natural gradient of density of A. mauritanica in the Garraf Natural Park near Barcelona. Total aboveground biomass nearly doubled from plots with low to high density through a combination of A. mauritanica replacing the biomass of other components of the community (predominantly native shrubs), and its absolute standing biomass increasing. The quantity of litter also increased. This increase in fuel load and changes in community functional composition resulted from the simultaneous decrease in shrub productivity and an increase in litter accumulation. Litter accumulation was the consequence of A. mauritanica litter decomposing 30% more slowly than that of shrubs. Under standardized conditions, A. mauritanica and its litter were considerably more flammable than any of the shrub species. This resulted in a more than 40-fold increase in calculated plot flammability from low-to-high-density plots. Feedbacks, at the landscape scale, were then analysed using the landscape simulation platform LAMOS. Invasion success and contribution to community biomass of A. mauritanica increased with decreasing fire return intervals. Total area burnt in the landscape during each fire year was positively and exponentially related to the total biomass of A. mauritanica. Simulations showed that landscapes can abruptly switch from regimes of small localized to extensive fires as a result of the spread of A. mauritanica. Therefore, increases in fires under climate change represent threats not only through their direct impacts on ecosystems, but also by promoting invaders such as A. mauritanica, which have the potential to induce powerful feedforward processes and, thereby, fundamental changes to ecosystems.
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fast regeneration of the Tussock Grass ampelodesmos mauritanica after clearing
Ecologia Mediterranea (France), 2002Co-Authors: Montserrat Vilà, Anna CasanovasAbstract:Les perturbations par debroussaillement sont une pratique commune dans les formations arbustives mediterraneennes du nord-est de l'Espagne comme technique de prevention contre les incendies afin de reduire la quantite de combustible disponible. Dans cette etude, nous avons compare la regeneration de communautes vegetales dominees par des graminees dans des placettes debroussaillees voisines de placettes non debroussaillees. Nous nous sommes particulierement interesses a la reponse de la graminee perenne couvrante Ampelodesmos mauritanica dans des placettes debroussaillees depuis 6 mois (recemment debroussaillee), depuis 2 ans (debroussaillee une fois) et dans une placette âgee d'une annee mais debroussaillee pendant deux annees consecutives (debroussaillee deux fois). Les placettes debroussaillees ont retrouve rapidement leur couverture vegetale apres le debroussaillement en liaison avec la dominance dans la communaute d'especes qui rejettent a partir d'organes souterrains suite a la perturbation. La richesse specifique n'est pas significativement differente entre les placettes debroussaillees et les placettes non debroussaillees adjacentes. De meme, le recouvrement vegetal total est plus faible dans les placettes recemment debroussaillees par rapport aux placettes adjacentes non debroussaillees, mais il n'y a pas de difference significative entre les placettes debroussaillees une fois et deux fois. Les individus d'Ampelodesmos mauritanica tondus ont de nombreux rejets survivants et vigoureux apres le debroussaillement. Bien que dans les placettes debroussaillees, les individus d'Ampelodesmos mauritanica soient plus petits que dans les placettes adjacentes non debroussaillees, le recouvrement vegetal n'y est pas significativement different. La reprise des plantules est superieure dans les placettes recemment debroussaillees par rapport aux placettes non debroussaillees adjacentes. Nos resultats suggerent donc que le debroussaillement n'est pas vraiment un outil de gestion efficace pour reduire l'abondance dAmpelodesmos mauritanica. Il n'est donc pas une technique de prevention efficace contre le feu parce que cette graminee dominante ne montre pas de mortalite apres le debroussaillement et accumule du combustible tres rapidement apres la destruction de sa biomasse epigee.
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Woody species tolerance to expansion of the perennial Tussock Grass Ampelodesmos mauritanica after fire
Journal of Vegetation Science, 2000Co-Authors: Montserrat Vilà, Francisco LloretAbstract:. In Mediterranean shrublands, post-fire accumulation of above-ground biomass of resprouters is faster than that of seeders. This suggests that resprouters may have a competitive advantage. To test this hypothesis, we used a removal experiment to study the effect of the presence of the dominant Tussock-Grass Ampelodesmos mauritanica on the resprouting shrubs Erica multiflora and Globularia alypum and on the seeders Rosmarinus officinalis and Pinus halepensis three and four years after a wildfire. Water potential of target plants was also measured to see if Ampelodesmos removal increased water availability. Ampelodesmos marginally reduced growth of all target species but did not influence survival or water potential of any target species. Our results suggest that the effect of climatically influenced water stress was stronger than the effect of Ampelodesmos neighbours. Plant-plant interactions in this Mediterranean community are weak after fire and the magnitude of the Ampelodesmos effect does not differ between seeders and resprouters.
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Seed dynamics of the mast seeding Tussock Grass Ampelodesmos mauritanica in Mediterranean shrublands
Journal of Ecology, 2000Co-Authors: Montserrat Vilà, Francisco LloretAbstract:Summary 1 The Mediterranean perennial Grass Ampelodesmos mauritanica may have the potential to expand its range. We analysed temporal variability of its reproductive components (seedfall, seed bank, seed predation, seed germination, seedling emergence, survival and growth) in three microsites (open areas, beneath Ampelodesmos and beneath shrubs) at two sites. 2 Reproductive components prior to seedling emergence were both closely linked and very similar between microsites within a site. Seedling survival and growth differed between microsites, being lowest in open areas. Recruitment patterns cannot therefore be predicted from seedfall. 3 Abundant seed production in 1996 was followed by successful germination and high seedling survival. In the following (non-masting) year, although Ampelodesmos has a low-density persistent seed bank, recruitment was much lower because germination was low and post-dispersal seed predation was high. 4 Our results suggest that Ampelodesmos reproduction is episodic. Expansion of its distribution may be triggered by intermittent seedling recruitment following masting, but is otherwise constrained by seed limitation, post-dispersal seed predation and a loss of viability in the seed bank.
Francisco Lloret - One of the best experts on this subject based on the ideXlab platform.
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Landscape-scale positive feedbacks between fire and expansion of the large Tussock Grass, Ampelodesmos mauritanica in Catalan shrublands
Global Change Biology, 2005Co-Authors: Karl Grigulis, Francisco Lloret, Sandra Lavorel, Ian D. Davies, Anabelle Dossantos, Montserrat VilàAbstract:In the northern Mediterranean Basin, agricultural land abandonment over the last century has resulted in increasing frequencies of very large, intense fires. In Catalonia (NE Spain) some fires have been locally associated with the expansion of the large, evergreen, resprouting Tussock Grass Ampelodesmos mauritanica. We tested the hypothesis of a positive feedback between the abundance of A. mauritanica and changing fire regimes. We used permanent plots distributed across a natural gradient of density of A. mauritanica in the Garraf Natural Park near Barcelona. Total aboveground biomass nearly doubled from plots with low to high density through a combination of A. mauritanica replacing the biomass of other components of the community (predominantly native shrubs), and its absolute standing biomass increasing. The quantity of litter also increased. This increase in fuel load and changes in community functional composition resulted from the simultaneous decrease in shrub productivity and an increase in litter accumulation. Litter accumulation was the consequence of A. mauritanica litter decomposing 30% more slowly than that of shrubs. Under standardized conditions, A. mauritanica and its litter were considerably more flammable than any of the shrub species. This resulted in a more than 40-fold increase in calculated plot flammability from low-to-high-density plots. Feedbacks, at the landscape scale, were then analysed using the landscape simulation platform LAMOS. Invasion success and contribution to community biomass of A. mauritanica increased with decreasing fire return intervals. Total area burnt in the landscape during each fire year was positively and exponentially related to the total biomass of A. mauritanica. Simulations showed that landscapes can abruptly switch from regimes of small localized to extensive fires as a result of the spread of A. mauritanica. Therefore, increases in fires under climate change represent threats not only through their direct impacts on ecosystems, but also by promoting invaders such as A. mauritanica, which have the potential to induce powerful feedforward processes and, thereby, fundamental changes to ecosystems.
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Woody species tolerance to expansion of the perennial Tussock Grass Ampelodesmos mauritanica after fire
Journal of Vegetation Science, 2000Co-Authors: Montserrat Vilà, Francisco LloretAbstract:. In Mediterranean shrublands, post-fire accumulation of above-ground biomass of resprouters is faster than that of seeders. This suggests that resprouters may have a competitive advantage. To test this hypothesis, we used a removal experiment to study the effect of the presence of the dominant Tussock-Grass Ampelodesmos mauritanica on the resprouting shrubs Erica multiflora and Globularia alypum and on the seeders Rosmarinus officinalis and Pinus halepensis three and four years after a wildfire. Water potential of target plants was also measured to see if Ampelodesmos removal increased water availability. Ampelodesmos marginally reduced growth of all target species but did not influence survival or water potential of any target species. Our results suggest that the effect of climatically influenced water stress was stronger than the effect of Ampelodesmos neighbours. Plant-plant interactions in this Mediterranean community are weak after fire and the magnitude of the Ampelodesmos effect does not differ between seeders and resprouters.
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Seed dynamics of the mast seeding Tussock Grass Ampelodesmos mauritanica in Mediterranean shrublands
Journal of Ecology, 2000Co-Authors: Montserrat Vilà, Francisco LloretAbstract:Summary 1 The Mediterranean perennial Grass Ampelodesmos mauritanica may have the potential to expand its range. We analysed temporal variability of its reproductive components (seedfall, seed bank, seed predation, seed germination, seedling emergence, survival and growth) in three microsites (open areas, beneath Ampelodesmos and beneath shrubs) at two sites. 2 Reproductive components prior to seedling emergence were both closely linked and very similar between microsites within a site. Seedling survival and growth differed between microsites, being lowest in open areas. Recruitment patterns cannot therefore be predicted from seedfall. 3 Abundant seed production in 1996 was followed by successful germination and high seedling survival. In the following (non-masting) year, although Ampelodesmos has a low-density persistent seed bank, recruitment was much lower because germination was low and post-dispersal seed predation was high. 4 Our results suggest that Ampelodesmos reproduction is episodic. Expansion of its distribution may be triggered by intermittent seedling recruitment following masting, but is otherwise constrained by seed limitation, post-dispersal seed predation and a loss of viability in the seed bank.
Francisco I. Pugnaire - One of the best experts on this subject based on the ideXlab platform.
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soil micro organisms and competitive ability of a Tussock Grass species in a dry ecosystem
Journal of Ecology, 2019Co-Authors: Yudi M. Lozano, Sara Hortal, Cristina Armas, Francisco I. PugnaireAbstract:Drylands are among the most threatened ecosystems in the world because of the effects of global change and because they are not particularly resilient. Regeneration after disturbance is quite slow and secondary succession can be delayed to the point of nearly stop. This is exacerbated when the community is strongly dominated by a single species able to quickly respond after disturbance. One example of such monospecific dominance is the colonization of abandoned fields in SE Spain by an early successional and native Tussock Grass, Lygeum spartum, that seems to halt succession. Here we tested the competitive ability of Lygeum against Salsola oppositifolia, a shrub species that can be found interspersed with Lygeum in mid‐successional stages, and assessed how plant–soil interactions mediate the outcome of plant–plant competition. To do so, we sowed seeds and grew plants of Lygeum and Salsola in either intra‐ or interspecific competition under controlled conditions using sterile field soils inoculated with either live (i.e., with micro‐organisms) or sterile soil extracts from the understories of either Lygeum or Salsola. Soil nutrient content, seed germination rate, and shoot mass growth were determined after 5 months, and soil bacterial communities were characterized by sequencing. Lygeum soil micro‐organisms and soil properties, such as the high content of N and organic matter, enhanced seed germination rate of Lygeum individuals. By contrast, Salsola adults outperformed Lygeum when growing in interspecific competition. Synthesis. The enhanced competitive ability of Lygeum, which was mediated by soil micro‐organisms, may lead to complete dominance of Lygeum in the plant community right after abandonment of agricultural fields. However, when the plant community is already developed, Lygeum would be unable to enforce such dominance. We conclude that positive plant–soil feedbacks combined with certain plant traits such as clonal growth support the strong resilience of Lygeum and allow for its dominance in extreme habitats.
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Soil micro‐organisms and competitive ability of a Tussock Grass species in a dry ecosystem
Journal of Ecology, 2018Co-Authors: Yudi M. Lozano, Sara Hortal, Cristina Armas, Francisco I. PugnaireAbstract:Drylands are among the most threatened ecosystems in the world because of the effects of global change and because they are not particularly resilient. Regeneration after disturbance is quite slow and secondary succession can be delayed to the point of nearly stop. This is exacerbated when the community is strongly dominated by a single species able to quickly respond after disturbance. One example of such monospecific dominance is the colonization of abandoned fields in SE Spain by an early successional and native Tussock Grass, Lygeum spartum, that seems to halt succession. Here we tested the competitive ability of Lygeum against Salsola oppositifolia, a shrub species that can be found interspersed with Lygeum in mid‐successional stages, and assessed how plant–soil interactions mediate the outcome of plant–plant competition. To do so, we sowed seeds and grew plants of Lygeum and Salsola in either intra‐ or interspecific competition under controlled conditions using sterile field soils inoculated with either live (i.e., with micro‐organisms) or sterile soil extracts from the understories of either Lygeum or Salsola. Soil nutrient content, seed germination rate, and shoot mass growth were determined after 5 months, and soil bacterial communities were characterized by sequencing. Lygeum soil micro‐organisms and soil properties, such as the high content of N and organic matter, enhanced seed germination rate of Lygeum individuals. By contrast, Salsola adults outperformed Lygeum when growing in interspecific competition. Synthesis. The enhanced competitive ability of Lygeum, which was mediated by soil micro‐organisms, may lead to complete dominance of Lygeum in the plant community right after abandonment of agricultural fields. However, when the plant community is already developed, Lygeum would be unable to enforce such dominance. We conclude that positive plant–soil feedbacks combined with certain plant traits such as clonal growth support the strong resilience of Lygeum and allow for its dominance in extreme habitats.
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Belowground zone of influence in a Tussock Grass species
Acta Oecologica, 2011Co-Authors: Cristina Armas, Francisco I. PugnaireAbstract:Belowground plant competition is strong and mediated by resource depletion as well as by high variety of exudates. Both factors contribute to active root segregation, affecting neighbours’ growth. In field and greenhouse experiments we investigated the belowground zone of influence of Stipa tenacissima, a Tussock-forming Grass which is the dominant species in many semiarid communities of the western Mediterranean Basin. Sometimes Tussocks show a fringe nearly devoid of annual plants, most likely caused by competition or interference. Fringe size was a function of water availability, so that the more water available the smaller the fringe and vice-versa. Aboveground mass of annual plants was higher in gaps than in the fringe, but root mass was higher in the fringe. More species emerged in soils from gaps than in soils from the fringe, and productivity was ten times higher in soils from gaps than in soils from the fringe. Growth of barley plants was inhibited in the vicinity of S. tenacissima Tussocks. S. tenacissima produced a belowground zone of influence around the Tussock through resource depletion, particularly water, but also likely through root exudates. Both mechanisms might inhibit the establishment of other annual and Grass species within the fringe. Fringe area has important effects for plant establishment, influencing population and community dynamics in these semiarid environments.
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Environmental control of canopy dynamics and photosynthetic rate in the evergreen Tussock Grass Stipa tenacissima
Plant Ecology, 1999Co-Authors: Peter Haase, Francisco I. Pugnaire, S.c. Clark, L.d. IncollAbstract:Seasonal changes in leaf demography and gas exchange physiology in the tall evergreen Tussock Grass Stipa tenacissima, one of the few dominant plant species in the driest vegetation of Europe, were monitored over a period of two years at a field site in semi-arid south-eastern Spain. Three age-classes of leaves – young, mature and senescent – were distinguished in the green canopy. Production of new leaves and extension growth of older leaves occurred exclusively from October–November to May–June. The rate of extension was significantly correlated with gravimetric soil water content. Leaf growth ceased after gravimetric soil water content fell below 0.015 g g−1 at the beginning of the dry season which corresponded to pre-dawn leaf water potentials of -3.0 MPa. Leaf senescence and desiccation reduced green leaf area by 43–49% during the dry season. Diurnal changes in the net photosynthetic rate of all three cohorts of leaves were bimodal with an early morning maximum, a pronounced midday depression and a small recovery late in the afternoon. Maximum photosynthetic rates of 10–16 μmol CO2 m−2 s−1 were attained from November 1993 to early May 1994 in young and mature leaves. Photosynthetic rate declined strongly during the dry season and was at or below compensation in September 1994. Gas exchange variables of young and mature leaves were not significantly different, but photosynthetic rate and diffusive conductance to water vapour of senescing leaves were significantly lower than in the two younger cohorts. Leaf nitrogen content of mature leaves varied seasonally between 2.9 and 5.2 g m−2 (based on projected area of folded leaves), but was poorly correlated with maxima of the photosynthetic rate. There was a stronger linear relationship between the daily maxima of leaf conductance and pre-dawn leaf water potential than with atmospheric water vapour saturation deficit. Seasonal and between-year variation in daily carbon assimilation were caused mainly by differences in climatic conditions and canopy size whereas the effect of age structure of canopies was negligible. Since water is the most important limiting factor for growth and reproduction of S. tenacissima, any future rise in mean temperature, which might increase evapotranspiration, or decrease in rainfall, may considerably reduce the productivity of the Grasslands, particularly at the drier end of their geographical distribution.
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Response of the Tussock Grass Stipa tenacissima to watering in a semi-arid environment
Functional Ecology, 1996Co-Authors: Francisco I. Pugnaire, Peter Haase, L.d. Incoll, S.c. ClarkAbstract:1. Stipa tenacissima is a perennial Tussock Grass of arid and semi-arid zones around the Mediterranean basin that occupies extensive areas in south-eastern Spain. The environment of this region is extreme, with low irregular rainfall, high temperature and high irradiance, so that S. tenacissima Tussocks are subjected to a high degree of environmental stress, especially during the summer months. 2. The ability of S. tenacissima to use a pulse of water applied in midsummer was tested in a field experiment in which extension growth and physiological performance of leaves of watered and unwatered plants were measured. 3. In unwatered plants, when leaf extension had ceased, leaf water potential, relative water content, leaf conductance and net photosynthetic rate were low and minimum fluorescence was high. 4. Leaf conductance and net photosynthetic rate doubled, leaf extension resumed, minimum fluorescence (F 0 ) fell and photosynthetic efficiency of photosystem II (F v /F m ) rose with watering. As the soil dried out again, values of these variables approached or equalled those of unwatered plants. 5. These changes in F 0 and F V /F m suggested that the photosynthetic apparatus had not been damaged permanently, i.e. that S. tenacissima has reversible photoprotective mechanisms. 6. We conclude that the decreased photosynthetic rate of unwatered plants in summer results from non-damaging photoinhibition and low leaf conductance. The latter is partly a consequence of the folding of leaves, which was inversely proportional to relative water content. 7. The arrested development of S. tenacissima leaves was apparently not due to summer dormancy because leaves responded opportunistically within days to an applied pulse of water.
Martin Schnittler - One of the best experts on this subject based on the ideXlab platform.
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Agamospermous seed production of the invasive Tussock Grass Nardus stricta L. (Poaceae) in New Zealand - evidence from pollination experiments
Flora - Morphology Distribution Functional Ecology of Plants, 2006Co-Authors: W. Daniel Kissling, Janice M. Lord, Martin SchnittlerAbstract:The breeding system of the European Tussock Grass Nardus stricta L. (Poaceae) was investigated with pollination experiments. Plants were sampled from two populations at Lake Pukaki, Canterbury, New Zealand, where the species is recognised as an alien invader. Bagging of flowers with king-sized cigarette paper and hand-pollination were used to test for three modes of reproduction in the greenhouse: (1) agamospermy (apomixis), (2) autogamy and self-compatibility, and (3) allogamy (outcrossing). Two control groups without experimental treatments were further tested for seed set under (1) greenhouse and (2) field conditions. The success or failure of all experimental treatments was assessed with seed set and germination trials. All agamospermy treatments showed high seed set and germination proportions arguing for an apomictic mode of reproduction in Nardus stricta. Cross-pollination treatments were also successful making it difficult to estimate the degree of outcrossing, selfing, and agamospermous seed production in Nardus stricta. Fecundity in field populations was considerably reduced, possibly due to environmental factors acting upon seed development during maturation. The reproductive strategy of Nardus stricta might be particularly beneficial during invasion because single Tussocks can form reproducing colonies and high reproductive output is ensured even in the absence of pollination. Genetic studies in combination with pollination experiments would be necessary to gain deeper insights into the breeding strategy of Nardus stricta.
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invasion ecology of the alien Tussock Grass nardus stricta poaceae at lake pukaki canterbury new zealand
New Zealand Journal of Botany, 2005Co-Authors: Daniel W Kissling, Martin Schnittler, Philip J Seddon, Katharine J M Dickinson, Janice M. LordAbstract:Abstract The European matGrass Nardus stricta has naturalised in New Zealand, often on damp soils within wetlands and Grasslands. In this paper, we present for the first time field data on the ecology of this alien invader in New Zealand, from eight kettle‐hole wetlands on lateral moraine along the western side of Lake Pukaki, South Canterbury. The invaded wetland sites were all acidic but varied in other soil characteristics. Nardus stricta was the most dominant species within these wetland communities with 40% of all plots showing more than 50% coverage, and 21% having more than 90% cover. Species richness (including vascular plants and mosses) at some sites was relatively high (c. 40 species), but species richness and abundance were significantly reduced in quadrats with high Nardus stricta density. Seedling densities of Nardus stricta were high but variable (overall mean of 38.6 ± 116 seedlings per m2), and establishment mainly occurred on the cushion‐forming sedge Oreobolus pectinatus. Most reproduct...
Ian D. Lunt - One of the best experts on this subject based on the ideXlab platform.
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Restoration of Themeda australis swards suppresses soil nitrate and enhances ecological resistance to invasion by exotic annuals
Biological Invasions, 2009Co-Authors: Suzanne M. Prober, Ian D. LuntAbstract:Understanding processes that underlie ecological resistance to weed invasion is critical for sustainable restoration of invaded plant communities. Experimental studies have demonstrated that invasive nitrophilic annuals can be controlled by addition of carbon to reduce soil nitrate concentrations, sometimes leading to enhanced establishment of native plants. However, effects of carbon supplements on soil nitrate are temporary, and the longer-term value of carbon supplementation as a restoration tool is dependent on the resistance of the re-established ecosystem to repeat invasion. We investigated whether re-established swards of the Tussock Grass Themeda australis (R.Br.) Stapf (a natural understorey dominant in mesic Grassy woodlands of SE Australia) could suppress soil nitrate concentrations, and through this or other means, could impart ongoing resistance to exotic invasion in restored woodlands. In a remnant invaded by exotic annuals, we applied three plot treatments (carbon supplements, annual spring burns and untreated control) and two seed treatments (± Themeda seed) in a replicated, factorial design. Within 3 years, successful establishment of Themeda swards on burnt and carbon-supplemented plots was associated with a reduction in soil nitrate to levels comparable with non-invaded, Themeda- dominated reference sites in the region (
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Fire frequency regulates Tussock Grass composition, structure and resilience in endangered temperate woodlands
Austral Ecology, 2007Co-Authors: Suzanne M. Prober, Kevin R. Thiele, Ian D. LuntAbstract:The importance of disturbance for regulating the structure and diversity of Grassy ecosystems is widely recognized, but disturbance-mediated interactions between Grassland composition and Grassland resilience, and consequent implications for conservation management, are less well documented. We established replicated burning, mowing and (non-livestock) grazing regimes in two contrasting Grassy woodland remnants in south-eastern Australia, and monitored the dynamics and resilience of the matrix-forming Tussock Grasses, Poa sieberiana (Poa) and Themeda australis (Themeda), over 12 years. Introduction of frequent burning to a Poa-dominated understorey in a rarely burnt woodland enhanced dominance by Themeda, and conversely, reduced fire frequency in a frequently burnt Themeda Grassland substantially increased Poa abundance. Burning was potentially detrimental in the Poa-dominated woodland, but sward resilience (recovery after the 2002 burn) increased as Themeda increased with repeated burning. By contrast, the Themeda Grassland was resilient to 4- and 8-yearly burning, but biennial burning led to poor resilience and high Tussock mortality under drought conditions. Contrary to other mesic Grasslands, cessation of burning had not caused sward collapse by 14 years post-fire despite high litter accumulation, potentially due to compensatory growth of Poa, lower site productivity and drought. Biennial mowing without slash removal was similar to 4-yearly burning in effects, while exclusion from kangaroo and rabbit grazing significantly increased sward biomass and contributed to increased Poa cover and inflorescence production. We conclude that functional complementarity associated with mixed dominants enhances resilience to variable disturbance regimes, and that below certain thresholds of abundance of each dominant, this resilience declines. Conservation management of Themeda-Poa ecosystems should thus aim to maintain an effective balance of these dominants.
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effects of time since fire on the Tussock dynamics of a dominant Grass themeda triandra in a temperate australian Grassland
Biological Conservation, 1999Co-Authors: John W Morgan, Ian D. LuntAbstract:Changes in Tussock attributes and sward structure with time-since-fire were documented for the dominant Tussock Grass, Themeda triandra, at the Derrimut Grassland Reserve in southern Victoria, Australia. When the inter-fire interval exceeded 6 yr, the number of tillers per Tussock and the total number of Tussocks declined, and by 11 yr, few live tillers or Tussocks remained in the sward. Below-ground biomass was also substantially lower at this time. With increasing time-since-fire, the canopy of live leaves was elevated high above the soil surface and dead leaves accumulated around and over the Tussock bases. Productivity declined in long unburnt areas and by 11 yr without disturbance, the canopy “collapsed” upon itself, forming a thick layer of dead thatch over the soil surface. A single fire in an area previously unburnt for 12 yr did not immediately return the Tussocks to a state more characteristic of a site with a 4 yr inter-fire interval burnt at the same time. Inter-fire intervals of ⩽5 yr would appear necessary to maintain the health and competitiveness of Themeda triandra. These findings have important implications for the maintenance of faunal habitat and the potential for weed invasion into remnant Grasslands.
