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Summary: It remains uncertain how perennial grasses with different photosynthetic pathways respond to fire, and how this response varies with stress at the time of burning. Resprouting after fire was examined in relation to experimentally manipulated pre‐fire watering frequencies. We asked the following questions: are there response differences to fire between C3 and C4 grasses? And, how does post‐fire resprouting vary with pre‐fire drought stress?Fifty‐two perennial Australian grasses (37 genera, 13 tribes) were studied. Three watering frequencies were applied to simulate increasing drought. Pre‐fire tiller number, tiller density, specific leaf area and leaf dry matter content were measured as explanatory variables to assess response.Most species (90%) and individuals (79%) resprouted following experimental burning. C4 grasses had higher probabilities of surviving fire relative to C3 grasses. Responses were not related to phylogeny or tribe. High leaf dry matter content reduced the probability of dying, but also reduced the re‐emergence of tillers.Post‐fire tiller number increased with increasing drought, regardless of photosynthetic type, suggesting that drought plays a role in the ability of grasses to recover after fire. This has implications for understanding the persistence of species in landscapes where fire management is practiced. [ABSTRACT FROM AUTHOR]

Questions Do nurse plant interactions significantly influence understorey vegetation diversity in a large, semi-arid, shrub-dominated wetland? How do the modes and net effects of nurse plant interactions vary spatially along a flood frequency gradient, and temporally in response to drying? Location Narran Lakes Ramsar site, New South Wales, Australia. Methods Microhabitat characteristics, understorey vegetation and germinable soil seed banks were investigated in shrub and open habitats across a flood frequency gradient in a large, semi-arid wetland dominated by open shrubland under productive conditions following floodwater recession and again following 6 mo of drought. Split-plot ANOVA and multivariate analyses were used to determine the effects of shrubs on microhabitat character, understorey vegetation cover, species diversity, richness and composition and germinable soil seed banks. Results Microhabitat characteristics, including canopy cover, litter cover and soil character, all differed between shrub and open habitats, especially in the most frequently flooded sites. Under productive conditions following flooding, lignum shrubs suppressed understorey vegetation cover but increased species richness at the site scale across the flood frequency gradient and, in the most frequently flooded sites, supported higher species density at a microhabitat scale. Under dry conditions, lignum shrubs had a positive effect on understorey vegetation cover, species richness and species density across the flood frequency gradient, but particularly in frequently flooded sites. A significant difference in soil seed bank composition between shrub and open habitats was only observed in frequently flooded sites. Conclusions Nurse plant interactions appear to play an important role in determining understorey vegetation diversity in the lignum shrubland of the Narran Lakes wetland system. The modes and net effects of these nurse plant interactions vary in space and time in relation to flood history and drying. Positive interactions, probably involving microhabitat amelioration, appear to be particularly important to plant diversity and abundance under dry conditions. Under more favourable wetter conditions, lignum shrubs also contribute to understorey vegetation diversity by facilitating the establishment of different species than those dominating open habitats. Our findings have implications for the management of perennial shrubs and hydrological regimes in such wetlands. [ABSTRACT FROM AUTHOR]

Question Increases in the cover of woody plants have been documented in woodland, savanna and grassland ecosystems across the globe, commonly attributed to changes in land use or disturbance regimes. This is often thought to result in alternative stable states resistant to reversal. However, some multi-decadal-scale studies have found woody plant cover fluctuates according to variations in rainfall. After a decade-long El Nino event, we ask: can severe drought reverse woody plant encroachment in a temperate Australian woodland? Location Temperate coastal woodland in Victoria, SE Australia that has remained unburned for over a century. Methods Using data spanning 41 yr, changes in basal area and tree density were assessed for the major woody species in a eucalypt woodland. Data were used to determine whether a decade of severe drought (1997-2009) had reversed a previously identified phase of woody plant encroachment (1971-1996). Results After an increase in stand density between 1971 and 1996, attributed to an increase in the fire-sensitive species Allocasuarina littoralis, total tree density then declined by 42% between 1996 and 2012. Changes in tree density differed across dominant woody species ( A. littoralis −34%, Allocasuarina verticillata +26%, Acacia pycnantha −78%, Banksia marginata −73%, Eucalyptus spp. −97%), and seedling recruitment almost completely ceased for all species. However, the basal area of A. littoralis (having almost doubled between 1971 and 1996) had continued to increase by 75%, with increases highest in areas where initial basal area was lowest. Despite this increase, total stand basal area remained relatively stable, with an increase of 5%, because of a combined decline in basal area for all other species of 62%. Conclusion Despite the most severe drought on record, site occupancy - as measured by basal area - did not decline between 1996 and 2012. Thus, severe drought did not reverse woody plant encroachment. Rather, findings were consistent with the previous trend of increasing A. littoralis dominance at the expense of other tree species in the long-term absence of fire. [ABSTRACT FROM AUTHOR]

Increases in drought and temperature stress in forest and woodland ecosystems are thought to be responsible for the rise in episodic mortality events observed globally. However, key climatic drivers common to mortality events and the impacts of future extreme droughts on tree survival have not been evaluated. Here, we characterize climatic drivers associated with documented tree die-off events across Australia using standardized climatic indices to represent the key dimensions of drought stress for a range of vegetation types. We identify a common probabilistic threshold associated with an increased risk of die-off across all the sites that we examined. We show that observed die-off events occur when water deficits and maximum temperatures are high and exist outside 98% of the observed range in drought intensity; this threshold was evident at all sites regardless of vegetation type and climate. The observed die-off events also coincided with at least one heat wave (three consecutive days above the 90th percentile for maximum temperature), emphasizing a pivotal role of heat stress in amplifying tree die-off and mortality processes. The joint drought intensity and maximum temperature distributions were modeled for each site to describe the co-occurrence of both hot and dry conditions and evaluate future shifts in climatic thresholds associated with the die-off events. Under a relatively dry and moderate warming scenario, the frequency of droughts capable of inducing significant tree die-off across Australia could increase from 1 in 24 years to 1 in 15 years by 2050, accompanied by a doubling in the occurrence of associated heat waves. By defining commonalities in drought conditions capable of inducing tree die-off, we show a strong interactive effect of water and high temperature stress and provide a consistent approach for assessing changes in the exposure of ecosystems to extreme drought events. [ABSTRACT FROM AUTHOR]

Interactions between annual grass and perennial legume species when they are grown together under drought and limited phosphorus (P) availability are likely to be very important for pasture productivity, but are not well understood. Therefore, the objective of this study was to compare the interactions of drought and species combination on growth, nutrition, hydraulic lift and photosynthesis of the Australian native legume Cullen australasicum and the exotic legume Medicago sativa when grown with the exotic annual ryegrass ( Lolium rigidum) with poorly soluble FePO as the source of P. Plants were grown for 22 weeks in monoculture and in legume-grass mixtures in 1-m tall pots filled with river sand. Two moisture treatments were applied, drought (top 70 cm of soil allowed to dry after 16 weeks of establishment) and control (field capacity). In monoculture, shoot dry weight (DW) pot of L. rigidum was higher than that of C. australasicum and M. sativa. In the mixtures, compared with the monocultures, an increase in shoot DW pot for L. rigidum and a decrease for both C. australasicum and M. sativa resulted in a relative yield total >1. Citrate was the main carboxylate in the rhizosphere of all species, except for the drought-treated L. rigidum in monoculture and mixtures, for which malate was the main constituent. Both C. australasicum and M. sativa had higher concentrations of Ca, Mg, S, Cu, Zn, Mn and Mo in their leaves than did L. rigidum. Hydraulic lift was not detected in M. sativa and C. australasicum; likely reasons are discussed. Photosynthetic rate was similar for all species, but L. rigidum had tighter stomatal control. C. australasicum survived longer under drought than did M. sativa. In conclusion, L. rigidum out-competed the legumes. The legumes provided benefits to the growth of L. rigidum through solubilising P, but not through hydraulic lift. In addition, L. rigidum conserved moisture through tight stomatal control and produced an extensive root system to take up water and nutrients efficiently. [ABSTRACT FROM AUTHOR]

The significantly lower annual rainfall experienced in Australia over the past decade together with projections of long-term climate change has placed increased emphasis on the use of pasture plants with superior tolerance to environmental stress, particularly drought, to ensure persistence for the grazing industries. Summer dormancy is one of the more important traits that grasses have to adapt to environments where there is little, variable, or no summer rainfall. In this article, the role that the summer dormancy trait has played in enhancing the survival of temperate perennial grasses in Australia is reviewed with special reference to orchardgrass (cocksfoot; Dactylis glomerata L.) and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]. The performance of cultivars and populations with this trait is assessed in comparison to germplasm without the trait. Other major factors such as the contribution of rooting depth to stress tolerance and their possible relationship with summer dormancy are documented and evaluated. Current knowledge of the physiological basis by which summer dormancy improves survival of summer drought is also summarized. [ABSTRACT FROM AUTHOR]

The Australian national vetch-breeding program is based on conventional breeding methods of gene recombinations from different parents to overcome the main limiting factors for vetch production in Australia: drought and diseases. The breeding program has a strong focus on breeding vetch varieties to fit into crop rotations in low rain fall areas (less than 320mm/yr). A second objective is to breed varieties with a toxic component of less than 0.60%, to enable vetch grain to be used to feed poultry and other monogastric animals. Since 1996 vetch-breeding material has been tested in South Australia (SA), Victoria (Vic), New South Wales (NSW) and Western Australia (WA), for grain and dry matter production, as well as live stock nutritional evaluation of the grain. [ABSTRACT FROM AUTHOR]

Investigates the possibility that drought causes dieback of Eucalyptus in rural Australia. Comparison of water potential and canopy condition in dieback and healthy rural Eucalyptus blakelyi and E. melliodora trees during and after an extreme drought; Influence of soil water deficit on plant water status; Lack of association between the degree of drought stress experienced by Eucalyptus and their initial ratings as dieback or healthy.

Summary 1. Determining the relative importance of anthropogenic and non-anthropogenic influences on structure is essential for informed management of savannas and for carbon accounting under greenhouse obligations. 2. The magnitude of drought and dieback was examined using the rainfall records for Queensland and historical records of dieback. Tree dieback was examined in Eucalyptus savanna in north Queensland by random sampling after a recent drought. 3. Analysis of rainfall records revealed that particularly severe droughts occurred three times this century in inland Queensland, while more local droughts of similar intensity had been less frequent elsewhere. A review of historical records confirmed extensive tree death following past droughts. 4. Approximately 29% of trees were dead or nearly dead over a sampled area of about 55 000 square kilometres. Dieback was greatest on alkaline igneous rocks, intermediate on metamorphics, sedimentary rocks and acid igneous rocks, and lowest on alluvia. 5. Of the widespread dominants, the Eucalyptus crebra–E. xanthoclada species complex was highly susceptible to dieback, E. brownii and E. melanophloia–E. whitei moderately affected, and Corymbia clarksoniana and Melaleuca nervosa less severely affected. Preferential death of large over small size classes was significant for only E. crebra–E. xanthoclada. 6. The 1990s drought was especially intense in the vicinity of the North Queensland study area. However, within the study area there were only weak correlations between dieback and rainfall deficits as derived from modelled data. A classification of seasonal rainfall revealed no evidence of localized aberrant rainfall events, such as might result from heavy localized storms, within the study area during the drought. Thus the substantial patchiness in dieback within the study area was only poorly related to local rainfall patterns. Significant correlations of the dieback of some taxonomic groups with... [ABSTRACT FROM AUTHOR]