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1.
Proc Natl Acad Sci U S A ; 117(47): 29720-29729, 2020 11 24.
Artigo em Inglês | MEDLINE | ID: mdl-33139533

RESUMO

Forest vulnerability to drought is expected to increase under anthropogenic climate change, and drought-induced mortality and community dynamics following drought have major ecological and societal impacts. Here, we show that tree mortality concomitant with drought has led to short-term (mean 5 y, range 1 to 23 y after mortality) vegetation-type conversion in multiple biomes across the world (131 sites). Self-replacement of the dominant tree species was only prevalent in 21% of the examined cases and forests and woodlands shifted to nonwoody vegetation in 10% of them. The ultimate temporal persistence of such changes remains unknown but, given the key role of biological legacies in long-term ecological succession, this emerging picture of postdrought ecological trajectories highlights the potential for major ecosystem reorganization in the coming decades. Community changes were less pronounced under wetter postmortality conditions. Replacement was also influenced by management intensity, and postdrought shrub dominance was higher when pathogens acted as codrivers of tree mortality. Early change in community composition indicates that forests dominated by mesic species generally shifted toward more xeric communities, with replacing tree and shrub species exhibiting drier bioclimatic optima and distribution ranges. However, shifts toward more mesic communities also occurred and multiple pathways of forest replacement were observed for some species. Drought characteristics, species-specific environmental preferences, plant traits, and ecosystem legacies govern postdrought species turnover and subsequent ecological trajectories, with potential far-reaching implications for forest biodiversity and ecosystem services.


Assuntos
Secas/mortalidade , Florestas , Biodiversidade , Mudança Climática/mortalidade , Ecossistema , Especificidade da Espécie , Árvores/fisiologia
2.
J Environ Manage ; 302(Pt B): 114051, 2022 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-34773778

RESUMO

Land-use change, and associated land clearing/conversion and fragmentation are major drivers of biodiversity decline across the globe. The spread of invasive species is a well-recognised consequence of land-use change. The extent and intensity of invasion however is often difficult to assess due to a lack of temporal data. Using detailed mapping information for 130, 950 km2 of sub-coastal Queensland, Australia and results from field surveys we investigated changes to land-use, the extent of remnant (intact) vegetation and the spread of prominent invasive plant species over time (1997-2018). In the 50 years prior to 1997 the area underwent significant land development (mostly for livestock grazing and crops), resulting in a reduction of 45% of its remnant vegetation. Despite key policy developments aimed at protecting the remaining vegetation and species, 7392 km2 was cleared/converted between 1997 and 2017, mainly for the expansion of grazing and cropping lands. Vegetation types specifically listed for national protection under these policies were some of the greatest affected, highlighting the need for improved implementation and regulation of these control measures. Within remaining fragments of remnant vegetation, the cover and presence of two invasive perennial grass species indian couch (Bothriochloa pertusa) and buffel grass (Cenchrus ciliaris) increased significantly during this time period. There was also a moderate increase in the cover and presence of the annual herb Parthenium weed (Parthenium hysterophorus). The spread of these species within the landscape likely reflects an 'invasion debt', incurred from an intense history of land-use within the region and we predict this trend will continue to threaten remnant ecosystems.


Assuntos
Biodiversidade , Ecossistema , Austrália , Conservação dos Recursos Naturais , Espécies Introduzidas , Plantas Daninhas
3.
Ecol Appl ; 29(5): e01911, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31017349

RESUMO

In many of the world's arid regions there has been a dramatic increase in grazing pressure with herds of livestock sustained by the provision of artificial water points. In these systems it has been suggested that grazing-sensitive plant species will have contracted to refuges distant from water points where grazing impacts are low. This association was tested using a large data set of presence/absence records for rare plant species throughout the northeastern Australian arid zone. The presence records of only one of 45 species were statistically associated with lower grazing activity, as a function of distance-to-water, than the absence records. The field observation that this species is rarely grazed suggests it is not susceptible to grazing pressure. In general, the study supports assertions that populations of short-lived plants in drylands are resilient in the face of exaggerated livestock grazing because herbivores are not in sufficient densities to have an impact during the sporadic periods of high rainfall when plants can complete their life cycles. However, long-lived palatable species may be extinction-prone in grazed landscapes over long time frames if recruitment is curtailed by grazing.


Assuntos
Gado , Água , Animais , Austrália , Herbivoria , Plantas
4.
Oecologia ; 191(1): 165-175, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31372894

RESUMO

Alternative vegetation types that switch from one to another under contrasting fire regimes are termed fire-mediated alternative stable states (FMASS). Typically, pyrophylic communities (i.e., vegetation assemblages favored by burning) dominate under high frequencies or intensities of fire. Conversely, fire-sensitive (pyrophobic) vegetation types persist under long fire-free conditions. As the persistence traits of plants of FMASS systems are generally poorly researched, threshold levels of pyric disturbance that trigger 'state-switching' are often unknown. Dense thickets of the obligate-seeder shrub waputi (Aluta maisonneuvei ssp. maisonneuvei [Myrtaceae]) form fire-retarding woody islands within highly flammable spinifex (Triodia spp.) grasslands in arid Australia. To examine the tolerance of Aluta thickets to burning, we investigated: (1) the influence of post-fire rainfall and fire severity on recruitment (a field study); (2) soil seedbank densities (a field study); and (3) fire-related dormancy cues in seeds (a germination trial). We found a positive relationship between recruitment and post-fire rainfall volume, and much higher mean recruitment at sites with high- (5.9 seedlings/m2) than low-severity-burnt (2.2 seedlings/m2) and unburnt shrubs (0.03 seedlings/m2). Post-fire regeneration was mediated by dense soil-borne seedbanks, and the germination trial indicated that smoke promoted germination. Although Aluta shrubs are invariably fire-killed, high-severity fires are unlikely to lead to state shifts from shrubland to grassland because of the ability of mature stands to regenerate from dense, fire-cued seedbanks. Nevertheless, given that Aluta seedlings are exceptionally slow-growing, post-fire droughts combined with fire-return intervals less than the Aluta primary juvenile period of c. 5 years could drive conversion from Aluta- to Triodia-dominated vegetation.


Assuntos
Incêndios , Austrália , Germinação , Sementes , Austrália Ocidental
5.
Ann Bot ; 121(1): 119-128, 2018 01 25.
Artigo em Inglês | MEDLINE | ID: mdl-29293879

RESUMO

Background and Aims: Plant species with fire-triggered germination are common in many fire-prone ecosystems. For such plants, fire timing in relation to the timing of reproduction may strongly influence post-fire population regeneration if: (a) flowering occurs infrequently (e.g. plants are mast seeders); and (b) seed survival rates are low and input from the current year's flowering therefore contributes a large proportion of the viable dormant seedbank. The role of fire timing in relation to masting as a driver of post-fire recruitment has rarely been examined directly, so this study tested the hypothesis that fires shortly after masting trigger increased recruitment of the obligate-seeding arid zone spinifex, Triodia pungens R. Br., an iteroparous masting grass with smoke-cued germination. Methods: Phenological monitoring of T. pungens was conducted over 5 years, while a longitudinal seedbank study assessed the influence of seeding events on soil-stored seedbank dynamics. Concurrently, a fire experiment with randomized blocking was undertaken to test whether T. pungens hummocks burnt shortly after masting have greater post-fire recruitment than hummocks burnt when there has not been recent input of seeds. Key Results: Triodia pungens flowered in all years, though most flowerings were characterized by high rates of flower abortion. A mast flowering with high seed set in 2012 triggered approx. 200-fold increases in seedbank densities, and seedbank densities remained elevated for 24 months after this event. The fire experiment showed significantly higher recruitment around hummocks burnt 6 months after the 2012 mast event than around hummocks that were burnt but prevented from masting by having inflorescences clipped. Conclusions: Fires shortly after masting trigger mass recruitment in T. pungens because such fires synchronize an appropriate germination cue (smoke) with periods when seedbank densities are elevated. Interactions between natural fire regimes, seedbank dynamics and fire management prescriptions must be considered carefully when managing fire-sensitive masting plants such as T. pungens.


Assuntos
Poaceae/fisiologia , Sementes/fisiologia , Clima Desértico , Incêndios , Flores/fisiologia , Reprodução , Fatores de Tempo
6.
Am J Bot ; 104(10): 1474-1483, 2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-29885224

RESUMO

PREMISE OF THE STUDY: Fire typically triggers extensive regeneration of plants with heat-stimulated germination by causing short periods of intense soil heating. If plants with heat-stimulated germination are also subject to seed predation and display mast-seeding cycles, postfire recruitment may be contingent on the seedfall density of prefire masts, and on whether granivores are satiated at the time of fire. METHODS: We conducted a longitudinal seedbank study and a mensurative field experiment in central Australia to examine whether fire and the variation in seedfall density across sites in a mast year interact to influence recruitment of slender mulga (Acacia aptaneura), an iteroparous masting shrub with heat-stimulated germination. KEY RESULT: The seedbank study showed seedbank pulsing after masting, with mean seed counts in the upper 4-cm soil layer being 132.8 seeds/m2 12-mo after a dense seedfall, but only 3.8 seeds/m2 following a year with no seed production. Consistent with this, recruitment increased postfire at sites where denser seedfall had occurred during the preburn mast year. Conversely, little recruitment occurred at unburnt populations, irrespective of prefire seedfall density. CONCLUSIONS: We attribute our findings to: (1) elevated soil temperatures during fires stimulating germination of heat-cued seeds; and (2) granivore satiation following masting facilitating assimilation of seeds into the soil seedbank. These results highlight the importance of rare seed-input events for regeneration in fire-prone systems dominated by masting plants, and provide the first example from an arid biome of fire interacting with masting to influence recruitment.


Assuntos
Acacia/fisiologia , Germinação/fisiologia , Austrália , Clima Desértico , Ecologia , Ecossistema , Incêndios , Temperatura Alta , Banco de Sementes , Sementes/fisiologia , Solo
8.
Glob Chang Biol ; 21(10): 3777-85, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25988872

RESUMO

Predicting the consequences of climate change on forest systems is difficult because trees may display species-specific responses to exaggerated droughts that may not be reflected by the climatic envelope of their geographic range. Furthermore, few studies have examined the postdrought recovery potential of drought-susceptible tree species. This study develops a robust ranking of the drought susceptibility of 21 tree species based on their mortality after two droughts (1990s and 2000s) in the savanna of north-eastern Australia. Drought-induced mortality was positively related to species dominance, negatively related to the ratio of postdrought seedlings to adults and had no relationship to the magnitude of extreme drought within the species current geographic ranges. These results suggest that predicting the consequences of exaggerated drought on species' geographic ranges is difficult, but that dominant species like Eucalyptus with relatively slow rates of population recovery and dispersal are the most susceptible. The implications for savanna ecosystems are lower tree densities and basal area.


Assuntos
Mudança Climática , Secas , Árvores/fisiologia , Florestas , Queensland , Especificidade da Espécie
9.
Sci Total Environ ; 887: 163936, 2023 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-37149179

RESUMO

An 'oasis' signifies a refugium of safety, recovery, relaxation, fertility, and productivity in an inhospitable desert, a sweet spot in a barren landscape where life-giving water spills forth from the Earth. Remarkable mythological congruencies exist across dryland cultures worldwide where oases or 'arid-land springs' occur. In many places they also provide specialised habitats for an extraordinary array of endemic organisms. To inform their management, and maintain their integrity, it is essential to understand the hydrogeology of aquifers and springs. Gravity-fed vs artesian aquifers; actively recharged vs fossil aquifers, and sources of geothermal activity are important concepts presented here. There consequences for oases of sustainable and unsustainable groundwater extraction, and other examples of effective conservation management. Oases are archetypes for human consciousness, habitats that deserve protection and conservation, and a lingua franca for multicultural values and scientific exchange. We represent an international Fellowship of the Spring seeking to encompass and facilitate the stewardship of oases and aquifers through improved knowledge, outreach, and governance.


Assuntos
Água Subterrânea , Nascentes Naturais , Humanos , Bolsas de Estudo , Ecossistema , Água Doce
10.
Trends Ecol Evol ; 35(7): 554-557, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32340836

RESUMO

Myrtle rust is a fungal disease that has spread rapidly across the globe, arriving in Australia in 2010. The tree species Rhodomyrtus psidioides is nearly extinct in the wild as a result of the disease, leading to potential disruption of ecosystem function. Many other Myrtaceae may also be threatened and unprecedented impacts of the disease are predicted.


Assuntos
Micoses , Myrtaceae , Austrália , Ecossistema , Humanos , Doenças das Plantas
11.
Science ; 343(6170): 548-52, 2014 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-24482480

RESUMO

Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the magnitude of these effects varied substantially, so that a single model cannot adequately represent savanna woody biomass across these regions. Historical and environmental differences drive the regional variation in the functional relationships between woody vegetation, fire, and climate. These same differences will determine the regional responses of vegetation to future climates, with implications for global carbon stocks.


Assuntos
Clima , Ecossistema , Incêndios , Árvores , África , Austrália , Umidade , Modelos Biológicos , América do Sul
12.
J Environ Manage ; 83(4): 392-401, 2007 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-16828220

RESUMO

The accurate assessment of trends in the woody structure of savannas has important implications for greenhouse accounting and land-use industries such as pastoralism. Two recent assessments of live woody biomass change from north-east Australian eucalypt woodland between the 1980s and 1990s present divergent results. The first estimate is derived from a network of permanent monitoring plots and the second from woody cover assessments from aerial photography. The differences between the studies are reviewed and include sample density, spatial scale and design. Further analyses targeting potential biases in the indirect aerial photography technique are conducted including a comparison of basal area estimates derived from 28 permanent monitoring sites with basal area estimates derived by the aerial photography technique. It is concluded that the effect of photo-scale; or the failure to include appropriate back-transformation of biomass estimates in the aerial photography study are not likely to have contributed significantly to the discrepancy. However, temporal changes in the structure of woodlands, for example, woodlands maturing from many smaller trees to fewer larger trees or seasonal changes, which affect the relationship between cover and basal area could impact on the detection of trends using the aerial photography technique. It is also possible that issues concerning photo-quality may bias assessments through time, and that the limited sample of the permanent monitoring network may inadequately represent change at regional scales.


Assuntos
Fotografação , Árvores , Austrália , Biomassa , Carbono
13.
J Environ Manage ; 68(4): 409-20, 2003 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-12877874

RESUMO

Features of the land management history over a 125,755 km(2) area of central Queensland, Australia were determined from a variety of sources. A random sample of 205 site locations provided the basis for determining trends in land use. Trends in vegetation clearing were determined using sequential aerial photography for the sample sites, revealing a steady rate averaging nearly 1% of the region per annum over 41 years. This measure of sustained clearing over a large region is higher than recently published clearing rates from South America. Land types have been selectively cleared with over 90% of the Acacia on clay land type having been cleared. A land-holder questionnaire pertaining to the random sites yielded a response rate of 71% and provided information on vegetation clearing, ploughing, tree killing (ring-barking or tree poisoning), and fire frequency, season and intensity. The land-holder responses were compared with independent data sources where possible and revealed no mis-information. However, land-holders may have been marginally less likely to respond if the sample area had been cleared, although this effect was not statistically significant. Ploughing and tree killing are variable depending on land type, but the former has affected about 40% of the Acacia on clay land type, effectively eliminating options for natural regrowth. The proportion of decade-site combinations that were reported as having no fires increased from 22% in the 1950s to an average of 42% for subsequent decades, although the reporting of more than one fire per decade has been relatively constant through the study period. The reporting of at least one fire per decade varies from 46% for the Acacia on sand land type to 77% for the Eucalypt on sand land type for decade-site combinations. Fires are more intense when associated with clearing than in uncleared vegetation, but the proportion of cool and hot fires is relatively constant between land types in uncleared vegetation. Nearly all fires reported were either in spring or summer and this seasonally restricted regime is probably at variance with Aboriginal fire regimes. This study describes the rapid transformation of central Queensland. This has yielded substantially increased agricultural production but may also result in a range of negative impacts and these are discussed.


Assuntos
Agricultura/história , Ecossistema , Agricultura Florestal/história , Havaiano Nativo ou Outro Ilhéu do Pacífico , Acacia/crescimento & desenvolvimento , Meio Ambiente , Eucalyptus/crescimento & desenvolvimento , Incêndios , História do Século XX , Humanos , Dinâmica Populacional , Queensland , Estações do Ano , Inquéritos e Questionários
14.
J Environ Manage ; 68(4): 421-36, 2003 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-12877875

RESUMO

Accounting of carbon stocks in woody vegetation for greenhouse purposes requires definition of medium term trends with accurate error assessment. Tree and shrub cover was sampled through time at randomly located sites over a large area of central Queensland, Australia using aerial photography from 1945 to 1999. Calibration models developed from field data for the same land types as those represented within the study area allowed for the extrapolation of overstorey and understorey cover, basal area and biomass values and these were modelled as trends over the latter half of the 20th century. These structural attributes have declined over the region because of land clearing with values for biomass changing from a mean of 58.0(+/-1.2)t/ha in 1953 to 41.1(+/-1.0)t/ha in 1991. The biomass of Acacia on clay and Eucalypt on texture contrast soils land types has declined most dramatically. Within uncleared vegetation there was an overall trend of increase from 56.1(+/-1.2)t/ha in 1951 to 67.6(+/-1.3)t/ha in 1995. The increase in structural attributes within uncleared vegetation was most pronounced for the Eucalypt on texture contrast soils and Eucalypt on clay land types. It was demonstrated that the sites sampled were representative of their land types and that spatial bias of the photography, undetected tree-killing, sampling error, inherent variability of structural attributes and measurement error should not have impacted greatly on bias or precision of trend estimates for well-sampled land types. Certainly the errors are not likely to be substantial for trends averaged over all land types and they provide an accurate assessment of the magnitude and direction of change. The technique presented here would appear to be a robust means of accounting for the above-ground woody component of woodlands and open forests and will also contribute to a broader understanding of savanna dynamics.


Assuntos
Monitoramento Ambiental/métodos , Modelos Teóricos , Desenvolvimento Vegetal , Austrália , Calibragem , Clima Desértico , Ecossistema , Fotografação , Dinâmica Populacional
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