Roderick J. Fensham

Savanna vegetation-fire-climate relationships differ among continents.

Surveying Savannas Savannas are structurally similar across the three major continents where they occur, leading to the assumption that the factors controlling vegetation structure and function are broadly similar, too. Lehmann et al. (p. 548) report the results of an extensive analysis of ground-based tree abundance in savannas, sampled at more than 2000 sites in Africa, Australia, and South America. All savannas, independent of region, shared a common functional property in the way that moisture and fire regulated tree abundance. However, despite qualitative similarity in the moisture–fire–tree-biomass relationships among continents, key quantitative differences exist among the three regions, presumably as a result of unique evolutionary histories and climatic domains. Evolution cannot be overlooked when aiming to predict the potential global impacts on savanna dynamics in a warming world. 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.

Buffel grass and climate change: a framework for projecting invasive species distributions when data are scarce.

Invasive species pose a substantial risk to native biodiversity. As distributions of invasive species shift in response to changes in climate so will management priorities and investment. To develop cost-effective invasive species management strategies into the future it is necessary to understand how species distributions are likely to change over time and space. For most species however, few data are available on their current distributions, let alone projected future distributions. We demonstrate the benefits of Bayesian Networks (BNs) for projecting distributions of invasive species under various climate futures, when empirical data are lacking. Using the introduced pasture species, buffel grass (Cenchrus ciliaris) in Australia as an example, we employ a framework by which expert knowledge and available empirical data are used to build a BN. The framework models the susceptibility and suitability of the Australian continent to buffel grass colonization using three invasion requirements; the introduction of plant propagules to a site, the establishment of new plants at a site, and the persistence of established, reproducing populations. Our results highlight the potential for buffel grass management to become increasingly important in the southern part of the continent, whereas in the north conditions are projected to become less suitable. With respect to biodiversity impacts, our modelling suggests that the risk of buffel grass invasion within Australia’s National Reserve System is likely to increase with climate change as a result of the high number of reserves located in the central and southern portion of the continent. In situations where data are limited, we find BNs to be a flexible and inexpensive tool for incorporating existing process-understanding alongside bioclimatic and edaphic variables for projecting future distributions of species invasions.

Rail survey plans to remote sensing: vegetation change in the Mulga Lands of eastern Australia and its implications for land use

There is a prevailing paradigm that woody vegetation is expanding at the expense of grassland with reduced burning under pastoralism in the Mulga Lands biogeographic region in eastern Australia. This raises the possibility that the region is acting as a carbon sink. Vegetation boundaries were precisely positioned from rail survey plans dating from 1895 to 1900. This baseline was compared with the position of boundaries on 1952 aerial photography and 2010 Google Earth imagery. The conversion of forest to non-forest by mechanical clearing was also mapped from satellite imagery. There was no consistent trend in the direction of boundary movement for mulga (Acacia aneura F.Muell. ex Benth.), gidgee (Acacia cambagei R.T. Baker) forest or miscellaneous other forest types. The stability of the boundaries, despite the transition from aboriginal management to rangeland pastoralism, contrasts with dramatic declines in tree cover resulting from mechanical clearing. Mapping of forest cover from satellite imagery reveals that conversion of forest to non-forest has reduced mulga forest to 74%, gidgee forest to 30% and miscellaneous forest types to 82% of their original area. Annual clearing rates for the period between 1997 and 2005 were 0.83, 0.95 and 0.43% for those forest types, respectively. Clearing has declined substantially in the period 2005–09 since the advent of recent regulations in Queensland. The area remains a source of carbon emissions but this situation may reverse if restoration of mulga dry forest becomes an attractive land use with an emerging carbon market.

The relative impacts of grazing, fire and invasion by buffel grass (Cenchrus ciliaris) on the floristic composition of a rangeland savanna ecosystem

The relative impacts of grazing, fire and invasion by buffel grass (Cenchrus ciliaris) on floristic diversity and composition were evaluated for a Eucalyptus savanna ecosystem used for rangeland pastoralism in north-eastern Australia. Floristic data from a 10-year fire and livestock grazing experiment spanning periods of drought and above-average rainfall and multi-scaled data from varying levels of invasion by buffel grass were analysed. These original data were supplemented by the results of other studies. Light grazing by cattle had no discernible impacts on plant diversity and composition and burning resulted in a short-term pulse of annual forb abundance. Minor variations in edaphic properties had a substantial influence on floristic composition. Large perennial grasses increased in abundance with rainfall and annual forbs were abundant after rainfall events during drought. Species richness was diminished substantially at scales up to 1000 m2 by buffel grass and native perennial grasses showed the greatest declines. Land clearing, which facilitates invasion by buffel grass, has been greatly reduced by legislative controls but after nearly half of the savanna ecosystem has been cleared. The study suggests that livestock grazing with light to moderate stocking rates and burning are compatible with the conservation of floristic diversity in savannas but the invasion of buffel grass will continue to diminish diversity and represents a threat for the future. Land clearing exacerbates the spread of buffel grass and the control of this practice is an important contribution to the conservation of savannas.

Future changes in climatic water balance determine potential for transformational shifts in Australian fire regimes

Most studies of climate change effects on fire regimes assume a gradual reorganization of pyrogeographic patterns and have not considered the potential for transformational changes in the climate-vegetation-fire relationships underlying continental-scale fire regimes. Here, we model current fire activity levels in Australia as a function of mean annual actual evapotranspiration (E) and potential evapotranspiration (E 0), as proxies for fuel productivity and fuel drying potential. We distinguish two domains in

Impacts of tree invasion on floristic composition of subtropical grasslands on the Bunya Mountains, Australia

E,{E}_{0}

Origins of a morphological cline between Eucalyptus melanophloia and Eucalyptus whitei

space according to the dominant constraint on fire activity being either fuel productivity (PL-type fire) or fuel dryness (DL-type fire) and show that the affinity to these domains is related to fuel type. We propose to assess the potential for transformational shifts in fire type from the difference in the affinity to either domain under a baseline climate and projected future climate. Under the projected climate changes potential for a transformational shift from DL- to PL-type fire was predicted for mesic savanna woodland in the north and for eucalypt forests in coastal areas of the south–west and along the Continental Divide in the south–east of the continent. Potential for a shift from PL- to DL-type fire was predicted for a narrow zone of eucalypt savanna woodland in the north–east.

Growth of Eucalyptus tetrodonta seedlings on savanna and monsoon rainforest soils in the Australian monsoon tropics

The effect of ongoing forest invasion on floristic composition of subtropical montane grasslands was considered by examining vascular plant species frequencies across 13 adjoining areas of grassland, invaded grassland (eucalypt forest 50 years old) on the Bunya Mountains in subtropical eastern Australia. Tree invasion of grasslands over the last 50 years has had substantial facilitative or antagonistic net impacts on populations of many plant species. Increases in species frequency, indicating net facilitation, generally appear to occur earlier in forest development than do decreases in frequency, indicative of net antagonism. Although more than 20% of the flora showed substantial association with either grassland or forest, the dominant ground-stratum species in each habitat were quite similar and very few grassland species were not recorded in grassy forests. Forb species composition appears to change more rapidly after tree invasion than grass species composition. Relatively few forbs preferred forest to grassland, whereas shrubs, trees or lianes were substantially more frequent in forests. Replacement of grasslands by grassy forests would reduce landscape diversity and impact on other values in the Bunya Mountains. However, this study suggests that most, if not all, vascular plants that currently occur on the grasslands will persist in the area provided the grassy character of the eucalypt forests is maintained.

Relationships between fire severity and recruitment in arid grassland dominated by the obligate-seeding soft spinifex (Triodia pungens)

Most theories to explain the origin and maintenance of clines in Eucalyptus are based on a morphological classification system. The true relationships between putative species along clines require detailed investigation of phylogenetic relationships. A cline between Eucalyptus melanophloia and E. whitei was examined using morphological and molecular analyses to determine whether genetic structuring in nuclear and chloroplast DNA along the cline could be explained by secondary contact between independent evolutionary lineages, or whether the cline represents a single species that has undergone primary differentiation. Morphological analysis showed phenotypic variation distributed continuously across the cline and that seedlings bred true to parental type. Microsatellite analysis indicated that there was little genetic structuring across the cline, and low levels of population differentiation. This result was further reinforced by analysis of the cpDNA. The phylogeographic distribution of cpDNA haplotypes is likely to have resulted from restricted seed-mediated gene flow with isolation by distance. A cogent explanation for the cline is that it has arisen by selection on leaf types promoted by a gradient in precipitation with the short-broad, subsessile leaves of E. melanophloia favoured under higher rainfall and the long, narrow, petiolate leaves of E. whitei favoured in arid environments.

Indigenous Use of Spinifex Resin for Hafting in North-Eastern Australia

A nursery experiment revealed that the growth of Eucalyptus tetrodonta seedlings is significantly inhibited by unsterilised monsoon rainforest surface soil, and that this inhibition can not be eliminated by the addition of fertiliser. This result is in marked contrast to similar previously published experiments performed on two rainforest tree seedlings. (Bombax ceiba and Sterculia quadrifida) and Eucalyptus nesophila. The results of this study suggest that the observed high densities of E. tetrodonta seedlings and saplings on a site formerly occupied by monsoon rainforest on Elcho Island could only have established once the rainforest soil biota had been killed. One possible cause of soil sterilisation is wildfire.