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Lars A Brudvig - One of the best experts on this subject based on the ideXlab platform.
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understory plant communities and the functional distinction between Savanna trees forest trees and pines
Ecology, 2013Co-Authors: Joseph W Veldman, Brett W Mattingly, Lars A BrudvigAbstract:Although Savanna trees and forest trees are thought to represent distinct functional groups with different effects on ecosystem processes, few empirical studies have examined these effects. In particular, it remains unclear if Savanna and forest trees differ in their ability to coexist with understory plants, which comprise the majority of plant diversity in most Savannas. We used structural equation modeling (SEM) and data from 157 sites across three locations in the southeastern United States to understand the effects of broadleaf Savanna trees, broadleaf forest trees, and pine trees on Savanna understory plant communities. After accounting for underlying gradients in fire frequency and soil moisture, abundances (i.e., basal area and stem density) of forest trees and pines, but not Savanna trees, were negatively correlated with the cover and density (i.e., local-scale species richness) of C4 graminoid species, a defining Savanna understory functional group that is linked to ecosystem flammability. In analyses of the full understory community, abundances of trees from all functional groups were negatively correlated with species density and cover. For both the C4 and full communities, fire frequency promoted understory plants directly, and indirectly by limiting forest tree abundance. There was little indirect influence of fire on the understory mediated through Savanna trees and pines, which are more fire tolerant than forest trees. We conclude that tree functional identity is an important factor that influences overstory tree relationships with Savanna understory plant communities. In particular, distinct relationships between trees and C4 graminoids have implications for grass-tree coexistence and vegetation-fire feedbacks that maintain Savanna environments and their associated understory plant diversity.
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influences of woody encroachment and restoration thinning on overstory Savanna oak tree growth rates
Forest Ecology and Management, 2011Co-Authors: Lars A Brudvig, Holly M Blunck, Heidi Asbjornsen, Vilma S Mateosremigio, Stephanie A Wagner, Jesse RandallAbstract:Abstract Midwestern Savannas historically covered >10 M ha in central North America, but are now rare due to agricultural conversion and anthropogenic modifications to disturbance regimes – particularly fire suppression. Throughout this range, Midwestern Savannas are characterized by scattered overstory trees; however, with fire suppression, these systems are invaded by non-Savanna trees. Restoration of encroached Savannas involves removal of invading trees, yet little is known about the impacts of encroachment or encroachment removal on the relict Savanna overstory trees, which define these systems. Here, we use tree ring analysis to investigate Savanna tree growth rates in encroached, non-encroached, and experimentally restored Midwestern oak Savannas in central Iowa. We found that woody encroachment led to pronounced declines in growth rate (ring width) of relict overstory white oak ( Quercus alba ), relative to Q. alba trees in competition-free, open-grown conditions, or in an encroachment-free remnant woodland. To further understand effects of encroachment removal on relict Q. alba Savanna trees, we conducted a large-scale restoration experiment, where encroaching trees were mechanically removed from four encroached Savannas, with an additional four Savannas retained as encroached controls. Restoration led to elevated tree growth rates, with these changes generally persistent through 7 years post-restoration (2003–2009). Over the course of this post-restoration study period, ring width, basal area increment, and relative basal area increased by 49%, 59%, and 55%, respectively, in trees from restored sites, relative to trees from encroached, control sites. These results suggest that woody encroachment has strong influence on overstory Savanna trees, through increased competitive dynamics; however, woody encroachment removal may help to restore relict Savanna tree growth rates, even after prolonged periods of encroachment (>40 years). To restore the oak Savannas at our sites, and perhaps elsewhere, we advocate a three step process: (1) mechanical woody encroachment removal, (2) maintenance of the encroachment-free state through prescribed fire, and (3) promotion of a diverse understory layer, characteristic of oak Savanna in our region. While promoting oak regeneration will be important for the long-term maintenance of these sites as oak Savanna, relict Savanna trees appear responsive to restoration and should maintain overstory conditions through the near-term.
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the confluence of landscape context and site level management in determining midwestern Savanna and woodland breeding bird communities
Forest Ecology and Management, 2010Co-Authors: Catherine M Mabry, Lars A Brudvig, Ryan C AtwellAbstract:Species distributions are determined by complex interplays between multi-scale factors. Conservation management, however, often occurs at a single scale of the site level. This is true for bird communities of restored Savannas and mixed woodlands in the central U.S. In this region, many historic open-canopy oak Savanna habitats have become closed canopy mixed woodlands due to loss of landscape-scale disturbance from fire and grazing. Site-level management efforts return some mixed woodland habitats back to Savanna through fire and mechanical thinning. Savanna and woodland historically formed complex mosaic landscapes at the ecotone between prairies and Eastern deciduous forests and now exist within landscapes that vary in amount of open (e.g., perennial grassland and row crop agriculture) and woodland habitat. To understand the interplay between site and landscape level factors in Savanna restoration, we sampled the breeding bird community in four combinations of site and landscape: restored Savanna in open landscapes, restored Savanna in woodland landscapes, and closed canopy woodland in both landscapes. We found that the outcome of site-level Savanna restoration depended on the surrounding landscape. Compared to other treatment types, restored Savannas in open landscapes supported a distinctive bird community characterized by high species richness, bird abundance, and percent of ground feeders, shrub nesters, and edge species. Both Savanna and woodland sites in the open landscape had a higher percent of species of conservation concern, while at both site and landscape levels, woodland was associated with a higher percent of area sensitive species and habitat specialists. Our results suggest Savanna restoration efforts should focus on sites that exist either in open country or on edges where closed canopy forest meets open country. This strategy would combine site and landscape level benefits of Savanna restoration for avian diversity, while also preserving the conservation benefits of large tracts of intact forest.
Guillermo Goldstein - One of the best experts on this subject based on the ideXlab platform.
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effects of fire on seedling diversity and plant reproduction sexual vs vegetative in neotropical Savannas differing in tree density
Biotropica, 2014Co-Authors: Ana Salazar, Guillermo GoldsteinAbstract:Little is known about the effects of fire on the structure and species composition of Neotropical Savanna seedling communities. Such effects are critical for predicting long-term changes in plant distribution patterns in these ecosystems. We quantified richness and density of seedlings within 144 plots of 1 m2 located along a topographic gradient in long-unburned (fire protected since 1983) and recently burned (September 2005) Savannas in Brazil. These Savannas differ in tree density and canopy cover. Sites along the gradient, however, did not differ in species composition prior to the fire. In recently burned Savannas we also evaluated the contribution of vegetative reproduction relative to sexual reproduction by quantifying richness and density of root suckers. Finally, we tested seed tolerance to pulses of high temperatures-similar to those occurring during fires on the soil surface and below-of five dominant Savanna tree species. Seedlings were more abundant and diverse in unburned than in burned Savannas. Seedling species composition differed among unburned and burned Savannas probably reflecting early differences in root: shoot biomass allocation patterns. In recently burned Savannas, root suckers were more abundant and diverse than seedlings. Relatively long exposures (>10 min) of temperatures of 90 °C reduced seed germination in all studied species suggesting a negative effect of fire on germination of seeds located at or aboveground level. Because vegetative reproduction contributes more than sexual reproduction in burned environments, frequent fires are likely to cause major shifts in species composition of Neotropical Savanna plant communities, favoring clonally produced recruits along tree density/topographic gradients. © 2014 The Association for Tropical Biology and Conservation.
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differential seedling establishment of woody plants along a tree density gradient in neotropical Savannas
Journal of Ecology, 2012Co-Authors: Ana Salazar, Guillermo Goldstein, Augusto C Franco, Fernando MiralleswilhelmAbstract:Summary 1. Seedling dynamics are crucial for understanding spatial plant distribution patterns, yet little is known about seedling establishment in Neotropical Savannas because empirical studies at the community level are scarce. 2. Over 2 years, we studied the recruitment and survival of an initial seedling assemblage and three cohorts of recruits of woody plants within 216 plots of 1 m 2 located along a tree density gradient in the Savannas of central Brazil. These Savannas differ in tree density and canopy cover, from closed (high canopy cover) to open Savannas (low canopy cover), and are located along shallow topographic gradients. 3. We measured community-wide seedling limitation (i.e. proportion of 1-m 2 plots without seedlings of any woody species), photosynthetic photon flux density, litter cover, soil moisture and soil nutrients in each Savanna type. Because closed Savannas had lower PPFD and higher leaf litter cover than open Savannas, we evaluated the effects of light level and litter cover on seedling emergence of nine dominant Savanna woody species under controlled conditions in a glasshouse. 4. Density, recruitment and survival of seedlings decreased over time because of mortality in all Savanna types, but they were consistently higher in closed than in open Savannas. Community-wide seedling limitation was significantly lower in closed (0.16 ± 0.03) than in open (0.30 ± 0.05) Savannas. 5. In the glasshouse, high litter cover and very low light levels reduced seedling emergence of most species, suggesting an adaptation to delay seed germination until the wet season when soil water availability is high and leaf litter rapidly decomposes. 6. Synthesis: In Neotropical Savannas, tree canopy cover facilitates seedling establishment of woody species by reducing stressful environmental conditions. In particular, low irradiance and high litter cover in closed Savannas enhance the recruitment and survival of woody seedlings relative to open Savannas by reducing soil water deficits and increasing nutrient availability in the upper soil layers. The higher seedling limitation of tree species in open than in closed Savannas contributes to maintain relatively different balances between trees and herbaceous plants along topographic gradients in Neotropical Savannas and helps to explain spatial distribution patterns of woody species in these ecosystems.
William J. Bond - One of the best experts on this subject based on the ideXlab platform.
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the Savanna grassland treeline why don t Savanna trees occur in upland grasslands
Journal of Ecology, 2012Co-Authors: Julia L. Wakeling, Michael D. Cramer, William J. BondAbstract:Summary 1. Treeless grasslands with climates that can support tree growth are common in upland regions around the world. In South Africa, the upland grasslands are adjacent to lowland Savannas in many areas, with an abrupt boundary between them that could be termed a Savanna-grassland ‘treeline’. Both systems are dominated by C4 grasses and burn regularly, yet fire-tolerant Savanna trees do not survive in the grasslands. The upland grasslands experience lower temperatures throughout the year and frost in winter, compared with the warmer Savannas. 2. We tested whether frost in the dormant season or slow growth in the growing season in conjunction with frequent fires may explain the tree-less state of grasslands. We measured Acacia seedling growth for a year in a transplant experiment at ten sites across an altitudinal gradient (42–1704 m) from Savannas to grasslands. The effect of frost on seedlings was scored during the following winter. 3. Across all species, height (t = −6.04, d.f. = 471, P < 0.001), biomass (t = −4.56, d.f. = 228, P < 0.001) and height increase (t = −3.40, d.f. = 471, P < 0.001) were significantly higher at Savanna sites. As the plants were irrigated and initially supplied with nutrients, the main factor affecting growth was likely to be growing season temperature. 4. Saplings that experience slow growing conditions will take longer to reach a height above the flame zone and will therefore have a lower probability of reaching adult tree height and surviving fires. Day length may be the most important cue for the end of the growing season in Savanna trees, as growth decreased with shortening day length in February–March while temperatures were still high and plants were not water limited. 5. Synthesis. Savanna trees grew more slowly in cooler upland grassland sites compared with lower elevation warm Savanna sites and, under frequent fire regimes, would be prevented from reaching maturity. This may be true globally for similar grasslands where tree growth can occur and could partly explain the lack of trees in grasslands.
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increased tree densities in south african Savannas 50 years of data suggests co2 as a driver
Global Change Biology, 2012Co-Authors: Robert Buitenwerf, William J. Bond, N Stevens, W.s.w. TrollopeAbstract:For the past century, woody plants have increased in grasslands and Savannas worldwide. Woody encroachment may significantly alter ecosystem functioning including fire regimes, herbivore carrying capacity, biodiversity and carbon storage capacity. Traditionally, increases in woody cover and density have been ascribed to changes in the disturbance regime (fire and herbivores) or rainfall. Increased atmospheric CO2 concentrations may also contribute, by increasing growth rates of trees relative to grasses. This hypothesis is still heavily debated because usually potential CO2 effects are confounded by changes in land use (disturbance regime). Here we analyse changes in woody density in fire experiments at three sites in South African Savannas where the disturbance regime (fire and herbivores) was kept constant for 30 and 50 years. If global drivers had significant effects on woody plants, we would expect significant increases in tree densities and biomass over time under the constant disturbance regime. Woody density remained constant in a semiarid Savanna but tripled in a mesic Savanna between the 1970s and 1990s. At the third site, a semiarid Savanna near the southern limits of the biome, tree density doubled from the mid 1990s to 2010. Interpretation of the causes is confounded by population recovery after clearing, but aerial photograph analysis on adjacent non-cleared areas showed an accompanying 48% increase in woody cover. Increased CO2 concentrations are consistent with increased woody density while other global drivers (rainfall) remained constant over the duration of the experiments. The absence of a response in one semiarid Savanna could be explained by a smaller carbon sink capacity of the dominant species, which would therefore benefit less from increased CO2. Understanding how Savannas and grasslands respond to increased CO2 and identifying the causes of woody encroachment are essential for the successful management of these systems.
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Juggling carbon: Allocation patterns of a dominant tree in a fire-prone Savanna
Oecologia, 2009Co-Authors: Alexander Ernest Noel Schutz, William J. Bond, Michael D. CramerAbstract:In frequently burnt mesic Savannas, trees can get trapped into a cycle of surviving fire-induced stem death (i.e. topkill) by resprouting, only to be topkilled again a year or two later. The ability of Savanna saplings to resprout repeatedly after fire is a key component of recent models of tree-grass coexistence in Savannas. This study investigated the carbon allocation and biomass partitioning patterns that enable a dominant Savanna tree, Acacia karroo, to survive frequent and repeated topkill. Root starch depletion and replenishment, foliage recovery and photosynthesis of burnt and unburnt plants were compared over the first year after a burn. The concentration of starch in the roots of the burnt plants (0.08 +/- 0.01 g g(-1)) was half that of the unburnt plant (0.16 +/- 0.01 g g(-1)) at the end of the first growing season after topkill. However, root starch reserves of the burnt plants were replenished over the dry season and matched that of unburnt plants within 1 year after topkill. The leaf area of resprouting plants recovered to match that of unburnt plants within 4-5 months after topkill. Shoot growth of resprouting plants was restricted to the first few months of the wet season, whereas photosynthetic rates remained high into the dry season, allowing replenishment of root starch reserves. (14)C labeling showed that reserves were initially utilized for shoot growth after topkill. The rapid foliage recovery and the replenishment of reserves within a single year after topkill implies that A. karroo is well adapted to survive recurrent topkill and is poised to take advantage of unusually long fire-free intervals to grow into adults. This paper provides some of the first empirical evidence to explain how Savanna trees in frequently burnt Savannas are able to withstand frequent burning as juveniles and survive to become adults.
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effects of four decades of fire manipulation on woody vegetation structure in Savanna
Ecology, 2007Co-Authors: Steven I. Higgins, William J. Bond, Edmund C February, Andries Bronn, Douglas I W Eustonbrown, Beukes Enslin, Navashni Govender, Louise Rademan, Sean Oregan, A L F PotgieterAbstract:The amount of carbon stored in Savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. We analyzed the structural response of woody plants to long-term experimental burning in Savannas. The experiment uses a randomized block design to examine fire exclusion and the season and frequency of burn in 192 7-ha experimental plots located in four different Savanna ecosystems. Although previous studies would lead us to expect tree density to respond to the fire regime, our results, obtained from four different Savanna ecosystems, suggest that the density of woody individuals was unresponsive to fire. The relative dominance of small trees was, however, highly responsive to fire regime. The observed shift in the structure of tree populations has potentially large impacts on the carbon balance. However, the response of tree biomass to fire of the different Savannas studied were different, making it difficult to generalize about the extent to which fire can be used to manipulate carbon sequestration in Savannas. This study provides evidence that Savannas are demographically resilient to fire, but structurally responsive.
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growing tall vs growing wide tree architecture and allometry of acacia karroo in forest Savanna and arid environments
Oikos, 2003Co-Authors: Sally Archibald, William J. BondAbstract:In order to investigate how environmental factors other than light availability affect tree architecture, differences in branching architecture and allometry were analysed in populations of Acacia karroo Hein. from three different environments in South Africa: forests, Savannas and arid-shrublands. Factors such as fire and herbivory have a large effect on tree life history in certain environments and are likely to have selected for trees that have different architectures from those of forest trees, whose major limitation is light assimilation. Significant differences were found in stem architecture and branching architecture between trees in each environment. Compared with forest trees, trees in Savannas had an elongated growth form with small canopy and leaf areas, and tall, thin, unbranched trunks. Trees in arid areas showed opposite trends with wider canopies, and increased lateral branching. Savanna trees had significantly smaller spines than trees in other environments, and both forest and Savanna trees showed delayed reproduction. These differences are probably related to a trade-off between an architecture geared towards rapid height-gain and one promoting lateral spread, and can be explained with reference to the different selective pressures in each environment. In forests, vertical and horizontal growth are both important. However, in Savannas there is a great pressure for rapid vertical growth to escape fires, while in arid areas a defensive, lateral growth form is selected for. Savanna trees and arid karoo trees have evolved architectures that are more extreme vertically and laterally than the range of architectures displayed in a forest community.
Jeremy Russellsmith - One of the best experts on this subject based on the ideXlab platform.
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fire regimes and woody biomass dynamics in australian Savannas
Journal of Biogeography, 2014Co-Authors: Brett P Murphy, Jeremy Russellsmith, Caroline E R Lehmann, Michael J LawesAbstract:Aim Many tropical Savannas are undergoing a trend of increasing woody biomass, or ‘woody thickening’. Management to reduce fire frequency and intensity in Savannas could substantially increase the amount of carbon stored in woody biomass. We addressed two questions: (1) are northern Australian Savannas thickening; and (2) to what extent, and by what demographic processes, does fire affect woody biomass accumulation? Location Three large national parks, covering 24,000 km2, in monsoonal northern Australia. Methods We examined changes in woody biomass carbon stocks – inferred from tree basal area and the density of woody understorey plants – over a 10-year period in 136 Savanna monitoring plots. We statistically assessed these changes in relation to fire frequency and severity. We used a meta-analysis to identify general trends in woody cover in Australian Savannas over the last half-century. Results Woody biomass carbon stocks were relatively stable across the three national parks, but rates of change were statistically indistinguishable from earlier findings of a weak thickening trend. Change was negatively correlated with fire frequency, particularly the frequency of severe fires. High frequencies of severe fires decreased rates of accumulation of biomass by existing trees (through reductions in tree growth and death of individual stems), rather than whole-tree mortality and suppression of recruitment. However, across northern Australia, our meta-analysis identified a general, albeit weak, trend of woody thickening. Main conclusions The drivers of northern Australia's weak thickening trend are uncertain, but likely candidates include increasing atmospheric CO2 concentration and water availability, and pastoral intensification. We demonstrate that changes to fire management have the potential to either increase or decrease rates of woody thickening relative to any underlying trend. Understanding how Savanna fires affect woody biomass, and how fire effects are mediated by climate and CO2, are essential research priorities to predict the fate of Savannas.
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managing fire regimes in north australian Savannas applying aboriginal approaches to contemporary global problems
Frontiers in Ecology and the Environment, 2013Co-Authors: Jeremy Russellsmith, Andrew Edwards, Garry D Cook, P Cooke, Mitchell Lendrum, C P Meyer, Peter J WhiteheadAbstract:Savannas constitute the most fire-prone biome on Earth and annual emissions from Savanna-burning activities are a globally important source of greenhouse-gas (GHG) emissions. Here, we describe the application of a commercial fire-management program being implemented over 28 000 km2 of Savanna on Aboriginal lands in northern Australia. The project combines the reinstatement of Aboriginal traditional approaches to Savanna fire management – in particular a strategic, early dry-season burning program – with a recently developed emissions accounting methodology for Savanna burning. Over the first 7 years of implementation, the project has reduced emissions of accountable GHGs (methane, nitrous oxide) by 37.7%, relative to the pre-project 10-year emissions baseline. In addition, the project is delivering social, biodiversity, and long-term biomass sequestration benefits. This methodological approach may have considerable potential for application in other fire-prone Savanna settings.
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assessing the carbon sequestration potential of mesic Savannas in the northern territory australia approaches uncertainties and potential impacts of fire
Functional Plant Biology, 2004Co-Authors: Richard J Williams, Andrew Edwards, Garry D Cook, Jeremy Russellsmith, Xiaoyong ChenAbstract:Tropical Savannas cover a quarter of the Australian landmass and the biome represents a significant potential carbon sink. However, these Savannas are subject to frequent and extensive fire. Fire regimes are likely to affect the productivity and carbon sequestration potential of Savannas, through effects on both biomass and carbon emissions. The carbon sequestration potential has been estimated for some Savanna sites by quantifying carbon storage in biomass and soil pools, and the fluxes to these pools. Using different techniques, previous work in these Savannas has indicated that net ecosystem productivity [NEP, net primary productivity (NPP) less heterotrophic respiration] was about –3 t C ha–1 y–1 (i.e. a carbon sink). However, the impacts of fire were not accounted for in these calculations. Estimates of NEP have been combined with remotely-sensed estimates of area burnt and associated emissions for an extensive area of mesic Savanna in Arnhem Land, NT, Australia. Combining NEP estimates with precise fire data provides an estimate of net biome productivity (NBP), a production index that includes carbon loss through disturbance (fire), and is thus a more realistic indicator of sequestration rate from this biome. This preliminary analysis suggests that NBP is approximately –1 t C ha–1 y–1 (i.e. a carbon sink). A reduction in the annual area burnt is likely to increase the sink size. Uncertainties surrounding these estimates of NBP and the implications of these uncertainties for land management in these extensive landscapes are discussed.
Garry D Cook - One of the best experts on this subject based on the ideXlab platform.
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managing fire regimes in north australian Savannas applying aboriginal approaches to contemporary global problems
Frontiers in Ecology and the Environment, 2013Co-Authors: Jeremy Russellsmith, Andrew Edwards, Garry D Cook, P Cooke, Mitchell Lendrum, C P Meyer, Peter J WhiteheadAbstract:Savannas constitute the most fire-prone biome on Earth and annual emissions from Savanna-burning activities are a globally important source of greenhouse-gas (GHG) emissions. Here, we describe the application of a commercial fire-management program being implemented over 28 000 km2 of Savanna on Aboriginal lands in northern Australia. The project combines the reinstatement of Aboriginal traditional approaches to Savanna fire management – in particular a strategic, early dry-season burning program – with a recently developed emissions accounting methodology for Savanna burning. Over the first 7 years of implementation, the project has reduced emissions of accountable GHGs (methane, nitrous oxide) by 37.7%, relative to the pre-project 10-year emissions baseline. In addition, the project is delivering social, biodiversity, and long-term biomass sequestration benefits. This methodological approach may have considerable potential for application in other fire-prone Savanna settings.
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contributions of woody and herbaceous vegetation to tropical Savanna ecosystem productivity a quasi global estimate
Tree Physiology, 2008Co-Authors: J Lloyd, E M Veenendaal, Gloria Djagbletey, Garry D Cook, Michael I Bird, Lins Vellen, Antonio Miranda, Heloisa Sinatora Miranda, Graham D FarquharAbstract:To estimate the relative contributions of woody and herbaceous vegetation to Savanna productivity, we measured the (13)C/(12)C isotopic ratios of leaves from trees, shrubs, grasses and the surface soil carbon pool for 22 Savannas in Australia, Brazil and Ghana covering the full Savanna spectrum ranging from almost pure grassland to closed woodlands on all three continents. All trees and shrubs sampled were of the C(3) pathway and all grasses of the C(4) pathway with the exception of Echinolaena inflexa (Poir.) Chase, a common C(3) grass of the Brazilian cerrado. By comparing the carbon isotopic compositions of the plant and carbon pools, a simple model relating soil delta(13)C to the relative abundances of trees + shrubs (woody plants) and grasses was developed. The model suggests that the relative proportions of a Savanna ecosystem's total foliar projected cover attributable to grasses versus woody plants is a simple and reliable index of the relative contributions of grasses and woody plants to Savanna net productivity. Model calibrations against woody tree canopy cover made it possible to estimate the proportion of Savanna productivity in the major regions of the world attributable to trees + shrubs and grasses from ground-based observational maps of Savanna woodiness. Overall, it was estimated that 59% of the net primary productivity (N(p)) of tropical Savannas is attributable to C(4) grasses, but that this proportion varies significantly within and between regions. The C(4) grasses make their greatest relative contribution to Savanna N(p) in the Neotropics, whereas in African regions, a greater proportion of Savanna N(p) is attributable to woody plants. The relative contribution of C(4) grasses in Australian Savannas is intermediate between those in the Neotropics and Africa. These differences can be broadly ascribed to large scale differences in soil fertility and rainfall.
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assessing the carbon sequestration potential of mesic Savannas in the northern territory australia approaches uncertainties and potential impacts of fire
Functional Plant Biology, 2004Co-Authors: Richard J Williams, Andrew Edwards, Garry D Cook, Jeremy Russellsmith, Xiaoyong ChenAbstract:Tropical Savannas cover a quarter of the Australian landmass and the biome represents a significant potential carbon sink. However, these Savannas are subject to frequent and extensive fire. Fire regimes are likely to affect the productivity and carbon sequestration potential of Savannas, through effects on both biomass and carbon emissions. The carbon sequestration potential has been estimated for some Savanna sites by quantifying carbon storage in biomass and soil pools, and the fluxes to these pools. Using different techniques, previous work in these Savannas has indicated that net ecosystem productivity [NEP, net primary productivity (NPP) less heterotrophic respiration] was about –3 t C ha–1 y–1 (i.e. a carbon sink). However, the impacts of fire were not accounted for in these calculations. Estimates of NEP have been combined with remotely-sensed estimates of area burnt and associated emissions for an extensive area of mesic Savanna in Arnhem Land, NT, Australia. Combining NEP estimates with precise fire data provides an estimate of net biome productivity (NBP), a production index that includes carbon loss through disturbance (fire), and is thus a more realistic indicator of sequestration rate from this biome. This preliminary analysis suggests that NBP is approximately –1 t C ha–1 y–1 (i.e. a carbon sink). A reduction in the annual area burnt is likely to increase the sink size. Uncertainties surrounding these estimates of NBP and the implications of these uncertainties for land management in these extensive landscapes are discussed.
