20 results on '"Lehmann, Caroline"'
Search Results
2. Contrasting architecture of key African and Australian savanna tree taxa drives intercontinental structural divergence
- Author
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Moncrieff, Glenn R., Lehmann, Caroline E. R., Schnitzler, Jan, Gambiza, James, Hiernaux, Pierre, Ryan, Casey M., Shackleton, Charlie M., Williams, Richard J., and Higgins, Steven I.
- Published
- 2014
3. Savanna Vegetation-Fire-Climate Relationships Differ Among Continents
- Author
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Lehmann, Caroline E. R., Anderson, T. Michael, Sankaran, Mahesh, Higgins, Steven I., Archibald, Sally, Hoffmann, William A., Hanan, Niall P., Williams, Richard J., Fensham, Roderick J., Felfili, Jeanine, Hutley, Lindsay B., Ratnam, Jayashree, San Jose, Jose, Montes, Ruben, Franklin, Don, Russell-Smith, Jeremy, Ryan, Casey M., Durigan, Giselda, Hiernaux, Pierre, Haidar, Ricardo, Bowman, David M. J. S., and Bond, William J.
- Published
- 2014
4. Fire regimes and woody biomass dynamics in Australian savannas
- Author
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Murphy, Brett P., Lehmann, Caroline E. R., Russell-Smith, Jeremy, and Lawes, Michael J.
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- 2014
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5. When is a 'forest' a savanna, and why does it matter?
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Ratnam, Jayashree, Bond, William J., Fensham, Rod J., Hoffmann, William A., Archibald, Sally, Lehmann, Caroline E. R., Anderson, Michael T., Higgins, Steven I., and Sankaran, Mahesh
- Published
- 2011
- Full Text
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6. Deciphering the distribution of the savanna biome
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Lehmann, Caroline E. R., Archibald, Sally A., Hoffmann, William A., and Bond, William J.
- Published
- 2011
7. Fire Controls Population Structure in Four Dominant Tree Species in a Tropical Savanna
- Author
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Lehmann, Caroline E. R., Prior, Lynda D., and Bowman, David M. J. S.
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- 2009
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8. Which of These Continents Is Not Like the Other? Comparisons of Tropical Savanna Systems: Key Questions and Challenges
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Lehmann, Caroline E. R., Ratnam, Jayashree, and Hutley, Lindsay B.
- Published
- 2009
9. Spatio-Temporal Trends in Tree Cover of a Tropical Mesic Savanna Are Driven by Landscape Disturbance
- Author
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Lehmann, Caroline E. R., Prior, Lynda D., Williams, Richard J., and Bowman, David M. J. S.
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- 2008
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10. Savanna Responses to Feral Buffalo in Kakadu National Park, Australia
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Petty, Aaron M., Werner, Patricia A., Lehmann, Caroline E. R., Riley, Jan E., Banfai, Daniel S., and Elliott, Louis P.
- Published
- 2007
11. Drought and fire determine juvenile and adult woody diversity and dominance in a semi‐arid African savanna.
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Trotter, Felix D., Lehmann, Caroline E. R., Donaldson, Jason E., Mangena, Happy E., Parr, Catherine L., and Archibald, Sally
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DROUGHTS ,DROUGHT management ,SAVANNAS ,FIRE management ,SPECIES diversity ,WOODY plants ,ADULTS ,PLANT communities - Abstract
The aim of this study was to understand how communities of adult and juvenile (seedlings and saplings) woody plants were impacted by fire and the 2014–2016 El Niño drought in Kruger National Park, South Africa. We used a landscape‐scale fire experiment spanning 2013–2019 in a semi‐arid savanna in the central west of Kruger National Park (mean annual precipitation, 543 mm). Adult and juvenile woody species composition were recorded during and after the drought in 40 plots that experienced a mix of no fire, moderate fire, and frequent fire treatments. Using multivariate modeling, we related community composition in juvenile and adult woody plants to year of sampling and the experimental fire treatments. Post‐drought, there was significant adult woody plant top‐kill, especially in dominant species Dichrostachys cinerea (81% reduction in abundance), Acacia nigrescens (30%), and Combretum apiculatum (19%), but there was no significant change in adult species richness. Two years post‐drought, abundance of all juveniles decreased by 35%, and species richness increased in juveniles in both the frequent fire (7%) and no fire treatments (32%). Counter‐intuitively, the El Niño drought increased species richness of the woody plant community due to the recruitment of new species as juveniles, a potential lasting impact on diversity, and where different fire regimes were associated with differences in community composition. Drought events in semi‐arid savannas could drive temporal dynamics in species richness and composition in previously unrecognized ways. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
12. Shade alters savanna grass layer structure and function along a gradient of canopy cover.
- Author
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Pilon, Natashi A. L., Durigan, Giselda, Rickenback, Jess, Pennington, R. Toby, Dexter, Kyle G., Hoffmann, William A., Abreu, Rodolfo C. R., Lehmann, Caroline E. R., and Pugnaire, Francisco
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LEAF area index ,SAVANNAS ,FOREST density ,UNDERGROUND storage ,WOODY plants ,GRASSES ,LEAF physiology - Abstract
Aim: In savannas, a grass‐dominated ground layer is key to ecosystem function via grass–fire feedbacks that maintain open ecosystems. With woody encroachment, tree density increases, thereby decreasing light in the ground layer and potentially altering ecosystem function. We investigated how light availability can filter individual grass species distributions and whether different functional traits are associated with response to a shade gradient in a landscape experiencing woody encroachment. Location: Savanna–forest mosaic in the Cerrado domain, southeastern Brazil. Methods: Along an encroachment gradient of increasing tree leaf area index (LAI) and shade, we determined how changing light availability alters grass diversity and ground layer structure relative to grass cover and grass functional traits (photosynthetic pathway, underground storage organs, bud protection and traits related to grass shape, size and leaf dimensions). Results: Increasing shade led to a decrease in grass cover and grass species richness, and also compositional and functional changes. We found that where tree LAI reached 1, grass cover was reduced by 50% and species richness by 30%. While C4 grass species abundances decreased with increasing shade, the opposite pattern was true for C3 grasses. There were only small differences in light preferences among C4 subtypes, with phosphoenolpyruvate carboxykinase (PCK) species tolerating slightly more shaded conditions. Persistence of some C4 species under more shaded conditions was possible, likely due to an ability to store starch reserves via underground storage organs. Conclusions: Woody encroachment changes diversity and structure of the grassy layer that is critical to the functioning of savanna ecosystems, highlighting the dependence of the diverse grass layer on open and sunny conditions. Our results suggest a threshold of tree cover close to LAI ≈ 1 as being critical to cerrado grassy layer conservation. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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13. Fire and grazing determined grasslands of central Madagascar represent ancient assemblages.
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Solofondranohatra, Cédrique L., Vorontsova, Maria S., Hempson, Gareth P., Hackel, Jan, Cable, Stuart, Vololoniaina, Jeannoda, and Lehmann, Caroline E. R.
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GRASSLANDS ,SAVANNAS ,FIRE ecology ,BIOTIC communities ,ECOLOGICAL disturbances ,FIRE ,CATTLE - Abstract
The ecology of Madagascar's grasslands is under-investigated and the dearth of ecological understanding of how disturbance by fire and grazing shapes these grasslands stems from a perception that disturbance shaped Malagasy grasslands only after human arrival. However, worldwide, fire and grazing shape tropical grasslands over ecological and evolutionary timescales, and it is curious Madagascar should be a global anomaly. We examined the functional and community ecology of Madagascar's grasslands across 71 communities in the Central Highlands. Combining multivariate abundance models of community composition and clustering of grass functional traits, we identified distinct grass assemblages each shaped by fire or grazing. The fire-maintained assemblage is primarily composed of tall caespitose species with narrow leaves and low bulk density. By contrast, the grazer-maintained assemblage is characterized by mat-forming, high bulk density grasses with wide leaves. Within each assemblage, levels of endemism, diversity and grass ages support these as ancient assemblages. Grazer-dependent grasses can only have co-evolved with a now-extinct megafauna. Ironically, the human introduction of cattle probably introduced a megafaunal substitute facilitating modern day persistence of a grazer-maintained grass assemblage in an otherwise defaunated landscape, where these landscapes now support the livelihoods of millions of people. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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14. Woody plant encroachment intensifies under climate change across tundra and savanna biomes.
- Author
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García Criado, Mariana, Myers‐Smith, Isla H., Bjorkman, Anne D., Lehmann, Caroline E. R., Stevens, Nicola, and Josée Fortin, Marie
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WOODY plants ,CLIMATE change ,SAVANNAS ,BIOMES ,TUNDRAS ,SHRUBLANDS - Abstract
Aim: Biomes worldwide are shifting with global change. Biomes whose extents are limited by temperature or precipitation, such as the tundra and savanna, may be particularly strongly affected by climate change. While woody plant encroachment is prevalent across both biomes, its relationship to temperature and precipitation change remains unknown. Here, we quantify the degree to which woody encroachment is related to climate change and identify its main associated drivers. Location: Tundra and savanna biomes. Time period: 1992 ± 20.27–2010 ± 5.62 (mean ± SD). 1876–2016 (range). Major taxa studied: Woody plants (shrubs and trees). Methods: We compiled a dataset comprising 1,089 records from 899 sites of woody plant cover over time and attributed drivers of woody cover change across these two biomes. We calculated cover change in each biome and assessed the degree to which cover change corresponds to concurrent temperature and precipitation changes using multiple climate metrics. Finally, we conducted a quantitative literature review of the relative importance of attributed drivers of woody cover change. Results: Woody encroachment was widespread geographically and across climate gradients. Rates of woody cover change (positive or negative) were 1.8 times lower in the tundra than in the savanna (1.8 vs. 3.2%), while rates of woody cover increase (i.e., encroachment) were c. 1.7 times lower in the tundra compared with the savanna (3.7 vs. 6.3% per decade). In the tundra, magnitudes of woody cover change did not correspond to climate, while in the savanna, greater cover change corresponded with increases in precipitation. We found higher rates of woody cover change in wetter versus drier sites with warming in the tundra biome, and higher rates of woody cover change in drier versus wetter sites with increasing precipitation in the savanna. However, faster rates of woody cover change were not associated with more rapid rates of climate change across sites, except for maximum precipitation in the savanna. Main conclusions: Woody encroachment was positively related to warming in the tundra and increased rainfall in the savanna. However, cover change rates were not predicted by rates of climate change, which can be partially explained by climate interactions in both biomes. Additional likely influences include site‐level factors, time‐lags, plant‐specific responses, and land use and other non‐climate drivers. Our findings highlight the complex nature of climate change impacts in biomes limited by seasonality, which should be accounted for to realistically estimate future responses across open biomes under global change scenarios. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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15. Human impacts in African savannas are mediated by plant functional traits.
- Author
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Osborne, Colin P., Charles‐Dominique, Tristan, Stevens, Nicola, Midgley, Guy, Bond, William J., and Lehmann, Caroline E. R.
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ANTHROPOGENIC effects on nature ,SAVANNAS ,FUNCTIONAL analysis ,HERBIVORES ,WOODY plants - Abstract
Summary: Tropical savannas have a ground cover dominated by C
4 grasses, with fire and herbivory constraining woody cover below a rainfall‐based potential. The savanna biome covers 50% of the African continent, encompassing diverse ecosystems that include densely wooded Miombo woodlands and Serengeti grasslands with scattered trees. African savannas provide water, grazing and browsing, food and fuel for tens of millions of people, and have a unique biodiversity that supports wildlife tourism. However, human impacts are causing widespread and accelerating degradation of savannas. The primary threats are land cover‐change and transformation, landscape fragmentation that disrupts herbivore communities and fire regimes, climate change and rising atmospheric CO2 . The interactions among these threats are poorly understood, with unknown consequences for ecosystem health and human livelihoods. We argue that the unique combinations of plant functional traits characterizing the major floristic assemblages of African savannas make them differentially susceptible and resilient to anthropogenic drivers of ecosystem change. Research must address how this functional diversity among African savannas differentially influences their vulnerability to global change and elucidate the mechanisms responsible. This knowledge will permit appropriate management strategies to be developed to maintain ecosystem integrity, biodiversity and livelihoods. [ABSTRACT FROM AUTHOR]- Published
- 2018
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16. Biomass burning fuel consumption dynamics in the tropics and subtropics assessed from satellite.
- Author
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Andela, Niels, van der Werf, Guido R., Kaiser, Johannes W., van Leeuwen, Thijs T., Wooster, Martin J., and Lehmann, Caroline E. R.
- Subjects
BIOMASS ,ENERGY consumption ,NATURAL satellites ,ECOSYSTEM dynamics ,SAVANNAS - Abstract
Landscape fires occur on a large scale in (sub)tropical savannas and grasslands, affecting ecosystem dynamics, regional air quality and concentrations of atmospheric trace gasses. Fuel consumption per unit of area burned is an important but poorly constrained parameter in fire emission modelling. We combined satellite-derived burned area with fire radiative power (FRP) data to derive fuel consumption estimates for land cover types with low tree cover in South America, Sub-Saharan Africa, and Australia. We developed a new approach to estimate fuel consumption, based on FRP data from the polar-orbiting Moderate Resolution Imaging Spectroradiometer (MODIS) and the geostationary Spinning Enhanced Visible and Infrared Imager (SEVIRI) in combination with MODIS burned-area estimates. The fuel consumption estimates based on the geostationary and polar-orbiting instruments showed good agreement in terms of spatial patterns. We used field measurements of fuel consumption to constrain our results, but the large variation in fuel consumption in both space and time complicated this comparison and absolute fuel consumption estimates remained more uncertain. Spatial patterns in fuel consumption could be partly explained by vegetation productivity and fire return periods. In South America, most fires occurred in savannas with relatively long fire return periods, resulting in comparatively high fuel consumption as opposed to the more frequently burning savannas in Sub- Saharan Africa. Strikingly, we found the infrequently burning interior of Australia to have higher fuel consumption than the more productive but frequently burning savannas in northern Australia. Vegetation type also played an important role in explaining the distribution of fuel consumption, by affecting both fuel build-up rates and fire return periods. Hummock grasslands, which were responsible for a large share of Australian biomass burning, showed larger fuel build-up rates than equally productive grasslands in Africa, although this effect might have been partially driven by the presence of grazers in Africa or differences in landscape management. Finally, land management in the form of deforestation and agriculture also considerably affected fuel consumption regionally. We conclude that combining FRP and burned-area estimates, calibrated against field measurements, is a promising approach in deriving quantitative estimates of fuel consumption. Satellite-derived fuel consumption estimates may both challenge our current understanding of spatiotemporal fuel consumption dynamics and serve as reference datasets to improve biogeochemical modelling approaches. Future field studies especially designed to validate satellite-based products, or airborne remote sensing, may further improve confidence in the absolute fuel consumption estimates which are quickly becoming the weakest link in fire emission estimates. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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17. Decadal dynamics of tree cover in an Australian tropical savanna.
- Author
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LEHMANN, CAROLINE E. R., PRIOR, LYNDA D., and BOWMAN, DAVID M. J. S.
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SAVANNAS , *SAVANNA ecology , *NATIONAL parks & reserves - Abstract
Spatio-temporal variation in tropical savanna tree cover remains poorly understood. We aimed to quantify the drivers of tree cover in tropical mesic savannas in Kakadu National Park by relating changes in tree cover over 40 years to: mean annual rainfall, fire activity, initial tree cover and prior changes in tree cover. Aerial photography, acquired in 1964, 1984 and 2004, was obtained for fifty sites in Kakadu that spanned a rainfall gradient from approximately 1200 to 1600 mm. The remotely sensed estimates of tree cover were validated via field survey. Linear mixed effects modelling and multi-model inference were used to assess the strength and form of the relationships between tree cover and predictor variables. Over the 40 years, tree cover across these savannas increased on average by 4.94 ± 0.88%, but was spatio-temporally variable. Tree cover showed a positive albeit weak trend across the rainfall gradient. The strength of this positive relationship varied over the three measurement times, and this suggests that other factors are important in controlling tree cover. Tree cover was positively related to prior tree cover, and negatively correlated with fire activity. Over 20 years tree cover was more likely to increase if (i) tree cover was initially low or (ii) had decreased in the previous 20-year interval or (iii) there had been fewer fires. Across the examined rainfall gradient, the greater variability in fire activity and inherently higher average tree cover at the wetter latitudes resulted in greater dynamism of tree cover compared with the drier latitudes. This is consistent with savanna tree cover being determined by interactions between mean annual rainfall, tree competition and frequent fire in these tropical mesic savannas. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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18. Savannas Need Protection.
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LEHMANN, CAROLINE E. R.
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SAVANNAS , *CARBON cycle - Abstract
A letter to the editor is presented on the savanna biome, the worldwide earth surface area it occupies, and fires that release stored carbon to the atmosphere.
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- 2010
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19. The Trouble with Trees: Afforestation Plans for Africa.
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Bond, William J., Stevens, Nicola, Midgley, Guy F., and Lehmann, Caroline E.R.
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AFFORESTATION , *FOSSIL fuels , *CARBON sequestration , *TREES , *TREE planting - Abstract
Extensive tree planting is widely promoted for reducing atmospheric CO 2. In Africa, 1 million km2, mostly of grassy biomes, have been targeted for 'restoration' by 2030. The target is based on the erroneous assumption that these biomes are deforested and degraded. We discuss the pros and cons of exporting fossil fuel emission problems to Africa. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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20. Savannas are vital but overlooked carbon sinks.
- Author
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Dobson, Andy, Hopcraft, Grant, Mduma, Simon, Ogutu, Joseph O., Fryxell, John, Anderson, T. Michael, Archibald, Sally, Lehmann, Caroline, Poole, Joyce, Caro, Tim, Mulder, Monique Borgerhoff, Holt, Robert D., Berger, Joel, Rubenstein, Daniel I., Kahumbu, Paula, Chidumayo, Emmanuel N., Milner-Gulland, E. J., Schluter, Dolph, Otto, Sarah, and Balmford, Andrew
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SAVANNAS , *CARBON cycle , *CLIMATOLOGY conferences - Abstract
The article asserts that the plan of 130 nations at the 2021 United Nations Climate Change Conference (COP26) to halt global deforestation by 2030 needs to be expanded to include savannas, which cover an area of 20 million square kilometers and are regarded as more important carbon sinks than forests.
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- 2022
- Full Text
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