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Grass Layer (grass + layer)
Selected AbstractsEffects of fire on surface carbon, energy and water vapour fluxes over campo sujo savanna in central BrazilFUNCTIONAL ECOLOGY, Issue 6 2003A. J. B. Santos Summary 1Tower-based eddy covariance measurements were used to quantify the effect of fire on subsequent carbon dioxide fluxes and water and surface energy balance characteristics for campo sujo savanna located near Brasília in Central Brazil (15°56, S, 47°51, W). Campo sujo is a xeromorphic, open shrub savanna with very scattered but definitely visible shrubs and tree-like shrub elements. We studied two areas, one exposed to a prescribed fire late in the dry season, and a second that had not been burned for the previous 4 years. 2The fire on 22 September 1998 consumed an estimated 26 mol C m,2. Immediately after the fire, evapotranspiration rates decreased and the savanna became a stronger net source of CO2 to the atmosphere. This was attributed to the removal of the still slightly physiologically active grass layer and higher soil CO2 efflux rates as a consequence of elevated surface soil temperatures post-burning. 3On the commencement of the first rains in early October 1998, this situation was reversed, with the burned area rapidly becoming a stronger sink for CO2 and with higher evapotranspiration rates than a nearby unburned (control) area. This difference persisted throughout the wet season (until at least June 1999) and was attributable to greater physiological activity of the regrowing vegetation in the burned area. Early in the growing season, higher soil evaporation rates may also have contributed to faster water use by the previously burned area. 4Overall, we estimate an annual gross primary productivity for the burned area of 135 mol C m,2 year,1, with that for the unburned area being 106 mol C m,2 year,1. Estimated ecosystem respiration rates were more similar on an annual basis (96 and 82 mol C m,2 year,1 for the burned and unburned areas, respectively), giving rise to a substantially higher net ecosystem productivity for the previously burned area (38 vs 24 mol C m,2 year,1). 5Stimulation of photosynthetic activity in the rapid post-fire growth phase means that the negative effects of fire on the ecosystem carbon balance were more or less neutralized after only 12 months. [source] Conundrums in mixed woody,herbaceous plant systemsJOURNAL OF BIOGEOGRAPHY, Issue 11 2003Joanna I. House Abstract Aims To identify approaches to improve our understanding of, and predictive capability for, mixed tree,grass systems. Elucidation of the interactions, dynamics and determinants, and identification of robust generalizations that can be broadly applied to tree,grass systems would benefit ecological theory, modelling and land management. Methods A series of workshops brought together scientific expertise to review theory, data availability, modelling approaches and key questions. Location Ecosystems characterized by mixtures of herbaceous and woody plant life-forms, often termed ,savannas', range from open grasslands with few woody plants, to woodlands or forests with a grass layer. These ecosystems represent a substantial portion of the terrestrial biosphere, an important wildlife habitat, and a major resource for provision of livestock, fuel wood and other products. Results Although many concepts and principles developed for grassland and forest systems are relevant to these dual life-form communities, the novel, complex, nonlinear behaviour of mixed tree,grass systems cannot be accounted for by simply studying or modelling woody and herbaceous components independently. A more robust understanding requires addressing three fundamental conundrums: (1) The ,treeness' conundrum. What controls the relative abundance of woody and herbaceous plants for a given set of conditions at given site? (2) The coexistence conundrum. How do the life-forms interact with each other? Is a given woody,herbaceous ratio dynamically stable and persistent under a particular set of conditions? (3) The net primary productivity (NPP) conundrum. How does NPP of the woody vegetation, the herbaceous vegetation, and the total ecosystem (woody + herbaceous) change with changes in the tree,grass ratio? Tests of the theory and conceptual models of determinants of mixed woody,herbaceous systems have been largely site- or region-specific and have seldom been broadly or quantitatively evaluated. Cross-site syntheses based on data and modelling are required to address the conundrums and identify emerging patterns, yet, there are very few data sets for which either biomass or NPP have been quantified for both the woody and the herbaceous components of tree,grass systems. Furthermore, there are few cross-site comparisons spanning the diverse array of woody,herbaceous mixtures. Hence, initial synthesis studies should focus on compiling and standardizing a global data base which could be (1) explored to ascertain if robust generalizations and consistent patterns exist; and (2) used to evaluate the performance of savanna simulation models over a range of woody,herbaceous mixtures. Savanna structure and productivity are the result of complex and dynamic interactions between climate, soils and disturbances, notably fire and herbivory. Such factors are difficult to isolate or experimentally manipulate in order to evaluate their impacts at spatial and temporal scales appropriate for assessing ecosystem dynamics. These factors can, however, be evaluated with simulation models. Existing savanna models vary markedly with respect to their conceptual approach, their data requirements and the extent to which they incorporate mechanistic processes. Model intercomparisons can elucidate those approaches most suitable for various research questions and management applications. Conclusion Theoretical and conceptual advances could be achieved by considering a broad continuum of grass,shrub,tree combinations using data meta-analysis techniques and modelling. [source] The use of teak (Tectona grandis) plantations by large mammals in the Kilombero Valley, southern TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2009C. Bonnington Abstract The establishment of plantations is impacting the large mammal populations of the Kilombero Valley, Tanzania. Animal spoors were used as a proxy for activity to determine the influence of teak stand age on mammals. Habitat variables were compared between different aged stands to investigate the relationship between mammal activity and vegetation characteristics. Vegetation surveys found plantation composition to differ with age; with young stands characterized by slender teak trees, limited leaf litter, abundant grass layer and substantial bare ground. Older plantations contained a high leaf litter layer and dead wood, low grass abundance and minimal bare ground. Spoor transects revealed that mammal species number decreased as the teak matured. Of those vegetation variables tested, grass and bare ground abundance explained significantly the variation in species number and in individual species' habitat use between differently aged stands; therefore this habitat use was influenced by the foraging value of the plantation. This study showed that several species (some of which warrant conservation attention, such as elephant) use plantations <6 years old to a greater extent than plantations >6 years. Thus, there is a need for conservation measures, such as wildlife corridors and staggered teak planting to be continued, allowing large mammal movements in the valley. Résumé L'installation de plantations a un impact sur les populations de grands mammifères de la Vallée de Kilombero, en Tanzanie. Les traces des animaux ont été utilisées comme signes d'activité pour déterminer l'influence de l'âge des bosquets de teck sur les mammifères. On a comparé les variables de l'habitat entre des bosquets d'âge différent pour étudier la relation entre l'activité des mammifères et les caractéristiques de la végétation. Des études de la végétation ont montré que la composition des plantations varie avec leur âge : les jeunes plantations sont caractérisées par des troncs de teck plus minces, une litière de feuilles plus restreinte, une couche herbeuse abondante et une partie non négligeable de sol nu. Les plantations plus anciennes présentent une litière de feuilles plus épaisse et du bois mort, peu d'herbes et très peu de sol nu. Les traces ont révélé que le nombre d'espèces de mammifères diminuait quand la plantation vieillissait. Parmi les variables de la végétation testées, l'abondance de l'herbe et la quantité de sol nu expliquaient de manière significative la variation du nombre d'espèces et celle de l'utilisation de l'habitat par chaque espèce en fonction de l'âge des plantations. L'utilisation de cet habitat était donc influencée par la valeur alimentaire de la plantation. Cette étude a montré que plusieurs espèces (dont certaines, comme l'éléphant, garantissent l'attention de la conservation) fréquentent les plantations de moins de six ans plus souvent que celles de plus de six ans. Il faut donc poursuivre les mesures de conservation, comme des corridors pour la faune sauvage et des plantations de teck décalées, qui permettent les déplacements des grands mammifères dans la vallée. [source] Impact of storm-burning on Melaleuca viridiflora invasion of grasslands and grassy woodlands on Cape York Peninsula, AustraliaAUSTRAL ECOLOGY, Issue 2 2009GABRIEL CROWLEY Abstract This paper examines invasion of grasslands on Cape York Peninsula, Australia, by Melaleuca viridiflora and other woody species, and the role of storm-burning (lighting fires after the first wet season rains) in their maintenance. Trends in disturbance features, fuel characteristics, ground layer composition, and woody plants dynamics under combinations of withholding fire and storm-burning over a 3-year period were measured on 19 plots in three landscape settings. Population dynamics of M. viridiflora are described in detail and 20-year population projections based on transition matrices under different fire regimes generated. Numerous M. viridiflora suckers occurred within the grass layer, increasing each year regardless of fire regime, and were rapidly recruited to the canopy in the absence of fire. Storm-burning had little impact on fuel, ground layer or woody plant composition, but maintained open vegetation structure by substantially reducing recruitment of M. viridiflora suckers to the sapling layer, and by reducing the above-grass-layer abundance of several other invasive woody species. Population projections indicated that withholding fire for 20 years could cause a sevenfold increase of M. viridiflora density on Ti-tree flats, and that annual to triennial storm-burning should be effective at maintaining a stable open vegetation structure. These findings argue against vegetation thickening being an inevitable consequence of climate change. We conclude that a fire regime that includes regular storm-burning can be effective for maintaining grasslands and grassy woodlands being invaded by M. viridiflora. [source] | ||||||||||