Burnt Grassland Research Articles

Influence of early dry season fires on primary production in western Serengeti grasslands, Tanzania

Short-term, i.e. 4-9 weeks aboveground net primary production (ANPP) temporal patterns during the first post-fire year in western Seren-geti National Park, and potential differences in the factors limiting ANPP between burnt and non burnt grasslands were examined and es-tablished. Fire stimulated growth at early post-fire stages, even during the dry season, July-October and led to larger increments in green phytomass compared to the non burnt grassland at the onset of short rains, Octo-ber-December. Further, ANPP in burnt plots correlated well with the ratio leaf/total standing phytomass suggesting that the accumulation of standing dead material can be a limiting factor to ANPP in burnt grass-lands. However, ANPP in burnt plots was unrelated to rainfall contrary to earlier arguments, but reached peak earlier and declined early in the rain season, perhaps due to the interactive effects of fire and grazing in the area. In non burnt plots, the temporal change in ANPP was more related to rainfall availability, at least until mid-growing season. Also, the phytomass structure differed between burnt and non burnt grasslands, and together with litter did not recover to non burnt levels within the first post-fire year. The study has demonstrated that the desire of the fire man-agement program in Serengeti National Park, which is to supply green forage to both migra-tory and resident populations during dry season is being fulfilled.

Early effects of fire on herbaceous vegetation and mycorrhizal symbiosis in high altitude grasslands of Natural Park of Estrela Mountain (PNSE)

Severe fires over the last decade have transformed the high altitude grassland biogenetic reserve in the Natural Park of Estrela Mountain (PNSE) of Portugal. Yet, there is little information about the impacts of the fires above and below ground. We assessed the species composition, richness and frequency of the herbaceous vegetation. We characterized the mycorrhizal symbiosis and analysed the soil properties in three cervunal areas of which one was destroyed by a severe fire in 2003. The results indicate that plant community in high altitude grassland of PNSE are rather poor in species but the number may increase after fire. The most remarkable change in the herbaceous vegetation after fire was the abrupt increase of Festuca trichophylla in the burnt area, to the detriment and abrupt decrease of Nardus stricta. Arbuscular mycorrhizas (AM) were the most widespread symbioses in all three grasslands. AM colonization of F. trichophylla was significantly lower in burnt grassland but the AM colonization in N. stricta increased. There was also a higher phosphorous content in soil of the burnt grassland. We put forward a hypothesis about the impacts of recurrent fires above and below ground and discuss its implications to functioning of high altitude ecosystems.

Floristic diversity and the richness of locally endangered plant species of semi-natural grasslands under different management practices, southern Kyushu, Japan

Background: The rapid decline of semi-natural grasslands in Japan threatens many relic and endemic plant species. There is insufficient knowledge on how the impacts of land-use changes and management of grasslands have been affecting grassland ecosystems and what conservation measures may be taken to conserve as much of the existing plant diversity as possible. Aim: We assessed the existing management regimes for their suitability for conserving Red Data Book (RDB) species. Methods: We conducted our study in four districts of Kushima, Kyushu, south-west Japan, with different land-use histories. We compared species richness, plant density and abundance in six grassland types: regularly burnt, regularly mown, paddy levee, roadside, landslip and wetland communities in a total of 289 1 m x 1 m quadrats, recorded in172 grassland patches. Species richness plant density and abundance were analysed with special reference to RDB species under different land use history. Results: Species richness of grasslands did not differ across different land use histories, yet our analysis showed that the reduced area of grasslands markedly affected the density of RDB species. Grassland types differed in their ability to support RDB species: regularly burnt grasslands were the richest in RDB species and poorest in alien species, followed by regularly mown grasslands, paddy levees, landslip, wetland and roadside communities. Conclusions: Traditional management regimes, such as regular burning or mowing of grasslands have the best potential for conserving RDB species, and thus should be part of conservation management practices of semi-natural grasslands.

Changes in soil organic matter composition are associated with forest encroachment into grassland with long‐term fire history

SummaryThis study investigates if Araucaria forest (C3 metabolism) expansion on frequently burnt grassland (C4 metabolism) in the southern Brazilian highland is linked to the chemical composition of soil organic matter (SOM) in non‐allophanic Andosols. We used the 13C/12C isotopic signature to group heavy organo‐mineral fractions according to source vegetation and 13C NMR spectroscopy, lignin analyses (CuO oxidation) and measurement of soil colour lightness to characterize their chemical compositions. Large proportions of aromatic carbon (C) combined with small contents of lignin‐derived phenols in the heavy fractions of grassland soils and grass‐derived lower horizons of Araucaria forest soils indicate the presence of charred grass residues in SOM. The contribution of this material may have led to the unusual increase in C/N ratios with depth in burnt grassland soils and to the differentiation of C3‐ and C4‐derived SOM, because heavy fractions from unburnt Araucaria forest and shrubland soils have smaller proportions of aromatic C, smaller C/N ratios and are paler compared with those with C4 signatures. We found that lignins are not applicable as biomarkers for plant origin in these soils with small contents of strongly degraded and modified lignins as the plant‐specific lignin patterns are absent in heavy fractions. In contrast, the characteristic contents of alkyl C and O/N‐alkyl C of C3 trees or shrubs and C4 grasses are reflected in the heavy fractions. They show consistent changes of the (alkyl C)/(O/N‐alkyl C) ratio and the 13C/12C isotopic signature with soil depth, indicating their association with C4 and C3 vegetation origin. This study demonstrates that soils may preserve organic matter components from earlier vegetation and land‐use, indicating that the knowledge of past vegetation covers is necessary to interpret SOM composition.

The antiquity of Madagascar’s grasslands and the rise of C4 grassy biomes

AbstractAim Grasslands and savannas, which make up > 75% of Madagascar’s land area, have long been viewed as anthropogenically derived after people settled on the island c. 2 ka. We investigated this hypothesis and an alternative – that the grasslands are an insular example of the post‐Miocene spread of C4 grassy biomes world‐wide.Location Madagascar, southern Africa, East Africa.Methods We compared the number of C4 grass genera in Madagascar with that in southern and south‐central African floras. If the grasslands are recent we would expect to find fewer species and genera in Madagascar relative to Africa and for these species and genera to have very wide distribution ranges in Madagascar. Secondly, we searched Madagascan floras for the presence of endemic plant species or genera restricted to grasslands. We also searched for evidence of a grassland specialist fauna with species endemic to Madagascar. Plant and animal species endemic to C4 grassy biomes would not be expected if these are of recent origin.Results Madagascar has c. 88 C4 grass genera, including six endemic genera. Excluding African genera with only one or two species, Madagascar has 86.6% of southern Africa’s and 89.4% of south‐central Africa’s grass genera. C4 grass species make up c. 4% of the flora of both Madagascar and southern Africa and species : genus ratios are similar (4.3 and 5.1, respectively). Turnover of grasses along geographical gradients follows similar patterns to those in South Africa, with Andropogoneae dominating in mesic biomes and Chlorideae in semi‐arid grassy biomes. At least 16 monocot genera have grassland members, many of which are endemic to Madagascar. Woody species in frequently burnt savannas include both Madagascan endemics and African species. A different woody flora, mostly endemic, occurs in less frequently burnt grasslands in the central highlands, filling a similar successional niche to montane C4 grasslands in Africa. Diverse vertebrate and invertebrate lineages have grassland specialists, including many endemic to Madagascar (e.g. termites, ants, lizards, snakes, birds and mammals). Grassland use of the extinct fauna is poorly known but carbon isotope analysis indicates that a hippo, two giant tortoises and one extinct lemur ate C4 or CAM (crassulacean acid metabolism) plants.Main conclusions The diversity of C4 grass lineages in Madagascar relative to that in Africa, and the presence of plant and animal species endemic to Madagascan grassy biomes, does not fit the view that these grasslands are anthropogenically derived. We suggest that grasslands invaded Madagascar after the late Miocene, part of the world‐wide expansion of C4 grassy biomes. Madagascar provides an interesting test case for biogeographical analysis of how these novel biomes assembled, and the sources of the flora and fauna that now occupy them. A necessary part of such an analysis would be to establish the pre‐settlement extent of the C4 grassy biomes. Carbon isotope analysis of soil organic matter would be a feasible method for doing this.

Forage selection of sable antelope in Pilanesberg Game Reserve, South Africa

Concern about the habitat requirements of sable antelope (Hippotragus niger) has increased due to population declines shown in some protected areas. Our study was prompted by the lack of initial increase by the sable antelope introduced into the Pilanesberg Game Reserve in North West Province, South Africa; 67 animals released between 1979 and 1983 had only grown to approximately 70 animals by 1988. We recorded forage selection by sable antelope within the context of the landscape units favoured in different seasons. Chrysopogon serrulatus, Panicum maximum, Heteropogon contortus, and Themeda triandra contributed most to the diet of sable antelope. Faecal crude protein content did not drop below 6.6% of dry matter during the dry season, with use of burnt grassland by sable contributing to an elevation in faecal protein levels at the beginning of the wet season. The sable population had increased to 127 animals by 1991, suggesting that the earlier lack of population growth had been due to below-average rainfall, lack of burns providing green regrowth during the dry season, or a delay in learning to exploit available forage resources efficiently.

Population of Humic Acid Degrading Microorganisms in Andosols under Different Vegetation Types and Grassland Management Regimens

To examine the effect of vegetation type and grassland management regimen on the distribution of humus-degrading microorganisms, populations of humic acid-degrading (HAD) bacteria and fungi at three Andosol sites were investigated using the dilution plate method. Each site had three different vegetation types (Eulalia grassland, bamboo grassland, and coniferous plantations). Among the six grassland sites, two were maintained by burning and the others by cutting. HAD microorganisms were found in all soil samples. Low densities and small percentages of HAD bacteria were detected with no significant differences in the number of bacteria found between different vegetation types and grasslands managed in different ways. In contrast, the densities and percentages of HAD fungi differed according to vegetation type and management regimen. Specifically, the percentages of HAD fungi were significantly higher for burned grasslands. At burned sites, the numbers and percentages of HAD bacteria remained at a consistently low level, and no distinct seasonal changes were observed. In contrast, marked seasonal fluctuations in HAD fungi were detected. The percentages of these fungi remained relatively high between April and December. These fluctuations are likely due to the effects of burning on soil microorganisms.

Effects of Habitat on Competition Between Kit Foxes and Coyotes

Abstract: San Joaquin kit foxes (Vulpes macrotis mutica) are an endangered species with a narrow geographic range whose natural populations are limited by predation by coyotes (Canis latrans). In the warm, arid grassland and shrubland habitats where kit foxes occur, coyotes are more cover dependent than kit foxes, creating the possibility of habitat segregation. Effects of habitat variation on coyote and kit fox competition are unknown. We assessed exploitation and interference competition between coyotes and kit foxes in grassland and shrubland habitats to determine if such competition varies among habitats. With respect to exploitation competition, we evaluated habitat and spatial partitioning, diet, prey abundance, and survival for kit foxes and coyotes at the Lokern Natural Area in central California, USA, from January 2003 through June 2004. Kit foxes partitioned habitat, space, and diet with coyotes. Coyotes primarily used shrubland habitats whereas kit foxes selectively used burned grasslands. Kit foxes and coyotes had high dietary overlap with regards to items used, but proportional use of items differed between the 2 species. Kit foxes selected for Heermann's kangaroo rats (Dipodomys heermanni), which were closely tied to shrub habitats. With respect to interference competition, predation was the primary source of mortality for kit foxes, and survival of individual kit foxes was inversely related to proportion of shrub habitat within their home ranges. Our results suggest that a heterogeneous landscape may benefit kit foxes by providing habitat patches where predation risk may be lower.

Effect of burn area on invertebrate recolonization in grasslands in the Drakensberg, South Africa

Our study examined the short-term response of grassland invertebrate communities to fire in the South African Drakensberg, in relation to distance from the edge of a burn. We aimed to establish which species survive fire and the dynamics of the post-fire recolonization process, and thereby contribute to establishing the ideal area of a prescribed burn for invertebrate conservation. Four transects were sampled two and 12 weeks after burning. Along each transect one unburnt control and four burnt sites were quantitatively sampled. Richness, abundance and diversity were calculated for each site and canonical correspondence analysis was applied to transect and morphospecies counts to determine the impact of distance from the edge of the burn on community structure. Distance from burn edge affected invertebrate richness and abundance, especially for flying insects. Burning appeared to minimally impact on wingless invertebrates, suggesting they tolerated fire by finding refuge. Invertebrate community structure changed with increasing distance from burn edge two weeks, but not 12 weeks post-burn. A distance of 280 m from burn edge appears to allow sufficient recolonization to maintain invertebrate diversity. Taxa found in the unburnt control and site closest to the edge in burnt grassland may be fire sensitive and require further study.

Short-term response of burnt grassland to defoliation in a semi-arid climate of South Africa

The impact of defoliation on the productivity and soil temperature of burnt grassland (head and back fires) was investigated over the short term (one and two growing seasons after burning). Head fires had greater flame height and rate of spread than back fires. However, back fires were more intense and exceeded 100°C at ground level. Botanical composition was little influenced by both head and back fires, though fire had a drastic impact on the basal cover and tuft die-back. Basal cover was still 28% and 11% respectively lower than that of unburnt grassland, one and two growing seasons after burning. Those grass species normally forming large tufts, such as Cymbopogon plurinodis and Themeda triandra, had the greatest percentage die-back per tuft. Defoliation up to and during October, after the grassland had rested for a full growing season after burning, still significantly (P ≤ 0.01) lowered production for the subsequent full growing seasons. For sustainable production in this semi-arid area, it seems grassland should not be defoliated before December of the second growing season following fire. When defoliation took place later in the same season following burning, it had a smaller negative impact on the water-use efficiency. Defoliation significantly (P ≤ 0.01) increased the soil temperature up to a depth of 50mm over the first half of the growing season right after the fire. The importance of the correct time of utilisation of burnt semi-arid grassland, with respect to sustained high production, has been emphasised.

Influence of fire on litter production and root and litter turnover in a semi-arid grassland of South Africa

Changes in litter production following back and head fires, some soil characteristics and root and litter turnover were quantified over two growing seasons for a semi-arid grassland. Sampling of litter production took place at approximately bi-monthly intervals to account for major seasonal changes over the 2000/01 and 2001/02 seasons. Soil compaction was determined by a simple rod penetrometer, soil temperature by mercury thermometers and soil-water content by a neutron hydroprobe. Litterfall of 5.88% and 1.13% (as a proportion of annual aboveground phytomass production) for unburnt and burnt grassland, respectively, was obtained. Two seasons following the fire, litter was still 47% lower due to fire. The litter production was not significantly different between the head and back fires. The fire, while causing a lower plant cover over the two years following burning, also significantly increased soil compaction and soil temperature. The biggest difference in soil temperature between burnt and unburnt grassland to a depth of 50 mm was 7 °C. After only two months the soil-water content over the first 900 mm depth decreased by 23% due to burning. Fire lengthened the period for replacement of the total root system by about a year and decomposition of litter by three months. Small changes caused by fire to the fragile ecosystems of semi-arid climates may have long-lasting consequences. The overall effects of fire on belowground systems and the resulting processes that feed back to aboveground systems are complex.

Influence of fire on root distribution, seasonal root production and root/shoot ratios in grass species in a semi-arid grassland of South Africa

The impact of fire (head and back fires) on the seasonal change in above- and belowground production in grass species, was quantified over two growing seasons (2000/01 and 2001/02) for semi-arid grassland. The behaviour of the head and back fires was also identified. Roots were extracted to a depth of 900 mm with 50 mm intervals, using a core and then separated from the soil by wet sieving and flotation. Sampling of both above- and below-ground phytomass, took place at approximately bi-monthly intervals to account for major seasonal changes. The intensity of the back fire was higher than the head fire at ground level. Most of the grass roots were found in the first 150 mm soil layer. While fire increased grass root distribution over the first 100 mm depth, it was decreased deeper in the soil. Root mass in semi-arid grassland is strongly seasonal, with the most active growth during the months of March and April when aboveground parts are dormant. Both above- and belowground phytomass production decreased significantly over the first year following burning. The above- and belowground phytomass (900 mm depth) was respectively 806 kg ha − 1 and 2 002 kg ha − 1 less due to burning, over the first year after burning. The seasonal root/shoot ratios for the unburnt and burnt grassland ranged between 1.62 to 2.80 and 1.20 to 3.12 respectively. It seems that root mass exceeds aboveground biomass for this semi-arid grassland. Over the short-term, fire decreased productivity and could subsequently influence the sustainable fodder production of a semi-arid grassland ecosystem.

The effect of fire on the soil seed bank of a semi-arid grassland in South Africa

During the dormant winter period the semi-arid grassland areas of South Africa are characterised by planned and unplanned fires, either by lightning or negligence by man. The influence of burning (head and back fire) on the germinability of grass species in the soil seed bank was quantified in the greenhouse over the 2000/01 to 2001/02 growing seasons for a semi-arid grassland. The behaviour of the head and back fires was also monitored. Soil seed bank samples were collected immediately after burning and then every third month over a two-year period from 0.25m2 blocks 50mm deep. The same was done on unburnt grassland. At ground level, the back fire exceeded 100°C, while the head fire had temperatures of less than 100°C. The fire caused a flush of seedlings from the seed bank over the first season after the fire. The head fire stimulated seedling density significantly (P ≤ 0.01) more than the back fire. The mean (head and back fire) seed bank density the first season following the fire, for burnt and unburnt grassland, was respectively 84.6 and 52.1 grass seedlings m− 2 for September, 50.5 and 21.9 grass seedlings m− 2 for December and 347 and 58 grass seedlings m− 2 for March. The pioneer species Aristida congesta and Tragus koelerioides only occurred in the soil seed bank of the burnt grassland, while the climax species Cymbopogon plurinodes, Digitaria eriantha and Panicum stapfianum only germinated in the unburnt grassland seed bank. The Eragrostis species showed the highest germination due to fire. The burning of semi-arid grassland did have a quantified impact on the soil seed bank over the short-term.

Short-term invasibility patterns in burnt and unburnt experimental Mediterranean grassland communities of varying diversities

This paper reports the findings of a short-term natural invasibility field study in constructed Mediterranean herbaceous communities of varying diversities, under a fire treatment. Three components of invasibility, i.e. species richness, density and biomass of invaders, have been monitored in burnt and unburnt experimental plots with resident diversity ranging from monocultures to 18-species mixtures. In general, species richness, density and biomass of invaders decreased significantly with the increase of resident species richness. Furthermore, the density and biomass of invading species were significantly influenced by the species composition of resident communities. Although aboveground biomass, leaf area index, canopy height and percent bare ground of the resident communities explained a significant part of the variation in the success of invading species, these covariates did not fully explain the effects of resident species richness. Fire mainly influenced invasibility via soil nutrient levels. The effect of fire on observed invasibility patterns seems to be less important than the effects of resident species richness. Our results demonstrate the importance of species richness and composition in controlling the initial stages of plant invasions in Mediterranean grasslands but that there was a lack of interaction with the effects of fire disturbance.

Distribuição da brioflora em diferentes fisionomias de cerrado da Reserva Biológica e Estação Experimental de Mogi-Guaçu, SP, Brasil

O trabalho refere-se à distribuição da brioflora ocorrente no cerrado Reserva Biológica e Estação Experimental de MogiGuaçu. Este bioma apresenta fisionomias que variam de florestas a campos. As coletas foram realizadas entre 1993 e 1995, na casca de 15 espécies de forófitos arbustivo-arbóreos, ao longo de um transecto, passando por cinco fisionomias diferentes de cerrado. Estudaramse 1.345 exsicatas de 49 gêneros e 92 espécies de briófitas. A brioflora está relacionada às fisionomias de cerrado e não aos forófitos arbustivo-arbóreos. As fisionomias são mais semelhantes quanto à flora de musgos do que em relação à flora de hepáticas. As briófitas distribuem-se em três grupos de fisionomias: cerrado sentido restrito, campo cerrado e transição / cerrado sentido restrito de Myrsine / campo cerrado queimado.

Carbon stocks, soil respiration and microbial biomass in fire-prone tropical grassland, woodland and forest ecosystems

A thorough understanding of the role of microbes in C cycling in relation to fire is important for estimation of C emissions and for development of guidelines for sustainable management of dry ecosystems. We investigated the seasonal changes and spatial distribution of soil total, dissolved organic C (DOC) and microbial biomass C during 18 months, quantified the soil CO2 emission in the beginning of the rainy season, and related these variables to the fire frequency in important dry vegetation types grassland, woodland and dry forest in Ethiopia. The soil C isotope ratios (δ13C) reflected the 15-fold decrease in the grass biomass along the vegetation gradient and the 12-fold increase in woody biomass in the opposite direction. Changes in δ13C down the soil profiles also suggested that in two of the grass-dominated sites woody plants were more frequent in the past. The soil C stock ranged from being 2.5 (dry forest) to 48 times (grassland) higher than the C stock in the aboveground plant biomass. The influence of fire in frequently burnt wooded grassland was evident as an unchanged or increasing total C content down the soil profile. DOC and microbial biomass measured with the fumigation–extraction method (Cmic) reflected the vertical distribution of soil organic matter (SOM). However, although SOM was stable throughout the year, seasonal fluctuations in Cmic and substrate-induced respiration (SIR) were large. In woodland and woodland–wooded grassland Cmic and SIR increased in the dry season, and gradually decreased during the following rainy season, confirming previous suggestions that microbes may play an important role in nutrient retention in the dry season. However, in dry forest and two wooded grasslands Cmic and SIR was stable throughout the rainy season, or even increased in this period, which could lead to enhanced competition with plants for nutrients. Both the range and the seasonal changes in soil microbial biomass C in dry tropical ecosystems may be wider than previously assumed. Neither SIR nor Cmic were good predictors of in situ soil respiration. The soil respiration was relatively high in infrequently burnt forest and woodland, while frequently burnt grasslands had lower rates, presumably because most C is released through dry season burning and not through decomposition in fire-prone systems. Shifts in the relative importance of the two pathways for C release from organic matter may have strong implications for C and nutrient cycling in seasonally dry tropical ecosystems.

Short-term influence of fire on seedling establishment in a semi-arid grassland of South Africa

The influence of burning (head and back fire) on seedling recruitment and survival of different grass species in a semi-arid grassland were quantified over the 2000/01 to 2001/02 growing seasons. The behaviour of the head and back fires was also monitored. Soil temperature and soil-water content were recorded once a week at 10mm and 50mm depth intervals respectively. At ground level, the back fire exceeded 100°C, while the head fire recorded temperatures of less than 100°C. Due to the lower basal cover (28% lower than for unburnt grassland over the first year after the fire) of the burnt grassland, the soil temperature, daily and seasonal to a depth of 50mm, increased (P - 2 respectively. Fire influenced the species richness negatively. Pioneer grass species ( Aristida congesta and Tragus koelerioide ) intruded in the burnt grassland, which were not present in the unburnt grassland. The seedling establishment of Eragrostis chloromelas , Themeda triandra and Elionurus muticus were heavily decreased by fire. Eragrostis chloromelas was the species forming most seed culms per tuft over the growing season regardless of burning, with Elionurus muticus most stimulated for seed formation due to the fire, and Themeda triandra not much influenced by fire. The burning of semi-arid grassland did have an important impact on the seasonal survival of seedlings over the short-term, and therefore the resultant functioning of the grassland ecosystem.

Fire and the dynamics of semi-arid grassland: influence on plant survival, productivity and water-use efficiency

There is a lack of knowledge concerning the effect of fire behaviour on the vegetation dynamics of semi-arid climates. Arising from this, an investigation was initiated to characterise the behaviour of fires burning with the wind (head fire) and against the wind (back fire). The behaviour of these fires was related to the response of the vegetation by monitoring the recovery and productivity of the grass sward after only one burn over a two year period (2000/01 to 2001/02 seasons). The results showed that head fires had significantly greater flame height and rate of spread than back fires. However, at ground level back fires were more intense and had a negative effect on recovery of the grasses, resulting in lower litter, yield and water-use efficiency (aboveground phytomass or crude protein produced per unit of evapotranspiration). Fire had a significant effect on plant density and cover, with basal cover 68% lower than that of unburnt grassland two months after the fire. Cymbopogon plurinodis with large tufts had the most die-back of all the species. With the exception of plant cover and density, which takes longer to recover, it takes approximately two complete growing seasons to recover from most of the detrimental effects of fire. The initial increased crude protein content of the plant material caused by fire did not off set the approximately 50% reduction in plant production the first growing season after the fire. Fire significantly decreased WUE (water-use efficiency), with an average over the two growing seasons of 3.06kg ha-1 mm-1 and 2.45kg ha-1 mm-1 for unburnt and burnt grassland respectively. In various semi-arid grassland areas, the use of fire as a management tool is questionable if there is no specific purpose for it.

A 3.5 ka record of paleoenvironments and human occupation at Angkor Borei, Mekong Delta, southern Cambodia

AbstractMicrofossil and sedimentological data from a 3.1 m core extracted from a reservoir (baray) at the ancient Cambodian settlement of Angkor Borei in the Mekong Delta have provided a continuous record of sedimentation and paleoenvironments dating from about 2000 cal yr B.C. Palynological data indicate that for much of the cal. 1st and 2nd millennia B.C. mangroves dominated the regional vegetation, while extensively and regularly burnt grasslands dominated the local vegetation. Turbid, nutrient‐rich standing water characterized the core locality, perhaps suggesting a connection with rivers in the area. An abrupt change during the cal. 5th to 6th centuries A.D. involved a dramatic reduction in grasslands and the expansion of secondary forest or re‐growth taxa. These changes are synchronous with an abrupt decline in the concentration of microscopic charcoal particles in the sediments, and the colonization of the core locality by swamp forest plants. These changes are taken to indicate a shift in land‐use strategies or, possibly, a period of land abandonment. The age for the construction of the baray is interpreted to be in the 17th–19th centuries, but this dating remains speculative. Construction of the Angkor Borei baray exploited a preexisting body of standing water, so its construction was fundamentally different from the methods used at the Angkorian capital in northern Cambodia. © 2003 Wiley Periodicals, Inc.

Fire and the dynamics of a semi-arid grassland: influence on soil characteristics

The short-term impact of fire burning with the wind (head fire) and against the wind (back fire) on soil characteristics (soil-water content, soil compaction, soil temperature, organic matter, pH, exchangeable Ca, Mg, K, Na and extractable P) were determined in a semi-arid grassland. This study was conducted over two growing seasons (2000/01 and 2001/02) after only one burning treatment in August 2000. The back fire moved approximately 7.5 times slower than the head fire, leading to the greatest change in hydrological characteristics. The decline in plant cover due to the fire resulted in a considerable increase in soil compaction, soil temperature and a decrease in organic material in turn leading to a lowered soil-water content. Much of the influence of these variables had not been completely reduced two growing seasons after the fire. Burning reduced the soil-water content (0mm to 300mm soil depth) after one month and one year by 13.4% and 31% respectively. Temporary wilting for all grass species occurred more rapidly with burning. During March of the first year, the greatest soil temperature difference (50mm depth) occurred between burnt and unburnt grassland, with the highest soil temperatures recorded in January. The highest temperature on the surface of the soil for each year after burning also occurred during January. Over the first growing season burning significantly reduced organic carbon (C) and total nitrogen (N) content and extractable phosphate, but increased the pH and concentration of exchangeable Ca, Mg, Na and K in the soil, over the first 0–50mm layer. There were no differences in the soil properties of head and back fires, except for organic material that was further lowered by the back fire. With depth, organic matter and K decreased significantly and Ca increased between surface (0mm to 50mm) and lower (50mm to 100mm) layers due to burning. Thus, an unplanned event can increase the intensity and frequency of seasonal droughts in the ecologically sensitive semi-arid grassland areas leading to increase risk management in the short-term.