Annual Fire Research Articles

Fire and land use change heighten tensions between pastoral nomads and mechanized farmers in Kordofan and White Nile States, Sudan

Environmental degradation and natural resource scarcity are cited as two of the underlying causes of conflict in Sudan. In a study of the rangelands (albaja) of Kordofan and White Nile States, we use biophysical data, interviews, and satellite data to reveal how owners of large-scale, mechanized agriculture operations are progressively modifying the landscape at the expense of pastoral nomads. Our analysis shows that annual vegetation fires are used by the farmers to create buffers around the expanding mechanized farming operations to keep nomads' livestock away. This annual burning in the short term is depriving pastoralists of fodder and in the longer term is degrading the rangeland by favoring tree and grass species unpalatable to livestock. These changes in the landscape render pastoralists and traditional small-scale farmers increasingly marginalized. The competing demands for land are resulting in heightened tensions with parallels to the underlying causes of conflict in the adjacent region of Darfur.

Potential effects of prescribed savannah burning on the diet selection of forest buffalo (Syncerus caffer nanus) in Lopé National Park, Gabon

AbstractSeasonality and management are factors that may affect the diet selection of the forest buffalo (Syncerus caffer nanus). Fire is considered a major driving force in savannah systems and prescribed burning is a commonly applied conservation tool in protected areas such as Lopé National Park, Gabon. Prescribed annual fires contribute to the maintenance of open areas and provide high‐quality forage for forest buffalo, a major herbivore in the park. We used microhistological faecal analysis to determine the diet selection of forest buffalo and measured the extent of variation between a dry season, preburn and a wet season, postburn sampling period. The buffalo diet comprised mainly of monocotyledons, primarily grasses (Poaceae) and sedges (Cyperaceae). Intake of open‐area‐associated plant species was higher in the wet season, postburn treatment sampling period (97%) than the dry season, preburn sampling period (87%), which corresponded conversely to a reduction in forest‐associated Marantaceae plants (10% versus 1%). High proportions of grasses and sedges in the diet signify the importance of open areas for forest buffalo. Controlled burning as tool for maintenance of open areas may play a key role in the meta‐population management of the forest buffalo.

Arson, Communities, and Social Conflict in Later Medieval England

Fires played a central role in medieval communities, whether they were licit, as in annual communal rituals, or illicit, and fires could draw communities together in protest or celebration as well as in creating boundaries between feuding parties. Arson attacks were open and public demonstrations of discontent, at the root of which could lie inter-personal disputes, including feuds, as well as wider social protest and revolt. Incendiarism was therefore a very public crime affecting whole communities, which drew these communities into the dialogue between the arsonist(s) and their victim(s). This article examines some aspects of the relationship between arson and communities, as well as the role of arson in the reification of certain communal bonds.

Annual vegetation burns across the northern savanna region of Ghana: period of occurrence, area burns, nutrient losses and emissions

This study has assessed the seasonal occurrence of annual vegetation fires and defined inter-seasonally burned area for the different vegetation cover types across Ghana and the northern region of Ghana using 10-year (2001–2010) remote sensing data. These values were used with fire induced elemental losses to estimate greenhouse gas emissions and net plant nutrient loss due to gross bush fire nutrient transfers and annual atmospheric nutrient depositions. About 21, 68, 10 and 1 % of annual burns across the northern region of Ghana take place in the months of November, December, January and February respectively. As much as 68 ± 4 thousand km2 (25–32 %) and 37 ± 2.6 thousand km2 (46–60 %) of dry land are annually burned across Ghana and the northern region of Ghana respectively, with 53–56 % of the total annual burns across the country taking place in the northern region. About 10,100–28,400 Gg of C, comprising 215–4,700 thousand Gg of CO2 equivalent (CO2, CH4) potential global warming green house gases and 48–324 thousand Gg of local pollutants (CO, NOx) are estimated to be released annually through bush fire occurrence across Ghana. Net negative balance for P between fire-induced nutrient transfers and, annual wet and dry nutrient deposits is of concern given the high P-sorbing mineral content of the soils. The temporal loss of P suggest an input source than wet and dry atmospheric P depositions for the sustenance of the ecosystem or predict a long term threat to regional food production.

Influências de Atta spp. (Hymenoptera: Formicidae) na recuperação da vegetação pós-fogo em floresta de transição amazônica

Este estudo investigou o papel das saúvas na recuperação da vegetação pós-fogo. Foi hipotetizado que a perturbação do fogo aumenta a abundância de ninhos de saúva (1) e as atividades de remoção de sementes (2) e desfolha (3), especialmente no ambiente de borda. Os ninhos de saúva foram inventariados e mapeados e após 17 meses, checados para o registro de sua atividade e de novas colônias emergindo na área. Realizou-se experimentos comparativos de remoção de sementes e desfolha de plântulas em duas parcelas de 50 ha, uma submetida a fogo anual (tratamento) e outra sem fogo (controle). A abundância de ninhos de saúva foi maior na parcela tratamento que na parcela controle, especialmente na borda da floresta. As espécies encontradas foram: Atta cephalotes, A. laevigata e A. sexdens , sendo esta última a espécie mais abundante e que mostrou aumento em número de colônias ativas após 17 meses. O aumento na abundância de ninhos na parcela tratamento foi acompanhado por um aumento na atividade dessas formigas. Enquanto mais de duas folhas foram arrancadas por plântula nessa parcela, menos de uma foi registrada na parcela controle. Também a abundância média de galhos desfolhados e de sementes removidas por saúvas foi maior na parcela tratamento que na parcela controle. As saúvas tanto podem diminuir ou retardar o processo de regeneração florestal pós-fogo, quanto acelerá-lo, devido à elevada predação seletiva que favorece as espécies menos palatáveis. Desta forma, suas atividades podem modificador apenas a composição da vegetação recuperando-se do fogo.

伝統行事「京都五山送り火」の形態と祭祀組織に関する研究

The traditional event, “Kyoto Gozan-Bonfire” is one of the annual fire festivals carried out at the Eastern, Northern and Western Mountain surrounding Kyoto city on August 16. It is in conjunction with the famous O-bon festival in Japan, a tradition of seeing the spirits of the dead off. Ritual organizing committees exist at Ginkakuji, Matsugasaki, Nishigamo, Kinugasa and Saga areas. This special tradition is no longer confined to these special areas, but has expanded to involve wider a resident of Kyoto and Japanese. Traditionally, Japanese red pines had been used as bonfire material and also as local resources for daily life or annual events, but the fuel revolution in 1955 caused abandonment of forestry management. As a result, red pines are scarce and only one of five organizing committees can barely manage to get them. There are other additional problems in continuing this tradition despite the people’s intentions to preserve. So, we studied to distinguish the morphology of each bonfire and features of the ritual organizing committees and what is necessary to make this event a success from three point of views: material, talented personnel and funding.

Forest fire activity in Sweden: Climatic controls and geographical patterns in 20th century

We used Swedish county-scale forest fire statistics to quantify modern fire activity, identify its main temporal and geographical patterns, and evaluate statistical performance of six fire-related weather indices as proxy of fire activity in Sweden over 1942–1975 and 1996–2008, the periods with available county-scale fire statistics. The analyzed indices were monthly precipitation, SPI, MDC, PDSI, calibrated PDSI, and DI, a Drought Index calculated as a ratio between actual and equilibrium evapotranspiration. The modern fire cycle (FC) in the northern part of Sweden varies between 2 × 10 3 and 3 × 10 4 years, whereas in southern Sweden the FC is somewhat shorter (10 3–2 × 10 4 years). No temporal trend in average FC was evident at the country scale between the two periods. Significant and negative values of a Mantel test, obtained on county data for both periods ( r = −0.494, p = 0.001 for 1942–1975 and r = −0.281 and p = 0.015 for 1996–2008) indicated the presence of a geographical pattern in annual forest fire activity. Over 1942–1975, PCA revealed that the central and northern counties formed one group with synchronized fire activity, and the southern and south–western counties formed another group. This pattern became less evident during the more recent period (1996–2008). Over 1996–2008, the analysis showed little synchronicity in annual fire activity across different parts of the country. The geographical position of a county had a clear effect on seasonal pattern of forest fires. In southern Sweden, the peak in the number of fires and the burnt area was in April–May, during a relatively short dry period immediately following the snowmelt. In northern Sweden, fires in the second half of fire season dominated the total annual area burnt. Analyzed indices differed considerably in their predictive power in respect to counties’ records of annual area burnt. Calibrated PDSI was a superior proxy of fire activity for the southern region ( R 2 = 60.8% in regression against total annual area burnt for respective provinces), and DI late (Drought Index for the first half of the growing season) was superior for the northern counties ( R 2 = 73.3%). Predictive power of the indices was much higher for the recent period (1996–2002), with R 2 values staying within 81.2 and 97.8%. Even if modern levels of forest fire activity in Sweden are very low from historical perspective, there is a strong spatiotemporal association between fire activity and climatic variability at regional scales, which provides a basis for modeling of the future fire hazard.

A 1416-year reconstruction of annual, multidecadal, and centennial variability in area burned for ponderosa pine forests of the southern Colorado Plateau region, Southwest USA

Fire history reconstructions from fire scars in tree rings have been valuable for assessing fire regime changes and their climatic controls. It has been asserted, however, that these two- to four-century long records from the western USA are unrepresentative of longer periods of the Holocene and are of limited use for understanding current or future fire regimes. The Medieval Climate Anomaly (800–1300 ce) is often suggested as a better analog for future Southwestern US climates but is beyond the chronological range of most fire-scar studies in this region. To evaluate fire regime changes over the past millennium, we build on centennial-length fire–climate studies to generate a 1416 year long reconstruction of fire activity in ponderosa pine forests of the Southern Colorado Plateau region of Arizona and New Mexico. We used a split-period calibration and verification protocol to test the reliability of a multiple regression model using annual and antecedent precipitation (reconstructed from tree-ring width chronologies) to predict the percentage of fire-scar localities (i.e. sites, N=45) that recorded extensive fires within those sites (>25% of recorder trees scarred) each year between 1700 and 1899 ce. The model explains approximately 50% of the variation in annual fire activity. Applying the model to the entire precipitation reconstruction provides a proxy for annual area burned since 572 ce. There are no statistically significant differences between the period available for fire-scar study (1600 ce–present) and the Medieval Climate Anomaly (800–1300 ce) in terms of predicted annual area burned or the frequencies of regional fire years. Multidecadal and centennial variation in the frequencies of regional fire years, however, does indicate reduced surface fire frequencies from approximately 700–800 ce and 1360–1455ce. We hypothesize that these were periods when some forests were vulnerable to altered canopy structure, accumulated fuels, and increased fire severity.

Global interannual variability in terrestrial ecosystems: sources and spatial distribution using MODIS-derived vegetation indices, social and biophysical factors

Variations in global vegetation activity were measured at a global scale, from 2000 to 2006, based on the Enhanced Vegetation Index (EVI) extracted from the 1km resolution Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. Interannual variations in phenology and/or in annual integrated vegetation index are mapped using change metrics. The relationships between interannual variability and climate, ecosystem disturbances and land use are also examined. Around 14% of the study area experienced high interannual variability in land surface attributes over the six years. The ecosystems most subjected to large fluctuations in surface conditions were the boreal ecosystems, temperate ecozones, and subtropical and tropical steppes. These changes were largely related to rainfall variability and were associated with mean annual rainfall, agriculture, fire regimes and population density. Large population concentrations were mostly found in more stable ecozones. Rainfall and natural fire regimes explained more than half of the land surface variability in Australia. An additional global analysis on trends in vegetation activity also shows that around 4.5% of the vegetated surface of the Earth, excluding deserts and frequently cloudy regions, experienced a continuous decrease in vegetation activity over the six years. This represents more than twice the area experiencing a greening trend over this time period and concerns mostly tropical, subtropical and temperate forest ecozones. The total change in vegetation activity at a global scale and per year amounted to –2% of the annual integrated EVI aggregated across all ecosystems of the study area, on average for the years 2001–2006.

Leafcutter Ant Nests Inhibit Low-Intensity Fire Spread in the Understory of Transitional Forests at the Amazon's Forest-Savanna Boundary

Leaf-cutter ants (Attaspp.) remove leaf litter and woody debris—potential fuels—in and around their nests and foraging trails. We conducted single and three annual experimental fires to determine the effects of this leaf-cutter ant activity on the behavior of low-intensity, slow-moving fires. In a transitional forest, where the southern Amazon forest meets the Brazilian savanna, we tested whether leaf-cutter ant nests and trails (i) inhibit fire spread due to a lack of fuels, and (ii), thereby, reduce the total burned area during these experimental low-intensity fires, particularly at forest edges where leaf-cutter ant abundance was higher. Fine-medium fuel mass increased with an increase in distance from ant nest, and the mean area of bare soil was greater on nests than on the forest floor. Between 60 to 90 percent of the unburned area was within 30 m of ant nests, and burned area significantly increased with increasing distance to ant nests. In addition, the number of ant nests declined with increasing distance from the forest edge, and, with exception of the first experimental fire, burned area also increased with increasing distance from the edge. The present study provides new insight to fire ecology in Amazon environments.

The role of savannas in the terrestrial Si cycle: A case-study from Lamto, Ivory Coast

Savannas currently occupy a fifth of the earth's land surface and are predicted to expand in the next few centuries at the expense of tropical forests, mainly as a result of deforestation and human fires. Can such a vegetation trend impact, through changes in plant Si cycling, the lithogenic silicon (LSi) release into soils (through chemical weathering) and the net dissolved Si (DSi) outputs from soils to stream water (through chemical denudation)? The first step of an investigation requires quantifying the net Si fluxes involved in the plant/soil system. Here, a schematic steady-state Si cycle, established for a tropical humid savanna (Lamto, Ivory Coast) that developed on a ferruginous soil and is subjected to annual fires, is presented. Erosion was assumed to be insignificant. LSi and biogenic Si (BSi under the form of phytoliths) pools were measured, and Si fluxes were estimated from Si concentrations and mass balance calculation. Identification of plant and soil phytoliths indicated that the soil BSi pool is in equilibrium with the current BSi input by the savanna. In the soil column, mixing between a young rapidly recycled BSi pool and an old stable BSi pool is attested by a mixing line equation. Storage of the old BSi pool is assimilated as a BSi output from the plant/soil system. A BSi output additionally occurs after annual fires, when ashes are exported. Both BSi outputs decrease as much the BSi dissolution. In order to uptake constant DSi flux, the savanna increases by three to eight times the net LSi release, depending upon the post-fire ash exportation scenario. A comparison between savanna and rainforest Si cycles that maximizes the differences in plant/soil systems and minimizes differences in climate is presented. The comparison revealed that BSi storage is higher in the savanna soil than in the rainforest soil, mainly due to BSi production that is twice higher in the savanna (127 vs 67 kg/ha/yr). The resulting LSi release that is enhanced by plant uptake is more than 1.5 higher in the savanna than in the rainforest (from 33 to 85 kg/ha/yr in the savanna vs 21 kg/ha/yr in the rainforest). On the contrary, DSi output from soils to stream water, which is not controlled by plant Si cycling but more likely by the soil hydrological regime (or meteoric weathering), is close to twice as high in the rainforest/ferrallitic soil ecosystem (16 vs 9 kg/ha/yr). This case study suggests that the predicted expansion of savannas at the expense of forests should significantly increase DSi uptake by plants, BSi storage in soils, BSi output with ash exportation, and, hence, LSi release through chemical weathering, without direct impact on DSi outputs from soils to stream water. Tracks for further assessing the role of plant Si cycling on chemical weathering, Si and C cycles were suggested: 1) estimates of BSi fluxes that were wrongly based on the assumption that the amount of DSi leached out from soils is linked to the magnitude of plant Si cycling and/or to BSi concentration in soils should be reappraised and 2) changes in the magnitude of plant Si cycling should be accounted in geochemical carbon cycle models, for one of the plant-induced weathering mechanisms.

Dominant species’ resprout biomass dynamics after cutting in the Sudanian savanna-woodlands of West Africa: long term effects of annual early fire and grazing

The potential of forest to regenerate after harvesting is a key element for sustainability of the ecosystem. For semi-arid tropical savanna environments, managing resprouts after tree cutting is ideally suited because of the natural ability of many indigenous species to regenerate vegetatively. Regeneration in this ecosystem is, however, prone to many disturbance factors such as fire and grazing by livestock. In this paper, we used a factorial experiment to examine the long-term effects of annual early burning and grazing on dominant species' resprout biomass dynamics after selective cutting in the Sudanian savanna-woodlands of Burkina Faso, West Africa Burning decreased shoot mortality of Crossopteryx febrifuga while grazing increased that of Detarium microcarpum. Burning, in later measurement years, reduced resprouts' size of Acacia macrostachya, C. febrifuga and D. microcarpum while an increased basal area was observed for Combretum glutinosum. There was no significant evidence of grazing hampering growth. Moderate livestock grazing could be integrated in the forest management prescriptions in Burkina Faso for the sake of multi-purpose uses, while more attention should be paid to burning practices to lower fire severity, as complete fire exclusion is utopian in this savanna ecosystem.

Implications of fires on carbon budgets in Andean cloud montane forest: The importance of peat soils and tree resprouting

Fire in tropical montane cloud forests (TMCFs) is not as rare as once believed. Andean TMCFs sit immediately below highly flammable, high-altitude grasslands (Puna/Páramo) that suffer from recurrent anthropogenic fire. This treeline is a zone of climatic tension where substantial future warming is likely to force upward tree migrations, while increased fire presence and fire impacts are likely to force it downwards. TMCFs contain large carbon stocks in their peat soils and their loss through fire is a currently unaccounted for regional source of CO 2. This study, conducted in the southern Peruvian Andes (>2800 m), documents differences in live tree biomass, fine root biomass, fallen and standing dead wood, and soil organic carbon in 4 paired-sample plots (burned versus control) following the severe ground fires that occurred during the 2005 Andean drought. Peat soils contributed the most to biomass burning emissions, with lower values corresponding to an 89% mean stock difference compared to the controls (mean ± SE) (54.1 ± 22.3 vs. 5.8 ± 5.3 MgC ha −1). Contrastingly, carbon stocks from live standing trees differed by a non-significant 37% lower value in the burned plots compared to the controls, largely compensated by vigorous resprouting (45.5 ± 17.4 vs. 69.2 ± 13.4 MgC ha −1). Both standing dead trees and fallen dead wood were significantly higher in the burned plots with a three-fold difference from the controls: dead Trees 45.2 ± 9.4 vs. 16.4 ± 4.4 MgC ha −1, and ca. a 2 fold difference for the fallen dead wood: 11.2 ± 5 vs. 6.7 ± 3.2 MgC ha −1 for the burned plots versus their controls. A preliminary estimate of the regional contribution of biomass burning emissions from Andean TMCFs for the period 2000–2008, resulted in mean carbon emission rates of 1.3 TgC yr −1 (max-min: 1.8–0.8 TgC yr −1). This value is in the same order of magnitude than South American annual fire emissions (300 TgC yr −1) suggesting the need for further research on Andean forest fires. On-going projects on the region are working on the promotion of landowner participation in TMCFs conservation through REDD+ mechanism. The heart of the proposed initiative is reforestation of degraded lands with green fire breaks enriched with economically valuable Andean plant species. The cultivation of these species may contribute to reduce deforestation pressure on the Amazonian cloud forest by providing an alternative income to local communities, at the same time that they prevent the spread of fire into Manu National Park and adjacent community-held forests, protecting forest and reducing CO 2 emissions.

Levantamento de Espécies Rústicas em Área de Pastagem e em Remanescente Florestal na Mata Atlântica, Piraí-RJ

Rustic species are those capable of being established on land with steep slopes; low infiltration; stony, shallow, poor-nutrient soil; such as the areas undergoing intense human activities, like cattle-raising and annual fires. This work sampled and examined the occurrence of arboreal rustic species in pasture areas and in disturbed 28-year-old forest remnants without conservation measures other than isolation from cattle. Both areas show similar physical environmental and ecological factors. The study was conducted within the ‘Cacaria’ river watershed, located in the ‘Cacaria’ district in Pirai, in the southern part of State of Rio de Janeiro. 131 individual trees were sampled in an approximately 22 ha disturbed pasture area. The trees were distributed in 14 species and grouped in nine families. 130 individual trees belonging to 21 species and 13 families were sampled in 10 ample plots (0.1 ha) in the forest remnants. The rustic species of greater abundance were: Guarea guidonia, Tabernaemontana laeta, Peltophorum dubium and Sparattosperma leucanthum, which were present in both study areas. These species colonized the area of pasture and the environment to promote the development of natural regeneration.

How does fire intensity and frequency affect miombo woodland tree populations and biomass?

Miombo woodlands are the largest savanna in the world and dominate southern Africa. They are strongly influenced by anthropogenic fires and support the livelihoods of over 100 million people. Managing the fire regime of these flammable systems is difficult, but crucial for sustaining biodiversity, ecosystem services, and carbon stocks. Fire intensity is more easily manipulated than fire frequency, because suppression is expensive and ineffective. However, there are important issues relating fire intensity to impacts on woody vegetation that need to be understood to inform management approaches. Such impacts include the links between fire intensity, tree top-kill, resprouting, and regrowth rates. Here we present results from a fire experiment in Mozambican miombo; the results of a 50-year fire experiment in Zimbabwean miombo; and observations of forest structure at a dry-forest site in Mozambique. We synthesize these data with a process-based gap model of stem growth, regeneration, and mortality; this model explicitly considers the effect of different frequencies and intensities of fire. We use the model, tested against the field data, to explore the sensitivity of woodland tree populations and biomass to fire intensity and frequency. The fire experiments show that large (> 5 cm dbh) stems are vulnerable to fire, with top-kill rates of up to 12% in intense fires. In contrast to idealized physical representations of tree mortality, stems of > 10 cm dbh did not gain further protection from fire with increasing dbh. Resprouting was very common and not obviously linked to fire intensity. The modeling showed that miombo tree populations and biomass are very sensitive to fire intensity, offering opportunities for effective management. At any achievable fire return interval (< 5 years), low-intensity fires are required to maintain observed biomass. Model predictions and field experiments show that no tree biomass can be sustained under annual fires.

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

Abstract:A fire-mediated recruitment bottleneck provides a possible explanation for the coexistence of trees and grasses in mesic savannas. The key element of this hypothesis is that saplings are particularly vulnerable to fire because they are small enough to be top-killed by grass fires, but unlike juveniles, they take several years to recover their original size. This limits the number of recruits into the adult size classes. Thus savanna vegetation may be maintained by a feedback whereby fire restricts the density of adult trees and allows a grass layer to develop, which provides fuel for subsequent fires. Here, we use results from a landscape-scale fire experiment in tropical Australia, to explore the possible existence of a recruitment bottleneck. This experiment compared tree recruitment and survival over 4 y under regimes of no fire, annual early and annual late dry-season fire. Stem mortality decreased with increasing stem height in the fire treatments but not in the unburnt treatment. Tree recruitment was 76–84% lower in the fire treatments than the unburnt treatment. Such fire-induced stem loss of saplings and reduced recruitment to the canopy layer in this eucalypt savanna are consistent with the predictions of the fire-mediated recruitment bottleneck hypothesis.

Hierarchical space-time models for fire ignition and percentage of land burned by wildfires

Policy responses for local and global fire management as well as international green-gas inventories depend heavily on the proper understanding of the annual fire extend as well as its spatial variation across any given study area. Proper statistical models are important tools in quantifying these fire risks. We propose Bayesian methods to model jointly the probability of ignition and fire sizes in Australia and New Zeland. The data set on which we base our model and results consists of annual observations of several meteorological and topographical explanatory variables, together with the percentage of land burned over a grid with resolution of 1° across Austalia and New Zealand. Our model and conclusions bring improvements on the results reported by Russell-Smith et al. in Int J Wildland Fire, 16:361–377 (2007) based on a similar data set.

Exercise Headcount: What do you do with 800 scientists who cannot return to the building they have just evacuated?

Annual fire drills serve a valuable purpose in ensuring familiarity with evacuation procedures. However, the limited duration of these exercises may be far from the reality of a real incident. In this situation, the ability to return back into a building may be restricted for hours or days. As an emergency manager, this raises a number of questions, including what to do with the evacuated colleagues, how to provide welfare support and how to identify those people who require the most immediate assistance. This paper focuses on these questions through a case study of ‘Exercise Headcount’. Developed in response to the situation Pfizer faced as a result of the 2007 New York steam-pipe explosion, the paper provides an overview of the post-evacuation mustering and triage system that was developed for the Pfizer Research &amp; Development site at Sandwich, UK.

Aboveground biomass of functional groups in the ground layer of savannas under different fire frequencies

Savannas with different fire histories should have differences in aboveground biomass due to varying responses of functional groups. We investigated the effects of different fire frequencies on total aboveground biomass and also the biomass of functional groups (the tussock grass Tristachya leiostachya Nees, other grasses, small woody individuals) and dry biomass in savannas subjected to annual fires, biennial fires, and protected from fire for 12 years. Total biomass in the protected area was more than twice that of the annually burned area. T. leiostachya aboveground biomass was higher in the protected area than in annually and biennially burned areas, which were not different. Biomass of other grasses was lower in the protected area, whereas woody biomass values did not differ among areas. In the biennially burned and protected areas, we found a positive relationship between T. leiostachya and dry biomass. In the annually burned area, T. leiostachya biomass was negatively correlated with the biomass of other grasses and woody individuals. This negative correlation supports the idea that frequent fires favour the former, and may indicate an outcompeting effect. Knowledge not only about biomass but especially about its functional components is necessary to understand the processes and management consequences of different burning strategies.

Herbaceous phytomass and nutrient concentrations of four grass species in Sudanian savanna woodland subjected to recurrent early fire

AbstractFire is an integral ecological factor in African savanna ecosystems, but its effects on savanna productivity are highly variable and less understood. We conducted a field experiment to quantify changes in herbaceous phytomass and nutrient composition in a Sudanian savanna woodland subjected to annual early fire from 1993 to 2004. Fire effects were also assessed on two perennial and two annual grass species during the following growing season. Early fire significantly reduced above‐ground phytomass of the studied species (P = 0.03), their crude protein (P = 0.022), neutral detergent insoluble crude protein (P = 0.016) and concentrations of Ca, Fe and Mn (P &lt; 0.05). Perennial grasses had higher above‐ground phytomass but lower total crude protein and fat than annual grasses. Nonstructural carbohydrates tended to be higher for annuals, while fibre and lignin contents were high for perennials. Except Na and Fe, the concentration of mineral elements varied between species. Fire did not affect measures of digestibility and metabolizable energy, but its effect differed significantly among species. In conclusion, the results illustrate that long‐term frequent fire will counterbalance the short‐term increase in soil fertility and plant nutrient concentrations claimed to be accrued from single or less frequent fire.