Post-burn reproduction of woody plants in a neotropical savanna: the relative importance of sexual and vegetative reproduction

1. Burning typically occurs at intervals of 1–3-years in the Brazilian cerrado, a rate that exceeds the precolonization fire regime. To determine if woody plants of the cerrado successfully reproduce within the short span of time between burns, experimental burns were used to quantify the effects of fire on sexual and vegetative reproduction of six species of resprouting trees and shrubs.
2. Four of the six species reproduce vegetatively by producing root suckers. For three of these species, Rourea induta , Myrsine guianensis and Roupala montana , sucker production was seven to 15 times greater in burned plots than in unburned controls.
3. Fire had a negative impact on sexual reproduction. Fire caused an immediate reduction in sexual reproductive success by destroying developing reproductive structures and seeds. Additionally, five of the six study species exhibited overall reductions in seed production in the years following fire. Fire had this effect by reducing the individual size of all species and, for three species, by reducing size-specific reproductive output. Only the tree Piptocarpha rotundifolia exhibited increased seed production following burning.
4. Fire caused substantial mortality to both seedlings and suckers. Suckers were larger than seedlings and experienced lower mortality rates for two of three species. Fire-induced mortality of seedlings varied greatly among species, ranging from 33% to 100%.
5. The results indicate that vegetative reproduction is much more successful than sexual reproduction under the high fire frequency typical of current fire regimes. It is concluded that current fire regimes must be causing a shift in species composition, favouring species capable of vegetative reproduction.     

Fire tolerance of perennial grass tussocks in a savanna woodland

Grass populations in tropical savannas are highly resilient in relation to different fire regimes, but the mechanisms conferring such resilience have been poorly studied. Here we examine one such mechanism, high adult survival during fire, for three perennial grass species in an Australian savanna: Eriachne triseta Nees ex Steud, Eriachne avenacea R.Br and Chrysopogon latifolius S.T.Blake. The study examined survivorship after 3 years, at plots subject to experimental fire regimes (experiencing 0, 1, 2 or 3 fires over the study period) at the Territory Wildlife Park near Darwin in the Northern Territory, Australia. Mean survivorship was 79.9%, 64.3% and 62.0% for E. avenacea, E. triseta and C. latifolius respectively. For the two species of Eriachne, mean survivorship was highest (E. avenacea, 94.6%; E. triseta, 77.1%) in unburnt plots, whereas survivorship of C. latifolius was highest (71.7%) under highest fire frequency. However, variation in survivorship among fire regime treatments was not statistically significant for any of the study species. This negligible difference in survivorship among regimes points to fire tolerance (sprouting ability) as an important mechanism contributing to the resilience and persistence of perennial grasses in these savannas.     

Distinct roles of savanna and forest tree species in regeneration under fire suppression in a Brazilian savanna

Questions: Has fire suppression relaxed barriers to the exchange of species between savanna and forest? Do all species or a subset of species participate in this exchange? Would current vegetation structure persist if fire suppression were to cease? Location: A gallery forest edge in the Cerrado region of central Brazil that burned only once in the past 35 years. Methods: Density of tree seedlings, saplings and adults, leaf area index (LAI), tree basal area and diameter were surveyed in 12, 10 m × 70 m transects centred on and perpendicular to the forest–savanna boundary. Community composition was assessed using non‐metric multi‐dimensional scaling (NMDS). Results: Basal area and LAI declined substantially from forest to savanna, with an associated shift in species composition. Savanna tree species were nearly absent in the forest, but accounted for the majority of stems in the savanna. In contrast, forest species comprised 14% of adults and more than one‐third of juveniles in the savanna. Despite the high diversity of trees (85 species) in the forest, five species play a particularly large role in this initial phase of forest expansion. Reintroduction of fire, however, would result in widespread topkill of juveniles and the majority of adult forest trees, thereby interrupting the succession towards forest. Conclusions: After 35 years during which the site burned only once, the savanna still remains dominated by savanna species. Nevertheless, the dominance of forest juveniles in border and savanna tree communities suggests that with a continued policy of fire suppression, the forest will continue to expand.     

Lopesia indaiensis (Diptera,Cecidomyiidae), a new species of gall midge feeding on Andira fraxinifolia Benth (Fabaceae), an endemic plant in Brazil

Lopesia indaiensis (Diptera, Cecidomyiidae), a new species of gall midge found causing galls on Andira fraxinifolia (Fabaceae), an endemic plant species in Brazil, is described based on larva, pupa, male and female. L. indaiensis galls were collected in Dores do Indaiá, State of Minas Gerais, Southeastern Brazil. Larvae were removed from the galls and pupae and adults were obtained by rearing. The specimens were mounted on slides and the most important morphological characters were illustrated. The new species was compared to the other species of Lopesia.     

Fire season effects on the recruitment of non‐sprouting serotinous Proteaceae in the eastern (bimodal rainfall) fynbos biome,South Africa

Abstract Research in Mediterranean‐climate shrublands in both South Africa and Australia shows that recruitment of proteoid shrubs (non‐sprouting, serotinous Proteaceae) is best after warm‐season (summer and autumn) fires and worst after cool‐season (winter and spring) ones. This pattern has been attributed to post‐dispersal seed attrition as well as size of pre‐dispersal seed reserves. Here we investigate patterns of post‐fire recruitment for four proteoid species in the eastern part of South Africa's fynbos biome, which has a bimodal (spring and autumn) rainfall regime. Despite the lack of significant differences in recruitment between cool‐ and warm‐season burns, we find some evidence for favourable recruitment periods following fires in spring and autumn, immediately before, and coinciding with, the bimodal rainfall peaks. This suggests that enhanced recruitment is associated with conditions of high soil moisture immediately after the fire, and that rapid germination may minimize post‐dispersal seed attrition. In two of the species, we also find a shift from peak flowering in winter and spring in the Mediterranean‐climate part of the fynbos biome, to summer and autumn flowering in the eastern part. Because these two species are only weakly serotinous, warm‐season flowering would result in maximal seed banks in spring, which could explain the spring recruitment peak, but not the autumn one. We conclude that eastern recruitment patterns differ significantly from those observed in the western and central parts of the biome, and that fire management protocols for the east, which are currently based on data and experience from the winter‐rainfall fynbos biome, need to be adjusted accordingly. Fire managers in the eastern fynbos biome should be less constrained by requirements to burn within a narrow seasonal range, and should therefore be in a better position to apply the required management burns.     

Ecology of Pericopsis elata (Fabaceae), an Endangered Timber Species in Southeastern Cameroon

Pericopsis elata (Fabaceae) is a tall tree of high commercial value of the moist semi‐deciduous African forests. As a result of decades of logging it is now considered as threatened and listed on the IUCN Red List and CITES Appendix II, even though essential biological parameters controlling its population dynamics remain unknown. This study aims at improving the knowledge of the species' ecological parameters, and at assessing the impact of selective logging on its populations in an 118,052 ha forest in Cameroon. After inventorying the species in 1432 ha, mortality and growth were assessed over continuous 5‐ and 2‐yr periods in unlogged and logged areas, respectively. Phenology was monitored in the unlogged forest during 5 yr. The population structure shows high relative abundance of trees in medium size categories. Mean annual diameter increments in both environments did not differ significantly between unlogged and logged areas. P. elata is a deciduous species that flowers at the end of the main dry season. The minimum reproduction and effective flowering diameters were 32 and 37 cm, respectively. Fruit maturation took place during 7 mo. With a minimum logging diameter of 90 cm, the recovery rate computed over a 30‐yr period was > 100 percent. Selective logging harvested only 12.1 percent of the total number of seed trees and had little influence on the species' biological parameters. Securing sufficient regeneration as a post‐logging action is probably the most important consideration for achieving long‐term sustainability.     

Heat effects on seeds and rhizomes of a selection of boreal forest plants and potential reaction to fire

To analyse the potential reaction to firegenerated heat pulses, seeds of 12 species of plants and rhizomes of three species were exposed to elevated temperatures for 10 min. The tested material split into three groups with respect to heat tolerance: (1) the rhizomes, for which the lethal temperatures were in the range 55–59° C; (2) the seeds of most of the species tested, for which the lethal temperatures were in the range 65–75° C; (3) The seeds of two species of Leguminosae and three species of Geranium for which the lethal temperatures were around 100° C. For all three Geranium species and for one of the legume species, Anthyllis vulneraria, exposure temperatures above ca. 45° C resulted in dormancy release, and maximum germination occurred above 60–65° C. Speed of germination was little affected for most species, except after exposure to nearlethal temperatures, where it slowed down dramatically, although the seedlings emerging were healthy. We conclude that due to sharp temperature gradients in the soil during fire, differences in heat tolerance between species in most cases are not large enough to be a decisive factor in their post-fire colonising success. There are exceptions: the seeds of certain taxa that are impermeable to water in the dormant state, some of which have heat triggered germination.     

Positive feedbacks between plant invasions and fire regimes: <Emphasis Type="Italic">Teline monspessulana</Emphasis> (L.) K. Koch (Fabaceae) in central Chile

Invasive species can increase fire frequency and intensity, generating favorable conditions for their self-perpetuation. Mediterranean south-central Chile may be especially prone to the effects of invasive species on fire regimes because it is less adapted to fire and it contains a highly endemic flora. Teline monspessulana (L.) K. Koch (syn. Cytisus monspessulanus L.; Genista monspessulana (L.) L.A.S. Johnson) is an introduced shrub that forms monotypic stands or is present as an understory species in native forests as well as in forestry plantations. Dense T. monspessulana stands are completely destroyed by fire, generating the conditions for it seeds to germinate and establish an abundant regeneration, with up to 900 plants/m². We report key evidence on abundance and biomass in adult stands, and patterns of seed bank and regeneration after fire in stands of T. monspessulana around the city of Concepción, Chile. We estimated living biomass in pure stands and underneath Eucalyptus plantations. In burned areas, we assessed T. monspessulana seed bank and studied regeneration patterns. We found that T. monspessulana densities reaches 52,778 plants/ha and 8.92 ton/ha in pure stands and 34,223 plants/ha and 2.31 ton/ha underneath Eucalyptus plantations. T. monspessulana generates small caliper fuel and acts as a ladder-fuel. Large soil seed banks allow for abundant regeneration after fire, with mean densities of 877,111 plants/ha, but an overall mortality of 37.2% in the first year after the fire. The high values of regeneration compared to final densities in adult stands suggest that density-dependent mortality. Our results indicate that T. monspessulana regeneration is not only favored by fires, but also that the species creates favorable conditions for intense and continuous fires, both under pure conditions, but also associated to exotic tree plantations. To understand the implications of positive feedbacks between invaders and fire, we recommend focusing in the mechanisms by which they increases fuel accumulation and fuel flammability, and how higher fire frequency and intensity favors invasive species recruitment over native species. Comprehension of this dynamics will allow for better management and control of these invasions which have major ecological, economical and social implications.     

Host specificity of a Brazilian mistletoe, Struthanthus aff. polyanthus (Loranthaceae), in cerrado tropical savanna

The aim of this study was to determine if the mistletoe Struthanthus aff. polyanthus shows host specificity, and if host abundance and twig architecture influence this specificity in Cerrado (senso strictu). An area of 1.3 ha of natural savanna was sampled for the occurrence of the mistletoe. The twigs of the hosts were classified as vertical or horizontal, and the bark as smooth or rough. We sampled a total of 666 trees in the study site and 118 individuals (17.7%) hosted S. aff. polyanthus. The abundance of mistletoe was significantly affected by the bark type, but not by the twigs inclination. In the cerrado, S. aff. polyanthus seems to be a generalist, with a tendency to be more common on some hosts (Kielmeyera coriacea, Pouteria ramiflora and Styrax ferrugineus), prefering that with rough bark type.     

Drivers of fire occurrence in a mountainous Brazilian cerrado savanna: Tracking long-term fire regimes using remote sensing

Fire is a natural disturbance in savannas, and defines vegetation physiognomy and structure, often influencing species diversity. Fire activity is determined by a wide range of factors, including long and short term climatic conditions, climate seasonality, wind speed and direction, topography, and fuel biomass. In Brazil, fire shapes the structure and composition of cerrado savannas, and the impact of fire on vegetation dynamics is well explored, but the drivers of variation in fire disturbance across landscapes and over time are still poorly understood. We reconstructed 31 years of fire occurrence history in the Serra do Cipó region, a highly-diverse cerrado landscape, located in the southern portion of the Espinhaço mountain range, state of Minas Gerais, Southeastern Brazil. We mapped burn scars using a time series of Landsat satellite images from 1984 to 2014. Our questions were 1) How does fire occurrence vary in time and space across the Serra do Cipó cerrado landscape? 2) Which climatic drivers may explain the spatial and inter-annual variation in fire occurrence on this landscape? 3) Is fire occurrence in this cerrado landscape moisture-limited or fuel-limited? We evaluated the inter-annual variation and distribution of burned areas, and used linear models to explain this variation in terms of rainfall amount (determinant of fuel load production), seasonal rainfall distribution (determinant of dry fuel availability), abnormality of precipitation (Standardized Precipitation Index – SPI), and vegetation type (Enhanced Vegetation Index – EVI). Contrary to our expectations, annual rainfall volume was weakly and negatively correlated with burned area, and the strongest predictor of burned area was drought during the ignition season. The length of the dry season and the distribution of rain along the season determined ignition probability, increasing fire occurrence during the driest periods. We conclude that the mountain cerrado vegetation at Serra do Cipó has a moisture-dependent fire regime, in contrast to the fuel-dependent fire regimes described for African savannas. These findings imply that savannas at different continents may have different recovery and resilience capabilities when subjected to changes in the fire regime, caused by direct anthropogenic activities or indirectly through climatic changes. The possible effects of these changes on cerrado landscapes are still unknown, and future studies should investigate if currently observed fire regimes have positive or negative impacts on vegetation diversity, recovery, resilience and phenology, thus helping managers to include fire management as conservation measure.     

Variable rainfall has a greater effect than fire on the demography of the dominant tree in a semi‐arid Eucalyptus savanna

Rainfall, fire and competition are emphasized as determinants of the density and basal area of woody vegetation in savanna. The semi‐arid savannas of Australia have substantial multi‐year rainfall deficits and insufficient grass fuel to carry annual fire in contrast to the mesic savannas in more northern regions. This study investigates the influence of rainfall deficit and excess, fire and woody competition on the population dynamics of a dominant tree in a semi‐arid savanna. All individuals of Eucalyptus melanophloia were mapped and monitored in three, 1‐ha plots over an 8.5 year period encompassing wet and dry periods. The plots were unburnt, burnt once and burnt twice. A competition index incorporating the size and distance of neighbours to target individuals was determined. Supplementary studies examined seedling recruitment and the transition of juvenile trees into the sapling layer. Mortality of burnt seedlings was related to lignotuber area but the majority of seedlings are fire resistant within 12 months of germination. Most of the juveniles (≤1 cm dbh) of E. melanophloia either died in the dry period or persisted as juveniles throughout 8.5 years of monitoring. Mortality of juveniles was positively related to woody competition and was higher in the dry period than the wet period. The transition of juveniles to a larger size class occurred at extremely low rates, and a subsidiary study along a clearing boundary suggests release from woody competition allows transition into the sapling layer. From three fires the highest proportion of saplings (1–10 cm dbh) reduced to juveniles was only 5.6% suggesting rates of ‘top‐kill’ of E. melanophloia as a result of fire are relatively low. Girth growth was enhanced in wet years, particularly for larger trees (>10 cm dbh), but all trees regardless of size or woody competition levels are vulnerable to drought‐induced mortality. Overall the results suggest that variations in rainfall, especially drought‐induced mortality, have a much stronger influence on the tree demographics of E. melanophloia in a semi‐arid savanna of north‐eastern Australia than fire.     

Fine-scale spatial genetic structure of Dalbergia nigra (Fabaceae), a threatened and endemic tree of the Brazilian Atlantic Forest

The Atlantic Forest is one of the most diverse ecosystems in the world and considered a hotspot of biodiversity conservation. Dalbergia nigra (Fabaceae) is a tree endemic to the Brazilian Atlantic Forest, and has become threatened due to overexploitation of its valuable timber. In the present study, we analyzed the genetic diversity and fine-scale spatial genetic structure of D. nigra in an area of primary forest of a large reserve. All adult individuals (N = 112) were sampled in a 9.3 ha plot, and genotyped for microsatellite loci. Our results indicated high diversity with a mean of 8.6 alleles per locus, and expected heterozygosity equal to 0.74. The co-ancestry coefficients were significant for distances among trees up to 80 m. The Sp value was equal to 0.017 and indirect estimates of gene dispersal distances ranged from 89 to 144 m. No strong evidence of bottleneck or effects of human-disturbance was found. This study highlights that long-term efforts to protect a large area of Atlantic Forest have been effective towards maintaining the genetic diversity of D. nigra. The results of this study are important towards providing a guide for seed collection for ex-situ conservation and reforestation programmes of this threatened species.     

Astragalus neo-assadianus (Fabaceae), a new species in sect. Alopecuroidei from Iran

Astragalus neo-assadianus (Fabaceae), a new species endemic to Iran, is described and illustrated. This species belongs to A. sect . Alopecuroidei and is distinct and interesting among the Iranian species. It is confined to the north-eastern part of Iran (Khorasan Province) and only known from a single collection close to the Turkmenistan frontier.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 197–200.     

Fire as a dimension of historical ecology: a response to Bowman et al. (2011)

Bowman et al. (Journal of Biogeography, 2011, 38 , 2223–2236) attempt a synthesis of the current status of study into human use of fire as an ecosystem management tool and provide a framework for guiding research on the human dimensions of global fire. While we applaud this ambitious effort, we believe the proposed ‘pyric phase and transition’ model to be too deterministic and simplistic to account for the complexity and diversity in human–fire relationships. After reviewing theoretical problems with the proposed framework, we question policy implications of their conclusions concerning tropical forest systems. We suggest that a theoretically informed perspective should build on an historical fire ecology framework for investigating social and ecological aspects of human–environment interactions.     

Effects of Prescribed Fire and Season of Burn on Recruitment of the Invasive Exotic Plant, Potentilla recta, in a Semiarid Grassland

Abstract Prescribed fire is often used to restore grassland systems to presettlement conditions; however, fire also has the potential to facilitate the invasion of exotic plants. Managers of wildlands and nature reserves must decide whether and how to apply prescribed burning to the best advantage in the face of this dilemma. Herbicide is also used to control exotic plants, but interactions between fire and herbicides have not been well studied. Potentilla recta is an exotic plant invading Dancing Prairie Preserve in northwest Montana. We used a complete factorial design with all combinations of spring burn, fall burn, no burn, picloram herbicide, and no herbicide to determine the effects of fire, season of burn, and their interaction with herbicide on the recruitment and population growth of P. recta over a 5‐year period. Recruitment of P. recta was higher in burn plots compared with controls the first year after the fire, but this did not lead to significant population growth in subsequent years, possibly due to drier than normal conditions that occurred most years of the study. Effect of season of burn was variable among years but was higher in fall compared with spring burn plots across all years. Herbicide effectively eliminated P. recta from sample plots for 3–5 years. By the end of the study density of P. recta was greater in herbicide plots that were burned than those that were not. Results suggest that prescribed fire will enhance germination of P. recta, but this will not always lead to increased population growth. Prescribed fire may reduce the long‐term efficacy of herbicide applied to control P. recta and will be most beneficial at Dancing Prairie when conducted in the spring rather than the fall. Results of prescribed fire on exotic plant invasions in semiarid environments will be difficult to predict because they are strongly dependent on stochastic climatic events.     

Harvesting Increases Reproductive Activity in Himatanthus drasticus (Mart.) Plumel (Apocynaceae), a Non‐Timber Forest Product of the Brazilian Savanna

The harvesting of non‐timber forest products (NTFP) can influence the pattern of resource allocation in plants, affecting their growth, survival, and reproduction. However, only a small number of studies have addressed the impacts of NTFP harvesting on the reproductive phenology of the exploited species. The aim of this observational study was to assess the effects of harvesting and climatic variables on the reproductive phenology of Himatanthus drasticus, a highly exploited medicinal tree from the Brazilian savanna (Cerrado). We evaluated the effects of two different debarking levels (50 and 100%) in comparison to a control (no harvesting). We performed monthly counts of the number of buds, flowers in anthesis, unripe and ripe fruits in each sampled tree (intensity index), as well as the number of trees in each phenophase (activity index), over 2 yr. We used circular statistics tools to compare the effects of each treatment on flower and fruit production and to test whether the reproductive peaks were related to climatic variables. Both the activity and intensity indexes exhibited the same patterns; flower and fruit production were lower in the control, intermediate in the 50 percent debarking group and higher in the 100 percent debarking group. To the best of our knowledge, this is the first study of NTFP to demonstrate an increase in reproductive activity after several years of harvesting. All phenophases were positively correlated with higher temperature and precipitation, as it is common in the Cerrado.     

Fire effects on the composition of a bird community in an Amazonian savanna (Brazil).

The effects of fire on the composition of a bird community were investigated in an Amazonian savanna near Alter-do-Ch?o, Pará (Brazil). Mist-net captures and visual counts were used to assess species richness and bird abundance pre- and post-fire in an approximately 20 ha area. Visual counts along transects were used to survey birds in an approximately 2000 ha area in a nearby area. Results using the same method of ordination analysis (multidimensional scaling) showed significant effects of fire in the 20 ha and 2000 ha areas and strongly suggest direct effects on bird community composition. However, the effects were different at different spatial scales and/or in different years, indicating that the effects of fire vary spatially and/or temporally. Bird community composition pre-fire was significantly different from that found post-fire. Using multiple regression analysis it was found that the numbers of burned and unburned trees were not significantly related to either bird species richness or bird abundance. Two months after the fire, neither bird species richness nor bird abundance was significantly related to the number of flowering trees (Lafoensia pacari) or fruiting trees (Byrsonima crassifolia). Since fire is an annual event in Alter-do-Ch?o and is becoming frequent in the entire Amazon, bird community composition in affected areas could be constantly changing in time and space.