Aim
Fire is a natural disturbance in many ecosystems throughout the world where plant populations can persist by the resprouting of individuals and/or by recruiting from seeds. We evaluated the ...post‐fire regeneration response for 41 coexisting species, including grasses, forbs, and shrubs, from an open Cerrado community (campo sujo) in Central Brazil.
Location
The study was conducted at the Reserva Natural Serra do Tombador (RNST) in Central Brazil. The vegetation of the study area is characterized by a continuous herbaceous layer dominated by grasses and scattered shrubs, which produces fine fuel loads that can burn frequently.
Methods
We examined both resprouting ability after experimental fires, accounting for bud location, and seed response to heat shocks caused by fire, where seeds were subjected to heat shocks of 100°C for one and three minutes, 200°C for one minute, and a control (untreated seeds).
Results
All species were able to resprout (R+) after fire, mainly from buds located in underground structures, but also from aerial and basal buds. Seeds of most species tolerated heat shocks of 100°C for one and three minutes, but heat treatments of 200°C decreased seed viability of nearly 50% of species. Seven species, all of which had dormant seeds, showed heat‐stimulated germination. In sum, 81% of the community was classified as R+PT (resprouters with heat‐tolerant propagules) and 17% was R+PS (resprouters with heat‐stimulated propagules). The remaining 2% (one species) was classified as R+P−, showing heat‐sensitive seeds.
Conclusions
Resprouting is the main post‐fire regeneration strategy in Cerrado open savannas, while fire‐stimulated germination, although possible, is less common in comparison to the frequency in other fire‐prone ecosystems. However, in Cerrado open savannas, heat tolerance is an important trait that enables germination when favorable conditions arise.
Fire episode in an open Cerrado community.
Given the current global environmental crisis, restoring degraded ecosystems stands out among the nature‐based solutions to mitigate climate change, reestablish ecosystem services, and maintain ...biodiversity and human well‐being. The high biodiversity of the Atlantic Forest (AF) and its severe degradation turned it into a “restoration hotspot.” We performed a bibliometric analysis of the research on restoration of the Brazilian AF to identify thematic trends, potential gaps, as well as networks and benefits of collaboration. We also explored the spatial distribution of degradation, restoration science, and practice within the AF. We analyzed 932 articles on the issue from the Web of Science platform (1990–2020). Publications abruptly increased in the last 15 years, first by Brazilian groups and later in collaboration with foreign groups. International collaboration increased the probability of highly cited articles. Topics addressed have changed greatly in their relative position over time, likely due to scientific advances refuting theories or invalidating failed techniques. Natural regeneration was the main trending topic, while forest succession was the main emerging topic, and ecosystem services appeared as a trending topic. Research and restoration initiatives were both unevenly distributed throughout the AF region, with the southeastern region of Brazil standing out (60% of publications). The percentage of the original AF undergoing restoration is very low in all regions, regardless of scientific publications or AF extent remaining. The knowledge gaps pointed—climate change and functional traits—should drive priorities for research funding, aiming to provide robust evidence to support decision‐making processes as well as restoration practices.
Fire is a main disturbance structuring vegetation worldwide, but few studies have addressed differences in time since last fire and its relationship to fuel load characteristics and fire behavior in ...Neotropical savannas. We aimed to investigate fire behavior in a Cerrado open savanna of Central Brazil by conducting prescribed fires in areas with different fire‐free intervals: one year (FI‐1), two years (FI‐2), and four years (FI‐4). Specifically, we evaluated (1) the amount of live, dead, and total biomass (components of the fuel load); (2) fire behavior, including fire temperatures in three different heights (1 cm belowground, on the soil surface, and 50 cm aboveground), fire duration, residence time, fire intensity, rate of spread, and flame height; and (3) the relationship between soil heating, fuels, and fire by identifying the most important parameters driving soil heating. Total and dead fuel loads were greater in areas with longer fire‐free intervals in comparison with areas burned the previous year, with the greatest increment to the fuel bed occurring in the first two years after fire. Greater fuel loads (consequently greater dead fuel loads) resulted in differences in belowground soil heating (‐1 cm), where temperatures varied from 39 to 82°C in FI‐2 plots and from 40 to 131°C in FI‐4 plots; in FI‐1 plots temperatures belowground varied from 29 to 68°C. Temperatures on the soil surface and 50 cm aboveground were also greater in plots with longer fire‐free intervals, reaching over 400°C on the soil surface and exceeding 500°C 50 cm aboveground. Finally, amount of dead fuel was the best predictor of belowground soil heating, highlighting the importance of fuel loads, which is a key factor to be monitored in fire management plans of Cerrado open savannas.
Some invasive grasses have been reported to change fire behavior in invaded plant communities. Urochloa brizantha is an aggressive invasive grass in the Brazilian Cerrado, an ecosystem where fire is ...a common disturbance. We investigated the effects of U. brizantha on fire behavior in an open Cerrado physiognomy in Central Brazil. Using experimental burnings we compared fire behavior at both the community and the individual plant level in invaded (UJ) and non-invaded (NJ) areas burned in July. We also assessed the effect of fire season in invaded areas by comparing July (UJ) and October (UO) burnings. We evaluated the following variables: fuel load, fuel moisture, combustion efficiency, maximum fire temperature, flame height, and fire intensity. Additionally, we evaluated the temperatures reached under invasive and native grass tussocks in both seasons. Fuel load, combustion efficiency, and fire intensity were higher in NJ than in UJ, whilst flame height showed the opposite trend. Fuel amount and fire intensity were higher in October than in July. At the individual plant level, U. brizantha moisture was higher than that of native species, however, temperatures reaching ≥600 °C at ground level were more frequent under U. brizantha tussocks than under native grasses. At the community level, the invasive grass modified fire behavior towards lower intensity, lower burning efficiency, and higher flame height. These results provide essential information for the planning of prescribed burnings in invaded Cerrado areas.
Tredennick et al. criticize one of our statistical analyses and emphasize the low explanatory power of models relating productivity to diversity. These criticisms do not detract from our key ...findings, including evidence consistent with the unimodal constraint relationship predicted by the humped-back model and evidence of scale sensitivities in the form and strength of the relationship.
No Brasil, varias espécies de gramíneas africanas introduzidas se tornaram importantes invasoras dos cerrados e constituem uma das principais ameaças para a sua biodiversidade. Atributos envolvendo ...trade-offs evolutivos que influenciam na adaptabilidade das espécies - aquisição, alocação e perda de recursos pelas plantas por meio de competição, facilitação, estresse e distúrbio - irão influenciar o desempenho dos indivíduos e a manutenção das populações nas comunidades vegetais. Deste modo, e de extrema importância entender quais os mecanismos que levam uma espécie invasora a ter um desempenho melhor sobre as espécies nativas. Comparações envolvendo características entre espécies exóticas e nativas podem levar a uma melhor compreensão sobre o processo da invasão. Diante disso, este trabalho procurou identificar algumas das estratégias competitivas adotadas por uma gramínea invasora, Urochloa decmbens, e por uma gramínea nativa, Echinolaena inflexa, em ecossistema de cerrado. Para verificar aspectos relativos às estratégias de colonização das espécies foram analisadas suas fenologias reprodutivas, as taxas de viabilidade e de germinação das sementes. Em um experimento com plantas envasadas, sementes de ambas as espécies foram semeadas em diferentes proporções relativas uma a outra. Três censos foram realizados durante o período de um ano para avaliar a sobrevivência, crescimento e fecundidade das espécies. Medidas da capacidade fotossintética e das taxas de assimilação foram tomadas para ambas as espécies tanto em parcelas puras quanto em parcelas mistas; também foi quantificada a área foliar especifica e total das espécies. No experimento com as plantas envasadas, quando sementes de ambas as espécies foram colocadas juntas, a nativa teve seu crescimento suprimido pela invasora. Nos tratamentos puros, os indivíduos da espécie nativa cresceram em tamanho, mas somente três se tornaram reprodutivos. No entanto, muitos indivíduos da espécie invasora cresceram em tamanho e se reproduziram em todos os tratamentos, mostrando uma alocação de recursos tanto para crescimento quanto para reprodução. A espécie invasora apresentou uma taxa fotossintética maior, porem ambas as espécies tiveram sua capacidade fotossintética e sua taxa fotossintética reduzida nos parcelas mistas, sugerindo que a competição afeta tanto a espécie nativa como a espécie invasora. Uma vez que a espécie nativa possui área foliar especifica menor em relação à espécie invasora, espera-se que ela apresente uma perda menor de nutrientes e, conseqüentemente, uma maior conservação/retenção dos nutrientes, o que favoreceria sua persistência em ambientes como o cerrado. No entanto, com a ocorrência de distúrbios e possíveis alterações na disponibilidade de nutrientes, a gramínea nativa pode ser deslocada pela invasora, que apresenta maior capacidade de colonizar novas áreas por meio de maiores taxas de germinação e estabelecimento; e maior produtividade, apresentando maiores taxas fotossintéticas, sendo mais eficiente no uso do nitrogênio.
Many African grasses have been introduced in Brazil and have invaded areas of Brazilian savannas, thus becoming a major threat to the biological diversity of this biome. Traits involving evolutionary trade-offs that influence the species adaptive strategies, such as differences in nutrient uptake, nutrient loss and biomass allocation in response to plant competition and facilitation, and environmental stress and disturbance, will influence individual performance and population maintenance in plant communities. Therefore, it is extremely important to identify the mechanisms associated with invasiveness that lead to a better performance of exotic species over co-occuring natives. Comparisons involving traits of both native and exotic species may lead to a better understanding concerning the success of invasions. This study sought to recognize possible competitive strategies adopted by an invasive grass, Urochloa decmbens, and a native grass, Echinolaena inflexa, in a Brazilian savanna. In order to identify aspects relative to their colonization strategies, the reproductive fenologies and seed viability and germination rates of both species were analyzed. An experiment with potted plants was performed where seeds of both species were sown in different relative proportions to each other. Three census were carried out during a period of 12 months to evaluate survival, growth and fecundity of both species. Gas exchange and chlorophyll fluorescence were quantified for each species in pure and mixed stands in the field; total and specific leaf area for both species were also measured. In the potted experiment, when seeds of both species were sown together, the growth of the native species was suppressed by the exotic species. In pure treatments, however, individuals of the native species grew in size, but only 2% reproduced. On the other hand, individuals of the exotic species grew in size and reproduced in all treatments, demonstrating that this species allocated enough resources for both growth and reproduction. The photosynthetic rates were greater for the invasive species, however, in mixed stands, both species had their photosynthetic rates and capacities decreased. The smaller specific leaf area of the native species suggests lower rates of nutrient loss than the invasive species, which would favor its persistence in nutrient poor environments, as the Brazilian savannas. Yet, with the occurrence of disturbances and variable nutrient availabilities, the native species might be displaced by the invasive species, since the later possesses traits leading to a higher competitive ability in such conditions.
The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate ...productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.
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Previous issue date: 2017-05-12
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Em ambientes onde ocorre o fogo, as espécies de plantas podem regenerar via rebrote, semente ou através de ambas as estratégias. Os mecanismos de regeneração são favorecidos ou limitados tanto pelas condições ambientais (produtividade e disponibilidade de recursos) quanto pelo regime de queima, incluindo sua frequência e época. Assim, o objetivo principal desta tese foi investigar a regeneração pós-fogo de espécies de uma comunidade de campo sujo de Cerrado localizada na Reserva Natural Serra do Tomabdor (Goiás). Avaliamos o papel da regeneração via rebrote e via semente e procuramos avaliar os fatores que estão envolvidos no rebrote das plantas após serem submetidas a diferentes tipos de distúrbio, e distúrbios que ocorreram em diferentes frequências e épocas do ano, visto que tanto o tipo do distúrbio quanto a época e a frequência em que ele ocorre podem afetar a regeneração das plantas. Verificamos que o rebrotamento é a principal estratégia de regeneração pós-fogo, ocorrendo principalmente a partir de gemas localizadas em estruturas subterrâneas que estão altamente protegidas pelo solo, e que o recrutamento via semente tem um papel pequeno na regeneração. No entanto, a tolerância das sementes a altas temperaturas é uma característica importante que permite o recrutamento quando as condições ambientais forem favoráveis. Também verificamos que as respostas pós-fogo, relacionadas tanto com o rebrote como com a floração, estão relacionadas com a disponibilidade de recursos no ambiente pós-fogo. A regeneração mais devagar das plantas queimadas no inicio da estação seca está provavelmente relacionada com o maior número de meses que estas plantas foram sujeitas a déficit hídrico, sendo que, após a estação chuvosa, as plantas queimadas nas diferentes épocas do ano apresentaram tamanhos similares. A regeneração após três queimas consecutivas não foi diferente da regeneração após queimas com intervalos maiores, sugerindo que a quantidade de reservas armazenadas não foi um fator limitante. Além disso, o fogo induziu a floração das espécies em relação a plantas não queimadas, sugerindo que o fogo é um fator importante na reprodução das espécies.
In fire-prone ecosystems, plant species can persist by resprouting, recruiting from seeds, or use both strategies. Such regeneration mechanisms can be favored or limited by both environmental conditions (site productivity and resource availability) and fire regimes, such as fire frequency and season. The aim of this thesis was investigate the post-fire regeneration mechanism of Cerrado plant species from an open savanna community located at the Reserva Natural Serra do Tombador (Goiás, Central Brazil). Thus, we evaluated the role of post-fire resprouting and post-fire seeding as regeneration mechanisms in Cerrado open savannas. Moreover, we evaluated the factors driving resprouting responses after plants are subjected to different disturbance types and to disturbances in different seasons and frequencies. We verified that resprouting is the main post-fire regeneration mechanism in Cerrado, originating mainly from buds located in underground structures, and that post-fire seeding plays a minor role in the post-fire regeneration of this community. However, seed tolerance is an important seed trait as it allows for seed germination and recruitment when favorable environmental conditions arise. Our results suggest that post-fire resprouting is driven mainly by availability of resources present in the post-fire environment. The slower recovery of plants burned during early-dry season fires is most likely related to the prolonged exposure to water deficits as plants endured all five months of the dry season. However, after the rainy season, plants burned in the different fire seasons had similar sizes. We found no difference in resprouting responses between annually and biennially burned plants, and plants resprouted vigorously after three consecutive burns, suggesting that amount of stored reserves was not a limiting factor. Moreover, fire induced flowering in most species in relation to unburnt plants, suggesting fire is an important factor for the reproduction of these species.
CNPq: 141949/2013-9
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