ABSTRACT Fire-related cues may enhance seed recruitment in flammable ecosystems and differences in fire-germination responses of invasive vs. native species can drive the invasion process. We evaluated the effects of heat shock and smoke water solution treatment on seed germination of invasive (Melinis minutiflora, Urochloa decumbens, U. brizantha) and native grasses (Axonopus pressus, Aristida setifolia, Gymnopogon foliosus) of the Cerrado. The effect of fire temperature was tested by exposing seeds to heat shock treatments of 60, 100, and 200 °C for one minute, comparing them to untreated seeds. The effect of smoke was tested by soaking seeds for 24-h in an aqueous smoke comparing them to seeds soaked in distilled water. Differences among treatments were evaluated by ANOVA and randomization tests. None of the tested species had germination stimulated by the temperature or smoke. Both species of Urochloa experienced decreased viability with increasing temperature, while seeds of native species and M. minutiflora tolerated heat shock up to 200 °C. The invasive grasses usually germinated faster than the native grasses. Germination time is therefore a crucial trait driving the invasion process, irrespective of fire-related cues. Other seed traits (e.g. dormancy) and higher resprouting capacity may help invasive species to persist in frequently burned savannas.

ABSTRACT Seed germination in many species from fire-prone ecosystems may be triggered by heat shock and/or temperature fluctuation, and how species respond to such fire-related cues is important to understand post-fire regeneration strategies. Thus, we tested how heat shock and daily temperature fluctuations affect the germination of four species from fire-prone ecosystems; two from the Cerrado and two from the Mediterranean Basin. Seeds of all four species were subjected to four treatments: Fire (F), temperature fluctuations (TF), fire+temperature fluctuations (F+TF) and control (C). After treatments, seeds were put to germinate for 60 days at 25ºC (dark). Responses differed according to species and native ecosystem. Germination percentage for the Cerrado species did not increase with any of the treatments, while germination of one Mediterranean species increased with all treatments and the other only with treatments that included fire. Although the Cerrado species did not respond to the treatments used in this study, their seeds survived the exposure to heat shock, which suggests they possess tolerance to fire. Fire frequency in the Cerrado is higher than that in Mediterranean ecosystems, thus traits related to fire-resistance would be more advantageous than traits related to post-fire recruitment, which are widespread among Mediterranean species.

The Cerrado is threatened by wildfires and invasive species. We aimed to evaluate in laboratory conditions whether temperature fluctuation at the soil surface, resulting from the absence of vegetation due to fire, can affect the germination of Urochloa decumbens and U. brizantha, two invasive African grasses. Seeds of both species were submitted to simulations: 1) temperature during fire at 1cm belowground (F); 2) temperature fluctuation at 1cm belowground without vegetation cover for a month (TF); 3) (F) + (TF); 4) control at 25ºC. After treatments, seeds were put to germinate at 25ºC for 40 days. We had four replicates per treatment and three temporal replicates. We compared germination percentage and the mean germination time among treatments using ANOVA. The treatments TF and F+TF had the highest germination values for both species. The results showed that fire per se could not stimulate seed germination, however, they suggest that a disturbance that produces a pattern of temperature fluctuation is able to break dormancy and enhance seed germination and, consequently, increase the invasiveness of the study species. Vegetation gaps resulting from disturbance may become new sites of invasion. This information is important for making management decisions regarding the control of these species.

Fire plays an important role in several grassland ecosystems in the world. Fire can trigger germination in several species, by breaking the physical dormancy of their seeds. Thus, we hypothesized that exposure to high temperatures during fire would break seed dormancy and enhance germination. We tested the effect of high temperatures on the germination of six species of legumes from Brazilian subtropical grasslands. We used heat shock experiments with the following treatments: 60, 90, 120 and 150ºC for one minute. Seeds were then placed to germinate for 60 days in 12/12 hours light/dark and 20/30ºC. Germination was generally low for all study species. Most species was not affected by heat shock treatments. However, Stylosanthes montevidensis was the only species that had its physical dormancy broken when exposed to 120ºC. The seeds of all the other species were neither stimulated nor killed by high temperatures. Although the exposure to high temperatures did not affect the germination of the study species (except for one), it also did not kill seeds, thereby showing that seeds are resistant to fire. Therefore, the rapid passage of fire in these grasslands is not sufficient to break the dormancy of most of the studied species of legumes.

Este estudo teve por objetivo investigar potenciais efeitos do fogo na germinação de sementes de capim-dourado (Syngonanthus nitens) (Bong.) Ruhland (Eriocaulaceae). Sementes coletadas na região do Jalapão, Tocantins, foram submetidas a choques de temperaturas de 60º, 100 ºC, 150 ºC e 200 ºC durante 1, 3 e 5 minutos. Foram feitas 5 réplicas, com 20 sementes para cada tratamento, e controle. As sementes foram dispostas em placas de Petri e em câmaras de germinação a 28 ºC, fotoperíodo 12h/12h, por 40 dias. As taxas de germinação das sementes foram analisadas por meio de ANOVA com teste de aleatorização. A maioria dos tratamentos resultou em altas taxas de germinação (>85%), exceto 200ºC/3' (50%) e 200ºC/5', que apresentou uma queda significativa (4,5%, P<0,05). Os resultados obtidos indicam que as sementes de S. nitens não são estimuladas nem mortas por altas temperaturas, exceto quando combinados temperatura e tempos de exposição extremos (200ºC/5'). A passagem do fogo é muito rápida durante queimadas nos campos úmidos, onde S. nitens ocorre e as temperaturas frequentemente não atingem os 150 ºC. Nessas condições, estes resultados indicam que as sementes de S. nitens potencialmente sobrevivem à passagem do fogo na maioria das queimadas. Esta informação é de utilidade imediata para o manejo desta espécie de alto valor comercial.

This study aimed to assess the effects of fire on germination of golden-grass (Syngonanthus nitens (Bong.) Ruhland, Eriocaulaceae) seeds. Seeds collected in Jalapão (Tocantins, Brazil) were exposed to heat shock treatments at 60 ºC, 100 ºC, 150 ºC and 200 ºC, for 1', 3', and 5'. For each treatment and control five replications were used (20 seeds each). Seeds were put on Petri dishes and placed inside germination chambers set at 28 ºC, 12h/12h, for 40 days. Germination rates were analyzed by two-factorial ANOVA, using randomization tests. Most treatments showed high germination rates (>85%), except for 200ºC/3' (50%), and 200ºC/5, which showed germination rates that were significantly lower (4.5%, P<0.05). The results indicated that S. nitens seeds were not stimulated or killed by high temperatures, except when an extreme temperature and time of exposure were combined (200ºC/5'). When wet grasslands burn, where S. nitens grows, the fire passes very quickly over the area and the temperature during the fire may not exceed 150ºC. Under these conditions, our results suggest that S. nitens seeds can potentially survive most fires. These findings are essential for making management recommendations for this species, which has high commercial value.

Species of Smilax, also known as greenbrier, are widely distributed in Brazil and their commercial trades are carried out by the extractivism of native species. We the aim to provide information about the germination and development of seedlings in four Smilax species, different experiments were developed under controlled conditions. We evaluated two germination treatments: temperature (30ºC and 20-30ºC) and light (presence/ absence), and for few cases the tetrazolium treatment was applied. A different treatment response was observed among the studied species. Light had a significant influence in S. brasiliensis, with the highest germination rates at 20-30ºC in dark conditions. S. campestris showed significant differences among temperature treatments, but not to light; while S. cissoides showed high germination rates (66-78%), independently of treatment. However, S. polyantha had low germination rates (19-24%). After one year, the expanded leaves showed different characteristics among the studied species. Leaves of S. brasiliensis were ovate, coriaceous, three main veins and prickle-like structures only on the midrib on abaxial face. S. campestris leaves were oblong, coriaceous and prickle-like structures were located at the leaf midrib and margin. S. cissoides had ovate-elliptic, membranaceous leaves, with three main veins with prickle-like structures on the abaxial face. S. polyantha leaves showed ovateelliptic, coriaceous leaves, with three main veins, translucent secondary veins and no prickle-like structures. A seedling identification key was elaborated based on morphological characteristics.

O Cerrado ocupa aproximadamente 23% do território brasileiro e 70% do bioma correspondem a cerrado stricto sensu (s.s.), sendo relevantes os estudos que buscam o entendimento da estrutura da vegetação nessas áreas. Com esse objetivo, foram estudadas cinco parcelas (10×25m) em um hectare de cerrado s.s., amostrando-se todos os indivíduos com perímetro no nível do solo igual ou acima de 3cm (exceto lianas e indivíduos mortos). Alguns parâmetros fitossociológicos foram analisados, assim como a distribuição de classes de diâmetro dos indivíduos amostrados e a estrutura vertical. Foram amostradas 1.747 indivíduos, distribuídos em 75 espécies, pertencentes a 31 famílias. A densidade total absoluta encontrada foi de 13.976 ind.ha-1 e a área basal total, de 4,902m². Leguminosae foi a família com o maior número de espécies (16). As espécies que apresentaram os maiores valores de Índice do Valor de Importância (IVI) foram Anadenanthera falcata (Benth.) Altschul, Myrcia guianensis (Aubl.) DC., Xylopia aromatica (Lm.) Mart., Ouratea spectabilis (Mart.) Engl. e Pouteria ramiflora (Mart.) Radlk. O Índice de Shannon encontrado foi de 3,623. A distribuição de classes de diâmetro apresentou curva na forma de "J" invertido, estando a maioria dos indivíduos na primeira classe. A área estudada não apresentou estratos bem definidos, estando a maioria dos indivíduos entre 1 e 3m de altura.

The cerrado covers about 23% of the Brazilian territory, and 70% of the cerrado area is stricto sensu physiognomy. To promote a better understanding of its physiognomic structure the cerrado s.s. study is of vital importance. Therefore, five plots (10×25m) were established in one hectare area of cerrado s.s. and all vascular plants with stem perimeter at ground level ³ 3cm (except vines and dead individuals) were sampled. The distribution of diameter classes and vertical structure, as well as the phytosociological parameters were analyzed. We recorded 1,747 individuals, distributed in 75 species belonging to 31 different families were sampled. The absolute density and the basal area were 13,976 ind.ha-1 and 4,902m², respectively. Leguminosae showed the highest number of species (16). The species Anadenanthera falcata (Benth.) Altschul, Myrcia guianensis (Aubl.) DC., Xylopia aromatica (Lm.) Mart., Ouratea spectabilis (Mart.) Engl. and Pouteria ramiflora (Mart.) Radlk. showed the highest VI. The Shannon's Index was 3,623. The distribution of diameter classes showed a curve in reverted-"J", most of the individuals being in the first class. There were no well defined vegetation strata, showing most of the individuals between 1 and 3m in height.