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Seed germination is determined by the environmental conditions typical of a habitat and also by the geographical origin of the source species pool. During the Quaternary, Brazilian Atlantic Rain Forest species expanded their distribution into the sandy coastal plains (restingas). Periods of water shortage, however, are frequent in the sandy substrate of the restinga. We investigated whether the germination characteristics of restinga species are more related to their biogeographical origin in the humid forest or to water shortage on sandy substrates. We characterized the seed dispersal phenology of a restinga community and conducted experiments to determine the water requirements for seed germination and the short-term seed dehydration sensitivity of different species. Species shed seeds throughout the year in the restinga. When subjected to C =À 0.37 MPa, seed germination percentage decreased and germination time increased in six of ten species when compared with C = 0 MPa. Most species showed high seed moisture content (MC 4 40 %) at seed dispersal. Seeds took 3-17 d to dehydrate when subjected to relative humidity 76 percent and only two of eight species had seeds sensitive to short-term dehydration. Thus, rather than a specific set of germination characteristics related to humid or dry habitats, we gathered evidence to show that the germination characteristics of restinga species represent a multiplicity of responses that may be found in both kinds of habitat.Abstract in Portuguese is available at

RESUMO -(Variação da biomassa e necromassa aérea de duas espécies invasoras na Floresta Atlântica, sudeste do Brasil). Este trabalho descreve a variação da biomassa e necromassa aérea, e da produção primária líquida (NAGPP) de duas espécies invasoras Panicum maximum Jacquin (Poaceae) e Pteridium arachnoideum (Kaulf.) Maxon. (Dennstaedtiaceae) em duas áreas da Reserva Biológica de Poço das Antas, no sudeste brasileiro. As duas espécies eram mono-dominantes nestas áreas, ambas localizadas na matriz entre fragmentos florestais. A matéria orgânica foi amostrada mensalmente durante dois anos, separada em biomassa e necromassa e a produção aérea primária líquida (NAGPP) foi calculada. Houve variação intra-sazonal bem marcada, para ambas as espécies; Pa. maximum geralmente apresentou os maiores valores para biomassa, necromassa, massa total e NAGPP (NAGPP, Pa. maximum = 3953 g m -2 ano -1 , Pt. arachnoideum = 2667 g m -2 ano -1 ). A NAGPP não variou entre as duas estações de crescimento para Pa. maximum, porém estas diferenças foram acentuadas para Pt. arachnoideum (2% comparados aos 44% de variação em relação a média). A segunda estação de crescimento foi mais seca e Pa. maximum produziu maior quantidade de necromassa do que na primeira estação de crescimento; Pteridium mostrou pouca variação sazonal de biomassa, mas uma maior produtividade na segunda estação de crescimento. Pteridium arachnoideum é aparentemente mais sensível ao clima, especialmente em relação à pluviosidade. Palavras-chave: fogo, Panicum maximum, plantas invasoras, Pteridium arachnoideumABSTRACT -(Variation in aboveground biomass and necromass of two invasive species in the Atlantic Rain Forest, Southeast Brazil). This paper describes the variation of the above-ground biomass, necromass, and net above-ground primary production (NAGPP) of two weed species, Panicum maximum Jacquin (Poaceae) and Pteridium arachnoideum (Kaulf.) Maxon. (Dennstaedtiaceae), at two sites in the Poço das Antas Biological Reserve, southeast Brazil. Both species form mono-dominant stands in the matrix surrounding forest fragments. The organic matter was sampled monthly from each site, separated into biomass and necromass, and net above-ground primary production (NAGPP) was calculated. There was marked intra-seasonal fluctuation for both species; Pa. maximum generally had the largest values for necromass, total mass and NAGPP (NAGPP, Pa. maximum = 3953 g.m -2 .y -1 , Pt. arachnoideum = 2667 g.m -2 .y -1 ). NAGPP did not vary between the two growth periods for Pa. maximum, but marked differences were found for Pt. arachnoideum (2% compared to 44% variation around the mean). The second growth year was drier and Pa. maximum produced much greater necromass in that year; Pt. arachnoideum showed little variation in biomass but much greater productivity in the drier second season. Pteridium arachnoideum appears to be more sensitive to climate, and especially rainfall.

Although palms play an important ecological role in tropical forests, characteristics related to their germinative niche remain largely unknown. We evaluated the seed germination characteristics of Geonoma schottiana, an abundant palm in the understory of different ecosystems of the Atlantic Rain Forest biome and the gallery forests of the Cerrado biome. We conducted experiments under light and dark conditions at Ψ = 0 MPa, and under two low-water-potential conditions and a flooded condition. Seed germination was highest at Ψ = 0 MPa under light (72%) and dark (67%) conditions. We observed moderate (51%) and low (18%) seed germination at Ψ = −0.4 and −0.8 MPa. About 20% of ungerminated seeds subjected to low water potentials for 300 days remained viable. No seeds germinated under flooded conditions; however, 23% of them maintained germinability. A delay in seed germination time was observed at low water potentials and an increase in synchrony occurred at Ψ = −0.8 MPa. G. schottiana seeds did not require specific light conditions to germinate, and the species possesses germinative characteristics to cope with deficit and excess of water. Probably, this wide germination niche allows for its seeds to germinate over a wide range of habitats in different types of ecosystems.

The spatial and temporal fluctuations of water availability can be an obstacle for recruitment of many species in the restinga and might restrict seed germination and seedling growth in specific regeneration safe-sites. Clusia hilariana is one of the most dominant species of Restinga de Jurubatiba. This species has a high proportion of seedling establishment occurring inside the tanks of soil bromeliads underneath vegetation patches. Given the thin seed coats, the fast germination time and seed dispersal of C. hilariana during the dry season, we hypothesized that their major regeneration niche (the tanks of soil bromeliads) is related to susceptibility of seed germination and also seedling growth to low water availability. To test this hypothesis, seeds were germinated under decreasing water potentials using PEG 6000 solutions and seedlings were grown under varying water regimes. The percentage of seed germination progressively decreased at lower water potentials. After 38 days in À1.0 MPa no seeds germinated. However, approximately 90% of seeds germinated when transferred to W = 0 MPa. The relative growth rates of seedlings of C. hilariana did not differ between water treatments. Thus, the major regeneration niche of C. hilariana is not a consequence of a high sensitivity of seeds and seedlings to water shortage. Nonetheless, C. hilariana showed an array of seed and seedling traits that may help to overcome establishment constraints of the harsh environment of restingas.

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Large seed banks have been found in tropical dry forests and also in habitats with high seasonality in rainfall. However, patchily structured vegetation could induce great spatial variation in the seed bank. We characterized the seed bank in a patchy vegetation of restinga, a common type of coastal vegetation found in the Atlantic forest biome. We also evaluated whether there is any spatial variation between the litter and soil layer, bare sand, and the edge and center of vegetation patches with distinct species dominance. We found 104 seeds/m 2 in the seed bank using a 5-cm-depth sampling. Seven out of 16 species found in the restinga seed bank germinated; two of these were found in the early stages of vegetation patches. We found a higher number of seeds at the edge than in the center of vegetation patches. However, there were no significant differences in the number of seeds in the seed bank between the litter and soil layer, and between vegetation patches with distinct species dominance. Bare sandy soils had lower seed bank densities than vegetation patches. A small seed bank size might be explained by the low proportion of seeds from herbaceous and woody species, which are pioneers in the Atlantic forest. However, seed bank might play an important role in the early stages of the successional process, due to the occurrence of the few species that are able to colonize new young vegetation patches.

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