Dinamica da dispersão de sementes e regeneração de plantas da planicie litoranea da Ilha do Mel, PR

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

(Seed dispersal and plant regeneration dynamics in a Sandy Coastal Plain on Ilha do Mel, southern Brazil): The island Ilha do Mel is located in the municipality of Paranaguá (25°29 /25°34 32"S e 48°17 15"/48°23 16"W) in the central coastal region of Paraná State, Brazil and comprises 2760ha. The higher areas above the Sandy Coastal Plain contains very heterogeneous vegetation in which it is possible to recognize three major vegetation types: beach/dune vegetation (P), scrub or "restinga" (R), and sandy coastal forest (F). Here, dispersal and regeneration mechanisms were studied along this P to F gradient and in two types of sandy coastal forests: Unflooded (FNI) and Flooded (FI). The morphologies of fruit, seeds, and seedlings of 238 plant species were analyzed, and the frequency of dispersal and seedling syndromes were compared in the P to F gradient. Zoochory was the most frequent dispersal syndrome (56% of total species), followed by anemochory (26%) and autochory (18%). Distribution of dispersal syndromes was associated with vegetation type. Abiotic processes (anemochory and autochory) were more important in open and stressed sites (P and R) while biotic processes (zoochory) were important in closed and more complex sites (F). Dispersal syndromes in vegetation types were related to seed sizes, i.e. seed size in P and R species were smaller than F species. This suggests that environmental features limit species occurrence due to fruit and seed shapes. Seedling types were phenerocotylar-epigeal-foliaceous (57%), cryptocotylar-hipogeal-reserve (39%), and the last 4% were either cryptocotylar-epigeal-reserve, phanerocotylar-epigealreserve or phanerocotylar-hipogeal-reserve. Photosynthetic and reserve cotyledonous seedlings were equally distributed along P, R and F, suggesting that seedling morphology is not related to environmental factors. The phenology of 55 canopy and understory plant species in the FNI and FI were studied over two years. In these sites, climate (mainly rainfall) in the wetter season (September to May) is similar to that of the less wet season (June to August). FI and FNI showed very similar phenological patterns in which leaf fali, flushing, flowering, and fruiting occurred during the wetter season. Most phenological phases were correlated with daylength and average temperature. Phenology of canopy specles was more predictable than that of understory species. To test whether putatively aseasonal forests show rhythms, the seed rain and seedling emergence in the FNI and FI was studied for two years on Ilha do Mel island. Despite soil moisture and light differences between the two forests, FNI and FI had similar dispersal and germination patterns. Seed rain was seasonal and bimodal. The first peak occurred at the end of the wetter season (April to May) and the second one in the less wet season (August). These peaks reflect, respectively, the peaks of zoochorous and anemochorous species. Other plant characteristics (life form, seed size and seedling morphology) apparently do not show clear patterns. Seedling emergence was seasonal and unimodal but also occurred along the entire year. Even in this apparently aseasonal forest approximately 57% of species had seedling emergence four or more months after dispersal. Therefore both seed dormancy and the timing of seed dispersal drive the rhythm of seedling emergence in these forests. The peak in germination occurs in the wetter season (January) when soil fertility is higher and other phenological events also occur. Dynamics of FNI and FI were studied on Ilha do Mel Island, specifically comparing community composition of seeds, seedlings and saplings in each forest. New individual plants are incorporated in forests mainly from seed rain of autochthonous species (FNI =75% and FI =84% of species). During the growth of the plants (from seed to adult stages) in both of these forests, declines in plant density (>98%) and floristic similarity (Sorensen s Similarity Index from -80% to -58%) occur, associated with an increase in diversity (Shannon s diversity index from 0,39 to 1,19 in the FNI, and 0,91 to 1,31 in the FI). This was due to a strong reduction in density of the common species. Plants are uncoupled in their density and spatial distribution (uncorrelated) among stages, suggesting independence of the stages during the regeneration processo Through the sapling stages, the FNI and FI forests are very similar (density and Shannon s diversity index), after which the FNI was more densely populated and less diverse than the FI, with consequent reduction in their floristic similarity. Dispersal limitation, emergence limitation, and establishment limitation are very different in the FNI and FI, which probably is associated with particular recruitment patterns. It is suggested that: 1) 80th environmental and life form differences along the Sandy Coastal Plain gradient reflect differences in plant reproductive, and plant growth, patterns. 2) Phenological, seed dispersal and seedling emergence rhythms are not only or always related to large climatic seasonality. In these sandy coastal forests the occurrence of phenological patterns associated with the wetter season fits the hypothesis of efficient nutrient cycling in plant communities in relatively infertile soils. 3) Sandy Coastal Forests are systems with a connected but singular regeneration pattern due to differences in establishment success of plant species. Probably the relationship between these forests and other vegetation types is due to a successional patterns along the Coastal Plain

ASSUNTO(S)

flora das restingas restingas seeds beach ridges ilha do (pr) mata atlantica sementes mel

ACESSO AO ARTIGO

Documentos Relacionados