Leaf demography and decline of Panicum racemosum populations in coastal foredunes of southern Brazil

Abstract

We studied the effect of nutrient status and sand movement on the population biology of Panicum racemosum Spreng. over a 5-year period (1982–1986) on mobile, semifixed and fixed coastal foredune habitats in southern Brazil. The soils were deficient in nitrate, phosphate, and potassium (<0.5, 0.2–1.2, and 3–5 mg/kg, respectively) in all habitats, and a gradient of decreasing availability existed from the mobile to the fixed dunes. Half-lives of leaves were shorter in the fixed dune as compared with the mobile dune. Similarly, half-lives of leaves were shorter in summer than in winter. Experiments using cuttings of P. racemosum tillers showed that as P. racemosum plants grew, so did the deposition of sand on mobile foredunes. The mechanical deposition of sand itself did not stimulate P. racemosum growth. The deposition of saline sand provided a substrate that supported vertical growth of P. racemosum rhizomes and tillers and was a source of adsorbed nutrients. Also, active sand deposition limited the invasion of frontal dunes by other species. Panicum racemosum populations changed from "invader" to "mature" to "regressive" age states over a 5-year period, apparently in response to the spatial patterns of sand deposition and salt spray input. Key words: Panicum, leaf demography, growth vigour, sand dunes, temporal changes.

Seed characteristics and dispersal of dimorphic fruit segments of Cakile maritima Scopoli (Brassicaceae) population of southern Brazilian coastal dunes

“…Large, rapidly growing plants are associated with sand containing macroalgal litter, whereas small stunted plants are found on foredunes above the limit of tidal inundation. Probably the small mass of Cakile seeds from southern Brazil reflects a low nutrient status (Costa et al 1991, Cordazzo 1994, because this population occurs not in a strandline habitat, but in the more stable conditions encountered at the base of foredunes (Seeliger 1992) where competition for nutrient may occur with the perennial grass Panicum racemosum (Beauv.) Spreng.…”

Composição e distribuição da vegetação herbácea em três áreas com fisionomias distintas na Praia do Peró, Cabo Frio, RJ, Brasil

“…Na área B, as espécies que se destacaram foram Panicum racemosum e Sporobolus virginicus, características da comunidade psamófila-reptante (Henriques et al 1986). Panicum racemosum tem ocorrência significativa em outras regiões do litoral brasileiro, principalmente em áreas próximas ao mar e com muita movimentação de areia (Pfadenhauer 1978;Costa et al 1984;Costa et al 1991) o que justamente caracteriza a área B. Segundo Costa et al (1996), o acréscimo de areia, oriundo de ação eólica ou antrópica, controla a germinação das sementes desta espécie e o estabelecimento da plântula, daí a preferência por estas áreas. Devido a esta característica, esta espécie age como pioneira, formadora e fixadora de dunas (Dansereau 1947;Henriques et al 1984;Cordazzo & Costa 1989;Cordazzo & Seeliger 1993).…”

Effect of seed mass on germination and growth in three dominant species in southern Brazilian coastal dunes

“…On the other hand, later-germinating seedlings can suffer increased mortality and/or reduced growth (Zimmerman & Weis, 1983). In the southern Brazilian sand-dune environment, the supply of nutrients is limited (Costa et al, 1991) and early germinating seedling probably have a better chance of growth and establishment at locations where seedling density is high, like depressions between dune ridges. The three species studied also showed that seedlings from large seeds present significantly higher elongation in darkness than do those from small seeds (Cordazzo, 1994).…”