Produção de detritos no manguezal de Guaratiba (RJ): o papel dos controles bióticos e abióticos

Abstract

Historical litterfall production in the Guaratiba mangrove ranged from 8.08 ± 2.08 t.ha- 1.year-1 at the transition to 12.15 ± 1.28 t.ha-1.year-1 at the fringe, with major contributions of leaves (58-57%), twigs and branches (11-20%), and propagules (8-19%). Interstitial water salinity ranged from 31.3 ± 3.0 at the fringe to 42.3 ± 5.5 at the transition. Analyses indicate litterfall response to the tidal flooding gradient, due to the differences found in litterfall production (F=24.216, p <0.001) and salinity (F=18.544, p <0.001) among physiographic types; negative regressions of litterfall with salinity (R²=0.2160, p<0.05) and stem density (R²=0.78, p<0.05); positive regressions of litterfall with structural parameters DBH (R²=0.84, p<0.001) and mean height (R²=0.83, p<0.001). Leaflitter production was dependent on basal area and leaf biomass (R²=0.69, p<0.001). Monthly production showed a seasonal pattern of high production in summer (3.14-6.37 g.m-².day-¹) and low production in winter (1.32-2.12 g.m-².day-¹). Significant trends of increasing production over time were identified for leaves, flowers, propagules and stipules, and decreasing for branches and twigs, which varied across physiographic types. Significant positive correlations between litterfall and climatological variables air temperature, precipitation, radiation, and potential evapotranspiration were identified. Through wavelet analysis, cycles of 12, 6-8,5-6 and 4-5 months were identified, with a predominance of seasonal cycle throughout the series in the fringe and basin. Caterpillar outbreak between 2009/2010 directly affected A. schaueriana, with a leaflitter production reduction ranging from 43-86% from 2009 to peak defoliation (2011) with reduced impact across physiographic types, with greater effects at the transition. In the fringe and basin, from 2009 to 2011, L. racemosa showed a 52 and 67% reduction in leaflitter production, respectively, and a 30% increase at the transition. R. mangle increased leaflitter production by 7% in the basin, became present in the transition, and reduced it by 25% in the fringe. The regeneration time of A. schaueriana leaflitter production was 8 years. The results still reflect the effect of the selective process of severe defoliation on the dynamics and ecological succession of mangrove forests.