26 research outputs found
Plant biomass and production and CO2 exchange in an ombrotrophic bog
Summary Above-ground biomass was measured at bog hummock, bog hollow and poor-fen sites in Mer Bleue, a large, raised ombrotrophic bog near Ottawa, Ont., Canada. The average above-ground biomass was 587 g mâ2 in the bog, composed mainly of shrubs and Sphagnum capitula. In the poor fen, the average biomass was 317 g mâ2, comprising mainly sedges and herbs and Sphagnum capitula. Vascular plant above-ground biomass was greater where the water table was lower, with a similar but weaker relationship for Sphagnum capitula and vascular leaf biomass. Below-ground biomass averaged 2400 g mâ2 at the bog hummock site, of which 300 g mâ2 was fine roots (\u3c 2 mm diameter), compared with 1400 g mâ2 in hollows (fine roots 450 g mâ2) and 1200 g mâ2 at the poor-fen site. Net Ecosystem Exchange (NEE) of CO2 was measured in chambers and used to derive ecosystem respiration and photosynthesis. Under high light flux (PAR of 1500 ”mol mâ2 sâ1), NEE ranged across sites from 0.08 to 0.22 mg mâ2 sâ1 (a positive value indicates ecosystem uptake) in the spring and summer, but fell to â0.01 to â0.13 mg mâ2 sâ1 (i.e. a release of CO2) during a late-summer dry period. There was a general agreement between a combination of literature estimates of photosynthetic capacity for shrubs and mosses and measured biomass and summer-time CO2 uptake determined by the eddy covariance technique within a bog footprint (0.40 and 0.35â0.40 mg mâ2 sâ1, respectively). Gross photosynthesis was estimated to be about 530 g mâ2 yearâ1, total respiration 460 g mâ2 yearâ1, and export of DOC, DIC and CH4 10 g mâ2 yearâ1, leaving an annual C sequestration rate of 60 g mâ2 yearâ1. Root production and decomposition are important parts of the C budget of the bog. Root C production was estimated to be 161â176 g mâ2 yearâ1, resulting in fractional turnover rates of 0.2 and 1 yearâ1 for total and fine roots, respectively
Cover and growth habit of Polylepis woodlands and shrublands in the mountains of central Argentina: Human or environmental influence?
To determine whether the cover and growth habit of the main forest forming species (Polylepis australis BITT.) in a mountain range with low human population density is mainly affected by anthropogenic activities or by environmental influences. Location: Central Argentina. Methods: Using GIS and field surveys we established 146 plots of 30 x 30 m located in five river basins differing in human impact. We measured P. australis cover, growth habit of each individual (number of basal ramifications), index of long term human impact (percentage of rock exposed by soil erosion due to livestock and fires), evidence of logging, fire scars, local relief, percentage of rock outcrops and altitude above sea level. We analysed the influence of independent variables on P. australis cover and growth habit (average number of basal ramifications per plot) using correlations and General Linear Models. Results: Polylepis australis cover was greater at intermediate altitudes above sea level and in areas with reduced long term human impact. Contrastingly local relief, percentage of rock outcrops and logging in the recent past did not have a major influence on P. australis abundance. Growth habit varied in complex patterns. Individuals with fewer ramifications were found in valley bottoms and more disturbed basins, while more ramifications were found at mid- and upper slopes and well preserved basins. In valley bottoms, ramifications decreased with increasing altitude whereas the opposite trend was observed for mid-slopes. Ramifications were positively related to fires in two river basins and in mid- and upper slopes but not in valley bottoms. Fire impact was always less in valley bottoms than at mid- and upper slopes. Main conclusions: Human impact had a major role on P. australis cover, while growth habit was determined by complex combinations of potentially cumulative natural and anthropogenic factors. Even in sparsely populated mountains, both human impact and their interaction with natural environmental gradients influence plant communities and need to be understood for effective management.Fil: Renison, Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones BiolĂłgicas y TecnolĂłgicas. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas, FĂsicas y Naturales. Instituto de Investigaciones BiolĂłgicas y TecnolĂłgicas; ArgentinaFil: Hensen, Isabell. Institute of Geobotany and Botanical Garden; AlemaniaFil: Suarez, Ricardo. Proyecto ConservaciĂłn y ReforestaciĂłn de las Sierras de CĂłrdoba; ArgentinaFil: Cingolani, Ana MarĂa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto Multidisciplinario de BiologĂa Vegetal. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas FĂsicas y Naturales. Instituto Multidisciplinario de BiologĂa Vegetal; Argentin