Showing papers on "Undergrowth published in 1985"

Day-night changes in the leaf water relations of epiphytic bromeliads in the rain forests of Trinidad.

Abstract: A study was made of the bulk-leaf water relations of selected species of epiphytic bromeliads growing in their natural habitat in Trinidad (West Indies). Field measurements were made during the rainy season at three forest sites centred on the wetter part of the island. The epiphytic bromeliads were sampled in situ using modified rock-climbing techniques at 4- to 6-h intervals during complete day-nigh cycles. Eleven species were studied that differed in their photosynthetic pathways and habitat preferences. The C3 species among the epiphytic bromeliads characteristically showed maximum values of xylem tension (measured with the pressure chamber) during the day, whereas the species with crassulacean acid metabolism (CAM) attained maximum values towards the end of the night. In addition, the CAM species showed large nocturnal increases in leaf-cell-sap osmotic pressure and titratable acidity. These nocturnal increases showed mean values of 0.601 MPa and 289 mol H+ m-3, respectively, for four species sampled at an exposed forest clearing (250 m), where CAM species were well represented. At the other two sites, a lowland forest (60 m) and a ridge forest (740 m), CAM bromeliads were found in the forest canopy, but in the lowest strata all the bromeliads were C3 species. This species distribution was associated with a marked vertical stratification of microlimate, the forest canopy being characterized by much bigger day-night changes in temperature and water-vapour-pressure deficit than the undergrowth. The C3-CAM intermediateGuzmania monostachia var.monostachia showed significant nocturnal acidification in the forest clearing but not in the understory of the lowland forest. Taken as a whole, the C3 and CAM bromeliads were very similar in the range of values observed for xylem tension and osmotic pressure, as well as in aspects of their leaf anatomy. However, epidermal trichomes covered a large percentage of the leaf surface area in xeromorphic species (e.g.Tillandsia utriculata), whereas they were poorly developed in shade-tolerant species (e.g.G. lingulata var.lingulata). The absolute values of sylem tension and osmotic pressure were low for all species. Mean minimum xylem tension during the day-night cycles was in the range of 0.18–0.23 MPa and mean maximum in the range 0.41–0.53 MPa; during periods of rain, xylem tension reached a mean minimum of 0.12 MPa. Mean minimum osmotic pressure was in the range 0.449–0.523 MPa. Such between-site and between-species differences as were observed in the water relations of the bromeliads could be related to the microclimatic conditions prevailing in the various epiphytic habitats.

The Magdalenian Avifauna at Erralla Cave

Abstract: In its situation at the head of the Gorge of the Alzolaras stream, the immediate environs of the Cave of Erralla (Cestona) command a varied habitat for bird life. In the Gorge itself vegetation is dense, mixed forest of deciduous species, presently dominated by hazel and with some evergreens. The stream bed is fast flowing and stony with little wed in the upper reachds near the cave. Above the valley the land rises sharply into steep pastures of lush grass, with a wide variety of limestone flora. Higher still, on the west bank to the immediate south of the cave is an area of forest plantation, mainly Dine with some beech and. an undergrowth of heathers, blackberry and bracken. The highest land lies to the south of the cave, where the Monte Gazume massif rises to 1000 metres, with a light afforestation, heathers and myrtle.

Fructification in dutch maianthemum bifolium populations

Abstract: SUMMARY Aspects of fructification in Maianthemum bifolium were studied, mainly in natural populations in The Netherlands, but also in additional laboratory experiments. C. 15% of the plants were found to produce flowers. On an average 25.1 ± 3.59 flowers and 2.7 ± 2.24 fruits were established per fruiting plant, and a mean of 1.2 fruits per flowering plant. It was ascertained that at soil pH ≤ 4 generally more fruits were produced than at higher pH values. At a coverage of ≥ 35%, a highly positive correlation was found to exist between the coverage percentage of undergrowth and the number of fruits produced. A presumed positive effect of the undergrowth via a raised air humidity on fruit production was affirmed by laboratory experiments. Syrphidae appeared to be the most important pollinating insects. However, insect pollination did not appear to be decisive for fruit production.