[1] Large-scale die-off of tidal marsh vegetation, caused by global change, is expected to change flow patterns over tidal wetlands, and hence to affect valuable wetland functions such as reduction of shoreline erosion, attenuation of storm surges, and sedimentation in response to sea level rise. This study quantified for the first time the effects of large-scale (4 ha) artificial vegetation removal, as proxy of die-off, on the spatial flow patterns through a tidal marsh channel and over the surrounding marsh platform. After vegetation removal, the flow velocities measured on the platform increased by a factor of 2 to 4, while the channel flow velocities decreased by almost a factor of 3. This was associated with a change in flow directions on the platform, from perpendicular to the channel edges when vegetation was present, to a tendency of more parallel flow to the channel edges when vegetation was absent. Comparison with hydrodynamic model simulations explains that the vegetation-induced friction causes both flow reduction on the vegetated platform and flow acceleration towards the non-vegetated channels. Our findings imply that large-scale vegetation die-off would not only result in decreased platform sedimentation rates, but also in sediment infilling of the channels, which together would lead to further worsening of plant growth conditions and a potentially runaway feedback to permanent vegetation loss. Citation: Temmerman, S., P. Moonen, J. Schoelynck, G. Govers, and T. J. Bouma (2012), Impact of vegetation die-off on spatial flow patterns over a tidal marsh, Geophys. Res. Lett., 39, L03406,
Understanding plant species distribution patterns along environmental gradients is fundamental to managing ecosystems, particularly when habitats are fragmented due to intensive human land-use pressure. To assist management of the remaining vegetation of the Eastern Afromontane Biodiversity Hotspot, plant species richness and diversity patterns were analyzed along the main elevation gradient (1,000-2,760 m) of the Great Rift Valley escarpment in northern Ethiopia, using 29 plots established at 100-m elevation intervals. A total of 129 vascular plant species belonging to 59 families was recorded. Species richness and diversity showed a hump-shaped relationship with elevation, peaking at mid-elevation (1,900-2,200 m). Beta diversity values indicated medium species turnover along the elevation gradient and were lowest at mid-elevation. Elevation strongly partitioned the plant communities (r = 0.98; P\0.001). Four plant communities were identified along the elevation gradient: Juniperus procera-Clutia lanceolata community (2,400-2,760 m), Abutilon longicuspe-Calpurnia aurea community (1,900-2,300 m), Dracaena ombet-Acacia etbaica community (1,400-1,800 m), and Acacia mellifera-Dobera glabra community (1,000-1,300 m). To optimize conservation of species and plant communities, it is recommended that a conservation corridor be established along the elevation gradient that includes all four plant communities. This strategy?in contrast to creating single isolated reserves in zones with high species richness?is necessary for the habitat protection of species with narrow elevational ranges, in particular the globally endangered Nubian dragon tree (Dracaena ombet)
& Key message Tree heights in the central Congo Basin are overestimated using best-available height-diameter models. These errors are propagated into the estimation of aboveground biomass and canopy height, causing significant bias when used for calibration of remote sensing products in this region.
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