Degree Of Spatiotemporal Variability Research Articles

Vegetation–environment interactions in a sub-arctic primary succession

Biological modification of the physical environment is a characteristic feature of primary succession that is of particular importance in stressful, high-latitude habitats. However, the degree of spatiotemporal variability in biotic reaction is poorly understood. This is a significant gap in our knowledge of primary succession, as spatiotemporal variability in biotic reaction may be linked to divergent development during succession. The aim of this research was to infer long-term, spatiotemporal changes in vegetation and environmental parameters during primary succession from a chronosequence of lava flows in Iceland. Vegetation surveys and measurement of key environmental variables (temperature, relative humidity and wind speed) were carried out on seven lava flows aged 26–848 years. The duration of snow cover was inferred from temperature data using a novel technique. Paired measurements were taken in topographical low and high points, as previous studies in this location have indicated divergent vegetation development according to topographical position. The analysis indicated the long-term amelioration of microclimate. Vegetation development was associated with increased soil temperatures, decreased wind speeds and increased duration of snow-lie. There was also evidence that microenvironmental changes paralleled changes in vegetation structure, although the relationship varied according to the environmental parameter studied. It is likely that positive feedback between shrub development and snow accumulation structures the vegetation on the study sites. These findings have implications for sub-arctic areas where shrub cover is expanding due to climate change and for the development of vegetation on terrain exposed by retreating ice.

Sedimentary Processes in Restricted Gulf Coast Estuarine System: Corpus Christi Bay, Texas: ABSTRACT

Corpus Christi Bay is a shallow (< 5 m), restricted estuary that is typical of estuaries on the Texas Gulf Coast. The distribution pattern of bay-floor sediments indicates that the bay's interior is a depocenter for mud derived from multiple sources; the bay's marginal areas are composed mainly of residual sandy deposits derived from shoreline erosion of a Pleistocene substrate (Beaumont Formation) and a modern baymouth barrier (Mustang Island). Synoptic time-sequence measurements of the bay's suspended sediment and hydrographic characteristics were taken by helicopter at 15 monitoring stations; the measurements represent 8 surveys conducted during a 2-year observation period. The measurements show a high degree of spatiotemporal variability and indicate a wind-dominated sediment-dispersal system. During all surveys, the bay was consistently turbid (mean baywide transmissivity < 15%/m); the mean baywide concentration of suspended sediment during individual surveys ranged from 11 mg/l to 52 mg/l. The suspended-sediment concentrations were primarily controlled by wind speed which determines the extent of wave-induced resuspension of bay-floor deposits; wind direction and tidal phase controlled the sediment-dispersal patterns Texturally, the baywide mean grain size of suspended sediments during individual surveys ranged from very fine silt to clay (7.63 to 3.22^phgr), and mean silt/clay ratios were within the 0.68 to 1.38 range; the sediment was consistently poorly sorted. In contrast to suspended-sediment concentrations, which largely appear to be a short term response to recent wind conditions, sediment textures appear to be a longer term response to earlier wind conditions, thus suggesting that finer grained particulate matter has substantial residence time within the shallow water column. End_of_Article - Last_Page 992------------