Forest fragmentation has been studied extensively with respect to biodiversity loss, disruption of ecosystem services, and edge effects although the relationship between forest fragmentation and human activities is still not well understood. We classified the pattern of forests in Massachusetts using fragmentation indicators to address these objectives: 1) characterize the spatial pattern of forest fragmentation in Massachusetts towns using Morphological Spatial Pattern Analysis (MSPA); and (2) identify regional trends using archetypal towns in relation to town history, geography and socioeconomic characteristics. Six fragmentation indicators were calculated using MSPA for each town to represent patterns and processes of fragmentation. We then used these indicators and the proportion of forested land to group towns across Massachusetts with similar patterns of fragmentation. Six representative towns typify different types of forest fragmentation, and illustrate the commonalities and differences between different fragmentation types. The objective selection of representative towns suggests that they might be used as the target of future studies, both in retrospective studies that seek to explain current patterns and in analyses that predict future fragmentation trends. 相似文献
A revised age provided by conodonts from the Gilwern Oolite of the Clydach area of South Wales allows a clearer understanding of the palaeohydrology, palaeoclimatic history and diagenesis of previously correlated oolitic units. Earlier uncertainty over the apparent sub-regional differences in climate during the early Visean (Chadian—Arundian) lowstand is resolved. Previously a humid interval evidenced by prominent palaeo-epikarst capping the Gilwern Oolite along the northern outcrops of the South Wales synclinorium, was not recognized in what were regarded as correlative outcrops in the Chadian Gully Oolite in the southern part of the synclinorium. Conodont dating now shows that the Gilwern Oolite is much older (Courceyan) than the Chadian Gully Oolite, and during the prolonged exposure of the former there was an interval of weathering under a humid climate. This also explains the contrast between the diagenesis seen between the Gilwern and Gully oolites, which are no longer seen as correlatives. 相似文献
We have used computer simulation methods to model the structure and energetics of the hydrogarnet defect in grossular. The predicted structure is in good agreement with experimental data. The calculated energy for the reaction of water with grossular to form the hydrogarnet defect is 1.02 Ev (98 kJ mol-1). This low energy of reaction suggests that such defects will be common in garnets where they could play an important role in effecting processes such as atomic transport. 相似文献
The fate of sediment seaward of river mouths involves at least four stages: supply via plumes; initial deposition; resuspension and transport by marine processes; and long-term net accumulation. The processes that operate at each stage, and relative roles of each stage in governing the long-term accumulation patterns, vary appreciably with river regime and coastal ocean environment. To illustrate the diversity and illuminate the process of dispersal, information is synthesized for six systems: Amazon, Changjiang, Mississippi, Columbia, Purari, and Huanghe. These systems differ markedly in terms of water discharge, sediment discharge, and coastal energy regime and much of the diversity of dispersal patterns is attributed to these differences as well as to the temporal sequencing of river discharge relative to oceanographic transport processes. Although the sediment: water ratio of the discharge of the Mississippi River is 70 times less than that of the Huanghe, both of these systems exhibit rapid deposition and accumulation of sediments near the river mouths. In contrast, sediments dispersed by, the other four systems are transported greater distances from the mouths by oceanographic processes, and are accumulating over relatively wide areas. 相似文献
Annual evaporation from groundflora, litter and soil of the jarrah forest was estimated from measurements of daily evaporation by ventilated chambers on several days over two separate 12-month periods. In the first year, when sampling ranged over 0.1 ha of forest, annual evaporation during daylight hours was estimated as 410 mm (0.32 rainfall). In the second year, sampling was more frequent, on a larger scale, and included the night hours. Annual evaporation was estimated at 360 mm (0.36 rainfall).
Similarly, in the second year, annual evaporation from two trees of the dominant middle storey species, Banksia grandis, was estimated at 7500 and 18,9001 respectively. The leaf area of these two trees was 9.6 and 22.4 m2, respectively, so that annual evaporation, when expressed as mm3 per mm2 leaf area, was similar for both trees (mean = 820 ± 30 mm). Applying that value to all Banksia trees in a hectare of forest, and using a measured estimate of leaf area index of 0.19, the estimated annual evaporation from the Banksia component was 155 mm (0.16 rainfall). For the upland part of the forest sampled, the combined annual evaporation from the lower and middle storeys accounted for about half (0.51) of the annual rainfall.
We conclude that reduced evaporation from the upper storey following clearing or thinning may be strongly counteracted by increased evaporation from the understorey due to increased availability of energy and water. 相似文献