Distribution Of Mounds Research Articles

Spatial Distribution of Dipodomys spectabilis Mounds

Spatial distribution of Dipodomys spectahilis mounds on a rectangular 47 hectare area of short-grass prairie was determined using nearest neighbor and Poisson analyses. A total of 121 mounds was mapped (density 2.57 mounds per hectare) of which 79 were active. A nearest neighbor analysis of active and inactive mounds together revealed a significantly uniform distribution. Active mounds alone were also found to be regularly dispersed. Numerous Poisson analyses were made with sample quadrats of various sizes. This method also showed the distribution to depart significantly from randomness toward uniformity as the quadrat size was reduced. As quadrats were made still smaller, the Poisson analyses produced inconsistent results. This suggests that the nearest neighbor method might be a more reliable measure of compound distributions. The regularity evident in the mound distribution indicates that D. spectabilis minimizes intraspecific interactions by spatial means.

Pimple Mounds: A New Viewpoint

The character and distribution of pimple mounds in Louisiana and adjoining territory points to a possible pedestal tree—erosion origin for such mounds.

Submerged vegetation of the Rotorua and Waikato Lakes

Abstract In Lake Rotoiti, North Island, New Zealand, ‘cyclic change’ apparently occurs among mounds of the ‘Low Mixed Community’ of plants; this is the first evidence of cyclic change in a wholly submerged community. The Low Mixed Community grows on gently sloping, sandy substrates ndar the shores of bays sheltered from the prevailing SW winds, and usually extends to depths of about 1.8 m, where dense beds of Lagarosiphon major begin. The work we report Was done in 1968–70. We sampled ithe community by transects, various types of quadrats, and by monitoring marked mounds, and from these data we analysed the composition, distribution, growth and fate of mounds at various depths. We observed that one species of five genera (namely Glossostigma spp., Elarine spp., Lilaeopsis lacustris, Elodea canadensis, and Myriophyllum propinquum) colonised bare sand and trapped more sand; as the mound grew, other species appeared. Mounds in deeper water (> 0.9 m) were larger and floristically richer than those in shallower water, and were thus probably older. In calm conditions, mounds sometimes fused to form a polytypic sward. Typically, however, the backwash of waves eroded the shoreward ends and sides of mounds; the mounds thus became elongated parallel to the wind direction. Provided that their growth at the offshore end at least balanced erosion at their shoreward ends, some marked mounds tended to grow downslope into deeper, less often disturbed water. Although backwash started mound erosion down to 0.6 m depth, it could also erode bare areas in mounds (caused by die‐off of plants, herbicide sprays, and mechanical damage) down to 1.2 m, the depth to which it normally influenced loose substrate. In exceptional easterly storms, backwash might influence plants at greater depths, and perhaps locally destroy the community so that the cycle would have to begin again. Briefly, we suggest that these characteristic signs of cyclic change in this community result from an interaction between fragile mounds of plants growing on an unstable, sandy substrate which is easily eroded by wave backwash. However, more observations over a longer time will be needed before our prima facie case for the occurrence of cyclic change can be proved. We also recorded an invasion of Lagarosiphon over mound plants into depths of only 0.9 m, and we proposed for the “Low Mixed Community” the appropriate name Glossostigmatum aquaticae because Glossostigma spp. predominated in all floristic analyses.

Fuarmolic Mounds and Ridges of the Bishop Tuff, California

Fumarolic mounds and ridges are prominent surface features of the southern part of the Bishop Tuff and are characterized by their greater induration relative to the surrounding ash or tuff. They stand 0.5 to 15 m above the surrounding terrain and are of two main types: (1) domical mounds up to 60 m in diameter, and (2) straight or curved vertical joint ridges 1.5 to 5 m high and up to 600 m long. Fumaroles were formed in greatest numbers where crystallization within the sheet was intense and are absent from areas where the sheet was thick and densely welded but remained vitric. Early conjugate joint sets, which followed welding but predated escape of fumarolic vapors, controlled the distribution of fumarolic mounds and ridges. Later random orthogonal joints, which postdate vapor-phase activity, resulted from release of thermal stress stored in the cooling sheet. Welding, conjugate fumarolic jointing, fumarolic activity, and random orthogonal jointing represent successive discrete stages in the cooling history of the Bishop Tuff. The general mineralogy of the fumarolic areas and the vapor-phase zone are similar, but hydro-biotite and marialite are identified in the inner alteration zone. Likewise, the chemical composition of the fumarolic mounds is similar to that of the vapor-phase zone. The inner zone around some fumarolic vents shows significant changes through a decrease in SiO 2 and an increase in A1 2 O 3 , K 2 O, and H 2 O.