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The drought culminating in 1967-68 opened water-traps in Murray Cave, thus permitting the re-exploration and survey in January 1968, of a further 1,000 feet of the main passage. Previous explorations, of which oral tradition persisted, are known to have taken place in 1902-3 and some details of the early visitors are presented. The characteristics of the extension are predominantly shallow phreatic in nature and about half of it episodically functioning in this way at the present time; the water-traps along it are inverted siphons in the strict sense and located at the sharpest changes in cave direction. The exploration limit consists of a rockfall beneath a doline, which appears, therefore, to be at least in part a collapse doline. Beneath two other dolines the cave has no sign of collapse, though tall avens reach towards the surface; these dolines are due to surface solution only. The forward part of the cave is overlain by a short, steep dry valley; the relationship between the two remains problematic but there is good reason not to regard the dry valley as the determinant of the cave's location. The evidence is now stronger for an earlier hypothesis that the cave was formerly the outflow cave of nearby River Cave, a perennially active stream cave. It also seems likely that the episodic activity of Murray Cave is due to flood overflow from River Cave. The hydrological regime of the cave is compared with precipitation records of the nearby stations. The episodic flow through the cave does not require an abnormally wet winter; it can follow fairly quickly after complete emptying of the water-traps and approaches an annual event. Draining of the water-traps is a much less frequent event, but whether a series of low rainfall years is necessary, or a single pronouncedly dry year is sufficient to achieve this, cannot be determined from available data. On either count, it seems probable that the cave opened up two or more times between the known occasions of 1902-3 and 1968 in the period 1909-53 when the cave was visited infrequently.
After brief descriptions of the geomorphology of the Cooleman Plain karst and in particular of the Blue Waterholes, the methods adopted to analyse the functioning of these major risings are detailed. The discharge regime of Cave Creek below them is oceanic pluvial in type perturbed by drought and snow. There is much annual variation both in seasonal incidence and total amount, with catchment efficiency correspondingly variable. Suspended sediment concentration is even more erratic and monthly determinations are inadequate for calculating corrasional denudation rates. Mean concentrations of suspended solids are about 1/18th of solute load. Total dissolved salts have a strong inverse relationship with discharge, and mean values are high compared with those for other catchments in eastern Australia but none of these determinations are from limestone catchments. Sodium, potassium, and chlorine contents are low compared with the same catchments but silica is relatively high. The ratio of alkaline earths to alkalis indicate that Cave Creek carries carbonate waters and there is an inverse regression of the ratio on discharge. There is inverse correlation of total hardness on discharge likewise due to concentration of surface waters by evaporation in dry periods, together with reduced underground solution rate at times of large, rapid flow. The spring waters remain aggressive. Close regressions of hardness on specific conductivity now permit the latter to be determined in the place of the former. Much evidence converges to indicate that all the springs at the Blue Waterholes are fed from the same conduit. The intermittent flow which comes down the North Branch on the surface to the Blue Waterholes differs significantly in many characters from the spring waters. Rates of Ca + M carbonate equivalent removal vary directly with discharge since hardness varies much less than does water volume. These gross rates have to be adjusted for (a) atmospheric salts entering the karst directly, (b) peripheral solute inputs from the non-karst two-thirds of the catchment and (c) subjacent karst solution before they can be taken as a measure of exposed karst denudation. The methods for achieving this are set out. The total corrections amount to about one third of the total hardness, though the correction for subjacent karst on its own lies within the experimental error of the investigation. The residual rate of limestone removal from the exposed karst also shows a winter/spring high rate and a summer/autumn low rate but the seasonal incidence and annual total varied very much from year to year. In comparison with results from karsts in broadly similar climate, the seasonal rhythm conforms and so does the high proportion (78%) of the solution taking place at or close to the surface. This reduces the importance of the impounded condition of this small karst but supports the use of karst denudation rate as a measure of surface lowering. Cave passage solution may however be more important in impounded karst than its absolute contribution might suggest, by promoting rapid development of underground circulation. The mean value of limestone removal is low for the climatic type and this is probably due to high evapotranspirational loss as well as to the process of eliminating atmospheric, peripheral non-karst and subjacent karst contributions. The difficulties of applying modern solution removal rate to the historical geomorphology of this karst are made evident; at the same time even crude extrapolations are shown to isolate problems valuably.
Widespread but patchily distributed drought death of forest trees occurred in early 1988 on a limestone ridge at Mole Creek in Tasmania. A close juxtaposition of damaged and undamaged vegetation probably reflects differences in the speed of soil moisture decline down the length of individual soil-filled solution tubes in which trees are rooted. Possible palaeoecological, geomorphological and sivicultural implications are briefly reviewed.
Understanding past environmental changes in tropical rainforests is extremely important in order to assess the response of such environments to present and future climatic changes and understand causes and the present patterns of biodiversity.
Earlier hypothesis on the origin of biodiversity have stressed the role of past climatic changes in promoting speciation. According to the “refuge hypothesis” (Haffer, 1982), dry periods could have led to forest fragmentation, isolating more humid forested zones (called refuges) within an environment largely dominated by savannas. The refuge hypothesis does not assign timescales for rainforest fragmentation, although recent studies have suggested that speciation could have occurred over timescales of millions of years (Knapp and Mallet, 2003). Although the focus of heavy criticism (Colinvaux, et a., 2000), the refuge hypothesis has generated a large amount of research. In general, pollen studies (Colinvaux, et a., 1996, Haberle and Maslin, 1999) tend to support a continuous forest cover throughout late Quaternary climatic shifts, although large variations in rainfall have also been demonstrated by other pollen and isotopic studies (van der Hammen and Absy, 1994; Maslin and Burns, 2000).
Amazon and Atlantic rainforests are the two major forested zones in South America. Amazon rainforest, the largest rainforest in the world, comprise a total original area of 4.1 million km2 and is renowned for hosting the large biodiversity in the world (30% of all the world’s known plant and animal species). Atlantic rainforest, also a biodiversity hotspot, occurs along the coast and has been subjected to heavy deforestation since European arrival. Nowadays only c. 7% of its original forested area of 1.3 million km2 remains. These two rainforests are separated by drought-prone semi-arid northeastern (NE) Brazil. Our study does not address the refuge hypothesis directly although it sheds new light on the dynamics of forest expansion in the past as well as indicates alternative ways of promoting speciation. It has long been hypothesized, due to botanical (Mori, 1989; Andrade-Lima, 1982) and faunistic (Costa, 2003) similarities, that the Amazon and Atlantic rainforests were once linked in the past. Although numerous connecting routes have been postulated (Bigarella, et al, 1975; Por, 1992; De Oliveira, et al, 1999), the timing of forest expansion and their possible recurrence have remained elusive.
The study area lies in the driest portion of NE Brazil “dry corridor”, close to the village of Laje dos Negros, northern state of Bahia. Mean annual precipitation is around 480 mm and potential evapotranspiration is in excess of 1,400 mm/year (Fig.1). Present vegetation comprises a low arbustive scrubland known locally as caatinga. The area contains a well-developed underground karst (Auler and Smart, 2003) with abundant secondary calcite precipitates, both underground (speleothems) and on the surface (travertines).
In 2000-2001, the fauna of and ecological conditions in the Železna jama cave near Dob in the isolated karst area of Domžale-Moravče (east of the town of Domžale, central Slovenia), were investigated. Fifty-three species were found in the cave, the dominant ones being Meta menardi, Amilenus auriantiacus, Troglophilus neglectus, T. cavicola, Laemosthenes schreibersi, Ceuthmonocharis robici, Limonia nubeculosa and an undetermined phorid species. The troglomorphotic taxa found were: Zospeum sp., C. robici, Anophthalmus sp. among others. Besides seasonal changes in the local and the cave climate, changes in drought intensity and the varying quantities of organic matter in the substrate were probably the most important factors triggering migrations. Animals migrated between the cave and the surface, adjacent fissure systems and the water channel in the bottom of the cave, which is inaccessible to humans.
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