Evaluating canalside hedgerows to determine future interventions

This paper describes a project undertaken during 2001/2002 which developed a method for valuing hedgerows adjacent to the inland waterway network of Great Britain. The method enables the landowner, British Waterways, to manage their valuable environmental asset to achieve a good level of biodiversity and robust habitat balanced against the heavy amenity use the 3000 km canal network endures. Valuation techniques were developed using a combination of new and existing ecological indices for components of biodiversity, hedgerow structure and amenity, and synthesised into an index in an innovative combined approach. The resultant index was then applied to a sample 20 km section of hedge alongside the Grand Union Canal in Southeast England. The results obtained reflect the hedgerows' present value, and highlight factors that might improve or limit their future increase in value. The results from the case study application also demonstrate that there is a positive relationship between hedgerow structure and biodiversity, and that hedgerows in urban areas are less biodiverse and structurally sound than those in rural areas. Furthermore, there is a zone within rural areas influenced by the adjacent urban areas and/or higher amenity use. The paper concludes with an assessment of the approaches' strengths and weaknesses with a view to its compatibility with other hedgerow evaluations, such as HEGS, its use by other agencies or landowners, and to aid hedgerow management and future development. (C) 2004 Elsevier Ltd. All rights reserved.

Ancient watercourses and biogeography of the Sahara explain the peopling of the desert

Evidence increasingly suggests that sub-Saharan Africa is at the center of human evolution and understanding routes of dispersal “out of Africa” is thus becoming increasingly important. The Sahara Desert is considered by many to be an obstacle to these dispersals and a Nile corridor route has been proposed to cross it. Here we provide evidence that the Sahara was not an effective barrier and indicate how both animals and humans populated it during past humid phases. Analysis of the zoogeography of the Sahara shows that more animals crossed via this route than used the Nile corridor. Furthermore, many of these species are aquatic. This dispersal was possible because during the Holocene humid period the region contained a series of linked lakes, rivers, and inland deltas comprising a large interlinked waterway, channeling water and animals into and across the Sahara, thus facilitating these dispersals. This system was last active in the early Holocene when many species appear to have occupied the entire Sahara. However, species that require deep water did not reach northern regions because of weak hydrological connections. Human dispersals were influenced by this distribution; Nilo-Saharan speakers hunting aquatic fauna with barbed bone points occupied the southern Sahara, while people hunting Savannah fauna with the bow and arrow spread southward. The dating of lacustrine sediments show that the “green Sahara” also existed during the last interglacial (∼125 ka) and provided green corridors that could have formed dispersal routes at a likely time for the migration of modern humans out of Africa.