06 Lodge (176-198) Master

The earth’s environments and ecosystems are not fi xed but vary over a wide range of space and time scales (Delcourt, and Webb 1982; see also fi g. 6.1). At the scale of tens of thousands of years, the wobble of the Earth on its axis causes variation in the solar radiation received at the earth’s surface, driving variation in climate. On shorter time scales, the Southern Oscillation of sea surface temperature in the eastern Pacifi c infl uences precipitation over large areas, causing fl oods at some locations and droughts at others. Change can be as gradual as the movement of continents and the uplift of mountain ranges and as abrupt as hurricanes and earthquakes. Because change is characteristic, present-day ecosystems must be understood in the context of their histories (Foster, Knight, and Franklin 1998), for example, in the context of ancient ice ages (Davis and Shaw 2001) and recent fi res (Covington et al. 1999). The ubiquity of change raises the issues that are the subject of this chapter—the relationship of ecosystem dynamics, conservation management, and environmental ethics. Among the most important sources of change at middle scales of space and time are natural disturbances (White and Jentsch 2001). These disturbances operate within the scales of our own lifespans and management choices, and a representative list of such events immediately suggests their relevance to humans, as well as to natural ecosystems: hurricane,