Forest change and disturbance

Abstract

Ecology of past forests The Palaeozoic era and tectonic plate theory Woodlands and forests of the past were often very different from those we know today. In this matter, as in so many others, the Greek philosopher Heraclitus was correct in stating that only change is constant. Moreover, the changes known to have occurred in the world's flora and fauna have sometimes been very abrupt (Toghill, 2000), as in the biggest mass extinction of all time which occurred at the end of the Permian period (245 Ma i.e. millions of years ago – see Fig. 1.1). The causes of these mass extinctions may well have been either large asteroids striking the earth or the eruption of supervolcanoes such as that now simmering beneath Yellowstone National Park, Wyoming, USA. Each of these possesses a huge magma chamber, the contents of which contain vast amounts of mainly sulphurous gases. Once an eruption begins these previously dissolved gases assume the vapour phase, hurling much of the magma high into the stratosphere where some of it remains as fine ash for such a long period that it entirely disrupts the climate, lowering the temperature to such an extent that few plants and animals survive. Many past changes, however, have been slow and gradual as climate has changed and new types of trees appeared.