INTERGLACIAL CYCLE

The cycle of responses of flora, vegetation and soils to changes in seasonal insolation according to milankovitch theory (see Figure). Originally proposed by Iversen (1958), and modified by Andersen (1966), the idea has been reviewed by Birks (1986). Iversen proposed four stages to the cycle: (1) cryocratic, (2) protocratic, (3) mesocratic and (4) telocratic. There are three key concepts: (1) a rise and subsequent fall in mean annual temperature, (2) progressive vegetation development (migration and ecological succession) in the early stages and (3) retrogressive succession in the later stages (see Figure). This concept has rather been sidelined as higher-resolution studies have allowed more detailed determination of patterns within individual interglacials, although very similar vegetation dynamics appear [Page 583]to be recorded during recent interglacials despite differences in orbital forcing.

Interglacial cycleAn interglacial cycle showing interrelated changes in climate, vegetation and soils (Birks, 1986).