We are examining the growth, growth history and climate sensitivity of white and black spruce trees on the floodplains of the major rivers fed by glacial meltwater in Interior Alaska. To date we have sampled 624 trees on 41 sites distributed across 1,783 km of the Yukon River, 375 km of the Tanana River, and 370 km of the Kuskokwim River, for a total of 2,528 km of river length.

Numerous physical, chemical, and biological processes operate in positive feedback loops during the invasion of C3 shrubs into C4 grasslands. These processes occur at multiple spatial and temporal scales, ranging from a few mm2 over a period of weeks to hundreds of km2 over a period of millennia.

Both slow and fast variables interact to produce ecosystem change observable in a human lifetime. Unfortunately, ecosystem processes that operate over hundreds to millions of years are difficult to document, but are likely essential for understanding future ecosystem changes. Ecologists have traditionally studied these long-term ecosystem variations using the chronosequence approach, which adopts a “space-for-time” substitution.