February 27, 2010

Life System Proxies: Forest cover

A few posts ago I noted that I would follow with some specific examples of Earth System proxies.  I got distracted, but here is a first one...

A clear indicator of the state of the Life subsystems of the Earth system is the amount of Earth's land surface that is covered by forests.  There are many reasons for this, not the least of which is that forested land is archetypal in western cultural images of "natural".  Forests house ecosystems that are more or less independent from humans; they provide homes to many of our cherished charismatic megafauna and they provide a whole host of ecosystem services ranging from materials to spiritual solace.  A couple of less obvious of these include gas exchange with the atmosphere that removes CO2 and releases O2 as through photosynthesis and moderating the hydrologic cycle - the rain forests of Brazil are sometimes referred to as the lungs of our planet.

So changes in the percentage and distribution of forest cover on Earth's land surface will change in very fundamental ways how the Earth system functions.  Prior to the Industrial Revolution (say 1776), the distribution of forest cover on Earth changed slowly in concert with other elements of the Earth system (e.g. during glacial cycles).  Following the industrial revolution and the attendant increased consumption of energy and expansion of human population that came with it, humans began to have a significant impact on where and how much forest there was on Earth.  For instance, much of what is now forest in New England, was cleared for farmland in the 18th century.  Those forests began to return as transportation corridors opened up to the west and allowed the much more fertile and easy to work lands of the midwest to take up some of the demand for food on along the East coast.

On a much larger scale (the economy is now global and removal rates are higher), similar economic pressures are driving the removal of rain forests in Brazil, Indonesia and parts of Africa in current times.  Rain forest soils and ecosystems are very different from the deciduous forests of New England and it is clear that re-growth of the rain forests will take much longer than those of New England.

If we monitor forests, where they are, how they are changing, we will be monitoring a part of Earth's Life system.  The challenge of course is to know what those variables tell us: Are those changes good or bad? and What futures do they signal or eliminate?