There is a major planet-wide experiment under way. Anthropogenic changes
to the atmosphere–biosphere system mean that all ecosystems on Earth are
now affected by our activities. While outright deforestation is physically
obvious, other subtler processes, such as hunting and surface fires, also
affect forests in ways that are less evident to the casual observer (cf. Estes
et al. 2011; Lewis, Malhi & Phillips 2004a; Malhi & Phillips 2004). Similarly,
anthropogenic atmospheric change is intensifying. By the end of the century,
carbon dioxide concentrations may reach levels unprecedented for at
least 20 million years (e.g. Retallack 2001) and climates may move beyond
Quaternary envelopes (Meehl et al. 2007). Moreover, the rate of change in
these basic ecological drivers may be unprecedented in the evolutionary
span of most species on Earth today. Additionally, these atmospheric
changes are coinciding with the greatest global upheaval in vegetation
cover and species’ distributions since at least the last mass extinction at
~65 million years ago (Ellis et al. 2011). Collectively, the evidence points to
conditions with no clear past analogue. We have entered the Anthropocene,
a new geological epoch dominated by human action