By Dr. Glen Barry
Independent Political Ecology and Data Scientist
glen.barry@gmail.com
+1 608 332 5650

Manuscript submission under review by Management of Environmental Quality*
June 16, 2013

Abstract

Old-growth forests make Earth habitable for all life

Planetary boundary science defines key thresholds in the Earth System’s biogeochemical conditions that precede ecosystem collapse and threaten human well-being. Terrestrial ecosystems enter into the nine originally defined planetary boundaries only indirectly, through boundaries such as biodiversity and land use. This study proposes a measurable terrestrial ecosystem boundary to answer the question: what extent of landscapes, bioregions, continents, and the global Earth System must remain as connected and intact core ecological areas and agro-ecological buffers to sustain local and regional ecosystem services as well as the biosphere commons? Two preeminent considerations are connectivity of large ecosystem patches, enabling them to persist as the matrix for the landscape, and critical collapse of the dominant large habitat patch -; or “percolating cluster” -; into smaller, more isolated habitats, amid a matrix of human development. This transition, found to occur at about 40% habitat loss in landscapes and bioregions, is likely to be similar at continental and global scales.

A new planetary boundary threshold is proposed based on ecology’s percolation theory: that across scales 60% of terrestrial ecosystems must remain, setting the boundary at 66% as a precaution, to maintain key biogeochemical processes that sustain the biosphere and for ecosystems to remain the context for human endeavors. Strict protection is proposed for 44% of global land, 22% as agro-ecological buffers, and 33% as zones of sustainable human use.

Because humanity is now the major force shaping the biosphere, up to 50% of Earth’s land surface has already been transformed from mostly wild to mostly anthropocentric; thus the biosphere may already have lost its global percolating cluster. If so, with diminished connectivity, the global ecological system is now composed of islands of nature within a sea of humanity, meaning critical water, climate, soil, and other ecosystems processes are at risk. This observation suggests that to sustain the biosphere it is urgent to protect remaining large, relatively intact terrestrial ecosystems, especially old-growth and primary forests. This will require acceleration of current approaches such as biosphere reserves, and embrace of new polices such as a carbon tax to fund protection and restoration of natural and agro-ecological terrestrial ecosystems. To ensure global ecological sustainability, it will be necessary to reconnect matrices of intact ecosystems across scales, so that globally the biosphere and its constituent ecological processes and patterns can percolate back to connected nature as the context to all life. Otherwise, it is hypothesized the global biosphere may collapse and the Earth System perish.

*Version 2.0 under review by Management of Environmental Quality (MEQ), editing a paper initially presented at Kerala Eco-Conference.

Introduction to Planetary Boundaries

From Malthus (1798), through Aldo Leopold’s land ethic (1949), to The Limits to Growth (Meadows et al. 1972), the Millennium Ecosystem Assessment (2005), and finally current planetary boundary and global change science (Rockstr