vrijdag 24 augustus 2012

Novel ecosystems [the science behind cryptoforestry]


16 names have signed 'Novel ecosystems: theoretical and management aspects of the new ecological world order'. It's something of a manifesto arguing for a new approach within ecology to the newly emerging landscapes of the anthropocene. The image is from a 2009 article in Nature on novel ecosystems as Raggamuffin Earth.
Most of the world’s ecosystems are now impacted by humans to a greater or lesser extent, and humans thus play an important role in modifying or regulating the types and rates of ecosystem change. In addition, global trading has breached biogeographical boundaries and facilitated the spread of species into regions that they would probably never have reached under normal
conditions.

Novel ecosystems (also termed ‘emerging ecosystems’) have species compositions and relative abundances that have not occurred previously within a given biome. The key characteristics are  (1) novelty: new species combinations, with the potential for changes in ecosystem functioning; and  (2) human agency: ecosystems that are the result of deliberate or inadvertent human action, but do not depend on continued human intervention for their maintenance. Such ecosystems result from biotic response to human-induced abiotic conditions and/or novel biotic elements (e.g. land degradation, enrichment of soil fertility, introduction of invasive species). This includes the cessation of management of systems that have been managed or created by humans (e.g. agroforestry systems, pastoral land). New species combinations arise frequently in today’s world in conditions of strong direct or indirect human impact. In particular, there are three main reasons for their existence.
1 - Human impact has resulted in local extinction of most of the original animal, plant and microbial populations and/or the introduction of a suite of species not previously present in that biogeographical region.
2 - Predominating urban, cultivated or degraded landscapes around target ecosystems create dispersal barriers for many animal, plant and microbial species.
3 - Direct (e.g. removal of natural soil, dam construction, harvesting, pollution) and indirect (e.g. erosion due to lack of vegetation or overgrazing) human impact has resulted either in major changes in the abiotic environment or a decrease in the original propagule species pool, both of which can prevent the re-establishment of pre-existing species assemblages.
These types of ecosystem can be thought of as occupying a zone somewhere in the middle of the gradient between ‘natural’ or ‘wild’ ecosystems, on one hand, and intensively managed systems on the other hand.

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