Alien Invasions, Ecological Restoration in Cities and the Loss of Ecological Memory

Schaefer, V. 2009. RESTORATION ECOLOGY 17 (2): 171-176.

This paper focuses on biological legacy in patches of urban habitat, particularly feed backs that build ecological memory capable of allowing sites to self-restore along appropriate trajectories. The author differentiates between internal memory (e.g. seed bank, genetic diversity) and mobile "link-species" that move species between patches. Remnant soil, microbes, and even decomposing logs can facilitate restoration of sites, whereas disturbed or fill soil may be resilient to restoration efforts, causing plants to be akin to the living-dead. On the other hand, invasive species are capable of creating their own, often persistent, ecological legacies and memories within sites.
The author (perhaps unnecessarily), includes an equation for Ecological memory (EM): EM = L - D where L is the original and latent species composition as well as ecological processes, and D is disturbance or processes causing memory loss. However, if original species are entirely lost, then the system may become a novel ecosystem (NE) with predominantly non-analogue or invasive species (I), thus NE = EM + I.
The equations above did little to enhance the concept, which is already incredibly straight-forward. While it is pertinent to consider the EM of a site, both native and non-native, the challenge, which this paper does little to address, is how to go about assessing EM, then using this information to construct restoration goals. The author invokes climate change a a factor to consider, but spends no time developing an argument concerning how ecological memory may be detrimental to adaptation to novel conditions or climate regimes.

Photo: Nature surrounding and providing corridors through city in Sonora, Mexico. H. Sardinas