Natural analogues of degraded ecosystems enhance conservation and reconstruction in extreme environments

Abstract

Ecosystem rehabilitation strategies are grounded in the concept that coexisting species fit their environments as an outcome of natural selection operating over ecological and evolutionary timescales. From this perspective, re-creation of historical environmental filters on community assembly is a necessary first step to recovering biodiversity within degraded ecosystems; however, this approach is often not feasible in severely damaged environments where extensive physiochemical changes cannot be reversed. Under such circumstances management goals may shift from restoring historical conditions to reconstructing entirely new ecosystems or replicating natural ecosystems that may be locally novel but of regional conservation importance. This latter goal may be achieved by introducing to damaged sites species already adapted to filters maintaining the degraded state, through targeting assemblages from natural ecosystems biophysically analogous to the degraded state, here termed "degraded-state analogue" (DSA) ecosystems. This hypothesis predicts that, in high-stress sites where recruitment of previous inhabitants is strongly microsite-limited, DSA species will be primarily propagule-limited; furthermore, communities invaded by DSA species should shift in structure to reflect properties associated with high-value DSA target ecosystems. We tested these predictions by experimentally sowing long-abandoned limestone quarry floors with 18 perennial grass and forb species characteristic of rare natural limestone pavements called "alvars." Alvar species established successfully under a range of microsite conditions manipulated to alter suspected constraints on colonization, including nitrogen deficiency, excessive CaCO3, and competition with weeds. Alvar species performed equivalently to seeded weed species known to thrive on quarry floors. Resident communities doubled in species richness following alvar species addition, supporting 17-20 species/0.18 m2 (95% confidence interval) and providing refuge to regionally restricted or threatened species including Iris lacustris, Solidago ptarmicoides, and Liatris cylindracea. In contrast, maximum-diversity reference plots on a pristine alvar supported 20-23 species/0.18 m2. Strong propagule limitation but weak microsite constraints on quarry colonization by alvar species combined with establishment of species-rich communities comparable to natural alvar biodiversity hot spots confirms that targeting DSA assemblages in ecosystem reconstruction can promote both efficient site colonization and ex situ biodiversity conservation within difficult-to-restore anthropogenic wastelands.

Can we Create Alvars or Fully Restore those Damaged?

“…Relatively rich species assemblages including some alvar components were developed, but experimentally seeded plots had only half the richness of alvar species as natural alvars and half the cover of vascular plants (Figure 4). Richardson et al (2010) provide evidence suggesting that targeting alvar assemblages in developing vegetation cover can promote efficient site colonization and ex situ biodiversity conservation. However, it is a skip, a hop and a jump (and a long hike) from here to saying that their data signifies that an alvar can be repaired or created.…”

“…(3) Richardson et al (2010) Alvars are regarded by these authors as a "degraded state analogue" for quarry bottoms. This suggests that some degree of restoration to alvar-like vegetation may be possible.…”

“…The Richardson et al (2010) experiment thus, while it produced valuable plant cover by seeding, did not include enough alvar species or biomass, continue for long enough, nor consider interactions and processes sufficiently to evaluate the possibility of repair or creation of a self-sustaining alvar plant community or an alvar ecosystem.…”

“…Although observations were not new (see text box), it was of interest because it suggested that alvars could be used as a model, or analogue, for efficiently greening quarries and simultaneously protecting some rare and at-risk alvar species (extended by Richardson et al 2010). Using artificial (built) landscapes for species conservation is a great improvement over filling a quarry with fertilized soil and planting it with alien Crested Wheatgrass!…”

Restoration of forest resilience: An achievable goal?

“…In the context of current rates of environmental change, the associated development of non-analogue communities (Keith et al 2009) and variation in recovery trajectories, a number of authors have suggested that it may not be possible to specify a single endpoint of a restoration project. Rather, the possibility of multiple end points might need to be explicitly recognised in restoration planning and management (Choi et al 2008;Suding and Gross 2006;Suding 2011), together with the creation of entirely novel ecosystems (Hobbs et al 2009;Richardson et al 2010;Seastedt et al 2008). This perspective has led to suggestions that terms other than ecological restoration should be used for such management interventions, for example reconciliation ecology or intervention ecology (Davis 2000;Hobbs et al 2011;Suding 2011).…”