Natural succession as a restoration tool ― Editorial

Ecosystems are continuously being serverely damaged by human activities, and we are now beginning to understand that these changes often disrupt ecological processes that we rely on.  Thus ecological restoration is becoming increasingly critical.  Practitioners of ecological restoration often use technical means, including the use of heavy machinery and large amounts of manual labor, to restore biodiversity to damaged areas.  This is often very expensive; nevertheless we must find a way to rehabilitate the overwhelmingly large amount of damaged ecosystems throughout the world.

In ecological restoration we are concerned with increasing the natural value of degraded areas.  Apart from technical restoration, changes within ecosystems occur through natural succession.  Often a primary goal in restoration is to increase the cover- and diversity of vegetion.  One doesn't expect to see these increases, at least not through natural succession alone, at sites which are extremely toxic or dry.  However, one could use technical restoration methods until the plant community becomes capable of continuing the succession process on its own.  On steep slopes, or other areas where the threat of landslides or erosion is great, re-vegetating the site as quickly as possible is clearly justafiable; and faster formation of continuous vegetation cover is a common advantage of technical restoration methods.  A study looking at erosion in Fujian Province, China, indicated that 20 % vegetation cover represents a restoration threshold, beyond which natural succession can be embraced.

A number of scientific investigations by Czech biologists suggest that leaving Czech post-mining sites to undergo natural succession can be beneficial for aquatic- and terrestrial communities.  Amphibians benefit from natural succession in these areas, as this process creates many small shallow ponds, rich in vegetation, throughout the landscape; while sites which are reclaimed by technical methods are typically flattened and contain only large deep ponds which are vegetated only within the riparian zone, and contain predatory fish.  Sites where natural succession prevails often represent various stages of succession, called seral stages; and landscape-scale studies have indicated that a greater diversity of seral stages tends to increase regional biodiversity.

Strategically embracing natural succession as a restoration tool can save time, money, and effort, and lead to more-diverse ecosystem development.  At many sites, technical measures may be necessary to prevent- or remediate extreme environmental damage.  Of course, there are countless degraded sites at which biodiversity can re-develop from natural succession alone.  At countless other sites we can surely find a balance between technical restoration methods and the strategic use of natural succession; this balance would be specific to the restoration site in question.  A limited-intervention approach has been suggested for wide use.  This limited-intervention approach involves assessing limiting factors for a particular site's development, leading to a restoration approach using the minimum effort required to meet specific restoration goals.  Additionally, as long-term monitoring remains one of the largest let-downs in conservation science- and practice, this approach may help the field move forward by allowing more-robust monitoring efforts due to the money saved on restoration methods.  Considering the amount of terrestrial- and aquatic habitat that currently requires restoration, the limited-intervention approach may be the wisest and most feasible option.

Arctic marine mammal conservation

Earth's marine mammals are disproportionately threatened compared to land mammals, and the 11 species of arctic marine mammals (hereafter AMMs) are particularly threatened due to their dependence on sea ice.  Some AMMs require sea ice for certain activities (e.g. reproduction, feeding, resting), while other use ice but are not dependent on it.  AMMs refer to species that occur north of the arctic circle (66° 33' N) for most of the year, as well as some species that seasonally inhabit arctic waters.  AMMs include 3 whales (narwhal, beluga, and bowhead); 7 pinnipeds (ringed, bearded, spotted, ribbon, harp, and hooded seals, and walrus); and the polar bear.  Throughout much of their range, these animals are important nutritional resources for indigenous people.  Recent research indicates that the greatest species richness of AMMs is in the atlantic regions of Baffin Bay, Davis Strait, and the Barents Sea (figure 1); while the lowest species richness was found in the Sea of Okhotsk and the Beaufort Sea.

Figure 1:  Geographic regions of the arctic marine ecosystem.

Warming in the arctic over the past several decades has been about 2 times greater than the global average, and scientists predict an ice-free arctic in summer by 2040.  Of the 12 arctic marine regions, 11 show significant trends (1979-2003) toward earlier spring sea-ice melting, later autumn sea-ice formation, and thus longer summers (figure 2).  Only the Bering Sea showed no trend.  The trend was most extreme in the Barents Sea.  The trend of sea-ice loss is surely guaranteed for at least the next several decades, regardless of global efforts to reduce greenhouse-gas emissions.

Figure 2:  Trends (1979-2013) in length of summer season (time from spring sea-ice melt to autumn sea-ice formation).

In addition to declining sea ice surface area, the thickness of sea ice has greatly decreased.  Continuation of this thinning is expected to further effect summer ice extent, as storms and other weather anomalies substantially impact thin ice.  Loss of sea ice has affected survival in some polar bear populations.  The survival of pinniped pups is impacted by the melting of sea ice because the young need sufficient time for suckling.  Snow depth (which has been decreasing in the arctic) directly affects whether ringed seals can construct lairs on the sea ice.  Additionally, loss of sea ice habitat will affect the ability for indigenous people to harvest AMMs because much of the hunting occurs on the sea ice or near the ice edge.

Climate change has widespread ecological implications for the arctic, yet the effects are under-reported despite changes exceeding those of temperate, tropical, and mountain ecosystems.  This is partly due to logistical challenges in assessing marine mammal populations in the arctic, due to wide distributions, cryptic behavior, and the remoteness of marine areas.  Population data are important for understanding conservation priorities, but estimates for most AMM populations are lacking.  AMMs are highly mobile, seasonally moving long distances, across regional- or international boundaries.  Thus management requires international collaboration.  Given the fast pace of these changes in the arctic, and the uncertainty in how AMM populations will respond, flexible- and adaptive management will be critical.

It is necessary to understand- and mitigate the impacts from industrial activities.  Longer open-water seasons are contributing to increased use of shorter international shipping routes.  Potential threats associated with oil- and gas development include underwater sound and oil spills.  International agreements may be needed to protect AMM habitats of high importance, especially those of industrial interest.

It is critical that all stakeholders recognize AMMs as organisms with innate value, and as resources connected to the well-being of the indigenous people who harvest, interact, and live with them.  Accurate scientific data will be central to making informed- and effective conservation decisions.

LINK to Laidre et al.'s 2015 article in Conservation Biology.