Developing Restoration Protocols for Degraded Limestone Barrens Habitat
Restoration ecology can be defined as the "assisted rehabilitation or recovery of an ecosystem that has been damaged, degraded or destroyed" (Society for Ecological Restoration (SER), 2004).
Within our own "limestone barrens", several important areas, key to the survival of rare plants, have been significantly compromised, over the years, by unchecked gravel pitting, community expansion, and off-road vehicle use (Environment Canada 2012).
The legacy effects of all of this disturbance are most striking where abandoned gravel pits remain highly disturbed, with little hope of restoration. These areas are almost devoid of native "limestone barrens" characteristics.
Sandy Cove Ecological Reserve: Developing Restoration Protocols -
Given that the Sandy Cove area, in the Strait of Belle Isle, is unique - being the primary home of the rare endemic plant, Long’s Braya (Braya longii) - efforts are currently underway there to test, develop, and monitor a "protocol" for the re-establishment of some of the key functional characteristics of its much-disturbed "limestone barrens" habitat (particularly the cold-soil (= "cryogenic") processes).
Such efforts coincide with Environment Canada’s Recovery Strategy for Long’s Braya (Environment Canada 2012).
Figure 1: Green Team small scale restoration at Sandy Cove. BEFORE. Photo: Dulcie House.
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Figure 2: Green Team small scale restoration at Sandy Cove. AFTER. Photo: Dulcie House.
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Research began in January 2012 on a degraded quarry pit within the "limestone barrens" habitat (Copp 2014).
To get a better understanding of how quarrying has affected the Sandy Cove Ecological Reserve area, over the years, aerial photography, dating back to 1948, was examined. The resulting picture of the original landscape is serving as an important "baseline" for guiding restoration efforts.
From the beginning of gravel extraction, in the 1960’s, until about the 1990s, quarry activity appears to have expanded northward (Figure 3).
Figure 3. Aerial photography demonstrating the expansion of gravel extraction and quarry activity (red hashed area) over time. a) 1968; b) 1979; c) 1989; d) 1995. Symbols: yellow lines: off road trails; blue lines: Viking hwy. [CLICK images to enlarge] Maps produced using ArcGIS software version 10.
As with most extraction, quarry, or mining operations, there was an alteration in landscape geomorphology.
In the Sandy Cove area, primary landscape characteristics such as beach ridges, which were formed via glacial activity and the subsequent rise and fall of the sea level (Grant 1992), have been degraded or
destroyed (Figure 4).
A once smoothly sloping surface landscape (Figure 4a), consisting of black crowberry (Empetrum nigrum) heath, frost shattered limestone, and limestone veneers (Grant 1992; Damman 1983), was also disrupted.
In place of the original natural landscape, there developed large overburden piles, containing large amounts of organic material, which created a rough landscape (Figure 4d) that no longer functioned as a natural "limestone barrens" habitat. Not otherwise valued, the area was used, in the past, for garbage dumping.
Figure 4. Aerial photography demonstrating the change in regional landscape topography of the site (purple elevation lines) over time. a) 1968; b) 1979; c) 1989; d) 1995. Symbols: yellow lines: off road trails; blue lines: Viking Trail. [CLICK images to enlarge] Map constructed using ArcGIS Software version 10.
The long term goal of the present project coincides with Environment Canada’s Recovery Strategy for Long’s Braya (Environment Canada 2012), which advocates the establishment of functional Limestone Barrens habitat at the degraded Sandy Cove site, on order to support long term viable populations of the species .
Historically, restoration efforts have usually strived to regain what has been lost. However, in the case of badly degraded areas such as quarries and gravel pits, a "novel" or replacement habitat can be created in place of an historical one (Hobbs et al. 2009).
The Sandy Cove site was historically characterized by Black Crowberry (Empetrum nigrum) heath, interspersed with open (non-vegetated) areas.
The former presence of heath explains the large amount of organic material present in the overburden piles.
The remaining, unvegetated, quarry floor has some qualities that mimic natural "limestone barrens" habitat, such as low nutrient availability and very low vegetative cover.
However, things are not quite that simple, since this site also lacks vital components necessary for classification as "limestone barrens" habitat. It will be these latter characteristics that will need to be re-established.
A key feature of "limestone barrens" habitat, that is absent in the degraded quarry pits, is a "disturbance regime", created and maintained primarily by both seasonal and diurnal freeze-thaw cycles.
Such freeze-thaw cycles assist in the formation of open, non-vegetated, areas and unique landscape features known as "sorted frost polygons" (Figure 5a).
Figure 5. Natural "limestone barrens" landscape vs. quarry floor landscape. Note the difference between: a) sorted frost features; b) quarry floor. [CLICK images to enlarge]
Substrate texture (i.e. the relative proportion of silt/clay to gravel) is an important factor in the re-establishment of a disturbance regime.
Vegetation and snow cover (insulated areas tend to experience fewer frost cycles), soil water chemistry (presence of dissolved solids can suppress freezing points), temperature (fluctuations above and below 0°C), topography, and aspect (north facing slopes may experience cooler temperatures than south slopes), also play key roles in the development of frost polygons (Greene 2002).
Aside from their unique appearance on the landscape, such disturbed non-vegetated areas provide preferential habitat for the recruitment of Long’s Braya (Hermanutz 2001), a pioneer species, with a contractile taproot, that is well adapted to such frost disturbance.
Sandy Cove Ecological Reserve: Testing of Restoration Protocols Begins -
In the fall of 2012, testing of restoration protocols began.
Heavy machinery was used to remove overburden piles located on the south side of the site. In general, the top sod layer was removed and piled (Figure 6a & b).
The remaining soil and substrate was distributed around the local vicinity to blend the material into the surrounding landscape, creating a smooth slope resembling the historical topography (Figure 6c & d).
Figure 6. Dismantling of an overburden pile on site. a) pile before sod removal; b) pile during sod removal; c) distribution of material around the area; d) after pile has been dismantled. [CLICK images to enlarge]
Coltsfoot and other Invasive Plants -
Special efforts were made to remove invasive plants such as Coltsfoot (Tussilago farfara) (see Figure 7).
Coltsfoot, like most invasive plants, thrives in disturbed areas.
Given the increasing presence of anthropogenic disturbance, and the "basic" pH of the substrate, Coltsfoot, and other invasive plants, have increasingly colonized the Sandy Cove area.
Figure 7. Patch of coltsfoot (Tussilago farfara) located on the site.
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The presence of invasive species tends to lead to a loss of native diversity, particular a loss of pioneering species, such as Long's Braya, which, similarly, require some degree of disturbance (Hendrickson et al. 2005).
However, it is very difficult to eradicate aggressive species such as Coltsfoot, once established. This is why heavy equipment was used to completely remove established populations, along with their root systems and all associated soil.
Nonetheless, it is inevitable that the disturbance associated with the restoration of the barrens will still favour the recolonization of invasive species, given their aggressive colonization strategies and their affinity for disturbed habitat, at least until native vegetation is firmly re-established in the area.
Experimental Blocks -
Following the dismantling of three overburden piles, three experimental blocks of six 2 x 2 m substrate test plots each were created (Figure 8a), to test various substrate texture compositions (i.e. differing fractions of silt/clays, gravel and organic material).
As noted above, substrate texture plays an important role in the disturbance regime. Thus, these plots will assist in determining how best to re-establish the natural freeze-thaw cycle and disturbance regime.
Such re-establishment will be monitored using heave devices, which measure maximum ground heave due to frost action, and data loggers which monitor soil temperature (Figure 8b).
Figure 8. Experimental test block construction after overburden piles have been restored to the natural contour to test the most effective substrate particle composition for the re-establishment of the natural freeze-thaw disturbance regime. a) One substrate test block with six, 2 x 2 m test plots; b) Installing a device to measure maximum ground heave due to frost. [CLICK images to enlarge]
The experimental test blocks were to be revisted in the spring of 2013. It is expected that experimental plots with more fine silt/clay material will experience more temperature fluctiations above and below 0°C (i.e. freezing) and will demonstrate greater maxiumum ground heave relative to those plots with no added fine material. Those plots with added organic material are expected to demonstrate suppressed frost heave.
Revegetation Studies -
Similarly, during the spring, revegetation studies will be conducted to determine an effective means for re-establishing native Limestone Barrens flora.
Prior to the fall restoration efforts, native Limestone Barrens flora such as Purple Saxifrage (Saxifraga oppositifolia), Common Juniper (Juniperus communis), Hoary Draba (Draba incana), Moss Campion (Silene acaulis), Mountain Avens (Dryas integrifolia), willow spp. (Salix spp.), and Roseroot (Rhodiola rosea) were removed and potted with the help of several plant experts and volunteers (Figure 9a).
Figure 9. Rescue plants collected from the site prior to restoration work with heavy machinery. a) Potted native plants from the site; b) Potted plants were transferred and sunk back on site to overwinter; c) Plants too large for pots (eg. Juniperus communis) were planted back on site after piles were dismantled. [CLICK images to enlarge]
The potted plants were then sunk back onto the restoration site to overwinter until the spring (Figure 9b). Those plants to large for pots were immediately planted back on site (Figure 9c).
Seeding Studies -
Additionally in the fall, seed from native flora such as Moss Campion (Silene acaulis), Purple Saxifrage (Saxifraga oppositifolia), Wooly Yarrow (Achillea millefolium subsp. lanulosa), Black Crowberry (Empetrum nigrum), Mountain Avens (Dryas integrifolia), and Harebell (Campanula gieseckiana [= Campanula rotundifolia]) was collected from the area surrounding the site with the help of volunteers.
After collection, the seed was cleaned, and underwent cold stratification in preparation for planting in the spring.
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