The use of the Inupiaq Technique of Tundra sodding to rehabilitate wetlands in Northern Alaska.
Key words: Inupiat; ivruq; sod; turf; wetlands; North Slope; Alaska; Prudhoe Bay oil field; land rehabilitation; revegetation; restoration
RESUME. L'engazonnement de la toundra, nouvelle technique qui permet de remettre en etat les zones humides perturbees de l'Arctique, s'appuie sur les connaissances traditionnelles Inupiaq. C. Hopson, aine Inupiaq de Barrow et auteur de cet article, a guide la mise au point et Papplication sur le terrain de cette nouvelle technique en faisant part des connaissances traditionnelles qu'il a acquises de ses aines alors qu'il etait jeune. Comparativement a d'autres techniques de rehabilitation, l'engazonnement de la toundra comporte plusieurs avantages, le plus important etant l'etablissement d'une communaute vegetale mure d'especes indigenes au cours d'une seule saison de croissance. Pendant toutes les annees d'echantillonnage, les communautes vegetales des sites engazonnes etaient dominees par deux plantes graminoi'des rhizomateuses, Eriophorum angustifolium et Carex aquatilis. Les latches etaient egalement dominantes au cours de toutes les annees de la toundra de reference. Par ailleurs, 18 autres especes vasculaires (poacees, plantes sempervirentes, arbustes caducs et plantes herbacees non graminoi'des) se retrouvaient couramment au sein des communautes vegetales de la toundra de reference et des sites engazonnes. Les resultats de deux a cinq saisons de croissance indiquent que l'engazonnement de la toundra peut reduire l'affaissement general en raison du degel du pergelisol peu profond. Nous avons recolte de la toundra a trois occasions dans un secteur destine a etre transforme en graviere. Au cours des etes 2007 et 2008, nous avons transplante 334 [m.sup.2] de toundra dans certaines parties de trois sites afin de mettre cette methode a l'epreuve. Puis a l'ete 2010, nous nous sommes appuyes sur l'experience tiree de ces travaux pour rehabiliter un site au grand complet (1 114 [m.sup.2]). La technique de l'engazonnement de la toundra exige beaucoup de main-d'oeuvre et coute cher comparativement aux autres techniques de rehabilitation, mais elle presente des avantages qui permettent de justifier le recours a cette technique lorsque le retablissement rapide d'un site perturbe s'impose.
Mots cles : Inupiat; ivruq; engazonnement; gazon; zones humides; North Slope; Alaska; champ petrolifere de la baie Prudhoe; rehabilitation des terres; revegetalisation; restauration
Traduit pour la revue Arctic par Nicole Giguere.
Oil production on the Arctic Coastal Plain of northern Alaska, commonly referred to as the North Slope, occasionally damages tundra wetlands, triggering rehabilitation requirements. Some cases require excavation and backfilling, which completely destroy wetland vegetation and soils. Less intrusive activities may damage vegetation. All but the most superficial of disturbances can upset soil thermal regimes, allowing shallow permafrost to thaw and ice-rich soils to collapse, forming thermokarst, as described by Lawson (1986) and Pullman et al. (2007).
A variety of site preparation and plant cultivation techniques, including various seeding and plugging methods that work well in temperate regions, are available to revegetate disturbed sites in the North Slope oil fields (Jorgenson and Joyce, 1994; Forbes, 1999; Forbes and McKendrick, 2002; Jorgenson et al., 2003; Streever et al., 2003; Kidd et al., 2004). However, none of these methods act quickly enough to prevent at least partial thermokarst. In addition, the short growing season, cold temperatures, low precipitation, high winds, low nutrient availability due to slow decomposition, restricted drainage, and poor soil aeration dramatically retard revegetation done by conventional methods (Billings, 1987; Chapin, 1987). Typically, revegetating disturbed sites on the North Slope requires at least 10-30 years (Ebersole, 1987; Forbes and Jefferies, 1999; Forbes and McKendrick, 2002; Jorgenson et al., 2003).
This paper describes the development of a new technique, tundra sodding, to rehabilitate tundra wetlands in the North Slope oil fields. This use of tundra sod, comprising blocks of intact soil with a fully developed plant canopy and root system, arose from Inupiaq peoples' use of sod blocks, sometimes called ivruq in Inupiaq, to construct traditional sod houses (Webster and Zibell, 1970; Arnold and Hart, 1992) and insulate the roofs of ice cellars. C. Hopson, an Inupiaq elder and lifelong resident of Barrow, Alaska, as well as an author of this paper, guided the development of this technique using traditional knowledge learned as a youth from his elders. C. Hopson also supervised the field effort by teams of Inupiaq workers recruited from Barrow and other communities on the North Slope, many of whom were already familiar with traditional uses of tundra sod.
Billings (1987) was one of the first to suggest that since many of the graminoid species in the Arctic reproduce largely by rhizomes that spread to form clonal colonies, sod could be used to rehabilitate tundra wetlands on the North Slope. This technique has also been used elsewhere to rehabilitate disturbed lands (Conlin and Ebersole, 2001; Backus, 2004; Densmore et al., 2006). Testing began in July 2007 and was continued in 2008. The insights and experience gained from that work was used in 2010 to achieve what we believe is a milestone for damaged tundra wetlands on the North Slope: the rehabilitation of an entire site (0.11 ha) within a single growing season. We hypothesize that tundra sodding can be used under a variety of conditions to (1) rapidly establish a diverse and productive community of indigenous plant species that is similar to those of undisturbed tundra wetlands, thereby improving site appearance and site suitability for some wildlife species, and (2) establish a thermal regime that prevents thermokarst, achieving two objectives for the rehabilitation of tundra wetlands.
Sod was harvested from tundra that was slated for gravel mining at the existing Put River 23 mine located on Alaska's North Slope (Fig. 1). The sod was used to rehabilitate wetlands at four sites (Sites A, B, C, and D) that were damaged during cleanup responses to oil spills (Fig. 1). Harvesting was allowed under a permit issued by the U.S. Army Corps of Engineers and a State of Alaska Material Sales Contract issued by the Alaska Department of Natural Resources.
The donor site included two types of tundra: wet sedge tundra, within the remnants of an ice-rich thaw basin, and moist sedge-shrub tundra on higher terrain surrounding the thaw basin. Rhizomatous perennial graminoids, including the grass Dupontia fischeri (Fisher's tundragrass) and the hydrophytic sedges Carex aquatilis (water sedge), Eriophorum angustifolium (tall cottongrass), and E. scheuchzeri (white cottongrass) accounted for nearly all of the live plant cover in the wet sedge tundra. C. aquatilis and E. angustifolium also occurred within the moist sedge-shrub tundra, as did C. bigelowii (Bigelow's sedge), the evergreen shrub Dryas integrifolia (entireleaf mountain-avens), and the deciduous shrubs Salix arctica (Arctic willow) and S. ovalifolia (oval-leaf willow). Soil in both donor areas was characterized by an organic soil horizon 15--56 cm thick overlying mineral soil. Water drained from the donor area for three years prior to harvesting as the result of previous activities at the mine site. At the time of harvest, surface water was absent and the soil was not saturated. These relatively dry conditions allowed heavy equipment to operate more efficiently than would be expected for most types of undisturbed tundra.
As part of the cleanups at Sites A and D, the plant canopy and 1.2-2 m of the underlying soil were removed because of contamination (Table 1). These excavations were backfilled to the elevation grade that was present before the cleanup began, and tundra sod was transplanted onto the backfilled surface (Fig. 2a). At Site C, excavation also removed the plant canopy, but excavation was limited to the top 5-10 cm of soil, and excavated material was not replaced with backfill (Fig. 2e). After two growing seasons and before a portion of Site C was treated with tundra sod, only a few sprouts of surviving vegetation were visible in the excavated area, indicating that most of the viable plant materials had been killed or removed during the excavation. The removal of soil had also lowered the elevation of the tundra surface, causing an adjacent pond to flood part of the site. Shallow permafrost thawed, resulting in subsidence. Thus, vegetation recovery was impaired as water in previously flooded areas grew deeper and the flooded area grew in size.
Instead of excavating, the cleanup at Site B gently flooded the site with fresh water to recover contamination while minimizing impacts to vegetation and soil. However, as often happens following apparently superficial damage to tundra plant communities, some plants died and vegetation cover was reduced. Plant death was especially apparent in a network of pre-existing ice-wedge troughs (Fig. 2c). Not only were these troughs mostly barren two years after the cleanup, but they were also becoming visibly deeper and wider over time as shallow permafrost thawed. As a result of these changes in topography (i.e., thermokarst), surface water persisted in the troughs during the entire growing season, which increased the rate of heat transfer into the soil compared to the rest of the affected area, where surface water was not present for the entire summer.
The cleanup at Site D was different from that at the previous sites, in that tundra sodding was incorporated into the rehabilitation plan during the early stages of the cleanup. This planning was possible in part because the testing in 2007 and 2008 had led to the addition of tundra sodding as a rehabilitation tactic in the Tundra Treatment Guidelines (Cater, 2010).
Developing Sod Harvesting Techniques
In July 2007, the first time that sod was harvested for wetland rehabilitation (Site A), workers used knives with serrated blades 36 cm long to cut 0.09 [m.sup.2] blocks (20 cm thick) from the ground at the harvest site (Table 1). To increase efficiency the second time sod was harvested (Site B), workers used serrated knives to make vertical cuts in the tundra that corresponded to the width (1.3 m) of a small front-end loader's bucket. The bucket was then pushed horizontally under the tundra surface at a depth of 20 cm until the bucket was full (approximately 45 cm width), and workers made the final cut along the bucket's leading edge. This technique removed approximately 0.6 [m.sup.2] of sod with each load. To further increase efficiency during the third test harvest (Site C), we developed a technique that largely eliminated the need for serrated knives. A specially fabricated 1.1 m diameter steel disc with a sharpened edge was mounted on the bucket of an excavator and then rolled through the tundra, easily cutting to a depth of about 0.5 m (Fig. 3a). A new Inupiaq phrase, nuna ulu, meaning "land knife," was coined to describe this rolling steel disc. An excavator bucket removed 0.4 [m.sup.3] of sod with each load. The most efficient harvesting method was used at Site D in 2010: the nuna ulu and serrated knives were used as before, but with a large front-end loader with a larger bucket, which removed approximately 2.9 [m.sup.2] of sod as a single block (Table 1, Fig. 3b).
For Sites A and D, sod was harvested in mid-July, after snow had melted and soils had thawed to a depth of about 20-25 cm. For Sites B and C, sod was harvested in mid-September 2008, when soils had thawed to a depth of about 50 cm, which generally resulted in the removal of blocks as thick as 60 cm. We estimated fresh bulk density to be 0.91-1.1 g/[cm.sup.3] (Table 1). Regardless of the harvest time or technique, Inupiaq workers familiar with harvesting requirements used serrated knives to process tundra into pieces that could be handled by a single person (< 22 kg). At Sites A, B, and D, each block was approximately 20 cm thick. Thicker pieces would have been preferred because plants would probably experience less transplant shock if the rooting systems were contained in a larger volume of soil. Also, thicker pieces should provide more insulation and decrease the potential for thermokarst. However, thicker pieces were too heavy for a single person to handle. Weight of individual blocks was an important safety consideration because workers needed to move sod underneath elevated pipelines that blocked Sites A, B, and D from the adjacent access road where the trucks hauling the sod were parked. Thus, workers typically trimmed soil from the bottom until each block was approximately 20 cm thick so that they could handle the blocks safely. Elevated pipelines were not blocking access to Site C, which allowed the use of an extendable boom forklift that could handle much larger blocks (approximately 60 cm thick, some weighing more than 450 kg). Before placing tundra sod, we applied fertilizer tablets or granules to ensure an abundant supply of nutrients (Table 1).
At Sites A, B, and D, sod was carefully placed by hand to maximize contact between the sides of adjacent blocks (Fig. 2a). At Site B, where sod was placed in the portions of the ice-wedge troughs that had subsided (Fig. 2c), blocks were sometimes stacked on top of each other to ensure that plants in the top layer of sod were above the water surface. At Site C, the large sod blocks were placed as close to each other as possible (Fig. 2f). Portable skate wheel conveyors, typically seen in warehouses, were used to move sod under the pipelines and across a site, dramatically reducing the distance workers had to carry sod blocks. Plywood supported the conveyors and provided a stable surface for workers, which limited physical damage to the ground surface.
Percent cover of vegetation at each site was measured using a standardized point-intercept method near the end of each growing season after planting (ITT, 1999). Because tundra vegetation has multiple canopy layers where multiple hits of vegetation can occur at the same point, the point-intercept method can yield cover estimates exceeding 100%. However, these cover measurements are generally well correlated with biomass (Jonasson, 1988). Sample points were distributed at 0.5 m intervals along transects, with the location and length of transects determined subjectively from the size and shape of the area treated with tundra sod (Table 2). Percent cover was also measured in undisturbed tundra situated immediately adjacent to the treated areas at Sites B, C, and D (Table 2). These data were pooled across sites and years to define a reference state by which vegetation development in the treated areas can be assessed (Forbes et al., 2001).
For sampling at each point on a transect, we used a laser pointer mounted on a 1.2 m long metal rod, which was pushed into the ground so that the laser beam pointed downward, delineating the sample point. Vascular species were identified using nomenclature that followed Viereck and Little (2007) for shrubs and Hulten (1968) for other vascular species. Dead vegetation that was attached or fallen was included in a separate "litter" category. We recorded litter or bare ground only if no live vegetation was present at a point, but we always recorded surface water where it occurred.
We calculated the cover separately for each vascular plant species as the percentage of the total number of points sampled. Total live vascular cover was calculated from the sum of individual cover values for all vascular plants sampled. We also calculated percent cover of eight general categories: evergreen shrubs, deciduous shrubs, sedges, grasses, forbs, mosses, lichens, and bare ground, which included soil, litter, water, and animal scat.
In addition to qualitative observations of changes in topography over time, we quantified the ability of tundra sodding to prevent subsidence at Site C, where excavation removed the plant canopy and the top 5-10 cm of soil. Immediately after excavation was complete (25 April 2007), ground surface elevation was measured using standard Global Positioning System Real-time Kinematic (GPS-RTK) techniques at 19 stations on a 4.6 m grid established across the site. We repeated the elevation survey on 14 October 2012, five growing seasons after excavation and four growing seasons after sod was planted.
The sodding rate ranged from 4.6 to 10.6 [m.sup.2]/person/day (Table 1), progressively increasing for the first three sites as the harvesting technique was refined. Using the nuna ulu and heavy equipment to harvest large blocks of sod eliminated the labor needed to trim and hand-carry smaller blocks of sod, which was considered the primary reason that the highest sodding rate was achieved at Site C (Table 1). At Site D, where the most efficient harvesting technique was used, the sodding rate was moderate (6.7 [m.sup.2]/person/day) because the sod needed to be trimmed for transport beneath elevated pipelines. This site required 2029 person-hours to complete, demonstrating that a moderate efficiency could be maintained over a one-month period.
Total live vascular cover on sodded sites in 2012 ranged from 77.0% to 143% (Table 3). These tundra sod plant communities comprised a combined total of 25 vascular species, 20 of which were also present in reference tundra. E. angustifolium and C. aquatilis dominated the sodded communities in all sampling years (see online Appendix 1). Also, these rhizomatous sedges were the dominant vascular species in reference tundra in all years. The other 18 vascular species common to both the reference tundra and sodded plant communities were other graminoids (e.g., C. bigelowii and D. fischeri), evergreen (D. integrifolia) and deciduous shrubs (Salix), and forbs (e.g., P. viviparum). In 2012, we observed an abundance of new shoots produced by E. angustifolium, which resulted in substantially higher cover of sedges at sodded sites compared to reference tundra (58.7%-140% vs. 34.5%). In contrast to vascular plants, nonvascular plants typically had lower cover at sodded sites compared to reference tundra. Mosses comprised nearly all of the nonvascular cover on both sodded sites and reference tundra.
Vegetation in the transplanted sod appeared healthy and productive at each site in 2012 (Figs. 2b, 2d, 2f, and 4a). New growth of roots between blocks and into the underlying soil was clearly visible upon close inspection. However, we did observe patches of dead vegetation (Fig. 4b) at each site in 2012, apparently the result of grazing by tundra voles (Microtus oeconomus) or other microtines, as well as their burrowing between and through some of the sod blocks.
The absence of depressions where surface water can accumulate suggests that the elevation of the ground surface after tundra sodding has remained relatively stable (Figs. 2b, 2d, 2f, and 4a). Quantitative measurements at Site C showed that the ground surface elevations at three points where tundra sod was transplanted were 2-20 cm higher in 2012 than in 2007, before sod was planted. Thus, although tundra sodding did not prevent thermokarst, the thickness of the sod pieces (up to 60 cm thick) offset the subsidence that did occur, resulting in the treated areas' having an elevation similar to the original tundra surface. In contrast, the ground surface elevations at the 16 stations without tundra sod were 5-78 cm lower in 2012 than in 2007. The ground surface at most of these stations has become incorporated into the adjacent pond.
Rehabilitating disturbed sites with blocks of intact tundra sod has some important advantages over other techniques typically used in the North Slope oil fields. Not only can tundra sodding revegetate a site in a single growing season, it also results in a plant community that is dominated by indigenous plant species, which is not always the case with other revegetation techniques. Also, the soil in tundra sod should contain the organic matter and microorganisms needed for a healthy soil environment, thereby maintaining natural soil processes (e.g., nutrient cycling). At sites where substantial excavation has occurred, tundra sod can replace at least the upper portion of the excavated soil, decreasing the volume of backfill needed to return the site to an elevation grade that is similar to the surrounding tundra. Tundra sod also establishes a fully developed root system, which provides protection against erosion much faster than plants developing from seed.
Our results demonstrate for the first time that relatively large, severely impacted sites can be rehabilitated within a single growing season, even in the extreme environment found on Alaska's North Slope. These results also demonstrate that tundra sodding reduces the overall subsidence of the ground surface, a factor that is directly linked with successful revegetation. Without the insulation provided by the sod, deeper thawing of shallow permafrost would have occurred, which often allows surface water to accumulate to depths that inhibit plant recovery. Thus, tundra sodding appears capable of rehabilitating tundra wetlands under a variety of conditions, resulting in a diverse and productive community of indigenous plant species.
The abundant supply of nutrients provided by the fertilizer treatment probably promoted vascular plant cover exceeding that found in nearby undisturbed reference tundra, but this difference is expected to decline over time. Increased shoot production was especially visible for E. angustifolium and C. aquatilis, the rhizomatous sedges that were the dominant species in the tundra sod plant communities. This result is consistent with that of Forbes et al. (2001), who identified the rhizomatous graminoid as the growth form most resistant to disturbance in Arctic ecosystems. The importance of the decline in cover of C. aquatilis at sites A and B between 2011 and 2012 remains to be seen. Differences in plant cover and species composition among sites were attributed mostly to natural variation at the harvest site, rather than the result of different environmental conditions among the four rehabilitation sites. For example, the sod used at Site D was harvested from higher terrain where species typical of drier tundra (e.g., D. integrifolia and P. viviparum) were common, whereas the sod used at the other sites was harvested from the lower area of a former thaw basin where conditions were wetter and rhizomatous graminoids (e.g., E. angustifolium and D. fischeri) dominated the plant community. The significance of the plant mortality caused by burrowing microtines for the long-term success of tundra sodding is unknown, but will probably vary between years as microtine populations fluctuate.
Despite the obvious benefits offered by tundra sodding, this technique is not a panacea for rehabilitation of disturbed tundra wetlands on the North Slope. Harvesting sod completely removes tundra vegetation, so only sites slated for mining or other activities that will destroy vegetation should be considered as possible donor sites. Ultimately, limited availability of donor sites significantly limits the availability of sod.
In addition, labor costs associated with sodding are dramatically higher than labor costs or even overall costs associated with other approaches. Sodding may reduce requirements for the long-term monitoring and earthwork that are sometimes required to reverse subsidence, but in our experience, the total cost per unit area for sodding is at least ten times higher than those associated with other methods, even after inclusion of reduced monitoring costs. Costs of sodding are expected to decline as the technique is refined, especially where heavy equipment can be used to both harvest and place sod; however, they are not likely to decline to a level at which sodding will be cost-competitive with other approaches. With the realities of cost and limited sod availability in mind, tundra sodding should be reserved for use on sites requiring rapid rehabilitation. If these initial results continue in the long term, using this new technique can also achieve the more ambitious objective of restoring the original wetland functions at disturbed sites on the North Slope.
We are grateful for the many people who made this work a success. Assistance with planning and fieldwork was provided by the employees of UMIAQ, a subsidiary of the Ukpeagvik Inupiat Corporation based in Barrow, AK, including John Quincy Adams, William Aguvluk, Jonas Ahsoak, Pricilla Ahsoak, Payuq Ahsogeak, Richard Bodfish, Jens Hopson, Riley Kaleak Jr., Gilbert Kanayurak, Victor Koonaloak, Jr., Nayuk Leavitt, William Jens Leavitt, Philip Low, Vincent Nageak, Charles Rexford, and Lawrence Sage. The BPXA Environmental Advisors for Greater Prudhoe Bay--Bryan Collver, Chuck Wheat, Alex Reyes, Todd Winkel, Chrissy May, and Bob Lipchak--provided invaluable safety advice, logistical suggestions, and other assistance throughout. Tatyana Venegas (Oasis Environmental, Inc.) provided logistical support. Employees of Alaska Clean Seas provided details about cleanup operations. F. Robert Bell & Associates conducted the elevation surveys and determined how much backfill was needed at Site D. We appreciate the constructive comments provided by Susan C. Bishop and Janet G. Kidd (ABR, Inc.). Daniel Uliassi and Steve Chronic (UMIAQ), and three anonymous reviewers.
The following tables are available in a supplementary file to the online version of this article at:
TABLE S1. Percent cover of vegetation and bare ground on areas treated with tundra sod at four rehabilitation sites in the Prudhoe Bay oil field. Species with trace cover (tr) were present but not hit during sampling.
TABLE S2. Percent cover of vegetation and bare ground in reference tundra at three of four rehabilitation sites in the Prudhoe Bay oil field. Species with trace cover (tr) were present but not hit during sampling.
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Timothy C. Cater, (1) Charles Hopson (2) and Bill Streever (3)
(Received 2 September 2014; accepted in revised form 22 April 2015)
(1) Corresponding author: ABR, Inc.--Environmental Research & Services, PO Box 80410, Fairbanks, Alaska 99708, USA; firstname.lastname@example.org
(2) UMIAQ, PO Box 955, Barrow, Alaska 99723, USA
(3) BP Exploration (Alaska), Inc., 900 E. Benson Boulevard, Anchorage, Alaska 99519, USA
TABLE 1. Characteristics of the four rehabilitation sites and the variables used to estimate efficiency of different techniques for harvesting and planting tundra sod. Units Cleanup date Contaminant recovery tactic Depth of excavation m Fertilizer treatment1 g/[m.sup.2] Sodding date Harvest technique Sod block size (1 x w x d) m Sod block volume [m.sup.3] Fresh bulk density (2) g/[cm.sup.3] Sod block weight kg Haul distance km Person hours (12 h day) # Team size # Days needed to sod # Area treated with sod [m.sup.2] Sodding rate (3) [m.sup.2]/person/12 h day 4.6 Rehabilitation sites A B Cleanup date March 2006 August 2006 Contaminant recovery tactic Excavation Flushing with water Depth of excavation [less than or 0 equal to] 2 Fertilizer treatment1 100 100 Sodding date 10-15 July 2007 19-22 September 2008 Harvest technique 36 cm serrated 36 cm serrated knives knives + small loader Sod block size (1 x w x d) 0.3 x 0.3 x 0.2 1.3 x 0.45 x 0.20 Sod block volume 0.02 0.17 Fresh bulk density (2) 0.91 (n = 2) 1.0 Sod block weight 16 260 Haul distance 20 15 Person hours (12 h day) 252 272 Team size 6 8 Days needed to sod 4 4 Area treated with sod 96 160 Sodding rate (3) 7.0 Rehabilitation sites C D Cleanup date April 2007 November 2009 Contaminant recovery tactic Excavation Excavation Depth of excavation 0.05-0.10 [less than or equal to] 1.2 Fertilizer treatment1 100 22 Sodding date 22-24 September 15 July-31 August Harvest technique 2008 nuna ulu + 2010 nuna ulu + zoom boom loader large loader + 36 cm serrated knives Sod block size (1 x w x d) 0.9 x 0.9 x 0.5 2.4 x 1. 2 x 0.20 Sod block volume 0.4 0.58 Fresh bulk density (2) 1.0 1.1 (n = 10) Sod block weight [less than or 576 equal to] 400 Haul distance 10 12 Person hours (12 h day) 89 2029 Team size 4 9 Days needed to sod 2.5 30 Area treated with sod 78 1114 Sodding rate (3) 10.6 6.7 (1) 21 g fertilizer tablets (20-10-5 NPK) were used except at Site D, where granules (20-20-10 NPK) were used. (2) Fresh samples were weighed immediately after harvesting. Bulk density of 1.0 was used as an estimate for Sites B and C. (3) Sodding rate = (Area treated / Person hours) x 12 hours/work day. TABLE 2. Description of transects used to measure plant cover each summer at the four rehabilitation sites treated with tundra sod and in undisturbed (reference) tundra adjacent to Sites B, C, and D. Length of Sample Distance Sampling Number of transects points between Site area transects (m) (#) transects (m) A Treated 5 7-12 100 1 B Treated 7 3-11.5 68 6 Reference 9 9-12 505 6 C Treated 2 3-9 10 6 Reference 5 2.5-14 102 2 D Treated 12 13-20 386 5 Reference 12 15 360 5 TABLE 3. Percent cover of vegetation and bare ground at four rehabilitation sites treated with tundra sod compared to mean cover ([+ or -] SD) measured in reference tundra. Site Cover type / Life form / Species A B C D Total live cover 148 119.2 140 82.7 Total live vascular cover 143 103.0 140 77.0 Evergreen shrubs 1.5 10.9 Dryas integrifolia 1.5 10.9 Deciduous shrubs 8 4.4 1.6 Salix arctica 4 2.9 Salix lanata 1.5 Salix ovalifolia 1 0.3 Salix pulchra 2 1.3 Salix reticulata 1 Sedges 113 97.1 140 58.7 Car ex aquatilis 9 14.7 130 0.3 Carex bigelowii 4 3.9 Carex membranacea 0.3 Carex mis an dr a 0.3 Eriophorum angustifolium 97 82.4 10 53.6 Eriophorum scheuchzeri 3 Eriophorum vaginatum 0.3 Grasses 13 2.1 Alopecurus alpinus 8 0.5 Arctagrostis latifolia 1 0.5 Deschampsia caespitosa 0.3 Dupontia fischeri 3 0.5 Hierochloe pauciflora Poa alpigena 1 Puccinellia angustata 0.3 Forbs 9 3.7 Braya sp. 0.3 Cardamine hyperborea 3 0.8 Cochlearia officinalis Equisetum arvense 3 Equisetum variegatum 1.5 Polygonum viviparum 3 0.8 Saxifraga cernua Saxifraga hirculus 0.3 Stellaria sp. Total live nonvascular cover 5 16.2 5.7 Mosses 5 16.2 5.7 Lichens trace Bare ground 23 27.9 40.2 Soil 2.9 3.1 Litter 23 23.5 37.0 Water 1.5 Goose scat Cover type / Life form / Species Reference tundra Total live cover 105.1 [+ or -] 27.2 Total live vascular cover 51.1 [+ or -] 10.6 Evergreen shrubs 0.8 [+ or -] 0.6 Dryas integrifolia 0.8 [+ or -] 0.6 Deciduous shrubs 8.0 [+ or -] 2.6 Salix arctica 3.3 [+ or -] 2.2 Salix lanata 0.6 [+ or -] 0.7 Salix ovalifolia 2.6 [+ or -] 2.6 Salix pulchra 0.4 [+ or -] 1.1 Salix reticulata 1.1 [+ or -] 0.6 Sedges 34.5 [+ or -] 8.9 Car ex aquatilis 12.1 [+ or -] 8.2 Carex bigelowii 3.0 [+ or -] 2.4 Carex membranacea 0.1 [+ or -] 0.2 Carex mis an dr a trace Eriophorum angustifolium 18.8 [+ or -] 7.2 Eriophorum scheuchzeri 0.5 [+ or -] 1.1 Eriophorum vaginatum <0.1 [+ or -] 0.1 Grasses 5.1 [+ or -] 6.4 Alopecurus alpinus 0.8 [+ or -] 1.8 Arctagrostis latifolia 0.1 [+ or -] 0.3 Deschampsia caespitosa Dupontia fischeri 4.1 [+ or -] 4.7 Hierochloe pauciflora 0.1 [+ or -] 0.2 Poa alpigena Puccinellia angustata Forbs 2.7 [+ or -] 1.2 Braya sp. 0.1 [+ or -] 0.4 Cardamine hyperborea <0.1 [+ or -] 0.1 Cochlearia officinalis 0.1 [+ or -] 0.2 Equisetum arvense Equisetum variegatum 2.0 [+ or -] 0.9 Polygonum viviparum 0.2 [+ or -] 0.4 Saxifraga cernua <0.1 [+ or -] 0.1 Saxifraga hirculus 0.1 [+ or -] 0.2 Stellaria sp. 0.1 [+ or -] 0.1 Total live nonvascular cover 54.0 [+ or -] 21.8 Mosses 54.0 [+ or -] 21.8 Lichens trace Bare ground 24.8 [+ or -] 15.3 Soil 1.4 [+ or -] 1.3 Litter 22.8 [+ or -] 15.2 Water 0.5 [+ or -] 0.7 Goose scat 0.1 [+ or -] 0.1
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|Author:||Cater, Timothy C.; Hopson, Charles; Streever, Bill|
|Date:||Dec 1, 2015|
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