British Columbia Mine Reclamation Symposium

Conifer seedling establishment on a rock disposal site at the Mount Polley Mine to assess competitive… Hunt, Janelle; Holmes, Gabriel; McMahen, Katie 2018

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CONIFER SEEDLING ESTABLISHMENT ON A ROCK DISPOSAL SITE AT THE MOUNT POLLEY MINE TO ASSESS COMPETITIVE EFFECTS OF VARIOUS HERBACEOUS GROUNDCOVERS WHEN USING BIOSOLIDS AS A SOIL AMENDMENT   Janelle Hunt, P.Ag.1 Gabriel Holmes2 Katie McMahen, P.Ag.2   1Metro Vancouver Regional District, 4330 Kingsway, Burnaby, BC 2Mount Polley Mining Corporation, Box 12, Likely, BC ABSTRACT A field-scale tree trial was established in 2013 and 2014 on rock disposal site slopes at Mount Polley Mine to evaluate herbaceous groundcovers’ ability to promote coniferous tree growth on parcels amended with biosolids. Parcels were amended with 20 cm of overburden and biosolids were applied at a rate of 110 dry tonnes per hectare (control parcels received no biosolids). The parcels were then seeded with either: native grasses and forbs (at 5 kg/ha or 10 kg/ha), native forbs, fireweed, or unseeded. The control parcels were also unseeded. Lodgepole pine, Douglas-fir, and deciduous tree and shrub seedlings were planted across all parcels.  After two and three growing seasons, herbaceous vegetative cover was highest on parcels seeded with native grasses and lowest on the forbs, fireweed, and unseeded parcels. Higher cover was associated with greater competition with conifer seedlings, increased vegetation/snow press, increased herbivory and reduced seedling survival. Growth of the conifers however, was higher on the parcels amended with biosolids compared to control parcels. These results suggest that the understory on biosolids amended soils should be seeded at low seeding rates with native forbs in order to have the highest conifer survival while still providing erosion and invasive plant control.  Key words: reclamation, native vegetation, trees, revegetation, organic matter   INTRODUCTION  The Mount Polley Mine (the “Mine”) is an operating open pit copper-gold mine in the interior of British Columbia, approximately 60 km northeast of Williams Lake, BC. In its first year of full time mining operations (1998), a reclamation research program was initiated at the site. The initial program was developed to determine the methods, materials and protocol for achieving specific end land use objectives.  The program continues today and is designed to be adaptable and evolve based on findings from progressive reclamation, site monitoring and research, and advancements in engineering and science.   The Mine takes an ecosystem approach to its end land use planning and designs its reclamation to re-establish forest ecosystems containing self-sustaining native vegetation and mimicking natural succession. To achieve this, the Mine has been testing use of treated, dewatered sewage sludge (biosolids) as a soil amendment to help establish vegetation and improve plant performance by adding essential plant nutrients and organic matter to the soil.   Trial plots using biosolids at the Mine were established from 1998 to 2000 to evaluate the depth of overburden and amount of different soil amendments required to establish native coniferous trees (Douglas-fir [Pseudotsuga menziesii] and lodgepole pine [Pinus contorta]) on a rock disposal site (RDS). Overburden, ranging in thickness from 0 to 65 cm, was applied to plots. Some plots were then amended with biosolids at 50, 75 or 150 dry tonnes per hectare (dt/ha), while in other plots trees received a 10 gram bag of chemical fertilizer at 16-6-8-3 NPKS (Meister, 2007). The experimental design also included un-amended controls. All plots were planted with lodgepole pine and Douglas-fir at a rate of 2000 stems per hectare (sph) in a ratio of 70:30 pine to fir. The plots were seeded with a mixture of native or domestic grasses at a rate of 20 or 40 kg/ha (Meister, 2008).  From these trials it was found that, in general, tree survival and growth increased with increasing soil depth up to 40 cm at which point there was no additional advantage to deeper soil. Douglas-fir had a positive response to soil amended with biosolids; Douglas-fir tree growth on plots with 15 cm of soil amended with biosolids was equal to the growth of trees on plots with 40 cm of soil and no biosolids. Lodgepole pine growth was not significantly impacted by the addition of biosolids over paired non-biosolids plots. Chemical fertilizer had no effect on seedling survival and a negative effect on long term growth of the trees. Overall, lodgepole pine and Dougals-fir survival was significantly lower on plots amended with biosolids and even more so on the slopes of the RDS than on the flat top; however, the trees that did survive generally had higher vigour and growth. It was theorized that the readily available nutrients in the biosolids caused a flush of understory vegetation, which out-competed seedlings and contributed to snow press. Additionally, it was thought that ammonia in the biosolids may be damaging the seedlings roots. No tree growth or survival differences were observed between treatments with native or domestic grasses. (Meister, 2012).  The objective of this trial is to build on the previous research trial and investigate if certain herbaceous understory vegetation can promote the establishment of (i.e. have reduced competition with) lodgepole pine and Douglas-fir on biosolids amended sites, while providing enough cover to prevent erosion and out-compete invasive plants. A secondary objective was to monitor the soil quality to determine if there is a risk of ammonia toxicity to seedlings planted in biosolids amended soils.  METHODS  Trials Sites The North Bell Dump is an inactive RDS that had been identified as ready for reclamation. Two sites on this RDS were selected for the study, as they represent different slope aspects, one facing northwest (Area 1) and the other facing southwest (Area 2) (Figure 1). The sites were selected purposefully to test the possibility that the different aspects may create different soil conditions and micro-climates with respect to moisture retention in particular. Both areas are divided into six equal-sized parcels, Area 1 is 2.8 ha in size and contains Parcels 1-6, while Area 2 is 2.0 ha and contains Parcels 7-12.      Figure 1: Map of the trial layout and location on the North Bell Dump Design Due to the limited area available for the trial, topographical constraints, and the desire to use parcel sizes that were operationally appropriate, large parcel areas were used rather than several replicates with small areas. This was done, in part, to try to reduce edge effects of migrating seeds from adjacent parcels. Each of the two areas received the same six treatments (Table 1). Parcels were laid out vertically down the slope so that each treatment would encompass a portion of the upper crest of the slope, mid-slope, and the lower toe and level portion of the slope (Figure 1).   Table 1: Parcel treatments and species seeded and planted Parcel Soil Groundcover Coniferous Trees/Shrubs Deciduous Trees/Shrubs 1 Glacial Till None Lodgepole pine –  1120 sph  Douglas-fir - 480 sph           Black cottonwood - 200 sph  (Populus balsamifera ssp. Trichoccarpa) Sitka alder - 200 sph (Alnus crispa) Paper birch - 50 sph (Betula papyrifera) Trembling aspen - 50 sph     (Populus tremuloides) Saskatoon - 50 sph  (Amelanchier alnifolia) Prickly rose - 50 sph (Rosa acicularis) Scoulers willow - 50 sph (Salix scouleriana) Black Huckleberry - 50 sph (Vaccinium membranaceum) 2 Glacial Till + Biosolids  Forb - 5.6 kg/ha 3 Fireweed - 75 g/ha 4 None 5 Grass/Forb Mix - 5 kg/ha 6 Grass/Forb Mix - 10 kg/ha 7 Glacial Till None Douglas-Fir – 1848 sph  (ran out of pine) 8 Glacial Till + Biosolids  Forb - 6 kg/ha Lodgepole pine –  1090 sph  Douglas-fir – 758 sph  9 Fireweed - 75 g/ha 10 None 11 Grass/Forb Mix - 5 kg/ha 12 Grass/Forb Mix - 10 kg/ha Native Forb Mix: junegrass (Koeleria macrantha), yarrow (Achillea millefolium), pearly everlasting (Anaphalis margaritacea), lupine (Lupinus arcticus), fireweed (Epilobium angustifolium), yellow mountain avens (Dryas drummondii). Native Grass/Forb Mix: junegrass, tickle grass (Agrostis scabra), mountain brome (Bromus marginatus.), red fescue (Festuca rubra), Rocky Mountain fescue (Festuca saximontana), blue wild rye (Elymus glaucus), blue bunch wheatgrass (Agropyron spicatum), lupine, fireweed.   A 20 cm layer of glacial till, 5 cm deeper than the minimum depth of soil required for adequate tree growth and survival, as determined in the 1998 – 2000 trials by Meister (2012), was applied to all of the parcels. Subsequently, Class A biosolids from Metro Vancouver’s Annacis Island Wastewater Treatment Plant were shipped directly to the top of the RDS and then pushed out on the slope at an average rate of 110 dt/ha. The biosolids were incorporated into the till to a minimum depth of 15 cm using an excavator with a rake attachment. The 1998 – 2000 trials (Meister, 2012) found no difference in survival or growth of conifers with biosolids application rates of 75 or 150 dt/ha; therefore, the targeted biosolids application rate of between 100-125 dt/ha was selected and achieved. The control parcels (Parcels 1 and 7) were not amended with biosolids.  The parcels were prepared and biosolids were applied in the fall of 2013 and 2014 for Area 1 and Area 2, respectively. In Area 1, the trees were planted and the groundcover was hand seeded six months later in the spring of 2014. Area 2 received a fall hand seeding of the groundcover immediately after biosolids application, and the trees were planted six months later in the spring of 2015.  The trial was designed to have lodgepole pine and Douglas-fir planted in a 70:30 ratio at 1600 sph. This was the case for Area 1; however, there was some deviation from this design on Area 2 which received a higher planting density (1848 sph) and had a planting ratio of 60:40 lodgepole pine to Douglas-fir. In addition, the control parcel received only Douglas-fir, as the designated lodgepole pine seedlings were used up during the higher density planting on the other parcels. These changes to the planting density and ratio for Area 2 are not expected to affect the results of the trial (McDougall, 2015).  Soil Sampling A soil sampling program was conducted to assess the risk of ammonia damage to seedlings’ roots. Soil samples were collected from the top 15 cm of soil using a hand auger. Ten grab samples were collected per parcel and were thoroughly mixed together to form one composite sample for each of the 12 parcels. All samples were placed on ice in a cooler and sent to ALS Environmental in Saskatoon, SK for analysis. Soil samples were collected immediately prior to biosolids application and following biosolids application prior to tree planting. Samples were also collected at a couple of intervals after tree planting to assess the lasting fertilizer effects of the biosolids. The samples were analyzed for ammonium, macronutrients (N, P, K, S, Cl), micronutrients (Cu, Mn, Zn, B, Fe), pH, moisture, organic matter, and electrical conductivity. The two forms of nitrogen, ammonia and ammonium, exist in equilibrium in the soil and the form depends on soil pH and moisture content. In the laboratory, all of the soil ammonia/ammonium were converted to ammonium and thus expressed as a combined value.   Vegetation Assessment Coniferous tree survival and growth were assessed in the spring of 2017, two and three years post-planting for Area 2 and Area 1, respectively. Survival assessments were conducted using BC silviculture survey methods. Five random sample plots were established in each parcel.  The circular sample plots were 50 m².  Survival was assessed by counting the trees in each plot to determine the sph for comparison to the planted densities. Statistical analysis of the conifer survival was completed using mixed effects models run in R software version 3.3.2 (R Core Team, 2016) using the function lme(), with area as the random factor. Data from grass contaminated plots (see discussion below) in Area 1 were not included in the statistical analysis. Each tree within the plot was assessed for vigor and growth. Within each plot, one representative sample tree of each species, as compared visually to the rest of the plantation, was selected and measured for total height, root collar diameter, and leader growth length. Forest pathology (biotic and abiotic) and vegetation competition was also noted.  Walk-through assessments of vegetation were completed in the first growing season and re-assessed in the fourth growing season for both areas, as well as after two growing seasons for Area 2. For each parcel, percent cover, average vigour, and average height of vegetation were estimated for the parcel. Percent cover of noxious species (as defined by the Cariboo Chilcotin Coast Invasive Plant Committee Regional Strategic Plan, 2014) was also estimated. Herbaceous species present and their individual percent covers were documented. Deciduous trees and shrubs were evaluated on a longitudinal transect and within 50 m² circular plots. They were identified as naturally ingressed or planted, and height and vigour were documented.   RESULTS AND DISCUSSION  Soil Quality Mechanically dewatered Class A biosolids were used in the trial. As produced, these biosolids contained ammonia at a concentration of approximately 9,500 ppm. The biosolids application rate was designed to result in an ammonia concentration of approximately 250 ppm in the soil at the time of incorporation (McDougall, 2014). Laboratory methods test for combined ammonia and ammonium and express the total present as ammonium. Ammonia and ammonium exist in equilibrium in the soil, dependent on the soil pH, with more alkaline soils having a higher percentage of nitrogen present as ammonia (Tisdale et al., 1985). At a soil pH 7, 99% exists as ammonium and 1% as ammonia, while at pH 8, 90% is in the ammonium form and 10% exists as ammonia (Tisdale et al., 1985). A six month rest period post-application of biosolids was included in the trial design to allow sufficient time for the ammonia to be ionized to plant-available ammonium, and for a portion of the ammonium to undergo nitrification to nitrite and nitrate.  Table 2: Average soil quality over time on the trial parcels * represents conservatively low results as some samples were greater than the detection limit  Results from soil samples obtained from the biosolids-applied parcels at the time of tree planting (6 months post-application) showed that the concentration of ammonia/ammonium in the soil was 10-100 ppm with an average of 25 ppm (Table 2). The application of biosolids lowered the pH of the soil to an average of 7.2 from 8.1 in the glacial till, thus it is reasonable to assume that at this time nearly 99% of the ammonia would have been ionized to ammonium, leaving an estimated soil concentration of 0.25 ppm ammonia. Comparatively, the control parcels had a pH of 8.35, so presumably 10% of the ammonium (0.145 ppm) would exist as ammonia. Thus, at the time of tree planting, it is assumed that the ammonia present on the  Average Soil Quality  Pre-application Pre-planting 1 year Post-application Spring 2017 Parameter (unit) Glacial Till Biosolids Parcels Control Parcels Biosolids Parcels Control Parcels Biosolids Parcels Control Parcels pH 8.12 7.18 8.35 6.9 8.4 7.063 8.58 Electrical Conductivity (mS/cm) 0.53 0.56 0.1 0.61 0.1 0.0954 0.077 Organic Matter  (% by weight) 0.52 3.82 0.8 3.4 0.8 4.314 0.2 Nitrate – N (ppm) 5.17 >42.35* 1.2 >44.9* 1.6 3.63 <1.0 Ammonium – N (ppm) 1.79 25.43 1.45 8.17 1.1 2.7 1 Phosphorus (ppm) 17.50 >33.7* 9.05 >36.4* 8.85 201.8 7.9 Potassium (ppm) 132.83 150.64 113.85 162.76 114 144.1 88.5 Sulfate-S (ppm) 46.83 >27 4.95 >27.38* 4.8 9.43 11.05 Chloride (ppm) 2.00 9.24 5.3 4.43 2.25 3.84 2.85 Boron (ppm) 0.05 0.77 0.2 0.888 0.405 0.445 <0.20 Available Copper (ppm) 29.02 72.38 52.3 97.32 40.4 80.26 29.45 Available Iron (ppm) 20.67 201.49 43.4 171.93 28.45 140.27 23.6 Available Manganese  (ppm) 13.43 52.92 8.95 32.79 5.75 14.064 4.395 Available Zinc  (ppm) 0.77 40.81 1.75 43.88 1.75 33.68 1.01 biosolids parcels and the control parcels were both very low and would not pose a risk to the seedlings’ roots.  Subsequent soil samples taken one year post-application and in the spring of 2017 show the lasting fertilization effects of the biosolids (Table 2). Although samples were collected from each parcel individually, the data in Table 2 are presented as the combined average soil quality on the biosolids amended parcels versus the control parcels that did not receive biosolids since the type of understory vegetation did not have an observable effect on the soil quality. As seen in Table 2, even 2 and 3 years post-planting (spring 2017), there is a marked elevation of micro- and macronutrients on the biosolids parcels as compared to the control parcels, and a greater than 20% higher organic matter content. The organic matter and macronutrient levels are within the optimum range (or slightly in excess) for conifer growth (Duryea, 1984), which is indicative of fertile soil.   The concentration of ammonium and nitrate on the biosolids amended parcels continued to decrease through to 2017, as this nitrogen was presumably preferentially taken up by the vegetation, volatilized to the atmosphere, or leached (Tisdale et al., 1985). Conifers, in particular Douglas-fir, grow well in soils where ammonium is the predominant nitrogen source (Duryea, 1984); thus, this nitrogen would have been readily taken up by the trees. Although the inorganic nitrogen (ammonium, nitrite and nitrate) decreased over time, it was still elevated when compared to the control parcels which did not receive biosolids.   Herbaceous Vegetation Growth During the application of biosolids to Area 1, the biosolids were stockpiled above an adjacent section of the RDS that had been previously reclaimed with a mixture of native grasses. Following application, the remaining biosolids on the ground at the stockpile location were scraped up and distributed equally across the crest of the slope on Parcels 2 – 6. In the process, seeds that had been spilled on the ground above the adjacent site during seeding (native grass/forb seed mix; Table 1) were transferred to this section across the crest of all of the biosolids parcels, resulting in a flush of grasses which established a relatively uniform treatment across the top quarter to third of each of these parcels. In addition, a number of weedy species (e.g. common groundsel, perennial sowthistle, prickly lettuce, common knotgrass, an unidentified yellow mustard, annual hawksbeard, and an unidentified morning glory-like vine) established themselves across Parcels 2 – 6. It is hypothesized that these species were present as seeds or propagules in the stockpiled soil and were able to take advantage of the biosolids nutrient source with minimal competition from the seeded species, as the forbs and fireweed are not as competitive and Parcel 4 was not seeded. Seeding of this area in the spring (as opposed to the fall) following biosolids application, may have also reduced the competitiveness of the seeded species. The herbaceous layer seeding treatments on Area 1 were therefore somewhat compromised; however, differences were still observed, especially when the seed-contaminated upper portion of Parcels 2 – 6 were removed from the assessment.  The herbaceous vegetation on Area 2 more closely resembled the trial design. Weedy species (e.g., perennial sowthistle, common groundsel, common knotgrass) were present, but to a lesser degree than on Area 1. This may have been due to using glacial till from a different stockpile source than was used on Area 1 which may have had less weeds seeds or propagules present.  As well, Area 2 was seeded in the fall following biosolids application. Overall herbaceous vegetation had a higher percent cover at the crest of the slope and a lower percent cover at the toe of the slope on both areas. As biosolids were applied from the top of the slope and pushed down, it is likely that the crest received a higher application rate and therefore more nutrients were available for vegetation growth. Despite weed ingress on both areas and particularly on Area 1, there were still a number of similarities between paired treatments on the two Areas:  • Parcels 1 and 7 (control) had very little herbaceous vegetation (scattered grasses, clover and thistle). • Parcels 2 and 8 (native forbs) were dominated by yarrow with limited emergence of fireweed, lupine and other seeded species. As such, non-target weedy species were able to establish. • Parcels 3 and 9 (fireweed) had limited germination of the seeded species. Therefore, these parcels were very similar to Parcels 4 and 10 (no seed), which were dominated by various weedy species. • The native grasses/forbs parcels (5, 6, 11, and 12) all established well, although weedy species dominated in Area 1. As expected, the higher seeding rate (10 kg/ha) resulted in denser grasses.  Table 3: Herbaceous vegetation as assessed in the first growing season Parcel (treatment) % Cover Herbaceous Species Dominant Species (in order of prevalence) Seeded Non-seeded 1  (no seed) n/a <1% Clover, common groundsel, perennial sowthistle, oxeye daisy 2  (forb mix) <2% (fireweed & lupine) 65% Common groundsel, common knotgrass, perennial sowthistle, prickly lettuce, annual hawksbeard, oxeye daisy and grasses 3 (fireweed) <1% 45% Perennial sowthistle, common groundsel, prickly lettuce, grasses, curly dock, and an unidentified vine 4 (no seed) n/a 75% Unidentified vine, perennial sowthistle, common groundsel, prickly lettuce,  and an unidentified yellow mustard  5 (grass 5 kg/ha) <5% 60% An unidentified vine, common groundsel, unidentified yellow mustard, perennial sowthistle, curly dock 6 (grass 10 kg/ha) 5% 70% Unidentified vine, common groundsel, perennial sowthistle, unidentified yellow mustard, common knotgrass, prickly lettuce 7  (no seed) n/a 2% Perennial sowthistle, clover 8  (forb mix) 10% (yarrow) 10% Yarrow, perennial sowthistle, common groundsel, common knotgrass 9 (fireweed) <1% 10% Common groundsel, common knotgrass, perennial sowthistle  10 (no seed) n/a 10% 11 (grass 5 kg/ha) 25% 20% Grasses, perennial sowthistle 12 (grass 10 kg/ha) 20% 40% Grasses, perennial sowthistle, common knotgrass Note: Dominant species were determined to be those with >5% cover on the parcel, or if total cover was 10% or less, then the most prevalent species are listed, generally >1% cover. Table 3 lists the dominant species found on each parcel within the first growing season (2014 for Area 1 and 2015 for Area 2). Area 1 (Parcels 1-6) was also re-assessed in the second growing season, 2015. At that time, species present in each of the parcels were relatively similar to those listed in Table 3; however, grass had become the dominant species in Parcels 4-6 and total vegetative percent cover across all of the parcels had increased. Across all parcels, the unidentified morning glory type vine had become highly prevalent and on Parcel 2 yarrow had emerged with an approximate cover of 15%.  At the time of the 2017 conifer survival assessment, most of the herbaceous species were dormant; however, some general observations were made and these mostly corresponded with what was seen after one growing season. However, a significant amount of grass had established in Parcels 2-4 and more heavily in Parcel 4. This is likely due to ingress from the adjacent grass treatment parcels (Parcels 5 and 6) due to their proximity and the length of time elapsed since initial seeding. In Area 2 there was some ingress of grass on Parcel 10 from the adjacent Parcel 11; however, very little grass has spread to the other parcels.  In the fourth growing seasons (2017 for Area 1 and 2018 for Area 2), the herbaceous vegetation was re-assessed to determine any changes to the vegetation and assess the density of the groundcover. In general, the parcels continued to follow the same trend that was seen in year one and year two with the percent cover increasing on all of the biosolids applied parcels. A summary of the assessment is presented below. • Area 1 had a greater diversity of herbaceous species than Area 2; however, this diversity was due to a larger number of non-seeded species ingressing to the site, likely from the adjacent land or as a result of a seed bank within the overburden soil. • Parcels 1 & 7 (control) continued to have very little herbaceous vegetation (2-3% cover). • Yarrow continued to be the dominant seeded species on Parcels 2 & 8 (forbs); however, grasses and weedy species (such as prickly lettuce and perennial sow thistle) had a higher percent cover overall. • Grass parcels on both areas were heavily vegetated (100% cover) and grasses were the dominant species. • Grasses had continued to spread into adjacent parcels. In Area 2, grasses had spread to Parcel 9 in addition to Parcel 10, both of which had approximately 20% cover of grass (out of a total herbaceous cover of 60-65%). Parcels 11 and 12 had 50% and 65% grass cover respectively. • Prickly lettuce had ingressed into Area 2 and was the dominant species in Parcels 8, 9 and 10. However all of the parcels in Area 2 contained some amount of prickly lettuce. One of the major changes seen in the fourth growing season was the addition of moss to all of the biosolids applied parcels. The percent cover of moss ranged from 3-45% on the grass parcels and 17-60% on the forbs, fireweed and no seed parcels. The higher percent cover of moss correlated to a lower percent cover of herbaceous vegetation. In Area 1, drought stress was noted on the conifers in Parcels 4-6 which had low moss cover (17% or less) and high grass cover (>90%). This suggests that moss could help prevent drought stress in conifers by retaining moisture or occupying space not used by herbaceous species, which compete with the conifers for available water. Drought stress was not observed on Area 2 which had a higher moss cover (35-60%) and lower herbaceous cover, but also had a different slope aspect than Area 1.  Although not the focus of the vegetation assessments, presence of noxious species and their relative abundance were documented. Noxious species observed included: Canada thistle (Cirsium arvense), perennial sow thistle (Sonchus arvensis L.), oxeye daisy (Leucanthemum vulgare), scentless camomile (Matricaria perforata), and orange and yellow hawkweed (Hieracium aurantiacum and H. caespitosumand). Noxious species abundance ranged from <1% to 10% in the first growing season but was lowest on parcels seeded with grasses and on the control. Noxious species abundance appeared to increase in the second growing season on Area 2, reaching up to 20% on the parcel seeded with fireweed. By the fourth growing season, Parcels 2 & 3 had 40% and 35% cover of perennial sow thistle, respectively, and Parcel 10 had 15% cover of scentless camomile (seeded with forbs, fireweed and no seed, respectively). The remainder of the parcels had only 1-4% cover of noxious species.  Coniferous Tree Survival and Growth The biggest factors impacting conifer survival were vegetation competition, vegetation/snow press and herbivory in the form of rodent damage (girdling). These impacts increased on parcels with a higher percentage of grasses. Although statistical analysis did not show significant differences in all cases, some clear trends are observable. The lowest survival rates were seen on the parcels applied with the native grasses and forbs mix (Parcels 5, 6, 11 and 12). On Area 1, the lower grass seeding rate (Parcel 5) had a relatively high survival rate; however, nearly half of the surviving trees were of such poor health, form or vigour that they would likely not mature. Parcel 4 also experienced low survival, likely due to the unidentified vine that covered large patches of that parcel, providing heavy competition. Large patches of the vine were also found on Parcel 6, which experienced a low survival rate of 21%. The parcels that were not seeded or were seeded with forbs or fireweed had highest survival rates (near 80%) and were not significantly different (Figure 2).   Notes: When comparing survival across parcels in Area 1, sample plots from within the grass band at the crest of the slope were removed from the data set, as this was not an intended treatment and represents a separate set of conditions.  2.  Uppercase letters show differences among cover types (data from both areas combined) and lowercase letters show differences among individual parcels. Figure 2: Percent of conifers surviving in each parcel (May 2017) When the parcels of the same seeding treatment were analyzed together (denoted with capital letters on Figure 2) more significant differences were seen, which indicates that the parcels in both Area 1 and Area 2 are behaving similarly with respect to conifer survival. There was no statistically significant difference in conifer survival between the control, the forbs and the fireweed seeded plots, indicating that forbs are non-competitive with the conifers. Additionally, a statistically significant decrease in survival is seen with the increase from 5 to 10 kg/ha grass seeding rate. Indicating that reducing the seeding rate of grasses to very low levels appears to improve the survival rate of the conifers.   Lodgepole pine and Douglas-fir appeared to have similar survival rates; biosolids application did not seem to favour one species, and the different ground cover treatments did not affect the planted ratios of pine to fir. For both Areas 1 and 2, survival was higher on the flat portion at the toe of the slope and lower on the slope and crest. This may have been due to the lower vegetation competition on this area which led to the lower risk of snow press and rodent damage, all potentially associated with a lower concentration of biosolids at the toe of the slope. Or, it may also have been due to a parameter associated with the topography, such as soil moisture content.    Although survival was very high on the control parcels, the trees that did survive on the biosolids applied parcels had notably improved growth and vigour. Between the different understory treatments there was no observable difference in growth of the trees based on the seeded species; however, differences were observed between the biosolids applied parcels and the control parcels and are discussed here.  In Area 1, the average height of lodgepole pine trees on biosolids applied parcels was double that of the control parcel (44.8 cm vs. 22.8 cm). Likewise, the Douglas-fir on Area 1 were approximately 50% taller than on the control parcel (39.7 cm vs. 27 cm). On Area 2 there was not a comparison for pine, but the Douglas-fir were approximately 30% taller on the biosolids applied parcels than the control (36.6 cm vs. 27.8 cm). Leader length on Area 1 was approximately 3 times greater on the biosolids applied parcels as compared to the control (17.3 cm vs. 4.6 cm for lodgepole pine and 12.1 cm vs. 4.0 cm for Douglas-fir) and on Area 2 it was approximately 7 times greater on the biosolids parcels (9.7 cm vs. 1.3 cm on the control).    Root collar diameter measurements from Area 1 found that for both pine and fir the biosolids applied parcels had trees with approximately 75% larger stem diameters than those on the control parcel (1.0 cm vs.            0.6 cm for both lodgepole pine and Douglas-fir). For Douglas-fir on Area 2, the root collar diameters were double that of the control parcel on the biosolids applied parcels (0.8 cm vs. 0.4 cm).   There was no observable difference between growth measurements on the different parcels applied with biosolids; however, the health and form of the trees was affected by the understory vegetation. Health and form of the trees on the biosolids applied parcels was mostly affected by vegetation/snow press and rodent damage, while on the control parcels the trees were limited by the low nutrient content of the soil resulting in chlorosis. On the control parcels, the majority of the trees fell into the ‘fair’ category. Of the parcels that were amended with biosolids, on those that were seeded with the native grasses and forbs mix (Parcels 5, 6, 11 and 12), the trees were generally classified as ‘poor to fair’ while on the forbs, fireweed and no seed parcels the trees generally were in the ‘fair to good.’ Parcels 9 and 10 (fireweed and no seed) had the most trees classified as ‘good’, likely due to the lack of graminoid species and their associated competitiveness. Observations of Deciduous Species Deciduous trees and shrubs were planted at lower densities across all parcels and were intended to augment biodiversity at the site, but were not the focus of this trial. General observations were made of their survival and performance, but accurate survival rates have not been determined.    In general, the Sitka alder, black cottonwood, Scouler’s willow and prickly rose appeared to exhibit the best survival and performance across all sites, while the paper birch, saskatoon and trembling aspen showed poor establishment. The majority of black huckleberry appeared not to have survived the transplant. Raspberry and elderberry were observed to be naturally ingressing in Area 1, which suggests these species do not need to be planted. As seen with the conifer seedlings, survival appeared to be best on the flat toe of the slope. This may be an indication of improved moisture retention and its positive effect on plant development but has not been proven.  Deciduous survival and vigour were highest on the control parcels, potentially due to preferential ungulate browsing on the biosolids amended parcels.  CONCLUSIONS AND RECOMMENDATIONS   The trial demonstrated that soil amended with biosolids will promote growth of herbaceous understory vegetation, which can be detrimental to the survival rate of conifers due to vegetative competition, vegetation/snow press, and increased rodent damage. These impacts were greatest on parcels seeded with native grasses, as even light seeding rates (5 kg/ha of a native grass/forb mix) produced heavy vegetative cover. Seedling survival was highest on the control, the native forbs, and fireweed parcels. Although survival was high on the control parcels, the tree growth was poorer and many trees were chlorotic, indicating nutrient deficiency. Surviving trees on the biosolids amended parcels had higher growth and vigour than the control. A seeding of native forbs and non-graminoid species was found to be non-competitive with conifer species and is recommended for biosolids amended reclamation to promote biodiversity while providing vegetative cover for the site. However, plots seeded only with fireweed or not seeded provided lower competition for invasive species, so a balance is needed to promote conifer survival and discourage invasive species establishment. Results from this trial indicate that this may be achieved by seeding with a mixture of native forbs.  Soil sample results indicate the fertilizer effects of biosolids persist through at least 3 growing seasons and that the macronutrients and organic matter content of the biosolids applied parcels are within the optimum range (or slightly in excess) for conifer growth. Further, at the time of tree planting the ammonia levels within the soil were low and did not pose a risk of damage to the seedlings’ roots. To mitigate any risk of ammonia damage to seedlings, a best management practice would be to apply and incorporate biosolids in the fall and allow for a 6 month rest period prior to planting conifer seedlings in the spring.    REFERENCES  Cariboo Chilcotin Coast Invasive Plant Committee (CCCIPC).  2014.  Regional Strategic Plan for Invasive Plant Management. Version 2.8.  Duryea, Mary L., and Thomas D. Landis (eds.).  1984.  Forest Nursery Manual: Production of Bareroot Seedlings. Martinus Nijhoff/Dr W. Junk Publishers. The Hague/Boston/Lancaster, for Forest Research Laboratory, Oregon State University. Corvallis.  p. 64-65  McDougall, R.  2014.  Mount Polley North Bell Dump Tree Trial - Trial Design and Establishment Report. Armstrong, BC.  p. 10.  McDougall, R.  2015.  Mount Polley North Bell Dump Tree Trial – Area 2 Site Assessment. Armstrong, BC.  p. 5.  Meister, R.P.  2008.  Mount Polley Mining Corporation Annual Reclamation Research Report. Forestmeister Services. 150 Mile House, BC.   Meister, R.P.  2012.  Mount Polley Mining Corporation Tree Plots Research Report. Forestmeister Services. 150 Mile House, BC.  Meister, R.P.  2007.  Reconstruction of Forest Ecosystems on Rock Disposal Sites at Mount Polley Mine. British Columbia Mine Reclamation Symposium.   R Core Team.  2016.  R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL  Tisdale, S.L., Nelson, W.L., and Beaton, J.D.  1985.  Soil Fertility and Fertilizers. 4th Ed. MacMillan Publishing Company, New York.  p. 120, 132-134, 147 


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