Carbon and Macronutrient Budgets in an Alder Plantation Grown on a Reclaimed Combustion Waste Landﬁll

: Combustion waste landﬁlls are unfavorable for revegetation due to nitrogen deﬁciency, and therefore, the introduction of nitrogen-ﬁxing organisms, such as alder species ( Alnus sp.), may be promising for reclamation and restoration of these sites. We investigated the carbon and macronutrient stocks in the combustion waste technosols and biomass of black alder ( Alnus glutinosa ) and grey alder ( Alnus incana) 10 years after introduction onto a combustion waste landﬁll. The alder species were planted with or without lignite addition in planting holes, the latter acting as control plots. Black alder biomass was higher than that of grey alder. The total macronutrient stocks were higher in the uppermost technosol layer (0–30 cm) than in the biomass nutrient stocks. However, the K and P stocks in the black alder biomass were still greater than the exchangeable K + and available phosphorus (Pav) stocks in technosols. This is important for the nutrition of the trees planted in combustion waste landﬁlls and conﬁrms the Pav deﬁcit in investigated technosols. The di ﬀ erentiation of nutrients in biomass shows that the largest stock was found in the wood of trunks and branches (40–70% of the stock of individual biomass macronutrients). Although foliage biomass represented approximately 7% of the total tree biomass, the nutrient stocks therein represented a signiﬁcant proportion of total nutrient stocks: approximately 27–29% nitrogen, 17–22% calcium, 28% magnesium, 7–10% potassium and 12–16% phosphorus. This is particularly important in the context of the turnover of nutrients from litterfall and soil organic matter and the circulation of nutrients in the ecosystem developed on combustion waste technosols.


Introduction
Production of electricity from lignite involves the creation of a large amount of combustion waste. Combustion waste is used, among other purposes, as a cement component in concrete [1,2] and as an additive for improving reclaimed mine soils (RMS) or other degraded soils for forestry and agriculture [3]. However, most combustion waste is stored on different types of landfills [4], which is environmentally problematic because of wind erosion and dust pollution. Their adverse effects could The research was conducted on a permanent experimental field established in 2006 and designed to evaluate the growth and adaptation of different alder species on the combustion waste disposal site. In September 2005, the Bełchatów Power Plant hydro-seeded the experimental field with sludge (4 Mg per hectare) mixed with grass seed (200 kg per hectare; primarily cat grass (Dactylis glomerata) and Italian rye (Lolium multiflorum). In the same year, NPK fertilizer was applied to the field at 60-36-36 kg ha -1 . In the spring of 2006, black, grey and green alder (Alnus glutinosa, A. incana and A. viridis, respectively) were planted in randomly selected plots (6 × 13 m in 3 blocks, 50 seedlings per plot). The plots were separated by 2 m wide strips. The three alder species (Sp) were planted using two treatments with 4 replications of each species/treatment combination. The two treatments (Tr) consisted of adding lignite culm (pH = 5.6, 3 dm 3 per planting hole) or no soil amendments in control plots [6,7]. The properties of the lignite culm used as an amendment were reported by Krzaklewski et al. [7]. Green alder introduced to the combustion waste landfill experienced gradual regression and is a shrub species, while black and grey alder did not. For this reason, plots with green alder were not included in this study. The following variants were selected: B-FA-black alder planted in pure combustion waste, G-FA-grey alder planted in pure combustion waste, B-FA+L-black alder planted in combustion waste with lignite addition in planting holes and G-FA+L-grey alder planted in combustion waste with lignite addition in planting holes ( Figure 2). The research was conducted on a permanent experimental field established in 2006 and designed to evaluate the growth and adaptation of different alder species on the combustion waste disposal site. In September 2005, the Bełchatów Power Plant hydro-seeded the experimental field with sludge (4 Mg per hectare) mixed with grass seed (200 kg per hectare; primarily cat grass (Dactylis glomerata) and Italian rye (Lolium multiflorum). In the same year, NPK fertilizer was applied to the field at 60-36-36 kg ha −1 . In the spring of 2006, black, grey and green alder (Alnus glutinosa, A. incana and A. viridis, respectively) were planted in randomly selected plots (6 × 13 m in 3 blocks, 50 seedlings per plot). The plots were separated by 2 m wide strips. The three alder species (Sp) were planted using two treatments with 4 replications of each species/treatment combination. The two treatments (Tr) consisted of adding lignite culm (pH = 5.6, 3 dm 3 per planting hole) or no soil amendments in control plots [6,7]. The properties of the lignite culm used as an amendment were reported by Krzaklewski et al. [7]. Green alder introduced to the combustion waste landfill experienced gradual regression and is a shrub species, while black and grey alder did not. For this reason, plots with green alder were not included in this study. The following variants were selected: B-FA-black alder planted in pure combustion waste, G-FA-grey alder planted in pure combustion waste, B-FA+L-black alder planted in combustion waste with lignite addition in planting holes and G-FA+L-grey alder planted in combustion waste with lignite addition in planting holes ( Figure 2).

Soil Study
In the autumn of 2015, mixed soil samples were collected from the 0-30 cm horizons of 5 points distributed diagonally across each plot. Independently, samples with intact structures were collected with 250 cm 3 cylinders to determine the bulk density (BD). In addition, four samples of freshly deposited combustion waste were collected to determine the initial properties of the waste. Samples of the organic horizons (litter layer, Oi + Oe) were collected from five 1.0-m 2 squares within each study plot. Each sample of the litter layer in the fresh state was weighed with an electronic balance to an accuracy of 1 g, and mixed samples were considered representative of each test area.
For the samples of mineral horizons (0-30 cm), the following parameters were determined: the texture was measured with a Fritsch GmbH Laser Particle Sizer ANALYSETTE 22, pH was measured potentiometrically in 1 M KCl with a 1:2.5 soil-solution ratio, and the total organic carbon (TOC) and total nitrogen (Ntot) contents were determined using a LECO TruMac ® CNS. Before determining the carbon content, the soil samples were treated with 10% HCl to remove carbonates. The total concentrations of all forms of macronutrients (Catot, Mgtot, Ktot, and Ptot) were determined after digestion in HNO3 (d = 1.40) and 60% HClO4 in a 4:1 ratio, and exchangeable forms (Ca 2+ , Mg 2+ and K + ) in 1 M NH4Ac using an ICP-OES iCAP™ 6000 Series spectrophotometer. The content of phosphorus available for plants (Pav) was determined in an extract of calcium lactate ((CH3CHOHCOO)2Ca) according to the Egner-Riehm method [26,27].

Soil Study
In the autumn of 2015, mixed soil samples were collected from the 0-30 cm horizons of 5 points distributed diagonally across each plot. Independently, samples with intact structures were collected with 250 cm 3 cylinders to determine the bulk density (BD). In addition, four samples of freshly deposited combustion waste were collected to determine the initial properties of the waste. Samples of the organic horizons (litter layer, Oi + Oe) were collected from five 1.0-m 2 squares within each study plot. Each sample of the litter layer in the fresh state was weighed with an electronic balance to an accuracy of 1 g, and mixed samples were considered representative of each test area.
For the samples of mineral horizons (0-30 cm), the following parameters were determined: the texture was measured with a Fritsch GmbH Laser Particle Sizer ANALYSETTE 22, pH was measured potentiometrically in 1 M KCl with a 1:2.5 soil-solution ratio, and the total organic carbon (TOC) and total nitrogen (N tot ) contents were determined using a LECO TruMac ® CNS. Before determining the carbon content, the soil samples were treated with 10% HCl to remove carbonates. The total concentrations of all forms of macronutrients (Ca tot , Mg tot , K tot , and P tot ) were determined after digestion in HNO 3 (d = 1.40) and 60% HClO 4 in a 4:1 ratio, and exchangeable forms (Ca 2+ , Mg 2+ and K + ) in 1 M NH 4 Ac using an ICP-OES iCAP™ 6000 Series spectrophotometer. The content of phosphorus available for plants (Pav) was determined in an extract of calcium lactate ((CH 3 CHOHCOO) 2 Ca) according to the Egner-Riehm method [26,27]. Samples collected intact with cylinders were sieved (2-mm mesh size), weighed, dried at 105 • C for 5 h and reweighed. The final weight was used to calculate the dry weight of the original sample, which was then divided by the volume to obtain the BD of the fine fraction (<2 mm) [16,28].
The samples of organic horizons (Oi + Oe) were oven-dried to remove moisture, and the measured moisture loss was used to calculate the dry mass. Dried samples were ground, and C and N content was determined using a LECO TruMac ® CNS, pH was measured potentiometrically in 1 M KCl in a 1:5 ratio. Calcium, Mg, K and P were measured after digestion in a mixture of HNO 3 acids (d = 1.40) and 60% HClO 4 on an ICP-OES iCAP™ 6000 Series spectrophotometer [26,27].

Alder Biomass Study
The diameter at breast height (DBH) and height (H) of the planted alder trees were measured in autumn 2015. The aboveground biomass of trees and leaves was estimated according to an allometric equation developed for young stands (6-20 years) growing in the climate of Poland (according to Ochał [29]). The coarse root biomass (>2 mm) was estimated as 25% of the total biomass [30]. The coarse roots and wood samples were collected from five trees regularly distributed along the diagonal of each plot. Leaves were also collected in summer from the crown top of the southwest exposure of five trees regularly distributed along the diagonal of each plot.
To determine the biomass of fine roots (diameter < 2 mm), five-volume samples (500 cm 3 ) of the rooted soil layer were collected to a depth of 30 cm. The samples were pre-sieved in the field using a 2 mm mesh and transported in plastic bags to the laboratory.
Samples of fine roots were stored at 4 • C for no more than 2 weeks. To isolate the roots, the samples were successively rinsed in distilled water. The fine root fraction (<2 mm) was measured with calipers, then dried at 65 • C and weighed on a laboratory scale with an accuracy of ±10 mg.
In the samples of biomass components (wood, leaves, and coarse and fine roots), the C and N contents were determined using a LECO TruMac ® CNS and the Ca, Mg, K and P contents using an ICP-OES iCAP™ 6000 Series spectrophotometer after digestion in a mixture of HNO 3 acids (d = 1.40) and 60% HClO 4 acid in a 4:1 ratio.

Nutrient Stock and Carbon Accumulation
The nutrient stocks (C, N, Ca, Mg, K and P) in organic (Oi + Oe) and mineral (0-30 cm) horizons of technosols were calculated by the equation: in which Estock (Oi+Oe) represents the nutrient stock in organic horizons (Oi+Oe), M Oi+Oe is the dry mass of Oi+Oe and Econc is the nutrient concentration in O i +O e in which Estock (mineral) represents the nutrient stock in the mineral horizons, Econc (mineral) is the nutrient concentration in mineral horizons, BD is the bulk density of the fine fraction (<2 mm), and T is the thickness of the soil layer.
To determine the soil organic carbon (SOC) and N stocks in technosols, the carbon and N contents in samples of freshly deposited combustion waste were subtracted from that determined for the soil samples collected from the alder plots. The contents of C and N in the samples of freshly deposited combustion waste corresponded approximately to the content of unburned organic carbon generated during the lignite combustion process at the power plant [31].
The nutrient stocks in alder biomass were calculated from the formula: Forests 2020, 11, 430 6 of 15 in which Estock (B) represents the nutrient stocks in total biomass of trees, B is the biomass of components (fine roots, coarse roots, wood and leaves) and Econc (B) is the nutrient concentration in components of biomass. Carbon accumulation was calculated by dividing the C stocks in technosols and alder biomass by the tree age.

Statistical Analyses
The effects of soil treatment (Tr) and alder species (Sp) on the studied technosol and biomass parameters were analyzed using two-way ANOVA. The differences (significance assigned at p < 0.05) between mean values of the measured parameters were calculated using Tukey's test (HSD). Statistical analyses were performed using STATISTICA 13.1 software [32].

Basic Soil Parameters
Freshly deposited combustion waste (fly ash, FA) was characterized by alkalinity (pH [in H 2 O] = 8.52), and low unburned C (1.56%) and N (0.025%) content. The P and Mg contents in freshly deposited FA were similar to those of technosols under alder species. Potassium content in freshly deposited FA was significantly lower than in technosols, and the Ca content in freshly deposited FA was higher than in technosols under alder species (Table 1).
The alder species and soil treatment had no impact on BD, pH and concentrations of macronutrient (P, K, Ca and Mg) in technosols. The SOC content (after subtracting unburnt lignite in the balance sheet) ranged from 1.48% (G+FA) to 33.35% (G+FA+L). The N tot content in technosols (after subtracting unburnt N in the balance sheet) varied from 0.01% to 0.02% (Table 1).

Carbon and Macronutrient Stocks in Technosols
Both alder species and lignite amendment had no impact on the carbon and different forms of macronutrient (N, P, K, Ca and Mg) stocks in technosols ( Table 2). The C stocks in the uppermost litter (Oi + Oe) horizon varied from 1.  (Table 2).
Freshly deposited fly ash

Alder Biomass
Both the alder species and the modified lignite had an impact on the biomass parameters (Table 3). Black alder displayed higher biomass values than the grey alder. Only the fine root biomass was not significantly different between the two alder species. The total biomass (sum of wood, leaves, coarse and fine roots) ranged from 19.77 to 67.80 Mg ha −1 and aboveground biomass from 15.6 to 55.41 Mg ha −1 , respectively, for G-FA and B-FA+L variants (Figure 3).

Alder Biomass
Both the alder species and the modified lignite had an impact on the biomass parameters (Table  3). Black alder displayed higher biomass values than the grey alder. Only the fine root biomass was not significantly different between the two alder species. The total biomass (sum of wood, leaves, coarse and fine roots) ranged from 19.77 to 67.80 Mg ha −1 and aboveground biomass from 15.6 to 55.41 Mg ha −1 , respectively, for G-FA and B-FA+L variants ( Figure 3).

Carbon and Macronutrient Stocks in Biomass
Similar to the alder biomass, the total carbon stocks in the biomass depended both on the tree species and lignite amendments ( Table 3). The total carbon stocks (in below and aboveground biomass) ranged from 10.13 Mg ha −1 in G-FA to 34.95 Mg ha −1 in B-FA+L (Figure 4a). The wood accumulated from 64% (G-FA) to 68% (B-FA+L) of C stocks in total biomass. Coarse roots accounted for approximately 24% of C stocks, foliage accounted for 6% (B-FA+L) to 8% (G-FA), and fine roots accounted for from 2% (B-FA+L) to 5% (G-FA) of the total carbon stock of the biomass ( Figure 5).
Similar to the alder biomass, the total carbon stocks in the biomass depended both on the tree species and lignite amendments ( Table 3). The total carbon stocks (in below and aboveground biomass) ranged from 10.13 Mg ha −1 in G-FA to 34.95 Mg ha −1 in B-FA+L (Figure 4a). The wood accumulated from 64% (G-FA) to 68% (B-FA+L) of C stocks in total biomass. Coarse roots accounted for approximately 24% of C stocks, foliage accounted for 6% (B-FA+L) to 8% (G-FA), and fine roots accounted for from 2% (B-FA+L) to 5% (G-FA) of the total carbon stock of the biomass ( Figure 5).   The total N stocks in the biomass depended both on the alder species and lignite amendment ( Table 3). The total N stocks (in below and aboveground biomass) ranged from 0.14 Mg ha −1 in G-FA to 0.43 Mg ha −1 in B-FA+L (Figure 4b). The wood biomass accumulated 41% (G-FA) to 48% (B-FA+L) of N stocks. The coarse root biomass accounted for 18% (G-FA) to 21% (B-FA+L) of N stocks, foliage accounted for 27% (B-FA+L) to 30% (G-FA), and fine roots accounted for 4% (B-FA+L) to 10% (G-FA) of the total N stock of the biomass ( Figure 5).
The total P, K and Ca stocks in the biomass depended on the alder species but did not depend The total N stocks in the biomass depended both on the alder species and lignite amendment ( Table 3). The total N stocks (in below and aboveground biomass) ranged from 0.14 Mg ha −1 in G-FA to 0.43 Mg ha −1 in B-FA+L (Figure 4b). The wood biomass accumulated 41% (G-FA) to 48% (B-FA+L) of N stocks. The coarse root biomass accounted for 18% (G-FA) to 21% (B-FA+L) of N stocks, foliage accounted for 27% (B-FA+L) to 30% (G-FA), and fine roots accounted for 4% (B-FA+L) to 10% (G-FA) of the total N stock of the biomass ( Figure 5).
The total P, K and Ca stocks in the biomass depended on the alder species but did not depend on the lignite amendment. In contrast, the total Mg stocks in the biomass depended both on the alder species and on the lignite amendment (Table 3). Variant B+FA+L was characterized by the largest accumulation of the remaining nutrients (P, K, Ca and Mg) in the total biomass, and the smallest accumulation was observed for variant G-FA (Figure 4).
The total K stocks in the biomass ranged from 0.05 to 0.17 Mg ha −1 (Figure 5d). The foliage accounted for from 8% (B-FA+L) to 12% (G-FA) of K stocks in biomass, and the wood accounted for 59% (G-FA) to 69% (B-FA+L), the coarse roots accounted for approximately 23% in each variant and fine roots 2% (B-FA+L) to 6% (G-FA) ( Figure 5).
The total Mg stocks in the biomass ranged from 0.02 to 0.06 Mg ha −1 (Figure 4f). The foliage accumulation accounted for from 27% (G-FA+L) to 31% (B-FA) of the Mg in the total biomass, accumulation in the wood was 40% (G-FA) to 51% (B-FA+L), coarse roots accounted for approximately 18% in each variant, and fine roots accounted for 3% (B-FA+L) to 11% (G-FA) ( Figure 5).

Whole Ecosystem Carbon Accumulation
The ecosystem (soil and biomass) C accumulation varied from 4.47 to 8.94 Mg ha −1 yr −1 and was higher in the black alder variants than the grey alder variants on FA. The alder species and soil treatment had no impact on C accumulation in the technosols, which varied from 2.31 to 4.67 Mg ha −1 yr −1 (Table 4).

Relationship between the Carbon and Nutrient Stocks in the Biomass and Soil
The alder species affected the ratio of P, K, Ca and Mg stocks in the biomass and P tot , Pav, K + , Mg tot , Mg 2+ Ca tot and Ca 2+ stocks in technosols. For black alder, the biom:soil ratio was usually higher than in the grey alder. The black alder had larger P and K stocks in the biomass relative to the potential resources of Pav and exchangeable K + in the 0-30 cm technosol horizon (Table 5). Table 5. The ratio of the carbon and nutrient resources in the total biomass (B tot ) to that in the soils (0-30 cm).

Discussion
The estimated biomass obtained for the two alder species (from 19.77 Mg ha −1 for A. incana to 67.80 Mg ha −1 for A. glutinosa) is similar to published data obtained from forests on natural soils. The total aboveground biomass of black alder stands aged 7-18 years in Sweden varied from 35.1 to 77.3 Mg ha −1 [33]. The aboveground biomass of black alder stands in natural sites in Poland varied from 8 to 75 Mg ha −1 at 6-20 years [29]. In a literature review surveying Scandinavia and Eastern Europe (Baltic countries and Russia), the total aboveground biomass of grey alder was reported to vary from 18.5 to 98.6 Mg ha −1 at 9-10 years [34]. Such high biomass confirms the alder species are highly adaptable to growing in combustion waste landfills [6].
The amendment of lignite culm did not affect the nutrient stock values in technosols but affected the nutrient stock in biomass of alders. This is because lignite was used in a small dose (3 dm 3 ) only to the planting holes, which were, in fact, not sampled around at the nearest trunk location. Instead, we collected the soil samples from 5 points distributed diagonally across each plot, not near the root collar of trees. However, the culm improved the conditions of tree growth in the years immediately after planting and achieving growth parameters [7], which would result in higher C, N and Mg stock in alder biomass. The largest stocks of nutrients were found in the stem and branch biomass (Bwood). These results were similar to those obtained from three 21-year-old experimental plantations of black alder (A. glutinosa) in Estonia. The largest amount of N (57.3-67.1%) and P (71.1-83.0%) was allocated to alder stems [35]. Although foliage biomass represented only approximately 7% of the total alder biomass, the nutrient stocks in the foliage biomass represented a significant part of the total nutrient stocks, i.e., approximately 27-29% N, 17-22% Ca, approximately 28% Mg, 7-10% K and 12-16% P. This is particularly important in the context of the creation of soil organic matter from litterfall and the circulation of nutrients in the developing ecosystem on fly ash technosols. In addition to the litterfall from the aboveground biomass, through an annual turnover process of death and renewal, fine roots can significantly contribute to the SOC and nutrient pool in the soil [36,37]. However, our research indicates that fine roots do not constitute a large pool of nutrients (up to 10% for N, P and K) compared to the other components of alder biomass.
The total forms of nutrient (N tot , P tot , K tot , Ca tot and Mg tot ) stocks were greater in the technosols than in the total biomass of the alder species. However, the K and P stocks in black alder biomass were greater than exchangeable K + and available Pav stocks in technosols. This is important for the nutrition of the trees planted on combustion waste landfills in the future and confirms the deficit of available Pav in combustion waste [6,9]. On oligotrophic sites, the accumulation of nutrients is often greater in the tree biomass than in the soil [38]. The deficits of nutrients in poor soils are balanced by a higher nutrient uptake efficiency [39]. In zones of abundant root biomass, a lower concentration of nutrients is often found in the zone immediately surrounding the roots than in bulk soil. This indirectly confirms that litterfall and its rapid decomposition can play a vital role in the supply of nutrients [40]. However, the rapid production of large amounts of biomass cannot always be the goal of forest management, especially on reclaimed post-industrial sites, as this will result in the depletion of available nutrient resources in soils [38,41]. Black alder, as an N-fixing species, can accelerate the availability of P in soil due to the increased production of phosphatase enzymes [42]. However, Compton and Cole [43] observed a decrease in P availability in soils under red alder (Alnus rubra Bong.) stands, whereas Giardina et al. [44] observed an increase.
Carbon accumulation in technosols under alder species was similar (to 6 Mg ha −1 yr −1 ) to that for post-mining soils in a temperate climate [15,45] and similar to C accumulation in technosols (3-4 Mg ha −1 yr −1 ) built from three technogenic parent materials: papermill sludge, thermally-treated industrial soil and green-waste compost [22]. Carbon accumulation in combustion waste technosol was greater than that in reclaimed sandy soils under Scots pine (Pinus sylvestris L.) stands on the sandy mine (0.73-1.08 Mg ha −1 yr −1 ) and the spoil heap of a sulfur mine (1.15 Mg ha −1 yr −1 ) [15] and is higher than that in sandy soils under natural succession with Scots pine and common birch (0.14 Mg ha −1 yr −1 ) on a sandy mine in Poland [14]. Similar results were also obtained on the spoil heap of the Sokolov lignite mine (Czech Republic), where C accumulation in neogene clayey sediments was 0.15 Mg ha −1 yr −1 under natural succession, and 1.28 Mg ha −1 yr −1 under linden (Tilia cordata Mill.) stands [46]. This may be because alders as N-fixing species can promote a more significant increase in the C accumulation rate in soil than other plant species [23,24]. However, our results also demonstrated greater C accumulation than in the reclaimed mine soils under alder stands on the spoil heap of the Sokolov lignite mine (0.92 Mg ha −1 yr −1 ) [47]. The rate of C accumulation in alder biomass (2. 16-5.89 Mg ha −1 yr −1 ) was similar to or higher than those reported in the literature. For example, the rate of C accumulation in the aboveground plant biomass in the Sokolov spoil heap varied from 0.60 Mg ha −1 yr −1 at the unreclaimed sites to 2.31 Mg ha −1 yr −1 at the larch sites [46]. Carbon accumulation in the biomass depends on the growth dynamics at a young age. Alder species are a pioneer and are characterized by rapid growth at a young age [34,48]. Our results also confirm the high adaptability of alder species to the unfavorable soil conditions of combustion waste landfills [6,7].

Conclusions
Our results confirm the high adaptability of the alder species, particularly black alder, and this should be an essential characteristic of the species utilised in the first phase of the biological stabilization of combustion waste disposal sites. However, the K and P stocks were greater in biomass of black alder than exchangeable K + and available Pav stocks in technosols. This is important for the nutrition of the trees planted on combustion waste landfills in the future and confirms the deficit of the available Pav in combustion waste.
The black alder was characterized by higher biomass than grey alder. The addition of lignite into planting holes positively influenced the ingrowth of the biomass of alder species. The highest amount of nutrients was that which accumulated in the wood of the trunks and branches (40-70% of the stock of the individual macronutrients in the biomass). Although the foliage biomass represented only approximately 7.0% of the total biomass of the trees, the nutrients accumulated in the foliage biomass represented a significant part of the total nutrient stocks, approximately 27-29% N, 17-22% Ca, approximately 28% Mg, 7-10% K and 12-16% P. This is particularly important in the context of SOM recycling from litterfall and the circulation of nutrients in the developing ecosystem on fly ash technosols and the next stage of afforestation by target (climax) species, e.g., oaks or Norway maples. However, vital field study is still needed on the adaptability of such species on combustion waste landfills.