Katri Ots

Use of biofuel ashes in forestry

Bioenergeetikas tekkivate jäätmete kasutamine metsanduses Negative environmental impacts of fossil fuel combustion have increased the use of biomass for energy production. As a consequence of the increased use of biofuels, the production of ashes will increase greatly in the near future. Because of relatively high contents of plant nutrients, biofuel ashes can be recycled as mineral fertilisers to compensate for the loss of nutrients resulting from tree harvesting. The present review aims to summarise the available information on factors affecting the quality of the wood and peat ash and the implications arising from ash application as fertiliser in the forest ecosystems. The understanding of the wood ash as fertiliser originates from the traditional slash-and-burn agriculture. During combustion most elements in wood are retained in the ash. The quality and chemical composition of ashes depends on many factors. The major elements in the ashes are calcium, potassium, magnesium, manganese, sodium, iron, phosphorus and sulphur. Trace elements found in different ash include barium, boron, cadmium, copper, mercury and zinc. The most abundant elements in peat ash are silicon, iron and aluminium. Ashes are characterised by high alkalinity with pH in the range from 11 to 13. Ashes raise the pH and reduce the total acidity in the humus layer and in the top of the mineral soil. The addition of wood ash does not result in a significant growth increase on mineral soils but increases the tree growth on peat soils. The Cd in wood ash did not become bioavailable and harmful to forest biota. The application of wood ash did not change or even decreased the 137Cs activity within forest soil. Wood ash application increased the coverage of the ground vegetation in upland forests and on peatland. Increase in microbial activity and growth rate after ash treatment was observed. Use of biofuel ashes in forestry The positive effect of wood ash on plant growth was understood long ago as better growth of grasses on areas burnt by natural fires was noticed. Scientific study of the effects of ashes began in the first half of the 20th century when the fertilisation experiments with wood ash were started in Sweden (1918) and in Finland (1937). Experiments of fertilisation with wood ash of drained peatlands in Finland are classical and the plots are used for studies up to now. The quality and chemical composition of ashes depends on many factors, including type of the fuel, tree species, type of the plant tissue, degree of the processing of the fuel before combustion, type of the burner and incineration conditions, and proportion of bottom and fly ash in the end product. The major elements in the ashes are calcium, potassium, magnesium, manganese, sodium, iron, phosphorus and sulphur. Ash is generally low on nitrogen because it is vaporises during combustion. Trace elements found in different types of ash include barium, boron, cadmium, copper, mercury and zinc. Compared to wood ash, peat ash contains essentially less mineral elements. The most abundant elements in peat ash are silicon, iron and aluminium. Ashes are characterised by high alkalinity with the pH ranging from 11 to 13. When applied to a soil, ashes will raise its pH and reduce the total acidity in the humus layer and in the top of the mineral soil. A rise in the concentration of base cations has been reported. Wood ash application has been found to increase the levels of extractable phosphorus in humus layer when higher ash doses are used and has little impact on total nitrogen concentrations in soil due to its low levels in the ash. The addition of wood ash does not result in a significant growth increase of trees on mineral soils. The limiting factor for tree growth on mineral soils is in most cases the availability of nitrogen. Wood ash promotes the growth of trees and improves the growth conditions on peat soils, and these positive effects are long lasting. Application of low peat ash doses did not increase the biomass production of trees but has a positive effect when larger amounts are applied. The effects of cadmium on ecosystems and a hazard to human health are of particular concern. There is currently not enough scientific knowledge available to recommend restrictions on the wood ash use as forest fertilizer due to high cadmium concentrations. Generally, the cadmium in wood ash did not become bioavailable and harmful to forest biota. Radionuclide content of forest biomass harvested for energy is related with wood ash application. Results based on experiments show that the application of wood ash does not change or even decreases the 137Cs activity within forest soil and vegetation. On peatlands an increase in the coverage of herbs and grasses and colonisation by nitrophiles has been observed. In addition, sphagnum mosses are substituted by forest mosses. However, wood ash may cause burn damages to bryophytes and lichens. According to some published data, the effect of wood ash on fauna consists in changes in the concentrations of heavy metals and radionuclides in body tissues. In most wood ash studies increased microbial activity and growth rate after ash treatment are reported.

Morphometric parameters of pine needles in Tolkuse bog in the dune field in Southwest Estonia.

Männiokaste morfomeetriast Edela-Eesti luitemaastikku ilmestavas Tolkuse rabas Needle characteristics of Scots pines (Pinus sylvestris L.) in Tolkuse bog (SW Estonia) their length, dry weight and area are discussed. Samples of needles and peat were collected from seven small forest stands in Tolkuse bog in summer 2004. The sampling sites were selected from transect across the bog margin towards its centre (site I - bog margin, site VII - bog centre). Sample branches (n = 30) were collected from the southern sides of the crowns of three trees at heights of 1.5 and 3.0 m. Soil analysis of the samples showed that the pH of peat in Tolkuse bog was in the range 3.3-4.2. The nutrient concentrations of Tolkuse bog peat (% of dry mass) varied as follows: total N 0.7-1.5, total P 0.07-0.14, total K 0.02-0.06, Ca 0.14-0.51 and Mg 0.06-0.22. As compared with other sampling sites a significantly higher concentration of nutrients was observed in the peat at site V. This may explain the best growth of the needles at this site. Site VII, located in the centre of the bog between hollows where bog water is closest to the surface, had the smallest measurements of needles. This indicates that this site has the least favourable conditions for pine growth. Needles growing in the crown at a height of 3 m from the ground had a considerably smaller needle area than those at a height of 1.5 m from the ground. Morphometric parameters of pine needles in Tolkuse bog in the dune field in Southwest Estonia Although in Estonia bog forests are ancient biotopes relatively little affected by human activity so far, the ever-intensifying anthropogenic impacts are beginning to threaten also the existence of bogs. In the Baltic States Tolkuse bog is the only bog with a peripherally oligotrophic development path whose central part has better nutrition conditions than its peripheral parts. In the course of the project changes in the length, dry mass and area of the needles of bog pines were studied moving from the margin of the bog towards its centre. Comparison of the concentrations of N, P, K, Ca and Mg in the upper peat layers in Tolkuse bog with the respective average concentrations in raised bogs, transitional bogs and moorlands revealed that Tolkuse bog was poorer in Ca and also N and P. Site V had significantly higher N, P and Ca concentrations than the other sampling sites. The height growth of 60-90-year-old bog pines was 5,6 ± 1,1 m and diameter 14,2 ± 4,1 cm. The pines of site I had the longest needles (in the crown at a height of 1.5 m from ground on average 3.7 cm and at 3 m 4.1 cm). This shows that marginal areas of the bog have the best conditions for pine growth. The shortest needles were observed in pines growing on site VII (on average 2.7-3.0 cm). This area is located in the centre of the bog and is surrounded by hollows. The average dry mass of a pine needle at a height of 1.5 m from ground was 0.006-002 g and at a height of 3 m, 0.008-0.01 g. Similarly to needle mass, the needle area was largest in site V, located at a somewhat higher position on a bog islet and having higher concentrations of nutrients in peat than other sites. It is important is to preserve the diverse and peculiar bog pine forests in Estonian scenery. In other European countries such forests have preserved only fragmentarily due to intensive human activity. Therefore it is absolutely necessary to continue the monitoring of the status of Estonian bogs and ecological investigations to get information on future trends.

Afforestation of cutaway peatlands: effect of wood ash on biomass formation and carbon balance

Abstract Alternatives to the restoration of cutaway peatlands include afforestation, energy forests, agricultural production, wetland restoration (restoration of peataccumulating function), reed canary grass (energy mower) or wild berries (blueberry, cranberry) cultivation, protected area for birds, and artificial lakes. Investigations made in several countries suggest that one of the most promising ways of regenerating cutaway peatlands is afforestation. The re-vegetation of Estonian cutaway peat production fields is mainly the result of natural processes, which are generally very slow: vegetation covers only 10–20% of a peat field. Carbon dioxide is not bound anymore in cutaway peatlands where vegetation layer has been destroyed and therefore photosynthetical processes no more occur. Using biofuel ashes (wood ash, etc.) for the afforestation of cutaway peatlands helps to balance the content of nutrients in peat substrate, which improves the survival of planted seedlings and significantly increases bioproduction. Drained and mined peatlands have become a significant source of CO2 but stimulated woody biomass production can be helpful to balance CO2 emission from cutaway peatlands. Because of the limited resources of fossil fuels and negative impacts on the environment in recent decades alternative sources of energy have been actively looked for. In Scandinavia a lot of attention has been paid to finding possibilities for using biofuels. The situation in Estonia is that only very few types of ashes (for example certified oil shale fly ash with product name Enefix) have been founded to be suitable for utilization and have been used for recycling in agriculture.

The ecological status of Puhatu cutover peatland

Puhatu ammendatud jääksoo ökoloogilisest seisundist The aim of the present study was estimation of the ecological status of Puhatu cutover peatland in Norteast Estonia. Results of the samples showed that the pH of peat in Puhatu cutover peatland was in the range 5.1-5.5. The nutrients concentrations of peat (%) varied as follows: total N 2.1-2.9, total P 0.016-0.032, K 0.004-0.02, Ca 1.2-3.5 and Mg 0.08-0.2. The height of pines was 3.0 ± 0.6 m and height growth in current year was up to 73 cm. Comparison of our results with the scale presented by Ingestad suggests that the content of P, K and Mg in pine needles and birch leaves is lower and Ca content significantly higher than the optimum level. The ecological status of Puhatu cutover peatland Differently form fields left to lie fallow or forest clearings, vegetation on cutover peatlands is not restored for a very long period of time because the original vegetation has been destroyed and the conditions for the germination of seeds and growth of plants are unfavourable. As the vegetation has been destroyed no photosynthesis occurs in cutover peatlands and so carbon dioxide is not bound any more. Therefore, reclamation of cutover peatlands is of vital importance from the standpoint of environmental protection. Analysis of the samples showed that the pH of peat in Puhatu cutover peatlands was in the range 5.1-5.5. The nutrient concentrations of Puhatu peatland peat (%) varied as follows: total N 2.1-2.9, total P 0.016-0.032, K 0.004-0.02, Ca 1.2-3.5 and Mg 0.08-0.2. The height of pines was 3.0 ± 0.6 m and height growth in current year was up to 73 cm. Comparison of our results of pine needles (100N: 2P: 11K: 13Ca: 3Mg) and birch leaves (100N: 4P: 19K: 14Ca: 6Mg) with the scale presented by Ingestad (scale for pine 100N: 14P: 45K: 6Ca: 6Mg; scale for birch 100N: 13P: 65K: 7Ca: 8,5 Mg) suggests that the content of P, K and Mg in pine needles and birch leaves is lower and Ca content significantly higher than the optimum level. Correlation analysis revealed a statistically significant relationship between mineral elements content (total N, total P, K, Ca and Mg) in pine needles and in peat. For birch significant correlation was established between K, Ca and Mg content in leaves and in peat. As cutover peatlands suffer shortage of nutrients, one of the ways for improving growth conditions of trees and accelerating their growth would be to add peat or wood ash to the growth substrate. The high concentration of P and K in wood ash is of special importance, which creates preconditions for N assimilation and forestation of cutover peatlands. Investigations conducted in Finland showed that the use of wood ash to amend peat soils is promising. Better results in using biofuel ashes to stimulate tree growth have been achieved in peat soils because wood ash contains all elements necessary for tree growth except N. This vitally important element is limiting to tree growth on mineral soils where its content is low, but peat soils contain sufficient amounts of this nutrient while other mineral nutrients are in short supply.