Articles containing the keyword 'drainage'

Models for individual-tree basal area growth were constructed for Scots pine (Pinus sylvestris L.), pubescent birch (Betula pubescens Ehrh.) and Norway spruce (Picea abies (L.) Karst.) growing in drained peatland stands. The data consisted of two separate sets of permanent sample plots forming a large sample of drained peatland stands in Finland. The dependent variable in all models was the 5-year basal area growth of a tree. The independent tree-level variables were tree dbh, tree basal area, and the sum of the basal area of trees larger than the target tree. Independent stand-level variables were stand basal area, the diameter of the tree of median basal area, and temperature sum. Categorical variables describing the site quality, as well as the condition and age of drainage, were used. Differences in tree growth were used as criteria in reclassifying the a priori site types into new yield classes by tree species. All models were constructed as mixed linear models with a random stand effect. The models were tested against the modelling data and against independent data sets.

• Hökkä, E-mail: hh@mm.unknown
• Alenius, E-mail: va@mm.unknown
• Penttilä, E-mail: tp@mm.unknown

The use of random parameter models in forestry has been proposed as one method of incorporating different levels of information into prediction equations. By explicitly considering the variance-covariance structure of observations and considering some model parameters as random rather than fixed, one can incorporate more complex error structures in analysing data.

Competition indices and variance component techniques were applied to 92 Scots pine (Pinus sylvestris L.) -dominated permanent sample plots on drained peatlands in Northern Finland. By quantifying stand, plot, and tree level variation, it was possible to identify the level (stand, plot or tree) at which the explanatory variables contributed to the model. The replication of plots within stands revealed little variation among plots within a single stand but significant variation occurred at stand and tree levels. Positive and negative effects of inter-tree competition are identified by examining simple correlation statistics and the random parameter model.

• Penner, E-mail: mp@mm.unknown
• Hökkä, E-mail: hh@mm.unknown
• Penttilä, E-mail: tp@mm.unknown

The paper is a review on utilization of peatlands in forestry in the countries of boreal zone: Finland, Norway, Sweden, Canada, the United States and the Soviet Union. First, the concept of peatlands, the types of peatlands throughout the zone are defined, and the use of natural peatlands is described. Finally, the drainage of peatlands for forestry purposes in the countries is reviewed. According to the statistics, a total of 13 million ha of peatlands have been drained in Fennoscandia and the Soviet Union.

• Päivänen, E-mail: jp@mm.unknown

The area of stands studied by line plot survey was 594 ha. On the basis of the length of the inventory line the estimated proportion of harvesting strips was 14% and that of ditch openings 6% of the area. The calculated strip road spacing was 29 m. The option of the minimum diameter made it difficult to use the number of stems as criterion for thinning intensity. Thinning intensity evaluated according to the basal area had been stronger than recommended with low values of dominant height and milder with high values. The estimated removal according to stumps was 38 m³/ha on the average between the strips. The real removal has, however, been larger than that, as the strip road openings are made in connection with the first thinning.

The PDF includes an abstract in English.

• Rantonen, E-mail: hr@mm.unknown
• Päivänen, E-mail: jp@mm.unknown

The effect of drainage on structure of tree stands is analysed by comparing the average structural characteristics (e.g. diameter distribution) of stands in the data for different drainage age classes and selected site types. The material consists of ca. 4,400 relascope sample plots, which are part of a large drainage area inventory project. The uneven-aged structure of the virgin peatland forest is preserved for several decades after drainage. This is enhanced by the post-drainage increase of small-diameter trees, especially birch. The number of trees per hectare increased during a period of ca. 30 years and levelled off thereafter. The increase in the number of saw log stems is clearly related to the fertility of the site and its geographical location.

The PDF includes a summary in English.

• Hökkä, E-mail: hh@mm.unknown
• Laine, E-mail: jl@mm.unknown

This bibliography consists of monographs, papers published in periodicals and journals and collections of scientific papers from research and educational institutes, and transactions from scientific congresses, seminars, symposia and meetings.

The publications have been divided into three basic sections. In each section the publications are listed in alphabetical order by the author(s) or title. The total number of the titles in this bibliography is 465.

• Mälkönen, E-mail: –
• Paavilainen, E-mail: –

The present paper deals with the most important factors of peatland hydrology and the influence of forest drainage on the hydrology of peatland itself and its surroundings. It is compiled of six seminar papers written by students in the Department of Peatland Forestry in the University of Helsinki. Special attention is paid to the hydrological consequenses of the maintenance of drained areas. Also ways and measures to minimize the negative environmental effects of these treatments are discusses.

The PDF includes a summary in English.

• Heikurainen, E-mail: lh@mm.unknown
• Joensuu, E-mail: sj@mm.unknown

The paper describes the results obtained from an investigation into the effect of ditch spacing, ditch depth and furrowing on ground water table and on development of a Scots pine (Pinus sylvestris L.) plantation on open small-sedge bog in Central Finland (60° 50’ N; 24° 20’ E), drained in 1967. The area was planted in 1968 with 2+1 Scots pine transplants, and fertilized with Y fertilizer for peat soils. The seedlings were measured in 1972.

The depth of the ground water table was greater, the narrower the ditch spacing. The water furrows shortened the duration of the high ground water and lowered the ground water table particularly in the case of ineffective drainage. The narrower the ditch spacing within the blocks, the higher were the young trees. On the other hand, the differences in the height of the trees between the ditch spacings were eliminated by the effect of the furrows.

The PDF includes a summary in English.

• Päivänen, E-mail: jp@mm.unknown

The study attempts to establish to what extent the present regional allocation of the forest improvement subsidies equalize the profitability of forest drainage in Finland. The benefit/cost ratio has been used to describe the regional variation of the profitability

The study revealed that the forest improvement subsidies granted in 1968, even the highest possible subsidies, did not equalize the profitability of forest drainage. According to the results, the northern regions are at a disadvantage compared to the southern parts of the country. To fully equalize the profitability of forest drainage the average subsidies granted in 1968 should have been raised in the second financing zone from 22 to 32%, in the third zone from 32 to 60%, and in the fourth, northernmost zone from 43 to 86%. The study also suggests that the boundary lines of the financing zones should run, at least in Central and Northern Finland, from southeast to northwest instead from east to west, as it is now.

The PDF includes a summary in English.

• Numminen, E-mail: jn@mm.unknown

The present paper is a preliminary report of a project designed to determine the order of profitability of various forest improvement measures – seeding and planting, drainage, and fertilization – in various types of stands and in different parts of the country on drained peatlands. Sample plot data on the effect of draining on increment was derived from areas drained 28– 36 years ago. The study was carried out in the southern half of Finland.

The observations on increment changes are based on two measurements of the sample stands 12 years apart. Supplementary calculations indicate that the stands on drained peatland, depending on site quality and tree species, have either continued to grow like mineral-soil sites of similar fertility or have somewhat increased their growth rate.

The effect of draining intensity was studied using strip measurements. It was found that both the total amount of wood produced (current stand + cutting removal + natural removal) and the current annual volume increment for the 5-year period systematically decrease as the ditch interval increases. The decrease is, however, relatively slight. In Eriophorum vaginatum pine swamps, the total amount of wood produced and the increment show a decrease of ca. 20% with an increase in ditch interval from 20 to 60 metres. In other sites, the decrease is ca. 5-10%

It can be concluded that if the increase in ditch interval do not result in considerably poorer timber assortment distributions than indicates by stand production and increment, it is profitable to pan for a relatively large ditch interval and a slightly smaller than maximum wood production. Supplementary data and check calculations may cause some changes in these preliminary results.

The PDF includes a summary in English.

• Seppälä, E-mail: ks@mm.unknown

One forest drainage undertaking in Finland often consists of woodlots belonging to several owners, and over hundred owners may be involved. In the present paper a method for allocation the costs to different owners in a joint drainage undertaking is worked out. The problem has been emphasised by the new Waterways Law, which enables also such drainage projects to be undertaken to which some of the land owners oppose. In those cased the costs must be allocated according to the benefit driven by each owner from the project.

The method attempts to assess the benefits to be driven from the forest drainage, those costs of the drainage that are joint and thus subjected to allocation, and what is the area affected by drainage as used as a basis for cost allocation.

The joined costs are apportioned in the following manner. The area of peatland adjusted to differences in the benefit obtained by drainage is ascertained by the land holder by multiplying the index number by the corresponding areas. In the case of cultivated agricultural land, also an index showing the need for drainage is used in computing the adjusted area. Each topographic unit in the map is provided with a notation of its apportionment area. Joined costs are allocated to different land owners in relation to their adjusted land areas.

The PDF includes a summary in English.

• Heikurainen, E-mail: lh@mm.unknown
• Keltikangas, E-mail: mk@mm.unknown
• Seppälä, E-mail: ks@mm.unknown

When ditches are dug in forest drainage, smaller stones are removed by hand, but the larger ones require the use of explosives or stone lifting machinery. Use of explosives have been a more common method for the larger stones. Due to development of detonation methods, it has also been used for smaller stones than earlier.

The investigation was a time study comparing five different stone lifting machines. Time needed for different stages of the work was measured. The stages lasted approximately as long for all of the machines. However, the effectivity of the machines could not be determined, because the stones removed were not similar enough. Stone lifting machine Pekka appeared slightly more effective than the other four machines. It was also easy to assemble, disassemble and move.

The article includes a summary in German.

• Yli-Vakkuri, E-mail: py@mm.unknown

According to the second National Forest Survey, peatlands covered before the World War II 11,156,000 hectares, 32% of the land area of Finland. The early drainage of peatlands in 1700th century had aimed at preventing frost and increasing area of agricultural land. The experiences proved that drainage of wet forests was lucrative also in the point of view of forestry. The drainage of state-owned forest lands was promoted by the Crown Forest Committee in its report in 1900. The systematic drainage work in state lands begun in 1909. In the end of 1920s 500-700 km of ditches was dug annually.

The drainage of private lands begun after 1928, when forestry promotion work in private forests begun. By the end of 1950, 4,815 forest drainage projects had been approved by the Forest Service in the private lands. In addition, 286,000 ha of peatlands was drained on work organized by the central forest associations in 1930-1950, and 239,272 ha by timber companies in 1902-1950. The drained area totalled 755,892 ha. The area of drainable and drained peatland was estimated to be 4.4 million ha.

The article includes an abstract in English.

• Tirkkonen, E-mail: ot@mm.unknown

Silva Fennica Issue 69 includes presentations held in 1948-1950 in the fourth professional development courses, arranged for foresters working in the Forest Service. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service.

This presentation describes the history and present stage of forest drainage in Northern Finland. The first peatlands were drained in the area in 1909. About 6% of the 600,000 hectares of peatlands suitable for drainage was drained at the time in Perä-Pohjola. The areas to be drained are characteristically very large.

• Metsänheimo, E-mail: um@mm.unknown

Silva Fennica issue 52 includes presentations held in professional development courses, arranged for foresters working in public administration in 1938. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service.

This presentation discusses forest management practices of drained peatlands and the allocation of responsibilities in draining of peatlands between district forest officers and forest officers responsible of drainage work. Problems has occured in those cases, when the process of draining had lasted so long that at the time of final assessment of the project the first ditches have already needed maintenance.

• Lukkala, E-mail: ol@mm.unknown

Silva Fennica Issue 39 includes presentations held in professional development courses in 1935 that were arranged for foresters working in public administration. The presentations focus on practical issues in forest management and administration, especially in regional level.

This presentation gives guidelines for draining of peatlands.

• Cautón, E-mail: ac@mm.unknown

The determination of biologically most favourable strip width in peatlands to be drained has been hindered by lack of information of the temperature conditions in the surface peat and in the air close to the ground after drainage of different intensities. Temperature measurements were carried out on peatlands drained to different degrees in Central Finland in the summers of 1960 and 1961. The ground water level in the measuring points, and the strip width served as the criterion for differences in water condition.

When the drainage became more intensive, the temperature of the surface peat decreased. However, temperature differences were small, and discernible only when the differences of water conditions were considerable. The effect of strip condition to temperature seems to be of similar nature than the ground water level. Even in extreme cases temperature differences due to different drainage intensity were relatively small, and seldom exceeded 2°C.

Differences in temperature dependent on the growing stock may be as high as 10°C. Thus, the temperature of the surface peat may be dependent on factors more important than temperature differences caused by aspects of drainage. A well-drained peatland is coldest at the beginning of a growing season compared with poorly drained peatland. The temperature differences increase deeper in the peat. This is caused by the better heat conductivity of the moist peat. Also, daily variations in temperature in the surface peat are large in moist peat.

The PDF includes a summary in English.

• Heikurainen, E-mail: lh@mm.unknown
• Seppälä, E-mail: ks@mm.unknown

The aim of the study is to find out 1) whether and how the original moor type can be found out based on vegetation regardless the phase of drainage; 2) whether the different phases of draining can be distinguished based on the vegetation; and 3) is it possible to classify the well drained moors into vegetation types that would reflect the productive capacity of the land.

The data consists of samples collected from ditched areas. There are 11 moor types from two climatic ditching zones. The results show that the original moor type can be determined based on vegetation, the phase of drainage can be determined under some limitations, and the classification for productivity can be done for practical purposes.    

The PDF contains a summary in Finnish. 

• Sarasto, E-mail: js@mm.unknown

The article deals with forest ditches dug by manual labour in drained peatlands in Central and Southern Finland, ranging in age from 16 to 25 years. The ditches have been allowed to develop in a natural state. A total 1,160 of randomly selected sample plots were studied.

The results show that the originally dug ditch depth has not been the decisive factor from the viewpoint of maintaining the ditch repair. Ditches dug in thick peat layer have maintained their repair better than those dug in thin peat layer. Apparently, the influencing factor is the type of soil, to a certain extent parallel to the thickness of peat layer. In ditches dug mainly in mineral soil, the type of soil has essentially contributed to maintaining the ditch repair. Ditches in coarse-grained soils maintained a better repair than those in fine-grained soils. Also, the steeper the gradient of the ditch the better the ditch repair has been maintained. There was no relationship between the thickness of peat and the filling up of ditch bottom, because of the influence of mineral soil. Filling up of a ditch seems to be mainly due to the sinking of peat. The filling up of ditch bottom was more pronounced in clay-silt soil than in other soil types. The filling up of ditch bottom by varying gradient is due to the fact that with a small gradient the speed of water is so slow as to permit the soil particles to sink to the bottom. Another factor affecting filling up of the ditches is wetness of the peatland. Deepening of ditches happens mainly through erosion, if the gradient is large enough. The study suggests that a 50-m spacing with about 60-cm ditchc depth would be most profitable.

The PDF includes a summary in English.

• Heikurainen, E-mail: lh@mm.unknown

According to the theory of peatland types, particular peatland types, after sufficient drainage, change into certain forest types. It has been found, that the range of forest types in peatlands in different stages of draining is as large as on mineral soil; and comprise Cladina, Calluna, Vaccinium, Myrtillus Oxalis-myrtillus and grove types. Poor peatland types change into poor forest types, better for better types. However, a Swedish scientist Mellin suggested that after effective drainage especially oligotrophic bogs, when well drained, change usually into Myrtillus type.

The different conclusions are due to the fact that the same bog type may develop into different forest types according to the effectiveness and duration of the drainage. Greater the decay of the peat bog layer, the more exacting is the type of vegetation which appears. Bog types of classes V, IV and III (Finnish classification of site quality) change into a Myrtillus type, as do the poorer peatland types of class II. The types vary, however, in their economical drainage value. The fact that bogs which in their natural stage are clearly different in their site quality change after through drainage into the same forest type, is explained by the chemical quality of the peat. However, class I and the best types of class II bogs change into better forest types because they as eutropchic bogs are richer in nitrogen and lime. This difference persists despite of effective draining.

It has been shown that the development of eutrophic peatland types at the forest type stage also differs clearly from the development of oligotrophic peatland types. The Finnish classification of drainage value shows correctly the relative drainability when using normal spacing of ditches. The notes on forest types on mineral soil should, however, be replaced by corresponding notes on the transitive types between bog and forest types.

The PDF includes a summary in Swedish and English.

• Keltikangas, E-mail: vk@mm.unknown

The aim of the study was to investigate how the drain network and dimensions of ditches change after the drainage. The studied drained peatlands were situated in the municipalities of Parkano and Virrat in Central Finland. The ditches were in average 15 and 17 years old. The depth and width in the surface of the peatland were in average one quarter smaller than after the drainage. The width at the bottom of the ditch has, however, almost doubled. Peat had sunken more in peatlands with thick peat layer and higher humidity. Sinking of peat influenced the depth of the ditches. The volume of the ditches decreased about 30%. The decrease of the ditches by the drying and sinking of the peat was greater than the increase caused by erosion.

The PDF includes a summary in German.

• Multamäki, E-mail: sm@mm.unknown

Stones can be removed in drain digging of peatlands by using explosives or hoisting devices. The report is based on observations, and time and motion studies on drainage sites in the state forests in Northern Finland in 1931‒1933. Dynamite has been previously the most common explosive used in drainage sites. The new explosives containing potassium chloride proved to be cheaper, and safer to handle and transport than dynamite. According to the time and motion studies, the use of hoisting devices to lift stones that are removable, was significantly cheaper than explosives.

The PDF includes a summary in English.

• Metsänheimo, E-mail: um@mm.unknown

The article presents the observations made on peatland “Savonneva” in summer 1929 in commune Pulkkila, north-west Finland. The study concentrates on the relationship between groundwater level and growth of trees. The areas was first ditched in 1894, when a main ditch and a side ditch were dug. The ditches were repaired several times, last time a year before the study took place.    

Parts of the area has been taken for agricultural purposes, and other areas have been naturally afforested. The size and abundance of trees varies strongly because the drainage of the area has been uneven. Closer to the main ditch the forest grows better than further away. There is a clear line between the afforested and open areas.

It seems that the tree growth decreases faster with certain groundwater levels than if the groundwater level is deeper.  

The volume 34 of Acta Forestalia Fennica is a jubileum publication of professor Aimo Kaarlo Cajander.

• Kokkonen, E-mail: pk@mm.unknown

The type of the peatland and its classification as forest site (height-over-age-classification) are important information when the drainage potential of a peatland is defined. The gradient and thickness of peat bed are also significant.

The observations for the study have been collected in state owned forests in middle-Finland. The thickness and gradient variations have no clear differences between different types of peatlands. The results show that from the view of drainage for afforestation, the peatlands that are good or suitable for afforestation are flatter and more even that those less suitable. The more suitable peatlands also have thinner peat bed and bigger gradient.

The volume 34 of Acta Forestalia Fennica is a jubileum publication of professor Aimo Kaarlo Cajander.

• Lukkala, E-mail: ol@mm.unknown

Approximately 320,000 hectares of peatlands and paludified lands had been drained for agriculture and forestry purposes in Finland by 1920. The ditch network was not optimal in the early drained areas, and the condition of the ditches declined over time. In this study, the condition of drainage system, and the natural processes that affect them, was inspected in 18 drained peatlands.

Several processes can reduce of the size of the ditches. The process of crumbling of soil in the sides of the diches can last up to three years after the draining. Erosion of the main drains, caused by water flow can, however, continue longer. The ditches also sink when the peat dries. Soil frost can affect the ditches, but as the vegetation grows its effect gradually decreases. The vegetation that grows in the ditches may finally block the ditch completely.

The PDF includes a summary in English.

• Kokkonen, E-mail: pk@mm.unknown

The aim of the study is to find out how do the peatlands develop after drainage and how does the type of peat affect the growing conditions of the forest on it. Study is based on measurements made in summer 1919 in about middle Finland (districts of Loppi, Yläne, Kihniö, Nerkoo, Orivesi, Vilppula, Multia and Karstula). The macroscopic identified content of the peat was analyzed: the different peat types were categorized according the species of the most abundant plant remains. The characteristics of the studied peat types are represented.

The conclusion of the study is that when deciding about the suitability of the drained peatland for afforestation, the thickness and content of the peat must be considered in addition to peat type.   

• Lukkala, E-mail: ol@mm.unknown

An extensive field-based survey was conducted to establish the distribution of site types on drained peatlands, the condition of the drainage networks, the post-drainage development of the tree stands, their structure and silvicultural condition and the corresponding requirements for operational measures. The data is based on sampling of the forest drainage undertaking during 1930–78 and consists of 1,312 km inventory transect, 6,030 relascope sample plots and 21,700 studied ditches.

Of the studied peatlands more than 60% were Scots pine (Pinus sylvestris L.) mires, slightly under 20% Norway spruce (Picea abies) mires, and under 10% each treeless mires and paludified upland forest sites. The remaining peatland area that is to be considered suitable for forest drainage according to criteria used by Heikurainen (1960) now consists mainly of spruce mires and paludified upland forest types; about 1 million ha both groups still remain undrained.

The proportion of ditches in need of ditch cleaning was estimated to be under 10% in the youngest drained areas and under 30% in the oldest. The mean tree stand volumes of the drained peatlands of different site types show the same dependence on the trophic level as in earlier studies but the volumes seem to be some 5–10% lower. These results compare favourably with those of the 7th national forest inventory.

Trends in the post-drainage development of tree stand volumes and increment are also, generally, in accordance with earlier findings but have somewhat lower values. The development of the nutrient-poor site type stands, especially in Northern Finland, seems to be significantly poorer than was earlier assumed.

The PDF includes a summary in English.

• Keltikangas, E-mail: mk@mm.unknown
• Laine, E-mail: jl@mm.unknown
• Puttonen, E-mail: pp@mm.unknown
• Seppälä, E-mail: ks@mm.unknown

Impact of drainage of organic soils in forest land on soil carbon (C) stock changes is of high interest not only to accurately estimate soil C stock changes, but also to provide scientifically based recommendations for forest land management in context of climate change mitigation. To improve knowledge about long-term impact of drainage on nutrient-rich organic soils in hemiboreal forests in Latvia, 50 research sites representing drained conditions (Oxalidosa turf. mel. (Kp) and Myrtillosa turf. mel. (Ks) forest site types) and undrained conditions as control areas (Caricoso-phragmitosa, Dryopterioso-caricosa and Filipendulosa forest site types) were selected. Soil C stock changes after drainage was evaluated by comparing current C stock in drained organic soils to theoretical C stock before drainage considering impact of soil subsidence. During the 53-years period after drainage, the peat subsidence was higher in nutrient-rich Kp forest site type compared to moderate nutrient-rich Ks forest site type (peat subsided by 37.0 ± 4.8 and 23.3 ± 4.8 cm, respectively). In nutrient-rich Kp forest site type, soil C stock decreased by 4.98 ± 1.58 Mg C ha^-1 yr^-1 after drainage, while no statistically significant changes in soil C stock (0.19 ± 1.31 Mg C ha^-1 yr^-1) were observed in moderate nutrient-rich soils in Ks forest site type. Thus, in Ks forest site type, the main driver of the peat subsidence was the physical compaction, while in Kp forest site type contribution of organic matter decomposition and consequent soil C losses to subsidence of the peat was significant.

• Lazdiņš, Latvian State Forest Research Institute ‘Silava’ (LSFRI Silava), Rigas str. 111, Salaspils, LV-2169, Latvia https://orcid.org/0000-0002-7169-2011 E-mail: andis.lazdins@silava.lv
• Lupiķis, Latvian State Forest Research Institute ‘Silava’ (LSFRI Silava), Rigas str. 111, Salaspils, LV-2169, Latvia E-mail: ainars.lupikis@inbox.lv
• Polmanis, Latvian State Forest Research Institute ‘Silava’ (LSFRI Silava), Rigas str. 111, Salaspils, LV-2169, Latvia https://orcid.org/0000-0003-2579-353X E-mail: kaspars.polmanis@silava.lv
• Bārdule, Latvian State Forest Research Institute ‘Silava’ (LSFRI Silava), Rigas str. 111, Salaspils, LV-2169, Latvia https://orcid.org/0000-0003-0961-5119 E-mail: arta.bardule@silava.lv
• Butlers, Latvian State Forest Research Institute ‘Silava’ (LSFRI Silava), Rigas str. 111, Salaspils, LV-2169, Latvia https://orcid.org/0000-0003-3118-1716 E-mail: aldis.butlers@silava.lv
• Kalēja, Latvian State Forest Research Institute ‘Silava’ (LSFRI Silava), Rigas str. 111, Salaspils, LV-2169, Latvia E-mail: santa.kaleja@silava.lv

We used a process-based hydrological model SUSI to improve guidelines for ditch network maintenance (DNM) operations on drained peatland forests. SUSI takes daily weather data, ditch depth, strip width, peat properties, and forest stand characteristics as input and calculates daily water table depth (WTD) at different distances from ditch. The study focuses on Scots pine (Pinus sylvestris L.) dominated stands which are the most common subjects of DNM. Based on a literature survey, and consideration of the tradeoffs between forest growth and detrimental environmental impacts, long term median July–August WTD of 0.35 m was chosen as a target WTD. The results showed that ditch depths required to reach such WTD depends strongly on climatic locations, stand volume, ditch spacing, and peat thickness and type. In typical ditch cleaning areas in Finland with parallel ditches placed about 40 m apart and tree stand volumes exceeding 45 m³ ha^–1, 0.3–0.8 m deep ditches were generally sufficient to lower WTD to the targeted depth of 0.35 m. These are significantly shallower ditch depths than generally recommended in operational forestry. The main collector ditch should be naturally somewhat deeper to permit water outflow. Our study brings a firmer basis on environmentally sound forestry on drained peatlands.

• Hökkä, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: hannu.hokka@luke.fi
• Laurén, University of Eastern Finland, Faculty of Science and Forestry, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: ari.lauren@uef.fi
• Stenberg, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: leena.stenberg@luke.fi
• Launiainen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: samuli.launiainen@luke.fi
• Leppä, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: kersti.leppa@luke.fi
• Nieminen, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: mika.nieminen@luke.fi

The aim of this study was to develop individual-tree diameter and height growth models for Scots pine, Norway spruce, and pubescent birch growing in drained peatlands in Finland. Trees growing in peatland sites have growth patterns that deviate from that of trees growing in mineral soil sites. Five-year growth was explained by tree diameter, different tree and stand level competition measures, management operations and site characteristics. The drainage status of the site was influencing growth directly or in interaction with other variables. Site quality had a direct impact but was also commonly related to current site drainage status (need for ditch maintenance). Recent thinning increased growth of all species and former PK fertilization increased growth of pine and birch. Temperature sum was a significant predictor in all models and altitude for spruce and birch. The data were a subsample of the 7th National Forest Inventory (NFI) sample plots representing northern and southern Finland and followed by repeated measurements for 15–20 yrs. Growth levels predicted by the models were calibrated using NFI11 data to remove bias originating from the sample of the modelling data. The mixed linear models technique was used in model estimation. The models will be incorporated into the MOTTI stand simulator to replace the current peatlands growth models.

• Repola, Natural Resources Institute Finland (Luke), Natural resources, Eteläranta 55, FI-96300 Rovaniemi, Finland E-mail: jaakko.repola@luke.fi
• Hökkä, Natural Resources Institute Finland (Luke), Natural resources, Paavo Havaksen tie 3, FI-90014 University OF Oulu, Finland E-mail: hannu.hokka@luke.fi
• Salminen, Natural Resources Institute Finland (Luke), Natural resources, Eteläranta 55, FI-96300 Rovaniemi, Finland E-mail: hannu.salminen@luke.fi

• Hökkä, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: hannu.hokka@metla.fi
• Hyttinen, Metsänhoitoyhdistys Keski-Suomi, Viitasaari, Finland E-mail: hh@nn.fi
• Marttila, University of Oulu, Water Resources and Environmental Engineering Lab, Oulu, Finland E-mail: hm@nn.fi
• Jämsen, Forestry Centre Keski-Suomi, Pihtipudas, Finland E-mail: jj@nn.fi
• Kløve, University of Oulu, Water Resources and Environmental Engineering Lab, Oulu, Finland E-mail: bk@nn.fi

• Moilanen, Finnish Forest Research Institute, Muhos and Parkano Research Units, Finland E-mail: mikko.moilanen@metla.fi
• Saarinen, Finnish Forest Research Institute, Muhos and Parkano Research Units, Finland E-mail: ms@nn.fi
• Silfverberg, Finnish Forest Research Institute, Muhos and Parkano Research Units, Finland E-mail: ks@nn.fi

• Laiho, University of Helsinki, Department of Forest Ecology, FI-00014 University of Helsinki, Finland E-mail: raija.laiho@helsinki.fi
• Sarkkola, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: ss@nn.fi
• Kaunisto, Finnish Forest Research Institute, Parkano Research Unit, Kaironiementie 54, FI-39700 Parkano, Finland E-mail: sk@nn.fi
• Laine, Finnish Forest Research Institute, Parkano Research Unit, Kaironiementie 54, FI-39700 Parkano, Finland E-mail: jl@nn.fi
• Minkkinen, University of Helsinki, Department of Forest Ecology, FI-00014 University of Helsinki, Finland E-mail: km@nn.fi

• Repola, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: jaakko.repola@metla.fi
• Hökkä, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: hh@nn.fi
• Penttilä, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: tp@nn.fi

• Hotanen, Finnish Forest Research Institute, Joensuu Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: juha-pekka.hotanen@metla.fi
• Maltamo, University of Joensuu, Faculty of Forestry, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: mm@nn.fi
• Reinikainen, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: ar@nn.fi

• Sarkkola, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: sakari.sarkkola@helsinki.fi
• Hökkä, Finnish Forest Research Institute, Rovaniemi Research Station, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: hh@nn.fi
• Penttilä, Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: tp@nn.fi

• Matero, University of Joensuu, Faculty of Forestry, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: jukka.matero@joensuu.fi

• Laiho, Univ. of Helsinki, Dept. of Forest Ecology, Peatland Ecology Group, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: raija.laiho@helsinki.fi
• Penttilä, Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: tp@nn.fi
• Laine, Univ. of Helsinki, Dept. of Forest Ecology, Peatland Ecology Group, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: jl@nn.fi

• Minkkinen, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: kari.minkkinen@helsinki.fi
• Laine, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: jl@nn.fi
• Hökkä, Finnish Forest Research Institute, Rovaniemi Research Station, P.O. Box 16, FIN-96301 Rovaniemi, Finland E-mail: hh@nn.fi

• Silfverberg, The Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: klaus.silfverberg@metla.fi
• Hartman, The Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: mh@nn.fi

• Hökkä, Finnish Forest Research Institute, Rovaniemi Research Station, PO Box 16, 96301 Rovaniemi, Finland E-mail: hannu.hokka@metla.fi
• Penttilä, Finnish Forest Research Institute, Rovaniemi Research Station, PO Box 16, 96301 Rovaniemi, Finland E-mail: tp@nn.fi

• Sundström, Swedish University of Agricultural Sciences, Dept. of Silviculture, S-901 83 Umeå, Sweden E-mail: erik.sundstrom@ssko.slu.se

At sites with either peat or mineral soils in large areas of boreal forests, high soil-water contents hamper tree growth and drainage can significantly increase growth. Hence, areas covering about 15 × 10⁶ ha of northern peatlands and wet mineral soils have been drained for forestry purposes. Usually ditches gradually deteriorate, thus reducing their functionality as drains, and ditch-network maintenance (DNM) might be needed to maintain stand growth rates enabled by the original ditching. This article reviews current knowledge on establishing the need for DNM in boreal forest stands, subsequent growth responses, and the financial outcome of the activity. The issues covered in the review are: (i) ditching, changes in ditches over time and the need for DNM; (ii) interactions between soil water and both stand properties and stand management; (iii) ground-water level (GWL) and tree growth responses to DNM; and (iv) financial viability of DNM. Conclusions about the current understanding of issues related to DNM are drawn and implications for DNM in practice are summarized. Finally, gaps in knowledge are identified and research needs are suggested.

• Sikström, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: ulf.sikstrom@skogforsk.se
• Hökkä, Natural Resources Institute Finland (Luke), Management and Production of Renewable Resources, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: hannu.hokka@luke.fi

The pulse density of airborne Light Detection and Ranging (LiDAR) is increasing due to technical developments. The trade-offs between pulse density, inventory costs, and forest attribute measurement accuracy are extensively studied, but the possibilities of high-density airborne LiDAR in stream extraction and soil wetness mapping are unknown. This study aimed to refine the best practices for generating a hydrologically conditioned digital elevation model (DEM) from an airborne LiDAR -derived 3D point cloud. Depressionless DEMs were processed using a stepwise breaching-filling method, and the performance of overland flow routing was studied in relation to a pulse density, an interpolation method, and a raster cell size. The study area was situated on a densely ditched forestry site in Parkano municipality, for which LiDAR data with a pulse density of 5 m^–2 were available. Stream networks and a topographic wetness index (TWI) were derived from altogether 12 DEM versions. The topological database of Finland was used as a ground reference in comparison, in addition to 40 selected main flow routes within the catchment. The results show improved performance of overland flow modeling due to increased data density. In addition, commonly used triangulated irregular networks were clearly outperformed by universal kriging and inverse-distance weighting in DEM interpolation. However, the TWI proved to be more sensitive to pulse density than an interpolation method. Improved overland flow routing contributes to enhanced forest resource planning at detailed spatial scales.

• Niemi, Department of Forest Sciences, University of Helsinki, FI-00014 University of Helsinki, Finland E-mail: mikko.t.niemi@helsinki.fi