Suo - Mires and peat 26 (1975)

This study is a sequel to papers previously published on the possibilities of extending the period of planting Scots pine (Pinus silvestris L.) on drained open peatlands over the entire growing season (Päivänen 1968, 1971), The study was carried out using the same plots as in the experiments described in the above-mentioned papers. This final investigation was carried out in order to find ou t whether the differences recorded in the previous studies had been leveled out or accentuated when 9—11 growing seasons in the field had elapsed since planting. As the smallest unit which the study was based on was a single row of young trees, the study must be considered as being completed by now. This is because the interactions between adjacent tree rows will become significant as soon as the crowns and root systems get closed. Mortality still increased by a few per cent units during the last 5—6 growing seasons. This increase, however, was of similar magnitude irrespective of the planting date. In the mean height of the trees, on the other hand, the differences caused by differences in the planting date were clearly visible in the final inventory (Figs. 1—3). The differences in height development had even become accentuated by the time of the final inventory, 9—11 growing seasons after planting. A clear correlation was observed, in the case of all experimental members, between the mean heights recorded in the final inventory and that carried out after the trees had spent four growing seasons in the field (Fig. 5). According to the results obtained the season-alness of planting work can be decreased on drained peatlands by extending the planting season of pine till the turn of the month between July and August. Plantings performed in the fall usually proved slightly less successful than those carried out in June and July. The nursery ought to be situated close to the areas to be planted since the handling and transportation of unrooted plants during the growing season must take place with extreme care.

• Päivänen, Sähköposti: ei.tietoa@nn.oo

The study showed that the levels of copper, boron, zinc and cobolt in organic soils are in general lower than those in mineral soils. However, for manganese it was quite the opposite. There were no clear differences found between the levels of molybdenum and selenium in different soil types. Trace element levels in different geographical areas varied considerably. Since the results of this study indicate that the trace element situation in agricultural soils appears to be following an unfavourable trend, the situation must be closely watched by means of cultivation studies. Good yields must be mainted if the food requirements of people and livestock are to be met.

• Kurki, Sähköposti: ei.tietoa@nn.oo

During the last five years a number of foresters and research workers in Finland have noticed the increasing occurrence of a growth distur-bance in 10—15 year old peatland stands. This phenomenon is referred to as "eskimosis" in this paper. The symptoms do not resemble those of any of the known nutrient deficiencies and as far as we know it does not appear to be caused by insects or fungi. The symptoms of eskimosis in Pinus silvestris are as follows; — young samplings have long branches — apical dominance is lost — lammas growth is common — terminal shoots may become branched — needle lenghts vary within wide limits — elongation growth is suppressed — dark green colouring and sturdy external appearance of saplings Apparently 1—2 years after these almost invisible symptoms first appear, eskimosis kills the apical parts of the "infected"" trees, usually from one to three whorls, during late winter (die back). Some trees develop 2—3 leaders without any additional symptoms, but usually eskimosis is repeated year after year causing cessation of height growth, giving the tree a flat-topped appearance with plenty of dead needles distributed throughout all parts of the trees. At this stage of eskimosis, resination of the buds, necrotic spots on the needles and browning inside the shoots proceeding from the apical parts, are typical secondary symptoms. After some years the cambial growth may also be suppressed as a result of the decreased amount of green needles. Eskimosis results in thick-stemmed and stunted trees which very often die. An investigation programme has been started by the Department of Peatland Forestry, the Finnish Forest Research Institute, and some preliminary results are published in this paper. Eskimosis may infect pines, spruces and birches on drained peatlands as well as on mineral soils. Phosphorus fertilization often increases the likelihood of eskimosis developing. The first attempt to cure eskimosis, was carried out in a drained spruce stand, by fertilizing with micro-and macro-nutrients. The greatest increase in radial growth was achieved with NP fertilization, although the spruces survived even without any fertilization. Boron had a slightly positive effect on visible symptoms. Eskimosis was apparently caused by P-rich litter from the previously felled pine stand which had been fertilized with phosphorus some years prior to felling. The young spruce stand lost its shelter stand and subsequently received much easily soluble phosphorus from the P-rich litter. The largest known eskimosis area lies at Kivi-suo Experimental Fields, Leivonmäki, in pine plantations established in 1959. Kivisuo, Exp. 1^ lay-out, 4x4x4 NPKwith two replications, planting spacing 2 m, ditch spacing 22 m, earlier used as a drying field for hydro peat, originally an open Sphagnum bog with rimpis, fertilization in 1959, refertilization 1968. During refertilization, the plots were divided into three parts; a = broadcast fertilization, PK(0-17-15) 500 kg/ha b =spot fertilization. PK(0-17-15) 50 g/ sq.m c = control A couple of years after refertilization was carried out, eskimosis appeared. It seems that eskimosis is largely a result of the original micro-relief of the bog and is further increased by the highest P and K levels (eg. Huikari and Paarlahti, 1973). Another investigation was carried out in 1975 with the following results: the elongation growth of the trees was decreased most on plots which received broadcast refertilization and least on the control plots (Fig. 1.). The situation was about the same in Experiment V which was spot fertilized in 1959 (spot size 0,25 sq.m) and refertilized in 1966 in a similar way as exp. 1. Eskimosis also appeared soon after refertilization. A decrease in tree heights induced by eskimosis was observed (Fig- 2). Experiments under greenhouse conditions using substrate taken from sites where eskimosis is prevalent have shown that this Scheuchzeria-rich peat is deficient in N, K and B even after previous site treatments with NPK and PK at high levels. This may be the solution to the problem at Kivisuo. It will require perhaps another 2—3 years to confirm this before our micronutrient experiments will provide us with the final details. "

• Veijalainen, Sähköposti: ei.tietoa@nn.oo

Total contents of various trace elements in Finnish soil types are presented. The tendency for the trace element content to decrease with increasing particle size in mineral soil is discussed. It is believed to be associated with the geological origin of the soil matrix and especially with the relative resistance to weathering of the minerals from which the trace elements are derived. Fine textured soils are likely to have been derived from more easily weatherable rocks and minerals than coarse soils, in which resistant minerals like quartz are known to be the main constituents. On the other hand, those minerals containing the trace elements in question are among the most easily weatherable, while quartz is likely to contain none of these elements. The characteristic distribution of 13 trace elements in two peat profiles X', as well as the low content of most elements in peats as compared with those in mineral soils are explained as a result of the transport of elements by plants from lower strata: The trace elements can be considered as originating from the mineral soil underlying the peat. Plants which grow and then decay, first on the mineral soil and later on the peat, obtain the trace elements from the subsoil and, when dying, cause these elements to accumulate on the surface layer. When the peat layer becomes thicker contact between the plant roots and the mineral subsoil is gradually reduced until finally the bulk of the roots are no longer in contact with the mineral soil. Subsequendy, the plants lift up elements from the lower peaty layers of the profile, thus decreasing the element content of the lower parts of the peat. For this reason, the trace element content in the peat profile decreases as the peat thickness increases; extreme cases of this development are the "raised bogs" of Sphagnum peat which are known to have a very low content of all the nutrients. The relatively high concentration at the immediate surface is obviously a result of the elements lifting activity of the most recent generations of plants; the elements have been lifted to the surface and are awaiting removal by future generations of plants. x) Orig. pubi.: Sillanpää, M. 1972. Distribution of trace elements in peat profiles. Proc. 4th Intern. Peat Congr. I-IV: 185-191.

• Sillanpää, Sähköposti: ei.tietoa@nn.oo

The article deals with the oligotrophic-eutrophic and ombrotrophic-minerotrophic gradients in peatlands. The use of these terms in Finland, Sweden, the Soviet Union, Central Europe, Canada and England is briefly reviewed. In the case of peatlands, the concept of eutrophy, as defined by most authors, implies high pH, high levels of calcium and nitrogen, but its relationship to phosphorus and potassium levels (which greatly affect the tree growth and productivity) is not so clear. It is important to make a distinction between trophic series related: (1) to primary production, and (2) to pH (Ca)gradient. For the former, the terms oli-go-, meso- and eutrophic seem appropriate (as in the case of limnology); for the latter, the following four categories could be used: ombrotrophic, weakly-, moderately- and strongly minerotrophic. Apparently some authors have also used the terms soligenic or rheotrop-hic as synonyms for minerotrofic.

• Pakarinen, Sähköposti: ei.tietoa@nn.oo

The results of an experiment concerning the artificial regeneration of a pine stand growing on old drainage area are presented in this article. The area was clear-cut during the winter 1970-71. Six experimental plots were laid out on the area in summer 1971, three of them being control plots. Soil preparation was carried out on the remaining three plots. A tractor digger was used to make turf hummocks by lifting scoop-fulls of peat and placing them upside down on the ground at two meter intervals. The hummocks were then compressed by the digger scoop. In spring 1972 Scots pine transplants (2+1 years) were planted out on the hummocks and on the untreated peat surface of the control plots. The survival rates of the transplants are presented in Table 1. The average height and height growth of the surviving plants in different years can be seen in Table 2. The transplants growing on the hummocks have survived and grown better than those on the untreated peat surface. Eriphorum vaginatum has spread vigorously on the untreated peat surface of the control plots and has tended to check the growth of the seedlings. Damage caused by frost heaving was not observed. This planting method thus appears to be a useful soil preparation technique in the regeneration of old drained stands.

• Mannerkoski, Sähköposti: ei.tietoa@nn.oo

A field experiment was established at the Arctic Circle Experiment Station (66°35') in Northern Finland in the year 1970. There were altogether four N-fertilization treatments: 75, 150, 300 and 600 kg N/ha and two PK-fertilization treatments: (43.5 P + 100 K) and (87.0 P + 200 K) kg/ha. The dry-matter yields are presented in Fig. 1, the crude protein yields in Fig. 2 and the crude protein contents in Fig. 3. It was found that the yields of Italian ryegrass were greater, the stronger the fertilization treatment used. The highest dry-matter yield was over 8000 kg/ha and the highest crude protein yield over 2000 kg/ha. Moreover, the crude protein content was surprisingly high: at its best over 25 %. The suitability of annual Italian ryegrass in Northern Finland in comparison to perennial grasses was discussed. The most important advantage of Italian ryegrass is perhaps its annual nature since, when fertilization is carried out, it is not necessary to make allowance for overwintering as is the case for perennial grasses in Northern Finland.

• Pohjonen, Sähköposti: ei.tietoa@nn.oo

• Ranta, Sähköposti: ei.tietoa@nn.oo

The study deals with the trampling tolerance of a drained pine swamp type, very common in Finland. Measurements of the sinking and wearing of peat and vegetation were performed at Jaakkoinsuo near Vilppula (62°04'N, 24° 34'E) on a thick (1—2 m) peat layer drained in 1909 (Fig 1). An assistant, weighing 70 kg made the trampling along the 5 meter long lines at the following levels: 0, 1, 2, 4, 8, 15, 30 and 50 times per week during 12 weeks (experiment a) and 0 or 100 times in June, July or august (experiment b). Measurements were carried out with ten replications. The main results of the study were as follows: All trampling levels differed significantly from 0 level. Trampling levels 1-8 did not differ significantly from each other. Trampling levels 30 and 50 differed from all the other levels significantly (Fig 2). This means that trampling 12 times per summer makes a visible path into the peat surface. Trampling 180—360 times per summer makes almost all living parts of the vegetation to die, small roots to crack and thicker roots to denude resulting obvious damages in rhizosphere. The monthly trampling experiment revealed that the august trampling produced the deepest pathway in the peat (Fig 3). A year after the trampling was carried out, another measurement at experiment a was conducted. No significant development was observed (Fig 4). It means that pathways, on peat-land types in question, take several years to recover after the trampling. Even the lowest levels of trampling were measurable and visible after one summer without trampling. All this calls our attention to the question about pathway construction on our experimental areas, along the excursion routes everywhere with more than 200 visitors per year.

• Veijalainen, Sähköposti: ei.tietoa@nn.oo

Mechanical forest drainage has been a rather extensive branch of Finnish forestry for some fifteen years already. At its peak in the late 1960s mechanical forest drainage reached an annual output of 80 000 km of ditches, corresponding to 60 mill, m3 of excavating and nearly 300 000 ha of drainage area. At the present time forest drainage, which is fully mechanized, produces some 65 000 km of ditches annually. About 10 % of this amount is dug for improving the drainage effect in old drainage areas. 5 000 — 6 000 km of old ditches are being cleaned annually. 75 % of the digging work is carried out using light excavators, 20 % using heavy plowing equipment and the remaining 5 % using ordinary excavators or rotary ditchers. Most of the mechanical work is carried out by contractors. Contract work in the field of forest drainage for the State, or supported by the State, has followed, since 1961, the general instructions for construction works for the State. These intructions, however, apply only poorly to drainage operations, and consequently, the 350 —400 small-scale enterpriser (owners of 1—2 machines) working in the field of forest drainage in Finland, have demanded for a long time already that guiding prices for forest drainage be worked out and that working contracts covering longer periods of time than before be arranged. The employers were ready for a positive attitude toward contract work based on guiding prices only as late as in the 1970s. On the basis of decisions taken by the authorities and of agreements concluded between the parties concerned, the first one-year period with guiding prices for mechanical digging began on the 1st of April 1975. The recommendation concerned is now used by the National Board of Forestry, the Central Forestry Boards, the State Fuel Centre and the Metsäkoneurakoitsijain Liitto (Union of Forest :- Machine Contractors). The recommendation covers slightly more than 90 % of all forest drainage activities. The former way of procedure, based on free competition, is still in use abreast with the new system, particularly in the case of plowing. The experiences gained so far from contract work based on guiding prices are mainly positive. The strain on the labor market has been reduced, and over-aged equipment is being changed to a large extent into new machines. Despite the positive initial experiences, however, the system is not ready yet, but the digging difficulty classification involved, for example, requires further revising.

• Niskanen, Sähköposti: ei.tietoa@nn.oo

The aim of the study was to clarify, in what degree nitrogen is needed when fertilizing drained pine swamps in North Finland. Particular interest was laid on the fertilization of peatland types rich in nutrients. Further, the dependence of the fertilizer-induced growth reaction on ditch spacing and thickness of peat layer were considered. The growth reaction resulting from fertilization was estimated by measuring the annual height and radial growth on differently treated experimental plots and by using analysis of covariance. Further factors considered in the analysis were peatland type and its so-called sub-class, depth of peat layer, ditch spacing, age, height and diameter of the sample trees at the time of fertilization, and sample tree growth before fertilization. When fertilizing tall sedge pine swamps and more fertile pine swamps for the first time in Ostrobothnia, Kainuu and southern Lapland nitrogen deficiency seems not to be a minimum factor as regards the growth of Scots pine. On the other hand, it seems necessary to include nitrogen in the first fertilization treatment on less fertile pine swamps than mentioned above. According to the study, the growth of Scots pine subsequent to fertilization appears to be the better, the narrower the ditch spacing and the thinner the peat layer. More detailed information has been published by Paavilainen and Simpanen (1975).

• Paavilainen, Sähköposti: ei.tietoa@nn.oo

Newfoundlands metsän tutkimuskeskuksessa on kolme tutkimusosastoa — metsänsuojelu, metsävarat sekä ympäristötieteet— joista kahdes-sa viimeksi mainitussa on suoritettu soiden metsätaloudelliseen käyttöön tähtäävää tutkimustoimintaa Puunjalostusteollisuus ja metsähallitus ovat olleet mukana näissä hankkeissa. Syksyyn 1974 mennessä oli kertynyt runsaasti biologista perustietoutta tältä alalta (aiemmin mainittujen lisäksi mm. Dickson 1971; Hall 1971; Pollett 1969, 1971; Pollett ym. 1970, 1974; Richardson ja Chaffey 1973; Wells ja Roberts 1973). Tämän vuoksi Newfoundlands metsäntutkimuskeskus kutsui kirjoittajan kuukaudeksi kehittämään paikallisiin olosuhteisiin soveltuvia kuivatusratkaisuja. Vanhimmat, vuodelta 1966 peräisin olevat, avosoiden ojitus- ja metsänviljelykokeet on perustettu lähinnä skotlantilaisten esikuvien perus-teella. Kentät sijaitsevat erittäin ravinneköyhillä» tuulille alttiina olevilla peittosoilla. Kun oikean ojituskaluston puuttuminen on johtanutvielä selvään vajaakuivatukseen, on metsänviljely lähes täysin epäonnistunut. Ravinnetaloudeltaan paremmilla ja suojaisemmilla alueilla japanilainen lehtikuusi (Larix leptolepis) (kuva 2), musta-kuusi (Picea mariana) ja meikäläinen mänty (Pinus silvestris) ovat tutkituista puulajeista menestyneet parhaiten. Koska vanhoja metsäojitusalueita ei ollut olemassa, pyrin tarkkailemaan satunnaisten kuivatusten vaikutusta soilla kasvavien puiden kasvuun. Saaren läpi kulkevan rautatien varsilla saattoi havaita, että pitkäaikainen kuivatus (noin 60 vuotta) oli parantanut mustakuusen kasvua (kuva 3). Parhailla suotyypeillä näytti Kanadan lehtikuusi (Larix laricina) reagoivan erittäin positiivisesti kuivatukseen. Esimerkkinä mainittakoon Potentilla — Campylium stellati -letto, jonka läpi on kaivettu noin kaksi metriä syvä valtaoja lähes pääkaltevuuden suuntaan valtatien reunaojien vesien poisjohtamiseksi. Yhdeksän vuoden kuluttua ojituksesta oli havaittavissa, että luontaisesti syntyneiden ja kaivuhetkellä n. 30 cm:n mittaisten lehtikuusten pituuskasvu oli ollut sitä suurempi, mitä lähempänä ojaa ne kasvoivat (kuva 4). Mahdollinen metsäojitus tulee tapahtumaan ilmastonsa puolesta saaren edullisimmassa osassa (kuva 1), jossa sademäärä on pienin ja tuuli ei ole yhtä voimakas kuin rannikkoalueilla. Valtaosa ojitettaviksi suunnitelluista soista on avosoita, ja koska tuulen haitallinen vaikutus pyritään minimoimaan, tulevat ojitettavat kuviot olemaan pienialaisia (1—10 ha). Ojitettavia suokuvioita löytyy kuitenkin hyvin läheltä toi-siaan, joten järkevän kokoisia ojitushankkeita on suhteellisen helppo muodostaa. Alueiden kaltevuussuhteet ovat yleensä hyvät. Luonnonpuroja on runsaasti, joten valtaojien kaivu tarve on vähäinen. Myös kasvualustan ravin te isuuden puolesta parhaita metsäisiä soita ja vedenvarvaamia kangasmaita tultaneen ottamaan ojituskohteiksi. Kotimaiset puulajit ovat tällöin mustakuusi ja Kanadan lehtikuusi. Metsänparannustoimenpiteiden suoritusta ajatellen saaren maanomistusolot ovat ihanteelliset Pääosa alueistahan on "kruununmaata". Alueilla, joilla hakkuuoikeudet on vuokrattu pitkäaikaisilla sopimuksilla metsäteollisuudelle, metsien hoito ja perusparannukset kuuluvat edelleen provinssin metsäviranomaisille. Käytettävissäni ollut aika oli tietysti liian lyhyt, jotta täydellisiä ojitussuunnitelmatöitä maastossa olisi voitu ajatellakaan. Valmistamani raportti sisältääkin lähinnä kuivatusteknistä perustietoutta sekä ojien asettelun malliesimerkkejä osaksi todellisiin suokuvioihin osaksi hypoteettisiin tapauksiin tarkoitettuina (Päivänen ja Pollett 1975). Suurimpana puutteena tähän mennessä suoritetuissa ojituskokeiluissa on ollut sopivan met-säojituskaluston puuttuminen. Vesivaotus on yleensä suoritettu Parkgate-auralla, vetokoneena on käytetty kahta 45 hv:n International T5 traktoria. Varsinaisten kuivatus- ja valtaojien kaivuun ei ole ollut sopivia koneita käytettävissä ja pelkkä vesivako-ojitus ei ole johtanut toivottuun kuivatustulokseen. Sopivan kaluston ja ammattitaitoisen miehistön puute on ajateltukin ensi vaiheessa ratkaista siten, että Newfoundlandin provinssin metsä-viranomaiset tekisivät sopimuksen jonkun suomalaisen kaivuriyrittäjän kanssa, joka koneineen ja koneen tarvitsemme huolto- ja korjausvälinein varustautuneena matkustaisi muutamaksi kuukaudeksi Newfoundlandiin näyttämään suomalaisen kaluston ja ojitustekniikan soveltuvuutta sikäläisiin olosuhteisiin. Tämän jälkeen päätöksentekijöiden on helpompi valita jatkavatko he ulkomaisten urakoitsijoiden käyttöä, ostavatko he koneet ulkomailta vai pyrkivätkö he kehittämään omista koneistaan suosovellutuksia. Selvää on myös, että itse suunnitteluhenkilöstö tulee tarvitsemaan koulutusta. Nähtäväksi jää joudummeko me Suomessa joskus järjestämään ojituskursseja kanadalaisille metsänhoitajille ja metsä teknikoille. Eräs mahdollisuus on tietysti jonkinlainen "avaimet käteen11 -urakointisysteemi täysin suomalaisin voimin. "

• Päivänen, Sähköposti: ei.tietoa@nn.oo

In the study of the effectiveness of forest drainage the conclusion has usually been made that trees grow better, the more effective the drainage. Thereby it has usually been understood that drainage should be effective all the year round. However, it is not self-evident that maximum effectiveness of drainage throughout the year is the best situation with regard to tree growth. Particularly the rapid discharge of water from melted snow leads often to overdrainage in the early summer in the case of effectively drained peatlands, and this may be unfavorable with regard to tree physiology and to the nutrient mobilization processes taking place in the soil. Likewise, the rapid discharge of melting water from drainage areas is an unfavorable phenomenon with regard to the water situation in watercourses. The aim of the present study was to assess the possible influence on the growth of Scots pine of a regulation of the runoff. In the expe-riments carried out the ground water table was artificially adjusted to a level very near the ground surface for periods of varying length in several subsequent years. Circumference growth of the trees included in the study was determined using the banding method. Fluctuations in the depth of the ground water table were also measured. According to the results so far obtained from these experiments, which are still very young, the requirements of trees on drainage are diffe-rent during different seasons of the year. A high ground water table, and on the other hand, effective drainage, influence tree growth in different ways during different seasons. In accordance with the results obtained so far effective drainage should be maintained at least during the late summer and fall. Keeping the ground water very near the ground surface for a period of some length in July-August affects the growth of pine to a considerable extent. A slight check of growth was observed even in those cases where the ground water table had been raised for a long time in September, October and November. On the other hand, at least up to the present time the experiments did not reveal any negative effect from ground water that had been kept at the ground surface in winter and spring. As a matter of fact, there are signs pointing toward the possibility that saving water in the site by damming during this season might even increase the growth of pine. On the basis of the results obtained from the present study the exact time when the water from melted snow should be released can not be told. It seems, however, that this moment is in the middle of June on the average. If the ground water table is kept at the ground surface from the spring until the month of July, a negative growth effect is recorded. The means required for the regulation of the runoff can be obtained at a relatively small additional cost. The possibility of regulating water discharging from forest drainage areas may be beneficial also in connection with reforestation of the drainage area, and with heavy fertilization, in fire control and for the promotion of berry production. Possible regulation of the runoff from drainage areas of course affects also the water situation in watercourses. This effect depends on the proportional share in the total area and the location of the dammed peatlands in the watershed area, and also, on the effectiveness of the measure.

• Pelkonen, Sähköposti: ei.tietoa@nn.oo

The article presents results of tensiometer measurements in peat soils. Measurements have been taken both in the field and in the greenhouse. The plots in the field experiment represented different stages of drainage in ordinary sedge bog. Plot 5 was in a virgin state, plot 6 had been drained in 1967, and plot 3, in the 1930's. Each plot had one tensiometer at each of the three measuring depths. (5, 20 and 40 cm). In the field the depth of the ground water table was also measured using self-registering gauges. In the greenhouse experiment the water table in the soil samples was artifically regulated by raising it straight from the deepest level to the topmost level, and lowering it after every 2-3 days (see Fig. 3). The results are presented in figures 1-4. The soil water tension and hydrostatic pressure values obtained with tensiometers show a close correlation with those concerning the ground water table in case when the measuring unit has been near the water table or below it. Evapo-transpiration and rainfall caused a variation to the relationship between the water table and soil water tension at the depth of 5 cm, particularly when the water table was deep (30-40 cm) (Fig. 2). The effect of evapotranspiration can be seen also in the results of the greenhouse experiment (Fig. 4). In this experiment the effect of the rise of the water table was not as great as expected. The reason for this may be too short a time for levelling (2 days). The results show that tensiometers can be used also for measurements on the depth of the ground water table if it has a sufficiently assu-rate manometer and if the measuring unit is kept near or below the ground water table.

• Laine, Sähköposti: ei.tietoa@nn.oo
• Mannerkoski, Sähköposti: ei.tietoa@nn.oo

In a drained area, the average flowing distance to a ditch is directly correlated to the ditch spacing. Accordingly, the flowing time and ditch spacing are directly correlated. Because the natural state is approached as ditch spacing is wide enough it is obvious that surface runoff is speeded up by drainage. If the runoff curve corresponding to a certain hydrograph is known for a drained peatland area with a 40 m ditch spacing, theoretical runoff curves corresponding to the same hydro-graph can be constructed for any alternative spacing (fig. 1). By constructing a runoff curve for a large alternative spacing, for instance 400 m, an estimate of the minimum change caused by drainage can be obtained. During a long spell of rainfall with a constant rain intensity, an equilibrium is achieved in which the surface runoff from a drained strip equals to the amount of precipitation falling on to it in unit time. Theoretically, the time required for achieving the equilibrium is independent of the rain intensity (Mustonen 1963) and directly correlated to the ditch spacing. Consequently, theoretical surface runoff curves corresponding to rainfalls with constant intensity can be constructed if the equilibration time (t ) is known for a drained peatland area. The outlines presented above might be used for estimating the effects of forest drainage on flooding provided that the runoff curves for the points susceptible to flooding are known (fig. 2). The most difficult part of the estimation process is to separate the drained-area-runoff from the totalrunoff curves. Further, it may be labourious to determine an average t value for the drained parts of a catchment area. The model may be critisized because infiltration and evaporation effects have been neglected, and because it is based on rainfalls with a constant intensity. It is probable, however that peak runoff is not much influenced by infiltration end evaporation if rainfalls causing floods are considered. The disturbing fact that the intensity of a rainfall usually varies with time can be partly eliminated by using the runoff distribution curve method (Mustonen 1963), which makes it possible to separate the influences of different rain intensities from a runoff curve. The ideas dealt with in this paper are based on the hydrological experimentation carried out by the Department of Peatland Forestry at the Finnish Forest Research Institute (Huikari 1959, Huikari et.al. 1966, Ravela 1967). The aim of this experimental activity is to understand the physical interdependencies connected with the hydrological influences rather than to determine the magnitude of the influences by direct observations and using time-series statistics. It is obvious that the empirical approach, based on representative experimental fields and decades of field measurements, proves unrealistic if the limited research capacity and the extensive drainage activity carried out in Finland are considered.

• Ahti, Sähköposti: ei.tietoa@nn.oo

The main content of this paper has been published in English by Valmari (1974). The use of organic waste materials for manuring forest seems to offer, at least in the conditions prevailing in Northern Finland, a method which both from an economic and from an ecologic view point is acceptable and available in cases where ploughing into the soil of tilled fields is for some reason an inferior method.

• Valmari, Sähköposti: ei.tietoa@nn.oo