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The present classification of wood degradation factors
1994 - IRG/WP 94-10071
The revised version of classification of wood degradation factors is presented after discussion and remarks sended by IRG-Members. The classification contains the biotic and abiotic factors in two aspects: etiological and symptomatical.
The present classification of wood degradation factors
1993 - IRG/WP 93-10031
Contemporary classification of biotic and abiotic wood degradation factors is presented in two aspects: etiological and simptomatical one.
Factors affecting leaching of preservatives in practice
1978 - IRG/WP 3113
At the 7th Meeting of the IRG in Poland in May 1975, the findings of collaborative laboratory leaching techniques were discussed, and the dangers inherent in using such results to predict the behaviour of preservative-treated components in service were emphasised. In order to improve our understanding of the factors governing leaching of preservatives in practice, and to identify areas where further research is required, it was agreed that a literature review should be prepared. This is presented below. Some points may be made regarding its format and content. First, the review shows that a large number of factors are of importance, including the properties of the wood, the leach water, the preservative and method of application and the nature of the environment to which the product is exposed. In many situations these factors interact and it is clearly impossible within the scope of this short paper to discuss all aspects of the problem in detail. However, the compilation of references will give ready access to the literature on particular topics. For ease of collation, the findings are discussed under a number of different headings. Secondly, less than one-third of the references cited deal with the results of service or field trials, while the others describe laboratory experiments designed to provide comparative data. The reservations expressed above concerning such small-scale experiments must be borne in mind when considering the validity of these findings. The information available on this topic up till 1964 was comprehensively reviewed by Wallace who identified and commented upon many of the factors discussed below. Her paper contained discussion on the performance of individual preservatives and on the mechanism of their fixation within the wood. These topics will not be considered here in any detail except insofar as they reflect general trends.
R Cockcroft, R A Laidlaw
Factors affecting the sorption of preservative during diffusion treatment of wood
1988 - IRG/WP 3500
The sorption of preservative into wood during soaking in aqueous solution was found to comprise absorption as well as diffusion of solute. Absorption was increased by partially seasoning the wood prior to soaking and was characterised by (a) a very rapid initial rate of uptake and (b) an extended period of slow uptake, the rate of which varied with prior conditioning. It was concluded that some partial seasoning was desirable to optimise absorption (and therefore reduce soaking times), but that extensive partial seasoning would not significantly increase the quantity of solution taken up during short soaking periods, because of the back pressure from air which tended to become embellished in the wood during soaking. The factors influencing the retention of solute following momentary immersion were identified and included: 1. Surface roughness (which may be influenced by the basic density of the wood species together with the wood sawing or machining processes used); 2. The critical surface tension of the wood substrate; 3. The solubility of the solute; 4. The surface tension of the solution. It was found that during momentary immersion the surfaces of the wood become saturated very quickly. When stored overnight under non-drying conditions however, there was movement of the solution from the surface to the coarse capillary structure of the wood. Subsequent dipping in solution resaturated the surface of the wood. Thus by a process of multiple dipping preservative retentions could be increased as though timber had been kept in the solution.
Influence of abiotic factors on the production of Basidiocarps by lignocellulolitic Hymenomycetes from native forest and plantations of Pinus elliottii Engelm in the Fontes do Ipiranga State Park, São Paulo, Brazil
1991 - IRG/WP 1469
A report on the influence of abiotic factors on the production of basidiocarps by lignocellulotic Hymenomycetes of native forest and Pinus elliottii. It was concluded that the climatic conditions (temperature, humidity, microhabitat) and the decay stage of the logs affected the production of basidiocarps by Hymenomycetes.
M Aparecida de Jesus
Controlled fixation technology
1995 - IRG/WP 95-50040-12
Controlled fixation techniques have been developed and adopted in a number of countries where chromium containing preservatives are predominantly used. The purpose of this technology is to reduce both on-site pollution and holding requirements for freshly treated timber. The fixation mechanism is complex and the time taken to complete the reaction is dependent upon a number of factors. A number of countries have proposed or introduced methods for measuring and standards for defining fixation. These are discussed in relation to the different technologies which have been commercially introduced throughout the world.
M Connell, W J Baldwin, T Smith
Chemical, physical and biological factors affecting wood decomposition in forest soils
2003 - IRG/WP 03-20281
Organic matter (OM) decomposition is an important variable in determining the potential of forest soils to sequester atmospheric CO2. Studies using OM from a particular location gives site-specific decomposition information, but differences in OM type and quality make it difficult to compare results among soils and forest ecosystems. By using a “standard” OM in decomposition studies, OM quality is held constant, and decomposition is a function of soil abiotic (moisture, temperature, O2/CO2, redox potential, pH, N, P, etc), and biotic (microbial biomass, functional diversity) properties. Wood is a good standard material to use in soil OM decomposition studies, since it is a normal soil component (woody residue, coarse roots), and a slow decomposition rate allows wood to remain in the soil for a number of years. In 1998 a wood stake study was initiated on both public and industry land throughout the U.S., Canada, and Europe. These sites represent a variety of climatic conditions and forest types, which cover a wide range of soil chemical, physical, and biological properties. Wood stakes of two tree species are being used to contrast different lignin types present in wood: loblolly pine (Pinus taeda), and aspen (Populus tremuloides). The objectives of this study are: (1) to determine the effects of abiotic soil properties on wood decomposition, and (2) to assess how these soil properties affect microbial activity and diversity during wood decomposition. This paper will present an overview of the study protocols, field and laboratory methods used, and discuss preliminary results from several of the study sites in North America and Europe.
M Jurgensen, P Laks, D Reed, A Collins, D Page-Dumroese, D Crawford
Moisture uptake and volumetric swelling as probable factors also affecting leaching in CCA-treated wood. A preliminary study of treated Eucalyptus saligna sapwood
2003 - IRG/WP 03-30318 IRG/WP 03-30318
A number of factors affecting leaching of CCA from treated wood have been variously investigated and discussed. However, the possible effects of moisture movement in treated timbers on leaching have not received attention yet. The present study examines and compares moisture uptake and volumetric swelling in CCA-treated and untreated sapwood of Eucalyptus saligna, and tries to establish a correlation between the mechanics of moisture movement, swelling and shrinking, and leaching. Small samples of E. saligna sapwood were air-dried to 12% MC, pressure-treated with CCA-C (oxide) at a commercial treatment plant, conditioned for 28 days, leached in static water, re-dried to 12% MC and average retentions (8.2 Kg/m3) calculated on a weight-gain basis. The samples were divided into two batches, including untreated controls, oven-dried to constant weight and weights recorded. One batch of samples (including controls) was soaked in de-ionised water until water-saturated, and moisture uptake calculated on a weight-gain basis. The second batch, including controls, was measured to calculate oven-dry volumes. They were then similarly water-saturated, removed, measured and volumetric swelling computed. Water-saturation increased the MC of the treated samples to 67.69% on average, compared to 89.29% in untreated samples. Volumetric swelling in treated samples was similarly lower (6.19%) than in untreated controls (6.59%). However, both moisture uptake and volumetric swelling were significant in treated samples. Exposure to conditions of alternating wetting and drying, as in soils, with intermittent moisture uptake and release, and resulting swelling and shrinking may accelerate removal of CCA from treated timbers, and allow faster microbial colonisation and degradation of the wood. High leaching of CCA and early microbial attack, especially bacterial and softrot fungal attack, is common in CCA-treated timbers exposed to wet soils, where a higher volume of treated timber is normally used. It is probable that leaching of CCA from timbers exposed to soils is accelerated by movement in the wood caused by intermittent moisture uptake, swelling and shrinking.
Investigation on different variation factors in the results of mycological test and means to reduce and avoid them
1986 - IRG/WP 2264
In order to clarify the causes of the dispersion observed in the results obtained with mycological tests made in accordance with standard EN-113, different factors assumed to be sources of the variations were studied. These included the moisture content of the test samples during the test, the influence of certain technological properties of the wood, the virulence of the fungus strains, the method by which the test pieces were treated and the effect of the solvent, and behaviour of the wood fungus in contact with the wood preservative. It turns out that certain factors which were supposed to be important are actually secondary (humidity). On the other hand, the virulence of the strains is a major problem and requires a serious examination. Treatment by dipping with a ready-to-use product might avoid errors due to obligatory dilutions. In the end, wood species other than beech and Scots pine be used. However, one must not lose sight of the fact that there is a risk that the toxic values may not always be identical.
Attractive factors of steam-treated larch wood to termite feeding
1998 - IRG/WP 98-10256
The hot water extractives from steam-treated Japanese larch wood were studied to understand the chemical properties of attractive factors of the treated wood to feeding behavior of a subterranean termite, Coptotermes formosanus. Hot water extractives were fractionated and analyzed using chromatography, gel filtration, and NMR methods. The stimulants yielded by the steam treatment were comprised of phenolics and saccharides, which were highly polar constituents. In addition, the stimulative effect was possibly accelerated by the degradation of flavonoids such as taxifolin originally included in untreated larch wood.
S Doi, Y Kurimoto, W Ohmura, M Aoyama, S Ohara
Some factors affecting the treatability of spruce roundwood with ammoniacal preservative solutions
1976 - IRG/WP 371
Permeable wood species for use in preservative-treated commodities are becoming depleted in Canada. Spruce can be a convenient replacement for them from local resources provided it can be treated to levels adequate for protection of commodities in ground contact. Basically, two approaches were taken to improve treatability of difficult-to-penetrate softwood species; first, to improve the permeability of wood and second, to improve the penetrating properties of liquids. The first approach involves various means of wood pre-treatment: biological (enzymes, moulds and bacteria including ponding), chemical (removal of extractives), mechanical (precompression) and technological (presteaming of green wood, replacement of water in wood by solvents). There are a great many publications devoted to individual topics mentioned here indicating the significance of the subject. The second approach is the selection of a solvent capable of penetrating into the wood better than conventional solvents for, preservative compounds.
A Review of the Factors Affecting Permeability in Softwoods
2004 - IRG/WP 04-40278
This paper reviews the literature discussing some of the qualities and properties of softwood that characterise its refractory nature and influence its treatability. This review covers mainly the period of 1954 to 1997. Literature prior to this period is included where it is thought that existing reviews have not adequately reported the subject matter or alternatively to provide background information for the topic. Earlier literature has been well covered by such reviews as Anderson et al. (1941), Tiemann (1944), Jane (1956), Hunt and Garratt (1967), Kollmann and Cote (1968), Comstock (1970), Siau (1971), Nicholas (1972), Skaar (1972), Arsenault (1973), Nicholas and Siau (1973), Stamm (1973), Wilcox (1973), Findlay (1975), Wilkinson (1979), Panshin and de Zeeuw (1980), Zobel and van Bujitenen (1980), Dinwoodie (1981), Siau (1984), Wilson and White (1986), Tsoumis (1991), Eaton and Hale (1993), and Langrish and Walker (1993). Aspects emphasised in this review are both direct and indirect factors which control permeability in softwoods, and how the softwood structure affects residual flow in respect to preservative treatment
Biostatic film as a primary treatment against pole failure in soil
1995 - IRG/WP 95-40053
Field liners of low density polyethylene (LDPE) film applied as primary treatment of soil-contact surfaces of creosote-treated poles prevented their detoxification and premature failure by establishing hurdles against microbiological colonisation. These hurdles include low water activity, low oxygen tension and nutrient limitations. Moreover, under conditions of high soil moisture, field trials showed that the hurdle of toxicity provided by creosote is maintained by LDPE films which prevent it from leaching. However, such liners must remain intact to confer sustained protection. Susceptibility of LDPE to termite damage and to possible microbiological damage in the long term led to the development of materials resistant to biodeterioration. A dry film preservative (DFP) was incorporated with masterbatch for use in LDPE manufacture. Laboratory tests showed the masterbatch granules to be biocidal against soil microorganisms, confirming that neither the moulding temperature nor the immobilisation of the DFP in the masterbatch had neutralised the antimicrobial properties of the DFP. The masterbatch was then used to produce LDPE film which, with unpreserved control film, was applied as liners to surfaces of untreated Eucalyptus grandis posts. All posts were placed under flood-irrigation in termite-infested soil in Natal for eight months. Preserved liners remained intact and the wood under these was uncolonised by microorganisms or termites. Some control films, and the wood under them, had been destroyed by termites, and wood surfaces under the other control films which appeared intact were visibly colonised by fungi.
A A W Baecker, M Behr
Factors affecting resistance to sapstain infection in freshly felled softwood logs
2003 - IRG/WP 03-10467
Previous studies in the UK have shown a marked difference in the susceptibility of logs of five softwood species to infection by sapstain fungi over a 4 month field trial. Recently this result has been confirmed and the rank order of greatest to least susceptibility in these commercially important species is lodgepole pine > Scots pine > Norway spruce > Japanese larch > Sitka spruce. Changes in moisture content and nutrient levels have also been assessed during the trial, as well as a study of differences in the resin composition of each wood species using GC-MS. Resin tapped from healthy, standing trees has been analysed and spectra derived from each species were compared. Resin formed at the edge of lesions on the outer sapwood surface, following inoculation of fresh billets with Sphaeropsis sapinea, has also been analysed. Factors influencing sapstain resistance are discussed.
E J Young, R A Eaton, J F Webber, M A W Hill
Field test design for service life prediction of wooden components
2005 - IRG/WP 05-20308
Wood is predominantly degraded by organisms. Thus, compared to other building materials, service life of wooden material is influenced by many more factors, which are divided into direct and indirect factors. Climate, geographical position, and construction criteria count to the indirect decay factors. Besides material inherent properties (natural durability, wood preservatives), wood temperature, wood moisture content, and the presence of certain species of wood degrading organisms are the strongest direct factors influencing service life of wooden building components. On this account an experimental set up was developed to quantify these direct decay factors: Field tests were performed in European Hazard Class 3 (EHC 3) to determine the influence of macro and micro climate on decay progress and decay factors such as temperature and moisture content of wood. Therefore Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) have been positioned in double layer test devices since 2000. Thirty-two sites in Europe and the United States representing preferably different climatic conditions were chosen for exposure of the test devices. For all sites, data on climate were available since they were located next to an official meteorological station. This way all relevant climatic factors (precipitation, air temperature, relative humidity, sunshine duration, wind) are correlated with MC and temperature of the samples to be measured once a minute and logged once a day. Furthermore the samples were evaluated respecting to decay and discolouration every year according to EN 252 (1990). Preliminary results concerning the influence of macro and micro-climate show that this approach will provide a sufficient data base for a better understanding of the most important factors determining decay.
A O Rapp, C Brischke
A non-pressure method of protection based on hurdle theory to control the spectrum of internal environmental factors which affect the decay of poles in soil contact
1993 - IRG/WP 93-20005
A field trial was conducted to establish whether superficial barrier linings on poles in soil contact could function as environmental hurdles against the growth of biological agents and thus provide preventative methodology to preclude premature failure of vineyard poles under flood-irrigation. Assessment after 52 weeks exposure to the prevailing conditions and sub-tropical environment showed that open-ended cylindrical linings of biologically inert heat-shrink polyethylene applied to the vertical soil-contact surfaces of Eucalyptus grandis poles unequivocally prevented termite-induced failure of untreated poles, basidiomycete decay of creosote-treated poles and fungal colonisation of CCA-treated poles. The success of the liners in prevention of incipient decay of these poles was explainable on the basis of hurdle theory and was therefore attributed to the ability of the former to control essential growth factors and create internal conditions inimical to the proliferation of decay agents in the poles. Consequently, sub-optimal conditions of Aw, Eh, and nitrogen content were considered to have arisen to function as environmental hurdles which decay agents could not overcome at wood-soil interfaces.
A A W Baecker
Factors affecting decay rates in a fungus cellar II
1986 - IRG/WP 2259
Tests were initiated to investigate the influence of various factors on the decay rate in a "Fungus Cellar". Birch and pine stakes treated with chromated copper arsenate and didecyldimethyl ammronium chloride, as well as untreated control stakes, were incubated in two soils in a Fungus Cellar test and installed at two field sites for comparative purposes. The visual rating vs actual stake weight loss relationship was also studied. Preliminary results from the initial Fungus Cellar test indicated differences in decay rates between birch and pine and also between soils. The decay rate observed for pine stakes was generally lower than birch in both soils. The decay rate was greatly accelerated in a Michigan soil with birch and pine over that observed in a Florida soil. Soil type had less impact on the primary decay present in the stakes. Soft rot was the primary decay associated with treated wood in both soils, while soft rot, basidiomycete, or combinations of the two were frequently found in untreated wood. The range of weight loss vs visual rating relationship was similar between wood species, treatment, and soil type. Weight losses tended to "overlap" the visual ratings regardless of the decay type.
P A McKaig
An investigation of the factors influencing the rate of deterioration of timber samples due to microfungi in laboratory tests
1997 - IRG/WP 97-20116
An investigation was performed into the comparative performances of test 1 (vermiculite burial) and test 2 (soil burial) as described in ENV 807. Two test preservatives were used - copper naphthenate and propiconazole. Copper chromate was included as a reference preservative. The wood species used was beech (Fagus sylvatica). Test 1 was performed using both a mixed inoculation of the five stipulated softrot fungi, and separate monocultures of the test fungi. This enabled an assessment to be made of the individual performance of each fungus with the various preservative types, highlighting any incidence of preservative tolerance. Test 2 was performed as described in ENV 807. Isolations were made from test blocks in both tests where weight loss approached 3% m/m. In test 1 isolations were performed on samples from the mixed inoculation test, and in test 2 every 8 weeks throughout the 32 week duration. The results of this investigation show that the tests do not yield comparable results. Test 2 proved to be a more virulent system. The vermiculite test can only be relied upon when the microbial ecology of the treated wood in practice is known, as with copper naphthenate.
I J Herring, D J Dickinson, S M Gray, J K Carey
Strategies for enhancing usage of treated wood in Indian context
2005 - IRG/WP 05-40305
India constitutes 2% of the world’s forest area but it has to support over 15% of the human and nearly 14% of the cattle population and therefore forests in India are under immense biotic pressure. The main concern today is the rate at which avoidable factors or man made threats accelerate the process of forest degradation and to evolve measures to check the same. Man made threats include exploitation and use of forests for commercial purposes in a non-scientific way. The need of the hour is to preserve our natural forests which can be done by utilization of man made forests scientifically. Wood continues to be an extensively used raw material for diverse, domestic, individual and structural applications such as housing, bullock carts, boats, toys, handicrafts, agricultural implements, furniture, fishing craft etc. Growing demands, diminishing supplies and the intensity of resource has led to acute shortage and phenomenal hikes in prices of conventionally preferred species and therefore, attention is now diverted towards fast growing plantation species to augment wood supply. However, most of these timber species are naturally non-durable or moderately durable and need protection from biological aspects like fungi, bacteria, termites, borers etc. Technologies such as preservative treatments can enhance the service life of timber several times and can save millions of well grown trees. However, the quantity of timber being treated in India is negligible as a favorable operation regime for scientific processing especially wood treatment does not exist. Compounding the problem is extremely weak, user group-researcher linkages, low level of technology development, technology absorption, extension efforts and non existence of R & D industry-researcher- end user association. These issues are discussed in detail in this paper.
P K Aggarwal, S C Gairola
Industrial fixation systems: key factors, limitations and optimisation through the use of computer simulation modelling. Discussion paper
1994 - IRG/WP 94-40026
This paper briefly describes four fixation operative in the Netherlands, namely: circulating and non-circulating steam fixation cylinders, steam fixation chambers and controlled climate rooms. The general limitations of industrial practice are reviewed against the background of established fixation theory. The controlling variables, both material and process-related, for fixation processing are specified. The capabilities of computer simulation modelling to highlight and provide solutions to these problems is illustrated.
A J Pendlebury, M Riepen, M J Boonstra, W Gard
Working plan: Second international collaborative field trial
1995 - IRG/WP 95-20056
This paper describes the scope, objectives, and approaches to be used in the second international collaborative field trial approved by the Scientific Programme Committee for partial funding in 1994. The trial is designed to develop a broad data base on causal mechanisms, interactions, and factor affecting the performance of treated wood in ground contact. The trial encompasses 12 different field test sites representing all continents except Antarctica. Preservatives were chosen to represent new technologies and include oilborne, waterborne copper-organic, and water-dispersible systems. CCA is used as the reference system. Task forces to research the following areas are described: accelerated soilbed testing, decay types/modes of failure, preservative depletion, abiotic factors, and copper tolerance.
H M Barnes, T L Amburgey
An analysis of the effects of some factors on the natural durability of pine (Pinus sylvestris L.) and spruce (Picea abies Karst.)
1986 - IRG/WP 1279
The effects of some factors on the natural resistance of pine and spruce sapwood against fungal decay and against attack of house-longhorn beetle larvae have been studied in laboratory tests and the results are evaluated by analysis of variance and regression analysis. Following conclusions were reached: Wood from summer-felled trees did not have a lower inherent natural durability against fungal decay and house-longhorn beetle than wood from winter-felled trees. Storage of pine logs in water had no significant effect on the weight losses obtained in laboratory tests with Gloeophyllum sepiarium and Fomitopsis pinicola but reduced the weight losses obtained with Phlebiopsis gigantea very significantly. In the case of outdoor use of wood, this result implies that the decreased nutritive value of wood from water-stored logs for certain fungi to some extent compensates for the effect of increased permeability. Wet storage also reduced the growth of house-longhorn beetle larvae. The effects of density on weight loss by fungal decay were different for the three test fungi. The growth rate of the house-longhorn beetle larvae in the inner sapwood was much lower than that in the outer sapwood. In comparison with between-trees variation and with differences between outer and inner sapwood the other observed effects, each on its own account, are of minor practical importance for larval growth.
J B Boutelje, T Nilsson, S Rasmussen
Factors affecting decay rates in a fungus cellar
1985 - IRG/WP 2242
Birch and pine stakes treated with chromated copper arsenate and didecyldimethylammonium chloride were incubated in two soils in a "Fungus Cellar" test. At three month intervals, sets of stakes were inspected and assigned visual ratings or removed from the soil beds for weight loss determination. Preliminary results after nine months exposure have shown differences in the decay rates between birch and pine and also between soils. Overall, the decay rate for pine, treated and untreated, has been considerably lower than birch in both soils. A Michigan soil accelerated the decay rates up to 3 times that observed for a Florida soil. Soil type also influenced the primary decay present in the stakes. Basidiomycete attack was observed in birch stakes treated with subthreshold retentions of both preservatives in the Michigan soil, while the primary decay in the Florida soil was soft rot. Untreated birch controls failed through basidiomycete attack in both soils. Soft rot was the primary decay in treated and untreated pine for both soils. However, more data is needed to determine if this trend will continue. Weight losses as low as 9.3% caused stake failure (visual ratings of 0). Basidiomycete damage caused stake failure at lower weight losses than soft rot. Regardless of the decay type, threshold retentions selected by weight loss or visual ratings were similar.
P A McKaig
Factors affecting the resistance of fibre building boards to fungal attack
1975 - IRG/WP 252
Fungal decay is initiated at lower moisture contents in standard and tempered hardboards (18%) than in pine sapwood (26%). In contrast, in a saturated atmosphere, the equilibrium moisture contents of standard hardboard (14%) and of tempered hardboard (12.5%) are much lower than the moisture content permitting decay initiation whilst the equilibrium moisture content of pine sapwood (25.1%) approaches its decay initiation level. When immersed in water the hardboard, especially when tempered, took much longer to wet to decay initiation moisture contents than the pine sapwood but, on the other hand, the hardboards dried at much the same rate as the solid wood. It is concluded that the physical changes which occur during hardboard manufacture are such that under fluctuating service conditions, even when liquid water is intermittently present, hardboards tend to remain at risk from fungal attack to a much lesser extent than solid wood.
C Grant, J G Savory
An Investigation on Use and Durability of Some Industrial and Domestic Woods of Iran against Destructive Factors in Caspian Sea
2008 - IRG/WP 08-10636
In this study the use of domestic and commercial woods of the Caspian Sea forest fringes and evaluation of their durability against marine destructive factors were investigated. The samples of elm (Zelkova carpinifolia), oak (Quercus castanifolia), beech (Fagus orientalis), Maple (Acer insgin), Alder (Alnus subcordata), and horn beech (Carpinus betulus) species were impregnated with CCA (Chrome–Copper-Arsenic). Treated and untreated (natural as a control) woods have been established for 3, 6, 9 and 12 months in Amirabad beach of Behsharhre under fishing environment. The results of observations showed that in this beach, the staining fungi and balanus were able to attack control woods or live on them. With increasing woods maintaining in the sea, their presence became longer. The numerical results of samples weight loss showed that durability of control wood samples after one year made less than 5 % in weight losses of elm, maple, alder, and horn beech. However, control samples of oak and beech had no weight losses. The treated samples not only had no weight reduction, the absorbed salts made their weight increase. Low salinity level of Caspian Sea with respect to salinity of large sea (oceans), made absence of wood drilling worms in Caspian Sea and this may be the main reason of non- destructive wood samples.
S M Kazemi