METEOROLOGICAL DISASTERS IN SLOVENIAN FORESTS-HOW TO APPROACH THE RESTORATION IN OUR SPECIFIC CONDITIONS

In recent years, forests are exposed to various meteorological disasters. The climate change and warming of atmosphere cause more intensive and frequent occurrences in the atmosphere. This is also reflected in Slovenian forests in particular in the form of windthrow, snow-damage, landslides and avalanches, and in 2014 a catastrophic ice storm. Some forecasts indicate that the future will bring more of this kind of disasters. The ice storm in the last year stroke the land the most in history, in particular in terms of damaged trees and areas. According to the available data, the damaged quantities of trees represent more than a two years planned annual cut in Slovenian forests, while about a half of the country was affected. The majority of the damaged wood comes from private forests. The remedying of such extensive meteorological disasters is demanding, dangerous and prolonged it is also hindered by the specific ownership structure of the forest land in Slovenia and its average size. 75% of all forest have private owners, and this land is fragmented with a large number of forest holders. An average forest land is only 2.3 ha per individual owner. In these conditions, the following questions have to be answered: who, how and in what time is it possible to remedy the caused damage? What is the current quality of wood which was damaged in many ways in the meteorological disaster? Is it possible to use more modern felling technologies and wood transports from the forest in so fragmented private land?


INTRODUCTION
In recent years, we are a witness of numerous climate changes and related meteorological events.The intensity and, in particular, the frequency of these events are visibly increasing.During such occurrences the amount of energy in the atmosphere is raising and also affects the forests -there is an increasing number of meteorological disasters resulting in damaged trees and forest floor.Recurrent heavy storms and damages they cause are measured and monitored by foresters in their analyses mainly by the quantity of damaged trees and the size of affected forest areas.
Disturbances in forests are not something new -they are constantly recurring.This article tries to point out the increase of meteorological disasters in Slovenia in the recent years.These are windthrow, snow-damage and damages caused by landslides and avalanches -in particular, the emphasis is put to the ice storm that in 2014 affected the highest number of Slovenian forests so far.This disaster was the largest in terms of scope and also the quantity of damaged trees so far.
What to expect in the future?According to the foreseen changes of weather, in particular the in-tensification of weather events, there is a strong likelihood of an increased number of meteorological disasters.Consequently, these will cause more damage in forests.The severity of damages may be reduced by implementing adequate measures -the knowledge and understanding of physical characteristics of individual types of meteorological disasters, their impacts on forests, as well as potential silvicultural and protective measures are essential in this regard (Jakša, Kolšek 2009).

FACTORS CAUSING METEOROLOGICAL DISASTERS
According to the definition, the meteorological disaster is an event where additional means of work must be used, special work organisation introduced and specialised work techniques applied in the restoration process.All the abovestated calls our attention that such phenomena cause different conditions of management in the affected area -the meteorological disasters are therefore emergency situations.
They are: • unpredictable in space and time; • unpredictable in terms of duration, location and scope; • suddenly there are large quantities of damaged or decayed standing trees; • timber harvesting is heavily hindered, additional qualified workers are required; • additional investments in the infrastructure, silviculture and protective works are necessary.In addition, the work costs are higher, the value of forest wood products is reduced due to damages, while large quantities of wood also cause problems related to its marketing and storage.
Unpredictable factors causing this situation and defining the conditions of measures are in particular the following: • wind; • snow; • landslides and avalanches; • ice storms.They usually occur separately, but even more often in combination with other meteorological events.Main findings and characteristics of indi-vidual factors are recapitulated from several previous publications (Jakša, Kolšek 2009, Papež et al. 1996).

Wind
Slovenia is located in the area with predominantly west winds.In particular, the lee location under the Alps causes predominantly poor average wind speed and a great share of calm.Occasionally, there are winds blowing during the summer storms causing damages in forests.In these cases, they reach the speed up to 40 m/s and more.In one of such thunderstorms in 2006, the wind blew over Jelovica breaking 85,000 m 3 of mainly spruce trees in the area of 106 ha in less than 20 minutes.In the central and north part of Slovenia, 20,000 ha of forest and 500,000 m 3 of wood mass of forest trees were damaged by the strong wind in the summer 2008.700 ha of forest were completely destroyed.The most known and frequent wind in Slovenia is the Bora -a strong, gusty, cold, predominantly dry wind blowing from the northern quadrant, in particular from the north-east.It is the strongest in the south-west part of Slovenia with its gusts reaching the speed over 50 m/s (180 km/h).This wind usually has no destructive impact on the forest, but blows through tree crowns that have truncate growth and expand in the wind direction.Due to the acclimatisation of vegetation and forests to the constant and strong Bora, it normally causes few mechanic damages in forests.However, in combination with fire, the Bora may also cause large-scale damages in forest stands.If forest catches fire during the Bora (in particular, the south-west part of Slovenia is an above-average dry area during the summer), the fire can spread also to large areas.With the wind, the fire may spread also with the speed of 100 m/min or spring across the distances of several hundred meters by small wood pieces afire.Similar to the Bora is the Karavankefoehn (north part of Slovenia), which caused large-scale damages in forest stands below the Karavanke mountain range in recent years.
The impact of the wind is very diverse.In addition to the impact on morphological characteristics of trees, drying of soil and plants, spreading the pollen and atmospheric pollution, this study of the impact of the winds focuses particularly on its uprooting and breaking of trees.The phenomenon can be local or affect large areas.It has many different forms: uprooting the whole tree, breaking a part of a tree and bursting a trunk.Regarding the forest protection and scope of damages caused by the wind, the most important impacts are the uprooting and breaking of trees.This in particular refers to those species which are more susceptible to the wind due to their shallow root system (spruce, Douglas fir, green pine) or tree species with large crowns (beech).A large devaluation of wood bass is caused by trunk bursts, whereas the uprooting of the whole tree causes the largest damages in terms of the ecosystem.The restoration after meteorological disasters is usually a very dangerous and demanding task and calls for experienced, well-equipped and patient workers.At the same time, the problems with wood storage, transport and marketing occur due to large quantities.

Snow
Snow-damages in Slovenia normally occur every year, in particular in the area of Alps -the reason lies especially in large amounts of snowfall and mainly one aged spruce stands that are particularly exposed to snow-damages.These types of damages generally affect the coniferous trees, i.e. spruce and pine trees.Deciduous trees may also be at risk -in particular if the snow falls on crowns with leaves still on.In older stand development phases, the wind breaks tree tops (spruce, pine), damages trunks, sways and uproots the whole trees.Snow often causes the breaking of trees also at the forest edge and damages to all edge vegetation in forest -i.e. in all those cases where trees develop asymmetric crowns.

Landslides and avalanches
Avalanches cause the most damages in forests.They are most frequent in the Alpine area, causing damages to coniferous trees in particular (Jakša, Kolšek 2009).In other areas, landslides are more frequent, in particular as a result of prolonged heavy rains.In this case, the deciduous trees are affected the most.

Ice storms
Ice storms cause glaze ice of different thickness on the trees.This phenomenon requires the temperature inversion, cold surface and heavy rain with the negative ground air temperature.It usually, occurs at higher altitudes of the Dinaric Alps up to 900 m.So far, glaze ice affected the south-west and south part of Slovenia.Last year (February 2014), it also covered the central part of Slovenia, at the largest surface up to date and also at lower altitudes.This was the largest ice storm disaster so far, causing damage to more than 9 million m 3 of timber.Our past experience in such events usually always shows a greater damage to deciduous trees that are also more susceptible due to their crown forms, position and surface of their branches.This event was no different, only that this time also older spruce stands were damaged due to a great quantity of glaze ice lasting for a couple of days.Not only the tree tops (red pine and spruce), but also the extensive stands of old spruce tree were affected.

THE IMPACT OF NATURAL DISASTERS ON THE STRUCTURE OF LOGGING IN FORESTS
Extreme weather events (wind, snow, landslides and avalanches, ice storms) can be a direct or indirect cause for salvage logging.The direct cause due to damages to trees (overturn, broken trees, damaged tree crowns), and indirect cause due to subsequent increase in number of insects harmful to trees.Often it is a combination of the weakening of trees after natural disastersand more favourable conditions for the development of harmful organisms.
According to the data of the Slovenian Forest Service (the 1995-2010 period) the share of salvage logging is 31%, i.e. 882.000 m 3 or 0.27% of the growing stock in terms of the total annual cut (Kolšek 2013).One third of logging is carried out due to damaged trees in natural disasters (34%), while one third is executed due to harmful insects (34%).The rest is felled due to various diseases, harbivores and pollution.The data by individual years are shown in Figure 1.Two periods stand out, i.e. the first in the 1995-1999 period -2 million m 3 of trees were felled in this period due to the snow and ice storm damage.2008 stands out in the second part with heavy windthrow resulting in approximately 500,000 m 3 of felled trees.
The disasters have an important impact on the DBH distribution of logging and therefore also on its assortment structure.Snow and ice storms more frequently damage thinner trees, with no significant differences between coniferous and deciduous trees.On the other hand, the wind causes more damage to trees with high DBH (Jakša and Kolšek 2009).Windthrow most frequently affects the lower part of a trunk, where there is a greater part of wood mass, and also the loss is the highest in terms of value.The figure shows that abiotic factors as causes of annual logging present an important share in the majority of areas.However, they are locally differently present.The forecasts of climate change shows that there will be more intensive events in the atmosphere above our territory -thus, meteorological disasters will be more recurrent in the future.Weather phenomena will definitively have an important impact on the share of damages in forests in the future -in addition, also growing sites and stand conditions may increase the level of damage.While we cannot change weather and growing site conditions, our proper forest management may create such stand conditions that will reduce the risk of forest tree damages.Damages after natural disasters are minimal in forests with established biotic diversity, i.e. in areas with natural structure of tree species, with appropriate vertical and horizontal structure of forest stands (Kolšek 2013).
The stated facts definitively contribute to the reduction of consequences of natural disasters.However, they only reduce and not prevent the consequences!This was also true for the ice storm last year, which exceeded all previous disasters in the past period in terms of its intensity and duration.

THE 2014 ICE STORM AND RESTORATION
A large part of Slovenia was affected by the so far the heaviest storm ice in the history between 30 January and 10 February 2014 -in terms of area as well as quantity of damaged trees.Snow also contributed to the severity of the disaster concerned, since it covered the tree tops just before and also during the glaze ice formation.The heavy rain, wetting and softening the forest floor a few day before the disaster added to its severity.Thus, this natural disaster may be defined as a combination of glaze ice, snow-damage and heavy rainfall.It was a combination of all three factors that caused such extensive and various consequences.The most intensive glaze ice formation occurred on February 1 and 2, while at higher altitudes snow additionally affected the spruce tree tops.Glaze ice was thickening on trees until 5 February 2014.It was the thickest in the area of Pivka in Postojna, i.e. up to 8 cm.According to the data of the Slovenian Forest Service, the forests in Slovenian Primorska region up to 500 m of altitude, in Sub-Pannonian area of the east Slovenia and upper mountain forests in the areas above 1200 m remained unaffected.The more affected areas are forests between the coastal-Karst area and the central area (area of Postojna), in the south-west edge of Ljubljana basin and in the Cerklje and Idrija area.
The situation is recapitulated according to the Slovenian Forest Service data and restoration plan prepared for this catastrophic event (Forest Restoration Plan ..., 2014).The Plan includes 51% of forest area in Slovenia affected by this disaster and also areas where the salvage logging and all measures for restoring damaged forest are necessary according to an expert opinion.The evaluation of the quantity of wood damaged by similar disaster is usually only an estimate due to difficult access to the affected areas in the first days after the event.The damage results mainly in uprooted, broken, burst, heavily leaning trees or trees with severely damaged crowns.In the whole area of restoration there prevail trees with damaged crowns, followed by trunk splits.The share of uprooted trees is also higher compared to the usual snow-damage and ice storms -the cause lies in a great wetness, in particular in shallow and steep forest floor.According to the estimate prepared by the Slovenian Forest Service (ZGS) two months after the disaster, the quantity of damaged trees is estimated to 9.3 million m 3 (one third falls to the coniferous trees).The highest amount of damaged wood mass, foreseen to be felled, was in the areas of Ljubljana (2.4 million m 3 ), Postojna (2.1 million m 3 ), Tolmin (1.8 m 3 ) and Kranj 1.0 million m 3 ).To get a realistic notion on the quantity of damaged timber, it should be mentioned that it represents more than a twoyear annual cut quantity in all Slovenian forests.
Within the scope of restoration of such damages we must not forget about the provision of safety at work in forest, transportability of forest roads (the construction of new ones, if necessary), prevention of secondary damage of bark beetles, maintenance of the quality or value of damaged valuable trees, preservation of the forest production potential in the affected areas and provision of ecological and social functions of forests.The plan mainly emphasises the issue of heavily damaged coniferous trees (3.1 million m 3 ) that should be restored first.The logging of heavily damaged deciduous trees (6.2 million m 3 ) may last longer.Due to a sudden great quantity of wood, it may be expected that the logging of heavily damaged coniferous trees will be carried out by spring 2015, while the restoration of deciduous trees will conclude by the end 2017.Due to their highest presence, spruce and beech trees are the most affected trees species.

STABILITY OF DAMAGED WOOD, FIRST ANALYSIS AFTER THE ICE STORM IN 2014
Huge quantity of suddenly affected wood, its level of damage and in particular a prolonged restoration of the meteorological disaster opens some important issues.In terms of coniferous trees these mainly refer to the subsequent risk of bark beetle attack, while in coniferous and deciduous trees they relate to the durability or decay of broken or fallen trees.The supply of water and minerals is drastically changed for these trees after the meteorological disaster (Jakša 2007).Usually, the damages caused by ice storm are more severe in deciduous trees.This is related to the durability of damaged wood and the possibilities of its application during the restoration.The speed of action is an essential question for forest owners.Thus, it is crucial to know the situation and durability of trees damaged in meteorological disaster, since it enables timely decision-making in terms of logging, skidding and use of damaged trees (Straže et al. 2015).
Within the national CRP project V4-1419 (Rational use of hardwoods with a focus on beechwood), the focus studied were developmental possibilities, survival options and physical characteristics of fallen common beech trees (Fagus sylvatica) at the end of the first vegetation period (8 September 2014) after the great ice storm in February 2014 (Straže et al. 2015).The study included the fallen (uprooted) trees after the ice storm with a partially (and differently at the same time) active root system (Figure 6).
The samples of selected trees were taken at three altitudes to study physical and mechanic characteristics of wood (especially moisture content and density).Authors established a significant relation between the share of active root system (connection of a tree with forest floor) and the level of tree crown dryness.In trees with the maximum of 20% of active tree roots, up to 5% of green leafy surfaces was established.The share of green leafy surfaces increased to 2/3 in trees with 30% of active roots, while the tree crown was green in trees with 40% of active tree root system.The level of sun exposure of the lying trees also plays an important negative impact.Thus, the study for the February-September 2014 period detected a greater dryness of tree crowns with direct exposure to the sun (Straže et al. 2015).
In trees with a more shaded tree crown and a higher part of the active root system (40%), it was confirmed greater average content of moisture, which exceeded 60% in the whole trunk section, i.e. the threshold of an effective durability of trees against the majority of harmful insects (Findlay 1985).The results of the project indicate changes in hydraulic system of the beech trees fallen by the ice storm at the end of the first vegetation period after the meteorological disaster.The reduction of wood moisture is significantly higher in trees affected by more extreme environmental changes, whereby the reduction in wood density during the February -September 2014 period is not yet detected -which is a significant finding.
It should be pointed out that this analysis is primarily focused on establishing the durability of such damaged wood.The first results therefore show that the changes in moisture are already present within the trees -the differences are more evident in trees that are more exposed to the sun, whereas the wood density and consequently its structure and usability have not changed significantly.This is the first data, the further analyses are yet to follow -on the basis of additional measurements and results we will be able to objectively provide an answer to the forest owners on the durability of wood and dynamics of their actions.

OWNERSHIP STRUCTURE OF THE AFFECTED FORESTS, ACCIDENTS RELATED TO THE FOREST WORK
The ownership of the affected forests is one of the most important factors that has a significant impact on the implementation of restoration works, in particular on its execution and timeliness.Private forests (515,400 ha) prevail among the affected forests.State forests affected by the glaze ice cover the surface of 83,000 ha, while some 3,500 ha of municipal forests are damaged.7.86 million m 3 of trees (84% of the total quantity of damaged trees to be felled) must be logged in private and municipal forests, while this figure is 1.46 million m 3 (16%) in state forests.This proportion of forest ownership is extremely unfavourable for quick restoration -the process of restoration is also hindered by fragmented forest land and poor equipment and qualification of the majority of forest owners to work in forest.
Figure 7 presents a share of private forest land in Slovenia, while Figure 8 displays the urgency of salvage logging compared to the 10-year annual cut.Areas with a distinctive private ownership structure are mainly overlapping with those heavily affected by this ice storm.
Poor equipment and lack of qualification of private forest owners are of a greatest concern in terms of safe implementation of restoration after the disaster.After such disasters and according to the fact that the most of the damaged wood is in the private ownership, the organisation of restoration must take into account the facts and actual state in this area.
The current situation in the field of occupational safety of private forest owners and unqualified workers is very poor.The Slovenian Forest Service (ZGS) has been monitoring the accidents related to forest work for many years now.To improve the situation, ZGS, according to available information, monitors and analyses all similar accidents (Beguš 2011).On the basis of its results and analyses, it can constantly modify the activities in the field of education and counselling on the safe work in forest.
It should be pointed out that the vast majority of accidents occur during logging operations.According to the ZGS data (Beguš 2011), during the past analysed period this occurred in 63% of cases (Figure 9).Thus, it is important to focus the education of forest owners on this type of work and emphasise the significance of personal protection equipment.Lack of knowledge, underestimation of dangers and non-use of personal protection equipment are also causes of accidents.
Only to make a comparison, we also show the results of the recent analysis of accidents of professional workers employed in forest companies that carry out forest works as concessionaires (Trebec 2015) -Figure 10.
Figure 10 shows similar results to private forest owners -here also the majority of accidents happened during the chainsaw felling and significantly less during other works in forest.
In recent period of monitoring the accidents in Slovenia, we established that from 8 to 9 persons got fatally injured during the forest work in private forests.The least fatal injuries according to this statistics occurred on 2006 with 3 deaths (Figure 11).According to the ZGS data (Beguš 2011), some 120 wounded persons per every deceased should be added to this number; thus some 1000 people got

APPLICATION OF MODERN TECHNOLOGIES IN THE PRIVATE AND FRAGMENTED FOREST LAND?
The data on the number, frequency and severity of accidents, in particular during felling operations, indicate the need and necessity to search for technological solutions in the field of timber harvesting.In particular in cases of restoring damaged stands after meteorological disasters.The ownership structure also forces us to find different, better and also safer solutions -a great majority of forests and stands affected by this ice storm is in private ownership.
It is the property of the forests affected by this meteorological disaster that poses additional requirements and possibility of finding solutions.The selection of machinery, its exploitation due to a predominantly small scope of forest land as well as factors and criteria influencing the selection of machines and equipment significantly differ from this issue in the professional forest works (Marenče, Winkler 1998, 2001).
The applicability of machines used in a predominantly private land and in particular in hindered and more difficult working conditions in this case is heavily dependent on their technical parameters.This kind of issue has been frequently discussed in previous research (Marenče, Košir 2006).In this regard, the capacity of individual machines currently used in forest production isof a significantly different kind.This is also shown by previous analyses of skidding of loads of different sizes (Košir, Marenče 2008).Some previous research already emphasized the crucial differences between various types of machinery and thus their different application.These mainly refer to those characteristics of machines and working conditions where the machines are pushed to their operating limits.A series of these values are an important information and a guideline in selecting suitable machinery for restoration works after this meteorological disaster -there are expectedly less limitations in the professional use (Košir, Marenče 2007, Marenče, Košir 2008), while in machinery in private ownership there are more limitations due to its poor technical characteristics (Marenče, Košir 2007, Marenče 2014).
In such conditions, a more modern mechanic felling could be a better solution to a standard chainsaw fellingand prevailing tractor skidding operations.The size of private forest land is the main factor that prevents a rational application and implementation of mechanic felling which can be carried out in large areas.The issue can be resolved in a part of private forest land -cooperation between forest owners can contribute to the more economic implementation where the fragmented land prevents the application of modern technologies (Marenče2013, Marenče et al. 2012).A possibility of spatial combining of private forest land has already been analysed in a special study.On the basis of selected criteria (tree structure, incline, rockiness), 54,460 ha of private forests were determined (Krč 2006).These areas relate to the

REVIEW OF THE CURRENT RESTORATION PROGRESS, THE MAY 2015 STATUS
The restoration of the February 2014 ice storm damages continues.According to the ZGS data (Review of the restoration progress ... 2105), approximately 700,000 m 3 of wood damaged by the disaster were felled only this year until mid-May 2015.In terms of the estimation of all damaged trees (9.3 million m 3 ), almost 3.7 million m 3 of wood, i.e. 41%, were felled so far.The share of felled coniferous and deciduous trees according to the total quantity is 61% and 30% respectively.This refers to the February 2014 -May 2015 period; the data only includes the trees affected by the disaster.
One part of damaged, mostly less quality wood mass, will stay in the forest according to the ZGS estimate.It is estimated that there is approximately 25% of such trees.This wood will be mostly located in difficult terrain with heavy skidding conditions and skidding costs higher than the income and also at the locations where forest owners are not interested in or qualified to fell in such demanding conditions.Unless these are coniferous trees, which could represent a risk for the development of bark beetles, the leaving of dead trees in forests is not an issue from the viewpoint of a forest ecosystem (ZGS, Review of the restoration progress ..., 2015).Mass increase of bark beetles is a serious threat in all natural catastrophes in coniferous forests.In 2014, Slovenia avoided large-scale damages in forests caused by bark beetles also due to cold and humid weather.
The felling of damaged and removal of fallen trees is followed by the preparation of stand and forest floor for restoration that has already started in the restored forests.Natural regeneration in adequately prepared areas takes place spontaneously, while the reforestation is carried out in areas where natural regeneration is not possible for various reasons.According to the estimate in the restoration plan, the reforestation will be required in approximately 900 ha of forest area, i.e. 6% of all areas that will have to be restored in Slovenia after the ice storm (total area is 14,000 ha) -ZGS, Review of the restoration progress ... 2015.
Further measures in restored areas refer to the tending of young forests.Tending measures (reaping, clearing) try to provide adequate conditions for the development of young forests and regrowth of quality and stable forest stands.The funds for restoring damaged forest, implementation of tending measures and protection of damaged forest and some works related to rehabilitation of forest roads will be provided mainly in the 2014-2020 Rural Development Plan (RDP).

Figure 11 .
Figure 11.Number of fatal accidents by years