Search

The age, size and morphology of trees, including crown dimensions, can influence crown defoliation. In Croatia, the selection management of silver fir (Abies alba Mill.) forests involves pure or mixed stands, either of which can be affected by various disturbances, resulting in unbalanced stand structures. The aim of this study was to estimate the probability of trees transitioning from one defoliation class to the next, examine the influence of tree attributes on that process and analyze the changes in survival over time. The study was conducted over a 18-year period (1990–2007) on two sites with contrasting stand structures: a uniform stand with a dominant share of silver fir (Site A) and an uneven-aged mixed beech–fir stand (Site B). Logistic regression was used to model tree transitions between defoliation classes. Uniform stand structure increased the likelihood of silver fir trees transitioning to a higher defoliation class, with limited dependence on the tree crown position. In contrast, suppressed and central trees in uneven-aged stands were more likely to transition to a higher defoliation due to greater competition between them. Diameter at breast height (DBH) was found to be a significant predictor of tree transition to higher defoliation classes, with a linear trend of increasing probability with increasing DBH. Crown position and crown length were also found to be significant predictors of changing defoliation class, with observed differences between sites occurring due to differences in stand structure. To ensure a balanced stand structure and enhance tree vitality, careful consideration of easily measurable tree elements such as DBH, crown length, and tree crown position is imperative when selecting trees for felling.

European beech (Fagus sylvatica L.) is an important component of forests in the alpine and continental biogeographical regions of Croatia. This study aimed to (1) analyze the long-term response of beech to climate, (2) identify potentially critical climatic conditions that could negatively affect the radial increment (RI) and vitality of beech, and (3) evaluate differences in the response of beech between the two biogeographical regions in Croatia. We used the 16 × 16 km Croatian ICP Forests Level 1 network. On a total of 25 plots, we cored between 5 and 24 trees for dendrochronological analysis. Tree-ring widths (TRW) were measured and standardized using cubic spline. TRW chronologies for the two regions were calculated and correlated to the temperature and precipitation data and Standardized Precipitation and Evapotranspiration Index (SPEI) using bootstrapped correlations. Continental region precipitation from April to August and alpine region precipitation from June to August were significantly important for RI. Temperature was less important for RI than precipitation in both regions, but the importance of the negative impact of above-average temperatures in the continental region and the positive impact of above-average precipitation in the alpine region has increased over the last two decades. A comparison with the 3-month SPEI confirmed the significant influence of high temperatures and the lack of precipitation in August on the RI of beech trees in both regions.

Sheep are one of the most important livestock species in Croatia, found mainly in the Mediterranean coastal and mountainous regions along the East Adriatic coast, well adapted to the environment and mostly kept extensively. Our main objective was therefore to map the positive selection of the X-chromosome (18,983 SNPs that passed quality control), since nothing is known about the adaptation genes on this chromosome for any of the breeds from the Balkan cluster. Analyses were performed on a sample of eight native Croatian breeds (101 females and 100 males) representing the East Adriatic metapopulation and on 10 mouflons (five females and males), all sampled in Croatia. Three classical within-population approaches (extreme Runs of Homozygosity islands, integrated Haplotype Score, and number of Segregating Sites by Length) were applied along with our new approach called Haplotype Richness Drop (HRiD), which uses only the information contained in male haplotypes. We have also shown that phylogenetic analyses, such as the Median-joining network, can provide additional information when performed with the selection signals identified by HRiD. Our new approach identifies positive selection signals by searching for genomic regions that exhibit a sudden decline in haplotype richness. In total, we identified 14 positive selection signals, 11 using the classical approach and three using the HRiD approach, all together containing 34 annotated genes. The most reliable selection signal was mapped by all four approaches in the same region, overlapping between 13.17 and 13.60 Mb, and assigned to the CA5B, ZRSR2, AP1S2, and GRPR genes. High repeatability (86%) of results was observed, as 12 identified selection signals were also confirmed in other studies with sheep. HRiD offers an interesting possibility to be used complementary to other approaches or when only males are genotyped, which is often the case in genomic breeding value estimations. These results highlight the importance of the X-chromosome in the adaptive architecture of domestic ruminants, while our novel HRiD approach opens new possibilities for research.

Despite being adapted to a wide range of environmental conditions, the vitality of European beech is expected to be significantly affected by the projected effects of climate change, which we attempted to assess with foliar nutrition and crown defoliation, as two different, yet interlinked vitality indicators. Based on 28 beech plots of the ICP Forests Level I network, we set out to investigate the nutritional status of beech in Croatia, the relation of its defoliation and nutrient status, and the effects of environmental factors on this relation. The results indicate a generally satisfactory nutrition of common beech in Croatia. Links between defoliation and nutrition of beech are not very direct or very prominent; differences were observed only in some years and on limited number of plots. However, the applied multinomial logistic regression models show that environmental factors affect the relationship between defoliation and nutrition, as climate and altitude influence the occurrence of differences in foliar nutrition between defoliation categories.

The Mediterranean vegetation belt on the eastern Adriatic covers an area of nearly 15,000 km2. It is comprised of forest stands that can be divided into three vegetation zones based on the presence of certain plant species within each: sub-Mediterranean, eu-Mediterranean, and steno-Mediterranean. The dominant ecological factors result in the domination of specific tree species within the floral composition between these vegetation zones. The aim of this study was to collect climate data from 38 weather stations over a 30-year period to compare climate data and bioclimate properties in the area of these three vegetation zones. The results confirmed statistically significant differences between the main climatic elements and most bioclimatic indices between the vegetation zones. Cooler and more humid conditions were found in the sub-Mediterranean zone, warmer and somewhat drier conditions in the eu-Mediterranean zone, and particularly pronounced warm and dry conditions in the steno-Mediterranean zone. However, the analysis of the main components for researching climate parameters showed that the mean annual air temperature, average minimum air temperature of the coldest month of the year and continentality index, length of the dry season, and de Martonne aridity index contribute the most to the grouping of vegetation in forest stands in the Mediterranean vegetation belt of the eastern Adriatic.

European beech (Fagus sylvatica L.) forests provide multiple essential ecosystem goods and services. The projected climatic conditions for the current century will significantly affect the vitality of European beech. The expected impact of climate change on forest ecosystems will be potentially stronger in southeast Europe than on the rest of the continent. Therefore, our aim was to use the long-term monitoring data of crown vitality indicators in Croatia to identify long-term trends, and to investigate the influence of current and previous year climate conditions and available site factors using defoliation (DEF) and defoliation change (ΔDEF) as response variables. The results reveal an increasing trend of DEF during the study period from 1996 to 2017. In contrast, no significant trend in annual ΔDEF was observed. The applied linear mixed effects models indicate a very strong influence of previous year drought on ΔDEF, while climate conditions have a weak or insignificant effect on DEF. The results suggest that site factors explain 25 to 30% DEF variance, while similar values of conditional and marginal R2 show a uniform influence of drought on ΔDEF. These results suggest that DEF represents the accumulated impact of location-specific stressful environmental conditions on tree vitality, while ΔDEF reflects intense stress and represents the current or recent status of tree vitality that could be more appropriate for analysing the effect of climate conditions on forest trees.

Background and Purpose: Forest trees are adapted to the specific climatic conditions and other ecological factors that dominate within their distribution range. However, the climate is in constant flux. In addition to natural climatic oscillations, the climate has also been changed directly or indirectly by human activities. The issue of climate change is tied mostly to air temperature and precipitation. The objective of this study was to assess the potential influence of climate change on a part of the ecological niche of pedunculate oak (Quercus robur L.) in Croatia. Materials and Methods: A forecast model was developed for the ecological niche of pedunculate oak in Croatia from the present day to 2080 using logistical regression, on the basis of a climate change model. Results: Within the lowland areas of Croatia, the model forecasts an increase in the minimum temperatures of the coldest month and maximum temperature of the warmest month, and reduced precipitation in both the driest and wettest months. Conclusion: The results indicate that climate change will negatively impact the ecological niche of pedunculate oak in the future.

Background and Purpose: Narrow-leaved ash (Fraxinus angustifolia Vahl) is one of the most important tree species of lowland floodplain forests in the Republic of Croatia. Recent significant climate changes, reflected in extreme temperatures and long dry periods, have had a direct impact on the dynamics and levels of groundwater, as well as on the dynamics of precipitation and floodwater, which are of decisive importance for the success of narrow-leaved ash. Our study aims to determine the morphological and physiological characteristics of seedlings of narrow-leaved ash after 72 days of drought, normal watering and substrate saturation. Materials and Methods: The experiment was established in three treatments (drought, normal watering and saturation), and each treatment included two containers or 24 seedlings. A total of 72 seedlings were replanted. After 72 days, height growth and increment, water potential, photosynthetic efficiency and the total chlorophyll content in the leaf mesophyll were measured. Results: Seedlings from the drought treatment wilted immediately. Seedlings saturated with water up to the root collar manifested better height and diameter growth, high water potential and a lesser physiological stress response as compared to the seedlings that were watered normally. Conclusions: Seedlings of narrow-leaved ash, which is a hygrophytic tree species, do not tolerate dry conditions and no watering. Seedlings saturated with water for 72 days showed a better morphological-physiological status than the seedlings that received normal quantities of water.

Although game meat quality has been under the spotlight in numerous studies, the quality of brown bear (Ursus arctos) meat is still unknown. The aim of this study was to determine the effects of sex and age on the proximate chemical composition, fatty acid profile, and lipid indices of brown bear meat. Nine (n = 9) females and nine (n = 9) males were hunted during the Croatian spring hunting period in 2018. Based on age, bears were divided into two groups: n = 9; five females and four males) and 4–6 years (n = 9; four females and five males). For analysis purposes, samples of M.semimembranosus were collected. Age was shown to have an effect on the traits analyzed, while sex-related differences were not found. Brown bear meat has a high fat content (average 6.12%), especially in older bears (~9%). The contents of protein, dry matter, and ash were similar to those of other game species. Monounsaturated fatty acids made up approximately 50% of all fatty acids, with the most abundant being C18:1n-9. More favorable profiles of essential polyunsaturated fatty acids were found in younger bears. The ratio of polyunsaturated and saturated fatty acids was closer to the recommended ratio than the ratio of n-6 and n-3 polyunsaturated fatty acids, and lipid indices were favorable. Further research is needed to determine seasonal changes in brown bear meat quality.

The aim of this study is to examine the effect of sex and age on proximate chemical, fatty acid, amino acid and mineral content of axis deer (Axis axis Erx.) meat. Sixteen (n = 16) animals were hunt-harvested and assigned to groups according sex and age (sub-adult and adult). All analyses were made on m. longissimus thoracis sampled between the 9th and 13th ribs. Minor differences in nutritional composition of axis deer meat were found between analysed sex and age groups. Axis deer meat has a high protein (22.8%) and low fat (1.39%) content. Saturated fatty acids accounted for 44.97% and polyunsaturated for 29.66% of the total fatty acids. Ratios of fatty acids were within the recommended values. Glutamic and aspartic acid were the most abundant non-essential, and lysine and leucine the most common essential amino acids. The ratio of essential to non-essential amino acids was

Background and Purpose: Animal migrations are a direct result of reproduction, behaviour characteristics, predators, population density, disturbance, loss of habitat, climatic, vegetational and nutritional factors. The availability and accessibility of natural food in winter months is dependent on snow cover. The main objective of this study was to determine the migrational activities of red deer and to examine the dependency between migrations and climatic factors. Materials and Methods: The study was carried out in the northwest Dinarid mountains, i.e. in the western part of Gorski Kotar region, which represents a large integral forest complex, distinctive due to its significant vertical drops, diverse relief characteristics and habitat conditions. Data on red deer migrations was collected over a 12 year period from hunting records, gamekeeper logs and records from game counting and monitoring. Results and Conclusions: The results of the macroclimatic analysis show a statistically significant difference (p

Background and Purpose: Forest cultures in continental part of Croatia are mainly based on bracken-covered areas and moors on deserted agriculture soils and pastures. Successful afforestation i.e. establishment of forest cultures depends among other things on the understanding of habitats and ecology of forest trees. The choice of best species of forest trees for afforestation needs to be based on the research in soil and climate characteristics of target habitats. The aims of this research were to show mesoclimatic characteristics of Ličko sredogorje and microclimatic and pedological characteristics of Ličko polje. Also, based on habitat characteristics and ecology of forest trees, the aim was to determine species of forest trees suitable for afforestation of bracken-covered areas. Materials and Methods: Climate, microclimate, pedological and plant nutrition researches were done at the area of Lika highlands. Climate analysis was done according to air temperatures, amount of precipitation, relative air humidity and other climate elements and appearances. Composite soil samples were taken from the depth of 0-30 cm in order to determine plant nutrition potential. Samples were prepared for further analysis in the laboratory. Results: The highest average annual air temperature of 9.6 °C was found at weather station Gračac and the lowest at Korenica station (8.1 °C). Average amount of precipitation for this region was around 1500 mm. Monthly rain factors were ranging from arid to perhumid. Considering thermal character of the climate, the area has moderately warm climate. Average volumetric soil humidity is 14.2 %. Soil has strong acid reaction, is very humus, good to richly supplied with total nitrogen, content of physiologically active phosphorus and potassium is low, and C/N ration normal. Conclusions: According to habitat characteristics in the area of Ličko sredogorje and ecological demands of forest tree species, forest cultures of Common birch (Betula pendula Roth.), Common spruce (Picea abies Karst.), Eastern white pine (Pinus strubus L.), Black pine (Pinus nigra subsp. austriaca Asch i Gr.), Common pine (Pinus sylvestris L.) and European trembling aspen (Populus tremula L.) can be established.

Pedunculate oak (Qercus robur L.) is one of the most important tree species in Croatia. As a dominant species, it covers about 10% of the forested area (about 210 000 ha), which accounts for about 12% of the total growing stock. This tree species is distributed in the lowland and floodplain area of the rivers Drava, Sava and Kupa and their tributaries. Forests of pedunculate oak are managed according to close-to-nature principles and with rotations of over 140 years. In the past 100 years, the management of pedunculate oak forests has been hindered by a serious management and ecological problem: the occurrence of tree dieback and decline. From the management point of view, the problem entails the increased quantity of dead or severely damaged trees, increased management costs and a disturbance in natural forest regeneration. From the ecological point of view, the problem centers around changed site conditions, which is unfavorable for both present and future growth of pedunculate oak trees. In the period from 1995 to 2007, an amount of 35% of the current pedunculate oak volume declined in Croatia, with mortality rising to 40% if the past several years are taken into account. Tree dieback incurs grave financial losses, which reach up to 40% of the potential market value of undamaged and healthy wood mass. The losses are further aggravated by increased costs of managing such forests and reduced non-timber forest functions. The mortality rate of pedunculate oak trees is an indicator of the instability of lowland forest ecosystems, especially when dieback occurs in optimal site conditions for the pedunculate oak (micro-elevations and micro-depressions). Individual, intensive and catastrophic tree dieback has been recorded. Salvage cuts are applied in the attempt to mitigate the effects of disturbances caused by tree dieback. These cuts are undertaken continuously, depending on tree dieback intensity, and are based on the assessment of tree condition. Tree condition is assessed on the basis of tree damage criterion, which comprises crown defoliation and leaf discoloration. These are indicators of lessened tree vitality, but have so far not proved adequate for the reduction of pedunculate oak tree dieback. In order to advance the current condition of forest ecosystems, additional indicators of decreased tree and stand vitality are being sought, and so are the indicators of their disturbed stability. Mortality rates that take into account the volume of dead tree mass are used for this purpose. The objective of this work is to establish spatial distribution of different mortality rates of pedunculate oak trees and assess their correlation with certain ecological factors.The research was carried out in three management units (MU) in the Forest Administration of Nova Gradiška. These include MU »Međustrugovi« in Stara Gradiška Forest Office, MU »Zelenika« in Novska Forest Office, and MU »Grede–Kamare« in Jasenovac Forest Office. »Međustrugovi« is situated in the area between the rivulets of Veliki and Mali Strug, the tributaries of the River Sava, »Zelenika« is situated along the Zagreb – Lipovac motorway and north of the rivulet Veliki Strug, and »Grede Kamare« is southeast of Novska between the Strug and the Sava.The data gathered involved marked damaged and dead pedunculate oak trees by compartments for the period from 1998–2007. The wood volume of these trees was calculated on the basis of tree diameter and local tariffs. Dead wood mass of every individual compartment was divided with the compartment area to obtain tree dieback per surface unit in the monitoring period (m³/ha). Based on the growing stock of pedunculate oak by compartments and wood volume of dead pedunculate oak trees per surface unit, the percentage share of dead wood mass was calculated.The wood volume of dead wood mass by compartments (m³/ha) was then divided by 10 to obtain the annual volume of dead wood mass of pedunculate oak per hectare. These values were juxtaposed with the current annual increment of pedunculate oak by compartments to obtain the percentage share of dead wood mass in relation to the current annual increment of the compartment.Based on the obtained values, every compartment was assigned a degree of wood mass mortality and a degree of increment decline. Wood mass mortality was classified into four degrees: I (0.1–10%, low mortality), II (10.1–25%, moderate mortality), III (25.1–50%, intensive mortality) and IV (50.1–100%, extreme mortality). Increment decline was also classified into four degrees, but with different percentages: I (0.1–25%, low), II (25.1–50%, moderate), III (51.1–100%, intensive) and IV (>100%, extreme).Based on the degree of wood mass mortality and degree of increment decline of each single compartment, maps of wood mass mortality rate and of increment decline rate were constructed. In the Management Unit »Međustrugovi«, the mortality rate of wood mass by compartments was relatively low. A total of 85 dieback-affected compartments over an area of 1302 ha were analyzed. In 98% of the compartments, low to moderate wood mass mortality rate was recorded (Fig. 2), but no intensive or extreme dieback was found. Rates of increment decline by compartments were unfavorable. Extreme decline was found in 6 compartments over an area of about 30 ha, intensive increment decline was recorded in 12 compartments, i.e., significant reduction in the increment was recorded in over 20% of the compartments (Fig. 3). Intensive and extreme increment decline was found in an area exceeding 260 ha. Compartments with the highest values of wood mass mortality did not manifest the most extreme values of increment decline. The map does not show any significant participation of the compartments with extreme increment decline, although the grouping of the compartments with intensive and extreme decline was observed, and so was their higher participation in the southern part of the management unit along the Strug watercourse.In relation to the three study areas, the lowest mortality of wood mass was recorded in the Management Unit of »Zelenika«. The research included 50 compartments over an area of 1065 ha. Moderate wood mass mortality was found in 6 compartments and slight mortality in the remaining compartments. Intensive and extreme increment decline was recorded in 10% of the compartments comprising an area of over 100 ha (Fig. 6). The grouping of compartments with a certain degree of increment decline is observed. This refers particularly to degrees II and III of increment decline, which were recorded in the compartments situated in the eastern part of the Management Unit of »Zelenika« (Fig. 7).The highest participation of compartments and sub-compartments with intensive and extreme rates of wood mass mortality was recorded in the Management Unit of »Grede–Kamare«. Of a total of 102 dieback-affected compartments and sub-compartments in an area of 1474 ha, wood mass mortality was extreme in 12 compartments and intensive in 30 compartments, in an area of over 570 ha. Moderate and low mortality of wood mass was found in 57% of the compartments (Fig. 8).An exceptionally unfavorable condition was recorded in relation to the degrees of increment decline. Extreme increment decline was found in over 55% of the compartments; in other words, every second compartment or sub-compartment in the Management Unit of »Grede–Kamare« was afflicted by disturbed stand growth and increment in an area of over 800 ha. Other degrees of increment decline had similar participation by compartments and sub-compartments (Fig. 9). The largest number of compartments and sub-compartments with extreme and intensive increment decline was recorded in the southeastern part of the management unit. They form larger units and are grouped in one part of the management unit in the map (Fig. 10).A comparison of increment decline rates by management units reveals the occurrence of intensive increment decline in a smaller number of compartments (10–15% of the compartments), and of extreme decline in fewer than 10% of the compartments in two management units. In one of the management units, extreme increment decline affected more than 50% of the compartments.Changes in the sites of pedunculate oak in the last 100 years have affected the stability of these forests and the vitality of trees, which has decreased considerably in recent times. Pedunculate oak trees of lessened vitality are permanently exposed to impact of a variety of adverse factors. This consequently leads to a gradual decline of trees, of which some die before the end of the rotation. Dieback of trees aged between 80 and 120 recorded in the Spačva forest area is an important indicator of disturbed growth and development of the most valuable forests in Croatia and a sign of general disturbances in the stability of lowland forests. Intensive tree mortality continues despite management procedures aimed at regulating the structure and quality of the stands. This phenomenon is particularly characterized by an uneven spatial distribution and intensity. In some areas of the pedunculate oak range in Croatia, dieback is the biggest management and ecological forestry problem, since management largely involves damaged and dead trees of pedunculate oak. As a result, the quality of the stands and total wood mass production are severely reduced. Since dead pedunculate oak trees are less exploitable and achieve lower market values, the consequences of tree dieback reflect unfavorably on the entire forestry sector.Monitoring the intensity and dynamics of tree dieback in stands is one of the ways to determine certain patterns of this phenomenon and improve the management with forests of disturbed stability. This requires more intensive and regular marking of damaged and dead trees. The most common indicators used for the marking of these trees are morphological features of the crown and biotic damage of the stem. However, these indicators are insufficient for achieving better stand vitality and reducing tree decline and dieback. Hence, spatial distribution of tree dieback by compartments and sub-compartments is one of the possible indicators that can be used in planning the management with stands of lessened vitality.Our research found chronic and continuous dieback of pedunculate oak trees, although dieback rates vary by years. Significant spatial differences were also found in the rates of wood mass mortality and increment decline, both among the management units and among their compartments and sub-compartments. Spatial grouping of compartments with intensive and extreme dieback shows correlation with site factors, which are considered the principal causes of dieback. Management with pedunculate oak forests with disturbed stability should be adjusted to the condition of individual ecosystems and to the trends that indicate their development. Presentations of spatial distribution of tree dieback can significantly contribute to this goal.

This paper deals with ecological and biological properties of Holm Oak trees (Quercus ilex L.) on the Island of Rab. Forest ecosystems are influenced by numerous local meteorological and climatic conditions. In spring 2006 four experimental plots (2x2 m), one in the middle forest (both seed and coppiced trees) and three in coppices of different age and structure, were established on the Island of Rab.Rotronic hygromers for measuring air temperature (°C), relative air humidity (%), wet bulb temperature (°C) and dewpoint/frostpoint (ºC) were placed on two sites (middle forest and coppice). The values were measured from May 2006 to May 2007. Lux-meter was used for measuring relative light intensity. In 2006 soil humidity (%) was measured five times with Theta Probes model ML2x at the average depth of Holm Oak seedling rooting. On three occasions 30 Holm Oak seedlings were samples for root analysis. The scanner Epson Expression 10000XL and software WinRHIZO ProLA2400 for the analysis of washed roots were used to determine the total root length (cm), average root diameter (mm), volume (cm3), number of tips (pcs), forks (pcs) and crossings (pcs). In order to determine the natural mortality, the seedlings and young plants of Holm Oak were counted on ten occasions during the three years of research (in 2006, 2007 and 2008). The seedling heights were measured at the end of the germination phase and at the end of the first growing season.Minimum air temperature in coppice was lower compared to the middle forest. Microclimatic conditions in coppice are less favorable for the growth and development of vegetation than those in the middle forest. Coppice has higher air temperature and lower relative air humidity compared to the microclimate in the middle forest. Large numbers of natural Holm Oak seedlings and young plants were recorded on all the four experimental plots, which can be attributed to favorable climatic factors influencing the yield on the Island of Rab. A large number of seedlings was obtained in coppice (480,000 – 1,190,000 pcs/ha) compared to the middle forest (465,000 pcs), which can be attributed to the age of the stand, i.e. the size of the fructifying trees and the shrub cover. There is a great variability between the four experimental plots with respect to the end of germination (4/7 – 3/10). The germination of Holm Oak seedlings in the middle forest reached its peak earlier (4 July 2006) than in the coppice (31 July 3 October), which implies the presence of better microclimatic site conditions. On some experimental plots Holm Oak acorns were germinating throughout 2006, which is an indicator of poor germination conditions. The key factor responsible for seed dormancy in this case was the lack of moisture in the soil. Statistically significant larger heights of Holm Oak seedlings were measured in the middle forest compared to the heights in the coppice. The mortality of young Holm Oak plants was also by 8.98% higher in the middle forest than in the coppice. The mortality of Holm Oak seedlings and young plants between 3 October 2006 and 30 January 2008 was 52.35%. The same trend of seedling and young plant mortality was recorded on all the experimental plots. After 27 months a large number of natural young plants of very good vitality survived on all the plots.A negative and very high correlation between the root length and average root diameter was obtained for Holm Oak seedlings and young plants (r=–0.7884). With respect to the measurement date there was no significant difference in root volume, which means that in the 20 months of research there was no significant increase in root volume of Holm Oak seedlings and young plants in the soil.

Dieback of silver fir in Croatia, especially in the Dinaric part, is associated with complex changeable effects of abiotic and biotic factors. In industrial forests, the volume of dieback trees or volume of trees cut down in salvage cutting is most often used for showing tree dieback intensity, and can be used as an indicator of forest stand health status (Capecki 1981).The aim of this research was to show the correlation of silver fir dieback with habitat and structural factors, calculate the intensity of dieback according to volume, and determine tree dieback dynamics and effects of habitat factors on concentration of essential mineral nutritive elements in needles and soil.The research was carried out in the mountainous part of Croatia, in beech-fir and fir forests of Gorski Kotar. The research included the forest stands of disrupted stability and structure, at the border of the natural range of sliver fir towards a warmer area and optimum area of silver fir i.e. central part of Gorski Kotar. Data for wood mass of dieback silver fir trees were collected for the selected management units at the level of all compartments and subcompartments in the management unit. The data were being collected for twelve years (1995–2007). In the researched area, needle sampling from tree crowns was carried out on trees with three different levels of defoliation (60%). Dry needle mass was determined as well as concentration of K, Ca and Mg. Soil chemical analysis included soil reaction, and amount of phosphorus (P) and potassium (K) in the soil.The average annual silver fir dieback intensity for forest stands at the border of the natural range was 18.3 m3/ha or 9.2% of silver fir growing stock, and in forest stands in the central part of Gorski Kotar it was 6.2 m3/ha or 4.1%.The maximum annual dieback intensity in forest stands at the border of the natural range was 113.0 m3/ha, and in forest stands in the central part of Gorski Kotar it was 55.4 m3/ha. For forest stands with recorded dieback, the average annual increment was 2.7 m3/ha, and in forest stands in the central part of Gorski Kotar it was 3.3 m3/ha. In forest stands with sliver fir dieback, dieback intensity was higher than the value of the growing stock (Table 1).Intensity of the average annual silver fir dieback at the border of the natural range was from 1.6 to 18.8 m3/ha, and in forest stands in the central part of Gorski Kotar from 5.0 to 7.5 m3/ha (Fig. 1).In forest stands at the border of the natural range, the highest average annual silver fir dieback intensity was recorded in silver fir forest with hard fern (18.63 m3/ha), and the lowest in silver fir forest with small-reed (11.5 m3/ha). Dieback intensity in the central part of Gorski Kotar was lower, the highest being in silver fir forest with small-reed (14.4 m3/ha), and the lowest in the Dinaric beech-fir forest (5.8 m3/ha) (Fig. 2).In forest stands at the border of the natural range, the highest dieback intensity was recorded at west and southwest exposition, and the lowest at northwest and east exposition. In forest stands in the central part of Gorski Kotar the highest dieback intensity was at southwest, and the lowest at north exposition. In relation to altitude, the most severe dieback intensity was observed at lower, and the lowest at higher altitudes (Table 2).According to the results shown in Table 3, in forest stands at the border of the natural range, tree dieback intensity significantly and positively correlates with exposition, growing stock (0.23*) and number of silver fir trees (0.12*), and negatively with terrain slope (– 0.15*), altitude (– 0.11*), precipitation quantities in vegetation period (– 0.11*), soil water balance (– 0.11*) and increment (– 0.16*). In forest stands in the central part of Gorski Kotar silver fir dieback intensity significantly and negatively correlates with altitude (– 0.14*), precipitation quantities in vegetation period (– 0.18*) and soil water balance (– 0.12*).Calcium negatively correlates with vegetation air temperatures (– 0.23*), and positively with vegetation precipitations (0.23*), which is important for drought periods because 2007 was a »drought« year (Review No. 18). The correlation coefficients of Mg concentration show the same trend with air temperatures (– 0.48*) and precipitation quantities (0.48*).The correlation of Ca concentration and soil pH value is positive and amounts to 0.34*, while the correlation of dry needle mass and defoliation is – 0.40* (Table 4).The concentration of phosphorous and potassium in the soil correlates positively with vegetation air temperatures (0.34*, 0.29*), and negatively with vegetation precipitations (– 0.34*, – 0.29*) and altitudes (– 0.52*, – 0.50*) (Table 5).Dry needle mass (g), concentration of potassium, calcium and magnesium (mg/g) decrease with the increase of tree crown defoliation (Table 6).In the current year the mass of dry needles is 0.48 g, and in the last year it was 0.52 g. In the current year the concentration of calcium in needles is 12.34 mg/g, and in the last year it was 17.06 mg/g (Table 7).The data of Fužine and Rijeka Forest Office show that the percentage share of salvage cutting or dieback of silver fir amounts up to 100% according to prescribed yield (annual allowable cut) for the area of management units Brloško, Kobiljak-Bitoraj and Jelenje Velo (border of the natural range). On the contrary, the percentage share of salvage cuttings according to prescribed yield in the area of the management units Ravna Gora and Višnjevica (central part of Gorski Kotar) amounts up to 15%. In the area of Gorski Kotar tree dieback was recorded on all types of geological basis and forest soils, and in all silver fir forest associations. At the border of the natural range the highest dieback intensity was recorded in silver fir with hard fern, and in the central part of Gorski Kotar in silver fir with small-reed. According to our research, the highest tree dieback volumes (m3 and m3/ha) occur at the lowest altitudes and on mild slopes. Tikvić et al. (2008) reported the same results. Due to higher air temperatures and lower precipitation quantities, soil evaporation is higher at lower altitudes. During drought periods at these altitudes, soil water balance is low. Thomas et al. (2002) found positive correlation between precipitation quantities and altitude and considers that this is suitable for forest tree development at higher altitudes.In forest stands at the border of the natural range, tree dieback volume (m3/ha) is the lowest at northeast expositions, and the highest at west exposition, followed by different variants of south expositions, and compartments of different expositions. This was expected since the south and west expositions are warmer and more exposed to unfavourable currents from west Europe. The decrease of vegetation precipitation quantities significantly increases the volume of silver fir dieback. These results correspond to the results reported by other authors (Markalas 1992, Thomas et al. 2002, Tikvić et al. 2008).Even within the silver fir areal in one country, there are significant differences in factors affecting tree dieback. This can be proved by comparing the factors that affect dieback at the border of the natural range and in the central part of Gorski Kotar. Air temperature increase and precipitation quantities decrease result in the decrease of concentration of calcium and magnesium in silver fir needles, which is significant for drought periods and air temperature increase. Dry needle mass and calcium concentration are significantly higher in the last year than in the current year needles. According to the Meteorological and Hydrological Service, the year 2007 (current year needles) was a drought year. In the forest stand at the border of the natural range where dieback was recorded, the average annual dieback intensity was six times higher than the average annual increment, while in forest stands in the central part of the area, dieback intensity was two times higher than the annual increment.Tree dieback was recorded at all expositions, terrain slopes and altitudes, as well as in all forest associations. At the border of the natural range, relief, climate and structural factors have dominant effect on tree dieback, while in the central part of Gorski Kotar climatic factors have dominant effect on tree dieback. The increase of tree crown defoliation causes the decrease of dry needle mass, as well as the concentration of K, Ca and Mg. Drought resulted in lower concentration of magnesium and calcium in silver fir needles, and lower dry needle mass.

Dieback of silver fir in Croatia, especially in the Dinaric part, is associated with complex changeable effects of abiotic and biotic factors. In industrial forests, the volume of dieback trees or volume of trees cut down in salvage cutting is most often used for showing tree dieback intensity, and can be used as an indicator of forest stand health status (Capecki 1981). The aim of this research was to show the correlation of silver fir dieback with habitat and structural factors, calculate the intensity of dieback according to volume, and determine tree dieback dynamics and effects of habitat factors on concentration of essential mineral nutritive elements in needles and soil. The research was carried out in the mountainous part of Croatia, in beech-fir and fir forests of Gorski Kotar. The research included the forest stands of disrupted stability and structure, at the border of the natural range of sliver fir towards a warmer area and optimum area of silver fir i.e. central part of Gorski Kotar. Data for wood mass of dieback silver fir trees were collected for the selected management units at the level of all compartments and subcompartments in the management unit. The data were being collected for twelve years (1995–2007). In the researched area, needle sampling from tree crowns was carried out on trees with three different levels of defoliation (60%). Dry needle mass was determined as well as concentration of K, Ca and Mg. Soil chemical analysis included soil reaction, and amount of phosphorus (P) and potassium (K) in the soil. The average annual silver fir dieback intensity for forest stands at the border of the natural range was 18.3 m3/ha or 9.2% of silver fir growing stock, and in forest stands in the central part of Gorski Kotar it was 6.2 m3/ha or 4.1%. The maximum annual dieback intensity in forest stands at the border of the natural range was 113.0 m3/ha, and in forest stands in the central part of Gorski Kotar it was 55.4 m3/ha. For forest stands with recorded dieback, the average annual increment was 2.7 m3/ha, and in forest stands in the central part of Gorski Kotar it was 3.3 m3/ha. In forest stands with sliver fir dieback, dieback intensity was higher than the value of the growing stock (Table 1). Intensity of the average annual silver fir dieback at the border of the natural range was from 1.6 to 18.8 m3/ha, and in forest stands in the central part of Gorski Kotar from 5.0 to 7.5 m3/ha (Fig. 1). In forest stands at the border of the natural range, the highest average annual silver fir dieback intensity was recorded in silver fir forest with hard fern (18.63 m3/ha), and the lowest in silver fir forest with small-reed (11.5 m3/ha). Dieback intensity in the central part of Gorski Kotar was lower, the highest being in silver fir forest with small-reed (14.4 m3/ha), and the lowest in the Dinaric beech-fir forest (5.8 m3/ha) (Fig. 2). In forest stands at the border of the natural range, the highest dieback intensity was recorded at west and southwest exposition, and the lowest at northwest and east exposition. In forest stands in the central part of Gorski Kotar the highest dieback intensity was at southwest, and the lowest at north exposition. In relation to altitude, the most severe dieback intensity was observed at lower, and the lowest at higher altitudes (Table 2). According to the results shown in Table 3, in forest stands at the border of the natural range, tree dieback intensity significantly and positively correlates with exposition, growing stock (0.23*) and number of silver fir trees (0.12*), and negatively with terrain slope (– 0.15*), altitude (– 0.11*), precipitation quantities in vegetation period (– 0.11*), soil water balance (– 0.11*) and increment (– 0.16*). In forest stands in the central part of Gorski Kotar silver fir dieback intensity significantly and negatively correlates with altitude (– 0.14*), precipitation quantities in vegetation period (– 0.18*) and soil water balance (– 0.12*). Calcium negatively correlates with vegetation air temperatures (– 0.23*), and positively with vegetation precipitations (0.23*), which is important for drought periods because 2007 was a »drought« year (Review No. 18). The correlation coefficients of Mg concentration show the same trend with air temperatures (– 0.48*) and precipitation quantities (0.48*). The correlation of Ca concentration and soil pH value is positive and amounts to 0.34*, while the correlation of dry needle mass and defoliation is – 0.40* (Table 4). The concentration of phosphorous and potassium in the soil correlates positively with vegetation air temperatures (0.34*, 0.29*), and negatively with vegetation precipitations (– 0.34*, – 0.29*) and altitudes (– 0.52*, – 0.50*) (Table 5). Dry needle mass (g), concentration of potassium, calcium and magnesium (mg/g) decrease with the increase of tree crown defoliation (Table 6). In the current year the mass of dry needles is 0.48 g, and in the last year it was 0.52 g. In the current year the concentration of calcium in needles is 12.34 mg/g, and in the last year it was 17.06 mg/g (Table 7). The data of Fužine and Rijeka Forest Office show that the percentage share of salvage cutting or dieback of silver fir amounts up to 100% according to prescribed yield (annual allowable cut) for the area of management units Brloško, Kobiljak-Bitoraj and Jelenje Velo (border of the natural range). On the contrary, the percentage share of salvage cuttings according to prescribed yield in the area of the management units Ravna Gora and Višnjevica (central part of Gorski Kotar) amounts up to 15%. In the area of Gorski Kotar tree dieback was recorded on all types of geological basis and forest soils, and in all silver fir forest associations. At the border of the natural range the highest dieback intensity was recorded in silver fir with hard fern, and in the central part of Gorski Kotar in silver fir with small-reed. According to our research, the highest tree dieback volumes (m3 and m3/ha) occur at the lowest altitudes and on mild slopes. Tikvić et al. (2008) reported the same results. Due to higher air temperatures and lower precipitation quantities, soil evaporation is higher at lower altitudes. During drought periods at these altitudes, soil water balance is low. Thomas et al. (2002) found positive correlation between precipitation quantities and altitude and considers that this is suitable for forest tree development at higher altitudes. In forest stands at the border of the natural range, tree dieback volume (m3/ha) is the lowest at northeast expositions, and the highest at west exposition, followed by different variants of south expositions, and compartments of different expositions. This was expected since the south and west expositions are warmer and more exposed to unfavourable currents from west Europe. The decrease of vegetation precipitation quantities significantly increases the volume of silver fir dieback. These results correspond to the results reported by other authors (Markalas 1992, Thomas et al. 2002, Tikvić et al. 2008). Even within the silver fir areal in one country, there are significant differences in factors affecting tree dieback. This can be proved by comparing the factors that affect dieback at the border of the natural range and in the central part of Gorski Kotar. Air temperature increase and precipitation quantities decrease result in the decrease of concentration of calcium and magnesium in silver fir needles, which is significant for drought periods and air temperature increase. Dry needle mass and calcium concentration are significantly higher in the last year than in the current year needles. According to the Meteorological and Hydrological Service, the year 2007 (current year needles) was a drought year. In the forest stand at the border of the natural range where dieback was recorded, the average annual dieback intensity was six times higher than the average annual increment, while in forest stands in the central part of the area, dieback intensity was two times higher than the annual increment. Tree dieback was recorded at all expositions, terrain slopes and altitudes, as well as in all forest associations. At the border of the natural range, relief, climate and structural factors have dominant effect on tree dieback, while in the central part of Gorski Kotar climatic factors have dominant effect on tree dieback. The increase of tree crown defoliation causes the decrease of dry needle mass, as well as the concentration of K, Ca and Mg. Drought resulted in lower concentration of magnesium and calcium in silver fir needles, and lower dry needle mass.

Pedunculate oak (Qercus robur L.) is one of the most important tree species in Croatia. As a dominant species, it covers about 10% of the forested area (about 210 000 ha), which accounts for about 12% of the total growing stock. This tree species is distributed in the lowland and floodplain area of the rivers Drava, Sava and Kupa and their tributaries. Forests of pedunculate oak are managed according to close-to-nature principles and with rotations of over 140 years. In the past 100 years, the management of pedunculate oak forests has been hindered by a serious management and ecological problem: the occurrence of tree dieback and decline. From the management point of view, the problem entails the increased quantity of dead or severely damaged trees, increased management costs and a disturbance in natural forest regeneration. From the ecological point of view, the problem centers around changed site conditions, which is unfavorable for both present and future growth of pedunculate oak trees. In the period from 1995 to 2007, an amount of 35% of the current pedunculate oak volume declined in Croatia, with mortality rising to 40% if the past several years are taken into account. Tree dieback incurs grave financial losses, which reach up to 40% of the potential market value of undamaged and healthy wood mass. The losses are further aggravated by increased costs of managing such forests and reduced non-timber forest functions. The mortality rate of pedunculate oak trees is an indicator of the instability of lowland forest ecosystems, especially when dieback occurs in optimal site conditions for the pedunculate oak (micro-elevations and micro-depressions). Individual, intensive and catastrophic tree dieback has been recorded. Salvage cuts are applied in the attempt to mitigate the effects of disturbances caused by tree dieback. These cuts are undertaken continuously, depending on tree dieback intensity, and are based on the assessment of tree condition. Tree condition is assessed on the basis of tree damage criterion, which comprises crown defoliation and leaf discoloration. These are indicators of lessened tree vitality, but have so far not proved adequate for the reduction of pedunculate oak tree dieback. In order to advance the current condition of forest ecosystems, additional indicators of decreased tree and stand vitality are being sought, and so are the indicators of their disturbed stability. Mortality rates that take into account the volume of dead tree mass are used for this purpose. The objective of this work is to establish spatial distribution of different mortality rates of pedunculate oak trees and assess their correlation with certain ecological factors. The research was carried out in three management units (MU) in the Forest Administration of Nova Gradiška. These include MU »Međustrugovi« in Stara Gradiška Forest Office, MU »Zelenika« in Novska Forest Office, and MU »Grede–Kamare« in Jasenovac Forest Office. »Međustrugovi« is situated in the area between the rivulets of Veliki and Mali Strug, the tributaries of the River Sava, »Zelenika« is situated along the Zagreb – Lipovac motorway and north of the rivulet Veliki Strug, and »Grede Kamare« is southeast of Novska between the Strug and the Sava. The data gathered involved marked damaged and dead pedunculate oak trees by compartments for the period from 1998–2007. The wood volume of these trees was calculated on the basis of tree diameter and local tariffs. Dead wood mass of every individual compartment was divided with the compartment area to obtain tree dieback per surface unit in the monitoring period (m³/ha). Based on the growing stock of pedunculate oak by compartments and wood volume of dead pedunculate oak trees per surface unit, the percentage share of dead wood mass was calculated. The wood volume of dead wood mass by compartments (m³/ha) was then divided by 10 to obtain the annual volume of dead wood mass of pedunculate oak per hectare. These values were juxtaposed with the current annual increment of pedunculate oak by compartments to obtain the percentage share of dead wood mass in relation to the current annual increment of the compartment. Based on the obtained values, every compartment was assigned a degree of wood mass mortality and a degree of increment decline. Wood mass mortality was classified into four degrees: I (0.1–10%, low mortality), II (10.1–25%, moderate mortality), III (25.1–50%, intensive mortality) and IV (50.1–100%, extreme mortality). Increment decline was also classified into four degrees, but with different percentages: I (0.1–25%, low), II (25.1–50%, moderate), III (51.1–100%, intensive) and IV (>100%, extreme). Based on the degree of wood mass mortality and degree of increment decline of each single compartment, maps of wood mass mortality rate and of increment decline rate were constructed. In the Management Unit »Međustrugovi«, the mortality rate of wood mass by compartments was relatively low. A total of 85 dieback-affected compartments over an area of 1302 ha were analyzed. In 98% of the compartments, low to moderate wood mass mortality rate was recorded (Fig. 2), but no intensive or extreme dieback was found. Rates of increment decline by compartments were unfavorable. Extreme decline was found in 6 compartments over an area of about 30 ha, intensive increment decline was recorded in 12 compartments, i.e., significant reduction in the increment was recorded in over 20% of the compartments (Fig. 3). Intensive and extreme increment decline was found in an area exceeding 260 ha. Compartments with the highest values of wood mass mortality did not manifest the most extreme values of increment decline. The map does not show any significant participation of the compartments with extreme increment decline, although the grouping of the compartments with intensive and extreme decline was observed, and so was their higher participation in the southern part of the management unit along the Strug watercourse. In relation to the three study areas, the lowest mortality of wood mass was recorded in the Management Unit of »Zelenika«. The research included 50 compartments over an area of 1065 ha. Moderate wood mass mortality was found in 6 compartments and slight mortality in the remaining compartments. Intensive and extreme increment decline was recorded in 10% of the compartments comprising an area of over 100 ha (Fig. 6). The grouping of compartments with a certain degree of increment decline is observed. This refers particularly to degrees II and III of increment decline, which were recorded in the compartments situated in the eastern part of the Management Unit of »Zelenika« (Fig. 7). The highest participation of compartments and sub-compartments with intensive and extreme rates of wood mass mortality was recorded in the Management Unit of »Grede–Kamare«. Of a total of 102 dieback-affected compartments and sub-compartments in an area of 1474 ha, wood mass mortality was extreme in 12 compartments and intensive in 30 compartments, in an area of over 570 ha. Moderate and low mortality of wood mass was found in 57% of the compartments (Fig. 8). An exceptionally unfavorable condition was recorded in relation to the degrees of increment decline. Extreme increment decline was found in over 55% of the compartments; in other words, every second compartment or sub-compartment in the Management Unit of »Grede–Kamare« was afflicted by disturbed stand growth and increment in an area of over 800 ha. Other degrees of increment decline had similar participation by compartments and sub-compartments (Fig. 9). The largest number of compartments and sub-compartments with extreme and intensive increment decline was recorded in the southeastern part of the management unit. They form larger units and are grouped in one part of the management unit in the map (Fig. 10). A comparison of increment decline rates by management units reveals the occurrence of intensive increment decline in a smaller number of compartments (10–15% of the compartments), and of extreme decline in fewer than 10% of the compartments in two management units. In one of the management units, extreme increment decline affected more than 50% of the compartments. Changes in the sites of pedunculate oak in the last 100 years have affected the stability of these forests and the vitality of trees, which has decreased considerably in recent times. Pedunculate oak trees of lessened vitality are permanently exposed to impact of a variety of adverse factors. This consequently leads to a gradual decline of trees, of which some die before the end of the rotation. Dieback of trees aged between 80 and 120 recorded in the Spačva forest area is an important indicator of disturbed growth and development of the most valuable forests in Croatia and a sign of general disturbances in the stability of lowland forests. Intensive tree mortality continues despite management procedures aimed at regulating the structure and quality of the stands. This phenomenon is particularly characterized by an uneven spatial distribution and intensity. In some areas of the pedunculate oak range in Croatia, dieback is the biggest management and ecological forestry problem, since management largely involves damaged and dead trees of pedunculate oak. As a result, the quality of the stands and total wood mass production are severely reduced. Since dead pedunculate oak trees are less exploitable and achieve lower market values, the consequences of tree dieback reflect unfavorably on the entire forestry sector. Monitoring the intensity and dynamics of tree dieback in stands is one of the ways to determine certain patterns of this phenomenon and improve the management with forests of disturbed stability. This requires more intensive and regular marking of damaged and dead trees. The most common indicators used for the marking of these trees are morphological features of the crown and biotic damage of the stem. However, these indicators are insufficient for achieving better stand vitality and reducing tree decline and dieback. Hence, spatial distribution of tree dieback by compartments and sub-compartments is one of the possible indicators that can be used in planning the management with stands of lessened vitality. Our research found chronic and continuous dieback of pedunculate oak trees, although dieback rates vary by years. Significant spatial differences were also found in the rates of wood mass mortality and increment decline, both among the management units and among their compartments and sub-compartments. Spatial grouping of compartments with intensive and extreme dieback shows correlation with site factors, which are considered the principal causes of dieback. Management with pedunculate oak forests with disturbed stability should be adjusted to the condition of individual ecosystems and to the trends that indicate their development. Presentations of spatial distribution of tree dieback can significantly contribute to this goal.