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Novo Mesto, Slovenia

We evaluated the response of active cambium of sessile oak (Quercus sessiliflora) and sycamore maple (Acer pseudoplatanus) to experimentally increased (20-22 °C) and decreased (9-11°C) temperatures. Heating and cooling experiments on 150-year old Q. sessiliflora were performed during the growth season of 2007 and on 30-year old A. pseudoplatanus in 2008. In 2009, heating experiment was carried out on 30-year old Q. sessiliflora. For each treatment, two trees were selected of each species and sampled at 21-day intervals during the vegetation period and investigated by means of light microscopy. Continuously elevated temperatures slightly promoted the development of xylem cells in old Q. sessiliflora trees in the first month of cambial activity. However, no effect of elevated or decreased temperature was detected in the timing and dynamics of wood and phloem formation. The applied treatments, therefore, had no visible impact on the structure or width of the xylem or phloem increments in 2007. On the other hand, heating young A. pseudoplatanus trees provoked the development of epicormic shoots two months after the onset of the experiment and finally the death of trees. The cambium of those trees did not reactivate in 2008; xylem and phloem increments were onsequently not formed. Low temperature treatments slowed down cell production at the very beginning of the growing season, but no alterations in wood or phloem formation dynamics or structure were observed later. The heating of young Q. sessiliflora trees caused the development of epicormic shoots and the death of trees four months after the experiment. The pattern of their dying was similar as in A. pseudoplatanus but with a two month delay. The observations indicate that tree age, thickness of dead bark and duration of the applied treatments influence the response of cambium. The development of dead bark is species specific and it occurs earlier in Q. sessiliflora than in A. pseudoplatanus. Thick dead bark acts as a very good insulation layer for the sensitive internal, living tissues of bark and cambium and therefore protects them against external abiotic and biotic factors.

Solute accumulation in plant leaves during drought through accumulation of organic compounds is known to compensate turgor loss andpromote higher stomatal conductance at lower water potentials. Recent studies have involved experiments on saplings and younger stands, while evidence of osmotic adjustment in adult pedunculate oak under natural stand conditions on different sites is scarce. Pressure volume curves technique was used to define differences in osmotic potential - water stress adaptation - of 120 year oldped unculate oak trees in two managedforest complexes andin virgin forest remnant. Tree response between the managedstandafter thinning andthe standwithout any silvicultural measures within same forest complex was also compared during summer months in two consecutive (dry and favourable) years with groundwater table. Significant differences were observed in adaptation between forest complexes and during dry (2003) and favourable (2004) years. Osmotic component of thinnedforest was the highest, showing most negative values of stress adjustment. Measured values on all plots responded well to drop in groundwater table, especially in pronounced drought conditions. Such response may be in relation with lower stand density and increased individual space for growth in thinned stand. Adult oaks did not loose their ability to water stress adaptation, in spite of their age and progressively decreasing health conditions.

Cas M.,Slovenian Forestry Institute
Sumarski List | Year: 2010

Capercaillie (Tetrao urogallus L.) populations in central and south-east Europe cover fragmented edge habitats and are recorded to decline since 1960ies. Capercaillie leks in Slovenia are present at the south-eastern edge of the Alpine metapopulation and at north-western edge of Dinaric. These populations were monitored at leks in two periods in 1980 (466 monitored leks) and 2000 (599). All leks were monitored by local specialists (hunters and/or foresters) and main causes of observed lek populations decline were addressed to each endangered lek. Special emphasis was given to predation at leks, as suggested by D. Jenkins (2008). The six named reasons in 1980ies affected 39 leks with logging of old-growth forests (at 71.8% of leks) and construction of forest roads (7.7%) as most pronounced. In 2000 nine reasons affected 92 leks: (i) mountain tourism (26.1%), (ii) cutting of old-growth forests (19.60%), (iii) predators attacks (18.5%), (iv) forest management in spring time (9.8%), (v) pastures of livestock with wire fences in forests (6.5%), (vi and vii) berries picking and overgrowing the last pastures in forest-landscape, (viii) constructions of forest roads and (ix) infrastructure. The most profound change in reasons between 1980 and 2000 mapping data were: predation at leks, mountain tourism development, increasing of forest management in spring time, wild pasturage of cattle and sheep in forests, overgrowing the last pastures in forest-landscape. A comparison of the increasing percentage of leks endangered by predators since 1980 has shown positive correlations with increasing of the main predator populations' densities. Population density of martens (Martes sp.) and wild boar (Sus scrofa) increased for 150% since 1980, while red fox (Vulpes vulpes,) density increased only after 1990. Our results confirmed the assessment of reasons for threats to leks based on descriptions and experiences of observers as a suitable approach for capercaillie habitat risk assessment. Results for past decline and differences regarding to the negative impacts on lek habitats are important guidelines for foresters and wildlife managers concerning sustainable forest management and maintenance of capercaillie populations.

Ogris N.,Slovenian Forestry Institute | Jurc M.,University of Ljubljana
Ecological Modelling | Year: 2010

A model is presented to predict sanitary felling of Norway spruce (Picea abies) due to spruce bark beetles (Ips typographus, Pityogenes chalcographus) in Slovenia according to different climate change scenarios. The model incorporates 21 variables that are directly or indirectly related to the dependent variable, and that can be arranged into five groups: climate, forest, landscape, topography, and soil. The soil properties are represented by 8 variables, 4 variables define the topography, 4 describe the climate, 4 define the landscape, and one additional variable provides the quantity of Norway spruce present in the model cell. The model was developed using the M5′ model tree. The basic spatial unit of the model is 1 km2, and the time resolution is 1 year. The model evaluation was performed by three different measures: (1) the correlation coefficient (51.9%), (2) the Theil's inequality coefficient (0.49) and (3) the modelling efficiency (0.32). Validation of the model was carried out by 10-fold cross-validation. The model tree consists of 28 linear models, and model was calculated for three different climate change scenarios extending over a period until 2100, in 10-year intervals. The model is valid for the entire area of Slovenia; however, climate change projections were made only for the Maribor region (596 km2). The model assumes that relationships among the incorporated factors will remain unchanged under climate change, and the influence of humans was not taken into account. The structure of the model reveals the great importance of landscape variables, which proved to be positively correlated with the dependent variable. Variables that describe the water regime in the model cell were also highly correlated with the dependent variable, with evapotranspiration and parent material being of particular importance. The results of the model support the hypothesis that bark beetles do greater damage to Norway spruce artificially planted out of its native range in Slovenia, i.e., lowlands and soils rich in N, P, and K. The model calculation for climate change scenarios in the Maribor region shows an increase in sanitary felling of Norway spruce due to spruce bark beetles, for all scenarios. The model provides a path towards better understanding of the complex ecological interactions involved in bark beetle outbreaks. Potential application of the results in forest management and planning is discussed. © 2009 Elsevier B.V. All rights reserved.

Gricar J.,Slovenian Forestry Institute
Wood Research | Year: 2010

We studied the timing of xylem and phloem formation, and the widths and structure of completed xylem and phloem increments in sessile oak (Quercus sessiliflora Salisb.) from Slovenia in the growing season of 2007. Weekly samples of inner phloem, cambium and xylem were analysed using light microscopy. Cambial reactivation and, consequently, xylem and phloem started before our first sampling at the end of March 2007. Weekly measured xylem and phloem increments revealed that phloem production was faster in the first part of the growing season (i.e., from the beginning of April until the third week of May), but thereafter xylem production accelerated. The period of most intense xylem cell production was assessed to be in the period April-May and that of phloem in April. Production of cells in the cambium stopped in the first half of August on xylem and phloem sides. The average width of the xylem increment of the investigated sessile oaks was 1837.55 ± 951.88 μm, phloem was 286.81 ± 232.04 μm and the ratio between phloem and xylem increments was 0.197 ± 0.118. Trees with wider xylem increments also had wider phloem increments, and vice versa. Lower ratios between phloem and xylem growth rings of 2007 were found in trees with wider increments, indicating that cambial cell production favours xylem (specifically late wood) formation in more productive trees. Inter-tree variability in xylem increment was relatively high (± 951.88 μm), whereas intra-tree variability was much lower (± 254.15 μm), but increased with the width of increment. The portion of late wood increased with the width of the xylem growth rings, whereby xylem increments narrower than 1000 μm consisted of more than 50 % of early wood but this portion gradually decreased to 30 % in wider rings.

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