Live Crown Ratio as an Indicator for Tree Vigor and Stability of Turkey Oak (Quercus cerris L.): A Case Study

Stability of forests represents a significant objective for climate change mitigation. As stand stability is influenced by the stability of individual trees, promoting stable trees is vital for a sustainable forest management. However, inside stands, trees experience intense competition. As a result, the crown recedes and diameter growth is affected, the trees becoming slender and more susceptible to biotic and abiotic disturbances. Finding effective indicators for tree vigor and stability is therefore important. This study aimed to assess the performance of the live crown ratio as an indicator in deciding the timing of tending operations for obtaining and maintaining vigorous Turkey oak trees. Live crown ratio (LCR) and height to diameter ratio (HDR) were determined for 80 sampled Turkey oak trees. A threshold of 100 for HDR was chosen to classify trees as slender or not slender. Next, conditional inference tree and logistic regression were used to determine the LCR threshold value where trees become slender. As the sample included small trees, using breast height to measure diameter may have affected the results. Therefore, small and large trees were also analyzed separately. For the entire dataset, the methods reached quite different results (LCR threshold of 0.371 for conditional inference tree and of 0.434 for the logistic regression), and relatively high values compared to the literature. For tall trees (height > 12.5 m), the methods reached similar results: 0.386 for the conditional inference tree and 0.382 for the logistic regression. For small trees (height < 12.5 m), the conditional inference tree method could not calculate any LCR threshold estimate, while the one from the logistic regression was unrealistically large (0.628). This confirms that using DBH for small trees to compute slenderness brings systematic errors. The live crown ratio was a good indicator of growth vigor for Turkey oak trees. Therefore, for stable trees (HDR < 100), a LCR of 0.36–0.39 must be maintained and could be used to decide the timing for thinning in Turkey oak stands.

AILANTHUS ALTISSIMA (MILLER) SWINGLE - INVASIVE SPECIES IN THE FOREST HABITATS IN THE UPPER BASIN OF THE MOTRU RIVER

Ailanthus altissima (Miller) Swingle is an invasive species found in forest habitats in Oltenia and beyond. The aggression and power of dissemination and development of this species is increasing. The thematic area provided in this paper is situated in the upper basin of the Motru river. Within this study had been aimed the identification and level of pressures and threats of the invasive species Ailanthus altissima in the forest habitats in the researched territory. These studies also noted the conservation status of the forest habitats in which this invasive species was encountered. In this area we identified this invasive species in the following forest habitats: 91E0* Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae), 91V0 Dacian Beech forests (SymphytoFagion), 9130 Asperulo-Fagetum beech forests, 91M0 Pannonian-Balkanic turkey oak - sessile oak forests. This species influence the succesional dynamics and the floristic composition of the forest habitats, occupying increasingly more and more space.

A comparison of ground-based count methods for quantifying seed production in temperate broadleaved tree species

• Key message Litter trap is considered the most effective method to quantify seed production, but it is expensive and time-consuming. Counting fallen seeds using a quadrat placed on the ground yields comparable estimates to the litter traps. Ground quadrat estimates derived from either visual counting in the field or image counting from quadrat photographs are comparable, with the latter being also robust in terms of user sensitivity. • Context Accurate estimates of forest seed production are central for a wide range of ecological studies. As reference methods such as litter traps (LT) are cost- and time-consuming, there is a need of fast, reliable, and low-cost tools to quantify this variable in the field. • Aims To test two indirect methods, which consist of counting the seeds fallen in quadrats. • Methods The trial was performed in three broadleaved (beech, chestnut, and Turkey oak) tree species. Seeds are either manually counted in quadrats placed at the ground (GQ) or from images acquired in the same quadrats (IQ) and then compared against LT measurements. • Results GQ and IQ provide fast and reliable estimates of seeds in both oak and chestnut. In particular, IQ is robust in terms of user sensitivity and potentially enables automation in the process of seed monitoring. A null-mast year in beech hindered validation of quadrats in beech. • Conclusion Quadrat counting is a powerful tool to estimate forest seed production. We recommend using quadrats and LT to cross-calibrate the two methods in case of estimating seed biomass. Quadrats could then be used more routinely on account of their faster and simpler procedure to obtain measurements at more spatially extensive scales.

Mixed mesophilic mountain beech forest (Fagetum submontanum serbicum) on the Vidlič Mountain

On the Vidlič mountain, mixed mesophilic mountain beech forests (Fagetum submontanum serbicum) have been recorded at altitudes of 700 - 1000 m, at the following localities: Crni vrh, Vazganica, Kranjci, Planinarski dom, and Visočka Ržana. Phytocenological research was performed on the mentioned localities by the Braun-Blanquet method (Braun-Blanquet, 1964). It was taken 11 phytocenological plots. Beech (Fagus moesiaca) and turkey oak cer (Quercus cerris) were the main edificators and have the highest degree of presence in the examined phytocenoses on the tree floor. In the floor of shrubs, the following species: Viburnum lantana, Crataegus monogyna, Rosa canina, Daphne mezereum, Clematis vitalba, and Ligustrum vulgare have been noticed with the highest degree of presence. Acer campestre has been dominated with the highest degree from the shoots of trees. In the floor of herbaceous plants, the species: Viola alba, Cruciata glabra, Brachypodium sylvaticum, Euphorbia amygdaloides, Helleborus odorus, Fragaria vesca were with the highest degree of presence.

General regularities of height-diameter curves in Hungarian oak, sessile oak and Turkey oak high forests

The height-diameter curves of natural even-aged Hungarian oak, sessile oak and Turkey oak forests in the regions of Staro Oryahovo, Sherba, Tsonevo and Aytos Forestry Districts have been studied. In order to explore the shape of the curves and, in particular, their steepness, the steepness index SI of Douhovnikov (&ldquo;the method of natural indicators&rdquo;) was applied. The curves were divided into three groups according to it: flat curves, medium steep curves and steep curves. Both the traditional height-diameter curves and the corresponding relative curves of Tyurin were studied. Consideration of the traditional height-diameter curves gives a certain ground for investigating to-gether the height-diameter curves of Hungarian oak and sessile oak, disregarding the tree species. This inference was confirmed by comparing the relative height-diameter curves for Hungarian oak, sessile oak and Turkey oak with Tyurin&rsquo;s uniform curve of relative heights. For these comparisons we used the Willcoxon test. A statistically significant great proximity in their shapes was found. As a uniform average curve of relative heights has been established for all tree species, this proximity indicates a possibility of creating a single fan of height-diameter curves for high Hungarian, sessile and Turkey oak.