The diversity of saproxylic beetles’ community from the Natural Reserve Voievodeasa Forest, North-Eastern Romania

Nature reserves harbour considerable richness and diversity of saproxylic organisms since dead wood is preserved in situ, this being also the case of Voivodeasa beech-spruce-fir forest in North-Eastern Romania, the area investigated under the present research. Flight interception traps were employed to capture insects during a vegetation season with the goal to characterize saproxylic Coleoptera community in terms of diversity and several other structural features. Among the captured insects, the majority pertained to obligate saproxylic species (217 species). However, the unexpected high species richness corresponded to an area with modest representation of deadwood due to previous status of commercial forest. The identified beetles were members of different habitat-guilds depending on what type of substrate they colonized: recently dead wood (23%), decomposed dead wood (41%), wood inhabiting fungi (34%) and treehollow detritus (2%). According to their trophic position, the identified saproxylic beetles pertained to the following guilds: xylophagous (40%), mycetophagous (39%), predatory (14%), and species relying on other food resources. The observed richness corresponded to the case of hyperdiverse communities where sampling never leads to the stabilization of species richness under a realistic sampling scheme. The diversity profiles constructed on Shannon, Gini-Simpson, Berger-Parker and evenness indices for the pooled inventory and for separate samples across the vegetation season indicated the aggregated saproxylic community as highly diverse and highly uneven, with rich representation of rare species, dominated by few abundant species. We assembled four bipartite, unweighted, and undirected networks to approach the temporal changes across the sampling period extended over one vegetation season. The topology of beetles’ community and of the three main trophic guilds (xylophagous, mycetophagous and predatory) networks linked to time sequences are characterized by high connectance, high nestedness and modularity, with the exception of the mycetophagous sub-network not displaying significant modularity. Among the identified species, 13% indicate high degree of naturalness of the Voievodeasa forest. 62 of the identified species are included in the Red List of European Saproxylic Beetles of which five are near threatened (Protaetia fieberi, Cucujus cinnaberinus, Crepidophorus mutilatus, Ceruchus chrysomelinus, Prostomis mandibularis), Ischnodes sanguinolentus is vulnerable and Rhysodes sulcatus is an endangered species. During the study, two Coleoptera species, new for Romanian insect fauna were identified: Denticollis interpositus Roubal, 1941 and Hylis procerulus (Mannerheim 1823).

Automated detection of individual juniper tree location and forest cover changes using Google Earth Engine

Tree detection is the first step in the appraisal of a forest, especially when the focus is monitoring the growth of tree canopy. The acquisition of annual very high-resolution aerial images by the National Agriculture Imagery Program (NAIP) and their accessibility through Google Earth Engine (GEE) supports the delineation of tree canopies and change over time in a cost and time-effective manner. The objectives of this study are to develop an automated method to detect the crowns of individual western Juniper (Juniperus occidentalis) trees and to assess the change of forest cover from multispectral 1-meter resolution NAIP images collected from 2009 to 2016 in Oregon, USA. The Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), and Ratio Vegetation Index (RVI) were calculated from the NAIP images, in addition to the red-green-blue-near infrared bands. To identify the most suitable approach for individual tree crown identification, we created two training datasets: one considering yearly images separately and one merging all images, irrespective of the year. We segmented individual tree crowns using a random forest algorithm implemented in GEE and seven rasters, namely the reflectance of four spectral bands as recorded by the NAIP images (i.e., the red-green-blue-near infrared) and three calculated indices (i.e., NDVI, NDWI, and RVI). We compared the estimated location of the trees, computed as the centroid of the crown, with the visually identified treetops, which were considered as validation locations. We found that tree location errors were smaller when years were analyzed individually than by merging the years. Measurements of completeness (74%), correctness (94%), and mean accuracy detection (82 %) show promising performance of the random forest algorithm in crown delineation, considering that only four original input bands were used for crown segmentation. The change in the calculated crown area for western juniper follows a sinusoidal curve, with a decrease from 2011 to 2012 and an increase from 2012 to 2014. The proposed approach has the potential to estimate individual tree locations and forest cover area dynamics at broad spatial scales using regularly collected airborne imagery with easy-to-implement methods.

Transpiration of Anatolian black pine and sessile oak forest stands in a sub-humid region of Turkey

Transpiration is a key component of the watershed water budget. Therefore, determining the transpiration of forest stands with different characteristics have been of interest for watershed hydrology and forest management practices in a wide range of environments. The objectives of this study were to compare transpiration of Anatolian black pine (Pinus nigra Arn. subsp. pallasiana (Lamb.) Holmboe) and sessile oak (Quercus petraea (Matt.) Liebl.) tree stands and to model transpiration based on the measured climatic factors. Stand transpirations were calculated from sap flow measurements made by the trunk heat balance method. We conducted an exploratory factor analysis (PCR) to detect affecting meteorological factors of stand transpiration, and we developed linear regression equations to predict transpiration of pine and oak stands. Mean daily and yearly canopy transpiration (Ec) were 1.05 mm day-1 and 378.3 mm year-1 for the pine stand and 3.52 mm day-1 and 801.7 mm year-1 for the oak stand. There was a highly positive correlation between daily stand transpiration and wind speed, global radiation, air vapour pressure deficit and air temperature, but a negative correlation with relative humidity for both stands. Soil water potential had little effect on stand transpiration. The model equations accounted for 81% of the variations in transpiration for the pine stand and 85% for the oak stand. Therefore, the transpiration of forest stands should be considered for effective vegetation management practices, as model equations to estimate the transpiration of pine and oak stands in the region.

Comparison of various growth functions for predicting long-term stand development associated with different initial spacing in 64-year-old Japanese cedar (Cryptomeria japonica (L.f.) D. Don) plantations

Establishing a plantation with varied distances between trees is one way to control stand density in an initial growth stage. Understanding how stand growth patterns are influenced by initial spacing can help maximize growth and yield. The purpose of this study was to examine the long-term effects of different patterns of initial tree spacing on stand development. A spacing trial with five initial distances, namely, treatments I: 1×1 m, II: 2×2 m, III: 3×3 m, IV: 4×4 m, and V: 5×5 m, was established in 1950 in Japanese cedar (Cryptomeria japonica (L.f.) D. Don) plantations in central Taiwan, managed by the Experimental Forest of National Taiwan University. Each treatment had three repetitions, and all plots were surveyed from 1955 to 2014, with eight records for each time series. We simultaneously employed six growth functions to predict stand basal area growth for each plot and assessed their predictability using the root mean square error (RMSE) as a criterion. Consequently, a total of twelve plots covering all treatments except treatment I, each with six RMSEs resulting from various models, were obtained. The repeated measures analysis of variance approach was adopted to compare predictability among models. The Richards growth function performed the best compared to all the other models. As a result, this model was used to analyse stand development following different initial spacing. We found that the predicted curves could effectively exhibit the growth patterns resulting from different initial spacing. Moreover, the parameters help explain some characteristics of stand development, such as growth potential and maximum growth rate achieved (t max). As a result, a clear trend emerged, showing that, with decreasing initial spacing, the growth potential increased and the t max decreased. These results provided valuable information for managing the stand density of this conifer.

Diversity and prevalence of entomopathogenic fungi (Ascomycota, Hypocreales) in epidemic populations of bark beetles (Coleoptera, Scolytinae) in spruce forests of the Tatra National Park in Slovakia

Bark beetles are serious forest pests in Slovakia. Their outbreaks may have significant ecological and economic impacts on spruce forests. There is a variety of natural enemies that activate themselves during population outbreaks of insects and entomopathogenic fungi belong to important antagonists with a potential to regulate populations of their hosts. In 2014–2016, species richness and prevalence of entomopathogenic fungi were evaluated during the bark beetle outbreaks in spruce forests affected by windstorms in the Tatra National Park in Slovakia. Three Beauveria species, B. bassiana, B. caledonica and B. pseudobassiana, with Metapochonia bulbillosa were identified from 271 specimens of three bark beetle species, Ips typographus, Ips amitinus and Pityogenes chalcographus. Beauveria bassiana was the dominant pathogen and infected all three bark beetle species. Phylogenetic analysis identified three phylogenetic groups of B. bassiana in the evaluated host populations. M. bulbillosa was reported for the first time from bark beetle hosts and Slovakia. The prevalence of fungal infection in natural populations of I. typographus was low, varied between 0.07 and 0.72%, and have little influence on the bark beetle abundance.

Analysis of a feller-buncher productivity: a case study of whole-tree harvesting from Marmara region, Turkey

In fully mechanized forest harvesting systems, tree felling activities are mostly performed by using harvesters or feller-bunchers. In some regions of Turkey, where terrain conditions and stand characteristics are suitable, fully mechanized harvesting systems have been recently practiced by some of the logging contractors as private forest industry demands for large amounts of forest products throughout the year. Thus, performances of these newly practiced harvesting systems should be carefully analyzed in order to implement productive and cost-effective mechanized harvesting systems. In this study, productivity of whole-tree harvesting using a feller-buncher was investigated based on stand parameters including tree height, DBH, and volume. The DBH of the felled trees were divided into four classes (i.e. very small: 16-19 cm, small: 20-23 cm, medium: 24-27 cm and large: 28-31 cm) to investigate the effects of various DBH class on the time consumption of cutting stage and productivity of the feller-buncher. To estimate productivity of feller-buncher in harvesting operation, multiple linear and polynomial regressions were also developed and discussed after the interpretation of diagnostic plots. The results indicated that the average productivity of the feller-buncher was 74.96 m3 /h which was closely related with tree height (r = 0.63), DBH (r = 0.67), and volume (r = 0.67). The average moving time was the most time-consuming stage (60%), followed by cutting (29%) and bunching stages (11%). It was found that DBH classes caused statistically significant (p < 0.05) effects on the time spent on cutting stage and productivity of the feller-buncher. The cutting time and productivity increased from very small to large diameter classes, while bunching time increased from very small to small diameter and then medium diameter to large diameter classes. Polynomial regression had a positive impact on the performance of the estimation model of manually field-measured data based on the error parameters.

Neighbourhood-based evidence of tree diversity promotion by beech in an old-growth deciduousconiferous mixed forest (Eastern Carpathians)

Neighbourhood models are useful tools for understanding the role of positive and negative interactions in maintaining the tree species diversity in mixed forests. Under such a presumption, we aimed at testing several hypotheses concerning the mechanisms of autogenic species coexistence in an old-growth, beech-fir-spruce stand, which is part of the Slătioara forest reserve (Eastern Carpathians). Univariate/bivariate spatial point pattern analyses, the individual tree species-area relationship, the species mingling analysis and generalised linear mixed models of neighbour interference were applied on data concerning the position and allometry of all saplings and trees occurring within a 0.24 ha plot. The monospecific distribution of either beech or spruce saplings did not support the spatial segregation hypothesis. There was no evidence of conspecific negative distance dependence, as no spatial segregation was detected between the saplings and trees of any species. Within 4 m-neighbourhood, the beech saplings appeared as diversity accumulators, which might be indicative of indirect facilitation (e.g., herd protection hypothesis). At tree stage, none of the three species showed either accumulator or repeller patterns in their neighbourhood with respect to sapling species richness. Signals of positive and negative interspecific association were found in tree-sized beech (at scales of 10 to 20 m) and spruce (at scales of 4 to 17 m), respectively. The former, highly interspersed pattern is in accordance with the hypothesis of positive complementary effects, whereas the latter, poorly intermingled pattern is probably linked to the unexpected, positive neighbouring effect of spruce trees on the stem growth of their conspecific saplings. Such self-favouring process might be due to a facilitative below-ground mechanism. Conversely, the beech saplings were suppressed through interference from the neighbouring conspecific trees. The beech appears to be the key promoter of tree species coexistence in the study forest stand, in contrast to the low interspersion of spruce in the overstorey leading to lower local tree diversity.

Production of valuable oak wood in Europe

Large dimension branch free wood of pedunculate oak (Quercus robur L.) and sessile oak (Q. petraea (Matt.) Liebl.) is highly valued, while small sized and low-quality oak timber generate little income. This paper describes how large dimensions of branch free wood can be produced by applying appropriate silvicultural measures. The results are based on measurements of oak trees in various regions in Germany and Denmark. Two management phases are distinguished: In phase 1 pruning is emphasized and at the beginning of phase 2 future crop trees are selected to promote diameter growth of these oak trees. The resulting guidelines provide a quantitative basis for objective-oriented oak management.

Characterization of the brown leaf spots pathosystem in Brazilian pecan orchards: pathogen morphology and molecular identification

Due to the increase in pecan nuts demand, plantation areas are expanding around the world and more frequent epidemics caused by fungal pathogens may occur in orchards and nurseries. Ragnhildiana diffusa is a pathogenic fungus reported to cause brown leaf spots on pecans in numerous countries. The scarcity of comprehensive information in symptoms on the host and morphology of the fungus lead this disease to be initially incorrectly identified in Brazil. In this study, we employed different approaches to characterize the pathogen morphology and pathogenicity and to molecularly identify the organism causing brown leaf spots in southern Brazil. A phylogenetic analysis based on the internal transcribed spacer (ITS) and the large subunit (LSU) gene sequences confirmed R. diffusa as the causal pathogen of the disease. Inoculation tests on healthy leaflets confirmed pathogenicity isolates, although some variation in their virulence was observed. Variation in the morphology of the asexual stage was observed among and within isolates. This study brought unprecedented morphological, genetic and pathogenic information that aids elucidating the disease. The accurate and prompt identification of the disease may assist in controlling further spread of the pathogen into orchards and nurseries still free of the disease in South America.

The anniversary conference "Structural Components of Forest Ecosystems: ecology, conservation and management" held in honour of Prof. Nicolae Donita

The celebration of the outstanding personalities of academia is always an occasion to exchange ideas, establish the state of art of a scientific area, and highlight the hallmarks and new paradigms. This was the case of the Anniversary Conference "Structural Components of Forest Ecosystems: ecology, conservation and management" held in honour of Prof. Nicolae Doniță, under the generous auspices of the Banat University of Agricultural Sciences and Veterinary Medicine "King Michael I of Romania" in Timișoara. The celebrated scientist, Professor Nicolae Doniță (also member of the Romanian Academy of Agricultural and Forest Sciences “Gheorghe-Ionescu Șișești” and, Doctor Honoris Causa of the Agricultural and Veterinary Sciences University of Banat "King Mihai I of Romania" and of the University Ștefan cel Mare of Suceava) marked in that occasion his 90th anniversary, surrounded by his fellow scientists, former students and collaborators. Fifty-three participants in the conference honoured the personality and lifetime achievements of one of the most prominent figures among the Romanian forest ecologists, who reshaped the fundamentals of the Romanian silviculture based on the ecosystemic approach. The most consistent section of the conference was dedicated to the presentation of oral communications and posters circumscribed to the conference's central theme. The systemic, holistic paradigm adopted in forest ecology was brought forward in the opening lecture given by Prof. Doniță: “On the formation of the forest ecosystem”. The rest of presentations focused on more specific topics or case studies, of which some are briefly mentioned hereinafter. The old-growth forests in Romania were presented from the perspective of significance for the conservation efforts and various hindrances, with special reference to the integration in the larger European concern raised by climatic change and anthropogenic pressures. The forest dynamics in terms of species composition was employed as a tool for the evaluation of forest naturalness in Bosco Quarto (Gargano, Italy). The overview of tropical monospecific forest plantations brought a close insight into an old and controversial problem related to the balance between economic benefits and biodiversity loss. The study of the complex interactions between herbs and tree saplings in southern Appalachian forests revealed the mediator effects of soil fertility and stand evergreenness. The current status of forest habitats in Romania was summarized by means of the second national report to the European Commission (article 17 in the Habitats Directive). The importance of dead wood preserved in situ was demonstrated by the high diversity of saproxylic beetles within the natural reserve Voievodeasa Forest (North-Eastern Romania). The analysis of data contained in management plans was shown to provide useful information for mitigating the consequences of climatic change by improving the ecological status of forests and enhancing their environmental services. The synthesis on the old-growth and virgin beech forests from Carpathians and other European regions, included in the UNESCO World Heritage List, was presented as an important contribution to the forest conservation effort at European level. The role of soil physical and chemical properties, as important determinants for the distinction of forest ecosystem types, was highlighted in the Subsidiary Timiș Forest. The old-growth beech forests included in the nature reserve Izvoarele Nerei (South-Western Romania), famous for its big trees and pristine status, were shown to harbour a high biodiversity encompassing species from different groups. The comparison of two estimation methods of the foliar area index in a beechfir old-growth forest provided interesting insights on the influence of environmental factors. The speakers referred to the scientific stature of Prof. Doniță, but also to his friendly human nature, his talent in gathering people around a common theme, his generous approach to science and scientists, being a leader but not misusing his authority, while always remaining a kind and patient guide. His achievements, spanning across six decades, consist of important international projects, seminal books and a vast array of scientific papers. Several outstanding books he coordinated or co-authored should be mentioned in this context: Forest Ecosystem Types of Romania (1990), Habitats of Romania (2005-2006), Forest Ecology (1978), The Vegetation of Romania (1992), Silviculture on Ecosystemic Bases (1997), The Virgin Forests of Romania (2001), Population, Species, Biocoenosis - An integrating Vision (2019). One of the milestones of Nicolae Doniță’s activity was his participation in the project “Map of the Natural Vegetation of Europe, Scale 1:2500000, with Explanatory Text”, which extended over 20 years of intensive collaboration between experts from across all Europe. Another notable achievement consisted in the elaboration (along with several co-workers) of the Forest Geospatial Database of Romania according to ecosystemic units and the corresponding digital map. In conclusion, the conference gave the rare opportunity of gathering around a hallmark personality of forest ecology and a series of valuable scientific contributions, while celebrating the lifetime achievements of Prof. Doniță in the context of the contemporary forest science. A selection of papers, either presented at the conference or submitted later on, are included in the first section of the current journal issue.