Manual versus Digital Classification of UAV Images in Oak Phenological Studies

Tree species have a remarkable impression on the physical, chemical and microbial properties of the soil. Some tree species like alders create a favorable environment for microbes in their soil–root interface in addition to carrying out soil reclamation. This study, conducted in the Western Black Sea Region of Turkey, compared the N-fixing in the roots of the black alder [Alnus glutinosa (L.) Gaertn.] and the non-N-fixing in those of the sessile oak [Quercus petraea (Matt.) Liebl.] species in terms of physical, chemical and microbiological soil characteristics. Samples of topsoil (0–6.5 cm) were collected randomly from under the black alder and the sessile oak trees, respectively, at seven different sites in the study area. Soil microbial biomass C and N were established by the chloroform fumigation extraction method. Basal respiration of soil was retained by the sodium hydroxide (NaOH) trap method. Contrary to expectations, the average organic C (2.59%), total N (0.22%), microbial biomass C (738.48 µg g−1) and N (99.56 µg g−1) were higher under the sessile oak trees, demonstrating the positive effect of sessile oak on soil microflora. The black alder and sessile oak tree soils exhibited significant differences in their content of organic C (Corg), total N, microbial biomass C (Cmic), and N. In addition, significant positive linear correlations were found between organic C and microbial biomass C, and also between organic C and basal respiration; however, the correlation between the metabolic quotient (qCO2) and Cmic/Corg percentages was negative for the black alder and sessile oak (r = − 0.589 and r = − 0.474, respectively), likely due to the fact that relatively more C was being utilized for growth than for respiration. These results indicated that, compared to the sessile oak, the relatively lower organic C and total N and subsequently, the microbial biomass C and N content under the black alder were most likely due to shallow and deep groundwater flow and thus, the loss of plant nutrients was probably brought about by weathering.

The presence of Cryphonectria parasitica (Murrill) M.E. Barr was studied in six natural and planted stands of sweet chestnut in Serbia. The fungus was detected on the sweet chestnut in five localities and on the sessile oak in one locality. In total, 77 isolates from the sweet chestnut and five isolates from the sessile oak were obtained. Based on the culture morphology, all the obtained isolates were proven to be free from Cryphonectria (Saccardo) Saccardo & D. Saccardo hypovirus. The isolates of C. parasitica from the sweet chestnut were compatible with three different vegetative compatibility types, EU-12, EU-2, and EU-1, while the isolates from the sessile oak belonged to EU-12. After inoculation in laboratory conditions, the isolate from the sweet chestnut and sessile oak caused the decline in 88 and 76% of the sweet chestnut plants, respectively. In the case of the sessile oak, both isolates caused the decline in 52% of the plants. In field conditions, both isolates were aggressive to sessile oak trees after previous bark wounds and they were statistically significantly different compared to the control trees. The isolate from the sweet chestnut caused significantly larger cankers compared to both the isolate from the sessile oak and the control.

Two 25-year old mixed stands including sessile oak and hornbeam or Hungarian oak were taken into account for studying the role of competition and subsequent natural mortality in sessile oak-dominated stands. Observations of health state and measurements of diameter at breast height of all trees in two control plots established in the two stands were carried out annually between 2004 and 2011. The main results of this research works are as follows: i) The rate of mortality was more important in case of sessile oak trees than of hornbeam or Hungarian oak. Consequently, the species composition has changed in favour of less light-demanding but more competitive tree species; ii) The majority of dead trees in all tree species were of small sizes (diameters) so the mean diameter has grown continuously since 2004; iii) The basal area has also continuously grown between 2004 and 2011; iv) The initial thickest sessile oak trees had shown the most important diameter growth so they should be used when selecting and marking potential final crop trees; v) The thick and tall hornbeam trees should be extracted by silvicultural interventions while the smaller hornbeam individuals should be kept as understory trees; vi) The large diameter Hungarian oak trees should be kept under control on favourable sites (with fertile and heavy soils), where they can represent a real threat to sessile oak trees.

Stand structure analysis was conducted before and after natural regeneration (on the same plot) on a site of monodominant sessile oak forest (Quercetum petraeae Cer. et Jov. 1953., subass. tilietosum). In this stage individual old sessile oak trees were still remaining in the stand. Before the regeneration in the 150-yr-old stand in 1992 only sessile oak was rep?resented in the upperstorey. The trees mostly had irregularly developed crowns and reduced growth potential. These were the elements used in planning the regeneration in management plans. Besides the remaining individual old sessile oak trees, silver lime dominates in the young stand in 2017. In the stand structure there is no biological potential of sessile oak trees that could represent the basis for further development because the sessile oak trees are suppressed by silver lime towards the understorey and even the herb layer. Because of the undefined significance of the silver lime in the stand, transient management was prescribed in the man?agement plan so a reconstrucion of the stand should follow in one of the next management periods in order to restore sessile oak on the site as it was suppressed due to an inedequate regeneration procedure. On the basis of the studied stand structure of the young stand, the abandonment of the transient management concept is recommended and introduction of the intensive management approach of slver lime in the current rotation. This was based on the available number of silver lime trees of good quality in the stand, i.e. the aspirants for tending by means of selective thinning and their strong growth response four years after selective thinning. Old sessile oak trees that are still present in the stand are only a simulacrum of the continuity of the current stand with the previous one and they should be removed by means of intensive and rationalized tending of silver lime, and partly integrated in the silver lime stand.

This paper provides characteristic and a comprehensive overview of the adaptation strategies of sessile oak (Quercus petraea [Matt.] Liebl.) in the context of global climate change (GCC). The GCC is primarily manifested by increasing air temperatures and changing precipitation distribution. It poses a significant challenge to tree species including sessile oak, affecting its capacity for adaptation and survival. Despite the challenge, sessile oak shows significant drought tolerance due to its deep-reaching root system, which allows the tree to use available water more efficiently. Other adaptive strategies include the establishment of mixed stands that increase the resilience and biodiversity of the ecosystem. Adjustments of stand density through tending interventions play a significant role, helping to improve the stress resistance of stands. Additionally, coppice forest cultivation is applied on extremely dry sites. The sessile oak is also significant for its ecological plasticity – its ability to thrive on versatile soil and climatic conditions makes it a promising tree species for future forest management. Mixed stands with sessile oak and other tree species can enhance the ecosystem services of forests and also increase their endurance to GCC events. However, sessile oak faces several challenges, including the increasing risk of damage from pests and pathogens that require targeted measures for its protection and sustainable cultivation. The literature review suggests that a comprehensive understanding of sessile oak’s ecological requirements and interactions with the environment is crucial for its successful adaptation to GCC and the formulation of effective strategies for its protection and use in forest management.

European oak species have long been considered relatively resistant to different disturbances, including drought. However, several recent studies have reported their decline initiated by complex changes. Therefore, we compared mature sessile oak trees (Quercus petraea (Matt.), Liebl.) infested versus non-infested by hemiparasitic yellow mistletoe (Loranthus europaeus Jacq.) during the relatively dry vegetation season of 2019. We used broad arrays of ecophysiological (maximal assimilation rate Asat, chlorophyll a fluorescence, stomatal conductance gS, leaf morphological traits, mineral nutrition), growth (tree diameter, height, stem increment), and water status indicators (leaf water potential Ψ, leaf transpiration T, water-use efficiency WUE) to identify processes underlying vast oak decline. The presence of mistletoe significantly reduced the Ψ by 1 MPa, and the WUE by 14%. The T and gS of infested oaks were lower by 34% and 38%, respectively, compared to the non-infested oaks, whereas the Asat dropped to 55%. Less pronounced but significant changes were also observed at the level of photosystem II (PSII) photochemistry. Moreover, we identified the differences in C content, which probably reduced stem increment and leaf size of the infested trees. Generally, we can conclude that mistletoe could be a serious threat that jeopardizes the water status and growth of oak stands.

<p>Abstract:</p><p>As a widespread species, sessile oak (<em>Quercus petraea</em>)<em> </em>populations occupy a wide range of ecological conditions with different local selection pressures, especially different drought exposure, which would have favoured different locally adapted populations. Water-use efficiency (WUE), which is defined at the tree level as the ratio between the biomass produced and the quantity of water transpired during the same period of time, is an interesting candidate trait for adaptation to drought. Six hundred trees from sixteen different provenances planted in 1993 in a common garden in the North-Eastern of France were harvested during the 2014-2015 winter. Intrinsic WUE (WUE<sub>i</sub>), estimated from carbon isotope composition (δ<sup>13</sup>C) measurements of tree-rings, was compared among and within provenances for three contrasted years: (i) 2000, a wet year; (ii) 2003, a severely dry year; (iii) and 2005, a moderately dry year. The main purpose was to assess the drought-adaptive character of WUE<sub>i</sub> for sessile oak trees. For this, (i) the adaptive character of WUE<sub>i</sub> was evaluated by relating population mean WUE<sub>i</sub> to the mean pedoclimatic conditions of their provenance sites. (ii) The phenotypic plasticity of WUE<sub>i</sub> to drought was evaluated by comparing  the values observed in 2003 and 2005 to those of  2000 ; this plasticity was also related to the mean pedoclimatic conditions of their provenance sites. (iii) The contribution of WUE<sub>i</sub> to tree and population fitness was assessed from the relationship between WUE<sub>i</sub> and tree growth. Significant differences in δ<sup>13</sup>C (thus WUE<sub>i</sub>) were found among populations. However, no linear relationship was established between mean population δ<sup>13</sup>C and the mean pedoclimatic conditions of the provenance sites. Based on these results observed on juvenile sessile oak trees in the relatively wet conditions of the common garden, no local adaptation in terms of WUEi was detected. An increase in drought intensity resulted in an increase in population WUE<sub>i</sub> and all provenances displayed a similar plasticity of WUE<sub>i</sub> to drought, suggesting no among population diversity for drought responses. A significant correlation between WUE<sub>i</sub> and tree growth was detected only during the wet year, when populations with a higher WUE<sub>i</sub> also had a higher growth index. Moreover, a much larger variability in WUE<sub>i</sub> was demonstrated within populations (2–4‰) than among-population (0.6‰).</p><p>Key words : Climate change, assisted migration, local adaptation, water-use efficiency, fitness, diversity</p>

ABSTRACTConcurrent measurements of sap velocity (heat pulse) and ultrasound acoustic emission were performed on the trunks of mature Turkey oak (Quercus cerris) and sessile oak (Quercus petraea) trees. Plant water status was assessed by measuring leaf water potential, leaf conductance and transpiration. Wood density was estimated non‐destructively on the trunk section of the plants by mobile computer tomography, which measures the attenuation of a collimated beam of radiation traversing the trunk in several directions, as the device rotates around the tree. Absorption is proportional to the density of the wood. As wood density is strictly correlated to water content, this non‐invasive method allows the water content in the trunk section to be evaluated as well as mapped. Leaf water potential declined each morning until a minimum was reached at midday and recovered in the afternoon, lagging behind changes in transpiration rate. Good correspondence was found between the patterns of sap velocity and cavitation rate. A close correlation was demonstrated between wood density, water content and sap velocity. Sap now was always higher in Turkey oak than in sessile oak. Trunk signatures by computer tomography appeared to differentiate the two oak species, with the Turkey oak stem clearly more hydrated than the sessile oak; water storage reservoirs could play an important role in tree survival during extended periods of low soil water availability and in the relative distribution of tree species, especially in the context of global climate change. Late‐wood conducting elements of oak species seem to play a significant role in water transport. The mobile computer tomograph was confirmed as a peerless tool for investigating stem water relations. Diurnal variations in the measured parameters under natural drought conditions and the differences between the two oak species are discussed.

Key messageSessile oak leaves showed a high degree of plasticity to atmospheric and pedospheric conditions.The aim of the present study was to elucidate the significance of current weather conditions for foliar traits of adult sessile oak (Quercus petraea), one of the most valuable forest tree species in Central Europe. For this purpose, structural and functional traits were analysed in fully expanded, sun exposed leaves collected in south-west Germany from five old-growth forest stands, representing the meteorological and pedospheric conditions in the growing region, but differing in aridity during the 12 days before harvest in two consecutive years. Across the forest stands, most foliar traits differed significantly between wet and dry weather conditions before harvest as indicated by partial least square discriminant analysis (PLS-DA). These traits included fresh weight/dry weight ratio, leaf hydration, leaf-C content, leaf-C/N ratio, structural N, soluble protein-N, total amino acid-N, cell wall composition, numerous specific amino acids as well as soluble sugar content. Structural biomass, δ13C signature, total N and total C as well as H2O2 contents were not affected by the weather before harvest. These results indicate a high plasticity of the foliar metabolism of drought-tolerant sessile oak to current weather conditions. They also suggest that sessile oak is characterized by a high potential to cope with the growth conditions expected as a consequence of future climate change.

Using X-ray CT based tree-ring width data for tree growth trend analysis

Shoot and bud dynamics of peripheral crown portions of mature pedunculate and sessile oak trees ( Quercus robur L., Q. petraea (Matt.) Liebl.) were monitored over almost three vegetation periods. The formation and shedding of buds and extension units (eus) was mapped in the form of simplified drawings. Branches were additionally subjected to manipulative treatments simulating herbivore (defoliation at different times, loss of certain bud types) and abiotic damage (artificial acid rain) and the effects on branch architecture analysed. Branch characteristics, such as branching order and age structure, had a large influence on the growth and dynamics of peripheral branch portions, even greater than that of the manipulative treatments, with the exception of spring defoliation and shoot tip removal, which led to increased shoot shedding. In order to quantify the observed changes in crown structure with time, new measures were introduced: the shedding ratio corresponds to the number of shed eus divided by the total number of eus present and produced since a given starting point. The vitality ratio was defined as the total number of eus produced in 1 year, divided by the total number of eus shed during the same time. The vitality ratio could thus be – on a small scale – the quantitative measure of Roloff's vitality classes (Roloff, 1987, 1988, 1989).

First dendrochronological studies of Quercus protoroburoides

Even-aged forest stands are competitive communities where competition for light gives advantages to tall individuals, thereby inducing a race for height. These same individuals must however balance this competitive advantage with height-related mechanical and hydraulic risks. These phenomena may induce variations in height-diameter growth relationships, with primary dependences on stand density and tree social status as proxies for competition pressure and access to light, and on availability of local environmental resources, including water. We aimed to investigate the effects of stand density, tree social status and water stress on the individual height-circumference growth allocation (Δh-Δc), in even-aged stands of Quercus petraea Liebl. (sessile oak). Within-stand Δc was used as surrogate for tree social status. We used an original long-term experimental plot network, set up in the species production area in France, and designed to explore stand dynamics on a maximum density gradient. Growth allocation was modelled statistically by relating the shape of the Δh-Δc relationship to stand density, stand age and water deficit. The shape of the Δh-Δc relationship shifted from linear with a moderate slope in open-grown stands to concave saturating with an initial steep slope in closed stands. Maximum height growth was found to follow a typical mono-modal response to stand age. In open-grown stands, increasing summer soil water deficit was found to decrease height growth relative to radial growth, suggesting hydraulic constraints on height growth. A similar pattern was found in closed stands, the magnitude of the effect however lowering from suppressed to dominant trees. We highlight the high phenotypic plasticity of growth in sessile oak trees that further adapt their allocation scheme to their environment. Stand density and tree social status were major drivers of growth allocation variations, while water stress had a detrimental effect on height in the Δh-Δc allocation.

We used long-term in situ (15)N labeling of the soil to investigate the contribution of the two main nitrogen (N) sources (N uptake versus N reserves) to sun shoot growth from bud burst to full leaf expansion in 50-year-old sessile oaks. Recovery of (15)N by growing compartments (leaves, twigs and buds) and presence of (15)N in phloem sap were checked weekly. During the first 2 weeks following bud burst, remobilized N contributed ~90% of total N in growing leaves and twigs. Nitrogen uptake from the soil started concomitantly with N remobilization but contributed only slightly to bud burst. However, the fraction of total N due to N uptake increased markedly once bud burst had occurred, reaching 27% in fully expanded leaves and 18% in developed twigs. In phloem sap, the (15)N label appeared a few days after the beginning of labeling and increased until the end of bud burst, and then decreased at full leaf expansion in June. Of all the shoot compartments, leaves attracted most of the absorbed N, which accounted for 68% of new N in shoots, whereas twigs and new buds accounted for only 28 and 3%, respectively. New N allocated to leaves increased from unfolding to full expansion as total N concentration in the leaves decreased. Our results underline the crucial role played by stored N in rapid leaf growth and in the sustained growth of oak trees. Any factors that reduce N storage in autumn may therefore impair spring shoot growth.

The main task of the present study was to investigate the root vitality of common beech Fagus sylvatica L., sessile oak Quercus petraea Liebl. and sycamore maple Acer pseudoplatanus L. in the optimal g rowth conditions in south-western Poland. The study was carried out in 130-year-old mixed stand located within natural range of studied tree species. The density of roots (g/100 cm3 of soil) and biomass of fine roots (g/m2) in topsoil layers (0-5 cm, 5-15 cm) were determined in the tree biogroups of the same species. The mean total root density ranged from 0.248 to 0.417 g/100 cm3 in the 0-5 cm soil layer, and it decreased in the deeper soil layer (5-15 cm). There were found no statistically significant differences of total root densities between tree biogroups in topsoil layers. Diversity of fine root biomass was comparable in the tree biogroups (H’ = 1.5), but common beech showed more intensive growth of fine roots in the topsoil 0-15 cm when compared to sessile oak and sycamore maple. The results of the study point out the stability of the multi-species structure of the mixed stand studied, and consequently - the ability of beech, sessile oak and sycamore maple trees to coexist in the mixed stands - in the area of natural range of these species.