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18 pages, 2977 KiB  
Article
Silicon Modifies Photosynthesis Efficiency and hsp Gene Expression in European Beech (Fagus sylvatica) Seedlings Exposed to Drought Stress
by Justyna Nowakowska, Monika Dang, Piotr Kiełtyk, Marzena Niemczyk, Tadeusz Malewski, Wiesław Szulc, Beata Rutkowska, Piotr Borowik and Tomasz Oszako
Genes 2024, 15(9), 1233; https://doi.org/10.3390/genes15091233 - 21 Sep 2024
Viewed by 880
Abstract
Background: Climate change is leading to severe and long-term droughts in European forest ecosystems. can have profound effects on various physiological processes, including photosynthesis, gene expression patterns, and nutrient uptake at the developmental stage of young trees. Objectives: Our study aimed to test [...] Read more.
Background: Climate change is leading to severe and long-term droughts in European forest ecosystems. can have profound effects on various physiological processes, including photosynthesis, gene expression patterns, and nutrient uptake at the developmental stage of young trees. Objectives: Our study aimed to test the hypothesis that the application of silica (SiO2) influences photosynthetic efficiency and gene expression in 1- to 2-year-old Fagus sylvatica (L.) seedlings. Additionally, we aimed to assess whether silicon application positively influences the structural properties of leaves and roots. To determine whether the plant physiological responses are genotype-specific, seedlings of four geographically different provenances were subjected to a one-year evaluation under greenhouse conditions. Methods: We used the Kruskal–Wallis test followed by Wilcoxon’s test to evaluate the differences in silicon content and ANOVA followed by Tukey’s test to evaluate the physiological responses of seedlings depending on treatment and provenance. Results: Our results showed a significantly higher Si content in the roots compared with the leaves, regardless of provenance and treatment. The most significant differences in photosynthetic performance were found in trees exposed to Si treatment, but the physiological responses were generally nuanced and provenance-dependent. Expression of hsp70 and hsp90 was also increased in leaf tissues of all provenances. These results provide practical insights that Si can improve the overall health and resilience of beech seedlings in nursery and forest ecosystems, with possible differences in the beneficial role of silicon application arising from the large differences in wild populations of forest tree species. Full article
(This article belongs to the Special Issue Genes and Genomics of Plants Under Abiotic Stresses)
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15 pages, 2061 KiB  
Article
Photosynthetic Response to Phosphorus Fertilization in Drought-Stressed Common Beech and Sessile Oak from Different Provenances
by Antonia Vukmirović, Željko Škvorc, Saša Bogdan, Daniel Krstonošić, Ida Katičić Bogdan, Tomislav Karažija, Marko Bačurin, Magdalena Brener and Krunoslav Sever
Plants 2024, 13(16), 2270; https://doi.org/10.3390/plants13162270 - 15 Aug 2024
Viewed by 598
Abstract
Increasingly frequent and severe droughts pose significant threats to forest ecosystems, particularly affecting photosynthesis, a crucial physiological process for plant growth and biomass production. This study investigates the impact of phosphorus fertilization on the photosynthesis of common beech (Fagus sylvatica L.) and [...] Read more.
Increasingly frequent and severe droughts pose significant threats to forest ecosystems, particularly affecting photosynthesis, a crucial physiological process for plant growth and biomass production. This study investigates the impact of phosphorus fertilization on the photosynthesis of common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.). In a common garden experiment, saplings originating from two provenances (wetter KA and drier SB provenances) were exposed to regular watering and drought in interaction with moderate and high phosphorus concentrations in the growing substrate. Results indicated that drought significantly reduced pre-dawn leaf water potential (ΨPD), net photosynthesis (Anet), stomatal conductance (gs) and photosynthetic performance index (PIabs) in both species. Phosphorus fertilization had a negative impact on Anet and PIabs, thus exacerbating the negative impact of drought on photosynthetic efficiency, potentially due to excessive phosphorus absorption by saplings. Provenance differences were notable, with the KA provenance showing better drought resilience. This research highlights the complexity of nutrient–drought interactions and underscores the need for cautious application of fertilization strategies in reforestation efforts under changing climatic conditions. Full article
(This article belongs to the Special Issue Water and Nutrient Uptake in Plants)
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11 pages, 849 KiB  
Article
Effects of Species of Leaves and Conditioning Time on Vernal Colonization by Temperate Lotic Isopods (Lirceus sp.)
by Renee E. Heller, Alison N. Stouffer and Erika V. Iyengar
Hydrobiology 2024, 3(2), 63-73; https://doi.org/10.3390/hydrobiology3020005 - 19 Apr 2024
Cited by 1 | Viewed by 1047
Abstract
While some streams have dense populations of aquatic detritivorous isopods, research on the colonization of leaf packs typically focuses on aquatic insects. To determine whether shifts in dominant local forest species might impact isopod populations, we placed leaf packs of red/sugar maple, American [...] Read more.
While some streams have dense populations of aquatic detritivorous isopods, research on the colonization of leaf packs typically focuses on aquatic insects. To determine whether shifts in dominant local forest species might impact isopod populations, we placed leaf packs of red/sugar maple, American beech, and red oak on the substratum of riffles and pools in Cedar Creek (Allentown, PA, USA) in April 2019. We retrieved the packs after one week, re-deployed them, and re-collected them after two weeks of submersion, enumerating the number of isopods (Lirceus sp.) upon each retrieval. Surprisingly, neither the species of leaf nor the stream microhabitat significantly affected the number of isopods. However, the duration of leaf conditioning was important; significantly more isopods inhabited leaves after two weeks of submersion than after only one week. Maple and oak leaves displayed significantly more skeletonization after two weeks than the beech leaves, which remained intact. However, the similar numbers of isopods across leaf species suggest either the presence of acceptable, consumable microbial communities on all three species of leaves or that a tradeoff exists between the value of food and the importance of refuge provided by intact leaves. Full article
(This article belongs to the Special Issue Ecosystem Disturbance in Small Streams)
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18 pages, 4665 KiB  
Article
The Impact of Phenological Gaps on Leaf Characteristics and Foliage Dynamics of an Understory Dwarf Bamboo, Sasa kurilensis
by Chongyang Wu, Ryota Tanaka, Kyohei Fujiyoshi, Yasuaki Akaji, Muneto Hirobe, Naoko Miki, Juan Li, Keiji Sakamoto and Jian Gao
Plants 2024, 13(5), 719; https://doi.org/10.3390/plants13050719 - 4 Mar 2024
Viewed by 1117
Abstract
Phenological gaps exert a significant influence on the growth of dwarf bamboos. However, how dwarf bamboos respond to and exploit these phenological gaps remain enigmatic. The light environment, soil nutrients, leaf morphology, maximum photosynthetic rate, foliage dynamics, and branching characteristics of Sasa kurilensis [...] Read more.
Phenological gaps exert a significant influence on the growth of dwarf bamboos. However, how dwarf bamboos respond to and exploit these phenological gaps remain enigmatic. The light environment, soil nutrients, leaf morphology, maximum photosynthetic rate, foliage dynamics, and branching characteristics of Sasa kurilensis were examined under the canopies of Fagus crenata and Magnolia obovata. The goal was to elucidate the adaptive responses of S. kurilensis to phenological gaps in the forest understory. The findings suggest that phenological gaps under an M. obovata canopy augment the available biomass of S. kurilensis, enhancing leaf area, leaf thickness, and carbon content per unit area. However, these gaps do not appreciably influence the maximum photosynthetic rate, total leaf number, leaf lifespan, branch number, and average branch length. These findings underscore the significant impact of annually recurring phenological gaps on various aspects of S. kurilensis growth, such as its aboveground biomass, leaf morphology, and leaf biochemical characteristics. It appears that leaf morphology is a pivotal trait in the response of S. kurilensis to phenological gaps. Given the potential ubiquity of the influence of phenological gaps on dwarf bamboos across most deciduous broadleaf forests, this canopy phenomenon should not be overlooked. Full article
(This article belongs to the Special Issue Molecular Basis of Morphogenesis and Development in Bamboo)
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15 pages, 7359 KiB  
Article
Large Differences in Bud Burst and Senescence between Low- and High-Altitude European Beech Populations along an Altitudinal Transect in the South-Eastern Carpathians
by Mihnea Ioan Cezar Ciocîrlan, Elena Ciocîrlan, Dănuț Chira, Gheorghe Raul Radu, Victor Dan Păcurar, Emanuel Beșliu, Ourania Grigoriadou Zormpa, Oliver Gailing and Alexandru Lucian Curtu
Forests 2024, 15(3), 468; https://doi.org/10.3390/f15030468 - 2 Mar 2024
Viewed by 1286
Abstract
Phenology is considered an indicator of environmental changes, with direct implications in the length of the growing season; therefore, it offers essential information for a better understanding of the tree–environment relationships that could lead to the right decisions for forests’ sustainable use and [...] Read more.
Phenology is considered an indicator of environmental changes, with direct implications in the length of the growing season; therefore, it offers essential information for a better understanding of the tree–environment relationships that could lead to the right decisions for forests’ sustainable use and conservation. A better understanding of how European beech (Fagus sylvatica) phenology responds to predicted climate change effects is important for forest management. This study aimed to assess bud burst and senescence among and within beech populations located along a steep elevational gradient. Phenological observations were carried out on 150 beech individuals along an altitudinal transect in the south-eastern Carpathian Mountains, from 550 to 1450 m, in five study sites in two consecutive years. The start of the bud burst, of senescence, and the duration of the growing season varied inversely proportionally to the elevational gradient in both monitored years. Individuals located at the highest altitude need 28 more days to start the growing season than those at the lowest altitude. There is an average difference of 14 days at the start of the growing season in the same beech populations between the two consecutive years. The first stage of senescence (yellowing of leaves) lasted longer in 2021 (21–32 days) than in 2022 (18–25 days), with a difference of 16%–28%, proportional to the increase in altitude. The association of field phenological data with meteorological data indicates that the start of the growing season occurs when the thermal threshold of 10 °C is exceeded, with an accumulation of a least 60 GDD (growing degree days) with a threshold of 0 °C in the last 7 days as a complementary condition. The appearance of the first stage of senescence, the yellowing of the leaves, was also influenced by the temperature and the accumulation of at least 72 SDD (senescence degree days) with a threshold of 0 °C in the last 7 days. Our results confirm that the temperature is the triggering meteorological factor for the onset of bud burst and leaf senescence in European beech. Full article
(This article belongs to the Special Issue Woody Plant Phenology in a Changing Climate)
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13 pages, 2053 KiB  
Article
Ecophysiological Behavior of Fagus sylvatica L. Growing at Its Southern Distribution Limit: Insights for Understanding the Fate of the European Beech under Warmer and Dryer Growth Conditions
by Maria Prigoliti, Maria Teresa Chiofalo, Francesco Petruzzellis, Maria Assunta Lo Gullo and Patrizia Trifilò
Forests 2023, 14(10), 2058; https://doi.org/10.3390/f14102058 - 15 Oct 2023
Cited by 2 | Viewed by 1679
Abstract
In the last 20 years, a significant mortality of Fagus sylvatica L. (European beech) has been documented in central and northern European forests. Surprisingly, no beech die off occurred at the southern limit. This fact leads us to hypothesize that European beech populations [...] Read more.
In the last 20 years, a significant mortality of Fagus sylvatica L. (European beech) has been documented in central and northern European forests. Surprisingly, no beech die off occurred at the southern limit. This fact leads us to hypothesize that European beech populations growing at the southern limit of the distribution might have a significant phenotypic plasticity to better cope with low water availability and rising temperatures. To check this hypothesis, we evaluated the ecophysiological behavior of F. sylvatica growing along an altitudinal transect in Calabria (Italy). We selected three study sites (750 m a.s.l., 976 m a.sl. m a.s.l., 1450 m a.s.l.) showing narrow ranges of temperature, rainfall and air humidity. Trees growing at 976 m a.s.l. showed the highest stomatal conductance values during the entire experimental period. The lowest gas exchange and highest leaf mass area were recorded in plants growing at 750 m a.s.l. In the European beech growing at 1450 m a.s.l., higher vessel density, lower mean vessel diameter and higher vessel grouping index values were recorded. Overall, our results highlighted that the measured populations show a considerable phenotypic plasticity leading them to adjust anatomical and physiological traits in response to narrow ranges of environmental parameters. Despite that, the distribution of F. sylvatica seems to be limited to areas with a growing season rainfall of at least 400 mm and vapor pressure deficit (VPD) values < 3 kPa, which may represent the main environmental thresholds which strongly limit the beech growth and, therefore, influence the ability of this species to cope with future environmental conditions. Full article
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26 pages, 5748 KiB  
Article
Discrimination of Leaves in a Multi-Layered Mediterranean Forest through Machine Learning Algorithms
by Cesar Alvites, Mauro Maesano, Juan Alberto Molina-Valero, Bruno Lasserre, Marco Marchetti and Giovanni Santopuoli
Remote Sens. 2023, 15(18), 4450; https://doi.org/10.3390/rs15184450 - 10 Sep 2023
Cited by 1 | Viewed by 1402
Abstract
Terrestrial laser scanning (TLS) technology characterizes standing trees with millimetric precision. An important step to accurately quantify tree volume and above-ground biomass using TLS point clouds is the discrimination between timber and leaf components. This study evaluates the performance of machine learning (ML)-derived [...] Read more.
Terrestrial laser scanning (TLS) technology characterizes standing trees with millimetric precision. An important step to accurately quantify tree volume and above-ground biomass using TLS point clouds is the discrimination between timber and leaf components. This study evaluates the performance of machine learning (ML)-derived models aimed at discriminating timber and leaf TLS point clouds, focusing on eight Mediterranean tree species datasets. The results show the best accuracies for random forests, gradient boosting machine, stacked ensemble model, and deep learning models with an average F1 score equal to 0.92. The top-performing ML-derived models showed well-balanced average precision and recall rates, ranging from 0.86 to 0.91 and 0.92 to 0.96 for precision and recall, respectively. Our findings show that Italian maple, European beech, hazel, and small-leaf lime tree species have more accurate F1 scores, with the best average F1 score of 0.96. The factors influencing the timber–leaf discrimination include phenotypic factors, such as bark surface (i.e., roughness and smoothness), technical issues (i.e., noise points and misclassification of points), and secondary factors (i.e., bark defects, lianas, and microhabitats). The top-performing ML-derived models report a time computation ranging from 8 to 37 s for processing 2 million points. Future studies are encouraged to calibrate, configure, and validate the potential of top-performing ML-derived models on other tree species and at the plot level. Full article
(This article belongs to the Special Issue New Advancements in the Field of Forest Remote Sensing)
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16 pages, 2829 KiB  
Article
Beech Leaf Disease Severity Affects Ectomycorrhizal Colonization and Fungal Taxa Composition
by Claudia Bashian-Victoroff, Alexis Brown, Andrew L. Loyd, Sarah R. Carrino-Kyker and David J. Burke
J. Fungi 2023, 9(4), 497; https://doi.org/10.3390/jof9040497 - 21 Apr 2023
Cited by 2 | Viewed by 3184
Abstract
Beech leaf disease (BLD) is an emerging forest infestation affecting beech trees (Fagus spp.) in the midwestern and northeastern United States and southeastern Canada. BLD is attributed to the newly recognized nematode Litylenchus crenatae subsp. mccannii. First described in Lake County, [...] Read more.
Beech leaf disease (BLD) is an emerging forest infestation affecting beech trees (Fagus spp.) in the midwestern and northeastern United States and southeastern Canada. BLD is attributed to the newly recognized nematode Litylenchus crenatae subsp. mccannii. First described in Lake County, Ohio, BLD leads to the disfigurement of leaves, canopy loss, and eventual tree mortality. Canopy loss limits photosynthetic capacity, likely impacting tree allocation to belowground carbon storage. Ectomycorrhizal fungi are root symbionts, which rely on the photosynthesis of autotrophs for nutrition and growth. Because BLD limits tree photosynthetic capacity, ECM fungi may receive less carbohydrates when associating with severely affected trees compared with trees without BLD symptoms. We sampled root fragments from cultivated F. grandifolia sourced from two provenances (Michigan and Maine) at two timepoints (fall 2020 and spring 2021) to test whether BLD symptom severity alters colonization by ectomycorrhizal fungi and fungal community composition. The studied trees are part of a long-term beech bark disease resistance plantation at the Holden Arboretum. We sampled from replicates across three levels of BLD symptom severity and compared fungal colonization via visual scoring of ectomycorrhizal root tip abundance. Effects of BLD on fungal communities were determined through high-throughput sequencing. We found that ectomycorrhizal root tip abundance was significantly reduced on the roots of individuals of the poor canopy condition resulting from BLD, but only in the fall 2020 collection. We found significantly more ectomycorrhizal root tips from root fragments collected in fall 2020 than in spring 2021, suggesting a seasonal effect. Community composition of ectomycorrhizal fungi was not impacted by tree condition but did vary between provenances. We found significant species level responses of ectomycorrhizal fungi between levels of both provenance and tree condition. Of the taxa analyzed, two zOTUs had significantly lower abundance in high-symptomatology trees compared with low-symptomatology trees. These results provide the first indication of a belowground effect of BLD on ectomycorrhizal fungi and contribute further evidence to the role of these root symbionts in studies of tree disease and forest pathology. Full article
(This article belongs to the Special Issue Friends of Plants: Mycorrhizal Fungi)
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14 pages, 2480 KiB  
Article
Leaf Phenological Responses of Juvenile Beech and Oak Provenances to Elevated Phosphorus
by Marko Bačurin, Saša Bogdan, Ida Katičić Bogdan and Krunoslav Sever
Forests 2023, 14(4), 834; https://doi.org/10.3390/f14040834 - 18 Apr 2023
Cited by 2 | Viewed by 1322
Abstract
The few studies dealing with leaf phenological responses to elevated nutrients in forest trees have given ambiguous results, i.e., while some reported delayed leaf-out and autumn leaf senescence, others reported advanced leaf phenology caused by increased nutrition. This study aimed to determine the [...] Read more.
The few studies dealing with leaf phenological responses to elevated nutrients in forest trees have given ambiguous results, i.e., while some reported delayed leaf-out and autumn leaf senescence, others reported advanced leaf phenology caused by increased nutrition. This study aimed to determine the effects of experimentally increased phosphorus (+P treatment) on the leaf phenologies of two juvenile provenances of common beech and sessile oak. Other objectives were to determine whether there were interspecific differences as well as intraspecific variations. Saplings were excavated in two mixed beech–oak stands and transplanted into four wooden boxes filled with a commercial soil substrate. Phosphorus fertilizer was added to two of the boxes, while the remaining boxes served as controls. Both species responded to +P treatment with advanced autumn leaf senescence in the first year of the experiment. Leaf senescence in common beech began significantly earlier, while in both species, the process was accelerated compared to that in the control. In the second year, the leaf senescence response to +P treatment was even more pronounced in both species. The +P effect on leafing phenology was absent in both common beech provenances and in an oak provenance. However, the other oak provenance showed advanced leafing, indicating the existence of intraspecific differences. Full article
(This article belongs to the Section Forest Ecology and Management)
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16 pages, 3119 KiB  
Article
Experimental Warming of Typically Acidic and Nutrient-Poor Boreal Soils Does Not Affect Leaf-Litter Decomposition of Temperate Deciduous Tree Species
by Nicolas Bélanger and Clémence Chaput-Richard
Soil Syst. 2023, 7(1), 14; https://doi.org/10.3390/soilsystems7010014 - 6 Feb 2023
Cited by 1 | Viewed by 2120
Abstract
Ongoing rapid climatic changes are expected to modify the structure, composition, and functioning of forest ecosystems. Studying the influence of such changes on biogeochemical processes is thus crucial for a fuller understanding of forest response to climate change. In a temperate forest of [...] Read more.
Ongoing rapid climatic changes are expected to modify the structure, composition, and functioning of forest ecosystems. Studying the influence of such changes on biogeochemical processes is thus crucial for a fuller understanding of forest response to climate change. In a temperate forest of Quebec, Canada, we emulated climate change by warming the acidic, nutrient-poor, and dry soils of two mixedwoods by 3 to 4 °C using heating cables. Leaf-litter mass loss of the local red maple, sugar maple, large-tooth aspen, and American beech were monitored to assess the ability of these tree species to condition boreal soils in the context of their northward migration under climate change. We hypothesized that decomposition rates of all leaf-litter types would be decreased equally by warming due to a drying effect of the soil and its surface, which is detrimental to microbial biomass and activity. Our results suggest differences in decomposition rates between tree species as follows: sugar maple > red maple ≥ American beech = large-tooth aspen. There was no indication of a slower turnover in these marginal soils compared to other studies conducted on typical hardwood soils. Moreover, no difference in litter mass loss was detected between treatments, likely due to a drying effect of the soil warming treatment. Results imply that climate change has a marginal influence on leaf-litter dynamics of temperate tree species on soils that are typical of the boreal forest. However, some variables that could play an important role on litter decomposition in the context of climate change were not measured (e.g., plant phenology, understory composition and density, microbes) and thus, uncertainties remain. The soil drying effect by warming also needs to be further documented and modeled. The study year was characterized by significant periods of water stress but was not considered an exceptional year in that regard. It would be relevant to test for leaf-litter dynamics during dry and wet summers and verify again our initial hypothesis of decreased leaf-litter decomposition rates due to soil warming/drying. Full article
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22 pages, 5336 KiB  
Review
Distinct Responses of European Beech (Fagus sylvatica L.) to Drought Intensity and Length—A Review of the Impacts of the 2003 and 2018–2019 Drought Events in Central Europe
by Shah Rukh, Tanja G. M. Sanders, Inken Krüger, Tobias Schad and Andreas Bolte
Forests 2023, 14(2), 248; https://doi.org/10.3390/f14020248 - 28 Jan 2023
Cited by 25 | Viewed by 6137
Abstract
A combined severe heatwave and drought, starting in 2018 and lasting for several months, restarted the discussion on the resistance of European beech to climatic changes, with severe growth reductions, early leaf senescence, leaf browning, and diebacks reported across Central Europe. These responses [...] Read more.
A combined severe heatwave and drought, starting in 2018 and lasting for several months, restarted the discussion on the resistance of European beech to climatic changes, with severe growth reductions, early leaf senescence, leaf browning, and diebacks reported across Central Europe. These responses may result in long-term impacts such as reduced vitality of beech, especially under potential future drought periods. While the 2003 drought caused severe crown damage and defoliation and a loss in vitality, resulting in insect and fungal infestations and subsequent dieback, the drought in 2018 was even more severe in terms of geographical scale, duration, and intensity with reports of complete diebacks and severe mortality across Central Europe. These impacts were exacerbated in some regions by the consecutive drought in 2019 and secondary attacks from pathogens, as well as a further loss in vitality. Such enhanced drought exposure of beech trees could push them beyond their hydraulic safety margins. Moreover, growth legacy effects due to past droughts may lead to lower recovery over time, potentially leading to subsequent tree death. In order to better predict the future of beech growth and vitality in Central Europe, both short- and long-term legacy effects of defoliation and their influence on post-drought growth should be explored, and adaptive forest management strategies evaluated. Moreover, synergistic or additive interactions of legacy effects with drought, as well as with biotic disturbances, require further investigation. Long-term forest monitoring data facilitates investigations of drought responses of beech. Full article
(This article belongs to the Section Forest Ecology and Management)
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12 pages, 747 KiB  
Article
Legacy Effects in Buds and Leaves of European Beech Saplings (Fagus sylvatica) after Severe Drought
by Frank M. Thomas, Lena Schunck and Alexis Zisakos
Plants 2023, 12(3), 568; https://doi.org/10.3390/plants12030568 - 26 Jan 2023
Cited by 1 | Viewed by 1563
Abstract
Against the background of climate change, we studied the effects of a severe summer drought on buds of European beech (Fagus sylvatica L.) saplings and on leaves formed during the subsequent spring in trees attributed to different drought-damage classes. For the first [...] Read more.
Against the background of climate change, we studied the effects of a severe summer drought on buds of European beech (Fagus sylvatica L.) saplings and on leaves formed during the subsequent spring in trees attributed to different drought-damage classes. For the first time, we combined assessments of the vitality (assessed through histochemical staining), mass and stable carbon isotope ratios (δ13C) of buds from drought-stressed woody plants with morphological and physiological variables of leaves that have emerged from the same plants and crown parts. The number, individual mass and vitality of the buds decreased and δ13C increased with increasing drought-induced damage. Bud mass, vitality and δ13C were significantly intercorrelated. The δ13C of the buds was imprinted on the leaves formed in the subsequent spring, but individual leaf mass, leaf size and specific leaf area were not significantly different among damage classes. Vitality and δ13C of the buds are suitable indicators of the extent of preceding drought impact. Bud vitality may be used as a simple means of screening saplings for the flushing capability in the subsequent spring. European beech saplings are susceptible, but—due to interindividual differences—are resilient, to a certain extent, to a singular severe drought stress. Full article
(This article belongs to the Special Issue Plant Responses to Future Climate Scenarios)
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21 pages, 3058 KiB  
Article
What Are We Missing? Occlusion in Laser Scanning Point Clouds and Its Impact on the Detection of Single-Tree Morphologies and Stand Structural Variables
by Thomas Mathes, Dominik Seidel, Karl-Heinz Häberle, Hans Pretzsch and Peter Annighöfer
Remote Sens. 2023, 15(2), 450; https://doi.org/10.3390/rs15020450 - 12 Jan 2023
Cited by 14 | Viewed by 3508
Abstract
Laser scanning has revolutionized the ability to quantify single-tree morphologies and stand structural variables. In this study, we address the issue of occlusion when scanning a spruce (Picea abies (L.) H.Karst.) and beech (Fagus sylvatica L.) forest with a mobile laser [...] Read more.
Laser scanning has revolutionized the ability to quantify single-tree morphologies and stand structural variables. In this study, we address the issue of occlusion when scanning a spruce (Picea abies (L.) H.Karst.) and beech (Fagus sylvatica L.) forest with a mobile laser scanner by making use of a unique study site setup. We scanned forest stands (1) from the ground only and (2) from the ground and from above by using a crane. We also examined the occlusion effect by scanning in the summer (leaf-on) and in the winter (leaf-off). Especially at the canopy level of the forest stands, occlusion was very pronounced, and we were able to quantify its impact in more detail. Occlusion was not as noticeable as expected for crown-related variables but, on average, resulted in smaller values for tree height in particular. Between the species, the total tree height underestimation for spruce was more pronounced than that for beech. At the stand level, significant information was lost in the canopy area when scanning from the ground alone. This information shortage is reflected in the relative point counts, the Clark–Evans index and the box dimension. Increasing the voxel size can compensate for this loss of information but comes with the trade-off of losing details in the point clouds. From our analysis, we conclude that the voxelization of point clouds prior to the extraction of stand or tree measurements with a voxel size of at least 20 cm is appropriate to reduce occlusion effects while still providing a high level of detail. Full article
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19 pages, 4717 KiB  
Article
Dynamic of Fluorescence Emissions at O2A and O2B Telluric Absorption Bands in Forested Areas with Seasonal APAR and GPP Variations
by Daniel Kováč, Jan Novotný, Ladislav Šigut, John Grace and Otmar Urban
Remote Sens. 2023, 15(1), 67; https://doi.org/10.3390/rs15010067 - 23 Dec 2022
Cited by 3 | Viewed by 2497
Abstract
We measured dynamics of solar-induced chlorophyll fluorescence at telluric oxygen absorption bands O2A and O2B in evergreen spruce and deciduous beech forests. Seasonal variations in fluorescence emissions were compared with NDVI. Daily changes in fluorescence emissions were compared with [...] Read more.
We measured dynamics of solar-induced chlorophyll fluorescence at telluric oxygen absorption bands O2A and O2B in evergreen spruce and deciduous beech forests. Seasonal variations in fluorescence emissions were compared with NDVI. Daily changes in fluorescence emissions were compared with canopy shadow fraction (αS) dynamics, which showed impact of branch and leaf positions on detected fluorescence signals based on comparison with canopy height model. Absorbed photosynthetically active radiation (APAR) was recognized as a large determinant of fluorescence changes within the O2A band (SIFA), with R2 > 0.68. Fluorescence within the O2B band was more directly linked to NDVI. Although, the seasonal dynamics of fluorescence within the O2B band (SIFB) were similar to SIFA in the spruce forest. In the beech forest, SIFB showed different seasonal dynamics as compared with SIFA. SIFA in the spruce forest showed a relationship to gross primary productivity (GPP), with R2 = 0.48, and a relationship of R2 = 0.37 was estimated for the SIFA-GPP connection in the beech forest. SIFB was better linked to seasonal GPP in the beech forest, but with a negative slope in the relationship with R2 = 0.61. We have shown that measurements of passive fluorescence signals at telluric oxygen absorption bands can contribute to understanding to photosynthesis processes in forest canopies. Full article
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21 pages, 5144 KiB  
Article
Predicting Leaf Phenology in Forest Tree Species Using UAVs and Satellite Images: A Case Study for European Beech (Fagus sylvatica L.)
by Mihnea Ioan Cezar Ciocîrlan, Alexandru Lucian Curtu and Gheorghe Raul Radu
Remote Sens. 2022, 14(24), 6198; https://doi.org/10.3390/rs14246198 - 7 Dec 2022
Cited by 5 | Viewed by 2219
Abstract
Understanding forest tree phenology is essential for assessing forest ecosystem responses to environmental changes. Observations of phenology using remote sensing devices, such as satellite imagery and Unmanned Aerial Vehicles (UAVs), along with machine learning, are promising techniques. They offer fast, accurate, and unbiased [...] Read more.
Understanding forest tree phenology is essential for assessing forest ecosystem responses to environmental changes. Observations of phenology using remote sensing devices, such as satellite imagery and Unmanned Aerial Vehicles (UAVs), along with machine learning, are promising techniques. They offer fast, accurate, and unbiased results linked to ground data to enable us to understand ecosystem processes. Here, we focused on European beech, one of Europe’s most common forest tree species, along an altitudinal transect in the Carpathian Mountains. We performed ground observations of leaf phenology and collected aerial images using UAVs and satellite-based biophysical vegetation parameters. We studied the time series correlations between ground data and remote sensing observations (GLI r = 0.86 and FCover r = 0.91) and identified the most suitable vegetation indices (VIs). We trained linear and non-linear (random forest) models to predict the leaf phenology as a percentage of leaf cover on test datasets; the models had reasonable accuracy, RMSE percentages of 8% for individual trees, using UAV, and 12% as an average site value, using the Copernicus biophysical parameters. Our results suggest that the UAVs and satellite images can provide reliable data regarding leaf phenology in the European beech. Full article
(This article belongs to the Section Forest Remote Sensing)
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