The use of unmanned aerial vehicles (UAVs) in vegetation remote sensing allows a time-flexible and cost-effective acquisition of very high-resolution imagery. Still, current methods for the mapping ...of forest tree species do not exploit the respective, rich spatial information. Here, we assessed the potential of convolutional neural networks (CNNs) and very high-resolution RGB imagery from UAVs for the mapping of tree species in temperate forests. We used multicopter UAVs to obtain very high-resolution (<2 cm) RGB imagery over 51 ha of temperate forests in the Southern Black Forest region, and the Hainich National Park in Germany. To fully harness the end-to-end learning capabilities of CNNs, we used a semantic segmentation approach (U-net) that concurrently segments and classifies tree species from imagery. With a diverse dataset in terms of study areas, site conditions, illumination properties, and phenology, we accurately mapped nine tree species, three genus-level classes, deadwood, and forest floor (mean F1-score 0.73). A larger tile size during CNN training negatively affected the model accuracies for underrepresented classes. Additional height information from normalized digital surface models slightly increased the model accuracy but increased computational complexity and data requirements. A coarser spatial resolution substantially reduced the model accuracy (mean F1-score of 0.26 at 32 cm resolution). Our results highlight the key role that UAVs can play in the mapping of forest tree species, given that air- and spaceborne remote sensing currently does not provide comparable spatial resolutions. The end-to-end learning capability of CNNs makes extensive preprocessing partly obsolete. The use of large and diverse datasets facilitate a high degree of generalization of the CNN, thus fostering transferability. The synergy of high-resolution UAV imagery and CNN provide a fast and flexible yet accurate means of mapping forest tree species.
•High structural heterogeneity reduces the diurnal temperature range (DTR).•Effects of stand structure on DTR are more pronounced in regions with low precipitation.•DTR is lower in unmanaged than in ...managed uneven-aged and even-aged stands.•Terrestrial laser scanning based approaches explain 79.4% of variance in DTR.
The microclimate in forest ecosystems can be altered by modifications of stand structure due to forest management or natural forest development. Current forest management practices in Central Europe and North America aim to promote structural heterogeneity and maintain forest canopy cover, which is known to be a major driver of forest microclimate. Here, we investigated the impacts of forest management and structural heterogeneity on the diurnal temperature range (DTR) in 128 managed forest stands in three climatically different locations (Swabian Alb, Hainich-Dün and Schorfheide-Chorin) in Central Europe. Increasing structural heterogeneity by promoting tree size diversity and differentiation increased vertical stratification and resulted in an impaired DTR during the vegetation period. Linear regression models with geographic location, elevation above sea level, canopy openness and measures of structural heterogeneity as explanatory variables explained 79.4–80.9% of variance in DTR. However, the overall effect of structural heterogeneity on DTR was small. Differences in DTR between plots of different main tree species could be attributed to differences in canopy openness and light transmission, whereas tree species diversity had no significant effect on DTR. Unmanaged forests were characterized by a significantly lower DTR than managed, even-aged forests. DTR in uneven-aged stands managed under single tree selection was comparable to unmanaged stands. Terrestrial laser scanning (TLS) derived measures of canopy openness and vertical structure allowed to explain 79.4% of variance in DTR considering geographic location and elevation, which can also be assessed by TLS with integrated GPS and an altimeter. We conclude that structural characteristics of forest stands other than canopy openness contribute marginally to variation in forest microclimate. However, the analyses of structure-microclimate analyses indicate that effects of stand structure on DTR might be more pronounced in regions with low precipitation during the vegetation period.
Abstract
The dynamical arrest of attractive colloidal particles into out-of-equilibrium structures, known as gelation, is central to biophysics, materials science, nanotechnology, and food and ...cosmetic applications, but a complete understanding is lacking. In particular, for intermediate particle density and attraction, the structure formation process remains unclear. Here, we show that the gelation of short-range attractive particles is governed by a nonequilibrium percolation process. We combine experiments on critical Casimir colloidal suspensions, numerical simulations, and analytical modeling with a master kinetic equation to show that cluster sizes and correlation lengths diverge with exponents ~1.6 and 0.8, respectively, consistent with percolation theory, while detailed balance in the particle attachment and detachment processes is broken. Cluster masses exhibit power-law distributions with exponents −3/2 and −5/2 before and after percolation, as predicted by solutions to the master kinetic equation. These results revealing a nonequilibrium continuous phase transition unify the structural arrest and yielding into related frameworks.
High quantum yield, photoluminescence tunability, and sensitivity to the environment are hallmarks that make carbon nanodots interesting for fundamental research and applications. Yet, the underlying ...electronic transitions behind their bright photoluminescence are strongly debated. Despite carbon-dot interactions with their environment should provide valuable insight into the emitting transitions, they have hardly been studied. Here, we investigate these interactions in a wide range of solvents to elucidate the nature of the electronic transitions. We find remarkable and systematic dependence of the emission energy and kinetics on the characteristics of the solvent, with strong response of the photoexcited dots to hydrogen bonding. These findings suggest that the fluorescence originates from the radiative recombination of a photoexcited electron migrated to surface groups with holes left in the valence band of the crystalline core. Furthermore, the results demonstrate the fluorescence tunability to inherently derive from dot-to-dot polydispersity, independent of solvent interactions.
Glasses behave as solids on experimental time scales due to their slow relaxation. Growing dynamic length scales due to cooperative motion of particles are believed to be central to this slow ...response. For quiescent glasses, however, the size of the cooperatively rearranging regions has never been observed to exceed a few particle diameters, and the observation of long-range correlations has remained elusive. Here, we provide direct experimental evidence of long-range correlations during the deformation of a dense colloidal glass. By imposing an external stress, we force structural rearrangements, and we identify long-range correlations in the fluctuations of microscopic strain and elucidate their scaling and spatial symmetry. The applied shear induces a transition from homogeneous to inhomogeneous flow at a critical shear rate, and we investigate the role of strain correlations in this transition.
Oocyte maturation is accompanied by changes in abundances of thousands of mRNAs, many degraded and many preferentially stabilized. mRNA stability can be regulated by diverse features including GC ...content, codon bias, and motifs within the 3'-untranslated region (UTR) interacting with RNA binding proteins (RBPs) and miRNAs. Many studies have identified factors participating in mRNA splicing, bulk mRNA storage, and translational recruitment in mammalian oocytes, but the roles of potentially hundreds of expressed factors, how they regulate cohorts of thousands of mRNAs, and to what extent their functions are conserved across species has not been determined. We performed an extensive in silico cross-species analysis of features associated with mRNAs of different stability classes during oocyte maturation (stable, moderately degraded, and highly degraded) for five mammalian species. Using publicly available RNA sequencing data for germinal vesicle (GV) and MII oocyte transcriptomes, we determined that 3'-UTR length and synonymous codon usage are positively associated with stability, while greater GC content is negatively associated with stability. By applying machine learning and feature selection strategies, we identified RBPs and miRNAs that are predictive of mRNA stability, including some across multiple species and others more species-restricted. The results provide new insight into the mechanisms regulating maternal mRNA stabilization or degradation.
Conservation across species of mRNA features regulating maternal mRNA stability during mammalian oocyte maturation was analyzed. 3'-Untranslated region length and synonymous codon usage are positively associated with stability, while GC content is negatively associated. Just three RNA binding protein motifs were predicted to regulate mRNA stability across all five species examined, but associated pathways and functions are shared, indicating oocytes of different species arrive at comparable physiological destinations via different routes.
The morula-to-blastocyst transition (MBT) culminates with formation of inner cell mass (ICM) and trophectoderm (TE) lineages. Recent studies identified signaling pathways driving lineage ...specification, but some features of these pathways display significant species divergence. To better understand evolutionary conservation of the MBT, we completed a meta-analysis of RNA sequencing data from five model species and ICMTE differences from four species. Although many genes change in expression during the MBT within any given species, the number of shared differentially expressed genes (DEGs) is comparatively small, and the number of shared ICMTE DEGs is even smaller. DEGs related to known lineage determining pathways (e.g.,
) are seen, but the most prominent pathways and functions associated with shared DEGs or shared across individual species DEG lists impact basic physiological and metabolic activities, such as TCA cycle, unfolded protein response, oxidative phosphorylation, sirtuin signaling, mitotic roles of polo-like kinases, NRF2-mediated oxidative stress, estrogen receptor signaling, apoptosis, necrosis, lipid and fatty acid metabolism, cholesterol biosynthesis, endocytosis, AMPK signaling, homeostasis, transcription, and cell death. We also observed prominent differences in transcriptome regulation between ungulates and nonungulates, particularly for ICM- and TE-enhanced mRNAs. These results extend our understanding of shared mechanisms of the MBT and formation of the ICM and TE and should better inform the selection of model species for particular applications.
In the past 30 years, many stand structural attributes (SSAs) have been suggested and structural indices have been developed to describe the complex structure of forests. Most studies, however, have ...explored the potential and limits of structural measures to quantify forest structures by applying multiple measures to one stand or few measures to several stands. However, the interdependencies of multiple structural attributes across many stands of different forest management types and developmental stages have not yet been explored. Using 20 structural attributes and 124 completely inventoried 1ha sized stands we tested to what extent structural characteristics reflect different stand types and management intensities, and how these characteristics change over time. We found that single SSAs do not show the clear gradients that they were intended to reflect, suggesting that stand structure should be described by multiple structural attributes, and that these should represent different structural aspects (including vertical, and horizontal heterogeneity, density, and diversity). A principal component analysis showed that combining several SSAs, allowed us to distinguish between stand types. The structure of mature stands remained rather constant over the observed period of about 6 years, while that of young stands changed more rapidly due to ingrowth and mortality. The older the stands, the less the large trees contributed to stand growth relative to their size. We conclude that multiple stand structural attributes are needed to characterise stand types, management effects and to explain stand productivity.
Trade-offs and synergies in the supply of forest ecosystem services are common but the drivers of these relationships are poorly understood. To guide management that seeks to promote multiple ...services, we investigated the relationships between 12 stand-level forest attributes, including structure, composition, heterogeneity and plant diversity, plus 4 environmental factors, and proxies for 14 ecosystem services in 150 temperate forest plots. Our results show that forest attributes are the best predictors of most ecosystem services and are also good predictors of several synergies and trade-offs between services. Environmental factors also play an important role, mostly in combination with forest attributes. Our study suggests that managing forests to increase structural heterogeneity, maintain large trees, and canopy gaps would promote the supply of multiple ecosystem services. These results highlight the potential for forest management to encourage multifunctional forests and suggest that a coordinated landscape-scale strategy could help to mitigate trade-offs in human-dominated landscapes.
PDF
