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1. Uniformly branching trees

   https://doi.org/10.1090/tran/8404  

   Bonk, Mario; Meyer, Daniel (April 2022, Transactions of the American Mathematical Society)

   A quasiconformal tree T is a (compact) metric tree that is doubling and of bounded turning. We call T trivalent if every branch point of T has exactly three branches. If the set of branch points is uniformly relatively separated and uniformly relatively dense, we say that T is uniformly branching. We prove that a metric space T is quasisymmetrically equivalent to the continuum self-similar tree if and only if it is a trivalent quasiconformal tree that is uniformly branching. In particular, any two trees of this type are quasisymmetrically equivalent. 

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2. The role of height-driven constraints and compensations on tree vulnerability to drought

   Fernandez_de_Una, Laura; Martınez-Vilalta, Jordi; Poyatos, Rafael; Mencuccini, Maurizio; McDowell, Nate (July 2023, New phytologist)

   Frequent observations of higher mortality in larger trees than in smaller ones during droughtshave sparked an increasing interest in size-dependent drought-induced mortality. However, theunderlying physiological mechanisms are not well understood, with height-associated hydraulicconstraints often being implied as the potential mechanism driving increased droughtvulnerability. We performed a quantitative synthesis on how key traits that drive plant waterand carbon economy change with tree height within species and assessed the implications thatthe different constraints and compensations may have on the interacting mechanisms (hydraulicfailure, carbon starvation and/or biotic-agent attacks) affecting tree vulnerability to drought.While xylem tension increases with tree height, taller trees present a range of structural andfunctional adjustments, including more efficient water use and transport and greater wateruptake and storage capacity, that mitigate the path-length-associated drop in water potential.These adaptations allow taller trees to withstand episodic water stress. Conclusive evidence forheight-dependent increased vulnerability to hydraulic failure and carbon starvation, and theircoupling to defence mechanisms and pest and pathogen dynamics, is still lacking. Furtherresearch is needed, particularly at the intraspecific level, to ascertain the specific conditions andthresholds above which height hinders tree survival under drought. 

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3. Stress Relaxation of Comb Polymer Melts

   https://doi.org/10.1007/s11249-021-01432-y  

   Wijesinghe, Sidath; Perahia, Dvora; Ge, Ting; Salerno, Michael K; Grest, Gary S (April 2021, Tribology letters)

   Branched polymers stress relaxation is at the center to their function as viscosity modifiers, though the fundamentals that underlie the correlation between the polymer topology and their impact on viscosity remains an open question. Here, the stress relaxation of short, branched polyethylene comb polymer melts is studied by molecular dynamics simulations. A coarse-grained model where four methylene groups constitute one bead is used, and the results are transposed to the atomistic level. For arms of length comparable to entanglement length ne of the linear polymer, we show that while increasing the number of branches with the same arm length decreases the plateau modulus, the terminal diffusive time does not change significantly. Increasing the arm length decreases the plateau modulus and increases the terminal time. As arms shorter than ne relax by the entanglement time, both the chain mobility and stress relaxation can be described by reptation of the backbone with an increased tube diameter and an increas 

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4. Evaluating Predictive Models of Tree Foliar Moisture Content for Application to Multispectral UAS Data: A Laboratory Study

   https://doi.org/10.3390/rs15245703  

   Lad, Lauren E.; Tinkham, Wade T.; Sparks, Aaron M.; Smith, Alistair M. (December 2023, Remote Sensing)

   Water supply is a critical component of tree physiological health, influencing a tree’s photosynthetic activity and resilience to disturbances. The climatic regions of the western United States are particularly at risk from increasing drought, fire, and pest interactions. Existing methods for quantifying drought stress and a tree’s relative resilience against disturbances mostly use moderate-scale (20–30 m) multispectral satellite sensor data. However, tree water status (i.e., water stress) quantification using sensors like Landsat and Sentinel are error-prone given that the spectral reflectance of pixels are a mixture of the dominant tree canopy, surface vegetation, and soil. Uncrewed aerial systems (UAS) equipped with multispectral sensors could potentially provide individual tree water status. In this study, we assess whether the simulated band equivalent reflectance (BER) of a common UAS optical multispectral sensor can accurately quantify the foliar moisture content and water stress status of individual trees. To achieve this, water was withheld from groups of Douglas-fir and western white pine saplings. Then, measurements of each sapling’s foliar moisture content (FMC) and spectral reflectance were converted to BER of a consumer-grade multispectral camera commonly used on UAS. These bands were used in two classification models and three regression models to develop a best-performing FMC model for predicting either the water status (i.e., drought-stressed or healthy) or the foliar moisture content of each sapling, respectively. Our top-performing models were a logistic regression classification and a multiple linear regression which achieved a classification accuracy of 96.55% and an r2 of 82.62, respectively. These FMC models could provide an important tool for investigating tree crown level water stress, as well as drought interactions with other disturbances, and provide land managers with a vital indicator of tree resilience. 

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5. Clustering and spatial distribution of mitochondria in dendritic trees

   https://doi.org/10.1103/PhysRevResearch.6.043312  

   Hidalgo-Soria, M; Koslover, E F (December 2024, Physical Review Research)

   Neuronal dendrites form densely branched tree architectures through which mitochondria must be distributed to supply the cell's energetic needs. Dendritic mitochondria circulate across the tree, undergoing fusion and fission to form clusters of varying sizes. We present a mathematical model for the distribution of such actively driven interacting particles in a branched geometry, showing that the density and localization of particles is highly sensitive to the fusion/fission balance and to the tree architecture. Our model demonstrates that “balanced” trees (wherein cross-sectional area is conserved across junctions and thicker branches support more bushy subtrees) enable symmetric yet distally enriched particle distributions and promote dispersion into smaller clusters. These results highlight the importance of tree morphology and radius-dependent fusion in governing the distribution of neuronal mitochondria. Published by the American Physical Society2024 

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