Scaling from single-point sap velocity measurements to stand transpiration in a multi-species deciduous forest: uncertainty sources, stand structure effect, and future scenarios impacts

ABSTRACT A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability ontranspiration upscaling and explore the potential impacts of future shifts in species composition on forest water budget. We measured sap velocity in five tree species (Fagus grandiflora, Acer rubrum, A. saccharum, Betula alleghaniensis, B. papyrifera) in a mature and young stand in NH (USA). Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpirationwill depend on the sap velocity, determined mainly by radial variation and tree size, but also on the sapwood area distribution in the stand

Scaling from single-point sap velocity measurements to stand transpiration in a multi-species deciduous forest: uncertainty sources, stand structure effect, and future scenarios impacts

ABSTRACT A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability ontranspiration upscaling and explore the potential impacts of future shifts in species composition on forest water budget. We measured sap velocity in five tree species (Fagus grandiflora, Acer rubrum, A. saccharum, Betula alleghaniensis, B. papyrifera) in a mature and young stand in NH (USA). Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpirationwill depend on the sap velocity, determined mainly by radial variation and tree size, but also on the sapwood area distribution in the stand

A Characterization of the optimal risk-Sensitive average cost in finite controlled Markov chains

This work concerns controlled Markov chains with finite state and action spaces. The transition law satisfies the simultaneous Doeblin condition, and the performance of a control policy is measured by the (long-run) risk-sensitive average cost criterion associated to a positive, but otherwise arbitrary, risk sensitivity coefficient. Within this context, the optimal risk-sensitive average cost is characterized via a minimization problem in a finite-dimensional Euclidean space.Comment: Published at http://dx.doi.org/10.1214/105051604000000585 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Robust Utility Maximization in a Stochastic Factor Model

We give an explicit PDE characterization for the solution of a robust utility maximization problem in an incomplete market model, whose volatility, interest rate process, and long-term trend are driven by an external stochastic factor process. The robust utility functional is defined in terms of a HARA utility function with negative risk aversion and a dynamically consistent coherent risk measure, which allows for model uncertainty in the distributions of both the asset price dynamics and the factor process. Our method combines two recent advances in the theory of optimal investments: the general duality theory for robust utility maximization and the stochastic control approach to the dual problem of determining optimal martingale measures.optimal investment, model uncertainty, incomplete markets, stochastic volatility, coherent risk measures, optimal control, convex duality

Langlands duality for finite-dimensional representations of quantum affine algebras

We describe a correspondence (or duality) between the q-characters of finite-dimensional representations of a quantum affine algebra and its Langlands dual in the spirit of q-alg/9708006 and 0809.4453. We prove this duality for the Kirillov-Reshetikhin modules and their irreducible tensor products. In the course of the proof we introduce and construct "interpolating (q,t)-characters" depending on two parameters which interpolate between the q-characters of a quantum affine algebra and its Langlands dual.Comment: 40 pages; several results and comments added. Accepted for publication in Letters in Mathematical Physic

A Control Approach to Robust Utility Maximization with Logarithmic Utility and Time-Consistent Penalties

We propose a stochastic control approach to the dynamic maximization of robust utility functionals that are defined in terms of logarithmic utility and a dynamically consistent convex risk measure. The underlying market is modeled by a diffusion process whose coefficients are driven by an external stochastic factor process. In particular, the market model is incomplete. Our main results give conditions on the minimal penalty function of the robust utility functional under which the value function of our problem can be identified with the unique classical solution of a quasilinear PDE within a class of functions satisfying certain growth conditions. The fact that we obtain classical solutions rather than viscosity solutions is important for the use of numerical algorithms, whose applicability is demonstrated in examples.Optimal investment, model uncertainty, incomplete markets, stochastic volatility, coherent risk measure, convex risk measure, optimal control, convex duality