A Model to Assess Eastern Cottonwood Water Flow Using Adjusted Vapor Pressure Deficit Associated with a Climate Change Impact Application

Ying Ouyang,Theodor D Leininger,Heidi Renninger,Emile S Gardiner,Lisa Samuelson

doi:10.3390/cli9020022

Ying Ouyang, Theodor D Leininger + Show 3 more

Open Access

https://doi.org/10.3390/cli9020022

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Abstract

Short-rotation woody crops have maintained global prominence as biomass feedstocks for bioenergy, in part due to their fast growth and coppicing ability. However, the water usage efficiency of some woody biomass crops suggests potential adverse hydrological impacts. Monitoring tree water use in large-scale plantations would be very time-consuming and cost-prohibitive because it would typically require the installation and maintenance of sap flux sensors and dataloggers or other instruments. We developed a model to estimate the sap flux of eastern cottonwood (Populus deltoides. Bartr. ex Marsh.)) grown in bioenergy plantations. This model is based on adjusted vapor pressure deficit (VPD) using Structural Thinking and Experiential Learning Laboratory with Animation (STELLA) software (Architect Version 1.8.2), and is validated using the sap flux data collected from a 4-year-old eastern cottonwood biomass production plantation. With R2 values greater than 0.79 and Nash Sutcliffe coefficients greater than 0.69 and p values < 0.001, a strong agreement was obtained between measured and predicted diurnal sap flux patterns and annual sap flux cycles. We further validated the model using eastern cottonwood sap flux data from Aiken, South Carolina, USA with a good agreement between method predictions and field measurements. The model was able to predict a typical diurnal pattern, with sap flux density increasing during the day and decreasing at night for a 5-year-old cottonwood plantation. We found that a 10% increase in VPD due to climate change increased the sap flux of eastern cottonwood by about 5%. Our model also forecasted annual sap flux characteristics of measured cycles that increased in the spring, reached a maximum in the summer, and decreased in the fall. The model developed here can be adapted to estimate sap flux of other trees species in a time- and cost-effective manner.

Highlights

Fossil fuel consumption has been strongly tied to various sources of environmental degradation
We investigated the relationship between adjusted VPD and eastern cottonwood sap flux to address the following objectives: (1) establish a model using diurnal patterns and annual cycles of adjusted VPD to predict those of measured eastern cottonwood sap flux; (2) validate the model using an independent sap flux dataset collected from sensor measurements; and (3) apply the model to predict eastern cottonwood sap flux in the absence of measured sap flux data under a changing climate
Though the results above show that measured sap flux correlated well with adjusted VPD, they do not confirm if sap flux predicted by the STELLA model accurately matches measured sap flux

Summary

Introduction

Fossil fuel consumption has been strongly tied to various sources of environmental degradation. Agronomic crops, grasses, trees, municipal wastes, and other biological materials can be sourced for biomass, and biomass can be converted to solid, liquid, or gaseous fuels to yield energy for industrial, commercial, and domestic uses. Tree and shrub cultivation in short-rotation (2–15 years) provides for high-yielding bioenergy feedstock production. Over the past several decades, researchers have refined improvements in short-rotation tree and shrub species such as eastern cottonwood Its suitability to plantation culture is driving current research and development towards application to large-scale biomass production in the southern United States [11,13]. Shrub willows have been selected for short-rotation intensive culture in the northeastern, north–central, and mid-Atlantic regions of the United States [14]

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