Three-dimensional (3D) structure model and its parameters for poplar shelterbelts

Abstract: The spatial functions of surface area density (vegetative surface area per unit canopy volume) and cubic density (vegetative volume per unit canopy volume) have been used as two three-dimensional (3D) structural descriptors for shelterbelt. The functions were defined by models as a general case. However, sub-models such as surface area, volume, and corresponding distributions were not explicitly defined for poplar trees, which are a dominant woody species in shelterbelts all over China, and this limits applications of the models in China and elsewhere. In order to define and develop these sub-models for shelterbelts, poplar trees were destructively sampled from multiple-row shelterbelts and then were measured for their surface area and volume. Using these measurements, we estimated parameters to define their equations explicitly. Based on the architecture and planting patterns of trees in shelterbelts, the distribution of the surface areas and volumes vertically and across the width for different tree heights were constructed for the three components of trunks, branches and leaves. Incorporating the defined equations into the models, we described the 3D structure of a multiple-row poplar shelterbelt. The results showed that, the spatial change in magnitude of surface area density (0.215–10.131 m²/m³) or cubic density (0.00007–0.04667 m³/m³) in shelterbelts is large and their distributions are not uniform. The assumption for boundary-layer flow modeling efforts that the 3D distribution of shelterbelt structure was uniform is not the case in field. The 3D structure model not only can be used to model the flow field as influenced by each tree component, but also can express the entire aerodynamic characteristics of a shelterbelt. The methodologies and equations that are developed in this study can be applied to estimate the 3D structure of a shelterbelt with a design similar to our studied poplar shelterbelts in terms of species composition and planting patterns. The fitted models can be used to describe the 3D aerodynamic structure of field shelterbelts. Furthermore, an improved description of shelterbelt structure has great potential to improve the simulation of boundary layer flows as influenced by that shelterbelt. Such insights can eventually be used to quantify the design of shelterbelt structure and/or adjustment for managing the function of shelterbelts and their effects on microclimate.