Terrestrial Laser Scanning to Predict Canopy Area Metrics, Water Storage Capacity, and Throughfall Redistribution in Small Trees

Mariana Baptista,Ebadat G Parmehr,Stephen Livesley,Marco Amati,Melissa Neave

doi:10.3390/rs10121958

Mariana Baptista, Ebadat G Parmehr + Show 3 more

Open Access

https://doi.org/10.3390/rs10121958

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Abstract

Urban trees deliver many ecological services to the urban environment, including reduced runoff generation in storms. Trees intercept rainfall and store part of the water on leaves and branches, reducing the volume and velocity of water that reaches the soil. Moreover, trees modify the spatial distribution of rainwater under the canopy. However, measuring interception parameters is a complex task because it depends on many factors, including environmental conditions (rainfall intensity, wind speed, etc.) and tree characteristics (plant surface area, leaf and branch inclination angle, etc.). In the few last decades, remotely sensed data have been tested for retrieving tree metrics, but the use of this derived data for predicting interception parameters are still being developed. In this study, we measured the minimum water storage capacity (Cmin) and throughfall under the canopies of 12 trees belonging to three different species. All trees had their plant surface metrics calculated: plant surface area (PSA), plant area index (PAI), and plant area density (PAD). Trees were scanned with a mobile terrestrial laser scan (TLS) to obtain their individual canopy point clouds. Point clouds were used to calculate canopy metrics (canopy projected area and volume) and TLS-derived surface metrics. Measured surface metrics were then correlated to derived TLS metrics, and the relationship between TLS data and interception parameters was tested. Additionally, TLS data was used in analyses of throughfall distribution on a sub-canopy scale. The significant correlation between the directly measured surface area and TLS-derived metrics validates the use of the remotely sensed data for predicting plant area metrics. Moreover, TLS-derived metrics showed a significant correlation with a water storage capacity parameter (Cmin). The present study supports the use of TLS data as a tool for measuring tree metrics and ecosystem services such as Cmin; however, more studies to understand how to apply remotely sensed data into ecological analyses in the urban environment must be encouraged.

Highlights

Trees are an important component of the urban environment, as they can cool to moderate air temperatures [1,2,3], decrease air pollution [4,5], reduce noise [6], stimulate social connection [7], and reduce storm runoff effects [8,9], as well as many other benefits
The number of points for each tree was assessed and derived tree metrics were calculated from the scanned data (Table 1)
terrestrial laser scan (TLS) metrics were correlated to directly measured metrics to validate the effectiveness of TLS data in predicting plant surface metrics (Figure 3)

Summary

Introduction

Trees are an important component of the urban environment, as they can cool to moderate air temperatures [1,2,3], decrease air pollution [4,5], reduce noise [6], stimulate social connection [7], and reduce storm runoff effects [8,9], as well as many other benefits. Understanding, quantifying, and communicating the benefits of trees is important from an urban planning perspective, as a raised awareness of a scientific evidence base may help set policies and future management planning for urban forests. Quantifying the role of urban trees in the mitigation of water runoff is important, as the frequency of floods has increased in densely urbanised areas in the last decades. Many cities in the world have set targets to increase tree canopy cover as one of the nature-based solutions to help mitigate the occurrence of floods [10,11,12]

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