Abstract
Abstract. Grasslands are important ecosystems to provide various economic and ecological services. In Japan, grassland of Miscanthus sinensis, which is a tall, perennial grass species, has been one of the symbolic landscape and require efficient monitoring system for better management. In this study, canopy height and biomass of M. sinensis in semi-natural grassland are estimated using time-series UAV imagery and structure from motion (SfM) and multi-view stereo (MVS) technique. The effect of complex topography on estimation of the canopy height and biomass is analysed as well as monitoring growth of M. sinensis. The results showed that UAV derived maximum canopy height and biomass have significant correlation with vegetation survey data producing R2 value of 0.92 and 0.78, respectively. The effect of topographic landforms was found to be smallest on top of the hill, followed by slope. Valley-like sunken place was affected worst. Analysis using time-series UAV data revealed that growth of M. sinensis is different between the landforms, and the best time to estimate its biomass was different between them. In order to accurately estimate canopy height and biomass of tall grass species such as M. sinensis, it is important to take plant growth stage into consideration as well as topographic landforms.
Highlights
Grasslands are important ecosystems to provide various economic and ecological services such as water conservation (e.g. Bilotta et al, 2010), carbon sequestration (e.g. O'Mara, 2012) and habitat for wildlife (e.g. Milligan et al, 2020; Port et al, 2019)
3.2.1 Maximum height: Table 1 shows the maximum height of M. sinensis in each plot in each month from May to August derived from unmanned aerial vehicle (UAV) data and the mean maximum height recorded in vegetation survey in September
The accuracy of z values of Digital Terrain Model (DTM) and Digital Surface Model (DSM) was considered to be reasonable with RMSE of 5.0-6.7 cm at Ground sampling distance (GSD) of 2.31-2.41 cm, compared to other grassland studies
Summary
Grasslands are important ecosystems to provide various economic and ecological services such as water conservation (e.g. Bilotta et al, 2010), carbon sequestration (e.g. O'Mara, 2012) and habitat for wildlife (e.g. Milligan et al, 2020; Port et al, 2019). In Japan, grassland of Miscanthus sinensis (Figure 1), which is a tall, perennial grass species and characterized by erect and tufted forms (Hayashi et al, 1981), has been one of the symbolic landscape and supplied food for livestock, compost for the crops, and materials for traditional roof It is a semi-natural grassland and requires controlled burn to maintain the grassland, otherwise it succeeds to forests due to a temperate climate and abundant rainfall. We use time-series UAV data, which covers whole growing season of M. sinensis This is because tall grass species tend to hang their canopy as they grow excessively, it may affect the estimation of canopy height and biomass. Growth of M. sinensis is monitored and analysed in conjunction with the topography
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