Abstract
The requirements for up-to-date tree data in city parks and forests are increasing, and an important question is how to keep the digital databases current for various applications. Traditional map-updating procedures, such as visual interpretation of digital aerial images or field measurements using tachymeters, are either inaccurate or expensive. Recently, the development of laser-scanning technology has opened new opportunities for tree mapping and attributes updating. For a detailed measurement and attributes update of urban trees, we tested the use of a multisource single-tree inventory (MS-STI) for heterogeneous urban forest conditions. MS-STI requires an existing tree map as input information in addition to airborne laser-scanning (ALS) data. In our study, the tested input tree map was produced by terrestrial laser scanning (TLS) and by using a Global Navigation Satellite System (GNSS). Tree attributes were either measured from ALS or predicted by using metrics extracted from ALS data. Stem diameter-at-breast height (DBH) was predicted and compared to the field measures, and tree height and crown area were directly measured from ALS data at the two different urban-forest areas. The results indicate that MS-STI can be used for updating urban-forest attributes. The accuracies of DBH estimations were improved compared to the existing attribute information in the city of Helsinki’s urban-tree register. In addition, important attributes, such as tree height and crown dimensions, were extracted from ALS and added as attributes to the urban-tree register.
Highlights
Trees and woodlands are part of the urban environment, and they play an important role in urban areas [1]
root-mean-squared error (RMSE) were calculated for each predictor-variable combination, and a minimum number of predictors were chosen before the out-of-bag prediction accuracy started to increase notably
This study showed the high potential of airborne laser-scanning (ALS) and terrestrial laser scanning (TLS) measurements in very heterogeneous urban-forest environments
Summary
Trees and woodlands are part of the urban environment, and they play an important role in urban areas [1]. Urban woodlands can improve people’s quality of life, but they improve the urban environment. Trees can reduce pollution effects [2] and improve air quality [3] in urban areas. Urban forests can store industrial carbon emissions [4], and when vegetation is sustained and maintenance practices are focused upon (e.g., energy conservation or producing long-term carbon storages), urban vegetation can be seen as a carbon sink [5]. Urban forests offer recreational environment for citizens. Use level, user composition, and the temporal distribution of activity types through commuting and recreation use may differ depending on the number and closeness of settlements, business areas and schools [6]
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