Crown widths of woody plant species growing in urban areas are of considerable importance as an overall indicator of health and also serve as an important factor for assessing leaf area and associated ecosystem services, such as carbon sequestration, air pollution removal, air temperature cooling, and rainfall interception. Unfortunately, assessing crown widths in urban environments is often challenging and time consuming. To help reduce data collection costs and provide consistency over time, models to predict crown widths for urban-grown species were developed using data from 49 cities across the U.S. and Southern Canada. The effort consisted of fitting mixed models for 29 species groups that encompassed 964 species. Cities were considered a random effect and were statistically significant for 22 of the 29 groups. The need for urban-specific crown width models was demonstrated via examination of prediction biases found when applying crown width models based on forest grown trees, where under-prediction up to about 20% was found for the same species growing in urban areas. Application of the models was evaluated by using crown width predictions instead of observed values for calculations of crown leaf area. Mean percent differences in leaf area were about ±10% across most species groups. Further improvements to national-scale urban crown width models should be pursued as additional data become available via i-Tree, Urban FIA, and possibly other sources where data collection protocols are compatible.

中文翻译：

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美国城市地区生长的木本植物树冠宽度模型

在城市地区生长的木本植物物种的冠冠宽度对于健康状况的总体指标非常重要，并且也是评估叶面积和相关生态系统服务的重要因素，例如碳固存，去除空气污染，气温冷却和降雨拦截。不幸的是，在城市环境中评估冠的宽度通常是挑战性的且耗时的。为了帮助减少数据收集成本并提供长期的一致性，使用来自美国和加拿大南部49个城市的数据，开发了预测城市生长物种冠状宽度的模型。这项工作包括对涵盖964个物种的29个物种组的混合模型进行拟合。城市被认为是随机效应，在29组中有22组具有统计学意义。通过检查基于森林生长树木的树冠宽度模型时发现的预测偏差，证明了对特定于城市的树冠宽度模型的需求，在该模型中，城市地区生长的同一个物种的低估率高达20％。通过使用树冠宽度预测代替观测值计算树冠叶面积来评估模型的应用。在大多数物种组中，叶面积的平均百分比差异约为±10％。随着可通过i-Tree，Urban FIA以及可能兼容数据收集协议的其他来源获得更多数据，应追求对国家规模的城市冠宽模型进行进一步的改进。在城市地区生长的同一物种的预测不足率高达20％。通过使用树冠宽度预测代替观测值计算冠叶面积来评估模型的应用。在大多数物种组中，叶面积的平均百分比差异约为±10％。随着可通过i-Tree，Urban FIA以及可能兼容数据收集协议的其他来源获得更多数据，应追求对国家规模的城市冠宽模型进行进一步的改进。在城市地区生长的同一物种的预测不足率高达20％。通过使用树冠宽度预测代替观测值计算冠叶面积来评估模型的应用。在大多数物种组中，叶面积的平均百分比差异约为±10％。随着可通过i-Tree，Urban FIA以及可能兼容数据收集协议的其他来源获得更多数据，应追求对国家规模的城市冠宽模型进行进一步的改进。