Key message

Street trees are vulnerable to extreme climate conditions such as precipitation, wind gust and high temperatures. But trees may also fail in the cities as a result of poor stewardship.

Urban trees are renowned for improving the livability in the cities through their ecosystem services. Long-lasting services, however, are only possible if local responsible authorities adequately manage the trees. Wood decay, inappropriate pruning, presence of xylophagous organisms, trunk constriction by the sidewalks, altogether increase the probability of trees to fall under adverse climate conditions. Tree fall is closely related to disservices like damages to the infrastructure, risks of injury and death. Given the previously reported poor conditions of the street trees in São Paulo/Brazil, one of the world’s largest cities, we assessed the main climate causes of tree fall. We evaluated a 3-year daily series of fallen trees in the city. The effects of precipitation, wind gust and temperature were evaluated using cross-wavelet analyses. Out of the 652,000 street trees of São Paulo, 7034 fell in the city during this period. Cross-wavelet analyses revealed that tree fall is seasonal and in phase with, and driven by, precipitation, wind gust and temperature during the wet season. While temperature directly influences tree fall, both precipitation and wind gust may show lagged effects. Such associations with climate were not observed during the dry season despite the records of fallen trees. Falling trees were observed in two-thirds of the days during the dry season. Although it could be partially caused by lagged effects of precipitation and wind gust, these records during the dry season confirm the poor stewardship and conditions of the street trees in the city. This study highlights how vulnerable street trees are to extreme climate conditions and that yet poorly managed trees fall on the streets daily without any apparent climate causes.

中文翻译：

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树木的气候驱动因素掉落在巴西圣保罗的街道上

关键信息

街头树木易受极端气候条件的影响，例如降水，阵风和高温。但是，由于管理不善，树木在城市中也可能会失败。

城市树木因其生态系统服务而提高了城市的宜居性而闻名。但是，只有在当地负责机构充分管理树木的情况下，才能提供长期服务。木材腐烂，不适当的修剪，木生生物的存在，人行道上的树干收缩等因素，完全增加了树木在不利的气候条件下倒下的可能性。树木倒下与诸如基础设施损坏，受伤和死亡风险之类的损害密切相关。鉴于先前报道的圣保罗/巴西（世界上最大的城市之一）的街头树木状况很差，我们评估了造成树木倒下的主要气候原因。我们评估了该城市中每3年一次的倒下树木系列。使用交叉小波分析评估了降水，阵风和温度的影响。在此期间，圣保罗的652,000棵行道树中，有7034棵落在该市。交叉小波分析表明，树木的倒落是季节性的，并且与雨季的降水，阵风和温度同步，并受其驱动。尽管温度直接影响树木倒下，但降水和阵风都可能显示出滞后效应。尽管有倒下树木的记录，但在干旱季节没有观察到与气候的这种联系。在干旱季节的三分之二的时间内，观察到倒下的树木。尽管这可能部分是由降雨和阵风的滞后影响引起的，但在干旱季节的这些记录证实了该市行道树的不良管理和条件。