Urbanization and climate jointly shape the composition of plant life forms

Urbanization and climate change are rapidly altering large-scale plant distributions and local community compositions, with profound impacts on ecosystem functions and services. However, it remains unclear how life form compositions, as one of the key functional biodiversity components in urban ecosystems, are influenced by urbanization under different climate scenarios.<b> </b>Here we investigated the life form compositions of 2,864 spontaneous plant species across 129 cities in a global biodiversity hotspot, Yunnan province of China. The results showed that, for naturally regenerated spontaneous plants in urban ecosystems, herbaceous plants (74.2%) significantly outnumbered woody plants (25.8%), while perennial herbs (45.0%) prevailed over annual herbs (29.2%). The compositions of plant life forms were significantly controlled by urbanization intensity and annual mean temperature. Specifically, annual plants were not sensitive to climate factors and thrived mainly in cities under intensive urbanization. Rising temperatures led to a monotonic decrease in the proportion of perennial herbs and an increase in woody plants. Along each temperature gradient, perennial herbs peaked under moderate urbanization intensity, while woody plants exhibited at troughs. Overall, perennial herbaceous were promoted by lower temperatures and moderate urbanization, while woody plants were mainly dominated in higher temperatures and lower degree of urbanization. Our findings highlight the profound combined effects of urbanization and climate in shaping functional traits of plants in human-dominated ecosystems.

城市化与气候变化正快速改变全球尺度的植物分布格局与本地群落组成，对生态系统功能与服务造成深远影响。然而，作为城市生态系统核心功能生物多样性组分（functional biodiversity components）之一的植物生活型组成（life form compositions），在不同气候情景下如何受城市化（urbanization）影响，目前仍不明确。
本研究针对全球生物多样性热点区（global biodiversity hotspot）——中国云南省的129座城市中2864种自发植物（spontaneous plant）的生活型组成展开调查。结果显示，对于城市生态系统中自然再生的自发植物而言，草本植物（74.2%）的数量显著多于木本植物（25.8%）；其中多年生草本（45.0%）占比高于一年生草本（29.2%）。植物生活型组成显著受城市化强度（urbanization intensity）与年平均气温（annual mean temperature）的调控。具体而言，一年生植物对气候因子不敏感，主要在城市化强度较高的城市中繁盛生长。气温升高会导致多年生草本的占比单调递减，而木本植物占比则随之上升。在每条温度梯度下，多年生草本的占比在中等城市化强度时达到峰值，而木本植物占比则在此区间处于低谷。总体而言，低温与中等城市化水平有利于多年生草本的生长，而木本植物则主要在高温、低城市化程度的区域占据优势。本研究结果凸显了城市化与气候变化的复合效应对人类主导生态系统中植物功能性状（functional traits）塑造的深远影响。