城市森林凋落物在分散降水、减缓地表径流、防控城市内涝等方面具有重要作用.本研究采用野外调查和室内实验相结合的方法,以长春市南湖公园内5种常见树种蒙古栎(Quercus mongolica)、白桦(Betula platyphylla)、樟子松(Pinus sylvestris var.mongolica)、油松(Pinus tabaliformis)和沙冷杉(Abies holophylla)的凋落物为对象,探究其各分解层累积量及水文效应关系.结果表明:凋落物的厚度与累积量呈正相关;未分解层蒙古栎林凋落物厚度显著高于其他林分(P＜0.05),而半分解层樟子松林和油松林凋落物厚度显著高于其他3种林分(P＜0.05);未分解层凋落物累积量为2.44～9.06 t·hm-2,半分解层累积量为3.85～11.79 t· hm-2,其中油松林和樟子松林数值均较高;凋落物持水量随浸水时间的增加呈现先增长后趋于稳定直至饱和状态,将不同树种各分解层持水率、持水量与浸水时间进行曲线拟合,两者均存在幂函数关系(Y=atb);凋落物未分解层最大持水量为4.52～18.72 t·hm-2,其中蒙古栎林显著高于其他4种林分(P＜0.05),而半分解层凋落物最大持水量为6.00～27.51 t·hm-2;阔叶林未分解层持水性能明显优于针叶林,而在半分解层则针叶林更具优势,林龄是调控凋落物水文特性的重要因素之一;凋落物未分解层最大失水量为2.58～8.00t· hm-2,半分解层最大失水量为2.39～13.78 t·hm-2,其中油松林最大失水量显著高于其他4种林分(P＜0.05).建议长春市及相似立地条件的城市在今后城市公园绿地规划中可考虑多栽植蒙古栎纯林,或蒙古栎与油松、樟子松的混交林,可使城市公园绿地最大化发挥其水文调节功能,解决城市内涝及地下水位下降等问题,助力国家海绵城市建设.

本文通过分析长春市PM2.5的时间序列变化特征及影响因素,为长春市和产业结构相近条件城市的PM2.5污染综合防治提供理论依据.从2016～2020年,长春市年平均PM2.5浓度分别为45.94μg/m3、45.76μg/m3、33.39μg/m3、38.14μg/m3、42.08μg/m3,季节变化表现为冬季>春季>秋季>夏季;月变化与季节变化相符合,PM2.5浓度在每年8月份达到最低值;PM2.5日变化表现为夜间浓度远高于白天浓度.同时,长春市PM2.5浓度与降水量、平均气温、平均相对湿度呈显著负相关,与平均气压间呈显著正相关;PM2.5浓度与平均风速和社会经济因素相关性不明显.因此,相关部门在精准调控长春市的PM2.5污染时,应结合气象条件等因素,制定合理的防控措施,其中应重点关注冬季燃煤造成的污染.

Atmospheric pollution caused by fine particulate matter (PM2.5) seriously damages human health. Urban forests have the ecological function of purifying the atmosphere, which can effectively reduce the ambient PM2.5 concentration. This paper analyzed the ability of different forest types to mitigate PM2.5 pollution and explored the effects of forest quality and morphological parameters on PM2.5 concentration on the forest patch level. The results concluded that the PM2.5 concentration of the Landscape and Relaxation Forest (LF) was significantly lower than that of the Roadside Forest (RF) and Affiliated Forest (AF) due to the environmental quality of their location. The effective distance of LF on PM2.5 reduction was 80 m, which was significantly higher than RF and AF. The Normalized Difference Vegetation Index (NDVI), which indicated forest growth status, was the most effective parameter for improving the urban forest PM2.5 mitigation ability. The concentration of PM2.5 decreased linearly with the increase in NDVI. The area and perimeter of the forest patches had a significant nonlinear negative correlation with PM2.5 concentration. In addition, the more irregular the shape of the forest patch, the lower the PM2.5 concentration of the forest. Moreover, the simpler shape of RF and AF helped to alleviate PM2.5 pollution. The round shape of AF more efficiently reduced PM2.5 concentration. Our study demonstrated that the surrounding environment, forest growth status, and patch forms determined the PM2.5 reduction capacity of an urban forest. The corresponding management and adjustment methods should be implemented in future urban forest management.