Urbanization in the Sahel is constantly competing with and greatly affecting the woody flora in urban areas. Urbanization can replace the species mix, leading to changes in plant community composition; however, there are limited studies that assess these attributes in Sahelian cities. This study assessed urban forests in Niamey and Maradi, two important cities of Niger, West Africa for differences between the cities and across LULC types in terms of species diversity and stand structure. Woody species were inventoried in 357 plots in urban forests located across seven land use/land cover types. Stem diameter at breast height of trees and shrubs ≥2.5 cm, total height and crown diameter were measured. Eighty-six species belonging to 69 genera with 33 families were inventoried in Niamey, while in Maradi 91 species belonging to 70 genera with 30 families were enumerated. Fabaceae was the dominant family in both cities. Azadirachta indica accounted for 41 and 54% of all stems in Niamey and Maradi. Residential areas had a higher species richness than other land uses. The majority of the species documented in the two cities were exotics representing 52% of all species encountered. Mean Shannon diversity index (H′) and standard deviation was 2.31 ± 0.43 for Niamey and 2.14 ± 0.74 for Maradi. The similarity index of the two cities was 70%. Urban forests of Maradi had significantly higher levels of species richness and evenness as well as tree density and canopy cover than urban forests of Niamey. Across LULC types, canopy cover varied significantly (p < 0.05) but basal area had a marginal variation whilst, stem density was not significantly different. There were significant positive relationships (p < 0.05) between species richness, basal area and canopy cover across the LULC types in both cities. The study shows that land use/land cover types influence the characteristics of urban forests and differences exist in diversity and stand structural characteristics of urban forests in the two cities. Future development of urban forests in the two cities must increase the planting of native species to improve their value for biodiversity conservation.

中文翻译：

---

尼日尔萨赫勒地区城市森林的多样性和结构

萨赫勒地区的城市化进程不断与城市中的木本植物竞争，并极大地影响着它们。城市化可以代替物种混合，从而导致植物群落组成的变化；但是，在萨赫勒地区，评估这些属性的研究很少。这项研究评估了西非尼日尔的两个重要城市尼亚美和马拉迪的城市森林，从物种多样性和林分结构方面来看，城市之间以及不同土地利用，土地利用变化和林业类型之间的差异。在七种土地利用/土地覆盖类型的城市森林中，对357个样地中的木本物种进行了盘点。测量≥2.5cm的树木和灌木的胸部高度处的茎直径，总高度和树冠直径。在尼亚美盘点了69个属33科的86种豆科是两个城市的主要家庭。在印度尼亚美和马拉迪，印度的印ica占所有茎的41％和54％。居民区的物种丰富度高于其他土地用途。这两个城市记录的大多数物种是外来物种，占所遇见物种的52％。尼亚美的平均Shannon多样性指数（H'）和标准偏差为2.31±0.43，对于马拉迪而言，则为2.14±0.74。两座城市的相似指数是70％。与尼亚美的城市森林相比，马拉迪的城市森林具有更高的物种丰富度和均匀度以及树木密度和树冠覆盖率。在所有LULC类型中，冠层的覆盖率差异很大（p <0.05），但基底面积有少量变化，而茎密度没有显着差异。 在这两个城市中，整个LULC类型的物种丰富度，基础面积和冠层覆盖度之间都存在显着的正相关（p <0.05）。研究表明，土地利用/土地覆盖类型影响城市森林的特征，两个城市的城市森林多样性和林分结构特征存在差异。两个城市中城市森林的未来发展必须增加本地物种的种植，以提高其对生物多样性保护的价值。