Abstract:

Aims: This research aimed to clarify the correlation between various environmental factors, such as anthropogenic impacts, and the insect diversity in urban forests, which can lead to the elucidation of key factors that can affect insect diversity in urban forests. Furthermore, this could result in the development and implementation of more efficient conservation guidelines and conservation strategies for the protection of urban species diversity.

Methods: From late July 2020 to early July 2021, with the use of sweeping method and Malaise traps, we collected insects from six habitats with different stand types from Zijin Mountain, Nanjing, including greenway in artificial broadleaf forest, greenway in broadleaf-conifer mixed forest, wetland in broadleaf-conifer mixed forest, as well as woodlands in artificial coniferous forest, broadleaf-conifer mixed forest, and broadleaf mixed forest. Insects were identified using morphological guides from taxonomic monographs. Shannon-Wiener diversity index, Pielou evenness index, Margalef richness index, and Simpson diversity index were used to evaluate α-diversity. Differences between insect diversity in different habitats and taxonomic orders were evaluated by Kruskal-Wallis analyses. Insect diversity in different habitats was estimated by rarefaction and extrapolation analyses. Bray-Curtis distance was calculated to evaluate the similarity of insect diversity and richness between different habitats. The influence of different environmental variables, both abiotic and biotic, on insect diversity was evaluated by redundancy analysis and Pearson correlation. Both samplings of the whole year and a part of summer were used.

Results: A total of 59,648 insects belonging to 145 species in 78 families and 9 orders were collected. Among these, the orders Lepidoptera, Hemiptera, Hymenoptera, and Diptera had the highest number of species and relative abundance. Most species were captured between July and September. Rarefaction and extrapolation analyses showed that the collections of specimens can represent the insect communities of each habitat. The α-diversity analyses indicated that woodland in broadleaf mixed forest had the highest insect diversity among sampled habitats, while woodland in artificial coniferous forest had the lowest. Although most habitats do not differ significantly in α-diversity, in terms of species composition, only the wetland in broadleaf-conifer mixed forest was moderately similar to the woodland in broadleaf mixed forest. Other habitats were all moderately dissimilar or very dissimilar to each other. The redundancy analyses showed that artificial interference of vegetation, pedestrian volume, altitude, temperature, sunshine duration, and precipitation were the major variables that significantly impacted insect diversity at the southern foot of Zijin Mountain. In addition, Pearson analyses indicated that most variables are correlated to insect diversity. Despite the different effects environmental variables have on the α-diversity of major insect orders, artificial interference of vegetation had the most significant effect, as our results showed that insect diversity significantly decreased with the increase of artificial interference of vegetation. Considering the correlations between insect diversity and other variables that can be attributed to artificial interferences, we determined that vegetation structure was the variable that has the highest degree of influence on insect diversity in urban forests.

Conclusion: This study clarifies key factors affecting insect diversity in urban forests. This could potentially provide theoretical guidance in urban species diversity conservation. Scientific planning and management of vegetation structure may be the key to preserving insect diversity in urban forests. It is thus suggested that more research on the dominant factors affecting the diversity of the major insect groups be carried out. This, even at a smaller scale according to local conditions, could greatly benefit the dynamic management of urban forests.

Key words: urban forest, insect diversity, influencing factors, artificial interference, Zijin Mountain