Prevalence and severity of Tilia cordata Mill. foliage damage in urban and forest plantings of Kharkiv region

Abstract

Introduction

Tilia cordata Mill., 1768 is widespread in European forests, as well as in shelterbelts and urban plantings. In urban ecosystems, changes in light and temperature, restricted root development, and air pollution influence both the spread of pests and the trees’ response to damage. These effects are often reflected in leaf appearance. For instance, technogenic air pollution manifests as leaf burns, fungal infections appear as spots of various shapes and colors, and insect damage includes gnaws, mines, punctures, galls, etc. Some species of fungi, mites, and insects increase reproduction only up to a certain level of pollution, while others generally avoid colonizing leaves under such conditions.

Studies conducted in various regions show a greater diversity of arthropod species in natural habitats compared to street plantings and a decrease in the proportion of species with an open lifestyle as technogenic load increases. However, the composition of insect, mite, and fungal species depends on factors such as geographic location, annual weather conditions, and the phase in the cyclical population dynamics, highlighting the need for further research.

This study aimed to identify the causes of foliar damage in T. cordata and to assess the prevalence and severity of their effects in relation to the type of planting, thus making it possible to use trees as bioindicators of anthropogenic stress.

Materials and Methods

Our research was carried out in 2018–2021 in forests, forest parks, parks, courtyards, and street plantings in the Kharkiv region and the city of Kharkiv. In July-August, leaves were randomly collected from the upper, middle, and lower canopy layers. During the cameral analysis, leaves were grouped according to the following damage types: “gnaws” (caused by insects with gnawing mouthparts and an open lifestyle), “mines” (galleries inside leaf tissues), “punctures” (caused by sucking insects), “galls” (tissue growths caused by insects or mites), “spots” (caused by phytopathogenic fungi), and “burns” (resulting from anthropogenic air pollution). The prevalence of each type of leaf damage was calculated as the percentage of leaves exhibiting specific symptoms within different planting types. The severity of leaf damage was calculated as the proportion of damaged leaf area (%), estimated with an accuracy of 5%. The average rate of leaf surface removal (leaf loss) was determined as the product of the first two indices and the average proportion of leaf damage in stands of a given type.

Results and Conclusions

On the leaves of Tilia cordata (Mill) “gnaws”, “mines”, “punctures”, and “galls” caused by arthropods, as well as “spots” of fungal lesions and “burns” from air pollutants were identified. Arthropods were represented by two species of the class Arachnida and 10 species of the class Insecta. These species belong to 9 genera, 7 families, 4 orders, with 5 species classified as monophages. On average 21.5±1.84 % of leaves exhibited damage, with “gnaws”: (9.8±1.33 %) and “galls” (5.8±1.05 %) being the most prevalent. The prevalence and intensity of “gnaws” decreased in the following order: Forest – Forest Park – Parks – Courtyards and Streets. “Galls” were most prevalent in parks, while “mines” were found only in the first three types of plantings. “Punctures” were most frequent in courtyard and street plantings, while “spots” were prevalent in forests, the Forest Park, and parks. “Burns” were found only in street plantings. The greatest loss of leaves in forest stands was caused by gnawing insects (8.9 %) and leaf miners (3.45 %). The greatest loss of leaves by insects causing “punctures” was found in courtyards and parks (0.45 % and 0.41 %, respectively). Gall-forming insects caused the most significant leaf loss in parks (3.1 %), while fungal “spots” contributed to 0.47 % leaf loss in parks. The highest leaf loss due to air pollution-induced “burns” was recorded in street plantings (0.6 %).

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