# Spatial and Temporal Dynamics of Birch-Mining Eriocrania Moths in an Urban Landscape over Four Decades

## TL;DR

A 40-year study in St. Petersburg shows birch trees decline near the city center, but birch-mining moths remain stable despite urbanization.

## Contribution

The study reveals long-term stability of Eriocrania moths in urban areas despite environmental changes.

## Key findings

- Birch presence and ground quality declined toward the city center and over time.
- Moth populations remained stable with no long-term decline despite urbanization.
- Habitat characteristics only moderately predict extinction risks for birches and moths.

## Abstract

We studied how urbanisation affects birch trees and their moth herbivores in St. Petersburg, the second largest city in Russia, over four decades. While birch presence and patch quality declined near the city centre, moth populations remained stable, showing no long-term decline. Habitat characteristics partly predict local risks for birch and moths, but do not fully determine their survival in urban areas.

Understanding how urbanisation shapes species distributions and ecological interactions requires long-term, spatially structured data. Using an exceptionally rare 40-year dataset (1986–2025) from 150 habitat patches and 102 downtown grid cells in St. Petersburg, Russia, we examined patterns in birch (Betula pendula and B. pubescens) persistence, ground conditions, woody vegetation, and the occurrence of Eriocrania leaf-mining moths. Birch presence, birch abundance, and ground quality declined both toward the city centre and over time, whereas woody plant cover showed no clear spatial or temporal pattern. Eriocrania occurrence within birch-containing patches was influenced primarily by habitat type, artificial ground, and birch abundance, while distance to the city centre, year, and woody cover exerted no consistent effects. Habitat characteristics offered only moderate predictive power for local extinction risk in both birches and Eriocrania, indicating that multiple drivers interact to shape patch dynamics. Contrary to the widespread declines observed in many insect taxa, Eriocrania populations exhibited no directional density trend across four decades. This long-term stability highlights the resilience of specialised herbivores in heterogeneous urban landscapes and underscores the value of extended temporal datasets for detecting subtle or unexpected ecological responses to urbanisation.