Lichen Transplantation for Assessing Intra-Urban Environmental Stress: A Case Study in Jelgava, Latvia

Lichen transplantation can reveal spatial variation in biological responses across urban environments, but visible vitality cannot identify specific pollutants. We transplanted the epiphytic lichen Hypogymnia physodes from a presumed lower-impact forest area to 20 sites in Jelgava, Latvia and assessed its visible condition monthly for 243 days. The primary endpoint was first-observed necrosis; discoloration was retained as a descriptive secondary state. Thirteen primary transplants developed necrosis, first detected between days 62 and 215. One transplant was right-censored at day 123 after pruning, and six had no observed necrosis by day 243. Kaplan–Meier analysis gave a median time to first-observed necrosis of 184 days (20 primary transplants; 13 events; and 7 censored). A descriptive Urban Stress Index summarized event timing for 19 sites with complete follow-up. Correlations between this index and land-use proportions were statistically non-significant. Exploratory correlations with co-located winter snow Pb and Zn concentrations were negative, contrary to a simple metal-toxicity interpretation. The observed necrosis may reflect altered environmental conditions after transplantation rather than metal accumulation; absent concurrent air and thallus chemistry, microcli-mate measurements, and site replication, pollutant-source attribution is precluded. The approach is therefore best used for exploratory spatial screening and hypothesis generation.