Svetlana VARŠOVÁ, Veronika LUKASOVÁ, Milan ONDERKA, Jiří KOPÁČEK, Dušan BILČÍK, Ján KREMPASKÝ

A 250-year reconstruction of average July air temperatures (1775--2024): A key climate indicator of vegetation growth in the alpine treeline ecotone of the High Tatra Mts, Slovakia

Introduction

A 250-year reconstruction of average july air temperatures (1775--2024): a key climate indicator of vegetation growth in the alpine treeline ecotone of the high tatra mts, slovakia. Reconstructs 250 years (1775-2024) of July air temperatures in High Tatra Mts, Slovakia, revealing alpine treeline shifts due to warming and impact on vegetation growth.

Abstract

The reconstruction of historical air temperatures over the past 250 years (1775–2024) in the alpine treeline ecotone (ATE) of the High Tatra Mts, Slovakia, provides insights into long-term climate variability. As a high-elevation region sensitive to climatic fluctuations, the alpine treeline is a key indicator of environmental change. A model-based approach allows estimation of air temperature where direct measurements are lacking, offering a tool for assessing long-term climate impacts in high mountains. This study models the July monthly average air temperature (JL-Tavg) and the 10°C July isotherm, a climatic threshold for vegetation growth. The regression model is based on the environmental temperature lapse rate (ETL), assuming a systematic decrease in temperature with altitude (∼0.65°C per 100 m). Using air temperature data from European stations spanning 191–3109 m a.s.l., the model estimated ETL, which was then applied to reconstruct JL-Tavg and track the 10°C isotherm across the Skalnatá dolina ATE profile. The regression model showed a good fit between observed and predicted values, with root mean square error lower than the standard deviation of average JL-Tavg. Reconstructed data indicate that the 10°C July isotherm fluctuated markedly between 1775 and 2024. The alpine treeline, defined as the elevation with zero probability of tree growth, varied from ≈ 2000 m a.s.l. during the cooler phase (1875–1974) to ≈ 2300 m a.s.l. in the warmer phase (1775–1874). Since 1975, accelerated warming has shifted this thermal boundary upward to ≈ 2400 m a.s.l., now representing the upper cold limit for alpine tree growth in the southern High Tatra Mts. Future work should integrate field monitoring, such as mapping dwarf pine above 2000 m a.s.l., to evaluate current distributional limits under ongoing warming.

Review

This study presents a valuable 250-year reconstruction (1775–2024) of average July air temperatures within the alpine treeline ecotone (ATE) of the High Tatra Mts, Slovakia. Addressing the inherent data scarcity in high-elevation environments, the research employs a model-based approach to provide critical insights into long-term climate variability. The focus on July temperatures and the 10°C isotherm is particularly pertinent, as these are well-established key climatic indicators for vegetation growth and the dynamics of the alpine treeline, a sensitive barometer of environmental change. This long-term perspective is essential for understanding the natural range of climate fluctuations against which contemporary warming trends can be assessed. The methodology utilizes a regression model based on the environmental temperature lapse rate (ETL), systematically derived from a broad dataset of European air temperature stations. This approach allows for the estimation and reconstruction of July monthly average air temperatures (JL-Tavg) and the tracking of the 10°C isotherm across the High Tatra's Skalnatá dolina ATE profile. The model's demonstrated good fit between observed and predicted values, with a root mean square error lower than the standard deviation, lends confidence to its results. The reconstructed data reveal marked fluctuations in the 10°C July isotherm, with the treeline, defined by the zero probability of tree growth, varying significantly from ≈2000 m a.s.l. during a cooler period (1875–1974) to ≈2300 m a.s.l. in an earlier warmer phase (1775–1874). Crucially, the study highlights an accelerated warming trend since 1975, pushing this thermal boundary upward to ≈2400 m a.s.l., establishing it as the current upper cold limit for alpine tree growth in the southern High Tatra Mts. This research offers a compelling long-term context for current climate change impacts on sensitive mountain ecosystems. The identified rapid upward shift of the thermal treeline boundary since 1975 underscores significant ecological pressures and the profound effects of ongoing warming on high-altitude vegetation dynamics. The abstract’s suggestion for future work, specifically integrating field monitoring such as mapping dwarf pine above 2000 m a.s.l., is a highly relevant recommendation. Such empirical validation would strengthen the model’s findings by providing direct evidence of current distributional limits, further solidifying the study's contribution to climate and ecological research in alpine environments.

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