Global warming leads to more uniform spring phenology across elevations

Area of Science:

• Ecology
• Phenology
• Climate Change Research

Background:

• Hopkins' bioclimatic law describes delayed tree leaf-out with increasing latitude, longitude, and elevation.
• Understanding how climate change impacts phenological laws is crucial for ecosystem management.

Purpose of the Study:

• To investigate if global warming has altered Hopkins' bioclimatic law, specifically the elevation-induced phenological shift (EPS).
• To quantify changes in EPS over time in the European Alps.

Main Methods:

• Analysis of approximately 20,000 leaf-out date observations for four temperate tree species.
• Data collected from 128 sites across various elevations in the European Alps between 1960 and 2016.

Main Results:

• The elevation-induced phenological shift (EPS) declined by 35% from 34 d·1,000 m⁻¹ in 1960 to 22 d·1,000 m⁻¹ in 2016.
• Phenological advancement was stronger at higher elevations, linked to increased late spring and warmer winter warming.
• Warmer preceding winters significantly reduced EPS, even under similar spring temperatures.

Conclusions:

• Empirical evidence shows a significant decline in EPS over the past six decades, indicating an alteration of Hopkins' bioclimatic law.
• Continued climate warming may further reduce EPS, potentially impacting mountain forest ecosystem structure, function, and plant-animal interactions.
• The full ecological consequences of this ongoing phenological change remain largely unknown.