Beech forests across Catalonia, including prominent areas like Montseny and Alt Berguedà, have turned green significantly earlier this year, a phenomenon attributed to unusually high April temperatures. This premature leaf emergence, observed from around 10 April in lower altitudes, is now widespread across all elevations of the Montseny massif and other regions.
The early budding of these iconic beech trees (Fagus sylvatica) is a departure from their typical rhythm, which usually sees spectacular green tones in spring after late October to mid-November autumn colours. According to Marc Noguera, a phenological observer for Meteocat, the leaf emergence in the Catllaràs massif (Alt Berguedà) occurred a week earlier than last year and 10 days earlier than in 2022. Data indicates that over 50% leaf cover was reached by 18-20 April this year, compared to 25-27 April in 2025 and 28-30 April in 2022.
While visually striking, this accelerated growth poses a significant risk to the beech trees. Beech is known for its particularly late budding because its new shoots are highly sensitive to sub-zero temperatures. Although dormant winter buds can withstand intense frosts of -20 or -30 degrees Celsius, tender new shoots can barely tolerate slightly negative temperatures. A few degrees below zero can cause severe damage, 'burning' and killing the new leaves and stems.
If damaged, the tree is forced to attempt to re-sprout, which is not always feasible. This re-budding process demands substantial energy, weakening the tree and making it more susceptible to diseases or, in the worst-case scenario, leading to its death.
Beech trees are characteristic of humid regions at mid-latitudes and are well-known in humid Catalonia. They are particularly prevalent at medium and high altitudes, typically above 800 or 1,000 metres, reaching up to 1,600 or 1,700 metres. Notable beech forests are found in Montseny, Ripollès, Alt Berguedà, Garrotxa, Alt Empordà (in Les Alberes), and parts of Osona. More isolated populations exist in Alta Ribagorça, Pallars Jussà, Solsonès, and Moianès. The Vall d'Aran and the northern slopes of the Pyrenees also host extensive beech populations, sometimes below 800 metres.
Climate Change and Vulnerability
A unique exception to the altitude rule is the Jordà Beech Forest in Garrotxa, where trees thrive at just over 400 metres. The small beech forests in the Ports de Tortosa massif, in the country's southern extreme, are considered the most southerly in Europe. Montseny's extensive beech forests benefit from high rainfall and frequent low clouds and fog.
The timing of leaf emergence and fall is a type of phenological information. These annual events, like the arrival of swallows, vary based on several factors, with meteorology being a key influence. Observing and recording these events year after year provides crucial data on how climate change is altering the rhythms of plants and animals.
Monitoring Natural Rhythms
The Meteorological Service of Catalonia has been operating the Phenological Network of Catalonia (Fenocat) since 2013. This network comprises 50 volunteer observers who systematically record the phenological states of 25 plant species, 14 bird species, and six butterfly species. Additionally, the CREAF research centre runs the 'Nature Rhythm' project, which collects phenological information contributed by citizens. These initiatives are vital for understanding and responding to the impacts of climate change on Catalonia's natural environment.
