Alnus viridis is a shrub species that has been increasing in many European mountains over the past decades, leading to a loss of agricultural areas and several negative environmental impacts. Recently, targeted livestock management systems have been investigated to reduce its encroachment. This study aims to provide an exhaustive assessment of A. viridis leaf composition and its temporal variation across the grazing season. A. viridis leaves were collected throughout the summers of 2020 and 2021 in four encroached sites across the Swiss and Italian Alps, characterized by different pedo-climatic conditions. Based on the data collected by meteorological stations, the growing degree days (GDD) were calculated for each site and year. The leaf functional traits (i.e., Leaf Dry Matter Content – LDMC – and Specific Leaf Area – SLA), chemical composition (macro- and micro-elements and fibre content), phenolic content, in vitro organic matter digestibility (IVOMD), and related gas production (CO₂ and CH₄) were assessed. The LDMC significantly increased throughout the season, whereas the SLA decreased. All macro- and micro-elements significantly varied during the season, with leaf nitrogen (N) and phosphorus (P) decreasing. In contrast, leaf fibre contents significantly increased as the season advanced. There was a significant increase in condensed tannin content during the summer season. Finally, adding A. viridis leaves (20% of diet on a dry matter basis) to cattle diets significantly reduced IVOMD, methane produced per digested organic matter (CH₄/dOM) and CO₂/dOM, compared to a 100% hay diet. Moreover, CH₄/dOM and CH₄/CO₂ ratio increased during the summer season. These results highlight the potential of A. viridis leaves as a valuable forage resource, especially at the beginning of the summer. Such information could be used to optimize grazing of robust livestock in A. viridis-encroached alpine pastures in order to reduce its invasion and minimize greenhouse gases production at the same time.

桤木（Alnus viridis）是一种灌木物种，过去几十年来，欧洲许多山区的数量不断增加，导致农业面积的减少和一些负面的环境影响。最近，对有针对性的牲畜管理系统进行了研究，以减少其侵占。本研究旨在对A. viridis叶子组成及其在整个放牧季节的时间变化进行详尽的评估。2020 年和 2021 年整个夏季，我们在瑞士和意大利阿尔卑斯山的四个被侵占的地点收集了A. viridis叶子，这些地点具有不同的土壤气候条件。根据气象站收集的数据，计算每个站点和年份的生长度日（GDD）。叶子功能性状（即叶子干物质含量 - LDMC - 和比叶面积 - SLA）、化学成分（常量和微量元素以及纤维含量）、酚类含量、体外有机物消化率 (IVOMD) 以及相关评估了气体产量（CO ₂和CH _{4 ）。}整个赛季 LDMC 显着增加，而 SLA 下降。所有常量和微量元素在季节期间都有显着变化，叶片氮 (N) 和磷 (P) 减少。相比之下，随着季节的推进，叶片纤维含量显着增加。夏季，缩合单宁含量显着增加。最后，与 100 % 干草日粮相比，在牛日粮中添加A. viridis叶（以干物质计占日粮的 20%）可显着降低 IVOMD、每消化有机物产生的甲烷 (CH ₄ /dOM) 和 CO ₂ /dOM 。此外，CH ₄ /dOM和CH ₄ /CO ₂比率在夏季增加。这些结果凸显了青蒿叶作为宝贵饲料资源的潜力，尤其是在初夏时。这些信息可用于优化在A. viridis侵占的高山牧场中健壮牲畜的放牧，以减少其入侵并同时最大限度地减少温室气体的产生。