Phylum: Ascomycota Family: Xylariaceae
Hypoxylon fuscum (Pers.) Fr.
As the common name suggests its preferred host is hazel (Corylus). However, it's not infrequently found on alder (Alnus)
Breitenbach & Kranzlin (1984) Fungi of Switzerland, Volume 1, Ascomycetes
Overall (2017) Fungi: Mushroom & Toadstools of parks, gardens, heaths and woodlands