A Ph.D. followed in 1948, titled Utbredningstyper bland nordiska barrträdslavar ("Distribution types among Nordic coniferous lichens"), after which Ahlner was appointed docent in plant biology.
[2] Ahlner authored many papers on the lichens of the Nordic countries, with an emphasis on phytogeography and field botany, rather than taxonomy.
On these excursions he made many scientific collections of lichens, which are now kept at the herbarium of Natur Historiska Riksmuseet.
Regarding his personality, his colleague Gunnar Degelius wrote "he was good-natured and sociable, natural and reliable; in his investigations very solid but conservative (as in other things)".
Ahlner died in Uppsala on 12 January 1991 after a few years of frailty caused by a hip ailment and a heart condition.