It is very unlikely that this work is public domain in the EU, or in any country where the copyright term is life-plus-70 years. However, it is in the public domain in Canada (where IMSLP is hosted) and other countries where the term is life-plus-50 years (such as China, Japan, Korea and many others worldwide). As this work was first published before 1924 or failed to meet notice or renewal requirements to secure statutory copyright with no "restoration" under the GATT amendments, it is very likely to be public domain in the USA as well.
|Composition Year||July 1919 in Denmark? see below.|
|Genre Categories||; ;; ; ;|
|Work Title||Poem for Strings|
|I-Catalogue NumberI-Cat. No.||IJS 1|
|Key||F major/D minor|
|Year/Date of CompositionY/D of Comp.||July 1919 in Denmark? see below.|
|First Publication.||1920s (possibly 1926?)|
|Composer Time PeriodComp. Period||Early 20th century|
|Piece Style||Early 20th century|
|Instrumentation||2 Violins, viola, cello - see below|
The New York Public Library has an extensive archive of Strimer manuscripts according to their library catalog. Listed is a manuscript (presumably?) of a Poem for string orchestra, possibly related to this work, perhaps a later transcription by the composer.
The date July 1919 is given on the Bessel score, by the way. Is this the date of composition or of publication? (Sibley assumes the former.) (The plate number, 8187, suggests publication in the mid-1920s. However, there is no copyright date aside from that 1919... - Schissel)
A Google Books search suggests that publication was in 1926, fwiw.-ES