Joan Tower is such a congenial, straightforward presence, one easily forgets that her complex compositional personality predates the full-fledged American neo-tonalists. She is of the era that broke free of serial restraints but wasn’t about to turn back the clock. If the works here written between 1986 and 2013 are called concertos, it’s a term of convenience. All four are single-movement pieces clocking in at 15-20 minutes, and are through-composed with anxiety-ridden rhythmic undercurrents bubbling about overtly or covertly. All have their own sound worlds. Tower, now 85, isn’t a difficult composer if only because she finds her way forwards, often by first looking backwards to composers from Beethoven to Stravinsky. That doesn’t mean these concertos are easy.

The 1986 Piano Concerto Homage to Beethoven is a highly abstract work with little of the usual competition between soloist and orchestra. Instead, a musical landscape unfolds, constantly and cogently moving forwards – unified mostly by aggressive rhythms. No individual moment has anything 21st-century ears haven’t heard before, but never have these elements been assembled like this. The collage-like quotation that reached my ears wasn’t Beethoven but a recurring, half-remembered variation on the ‘Dies irae’. Elsewhere, the piano-writing intriguingly trails off into uncharted regions, occasionally echoing Stravinsky’s Petrushka – rendered with special clarity, sparkle and narrative momentum by Marc-André Hamelin. To the composer’s credit, there’s not a nice ending pasted on. The concerto just finishes doing what it has to do and stops with only a moderate sense of resolution.

The 2010 flute-and-orchestra work Rising reveals its origins as a chamber work for flute and string quartet with exceptionally candid introspective writing. Flute solos search at length and go deep, thanks partly to meaningful phrasing from Carol Wincenc. Nervous rhythms are more nervous. The usual stability established by ostinatos is missing as they keep moving and morphing into different corners of the musical landscape.

Most original and inviting is the modestly scaled 2013 Red Maple for bassoon and orchestra, with its aria-like melodic lines in a constant state of organic development – benefiting enormously from Adrian Morejon’s honeyed tone quality. The first cadenza can seem perversely unspectacular but emerges into mysterious terrains with the bassoon lyrically navigating the waves of ostinato-driven orchestral writing. As a whole, the piece burns at a cooler temperature than the other works, with bassoon-writing recalling how Nielsen treated the instrument in his Fifth Symphony.

Nielsen also comes to mind in the 1989 Flute Concerto – specifically his oblique, puzzling late works. I admit to being quite lost when repeatedly hearing this piece, not understanding what the discursive individual musical events are saying or what they collectively add up to. The opening flute solo seems unmoored from any point of reference that I have. It hits a dissonant catastrophe and moves on to a series of events that aren’t exactly musical non sequiturs, though it’s hard to account for why they’re in the same piece. Either Tower went down a rabbit hole on this one or I’ll understand the concerto in 10 years’ time. I suspect it’s the latter, because flautist Wincenc and the Boston Early Music Project under Gil Rose handle themselves with charisma and a strong sense of what they’re about. Hints of labour are audible in the orchestra, but that’s to be expected in music that the world will ponder for years to come.