  We study BPS dominated loop amplitudes in M-theory on T^2. For this purpose
we generalize the concept of helicity supertraces to nine spacetime dimensions.
These traces distinguish between various massive supermultiplets and appear as
coefficients in their one-loop contributions to n-graviton scattering
amplitudes. This can be used to show that only ultrashort BPS multiplets
contribute to the R^4 term in the effective action, which was first computed by
Green, Gutperle and Vanhove. There are two inequivalent ultrashort BPS
multiplets which describe the Kaluza-Klein states and the wrapped membranes
that cover the torus a number of times. From the perspective of the type-II
strings they correspond to momentum and winding states and D0 or D1 branes.
