  M-type stars are quickly stepping into the forefront as some of the best
candidates in searches for habitable Earth-like exoplanets, and yet many
M-dwarfs exhibit extraordinary flaring events which would bombard otherwise
habitable planets with ionizing radiation. In recent years, observers have
found that the fraction of M-stars demonstrating significant magnetic activity
transitions sharply from roughly $10\%$ for main-sequence stars earlier (more
massive) than spectral type M3.5 (0.35 M$_\odot$) to nearly $90\%$ for stars
later than M3.5. Suggestively, it is also later than M3.5 at which
main-sequence stars become fully convective, and may no longer contain a
tachocline. Using the spherical 3D MHD simulation code Rayleigh, we compare the
peak field strengths, topologies, and time dependencies of convective dynamos
generated within a quickly rotating (2 $\Omega_\odot$) M2 (0.4 M$_\odot$) star,
with the computational domain either terminating at the base of the convection
zone or including the tachocline. We find that while both models generate
strong ($\sim$10kG), wreathlike toroidal fields exhibiting polarity reversals,
the tachocline model provided a further reservoir for the toroidal field, which
slowed the average reversal period from 100 rotations to more than 220
rotations and increased the spectral power of the low-order modes of the
near-surface radial field by a factor of 4.
