  Brown dwarfs straddle the mass range transition from planetary to stellar
objects. There is a relative paucity of brown dwarfs companions around FGKM
stars compared to exoplanets for orbital periods less than a few years, but
most of the short-period brown dwarf companions fully characterised by transits
and radial velocities are found around F-type stars. We examine the hypothesis
that brown dwarf companions could not survive on close orbit around stars with
important convective envelopes because the tides and angular momentum loss
through magnetic breaking should lead to a rapid orbital decay and quick
engulfment of the companion. We use a classical Skumanich-type braking law, and
constant time-lag tidal theory to assess the characteristic timescale for
orbital decay for the brown dwarf mass range as a function of the host
properties. We find that F-type stars may host massive companions for a
significantly longer time than G-type stars for a given orbital period, which
may explain the paucity of G-type hosts for brown dwarfs with orbital period
less than 5 days. On the other hand, we show that the small radius of early
M-type stars contributes to orbital decay timescales that are only half those
of F-type stars, despite their more efficient tidal dissipation and magnetic
braking. For fully convective later type M-dwarfs, orbital decay timescales
could be orders of magnitude greater than for F-type stars. For orbital periods
greater than 10 days, brown dwarf occurrence should largely be unaffected by
tidal decay, whatever the mass of the host. On closer orbital periods, the
rapid engulfment of massive companions could explain the lack of G and K-type
hosts in the sample of known systems with transiting brown dwarfs. However, the
paucity of M-type hosts can not be an effect of tidal decay alone, but may be
the result of a selection effect in the sample and/or the formation mechanism.
