  We present a comprehensive study of disks around 81 young low-mass stars and
brown dwarfs in the nearby ~2-Myr-old Chamaeleon I star-forming region. We use
mid-infrared photometry from the Spitzer Space Telescope, supplemented by
findings from ground-based high-resolution optical spectroscopy and adaptive
optics imaging. We derive disk fractions of 52 (+/-6) % and 58 (+6/-7) % based
on 8-micron and 24-micron colour excesses, respectively, consistent with those
reported for other clusters of similar age. Within the uncertainties, the disk
frequency in our sample of K3-M8 objects in Cha I does not depend on stellar
mass. Diskless and disk-bearing objects have similar spatial distributions.
There are no obvious transition disks in our sample, implying a rapid timescale
for the inner disk clearing process; however, we find two objects with weak
excess at 3-8 microns and substantial excess at 24 microns, which may indicate
grain growth and dust settling in the inner disk. For a sub-sample of 35
objects with high-resolution spectra, we investigate the connection between
accretion signatures and dusty disks: in the vast majority of cases (29/35) the
two are well correlated, suggesting that, on average, the timescale for gas
dissipation is similar to that for clearing the inner dust disk. The exceptions
are six objects for which dust disks appear to persist even though accretion
has ceased or dropped below measurable levels. Adaptive optics images of 65 of
our targets reveal that 17 have companions at (projected) separations of 10-80
AU. Of the five <20 AU binaries, four lack infrared excess, possibly indicating
that a close companion leads to faster disk dispersal. The closest binary with
excess is separated by ~20 AU, which sets an upper limit of ~8 AU for the outer
disk radius. (abridged)
