  We report results from monitoring Pluto's 0.8 to 2.4 {\mu}m reflectance
spectrum with IRTF/SpeX on 65 nights over the dozen years from 2001 to 2012.
The spectra show vibrational absorption features of simple molecules CH4, CO,
and N2 condensed as ices on Pluto's surface. These absorptions are modulated by
the planet's 6.39 day rotation period, enabling us to constrain the
longitudinal distributions of the three ices. Absorptions of CO and N2 are
concentrated on Pluto's anti-Charon hemisphere, unlike absorptions of less
volatile CH4 ice that are offset by roughly 90{\deg} from the longitude of
maximum CO and N2 absorption. In addition to the diurnal variations, the
spectra show longer term trends. On decadal timescales, Pluto's stronger CH4
absorption bands have been getting deeper, while the amplitude of their diurnal
variation is diminishing, consistent with additional CH4 absorption at high
northern latitudes rotating into view as the sub-Earth latitude moves north (as
defined by the system's angular momentum vector). Unlike the CH4 absorptions,
Pluto's CO and N2 absorptions appear to be declining over time, suggesting more
equatorial or southerly distributions of those species. Comparisons of
geometrically-matched pairs of observations favor geometric explanations for
the observed secular changes in CO and N2 absorption, although seasonal
volatile transport could be at least partly responsible. The case for a
volatile transport contribution to the secular evolution looks strongest for
CH4 ice, despite it being the least volatile of the three ices.
