Hurricane disturbance accelerated the thermophilization of a Jamaican montane forest

Thermophilization – changes in community composition towards greater
relative abundances of species associated with warmer environments – has
been described for plants and animals in many locations around the world.
Disturbances of various kinds have increased rates of thermophilization in
temperate sites, and this has been proposed, but not demonstrated, for
some tropical environments. In this study, we tested whether disturbance
by a Category four hurricane in 1988 (Hurricane Gilbert) increased
thermophilization in a Jamaican montane forest by using pre- and
post-hurricane data collected over four decades (1974–2014). We analysed
tree species composition in permanent plots at c. 1580 m elevation in
Jamaica’s Blue Mountains. There were 66 tree species with stem diameters
≥3 cm at breast height. We used published data on the altitudinal
distribution of 62 species (94% of genetic individuals (genets)) to
calculate the mean community altitude scores (MCAS) of the trees recorded
in each census, as well as the MCAS of the survivors, recruits and dead
trees after each decade. We found that thermophilization did occur (i.e.,
MCAS decreased significantly over time), and that this was due both to a
decreasing MCAS of recruits through the four decades (significantly lower
than expected in the last three decades) as well as a high MCAS of trees
that died. Thermophilization was fastest in the post-hurricane decade,
during which time there was marked and significant increase in the MCAS of
dead trees; this change was above and beyond expectations of long-term
successional dynamics. The rate of compositional change equates to an
overall decrease in MCAS of 1.6 m yr-1 over the forty-year study period.
We conclude that this Jamaican montane forest is undergoing
thermophilization (likely due to rising temperature) and that the
hurricane-caused disturbance accelerated thermophilization through
differential mortality.