Tropical montane vegetation dynamics near the upper cloud belt strongly associated with a shifting ITCZ and fire

1. Tropical montane forests house unusual and diverse biota and are considered highly vulnerable to climate change, particularly near the trade wind inversion (TWI) – the upper end of the cloud belt that defines tropical montane cloud forest (TMCF). The upper cloud belt has two possible futures: one hypothesis postulates a ‘lifting cloud base’, raising both the upper and lower ends of the cloud belt; the other expects the upper end of the cloud belt will change independently, with a ‘shifting TWI’. 2. We used a ~5900-year-long palaeorecord of vegetation and fire from a small forest hollow at 2455 m in the Cordillera Central, Dominican Republic. The site sits near the upper limit of TMCF taxa and the TWI and allows us to evaluate the relationship between vegetation dynamics and two potential drivers of TWI elevation – the Intertropical Convergence Zone (ITCZ) and the El Ni~no/ Southern Oscillation (ENSO). 3. Vegetation changed from cloud forest (~5900–5500 cal. years BP) to alpine grassland (~4300–1300 cal. years BP), to pine savanna (~1300–600 cal. years BP) and finally to closed pine forest (after ~600 cal. years BP). Habitat distribution models for TMCF and pine forest taxa show that these state changes were strongly associated with position of the ITCZ (cloud forest xR = 0.63; pine forest xR = 0.53), providing support for the shifting TWI hypothesis. 4. We find a negative relationship between fire and TMCF and a hump-shaped relationship between fire activity and pine. 5. Synthesis. Shifts upand downslope of the upper limit of the cloud belt over the last 5900 years produced major vegetation changes. Fire also played a significant role, in particular when pine occupied the site after ~1300 years ago and from 1965 AD when fire suppression led to a rapid return of cloud forest taxa. Our results strongly suggest that latitudinal shifts in the ITCZ position have controlled the upper limit of cloud forest in the Caribbean and understanding how the ITCZ will respond to climate change will be critical for tropical montane conservation strategies.