Results
T50 of the tropical forest species averaged 50.0 ± 1.5 °C (mean ± SD) and ranged from 45.8°C in Hedyosmum bonplandianum , a montane forest tree, to 53.7°C in Rhizophora mangle , the pan-tropical red mangrove (Table S2), with 90% of observations falling between 47.8 and 52.5°C. Even higher values were found in non-forest CAM plants, with T50 of 55°C in Agave americana . Within ecosystems there was also a considerable range in T50 values: among the 117 lowland species, values ranged from 47.7°C in Luehea speciosa to 53.5°C in Cecropia longipes . TCrit likewise varied considerably, from 42.0°C in H. bonplandianum to 50.9°C in the palm Dypsis lutescens , with an average of 46.7 ± 2.0°C and 90% of observations falling between 43.5 a 49.7°C. Values of T50 were more narrowly distributed around the overall mean than TCritvalues (Fig. S3). T50 and TCrit were highly correlated (F1,150=231.2,p <0.001, r2=0.61). T50 was on average 3.2°C higher than TCrit. Fv/Fm declined more steeply around T50 in species in which the decline started at a higher temperature, i.e., the distance between TCrit and T50 decreased as TCrit increased. This was indicated by a decrease in the b parameter—b becoming more negative—with increasing TCrit (F1,150=62.2,p <0.001, r2=0.29).