Leaf demography and leaf traits of temperate-deciduous and tropical evergreen-broadleaved trees in a Mexican montane cloud forest

Abstract

Leaf demography of four deciduous and five evergreen broadleaved tree species was studied in two replicate tropical montane cloud forest fragments (1250-1400 m elevation) in Veracruz, Mexico. The objectives were to investigate leaf life spans, expansion rates, survivorship curves, specific leaf area (SLA) and nitrogen concentration in tree species of contrasting leaf habits and phytogeographical affinities growing naturally in the same forest type. Tagged leaves were located in the mid forest canopy and were reached with a six-m ladder. A total of 2688 leaves from 78 trees were monitored from bud burst to death. Mean leaf longevity was 8.25 mo for deciduous tree species and 15.0 mo for evergreens. Mean leaf longevity was highly variable among evergreen species which included both the longest (Magnolia, 36.4 mo) and the shortest (Hedyosmum, 6.4 mo) values. Patterns of leaf emergence were similar for eight species with a pronounced peak at the beginning of the calendar year. The only exception was Hedyosmum with a multiple flush pattern. More than 50% leaf expansion occurred in less than a month for three deciduous species (Carpinus, Liquidambar, Quercus) and two evergreens (Oreopanax and Magnolia), but required more than a month for Clethra (deciduous) and Cinnamomum, Hedyosmum and Turpinia (evergreen). Leaf survivorship curves were similar between the two study sites, but they differed between deciduous and evergreen species. There was no significant difference between leaf habit groups in SLA, leaf area, or nitrogen concentration, however, SLA was inversely correlated with leaf longevity. Arranging the studied taxa from primitive to advanced reaveled that species in more primitive groups have the longest life-spans (Magnolia, Cinnamomum) and more advanced taxa have the shortest life spans (Carpinus, Quercus). Phylogenetic relationships between species should be taken into account when studying leaf traits.