Leaf phenology in relation to canopy closure in southern Appalachian trees

Abstract

Leaf phenology varies markedly across tree species of temperate deciduous forests. Early leafing in spring may increase light capture and carbon gain prior to canopy closure, allowing saplings to survive in understory sites deeply shaded in midsummer. We quantified sapling leaf phenology for 18 tree species and seasonal variation in understory light availability at three sites along a ridge-slope-cove landform gradient in the Great Smoky Mountains National Park. Early leafing species (e.g., Aesculus flava, Carpinus caroliniana) broke bud an average of 24 d before late leafers (e.g., Magnolia fraseri, Nyssa sylvatica). Canopy closure occurred 14-18 d earlier and summer understory light was on average 63-74% lower on intermediate and mesic sites than on the xeric site. Early leafing species intercepted 45-80% of their growing season photon flux before canopy closure vs. 8-15% for late leafers. However, earlier leafing increased exposure to freezing temperatures by 5.5% per week near the mean time of bud break. Early leafing is strongly correlated with midsummer shade, risk of freezing temperatures, and distribution on mesic sites across a "main spectrum" of 15 deciduous species. Differences in leaf phenology and resultant impacts on spring carbon gain may help determine tree shade tolerance and distribution in southern Appalachian forests.

Causes of ecological gradients in leaf margin entirety: Evaluating the roles of biomechanics, hydraulics, vein geometry, and bud packing

“…Craspedodromous or semicraspedromous venation may also allow rapid expansion of preformed leaves in the bud; plication of areas between parallel secondary veins could allow them to unfold rapidly as the buds open, providing a potential advantage in areas with a short growing season. Fagus grandifolia exemplifi es this strategy; it has craspedodromous venation, plication, and the highest rate of leaf expansion among the tree species of the Great Smoky Mountains studied by Lopez et al (2008) .…”

Differentiation of seed germination traits in relation to the natural habitats of threeUlmusspecies in Japan

“…Because late germination in the same season results in a shorter growing period for the dormant seeds, to wait until the following spring may be a more advantageous strategy especially for the summer-fruiting Ulmus. ''Phenological gaps'' with the sunlight reaching the ground and the fluctuating daily soil temperature, will be formed under a deciduous forest canopy in the following early spring (Seiwa 1997;Augspurger 2008;Lopez et al 2008). The multiplier effect of light and alternating temperatures should also have a profound effect on appropriate timing of seed germination.…”

Predicting phenology of European beech in forest habitats

“…High inter-annual variation in beech phenology has been reported by several authors (Lopez et al 2008, Davi et al 2011. As beech shows a high phenotypic plasticity in leaf phenology, it reacts directly to temperature changes (Vitasse et al 2010), which could be reflected in changes in the phenological phases among years.…”