Ecophysiology of seed germination in riparian trees and implications for restoration and conservation

Abstract Riparian ecosystems are essential for ensuring linear habitat connectivity and providing thermal refugia for wildlife. However, they are increasingly vulnerable to global change, resulting in widespread degradation. Four riparian trees, specifically Alnus glutinosa , Alnus incana , Platanus orientalis , and Liquidambar orientalis , have been designated as case studies for ex situ conservation due to their ecological importance and vulnerability to habitat degradation. Seeds of the four species were collected in Greece. Germination experiments were conducted at seven constant and three daily alternating temperature regimes, under light or dark conditions. In A. glutinosa , A. incana , and L. orientalis , germination was also tested following a cold stratification pretreatment. For all species, the highest germination was obtained at high temperatures (30°C and 30/20°C). Cold stratification pretreatment expanded the temperature range suitable for germination and increased the germination percentage under unfavorable temperatures. Light promoted germination of untreated seeds across all species. Secondary physiological dormancy by adverse temperatures (thermodormancy) or darkness (skotodormancy) was not imposed. The seeds of all four riparian trees exhibit orthodox storage behavior, as there is no differentiation in germination (both in terms of final percentage and rate) among (a) untreated seeds, (b) desiccated seeds, and (c) seeds that have been desiccated and stored at −20°C. The germination responses of seeds of the four species to temperature, light, and cold stratification reveal the mechanism that delays germination from autumn/early winter (time of seed dispersal) until spring, when conditions are favorable for seedling establishment.