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Heberling, Mason [1], Muzika, Rose-Marie [2].

Why do some deciduous plants retain dead leaves through winter?: Exploring marcescence.

Temperate deciduous forests by definition include a large proportion of woody species that shed their leaves each autumn and are completely leafless during winter months. Leaf senescence in deciduous trees is an active, complex process typically involving the physiological formation of an abscission layer causing the petiole to mechanically detach from the stem. However, several deciduous species retain senesced leaves on stems through much of winter, a phenomenon called leaf marcescence. Marcescent leaves in the Eastern Deciduous Forest of North America have long fascinated botanists, including Pehr Kalm as early as 1749. Yet, surprisingly little research had been done to date. We explored patterns and mechanisms of leaf marcescence, reviewing six non-mutually exclusive but separately proposed hypotheses: 1) Marcescence has no adaptive function but rather, an evolutionary byproduct; 2) Marcescent leaves deter winter browsing herbivores; 3) Leaf retention through winter improves nutrient resorption during autumn senescence; 4) Prolonged leaf shedding into spring minimizes nutrient leaching and promotes decomposition; 5) Marcescent leaves protect overwintering buds from frost or desiccation; and 6) Marcescent canopies provide winter cover for animals (including insects, birds, bats), thereby affecting plant nutrient availability via excrement. We experimentally and observationally explored some of these hypotheses in a forest in southwestern Pennsylvania. Species in the order Fagales exclusively exhibited marcescence, though strongly variable across and within species. We quantified mid-winter leaf marcescence of 62 American beech (Fagus grandifolia) trees, comparing percent marcescence in upper, mid, and lower canopies of each plant, ranging in height from 0.5 to 34 meters. Overall percent marcescence was substantially greater in understory trees less than 5 m tall (mean=33%, std. error = 5%) compared to overstory trees (>15 m tall; mean= 3%, se=1%). Marcescence was notably strongest in the lower portion of canopies regardless of tree size but virtually absent in upper canopy of large trees. Tagging individual branches of understory saplings, we tracked phenology of marcescent leaves through winter and spring budbreak. We also defoliated marcescent leaves in half of these branches in mid-winter. In some trees, more than 50% of marcescent leaves remained by spring. Despite increased interest in plant phenology in recent years and prevalence of the trait, much remains to be understood on the physiology, evolution, function, and ecological implications of leaf marcescence.

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1 - Carnegie Museum Of Natural, Section Of Botany, 4400 Forbes Ave, Pittsburgh, PA, 15213, United States
2 - Carnegie Museum of Natural History, 4400 Forbes Ave, Pittsburgh, PA, 15213, US

leaf senescence
Fagus grandifolia.

Presentation Type: Oral Paper
Session: ECO4, Ecology: Community Assemblages, Succession and Marcescence
Location: /
Date: Thursday, July 22nd, 2021
Time: 11:00 AM(EDT)
Number: ECO4005
Abstract ID:188
Candidate for Awards:None

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