Adaptive significance of evergreen vs. deciduous leaves : solving the triple paradox

By T. Givnish. 2002

590 citations recorded by the source corpus.

Patterns in the dominance of evergreen vs. deciduous plants have long interested ecologists, biogeographers, and global modellers. But previous models to account for these patterns have signifi cant weaknesses. Bottom-up, mechanistic models – based on physiology, competition, and natural selection – have often been non-quantitative or restricted to a small range of habitats, and almost all have ignored belowground costs and whole-plant integration. Top-down, ecosystem-based models have succeeded in quantitatively reproducing several patterns, but rely partly on empirically derived constants and thresholds that lack a mechanistic explanation. It is generally recognized that seasonal drought can favor deciduous leaves, and that infertile soils can favor long-lived evergreen leaves. But no model has yet explained three great paradoxes, involving dominance by 1) evergreens in highly seasonal, boreal forests, 2) deciduous larch in many nutrient-poor peatlands, and 3) evergreen leaf-exchangers in nutrient-poor subtropical forests, even though they shed their leaves just as frequently as deciduous species. This paper outlines a generalized optimality model to account for these and other patterns in leaf longevity and phenology, based on maximizing whole-plant carbon gain or height growth, and building on recent advances in our understanding of the quantitative relationships of leaf photosynthesis, nitrogen content, and mass per unit area to leaf life-span. Only a whole-plant approach can explain evergreen dominance under realistic ecological conditions, or account for the boreal paradox, the larch paradox, the leaf-exchanger paradox, and expected shifts in shade tolerance associated with leaf phenology. Poor soils favor evergreens not merely by increasing the costs of nutrient acquisition, but also by depressing the maximum rate of photosynthesis and thus the seasonal contrast in photosynthetic return between leaves adapted to favorable vs. unfavorable conditions. The dominance of evergreens in western North America beyond the coastal zone of mild winters and winter rainfall appears related to the unusually long photosynthetic season for evergreen vs. deciduous plants there. Future models for optimal leaf phenology must incorporate differences between evergreen and deciduous plants in allocation to photosynthetic vs. non-photosynthetic tissue, rooting depth, stem allometry, xylem anatomy, and exposure to herbivores and leaching, and analyze how these differences interact with the photosynthetic rate, transpiration, and nutrient demands of leaves with different life-spans to affect rates of height growth in specifi c microsites.

Subfields: Ecology, Global and Planetary Change, Plant Science

View Paper: https://www.semanticscholar.org/paper/ac2e3d88d757081cf438f7110e966b15e287de3e

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Citations in the corpus

Elegance versus Speed: Examining the Competition between Conifer and Angiosperm Trees (2012, background): “Species associated with nutrient-poor soils often have longlived leaves (Grime 1977; Chapin 1980), because a long life span reduces the annual rate of mineral nutrient loss via abscission (Monk 1966; Small 1972; Givnish 2002).”
Global quantification of contrasting leaf life span strategies for deciduous and evergreen species in response to environmental conditions (2012, methodology): “In particular, the distribution of deciduous versus evergreen species has attracted considerable attention since it was first reported by Harper in 1914 (Monk, 1966; Kikuzawa, 1991; Reich et al., 1992; Kikuzawa & Ackerly, 1999; Givnish, 2002; Lavorel & Garnier, 2002).”
How Forests Attract Rain: An Examination of a New Hypothesis (2009, background): “Among trees, evergreen foliage is favored by high seasonal unpredictability and also by low seasonal variation in moisture availability, while deciduous foliage is favored by intense and extended droughts as well as by seasonal predictability (Givnish 2002).”
Ecology of Leaf Longevity (2011, background): “Considering the carbon costs of acquiring the nitrogen and phosphorus to construct a leaf (Givnish 2002), we might expect that interspecific variation in NRE and PRE would be related to leaf longevity.”
Vulnerability of Mediterranean Basin ecosystems to climate change and invasion by exotic plant species (2006, background): “…to temperature, but are also at a disadvantage in comparison with evergreen trees and shrubs, as the period of physiological activity for summergreen types coincides with the most unfavourable season with regard to water availability in the Mediterranean area (Damesin et al., 1998; Givnish, 2002).”
Plant Phenotypic Plasticity in Response to Environmental Factors (2014, background): “Moreover, leaf trait variations in response to the light gradient within the canopy change in different species and forest types [105–108].”
Differential responses to changes in growth temperature between trees from different functional groups and biomes: a review and synthesis of data. (2010, background): “The evergreen strategy most commonly occurs in sites with low nutrient or water availability (Chabot and Hicks 1982, Givnish 2002).”
Slow‐growing species cope best with drought: evidence from long‐term measurements in a tropical semi‐deciduous moist forest of Central Africa (2013, background): “Given that leaf habit is a proxy for leaf life span (in short, evergreen leaves are long-lived and deciduous leaves are short-lived; Givnish 2002), this relationship corresponds to a pattern where slow-growing species have longlived leaves, and fast-growing species shorter-lived leaves (Poorter &…”
Global patterns in leaf 13C discrimination and implications for studies of past and future climate (2010, background): “Lower Δleaf implies greater WUE of EGs relative to other woody plants, conferring a potential advantage where water is limiting and a limitation on A when water availability is high (24).”
Why do evergreen trees dominate the Australian seasonal tropics (2005, background): “Introduction The relative advantages of evergreen and deciduous plants, and the factors determining community dominance, have intrigued plant scientists for decades (e.g. Chabot and Hicks 1982;Aerts 1995;Givnish 2002).”
Leaf phenology is associated with soil water availability and xylem traits in a tropical dry forest (2012, background): “This drought-avoidance strategy allows plants to survive the dry season without compromising their hydraulic pathway and ultimately their fitness (Borchert 1994; Givnish 2002).”
Modulation of leaf economic traits and trait relationships by climate (2005, background): “The linkage between LL and A mass has been emphasized in models seeking to understand the costs and benefits of different leaf phenologies, with A mass being a major determinant of the time taken to pay back the construction cost of a leaf (Kikuzawa, 1991; Poorter, 1994; Kikuzawa & Ackerly, 1999; Gi”
Leaf functional traits of Neotropical savanna trees in relation to seasonal water deficit (2005, background): “(Sobrado 199 1) and lower amortized leaf construction costs to replace the tree crown, provided that the leaves are held by more than a year (Givnish 2002).”