Nasty, Brutish, and Short

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Science  23 Nov 2007:
Vol. 318, Issue 5854, pp. 1218
DOI: 10.1126/science.318.5854.1218b

Leaves are a vital organ for plants and for their environments. Their structure and life span influence photosynthesis, resource acquisition, and growth rates; they also influence the plant's ability to resist being eaten, for instance by insects. And leaves have important effects on the local ecosystem through leaf litter decomposition.

Knowing how leaves influenced paleoenvironments can provide key insights into past ecosystem functions. Leaf mass per area is a metric that correlates with various ecological traits but has not been applied systematically to fossil data. Royer et al. measure the petiole width (the petiole being the small stalk that attaches the leaf to the stem of the plant) and leaf area of fossil leaves and, through a scaling relationship they develop for these characteristics in extant leaves, use these to estimate fossil leaf mass per area. In a comparative analysis of two Eocene fossil lake floras (Republic, in the Klondike Mountains, and Bonanza, in Utah), the leaf mass per area was uniformly low at Republic, whereas Bonanza exhibited a broad range of values. These biosynthetic choices are consistent with the respective paleoclimates: The former was dominated by trees bearing short-lived leaves, which suffered fairly high levels of herbivory, and was associated with rapid leaf litter decomposition; whereas the latter showed wider ranges of these same traits. — GR

Paleobiology 33, 574 (2007).

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