Ancient Climate (Unit 5) - Leaves as Climate Indicators
Modified from Wolfe (1978).
Particular environments contain plants that have adapted physical characteristics, such as drip tips (like the tip of the entire-margined leaf in Fig. 1) in areas that receive a great deal of rain. Leaf margins are a particularly useful indicators of mean annual temperature (MAT). Typically, warm climates will select for plants with entire-margined (smooth) leaves, whereas colder climates will select for plants with non-entire-margined (serrate, dentate, or lobed) leaves (Fig. 2).
Leaf physiognomy (the physical aspects of leaf assemblages) allows scientists to correlate the marine temperature record with that of the continental climatic record. Two primary methods exist to study how leaf physiognomy relates to climate: leaf-margin analysis and CLAMP (Climate-Leaf Analysis Multivariate Program). Leaf-margin analysis simply measures the proportion of entire-margined species, whereas CLAMP adds more variables with which to derive paleoclimate estimates. Some scientists contend that the added variables CLAMP provides allows for greater accuracy in certain environments, but others argue that leaf-margin analysis alone provides accurate estimates of temperature.
Leaf-margin analysis simply involves adding up the number of entire-margined and non-entire-margined species (not individual leaves). Wolfe (1978) demonstrated a correlation between the percentage of entire-margined species and the MAT in humid to mesic broad-leaved forests of eastern Asia (Fig. 2).
The same technique can be applied to fossil floras, given a large enough sample. Several scientists have conducted leaf physiognomy studies at Florissant, using both LMA and CLAMP.