Plants & Human Affairs
Cherries.wmf (7140 bytes) Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe

Are Leaves Good Predictors of Climate?

Objectives:  The purpose of this lab is to:

  1. use leaf models to test predictions concerning water loss and leaf shape
  2. use leaf models to test predictions about heat and leaf shape
  3. determine if leaf margins of deciduous trees provide a good estimate of mean annual temperature

Introduction: 
    Since plants are stationary they must respond developmentally, and ultimately evolutionarily, to their environment.  As a result, it's not surprising that leaf morphology (shape) has been shown to be related to climate.  For example, some the following correlations have been reported (Wiemann et al, 1998):  (a) leaf length is directly related to the mean annual temperature (MAT), (b) leaf area is directly correlated to both mean annual precipitation (MAP) and MAT; and (c) leaf width is directly correlated with MAP.  Thus, leaves are longer and larger in climates with warmer temperatures and higher rainfall. 

    Another interesting observation that was first reported more than 100 year ago is that woody deciduous plants having leaves with toothed margins (termed serrate) predominate in temperate climates while species with smooth (termed entire) leaf margins predominate in frigid (arctic) and tropical climates.  This relationship has been used to derive a mathematical model for predicting climate from leaf margins.  This has been particularly useful in determining MAT in the geological past by analyzing the leaf margins of fossil plants.

    It is not clear why there should be such a strong correlation between leaf margin and temperature.  It is suggested that teeth may help to increase sap flow in plants which may be a benefit in temperate environments. 

  Wiemann et al, (1998) report that the following equations have been derived to predict MAT (in degrees C) or MAP (in cm) from leaf margin structure (% is expressed as a whole number, not a decimal):

    The purpose of today's lab is to test the accuracy of these models for our area. 

Methods:

  1. Examine the checklist of Common Woody Plants of St. John's (or Checklist of Trees and Shrubs of the College of St. Benedict & St. John's University).
  2. Remove any species that are not native to our area and then record the names of native species in Table 1.
  3. For each native species, examine the herbarium specimens to determine if the leaves for your assigned species has an entire or serrate (or lobed) margin.  To be considered serrate, the tooth be an extension of a vein (vascular extension).  In other words, veins should run into the teeth.  Do not count "spines" as teeth.  Record your observation in Table 1.
  4. Then, determine if the leaf is "large" or "small."  By definition (Wiemann et al., 1998), any leaf that has an area greater than 33 cm2 is considered "large."  To do this, compare an "average" leaf of each species to a model that you cut out of paper that is 33 cm2 (or 5.8 x 5.8 cm).  Alternately, a quick method to approximate the size of a leaf is to multiply leaf length x leaf width x 2/3 (Manual of Leaf Architecture). 

Analysis:

  1. Once you have examined all of the specimens, complete Table 2.
  2. Then, calculate the predicted MAT based on equations 1, 2 & 3 (Table 3). 
  3. Calculate predicted MAP based on equation 4 in Table 4.
  4. Obtain MAP and MAT data and complete Table 5.
  5. How accurate are the temperature and precipitation models?
Table 1.  Margins and size of leaves of native deciduous woody plants in Central Minnesota
Common Name Margin (E = entire or S = serrate) Leaf Size (L = large > 33 cm2; S = small, < 33 cm2)
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     

 

Table 2.  Data Summary
total species  
species with entire leaves  
% species with entire leaves [= (# entire/total) x 100)  
species with large leaves  
% species with large leaves  (= # large lvs / total x 100)  

 

Table 3.  Predicted MAT  for central Minnesota
Model degree C
predicted MAT (based on equation 1)  
predicted MAT (based on equation 2)  
predicted MAT (based on equation 3)  
mean MAT (from three equations)  

 

 

Table 4.  Predicted MAP  for central Minnesota
Model cm
predicted MAP (based on equation 4)  

 

 

Table 5.  Actual Climate Data for Central Minnesota
MAP deg C deg F
MAP inches cm
source:  
if web site, date accessed:  

 


References:

Climate Sites:

| Top | PHA Home | SGS Home |

Last updated:  09/21/2005 � Copyright  by SG Saupe