TREE LIFE HISTORY AND WOOD DENSITY

In lecture, we have discussed life history strategies of trees: greybeards, gap-phase species, and pioneers. These contrasting strategies are associated with a number of traits such as shade-tolerance of juveniles and adults, timing of reproduction, and longevity. We’ve also discussed stem anatomy, and you are aware that there are trade-offs involved in the construction of tissues: energy allocated to building thick secondary walls, for example, is energy that cannot be used to make seeds. You are also aware that different groups of trees have different phylogenetic heritage, which will affect the ways in which natural selection can shape wood density. For example, conifers have tracheids only whereas angiosperms have both vessels and fibers. In this laboratory, we will explore whether or not there is a connection between life history strategy of trees and the amount of energy invested in wood, as assessed by wood density.

We will provide basic materials; you will be responsible for developing and defending your methods, as well as generating and analyzing results.

  1. What is your prediction?
  1. How will you measure density? We will provide a balance and graduated cylinders.
  1. What species will you compare and how will you categorize them? See list of available species on the next reverse. Consider using web resources such as those you used in your species report to provide objective categorization of species. Will you put species in two groups, three groups, or along a continuum (say, of % full sun needed for growth)? Another approach would be to contrast pairs of closely-related species that you believe to have contrasting life-histories. You may also want to control for wood anatomy, keeping in mind that conifers have tracheids only, whereas angiosperms have both vessels and fibers, and can be divided into diffuse-porous and ring-porous species.
  1. How will you analyze the data? This depends partly on your approach in question 3.
  1. Interpretation. Do the results fit your prediction? If not, are there interesting anomalies? Is there another hypothesis that you would like to test?
  1. Write a short paper, due next week’s lab. No outside references are necessary, but include websites accessed if appropriate.

We have three sets of wood samples. You can use any or all that you like. Sometimes these are identified only to the level of genus.

Set 1 consists of small, uniformly-sized squares. Set 2 consists of small, uniformly-sized samples in a bookcase, collected from Maine trees. Set 3 consists of branch/trunk sections, many from more southern species.

Please do not submerge the “books” of Maine unnecessarily, and dry them off when you are finished with them.

Species / Squares / “books” of Maine / Branch sections
Eastern white pine / X
Red pine / X
White spruce / X / “spruce”
Red spruce / X
Eastern hemlock / X
Balsam fir / X / X
Tamarack / X
Northern white cedar / X
Red cedar / X
Douglas fir / X
Cypress / X
Yellow birch / X
Paper birch / X
Sugar maple / “hard maple” / X / “maple”
Northern red oak / X / X / Southern red oak
White oak / X / X
American beech / X
White ash / X
Black ash / X
Basswood / X / X
Black cherry / X / “wild cherry”
Quaking aspen / X
Elm / X / X / X
Butternut / X
Hickory / X
Black locust / X
Apple / X
Pecan / X
Blackgum / X
Dogwood / X
Persimmon / X

Note that Douglas fir is in a different genus than true firs and that red cedar is in a different genus than white cedar.