Handout: Warren Woods (forest ecology) field-trip
The Place: The following description is written by and taken from: A Naturalist’s Tour of Southern Lake Michigan by Joel Greenberg —
“Within this [Warren Woods] 480-acre site is a 50-acre tract of virgin beech-maple forest that some believe is the finest of its type in the world. Towering trees and a rich understory sprout from the banks of the Galien River. Because of its high quality, scientists have been studying it since the early 1900s. One aspect of the forest that has long fascinated these scientists is the competition between the forest’s two principal trees—sugar maple (Acer saccharum) and beech (Fagus grandifolia). Sapling maples are abundant in the understory, and have led many to conclude that they will take over the canopy now dominated by the beech. Researchers have found, however, that the process is more complicated.
Although not as swift growing as the maple in full light, the beech continues to rise even after an opening in the canopy is mended. The beech is better suited to the waiting game because of an evolutionary tradeoff. The speed with which it increases in height is sacrificed for lateral growth. In the summer forest, muted flecks of light drizzle through little slits in the canopy. Beech send forth long horizontal branches that seek out these glints, and thus over the centuries can pierce the maple curtain. (One beech took over 300 years to reach the canopy.)
The conclusion that beech will maintain their position in Warren Woods is predicated on the assumption that the rate of disturbance, natural or human, will remain low. If large openings in the canopy develop, closure will not be rapid enough to exclude maples. Since 1975, a series of severe storms has dramatically increased the rate of windfall in the woods. For the first three-quarters of this century, the rate of windfall at Warren Woods was about one-tenth of a tree per year per hectare. It is now one to one and a half trees per year per hectare. The forest looks very different now, with numerous maples of all sizes. The ratio of beech to maple in the canopy has dropped to four to one and in about 100 years it is likely to be only two to one, or even one to one. But it is unlikely that Warren Woods will lose its magnificent beech, for enough will win the race to the canopy to ensure survival. Beech-maple forests feature some of the most beautiful scenes to grace the region. The beech in any season is an exquisite mixture of form, color, and texture that has few equals among its arboreal relations. Open-grown trees are wider then they are tall; limbs of ancient trees bend to touch the earth, the strain of carrying the burden of their age. But lending grace to the massiveness of beech trunks and major branches, delicate twigs reach out with thin and sharply pointed buds.
The slate gray bark, smooth and taut, seems muscular but not sinewy. In the fall, it contrasts with the pale golden leaves in an elegant combination of muted hues. Unfortunately, beech bark creates another effect: whether it is Daniel Boone marking the place where he “cilled a bar” in 1760 or a young couple proclaiming their first love, some citizens get an irresistible urge to carve memorials on the fair surface of the tree. Few local beeches have escaped defacement.” By Joel Greenberg.
The Objectives: To collect data on beech and maple to investigate and test hypotheses regarding competition in trees, and the maintenance and regeneration of beech and sugar maple within Warren Woods. We will collect data as two exercises to investigate three questions:
Are trees regenerating in a lottery competition-like pattern at Warren Woods?
A lottery competition-like pattern (seedlings > saplings > poles > canopy trees) would suggest that trees are reproducing, but very few ever make it to the canopy.
Are American beech and sugar maple coexisting at Warren Woods?
If both species are regenerating (poles > canopy trees), then this suggest that both species are recruiting and therefore coexisting.
What is the mechanism of coexistence?
Tradeoffs in Performance
If beech and maple have different ecological strategies for occupying space (vertical growth vs. lateral growth) this could explain how they coexist.
via Reciprocal Replacement:
If the trees themselves create environmental heterogeneity that favors the other species (maple replaces beech & beech replaces maple), this could promote coexistence.
via Microhabitat Preference:
If each species has a microhabitat preference (e.g., soil quality), this could promote coexistence (maple replaces maple & beech replaces beech).
Exercise 1: Measuring seedlings, saplings, and poles of beech & maple (10m by 10m quadrat)
Step 1: Select a corner for your quadrat by tossing a stick as far as you can.
Step 2: Use your tape measure to place your four poles as the corners of a square that is 10 meters on a side, using the location of your tossed stick as the first pole.
Step 3: Within your quadrat record 1) the species and circumference of each canopy tree (there will be from 0 to 4 of these), 2) the species (if you can) and circumference at breast height of each sub-canopy tree over 3m tall, 3) count the number of saplings between 1-3 m tall, and 4) count the number of seedlings less than 1m tall (use a 2 x 2 m quadrat for counting seedlings).
Step 4: Repeat Steps 1-3 for five different quadrats. Wander through the woods a bit to ensure that your quadrats are widely and randomly placed.
Exercise #2: Focal Sampling of Canopy Beach and Maple
Step 1: Select a canopy beech or maple (different than those from your quadrats).
Step 2: Measure the tree’s circumference at breast height.
Step 3: Measure the distance to the nearest canopy tree and note the circumference of this tree and whether it is a beech or maple. Call this direction “North”. Then measure the distance to, the circumference of, and the species of the nearest canopy tree in the other directions of “south”, “east”, and “west”.
Step 4: Measure the size of the tree’s canopy. Do this measurement along four “cardinal” directions using the direction towards the nearest canopy tree as “North”. To measure the canopy size have one person hold the tape measure to the tree trunk and then have another person walk away from the trunk along the designated cardinal direction. This person walks away from the tree until he/she is directly under the edge of the canopy in that direction (there is a lot of looking up). Repeat this for each of the four directions.
Step 5: Using your tape measure to make a 5m x 5m quadrat around your focal canopy tree. Count the number of canopy trees, if any, >3m tall sub-canopy trees, 1-3m tall saplings, and
Handout: Warren Woods (forest ecology) field-trip