The Effect of Population Density on Leaf Size in Sugar Maples
Abstract: To be written after results are completed
Introduction
Due to favorable soil conditions and the temperate climate, the deciduous sugar
maple tree, found in the family Aceraceae, is probably the most common shade tree on the
Oxford campus of Miami University. However, its abundance and growth is unusual
because there are only two genera and about 120 species found in this tree family. The
sugar maple thrives in a rich to dry soil, particularly the calcareous type, which is high in
calcium. It also grows well in shade. All of these characteristics contribute to its ability to
overcome its lack of species types and dominate many New York, New Hampshire,
Vermont, Pennsylvania, Maine, and Ohio forests. The sugar maple grows only in these
states and parts of eastern Canada due to the environmental conditions needed. It has
been introduced to the Arizona, New Mexico, and California areas in an effort to prevent
soil erosion. This venture has had little success, although the reasons for failure are
unclear. Possibly the hot arid climate and sandy soil characteristic of the American
Southwest are too harsh for the sugar maple to survive.
The sugar maple is also frequently found in residential areas because of the large
amount of shade it provides and the beautiful orange and red colors produced in its leaves
during the Autumn months. The wood of the sugar maple is dark brown or red and has a
smooth grain, unlike the bark which is gray and rough. Maple lumber is used extensively
in the manufacturing of furniture for its durability and strength and for the luxurious
darkness it acquires with age. The stouts and strength of the wood also makes it ideal for
paneling, flooring, or any place durability is an issue. It is common for bowling pins, tool
handles, and cutting blocks to be made of sugar maple logs.
Maples have a lifespan of about 150 years, but some trees have lived three hundred
or even four hundred years. This longevity causes a slow change in forest conditions and
evolution. It is not unusual to find little or no vegetation under a sugar maple. This is
primarily because the dense foliage blocks a large percentage of sunlight and the extensive
root system absorbs much of the water and nutrients in the soil. The lack of shrubbery
found around the tree helped early settlers in America identify the maple as a previously
unrecognized species; there are few trees in Europe which share the same phenomenon.
About fifty years later, when importing sugar to the New World became difficult, Native
Americans introduced the sugar maple to the settlers as a good source of sugar and syrup.
Over the years, the tapping of the maples has grown from a local event as described by
Laura Ingots Wilder in her book Little House in the Big Woods to a booming industry
grossing over $7 million a year. Today, sugar maples are also the primary source of maple
syrup an artificial brown sugar.
The shape of the sugar maple's leaves is commonly recognized as the central
decoration of the Canadian flag. Besides being the only leaf to represent a country, the
sugar maple is unusual for its leaf structure. A sugar maple leaf has five lobes, or ridges,
running from the stem to the edges. It contains high levels of calcium, magnesium, and
potassium when the leaves are shed in the fall. The leaves generally drop in early autumn,
although the exact time is determined by the weather. The fruit produced by the maple is
commonly referred to as a "helicopter" or "whirly-bird" due to the spinning motion it has
as it falls. While the shapes of the leaves and fruit remain fairly constant, there is a large
variation in size.
In this investigation we propose to investigate the effects of neighboring trees on
the leaf size of sugar maples by studying five secluded maple trees and five maples
growing in groups. A group is defined as at least three trees growing within an eight-foot
radius, which is the recommended distance for planting sugar maples. Within our
sampling area of Western Campus, we predict sugar maples standing alone will have larger
leaves than those growing in groups of three or more due to the lower level of competition
for nutrients, water, and sunlight experienced by isolated trees. Our hypothesis is based
on a study done in Quebec to determine the cause for widespread deaths among sugar
maple trees there. The study found that imbalances of calcium and magnesium in the soil
led to sickness and death for the sugar maples growing there. Leaf size is a good indicator
of a sugar maple's health, according to previous research. In this experiment, a difference
of two or more inches in length will constitute a significant difference in leaf size, and a
possible sign of illness.
This study will be of interest to several groups, in particular, nurseries which plant
sugar maples and individuals deciding which trees to tap for maple syrup.
Methods
In this experiment, five isolated trees and five groups of trees, all located on
Western Campus and all with trunk diameters of five to seven inches, were studied by our
research group. We selected Western Campus as our study area because of its abundance
of sugar maples and its proximity to both our living quarters and the science lab. Five
samples were selected because we could only find five isolated trees meeting our criteria
for study. From each tree or group, we selected and marked a branch with twine.
Unfortunately, only branches which could be reached with the aid of a step-stool could be
studied because it is illegal to climb trees on campus. We measured the lengths, in
centimeters, of each leaf on these branches from the tip of the leaf to the base of the stem.
As each leaf was measured, it was removed from the branch to ensure that all leaves were
measured and that none were measured twice. All data were collected in one sampling,
and all samples were collected at the same time to eliminate as much variation as possible.
From these data we calculated an average length for the leaves of each tree. The
averages were used to find an approximate leaf size for trees growing alone and in groups.
From each tree, we also measured and preserved the smallest and largest leaf found on the
sample branch for further comparison.
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