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Factors Effecting Moss Growth in Allendale’s Ravines

Nikki Bush, Sarah Byce, Andrea Kretchman, Dillon Leistner, Abigail VanderMeulen

Ravines at Grand Valley State University, Allendale Michigan 49401 USA

Abstract

Moss grows in certain locations and not others. We tested soil temperature, soil pH, soil

saturation, relative humidity, air temperature, and canopy cover to see if they had an influence on

moss growth. We performed our investigation in the Ravines at Grand Valley State University

during September and October 2014. We found the average air temperature in location 3 to be

almost 2 degrees lower than in location 1 and 2. Also, the relative humidity of location 3 was

found to be greater than 10% lower than in locations 1 and 2. Overall based on this data and

statistical analysis, the factors of average air temperature and relative humidity were found to be

statistically significant between the north and south sides of the Ravines.

Key Words: moss, bryophyte, relative humidity, canopy cover, pH, soil temperature, air

temperature, soil saturation, percent moss cover, Ravines

Introduction

Moss is classified as a bryophyte, meaning that it does not have a true vascular system.

Having a nonvascular true root system restricts the size that moss can grow (Danneberger, 2014).

Moss has rhizomes, similar to roots, which are underground stems with branching out buds that

give way to leaflets (Beentje, 2010). There is a male and female gametophyte, where the male

holds the sperm and the female holds the eggs. The life cycle of a bryophyte starts when the

female is fertilized by the male sperm when it swims in water (Whitbeck, 2000). After the female

plant is fertilized, a sporophyte is produced. A sporophyte holds spores which are released and

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carried by the wind or water to new locations with adequate conditions (Whitbeck, 2000). These

spores then grow to form new moss patches (Fig. 1). While making observations in the ravines at

Grand Valley State University, a few questions arose about abundance of moss growing along

bases of trees and along decomposing logs on the forest floor. The main question we were asking

was why there is moss growth in some locations and not in other locations. Our objective is to

see how canopy cover, air temperature, soil temperature, soil saturation, pH, and relative

humidity of the air effect moss growth.

Figure 1. Life cycle of a moss (Campbell, 2005)

There are about 15,000 species of moss worldwide, the most common include tufted and

carpet-type moss (Danneberger, 2014). Since there is a wide array of moss species it was

unrealistic to identify each species of moss found. Moss found on logs was different

characteristically when compared to moss found on the dirt. Log moss was “draped” and had

many leaves that hung over the side of the log. Moss found on the soil had short flat leaves that

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are perpendicular to the ground. Research shows that moss generally grows on trees and tree

roots due to the stemflow, which is precipitation running down the trunks of trees (Dobson and

Frasco, 2010). Along with stemflow playing an important role in the growth of moss, it has been

proven that mosses prefer shaded forests (Smith and Patchan, 1986).

Bryophytes are shade plants that thrive in low light intensities (Glime, 2007). Canopy

cover influences the amount of shade that occurs over the ground that is caused from the leaves

and tree branches blocking out the sun from hitting the soil below (Jennings, 1999). The stronger

the sunlight, the more the water will likely evaporate from the ground and the moss. As a result,

moss reproduction decreases as the amount of moisture decreases because the sperm cannot

swim to reach the female egg due to lack of water.

Soil and air temperature change due to depth, seasons, and the time the sample was found

(Posudin, 2014). Bryophytes prefer temperatures around 20 degrees Celsius, but can grow in

much lower surfaces temperatures (Glime, 2007). The lower the surface temperature, the more

water it can hold, allowing bryophytes to reproduce. Given this information and the fact that

temperature and relative humidity are directly related, we decided to measure the temperature of

the plots continuously over a few days in order to compare this data to the amount of water in the

air. We also decided to measure the sub-surface temperature in order to look for a possible

difference between the surface and sub-surface temperature.

It is imperative for bryophytes to have adequate amounts of water so that dehydration

does not occur. One way bryophytes get the amount of water they need to survive is through the

relative humidity. Relative humidity is the amount of water in the atmosphere at a given time. It

can be found in any phase: gas, liquid, and solid (Posudin, 2014). The temperature of air

determines how much water vapor the air can hold, or how humid it will be. The colder the air,

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the higher the relative humidity, and the warmer the air the lower the relative humidity. Relative

humidity is an important factor in moss growth because it enables moss spores to move

throughout the plant and reproduce (Whitbeck). One way humidity can be measured is by using a

hygrometer (Posudin, 2014).

Water is generally neutral to slightly acidic when it comes to its pH. In addition, we have

discovered that mosses prefer soil that is slightly acidic within a pH range of 5.0 to 5.5

(Dannenberger, 2014). Because of these facts, we have determined that it would be informative

to measure the pH of the soil to see if the growth of moss within our plots is affected by the pH

of the soil. Soil pH is determined by how basic or acidic a given sample is on a scale of 0 (acidic)

to 14 (basic). The acidity is defined by the amount of ions in the soil (Posudin, 2014).

Our hypothesis is that water is the most important factor in moss growth because water is

the driving force behind reproduction by transporting spores to new destinations for growth.

Water is related to other factors contributing to moss growth such: as canopy cover, temperature,

soil saturation, and humidity. Therefore, we are interested in whether there is a relationship

between the abundance of water in a certain area and the percent cover of moss.

Our prediction for our investigation is that there will be a larger abundance of moss and

more occurrence of moss growth where there is a higher concentration of moisture in the

environment. We also predict that moss will grow where the soil pH is between 5.0 and 5.5

because those are the preferred conditions for optimal moss growth.

Study Area

The study was conducted at Grand Valley State University, in the ravines behind the Ott

Living Center where the area consists of a moist and semi-shady climates. The approximate

coordinates of this location were 42°57'55.62"N, 85°53'4.39"W (“GoogleEarth”, 2014). The

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elevation changes from 213.36 m at the top of the ravines to 182.88 m where the creek runs at

the bottom of the slope (“Allendale Quadrangle”, 1972). The average annual high temperature of

this area is 13.43 degrees Celsius and the average annual low is 5.32 degrees Celsius. The

average high temperature in the months of September and October was 18.61 degrees Celsius

and the average low was 9.72 degrees Celsius. The average monthly precipitation for September

and October was 8.204 centimeters for Grand Valley’s ravines ("Average Weather for Allendale,

MI - Temperature and Precipitation", 2014). The average climate in the Ravines is important

know because the abundance of moss in this area shows that these are optimal growing

conditions and are factors that contribute to moss growth.

Methods

The fieldwork on the moss study was done between September 30 and October 9,

2014. Three locations were selected in various locations throughout the ravines. Our first

location was on the north side of the ravines directly behind Ott Living Center, at the top of the

hill before it descends to the creek. The second location was in close proximity to the north of

the creek that flows into the Grand River at the bottom of the ravines. Thirdly, we created a plot

on the south side of the ravines to the south of the creek, between the top and bottom of the hill.

The size of each of our data collection locations were 3m x 3m plots. Each plot was split into

nine, 1m x 1m quadrants. These quadrants were selected at random by using a number generator

in order to compare moss growth in different locations.

An estimation of moss ground cover was taken over each of the three selected quadrants

within our plots. Percent of ground cover was recorded by visually breaking each quadrant into

four equal sections, then we estimated the percent of moss within each quadrant and added them

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together. The occurrence of vertical moss production, upon trees or rocks, was not included in

total percent ground cover.

Canopy cover was measured using a spherical densiometer, Concave Model C. Generally

speaking, canopy cover affects the amount of sunlight that reaches the forest floor through the

canopy layer of the leaves on the trees. Because of this, we decided to measure how canopy

cover affects the growth rates of moss. This measurement infers that the rate of evaporation in

the shade should be less than it would be in the sunlight, promoting moss growth. This

determined the amount of shade and light reaching the ground covered moss. The measurements

were taken from the center of each plot because the mirror of the spherical densiometer is large

enough to measure the canopy cover for the entire plot. We measured the canopy cover of each

plot once daily because, due to the changing of seasons, leaves started falling off trees, which

allowed more sunlight to reach the forest floor. We took an average of the canopy cover of each

plot across the four days of measurement in order to ensure uniformity in our data collection.

In addition to measuring canopy cover, light intensity was also calculated using a Sun

System 716740. This light intensity meter was used to determine the amount of light reaching the

ground within each of the quadrants. An average of these measurements was calculated.

The temperature of the air and humidity were measured using a Hobo Pro V2

Temperature and Relative Humidity device. Over the first two continuous days of data

collection, this device was attached to a tree and camouflaged within the first and second plots.

The device was later relocated to the remaining plot for another two continuous days. Each

device calculated the temperature and humidity over a forty-eight hour period. These

calculations were then averaged among the two days for each location.

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We used an AMS soil auger to extract a sample of soil in order to measure the saturation,

the temperature, and the pH of the soil. The auger was marked with a piece of tape at 30 cm to

ensure the depth remained consistent for every location and measurement. After the soil samples

were extracted, the temperature of the soil was immediately tested using a Mini IR Thermometer.

This device takes the temperature reading of the sample with a laser. The same soil samples were

also used to measure the soil saturation. One of the samples was used to find the soil saturation

and the other was used to measure the pH. The original soil sample was weighed to find the

mass in grams, baked at 60 degrees Celsius for 48 hours to remove the water, and weighed again

to determine the final mass of the soil in grams. The difference in mass was used to determine

the soil saturation of the sample plots. The other soil sample was used to measure the pH of the

soil. The pH was measured by mixing the soil sample with water at a one to one ratio and testing

the mixture with pH test strips.

Paired t-tests were used to determine if there was a difference between the averages of air

temperature, relative humidity, soil pH, soil temperature, soil saturation, light, and canopy

cover. A p-value of p≤ 0.05 was defined to see if the data is statistically significant, meaning the

potential relationship is due to more than just chance alone. Because we tested more than two

locations, a Bonferroni Correction is necessary to make sure the data is statistically significant

(Napierala, 2012). In order to ensure we are minimizing the likelihood of a false positive, we

divided the p-value of 0.05 by three because we are testing the relationship of three

locations. This resulted in a new acceptance level of p≤0.017.

Results

At each location in our study we collected eight measurements of data. The total percent

moss cover was 17.50% in location 1, 15.50% in location 2, and 46.57% in location 3. The

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average pH of location 1 was 6.75, of location 2 was 6.75, and of location 3 was 6.50. The

average soil saturation of location 1 was 10.89 g, of location 2 was 10.39 g, and of location 3

was 16.01 g. The average soil temperature of location 1 was 10.25 °C, of location 2 was 11.25

°C, and of location 3 was 10.88 °C. The light and canopy cover was also found at each location.

The average light at location 1 was 3.28 fc, at location 2 was 2.84 fc, and at location 3 was 2.41

fc. The average canopy cover at location 1 was 77.90%, at location 2 was 79.46%, and at

location 3 was 76.60%. Finally continuous data was collected on the air temperature and relative

humidity at each location during our study. The average air temperature at location 1 was 12.53

C, at location 2 was 12.58 C, and at location 3 was 10.70 C. The average relative humidity was

found to be 94.39% at location 1, 91.10% at location 2, and 79.36% at location 3. A summary of

the averages from the data collection is compiled in Table 1.

The average air temperature in location 3 was found to be almost 2 degrees lower than

location 1 and 2 (Table 1). The relative humidity of location 3 was found to be more than 10%

lower than in location 1 and 2 (Figure 2). Based on these means, it was found that the average air

temperature was statistically significant between location 1 and 3 and location 2 and 3 (Table 2).

It was also found that the relative humidity was statistically significant between location 1 and 3

and location 2 and 3 (Table 2). Percent moss cover in location 3 was greater than that found in

location 1 and 2.

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Figure 2: The air temperature and relative humidity in our 3 plots across a 48 hour period,

Ravines of Grand Valley State University, September-October 2014.

Table 2: Air Temperature and Relative Humidity (mean and t-test results) in the Ravines, Grand

Valley State University, September-October 2014.

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Discussion

Based on the p-values being less than 0.017, it was determined there was a significant

difference in air temperature and relative humidity among the locations we studied. According to

our results, there is a significant difference between these two factors in location 1 and 3 and

location 2 and 3. In location 3 there was a greater abundance of percent cover than in location 1

and 2. From this data, we concluded that moisture is the most important factor in moss growth.

The factors we tested influence moisture in many ways.

Moisture will increase and decrease based on canopy cover and light intensity

fluctuation. Soil saturation and relative humidity will increase when there is a decrease in

temperature. Although we tested pH, it was relatively the same in all locations thus was not a

factor in moss abundance.

During an investigation such as this, we want to increase sample size. Increasing sample

size includes amounts of time for the investigation and more plots tested for data collection. By

doing this, weather and random sampling will be accounted for and results can be precisely

concluded.

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Overall, our preliminary data collection shows that air temperature and relative humidity

are significantly different between plot 3 on south side than plots 1 and 2 on the north side of the

ravines. Through further studies we would look into the difference in the environments of the

north and south sides of the hill in the Ravines and its relationship to moss abundance.

Acknowledgement

All resources (baking oven, soil auger, beakers, spherical densiometer Concave Model C,

string, flag markers, Sun System 716740 light intensity meter, Hobo Pro V2 Temperature and

Relative Humidity device, pH paper, mini IR thermometer, tape measure, paper bags, scale, and

graduated cylinder) were provided by Dr. Rybczynski and Grand Valley State University.

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