Ecological Interactions of North American Beech (Fagus grandifolia) and Sugar Maple (Acer saccharum) in Warren Woods

By Julia Aydin

University of Illinois at Chicago1200 W Harrison St, Chicago, Illinois 60607

1

Abstract:

In Warren Woods in Berrien County, Michigan, ecological interactions of F. grandifolia and A. saccharum were investigated. The canopy growth, distribution of size classes, biomass distribution, and interspecies competition of F. grandifolia and A. saccharum were analyzed through data collected. Results showed that F. grandifolia was far more effective at reproducing, likely due to the species root-sprouting proliferation being favored by the environment. Data on biomass distribution and frequency of size classes showed inverse relationships. Canopy growth extent and direction was similar in both species, displaying asymmetry due to growth in the opposite direction of the nearest neighbor.

Introduction: Warren Woods is the last untouched maple-beech climax forest in Michigan. Because trees are allowed to grow without the limits of urban interferences, interesting ecological interactions can be observed that would otherwise not occur. Because of these fascinating interactions, there is a lot of existing literature on the coexistence of F. grandifolia and A. saccharum. An important factor that facilitates competitive interactions is the ability of F. grandifolia to form clumps of stems by sprouting from the superficial roots of mature trees. This root sprouting activity makes seedling and of the same species more common around canopy trees. F. grandifolia can also reproduce by seed dispersal (Takahashi, Arii, and Lechowicz, 2010). In contrast A. saccharums only method of reproduction is via seed dispersal, but its seeds are considered more viable. An advantage of F. grandifolias root sprouts is that they tend to grow faster than sprouts of seed origins and higher survival rates in low-sunlight conditions while A. saccharum seedlings are vulnerable to low light (Beaudet, et. al, 2010) Although they are more vulnerable to low sunlight, A. saccharum displays higher levels of phototropism by filling in canopy gaps faster when the canopy is disturbed (Poulson and Platt, 1996). The purpose of this research was to explore the distribution and competition of these two tree species to accept or reject hypotheses made based on the data collected. One hypothesis was that if there were equal or greater amount F. grandifolia canopy trees than A. saccharum, smaller size classes of F. grandifolia would be more abundant. Another hypothesis was that if A. saccharum canopies were measured, they would have a greater canopy asymmetry and overall canopy length than F grandifolia. Another hypothesis on competition between trees regardless of species was that if there was a general distribution of size classes, then it would be inversely proportional to largeness of size due to canopy despotism; however, biomass proportion would reflect the opposite distribution, showing the advantage of winning the canopy lottery (Robson, 1990).

Materials and Methods:Data was collected at Warren Woods in Berrien County, Michigan, which is considered to be a anthropologically untouched beech-maple climax forest. In the first part of the data collection, quadrats of 10X10 meters were established by marking the corners with neon flags and measuring the distance between them with a tape measure. The first flag put down represented the first corner of the quadrat. One person held the tape measure end at that corner while another person pulled the end of it until the person who could read the measurements indicated the tape measure had reached 10 meters. Then another flag was put down to mark the second corner. This procedure was repeated to form a square quadrat with four corners. A total of five 10X10 meter quadrats were set up in this fashion. Subcanopy and canopy trees were counted within each quadrat and recorded on data sheets. The circumferences of the subcanopy and canopy trees were recorded by wrapping a tape measure around the trunk of the tree. Saplings and seedlings were counted in a 2X2 meter quadrat within the 10X10 meter quadrants. The same methods and materials used to establish the 10X10 meter quadrats were used for the 2X2 meter quadrants. In the second part of the data collection, 5 canopy F. grandifolias and 5 A. saccharums had their circumference at breast height measured. The nearest neighbor canopy tree to each of these trees also had its circumference measured at breast height as well as its distance from the focal tree. The direction of the nearest neighbor canopy tree was designated as the north direction. Canopy length from north, south, east and west was then measured with a tape measure. To accomplish this, one person stood with the tape measure by the focal tree and then the other person pulled the tape to the end of the canopy while looking up to visually estimate the end of the canopy. All data was converted to centimeters before it was analyzed. To calculate the diameter necessary for basal area calculation the circumference was divided by pi. Statistical tests performed on the collected data were ttests and chi-squared tests that were carried out on excel. These tests showed if there was significant variance in data that would be relevant to accept or reject hypotheses. Results:

1. Size class distributions of both F. grandifolia and A. saccharum displayed the classic despotism of canopy trees in data collected from five 10X10 meter quadrats (Table 1). Figure 1 shows the average abundance per 100 meters squared in each size class and the standard error. Ordered from highest density to lowest density the size classes were Seedling, Short Sapling, Tall Sapling, Subcanopy, and Canopy (Fig. 1).

2. The basal area distribution of both species was generally inversely proportional to size class distribution based (Fig 2). Basal area also reflected biomass distribution. Data from Table 1 on average densities in size classes per 100m2 was used to calculate the basal area. This reversal in proportion is reflected visually in Fig. 2, which shows the general opposite trend of Fig. 1. Ordered from highest to lowest basal area the size classes were canopy, subcanopy, tall sapling, short sapling, and seedling.

3. There was a disparity between ratios of canopy to subcanopy trees between F. grandifolia and A. saccharum. Figure 3 shows that this difference is visually obvious. Additional statistical tests confirm the significant variance in canopy to subcanopy ratios between the different tree species. A ratio of subcanopy to canopy of was F. grandifolia calculated and then used to create an expected A. saccharum frequency. A 2 test yielded a p value that was significantly lower than .05, showing that the difference between species was statistically significant (p= 5.894*10-6, Table 3).

4. There was also a disparity between species of focal trees with respect to the species abundance of its neighbor trees. F. grandifolia was far more prominent around focal trees of the same species and also slightly more prominent around A. saccharum focal trees. Figure 4 displays this obvious disparity visually. A 2 test yielded a p value significantly lower than .05, showing that the difference between species was statistically significant (p=2.58504E-15, Table 4).

5. Calculation of average symmetry indices showed that both F. grandifolia and A. saccharum were similarly asymmetric. This is reflected by Fig 5 and Table 5, which showed that the average greatest differences in canopy length were close to the same value (538.228 cm, 524.924 cm). The greatest differences were mostly between north and south, north being defined as the in the direction of the nearest neighbor canopy tree. A statistical ttest confirmed the insignificance of the variance in symmetry indices with a probability value over .05 (p=.80009454, Table 6).

6. Both F. grandifolia and A. saccharum showed tendencies of canopy growth in the opposite direction of the nearest neighbor tree (south). Figure 6 visually displays this tendency of growth. Concurrent with their similar asymmetries, average north and south extents were relatively similar, not differing by more than 100 centimeters on average between F. grandifolia and A. saccharum (north: 557.856 cm, 467.868 cm and south: 792.28 cm, 699.008 cm, Table 7).

Figure 1

Data displayed was based on averages from the 5 quadrats and included both F. grandifolia and A. saccharum. Quadrats established were 10X10 meters and densities of Canopy and Subcanopy trees were counted. Tall Sapling, Short Sapling, and Seedling densities were estimated from a 2X2 meter quadrat within the 10X10 meter quadrat, then multiplied by 25. Error was derived from a standard deviation divided by the square root of the number of quadrat samples.

Data included both F. grandifolia and A. saccharum. Quadrats established were 10X10 meters and densities of Canopy and Subcanopy trees were counted. Tall Sapling, Short Sapling, and Seedling densities were estimated from a 2X2 meter quadrat within the 10X10 meter quadrat, then multiplied by 25. Error was derived from a standard deviation divided by the square root of the number of quadrat samples.Table 1

Average Abundance of Size Classes

Figure 2

Data included both F. grandifolia and A. saccharum. Basal Area is based on the average diameter at breast height of Canopy and Subcanopy trees and previously calculated average densities. Average dbhs were derived from the circumference measured in all five 10X10 meter quadrats. Average diameter was calculated by dividing the average circumference by pi. Tall Sapling, Short Sapling, and Seedling average diameters were assumed to be 2 cm, 1 cm, and .5 cm respectively. The formula for basal area used was (average dbh)2/2*average density per 100 m2.

Data included both F. grandifolia and A. saccharum. Average dbhs were derived from the circumference measured in all five 10X10 meter quadrats. Average diameter was calculated by dividing the average circumference by pi. Tall Sapling, Short Sapling, and Seedling diameters were assumed as 2cm, 1cm, and, .5 cm respectively. Average densities were calculated previously in Table 1. The formula for basal area used was (average dbh)2/2*average density per 100 m2.

Table 2

Average Diameter at Breast Height of Size Classes in centimeters

canopysubcanopytall saplingshort saplingseedling

205.7430.48ASSUMED AVERAGES

271.7838.1D=2D=1D=.5

195.5838.1

224.3666667149.86

AVERAGE CIRCUMFRENCE121.92

D= 71.4130.48

AVERAGE DIAMETER45.72

45.72

48.26

15.24

27.94

33.02

30.48

38.1

27.94

30.48

20.32

48.26

22.86

66.04

22.86

124.46

43.18

47.81826087

AVERAGE CIRCUMFRENCE

D=15.22

AVERAGE DIAMETER

Density Average0.65.4145195310

Basal Area (cm2)2403982.455455.53153.15260.86

Figure 3

Data was collected from counts of F. grandifolia and A. saccharum canopy and sub canopy trees in multiple 10X10 meter quadrats.

Species

F. grandifoliaA. saccharum

ClassCanopy285

Subcanopy5053

Ratio C/SC0.560.0943

Species Expected

F. grandifoliaA. saccharum

ClassCanopy2829.68

Subcanopy5053

Ratio C/SC0.560.56

P=5.894E-06

Table 3

Data was collected from counts of F. grandifolia and A. saccharum canopy and sub canopy trees in multiple 10X10 meter quadrats. A ratio of subcanopy to canopy trees of F. grandifolia, .56, was calculated and then used to create an expected A. saccharum frequency (53*.56=29.68). A 2 test yielded a p value significantly lower than .05, showing that the difference between species was statistically significant

Heterogeneity Table of Observed and Expected Canopy and Subcanopy Frequencies with 2 Probability

Data was collected from counts of F. grandifolia and A. saccharum canopy and sub canopy trees in multiple 10X10 meter quadrats.

Figure 4

Table 4

Data was collected from counts of F. grandifolia and A. saccharum canopy and sub canopy trees in multiple 10X10 meter quadrats. A ratio of same neighbor species to different neighbor species of F. grandifolia, 4.83, was calculated and then used to create an expected A. saccharum frequency. A 2 test yielded a p value significantly lower than .05, showing that the difference between species was statistically significant

Focal tree

F. grandifoliaA. saccharum

NeighborF. grandifolia2919

A. saccharum616

Focal F. grandifoliaF/A neighbor ratio 4.83

Focal A. saccharumA/F neighbor ratio0.8421

Expected Focal tree

F. grandifoliaA. saccharum

Expected NeighborF. grandifolia2919

A. saccharum691.77

Focal F. grandifoliaF/A neighbor ratio 4.83

Focal A. saccharumA/F neighbor ratio4.83

P=2.58504E-15

Focal Tree Neighbor Species Heterogeneity Observed and Expected Frequencies with 2 Probability

Figure 5

Data on average symmetry index was calculated from the average difference in canopy length in centimeters using the largest difference of extent between any combination of north, south, east, or west. North was defined as the direction pointing towards the nearest neighbor canopy tree. Standard error is indicated by grey bars.

Table 5

Data on average symmetry index was calculated from the average difference in canopy length in centimeters using the largest difference of extent between any combination of north, south, east, or west. North was defined as the direction pointing towards the nearest neighbor canopy tree. Standard error was calculated from the standard deviation of symmetry indexes divided by the square root of 5 because data came from five 10X10 meter quadrat samples.

F. grandifolia CANOPY CM

NorthSouthEastWest INDEX OF SYMMETRY (LONGEST-SHORTEST)

327.66622.3393.7909.32 581.66

701.4547.64541.02784.86243.84

434.341247.14589.6640.08812.8

708.66848.36251.461201.42949.96

617.22695.96944.88693.42327.88

AVERAGE S.I.583.228

STANDARD ERR0R135.570081

A. saccharum CANOPY CM

523.24335.281137.92233.68904.24

487.681254.761008.38754.38767.08

312.42535.94424.18609.6297.18

492.76718.82518.16360.68358.14

523.24650.24302.26452.12347.98

AVERAGE S.I.534.924

STANDARD ERROR125.1026713

Table 6

Data on symmetry indices were calculated from the difference in canopy length in centimeters using the largest difference of extent between any combination of north, south, east, or west. This table shows the indices of the different tree species. Data came from five 10X10 meter quadrat samples. A ttest statistical comparison between revealed a probability value of .80009454. This value was above.05 and showed the variance was not statistically relevant.

Symmetry Index F. GrandifoliaSymmetry Index A. saccharum

581.66904.24

243.84767.08

812.8297.18

949.96358.14

327.88347.98

p=.80009454

Figure 6

North was defined as the direction towards the nearest neighbor canopy tree. Data was collected from measurements from five 10X10 meter quadrats. Data of extents before averages and after averages can be found n Table 5. Grey bars indicate standard error.

Table 7

Data was collected from five 10X10 meter quadrats. North is defined as in the direction of the nearest neighbor canopy tree. Error was calculated from Table 5 values before they were averages by the standard deviation divided by the square root of 5 (5 quadrats).

Tree Species

F. grandifoliaA. saccharum

North557.856467.868

South792.28699.008

North error75.8639.56

South error124.109153.381

Average Extent of F. grandifolia and A. saccharum to the North and South in Centimeters

Discussion: The results of the data analysis supported the hypothesis that if there was a distribution of size classes, then it would be inversely proportional to overall size. This makes logical sense because of the intense competition for light and nutrients among the lower size classes. The basal area results also proved the hypothesis that most amount of biomass would be sequestered in size classes from largest to smallest. This showed that although smaller size classes have greater frequencies, the pay off for winning the lottery and becoming a canopy tree is biomass (Robson, 1990). The next part of the data analysis concerning canopy trees and subcanopy tree relationships supported the hypothesis that if there was greater or equal amounts of F. grandifolia than A. saccharum, there would be greater frequency of smaller size classes of F. grandifolia. In fact, the data revealed a staggering amount of greater frequencies of beech subcanopy trees even in the presence of a canopy maple. This is likely due to the root sprouting proliferation capability of F. grandifolia having a greater evolutionary advantage of the seed dispersal of A. saccharum (Takahashi, Arii, and Lechowicz, 2010). In the last group of data analysis concerning canopy growth extent and direction, both species showed a favorable growth patter away from neighboring canopies. The hypothesis that if there were A. saccharum canopy trees, then they would show a greater amount of growth towards light was not strongly supported the data. The variances in asymmetry and overall extent were not statistically significant. Additionally, F. grandifolia showed slightly larger extents of asymmetry and growth away from the neighbor canopy. This might be due to the fact that A. saccharum requires a more drastic gradient of light, such as a sudden disturbance in the canopy, to make a significant growth pattern. Because there were not excessive canopy disturbances in the quadrats that were analyzed, it may be why A. saccharum did not show greater asymmetry and phototropism (Beaudet, et. al, 2007).

Literature CitedBeaudet, M., J. Brisson, D. Gravel and C. Messier. 2007. Effect of a major canopy disturbance on the coexistence of Acer saccharum and Fagus grandifolia in the understorey of an old-growth forest. Ecology 95: 458-457.Poulson, T. and W. Platt. 1996. Replacement Patterns of Beech and Sugar Maple in Warren Woods, Michigan. Ecology 77: 1234-1253.Robson, Arthur J. 1990. Efficiency in Evolutionary Games: Darwin, Nash and the Secret Handshake. Journal of Theoretical Biology 144: 379396.Takahashi, K., K. Arii, and M. Lechowicz. 2010. Codominance of Acer saccharum and Fagus grandifolia: the role of Fagus root sprouts along a slope gradient in an old-growth forest. Journal of Plant Research 123: 665-674.