The Exploration of the behavior of Sugar Maple (Acer saccharum) and American

The Exploration of the behavior of Sugar Maple (Acer saccharum) and American Beech (Fagus grandifolia) as coexisting species in Warren Woods.
Abstract This experiment took place at Warren Woods, Michigan in an attempt to understand the behavior of Sugar maple (Acer saccharum) and American Beech (Fagus grandifolia). The aim was to understand if there was lottery competition pattern across the distribution of different class sizes. Alongside that we were trying to understand if there is coexistence between the two species and what kind of coexistence mechanisms that took place. We noticed a lottery competition like patterns of distribution along the different classes (seedlings> sampling> poles> canopies) except that our data had disparities between samplings and poles. Our data also supports the presence of coexistence between A. saccharum and F. grandifolia. As for the mechanisms of survival we were not able to observe any tradeoffs performance and our data supported habitat preference for beech but reciprocal replacement for maples. Overall, we were not able to support the mechanisms of coexistence thus we can infer that the distribution of species is due to chance.
Introduction Warren Woods State Park is a nature preserve that is located in Berrien County, Michigan. Warren Woods serves as a home to two dominant species of shade tolerant trees, namely Sugar maple (Acer saccharum) and American Beech (Fagus grandifolia). American beech is unique in its grey and smooth bark while the sugar Maple is known for its brown and tough bark. The reason why this forest is considered a national preserve is because of the unique interactions between the two tree species in which they coexist in the forest (Greenberg 2004). For the purposes of this research paper Warren woods was visited to examine the behavior and coexisting mechanism of survival between A. saccharum and F. grandifolia. Both A. saccharum and F. grandifolia are shade tolerant trees that are expected to compete with one another for light and other resources. Both trees are dominant in their nature, thus one could expect that one species would wipe out the other in case of the presence of both (Canham 1988).
In the presence of both tree species A. saccharum and F. grandifolia competition is also present. But what makes Warren Woods special is the type of competition called lottery competition that leads the survival of both species. Lottery competition model is used as a way to explain how two or more species compete. Under this type of competition many offspring compete for limited amount of resources such as light and space (Hatfield et al 1997). And due to the Ecological principle of competitive exclusion the two tree species, Sugar Maple and American Beech, cannot occupy the same niche Fox (1977) has attempted at explaining this interaction by stating that it is due to reciprocal replacement that both species has succeeded in surviving. Reciprocal replacement works by the growing of Sugar maple after a Beech dying off and creating a gap in the canopy of the forest. And the vise versa happens when a Maple tree gets knocked off and the Beech grows in its place (Fox 1977). But this theory was dismissed by another explanation by Poulson and Platt (1996) stating that both A. saccharum and F. grandifolia exhibit different responses to low light levels in the understory. F. grandifolia is better capable of surviving in longer periods of no light while A. saccharum on the other hand does not grow as good in the shade, thus Beech trees are better at staying under the canopy for longer periods of time while waiting for an opportunity to grow later (Poulson and Platt 1966).
Based on previous research lottery competition seemed like the best explanation of why A. saccharum and F. grandifolia are able to coexist at Warren Woods. Thus, this research study was conducted in an attempt to understand and examine the competition and coexistence of both A. saccharum and F. grandifolia. The three main research question that are being examined in this study are 1) Do the trees at Warren Woods exhibit a lottery competition like pattern? 2) Are A. saccharum and F. grandifolia actually coexisting at Warren Woods? And finally, 3) What are the mechanisms of coexistence between the two species in regard to Tradeoffs and Environmental Heterogeneity? The first question will be answered by looking at the distribution of size classes among both species. Due to the lottery competition the number of smaller classes like seedlings are expected to be more than saplings which are more than subcanopies which in turn are more than the canopies. As for whether the two species, A. saccharum and F. grandifolia, coexist at Warren Woods we examined recruitment of canopies and subcanopies of both species. If there were more canopies than poles then there would have been competition, and if it is the other way around that would mean there was recruitment which leads to coexistence.
Lastly, when examining the mechanisms of coexistence, we looked at two main one’s tradeoffs of performance and environmental heterogeneity. When looking at tradeoffs we asked whether there was a significant difference between the index of symmetry of beech and the index of symmetry of maple. As for Environmental heterogeneity we looked at the distribution of maple and beech and whether they grow dependent of each other. If they do grow independent of one another was it because of reciprocal replacement or habitat preference.
Materials and Methods This experiment took place at Warren Woods State Park in Michigan, Berrien County, where is it home to the 2 dominant shade tolerant species of Sugar Maple (Acer saccharum) and American Beech (Fagus grandifolia). The experiment was conducted on Saturday February 29, 2020. Temperature that day was a high of 29 degrees Fahrenheit and a low of 20 degrees, and the forest was covered with snow.
The whole class was split into groups and was scattered along the trail of the forest. Each group was responsible to record their own data and to occupy a different area than the other group for variation purposes. For the first part of the experiment maple and beech measurements of all class sizes (seedling, sampling, poles and canopy) was taken. For this groups divided up the forest area into 10-meter by 10-meter quadrants using a tape. Within this 100-meter square the number of canopies, poles and sampling of each species was recorded. As for the seedlings a 2m by 2m smaller quadrant was measured inside the bigger one to count the seedlings. This same process was used for 4 other quadrants that are randomly chosen and as far from each other as possible for accuracy in measurements and to avoid overlapping of data. Aside from this we needed to collect the circumference at breast height for each canopy in every quadrant but due to lack in supplies we were not able to collect it for this part.
For part 2 of the experiment one canopy tree from either A. saccharum or F. grandifolia was selected to be the focal tree. Once that tree is selected the circumference at breast height for that tree was recorded as well as the distance to the nearest canopy tree of either species. Once that nearest neighbor tree is determined the circumference at that tree was also recorded and that tree became the North direction. We recorded South, East and West with distances from focal tree and circumference as well as the species type. Besides all these measurements we had to collect the canopy of each focal tree spreading north, east, west and south. To do this one student would stand with the tape next the bark of the focal tree and someone else would extend the tape as far as they reach the end of the branches.
All data collected was entered into an Excel spreadsheet and to visualize the distribution of classes throughout the quadrants a bar graph was crated. The same goes for the numbers comparing canopies vs poles in each species. As for the index of symmetry a statistical T test was made with the data to determine if there was a significant difference between the SI for beeches and the SI for maple. As for the Nearest neighbor data we would use a statistical Chi-square test to determine of there is a significance between the mechanism of coexistence. This test would help in determining whether coexistence is not due to chance by habitat preference or reciprocal replacement.
Results The data collected to answer the question regarding lottery competition are compiled in a bar graph (Fig. 1). The bar graph shows that the average density per hectare of seedling is much more of that of the saplings. While saplings are a little bit less that poles which are still by far a lot more than the canopies. These data collected are a sum of both A. saccharum and F. grandifolia of all 5 quadrants where data was collected from. To test for the second question on the coexistence of both sugar maple and American beech data from exercise one was isolated on the bases of canopies and poles. This data now requires the differentiation of either species, and the bar graph shows results of the number of tress per hectare (Fig. 2). This graph shows that there were more maple poles than beeches, but there was more beech canopy than maple.
For the last part of our experiment we were trying to examine the mechanisms of coexistence in terms of tradeoffs of performance. For this, data collected from part two on measurements of index of symmetry from all directions around the focal tree of A. saccharum and F. grandifolia separately. The data showed that the index of symmetry of maple trees was much higher than the one for beech trees (Fig. 3). From the statistical t- test performed on this set of data there was no significant difference between the index of symmetry between A. saccharum and F. grandifolia (Table 1: t= -1.29, d.f.= 8, p>0.05). We also explored the mechanism of coexistence in terms of environmental heterogeneity. For that the data set for the whole class was compiles into one bar graph that showed the nearest neighbor species of each focal tree from either A. saccharum or F. grandifolia (Fig. 4). Both beech and maple focal trees had more beech trees as nearest neighbor to them. This data along with the statistical chi-square test shows that the distribution of trees along the forest was by chance (Table 2: x2=0.08, d.f.=1, p>0.05).
Discussion This research was set to examine the relationship between A. saccharum and F. grandifolia and the coexisting mechanism that drove their survival at Warren Woods State Park. Looking back at the distribution of classes we expected that there would be lottery competition between sugar maple and American beech that would produce data that decreased count of organisms with the increase in the class sizes. This decrease in density per hectare for each class is what classifies this type of competition and has been supported by other researches as well (Tatina 2015). The biological reasoning behind why trees exhibit this type of survivorship is because they are type 3 organisms. This type of organisms tends to have high mortalities early in life and their mortality decreases with age (Roman and Scatena 2011). Thus, we expect a large number of seedlings and once one wins the lottery, the payoff becomes that they become big and increase in the biomass. Our results as shown below suggests that there was that general trend in the decrease in the number of counts as the size classes increase. Although there was a data disparity between the count of samplings and poles (Fig. 1). This could be explained by human error due to miscollection of data.
The other concept we were trying at exploring in this experiment is whether A. saccharum and F. grandifolia are coexisting at Warren Woods or not. For this we were able to separate out canopies and subcanopies into their species and examined them both (Fig. 2). Now this data is also used from each quadrant and since the species are known we were testing to see if there is a difference between class sizes in proportion to A. saccharum versus F. grandifolia. When we look at the data, we see poles > canopies suggesting the presence of recruitment, which suggests coexistence between the both species (Poulson and Platt 1996). If the vise versa would have happened (canopies > poles) then there would have been competition rather than coexistence. On the other hand, when we look at the subcanopy counts while comparing them across sugar maple and beech we see that beeches are a bit lesser than maple. Since Beech are able to survive longer in the shade than do maple, we would have expected the beech poles to be more and that would have further supported the coexistence hypothesis Fox (1977). But since our data show more maples poles, we are to infer that there is some kind of competition solely based on our data.
After establishing the relationship in Warren Woods between A. saccharum and F. grandifolia to be that of coexistence we then looked at the mechanisms of coexistence. First, we explored the tradeoffs of performance by examining the canopy extend of 5 trees from each species. Research have shown that beech tend to give up vertical growth for lateral growth due to its ability to stay in the shades longer. Thus, we would expect a more asymmetrical growth of beech and a more symmetrical growth of maples (Poulson and Platt 1996, Fox 1977). The beech would then show a larger index of symmetry because of the asymmetrical shape while maples would have a smaller SI due to symmetry. Our data though shows the opposite of what was expected, Maples had a much higher SI (Fig. 3). Additionally, our raw data of nearest neighbor shows more asymmetrical growth and skewedness in maple trees than in beeches. Furthermore, our statistical t-test shows a high p-value (Table 1: p=0.23309) suggesting that there is no significant difference between index of symmetry between sugar maple and American beech. Based on this we cannot conclude that tradeoffs of performance are a mechanism of coexistence between A. saccharum and F. grandifolia.
Finally moving to our last part of the study we asked the question of whether environmental heterogeneity is a mechanism of coexistence between sugar maple and American beech. For this class totals were put together to compare and contrast each focal tree and the number of trees around it from either species (Fig. 4). Possible outcomes are either that the trees exhibit a reciprocal replacement where one species replaces the other when one dies, or we could see beech and maple growing dependently on each other through habitat preference (Fox 1977). Our data showed that there was more beech around both species of focal trees than there was maple. From this we can conclude that beech focal trees exhibited a habitat preference because it was surrounded by more beech than maple. Because of the data available environmental heterogeneity is independent of tree species. While maple focal trees exhibited a reciprocal replacement pattern because of the presence of other beech around it more than maples. With this observation environmental heterogeneity was created by the trees. Both of these patterns support the idea that distribution of maples and beech is not due to chance and that they are dependent on each other. But our statistical chi-square test does not support that (Table 2: p=0.7773) and suggests that there is no significance between the distribution of trees, thus environmental heterogeneity cannot be supported as a mechanism of coexistence. This p value further supports the idea that nearest neighbor identity is the same as we would expect by chance.
There might be different reasons why our data did not match what was expected including the fact that it could be because of human error. Another factor that could have affected out data is the smaller data set when compared to other research that was taken in much larger data. We also as a team did not go deep into the forest and restrained from collecting data from deeper areas, thus collections made could have been influenced by human or other animal disturbances. Finally, we can see that lottery competition patterns exist at Warren Woods and that coexistence is what drove A. saccharum and F. grandifolia to survive at this natural preservative forest. Unfortunately, our data failed at supporting the proposed mechanisms of coexistence but like said above it could have been due to human error.
Literature Cited
Canham, C. D. (1988). Growth and Canopy Architecture of Shade-Tolerant Trees: Response to Canopy Gaps. Ecology, 69(3), 786–795.
Fox, J. F. (1977). Alternation and Coexistence of Tree Species. The American Naturalist, 111(977), 69–89.
Greenberg, J. (2004). A natural history of the Chicago region. Chicago, IL: University of Chicago Press.
Hatfield, J. S., & Chesson, P. L. (1997). Multispecies Lottery Competition: A Diffusion Analysis. Structured-Population Models in Marine, Terrestrial, and Freshwater Systems, 615–622.
Poulson, T. L., & Platt, W. J. (1996). Replacement Patterns of Beech and Sugar Maple in Warren Woods, Michigan. Ecology, 77(4), 1234–1253.
Roman, L. A., & Scatena, F. N. (2011). Street tree survival rates: Meta-analysis of previous studies and application to a field survey in Philadelphia, PA, USA. Urban Forestry & Urban Greening, 10(4), 269–274.
Tatina, R. (2015). Changes in Fagus grandifolia and Acer saccharum Abundance in an Old-Growth, Beech-Maple Forest at Warren Woods State Park, Berrien County, Michigan, USA. Castanea, 80(2), 95–102.
Figure 1. Density of different size classes across all five quadrants per hectare.
Figure 2 Density of Canopy and subcanopy trees of the two species, Sugar Maple and American Beech.
Figure 3 Index of symmetry across American Beech and Sugar Maple canopies.
Figure 4 Nearest neighbor counts for class data with alternating focal tree species.
Statistical T- test
T- Value
Degrees of freedom
P value
(Two- Tailed)
-1.29
8
0.233088
Table 1 Two sample T-test for independent samples of index of symmetry across different species.
Statistical Chi-squared test
X2 Value
Degrees of freedom
P value
0.08
1
0.7773
Table 2 Statistical Chi-squared test for Nearest Neighbor data across both species.
2