The Distribution of Plant Species in Hemlock Forest

Relatively little is known about the diversity of plant species and environmental gradients in the vast Hemlock Forest. In a classification study of upland ecosystem Hemlock Forest, a tabular, field-oriented sampling technique was used to perform species diversity and identify the strongest correlation between the environmental gradients and the distribution of plant species. Twenty nine plant species groups were analyzed, comprising of a total of 63 upland, moss, and shrub and herb species. The groups dispatched into the forest were tasked to cover various aspects of plant species, including their ecological niche, soil moisture, soil fertility and shade tolerance. However, based on the tabular, the groups were separated majorly along fertility gradient than moisture gradient, thus implying that the ecological responses of species were quite similar. In regard to the method used, a post-hoc test was used to confirm where the difference occurred between sets of data collected. This helped the groups to identify the strongest correlation between the environmental gradients and the distribution of plant species. With the use of the Index of Dispersion, the results indicated that at least 24 species had an index value significantly greater than one, equal to one or significantly less than one. Furthermore, random distribution of species in the ecosystem indicated scarcity of resources such as essential mineral compounds, sunlight, and water.

Introduction

The relevance of environmental gradient and species diversity in relation to soil moisture and fertility was studied at Hemlock Forest (Banes, 2011). A group of researchers embarked on a mission to study the distribution of plant species as correlated to an environmental gradient generated by the distribution of adult hemlock and maple trees. At least twenty nine plant species groups were analyzed, comprising of a total of 63 upland, moss, and shrub and herb species (Banes, 2011). A walk through the forest did not show the tell-tale signs of a homogeneous landscape that one would expect, but a strikingly heterogeneous landscape where forest mounds and forest depressions alternate in quick succession on a scale of 10’s of meters were identified.

To a greater extent, patterns of forest plant diversity appeared to have been as a result of environmental gradient where a floral species some of which (for example, hemlock and red maple seedlings) were found common to both habitats (Rei, 2006). The purpose of this lab report, therefore, is to determine whether the community of plant species is evenly dispersed throughout the forest floor, or if the distribution of plant species is correlated to an environmental gradient generated by the distribution of adult hemlock and maple trees.

Methods

The research area was located in the Hemlock Forest in the Greenbelt of Ottawa, twenty kilometers east of Carleton University.The Hemlock Forest is unique for its vast heterogeneous landscape, where forest mounds and depressions have an abrupt turnover rate within tenmeters along a single transect line (Spies & Banes, 2011). Each group of ten students was responsible for twotransects, one half of the group was working atop a forest mound and the other along a forest depression. The abundance of each stemmed species, a soil sample and the percentage of forest canopy cover were all recorded for eachquadrat in the study area, for a total of eight quadrats per transect. Due to the vastness of the study area, sampling and collection of data werecontributed from both ends of the group for the overall data collected (Busing & White, 1997).

A post-hoc test is used to confirm where the difference occurred between sets of data collected, in order to identify the strongest correlation between the environmental gradients and the distribution of plant species. The objectives of the lab are divided into testable statistical hypotheses. Each hypothesis has a null and an alternative hypothesis associated with it (Rei, 2006).

Hypothesis 1: Plant assemblages are not evenly distributed.

H0: Plant assemblage dispersion patters (random, uniform and clumped) are not significantly different from an even distribution.

H1: Plant assemblages are significantly different from an even distribution of random, uniform and clumped dispersion patterns.

Mean, variance, chi-squared and chi-squared critical are calculated for each species present in the transect. The Index of Dispersion is calculated for each species, then analyzed how many species have an index value significantly greater than one, equal to one or significantly less than one. Results are compared from the Chi-Squared Critical values to determine the dispersion patterns associated with each species. The null hypothesis is tested by way of the P-value in order to reject or accept hypothesis 1.

Hypothesis 2: Changes in plant assemblage are correlated with changes in an environmental gradient.

H0: Changes in plant assemblage composition are no significantly correlated with measured environmental gradients

H1: Changes in plant assemblage composition are significantly correlated with at least one measured environmental gradient.

The Wilson &Shmida’s beta diversity index is used to analyze the change in plant assemblages in each quadrat studied. Limited change is associated with a value close to zero and greater change is associated with increasing high values. Likewise, a value must be calculated for each environmental variable measured (CV-O, CV-A, CV-pH, and CV-FCC).The Pearson correlation coefficient (r-value) determines which environmental variable is affiliated with changes in the plant assemblages. The null hypothesis is tested by way of the r-value in order to reject or accept hypothesis 2 (Brockway, 1997).

Results

Base on Wilson & Shmida’s diversity index, the following data was generated to show a single value for species change in plant assemblage composition for the measured transect.

WS

CV-O

CV-A

CV-pH

CV-FCC

3.583

0.688

0.417

0.126

0.043

2.370

0.539

0.313

0.049

0.024

3.660

0.219

0.381

0.045

0.033

2.612

0.307

0.258

0.141

0.060

1.778

0.449

0.464

0.193

0.017

2.717

0.608

0.266

0.054

0.032

2.468

0.524

0.383

0.168

0.027

2.222

0.599

0.506

0.422

0.014

2.480

0.258

0.689

0.053

0.022

3.111

0.764

0.442

0.100

0.013

3.071

0.593

0.511

0.048

0.045

2.298

0.749

0.417

0.102

0.066

2.286

0.466

0.617

0.204

0.030

3.243

0.826

0.827

0.123

0.118

2.298

0.685

0.721

0.102

0.027

3.404

0.551

0.631

0.087

0.062

1.760

0.388

0.387

0.100

0.025

2.261

0.621

0.497

0.117

0.083

2.842

0.313

0.284

0.077

0.026

2.566

0.345

0.422

0.067

0.038

3.037

0.912

0.648

0.088

0.062

1.778

0.823

0.444

0.160

0.068

2.778

0.885

0.552

0.103

0.021

When calculating the number of species present in each Quadrat, the following data was compiled.

0

0

2

0

17

2.298

0.685

0.721

0.102

0.027

18

3.404

0.551

0.631

0.087

0.062

0

0

0

2

19

1.760

0.388

0.387

0.100

0.025

5

0

15

2

20

2.261

0.621

0.497

0.117

0.083

0

3

0

0

21

2.842

0.313

0.284

0.077

0.026

22

2.566

0.345

0.422

0.067

0.038

5

9

0

30

23

3.037

0.912

0.648

0.088

0.062

0

0

0

0

24

1.778

0.823

0.444

0.160

0.068

0

0

0

0

25

2.778

0.885

0.552

0.103

0.021

4

5

3

5

0.988338

-0.37955

-0.42434

-0.38809

13

23

12

9

3.5

4.1

3.3

3.5

87.52

79.2

92.72

92.72

9

9

7

9

The ecological mechanism of genetic drift and mutation were the major driving patterns of co-dominance at maturity on a spatial scale of 10’s of meters.  This is because most plant species were roughly equally distributed as seedlings, but then as mature adults their spatial distribution became quite separate, a unique characteristic of the hemlock forest (Brockway, 1997).  Several floral species (for example, hemlock and red maple seedlings) were examined and found common to both the diversity of plant species and environmental gradients habitats. However, as these seedlings grow to maturity the hemlocks dominate the mounds and the red maples dominate the depressions (Banes, 2011). It was also established that the environmental tolerance of the plant species in relation to forest floor, soil moisture, fertility gradient were greater. The results indicated that at least 24 species had an index value significantly greater than one, equal to one or significantly less than one (White, 1997).

It was also established that red maple seedlings germinate and grow quickly in the sun exerting their dominance within the gap environment when a gap in the forest canopy occurs. With time however, the slower growing hemlocks seedlings growing beneath the red maples grow taller than the red maples thus committing the red maples to the world of perpetual shade. With not enough sunlight the red maples die leaving behind the slower growing but overall competitively dominant hemlock. The hemlocks continue to dominate the mound-based landscape until another hemlock dies, a new gap is produced, and the process starts all over (White, 1997).

Discussion

Hypothesis 1: plant assemblages are not evenly distributed

In the analysis table xx, against an expected number of 8 species per quadrant, 21 species were observed to be clumped. This suggests that the soils in the particular habitat may be fertile and support growth of many species, or that the species clump together because they are covered under a thick layer of tall trees that form a canopy. Additionally, when taller trees dry and fall, some small plant species seeds are exposed to sunlight and germinate and colonize the specific area. This makes them to be seen as clumping. The pattern is observed in hemlocks that grow in the mounds and red maples thrive well in depressions. Hemlocks require well aerated soils to grow which is a characteristic of soils on the mounds. Red maples dominate the depressions because of the reason that hemlocks cannot survive there, even though they are also stunded and appear thin.

Four of the plant species were randomly distributed within the quadrants while none of the species was found to be evenly distributed.  Random distribution of species in the ecosystem indicates scarcity of resources such as essential mineral compounds, sunlight, and water; whereas none of the species was found to be evenly distributed from the data analysis, it does not suggest that all species are clumped of randomly distributed. Some of the species were evenly distributed in a particular section of the quadrant. This may be as a result of other features such adaptability to a particular place and absence of disturbances such as animals which feed on them. In this case the null hypothesis of all assemblages dispersion patterns are not significantly different from an even distribution is confirmed true.

Hypothesis 2: changes in plant assemblage are correlated with changes in an environmental gradient

References

Banes, T. A. (2011, Feb). Ecological species groups of upland northern hardwood – Hemlock Forest ecosystems of the Sylvania Recreation Area, Upper Peninsula, Michigan. Canadian Journal of Forest Research , 15(5):961-972.

Brockway, D. G. (1997, Oct 29). Forest plant Diversity at Local and Landscape Scales in the Cascade Mountains of Southwestern Washington. Rocky Mountain Research Station , 1-24.

Rei, M. C. (2006). Assessment of Fire Severity And Species Diversity In The Southern Appalachians Using Landsat Tm And Etm+ Imagery. Warnell School of Forest Resources, University of Georgia, , 1-31.

White, R. T. (1997). Species Diversity and Small-Scale Disturbance in an Old-Growth Temperate Forest: A Consideration of Gap Partitioning Concepts. Oikos , 3

(78), pp. 562–568.