Download Lab 4 - Temporal Patterns in Plant Communities

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LAB 4
TEMPORAL PATTERNS IN
PLANT COMMUNITIES AT NIXON COUNTY PARK
DISTURBANCE AND TEMPORAL CHANGE IN PLANT COMMUNITIES
A primary determinant of species composition at a site is disturbance history. Some species
(shade intolerant, but fast-growing pioneer species) are well-adapted to disturbances, but do poorly in
the absence of disturbance or are intolerant of competition (such as for light), whereas others (shade
tolerant, slow-growing climax species) exhibit the opposite response. These latter species can grow
and/or persist beneath the canopy of other species. Where disturbances are more recent, frequent, or
intense, pioneer species will predominate; in very undisturbed sites (e.g., old growth forests), more
competitive species will predominate.
The species composition of the forests at Nixon County Park today is a product of human
intervention and natural disturbance. Three hundred years ago or even fifty years ago the forest at these
sites probably differed substantially from what we see today. For example, the oaks and black cherry
probably owe their overwhelming dominance to the combination of cutting and fire in the past and the
introduction of chestnut blight (Cryphonectria parasitica). On the other hand, species such as black
gum (Nyssa sylvatica), American beech, red maple, sugar maple (Acer saccharum) are shade-tolerant
species, and do not necessarily rely on disturbance to attain or maintain dominance in the canopy.
However, a disturbance will enhance their growth.
We could decipher the recent history of a stand by using tree rings. We could take increment
cores from a representative sample of the trees. From ring counts, we could then uncover which
species colonized the site first, which species invaded later, and how fast the various species grew in
covering these sites with today's forest.
This discussion of forest change may spark a question in your mind: "Has the forest reached
some equilibrium or will its species composition continue to change in the future?" That's what this lab
is about. How can we predict the future composition of the forest? Consider where the future canopy
trees will come from -- the current cohort of juvenile trees. So, simply quantifying the species
composition of the seedlings and saplings in the understory will provide a good start at predicting what
the forest will look like in the future, assuming no further major disturbances occur. This idea suggests
that in the future, the current canopy individuals will one by one, succumb to the elements, thus
opening up a canopy gap that will be filled by juveniles "waiting" in the understory. This is known as
the "reorganization" response of canopy disturbance.
The only problem with this approach is that such an event -- the death of a canopy tree -represents a small disturbance in the forest. Depending on the size of the canopy opening, these may
be sites that favor pioneer species rather than climax species. Therefore, the species composition of
juveniles in gaps may be very different than that in the shaded, intact understory. This represents the
"new establishment" response of forest gaps, i.e. the origin of new plants in the disturbed area. Species
diversity in the new gap may be greater than the surrounding understory because pioneer (or fugitive)
species invade these areas. The increase in light, temperature and the loss of canopy cover alters the
microclimate at these gap sites, favoring species other than those suppressed in the understory. For
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example, shade-intolerant species might invade a newly formed gap and dominate shade-tolerant
species that would have been expected to assume dominance. Which of these responses will be more
important in the future forest at Nixon County Park?
QUESTIONS AND HYPOTHESES
These ideas suggest the following two major questions to address concerning the forest on the
southwest-facing slope at Nixon County Park:
1. Is the species composition of the forest changing after a disturbance?
2. Does the juvenile species composition differ between intact understory and canopy gaps?
Your approach will be to consider the probability that the gapmaker (red or black oak) will be replaced
by an individual of the same species. This is the part of the “reorganization hypothesis” proposed by
Joan Ehrenfeld (1980; see bibliography). Her alternate hypothesis is the “new establishment
hypothesis.” This alternate hypothesis suggests that the species composition in the gap differs from the
intact understory, thus leading to a potential change in the composition of the forest canopy.
PROCEDURES DURING LAB
You will sample all age classes in
1) A canopy gap – A recently fallen tree
2) Intact understory around a tree of the same species as the gapmaker.
The class will sample 4 gaps and 4 understories. Each group will sample one of each.
Sampling today will involve
 Measuring the size of the gap (2 diameters at 90° to each other)
 The identity of any tree ranging from seedling size ►> 5 cm dbh (sapling)
 The size (dbh) and identity of any tree between 5 – 20 cm = saplings to pole size (sub-canopy)
 You may be asked to “ignore” the presence of trees greater than ~ 25 cm dbh.
Trees that you may encounter
Trees that will not reach the canopy
Sassafras (Sassafras albidum)
Dogwood (Cornus florida)
Black cherry (Prunus serotina)
Red maple
(Acer rubrum)
Shrubs that you may encounter
Red oak
(Quercus rubra)
Spicebush (Lindera benzoin)
Black oak
(Quercus velutina)
Maple-leaf viburnum (Viburnum acerifolium)
Chestnut oak (Quercus prinus)
White oak
(Quercus alba)
Black Tupelo (or Black Gum) (Nyssa sylvatica)
Yellow (Tulip) Poplar (Liriodendron tulipifera)
American Chestnut (Castanea dentata)
Mockernut hickory (Carya tomentosa)
Pignut hickory (Carya glabra)
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Witch Hazel (Hamamelis vernalis)
Blackberries (Ribes spp.)
Blueberries (Vaccinium sp)- no yellow resin dots
on underside of leaf
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LAB REPORT
For each gap/understory sampled, calculate the following for
 Tree species only.
1) Species richness
2) Density = # of individuals/ area sampled (both size classes combined (do for each gap and each
understory).
3) Relative density = density for a species/total density of all species (this is #2 above) [Express
relative density as a decimal value]
a. Calculate Relative density for seedlings & saplings.
b. Calculate Relative density for pole size trees.
Note: Use the density (#2 above) for in the denominator for a & b.
Calculating relative density for each size class will help you discern successional trends.
The calculations of #1, 2 & 3 for all plot types (e.g. all gaps) can be put into 1 table for ease of
comparison. Make your table in landscape format.
1) Simpson’s index (tree species only!) – is derived from probability theory. What is the probability
that two specimens picked at random in a community of infinite size will be the same species? It is
a measure of the probability of interspecific encounter – in a diverse collection, the probability that
two of the same species will meet (or be randomly selected) is low. For example, if a person went
into a boreal forest in northern Canada and picked two trees at random, there is a fairly high
probability that they would be the same species. If a person went into the tropical rain forest by
contrast, two trees picked at random would have a low probability of being the same species
So, if two individuals are selected at random from a community, the probability that they will be of the
same species can be described by:
l
 n (n  1)
i
i
N ( N  1)
Where N = total number of individuals and ni= number of individuals of species i. The quantity l is a
measure of dominance. Dominance is the concentration of N individuals among s number of species.
A collection of species with high diversity will have low dominance. Values of l will be low if the
number of individuals is spread out over many species and l will be high if the number of individuals is
concentrated in a few species (see page 32 of Ehrenfeld 1980). Your values of l should range between 0
and 1 and should be comparable to Ehrenfeld’s.
Calculate the Simpson’s Index for each gap & understory.
5) Sorensen’s coefficient of similarity. CC S =
2c
s1  s 2
where s1 and s2 are the number species in community 1 and 2 respectively, c is the number of species
common to both communities. For example, if community 1 contains 20 species, community 2
contains 18 species, and both contained 12 species in common, then
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CC S =
2(12)
= 0.63 or 63%
20  18
The value of CCS can range from 0 (when no species are found in both communities) and 1.0, (when
all species are found in both communities).
Calculate Sorensen’s coefficient of similarity for each gap/understory pair (e.g. Gap #1 with
Understory #1)
FOR YOUR REPORT – IMRAD format for the section that you write.
2) Prepare an introduction that outlines the theory presented by Ehrenfeld. Be sure to include a
hypothesis – perhaps based on your own observations.
3) No methods section.
4) Results should be presented primarily in the form of a table. Be sure to include written text
describing your results.
5) Discussion. I want you to use the data that you have collected and the subsequent calculations to
address the question as to whether the vegetation in the new gaps appears to follow the
‘reorganization’ or the ‘new establishment’ response.
6) Bibliography – Don’t forget it.
The overriding question is: Is the composition of the forest canopy going to change in response to
disturbance? The questions below will help you address this.
Questions to consider in your report:
1) Do the patterns in the gaps suggest a ‘reorganization’ response or ‘new establishment response?’
This is your hypothesis, so this should be broadly addressed at the beginning of your discussion.
Use your calculations and the remaining questions as a means to explain your conclusion at the
beginning of the discussion.
Examine the density and frequency data along with the Simpson diversity index and Sorensen’s
similarity coefficient to guide your conclusion. Use Ehrenfeld’s approach as your guide. Also
examine the life history of the tree species (listed under “reaction to competition” in Burns and
Honkala 1990).
2) Does the relative density of the understory species differ between gaps and understories?
3) Does the shade tolerance of the species in the gap differ from those in the understory?
4) What is the probability that the gap maker at the center of each of your plots will be replaced by
another of the same species? If not, what is the likely species that will replace the gap maker?
5) Is the species composition of the overstory going to change in either gap or understory plots?
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Consult your relative density table. This is very much like the transition matrix (Table 21.2) that
Henry Horn created (see pp 409-411 in Krebs, your textbook, or Horn 1975 on Ereserve. Your
relative density table is like Table 21.2 except a) your probabilities represent only 1 overstory tree,
not a whole forest, and b) your probabilities are for seedlings and saplings separately
6) Is there understory vegetation (e.g. ferns or shrubs acting as competitors) that will not reach the
canopy playing a role in successional progress of the gaps?
7) What other factors might be playing a role in the regeneration of these gaps?
For questions (1), (2), examine your data and read Ehrenfeld (1980) to see how she works through her
data to reach a conclusion. This is the core hypothesis of your lab. For (3) read through the species
descriptions (Honkala & Burns 1990 – on-line) and the articles on tree ‘shade’ tolerance (Baker,
Downs) and types of trees in gaps (Whitmore 1989). For question (4) – think. You might also examine
Henry Horn’s ‘matrix of probabilities’ on page 97 of his article, Forest Succession (Ereserves)
Baker, Frederick S. 1949. A revised tolerance table. Journal of Forestry 47:179-181.
Burns, Russell M. and Barbara H. Honkala. 1990 Silvics of North America. USFS Agriculture
Handbook 654.
Available on-line (URL below), but cite as Burns & Honkala, 1990.
http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm
Bray, J. Roger. 1956. Gap phase replacement in a maple-basswood forest. Ecology 37(3):598-600
(JSTOR) http://www.jstor.org/view/00129658/di960147/96p0342f/0 Bray presents a good
discussion on which tree species might become the future canopy.
Downs, Albert A. 1946. Response to release of sugar maple, white oak and yellow poplar. J. Forestry
44:22-27.
Ehrenfeld, Joan G. 1980. Understory response to canopy gaps of varying size in a mature oak forest.
Bulletin of the Torrey Botanical Club. 107:29-41.
Horn, Henry S. 1975. Forest Succession. Scientific American 232(5):90-98.
Whitmore, T.C. 1989. Canopy gaps and the two major groups of forest trees. Ecology 70:536-538.
Muzika and Twery discuss the types of species that respond to canopy thinning.
Muzika, R.M. & M.J. Twery. 1992. Regeneration in defoliated and thinned hardwood stands of northcentral West Virginia. Pp 326-340 IN: Proceedings, 10th Central Hardwood Forest Conference;
1995 March 5-8; Morgantown, WV.
http://www.fs.fed.us/ne/newtown_square/publications/technical_reports/pdfs/scanned/gtr197a.pdf
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Red maples role in forests today
Abrams (1998) and Clinton et al. (1998) discuss the ubiquity of red maple.
Abram, M.A. 1998. The red maple paradox. BioScience. 48(5): 355-364. (JSTOR)
http://links.jstor.org/sici?sici=0006-3568(199805)48%3A5%3C355%3ATRMP%3E2.0.CO%3B2-A
Clinton, Barton D.; Boring, Lindsay R.; Swank, Wayne T. (1994) Regeneration Patterns in Canopy
Gaps of Mixed-oak Forests of the Southern Appalachians: Influences of Topographic Position
and Evergreen Understory. American Midland Naturalist 132:308-319. avail. at:
http://www.srs.fs.usda.gov/pubs/viewpub.jsp?index=4703
A classical example of a non-competitive species gaining access to the forest canopy.
Knapp, Liza B. and Charles D. Canham. 2000. Invasion of an Old Growth Forest in New York by
Ailanthus altissima: Sapling growth and recruitment in Canopy Gaps. Journal of the Torrey
Botanical Society 127(4):307-315. (JSTOR)
http://www.jstor.org/view/10955674/sp030004/03x0029c/0]
The impact of deer on forest regeneration.
Horsley , Stephen B., Susan L. Stout, David S. deCalesta (2003) Whitetail deer impact on the
vegetation dynamics of a northern hardwood forest. Ecological Applications 13(1):98-118,.
http://www.esajournals.org/perlserv/?request=get-document&issn=10510761&volume=13&issue=1&page=98&ct=1
Nancy G. Tilghman 1989. Impacts of White-Tailed Deer on Forest Regeneration in Northwestern
Pennsylvania. The Journal of Wildlife Management, Vol. 53, No. 3, pp. 524-532. Only page one
is available.
http://links.jstor.org/sici?sici=0022-541X(198907)53%3A3%3C524%3AIOWDOF%3E2.0.CO%3B2N
The above articles are summarized, in part in the following on-line resources.
deCalesta, David S. Deer, Ecosystem Damage, and Sustaining Forest Resources
at: http://www.arec.umd.edu/policycenter/Deer-Management-in-Maryland/decalesta.htm
Forest Science Review (2004) USDA Forest Service Northeastern Research Station
http://www.fs.fed.us/ne/newtown_square/publications/FSreview/FSreview1_04.pdf
http://links.jstor.org/sici?sici=0022-541X(198907)53%3A3%3C524%3AIOWDOF%3E2.0.CO%3B2N
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TEMPORAL PATTERNS IN PLANT COMMUNITIES
DATA SHEET
NAME OF SAMPLERS____________________________________
DATE____________
Type of Plot (Gap or Understory) __________________
Plot #__________
Only record tree species, but note presence of other species.
# (if < 5cm)
DBH
Species____________________________
______
_______
Species____________________________
______
_______
Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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TEMPORAL PATTERNS IN PLANT COMMUNITIES
DATA SHEET
NAME OF SAMPLERS____________________________________
DATE____________
Type of Plot (Gap or Understory) __________________
Plot #__________
Only record tree species, but note presence of other species.
# (if < 5cm)
DBH
Species____________________________
______
_______
Species____________________________
______
_______
Species____________________________
______
_______
Species____________________________
______
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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TEMPORAL PATTERNS IN PLANT COMMUNITIES
DATA SHEET
NAME OF SAMPLERS____________________________________
DATE____________
Type of Plot (Gap or Understory) __________________
Plot #__________
Only record tree species, but note presence of other species.
# (if < 5cm)
DBH
Species____________________________
______
_______
Species____________________________
______
_______
Species____________________________
______
_______
Species____________________________
______
_______
Species____________________________
______
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
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Species____________________________
______
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Species____________________________
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Species____________________________
______
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Species____________________________
______
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Species____________________________
______
_______
Species____________________________
______
_______
Species____________________________
______
_______
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