Ecology
Lab, PCB 3043L
Field
sampling is an integral part of any ecological study.
It is thus very important that you have a solid understanding of the
methods employed. This assignment
will introduce several basic techniques that ecologists frequently use to sample
ecological parameters. Notably,
very different techniques are generally used to field sample plants and animals.
This lab will emphasize plant sampling.
Most often, plant communities are sampled for either:
1) species composition and relative abundance of each species in the
entire system, or 2) biomass and relative importance of each species to the
system. Both are measures of the structure
of the community or ecosystem you are sampling. However, biomass data, collected through time, also allow you
to estimate productivity (as the rate of change of biomass), which is a measure
of function.
Plant
species composition is most often sampled in 1 of 2 ways. The Braun-Blanquett method involves identifying a specific
area (called a “plot” or “quadrat”), identifying all species represented
in that area, then assigning each a code based on its contribution to the total
area. An example of Braun-Blanquet
codes is:
0:
species not present
1:
species <5% of total
2:
species=5-10% of total
3:
species=10-25% of total
4:
species=25-50% of total
5:
species=50-90% of total
6:
species>90% of total
Clearly,
these are somewhat subjective classifications.
It is thus important that the same observer make code classifications
whenever possible. The second way
to sample plant species composition involves identifying a plot or quadrat, as
with Braun-Blanquet, but then counting the total number of individuals of each
species within that area. Clearly,
the second method is much more objective, but it is also much more time
consuming.
Plant
species biomass may be sampled either destructively (using harvest methods) or
non-destructively. The former
nearly always involve identifying a plot, clipping all aboveground vegetation
within the plot, sorting this vegetation by species, drying it, and weighing it.
Non-destructive sampling methods are numerous and variable.
In some settings, such as wetlands and grasslands, clip-plot destructive
techniques work very well. In other
systems, such a forests, harvest methods are not tenable and non-destructive
methods must be used. There are
many ecological situations where it is against the best interest of either your
ecosystem or your study to destructively sample plants.
In these cases, you must think of ways to estimate plant biomass without
actually harvesting your plants.
In
lab today, we will measure both species composition and biomass using the
following sampling techniques:
1. Plot sampling, or
quadrat sampling, is most often used to intensively study a small portion of the
system in question in order to obtain a representative sample.
Most often plot samples are replicated
a number of times, in a random or haphazard way, to ensure that the data represent an unbiased picture
of the system.
2.
Point-quarter sampling is more
complex but expands on plot sampling in an attempt to reduce the amount of
intensive labor involved in plot sampling.
Rather than quantify the exact make-up of a specific plot a random number
of individuals are selected to provide the unbiased
picture of the system. Replicate
samples using this method should also be taken to ensure statistical validity.
3.
Transect sampling is another
often-used method for sampling ecological systems.
This method may be thought of as a long, narrow plot sample.
Measurements are taken for all individuals who fall along the transect
line.
The
lab exercise today will involve working in the shallow wetland region of
Hennington Pond, which is located just west of our Great New Golden Panther
Arched Gates entrance to campus. The
objectives are: 1) to compare and
contrast the above 3 methods of sampling plant species composition in wetlands;
2) to compare and contrast several different destructive and non-destructive
methods of sampling plant species biomass, and; 3) to identify important
environmental factors (i.e. water depth, soil depth) that appear to control
plant species composition and biomass patterns in the Hennington Pond wetlands.
1.
Generate several testable hypotheses as a class that you can test with
today’s exercise (Hint: the
objectives, above, may help with this).
2.
Discuss how to keep track of data when doing field ecological sampling.
Set up field data sheets.
3.
Divide into groups and work as teams in the field.
Work should be divided up so that all team members get to experience each
aspect of the exercise. In other
words, don’t make one person record data for the entire lab exercise!
4.
Be sure that you have all field sampling equipment that you will need.
Read below and make a list before you leave the lab.
5.
Field teams will be rotating through the four sampling method stations
noted below. Decide before you
leave for the sampling site which groups will do which stations and in which
order, to reduce confusion.
The
following exercises must be performed by each field team, in orderly rotation:
1.
A 10m X 10m area has been set up for the plot sampling.
Use the “over the shoulder toss” method to identify a random quadrat
location in this plot. Use a 1m X
1m quadrat for this exercise. In
this quadrat, determine plant species composition using both the Braun-Blanquet
and count methods. Remember to
identify one member of your group who will consistently identify the B-B codes
all day. Within the quadrat, be sure to measure water depth, soil depth, and any
other environmental variables that you think are important (remember your
hypotheses!).
2.
A point-quarter sampling “anchor post” has been established in the
Hennington Pond wetlands. Using the random numbers table on p. 246 of your lab
manual, identify a compass heading for your first sampling (if the number from
the table is ≤360, this is your heading; if not, then subtract 360 from it
until you have a value ≤360). Use
the last digit of the next random number in that row to determine your distance.
Measure this distance off using a Keson tape and following your compass
heading. At the end of this
distance, place a 1m X 1m quadrat and determine plant species composition using
both the Braun-Blanquet and count methods.
Remember to identify one member of your group who will consistently
identify the B-B codes all day. Within the quadrat, be sure to measure water
depth, soil depth, and any other environmental variables that you think are
important (remember your hypotheses!).
3.
A cross-wetland transect has been identified for you.
First, measure the total length of the transect using a Keson tape. Now, using the random numbers table on p.246 of your lab
manual, identify two distances from one end of your transect to be sampled.
Use the last 2 digits of the number for these, in meters, and if the
number is too large, continue across the row to the next random number. At the
first of these distances along your transect, place a 1m X 1m quadrat and
determine plant species composition using the Braun-Blanquet method.
Remember to identify one member of your group who will consistently
identify the B-B codes all day. At
the other distance location, place a 1m X 1m quadrats and determine plant
species composition using the count method.
Within each quadrat, be sure to measure water depth, soil depth, and any
other environmental variables that you think are important (remember your
hypotheses!).
4.
Plant species biomass will be sampled three different ways—and with
varying degrees of destructiveness. In
the area set aside for biomass sampling, randomly locate a 25cm X 25cm quadrat
(see #1 for how to do this). Within
this quadrat: 1) sample biomass
nondestructively by counting the number of individuals of each species then
haphazardly selecting 10 individuals of each species and measuring their height
with a meter stick. Your haphazard
selection of individuals to measure should encompass the entire size range you
observe in your quadrat. Thus,
height is your surrogate for biomass. 2)
now haphazardly select 10 individuals of each species and clip them at the soil
level. Measure their length and
record it. Tag each individual with
labelling tape and return it to the lab to be dried and weighed (making sure you
can later identify the height and weight of each separate individual plant).
You now have a haphazardly selected subsample of your population on which
you can get actual weights, then extrapolate this weight to your plant counts.
3) Now completely harvest
the plants in your quadrat and place all of the clipped plants carefully into a
garbage bag. Mark the bag to
identify where you harvested it, and return it to the lab to be dried and
weighed. This, of course, will give
you actual total biomass. Within
your quadrat, be sure to measure water depth, soil depth, and any other
environmental variables that you think are important (remember your
hypotheses!).
5.
Hand in all of your group’s field notes to your TA at the end of the
lab. She/he will combine them with
those from the other groups and return a compiled dataset to you next week (this
is an excellent reason to take clear and copious field notes!).