|It is important that the vegetation surrounding each trap is
recorded in a manner which allows distance weighted abundance to be calculated
for each plant taxon. It is recommended that this is done in two stages, one,
in the field and the second using digitised maps, air photos or forest
|Pollen deposited in the traps has its origin in sources which
may be at a whole range of distances. However, modelling has demonstrated that
the pollen source area can be divided into two, the relevant source area
(within which different mosaics of vegetation communities are separately
reflected in the pollen assemblage) and the area beyond this, from which the
pollen signal is homogenous (whatever the mosaic of vegetation communities).
This latter can be classed as background pollen (Sugita 1994, Davis 2000).
For this reason it is necessary to map vegetation out to several hundred metres
(even kilometres) from the trap but the degree of detail of the mapping needs
to be highest closest to the trap.
|We suggest three scale categories:
- Within 10.5 m of the trap. Within this area it will be primarily the
herbaceous vegetation which is recorded and the plants will be identified to
species. For this mapping we recommend the walking in circles method
- For the area between 10.5 and 500 m from the trap the main focus will be
on the abundance and distribution of the trees, while the herbaceous and
shrub vegetation will be mapped as vegetation units for which, as far as
possible, the average species composition and abundance is known. Depending
upon availability of data and the nature of the trapping locality, these
vegetation data may be obtained from existing forest inventories or remote
sensing of air photos. In some instances it may be most practical to map this
intermediate area using the Bitterlich method described below.
- For the area from 500 m out to 1 - 2km it is significant to know the
patchiness of the vegetation, the relative distribution of forested and
unforested land and, where possible, the species composition of distinguishable
vegetation units. Such information may be obtained from forest inventories,
remote sensing of air photos or basic topographical maps, depending upon
Recording vegetation in the field by walking in circles
The mapping method described here has been developed primarily by the
POLLANDCAL (Pollen Land-use
Calibration) group and we are grateful to them for inspiring discussions about pollen
dispersal and for permission to adapt their mapping strategy for PMP.
A series of concentric rings are considered around each pollen trap. The innermost
of these is a circle, centred on the trap with a radius of 50 cm. Beyond this circle,
rings of 1 m diameter are considered out to a distance of 6.5 m from the trap. Beyond
this the width of the ring is increased to 2 m, out to a distance of 10.5 m. This
gives an inner circle and 8 surrounding concentric rings (Figure 1). These are
located in the field using a series of wooden stakes and a rope, marked off at 0.5m
and then in 1 m intervals. The rope is anchored at the trap and the person making the
analysis literally walks in circles with it around the trap, recording the
percentage cover of each species in each individual concentric ring, on a pre-prepared
form (Figure 2).
Figure 1: Plan for vegetation analyses to give distance
weighted plant abundance.
The innermost circle may be used to facilitate estimation of plant coverage
during a vegetation survey using the walking in circles approach (Figure
3). Make a ring or hoop in a light material e.g. plastic or metal, with a radius
of 0.5 m. Use coloured tape to mark percentage sectors around the circle. When
walking in circles wind the walking rope around the centre pole (cp).
Let one end of the rope remain fixed, aligned to the north, out until 10 m and
the other end moveable around the circle. The two rope ends allow you to divide
your circle into cake slices of various percentage size. This enables
you to train your perception for percentage coverage in a circle before starting
the actual survey. This is particularly important each time you move out to a
circle with larger radius.
Figure 2: Vegetation record form.
Bearing in mind the pollen taxonomic resolution, grasses and sedges may be
recorded as Gramineae and Cyperaceae respectively and not identified to species.
Note that with overlapping vegetation the total coverage in one ring may exceed
100%. Mosses/rocks/bare ground should also be given a percentage cover value.
The position (compass orientation and distance) of individual trees occurring
within the concentric rings is also marked on a paper copy cf. Figure 1. This
field method has been developed by Anna Broström in consultation with
Shinya Sugita. See also Broström 2002.
Figure 3: Vegetation analysis of the innermost circle when using
the walking in circles approach.
The Bitterlich method of estimating tree abundance
The Bitterlich method provides an easy, fast, simple and inexpensive way of
estimating tree abundance as basal area per hectare. With the use of an
angle-gauge (Bitterlich stick see Figure 4) all trees that are larger in diameter
than a specified angle are counted in a circle from a central sampling point. The
angle is set by the configuration of the Bitterlich stick. For simplcity using
a stick of 1 m length with a 2 cm wide crosspiece made of cardboard, plastic
or metal is suggested. The crosspiece is mounted to one end of the stick while
a notch or peephole can be fixed to the other side. When using a round stick
the notch may not be necessary. The trees should be measured at breast height
and those that are seen as wide as the crosspiece may be counted as half.
If a Bitterlich stick with the above suggested configuration is used the
number of trees counted from the sample point is a direct estimate of abundance
as basal area per hectare (m2 * ha-1). Because this way of estimating tree
abundance is relatively quick it is possible to survey larger areas around the
pollen trap. In order to later distance weight the abundance of different trees
it is important to record the positions at which the abundance was estimated.
Two ways are suggested here, but different approaches may be followed.
Figure 4: Bitterlich stick for estimating tree abundance. The stick is
held to the eye and pointed horizontally with the crosspiece end to each tree
surrounding the sample point. If the tree appears wider than the crosspiece it
is counted otherwise it is excluded.
Figure 5: Suggested format for a table containing the results of
estimating tree abundance using a hand held GPS. UTM coordinates should be
given to 1 metre; the UTM zone needs to be indicated.
In both cases the exact sample design should be adopted to the specific situation.
If the pollen trap site is in a forest opening the first ring of sampling points
should be arranged near the forest edge. If the pollen trap is positioned more or
less inside the forest, the first estimate should be made at the position of the
pollen trap. The size of the opening should be estimated and recorded separately.
- A hand held GPS can be used to record the positions at which the count was
conducted. This way the surveyor can move around freely and a large number of
points can be used. Sampling points should be more frequent closer to the
pollen trap and a very homogenous forest may be covered with a lower amount of
points than a patchy forest. The coordinates can later be saved in a table as
UTM coordinates and combined with the abundance of the different trees in m2 *
ha-1 (Figure 5).
If no hand-held GPS is available the position of sampling points can be
recorded with a compass and some means of estimating distance (e.g. measuring
tape, counting steps, topographical map). Along the compass directions sampling
points can be set up at increasing intervals (Figure 6). At or near these points
the tree abundance can be estimated a few times and averaged. The results
should be presented in a table with the direction and distance from the trap as
coordinates (Figure 7).
Figure 6: Suggested sampling design for estimating tree abundance around
a pollen trap in a forest opening of about 100 metre in diameter.
The description of the Bitterlich method of estimating tree abundance is largely
based on the relevant chapters in the text book Aims and Methods of Vegetation
Ecology by Mueller-Dombois, and Ellenberg (1974). Jackson and Kearsley (1998)
make use of the method and present another sampling setup that enables the
presentation of the sampling points in a table format.
Figure 7: Suggested format for a table containing the results of
estimating tree abundance when the sapling points are described by direction
and distance measurements.
Vegetation mapping by remote sensing of digitised air photographs (ground
resolution of 1m)
Precise details of this will be provided at a later date.
Broström, A. 2002. Estimating source area of pollen and pollen productivity
in the cultural landscapes of southern Sweden - developing a palynological tool
for quantifying past plant cover. Doctoral Thesis, Lund University, Lund.
Davis, M.B. 2000. Palynology after Y2K - understanding the source area of
pollen in sediments. Annu. Rev. Earth and Planet Sciences 28:1-18.
Sugita, S. 1994. Pollen representation of vegetation in Quaternary
sediments: Theory and method in patchy vegetation. Journal of Ecology 82:881-897.
Mueller-Dombois, D. and Ellenberg, H. 1974. Aims and Methods of Vegetation
Ecology. J. Wiley and Sons.
Jackson, S.T. and Kearsley J.B. 1998. Quantitative representation of
local forest composition in forest-floor pollen assemblages. Journal of Ecology