Indicator assessment
This indicator presents the change in plant
species richness in survey plots across Great Britain between 1990
and 2007 for a range of widely occurring habitats. The results from
seven habitat types are presented, grouped into three measures for
the assessment.
Within arable and horticultural land there has
been increase in plant species richness both in the longer term
(1990 – 2007) and shorter term (1998 – 2007).
In woodlands and grasslands, plant diversity
has declined in both the long and shorter term. The shorter term
decline is significant in neutral grassland habitats but not in
woodland or improved grassland habitats (i.e. the observed change
may be due to random fluctuations rather than a genuine
change).
In boundary habitats boundaries plant
diversity has also declined significantly in both the long and
shorter term.
Description of trends
Within arable land, plant diversity increased
to 12% above the 1990 baseline by 1998 and 45% above the baseline
by 2007. The increase between 1998 and 2007 was larger than the
increase between 1990 to 1998.
Within broadleaved, mixed and yew woodlands,
plant species richness fell between 1990 and 1998 and between 1998
and 2007, although the decrease was only significant between 1990
and 2007. Within improved grasslands there was a similar decrease
between 1990 and 1998 and between 1998 and 2007, although again it
was only significant between 1990 and 2007.
In the smaller, targeted neutral grassland
plots, species richness fell significantly between 1990, 1998 and
2007.
In boundary habitats (hedgerow ground flora,
field boundaries and streamsides), plant diversity also fell
significantly between 1990, 1998 and 2007.
Species richness is presented as an index in
the indicator so that the percentage change between the years in
plots of different size can be compared. Table 2.1 shows actual
species richness in each habitat along with information on the type
and size of the survey plots.
Table 2.1. Plant species richness in Countryside Survey
vegetation plots in Great Britain, 1990-1998
|
Measure
|
Broad Habitat
|
Mean no. of
species per plot
1990
|
Mean no. of
species per plot
1998
|
Mean no. of
species per plot
2007
|
Is change
significant 1990-2007
|
Is change
significant 1998-2007
|
Countryside Survey
plot type
|
|
Arable land
|
Arable and horticulture
|
7.1
|
7.9
|
10.3
|
Yes
|
Yes
|
Arable and Horticulture Broad Habitat, Main
Plots 14x14m
|
|
Woodlandand
Grassland
|
Broadleaf woodland
|
22.6
|
21.3
|
20.9
|
Yes
|
No
|
Broadleaf. Mixed, and Yew Woodland, Broad
Habitat, Main Plots 14x14m
|
|
Improved grassland
|
15.0
|
14.7
|
14.3
|
Yes
|
No
|
Improved Grassland, Broad Habitat, Main Plots
14x14m
|
|
Neutral grassland
|
15.8
|
14.3
|
12.9
|
Yes
|
Yes
|
Neutral Grassland Broad Habitat, Targeted
Plots 2x2m
|
|
Boundary habitats
|
Hedgerows (ground flora)
|
11.0
|
11.0
|
10.4
|
Yes
|
Yes
|
All Broad Habitats, Hedgerow Plots, 1x10m
|
|
Field boundaries
|
14.9
|
14.4
|
14.0
|
Yes
|
Yes
|
All Broad Habitats, Field Boundaries,
1x10m
|
|
Streamsides
|
19.7
|
18.6
|
17.2
|
Yes
|
Yes
|
Rivers and Streams Broad Habitat, Streamside
Plots, 1x10m
|
Relevance
Today’s countryside has been shaped and
maintained largely by agriculture. Wild plants in agricultural
fields and field boundaries provide important food sources and
cover for farmland birds and other species which have also declined
over the same period. For this reason, hedgerows and arable field
margins are Priority Habitats in the UK Biodiversity Action
Plan.
Neutral grassland is a semi-natural habitat
that was once common in lowland Britain but has declined
dramatically in extent since the 1950s. Table 2 shows that neutral
grassland has one of the higher values for plant diversity despite
having the smallest plot size. It is because of this diversity, the
scarcity of the habitat and its associated fauna that the best
examples are identified as Lowland Meadow Priority Habitats in the
UK Biodiversity Action Plan.
The woodland index records plants on the
woodland floor – the ground flora. Woodland ground flora such as
bluebells (Hyacinthoides non-scripta ), wood
anemones(Anemone nemorosa) and wild garlic
(Allium ursinum) are aspects of woodland biodiversity that
are highly appreciated by the public.
The vegetation on the banks of small rivers, streams and ditches
provides an important habitat for small mammals, birds and
invertebrates throughout the countryside. Such streamsides also
provide a relatively undisturbed refuge for plants which were
formerly much more extensive in unimproved meadows and
wetlands.
Background
The Countryside Survey includes a random
sample of vegetation plots located in arable and horticultural
fields, agricultural grasslands, woodlands and along boundary
habitats in Great Britain. There are no equivalent data for
Northern Ireland.
The indicator compares species richness per
plot for the same plots surveyed in 1990, 1998 and 2007. For each
broad habitat type, the data are converted to an index (on a
scale of 0-100) to compensate for the difference in plot size
between habitats.
As a result of agricultural intensification
(use of herbicides, artificial fertilizers and cropping and land
management practices) over many years arable fields and improved
grassland already had low plant diversity in 1990. There is some
evidence that arable set-aside schemes in England contributed to a
slight increase in diversity by 2007.
Supplementary data from the Botanical Society of the British
Isles
Countryside survey provides data from across
Great Britain on changes in the extent and condition of different
habitats. However, because it is a sample-based survey of the whole
country, it tends to record only widespread plant species. Further
data on a wider range of species are available from species records
collected by the Botanical Society of the British Isles (BSBI). The
BSBI compared the distribution of species found in Great Britain in
two systematic surveys completed in 1987-88 and 2003-04. These
surveys recorded plant species present in a grid of 2 km x 2
km plots (tetrads).
The change in extent between the two dates can
be calculated for 860 species, many of which are typically
associated with semi-natural habitats. To combine these data and
provide a measure of change for groups of species associated with
different habitats, the change values for the individual species
are weighted to account for their relative abundance. The weighted
statistics are then combined to give a ‘change statistic’ for each
habitat. The change statistic is a measure of the relative change
in the geographical extent of a plant species. It does not
represent the number of tetrads gained or lost between the years,
because of the weighting applied before combining individual change
values (it more closely represents the degree of loss in tetrads at
the edge of the range of the species). A positive figure indicates
an increase in extent, a negative figure indicates a reduction. The
higher the figure, the greater the change in extent at the edge of
the range of component plants. Further details on the method are
given in Braithwaite et al. (2006).
Table 2.2 shows the mean change statistic for
plants associated with a range of artificial and semi-natural
habitats. This shows similar results to the main indicator, with an
increase in plants associated with agricultural land and a decrease
in species of woodland and grassland. The figures also suggest this
decline extends to upland habitats. The method does not lend itself
to an assessment of change in boundary and improved grassland
habitats.
The average change statistic for individual
species show much larger changes than the habitat groupings, for
instance, within neutral grassland species, wild carrot (Daucus
carota) has a change statistic of -20 and meadow cranesbill
(Geranium pratense) has a change statistic of +22.
Table 2.2. Change in plant species associated with selected
habitats from BSBI surveys conducted in 1987-88 and 2003-04
|
|
Broadleaf woodland
|
Arable and horticultural
|
Neutral grassland
|
Calcareous grassland
|
Dwarf shrub heath
|
Montane habitats
|
Built-up areas and
gardens
|
|
Mean change statistic
|
-2
|
+7
|
0
|
-6
|
-5
|
-8
|
+23
|
|
Number of species
|
116
|
82
|
79
|
102
|
39
|
27
|
53
|
References
Braithwaite M E, Ellis, R W and Preston C D.
The British Flora 1987-2004 2006, Change in the British Flora
1987-2004. Botanical Society of the British Isles,
London