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Quite often plants are seen as the background against which the more interesting
(animal) wildlife occurs.
After all, often, when we use the word 'habitat', we are actually using it as shorthand for
plant communities. So the habitat for the Marbled White is chalk or limestone grassland.
But, of, course, habitats consist of a mix of both animal and plant species - for a wasp
parasitic on the Marbled White, it's the animal component that its most important.
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So what I want to do is just try to put plants on a more equal footing with the animal
species of grassland. Because the relationship between plants and the environment is
the same as the relationship between animals and the environment.
They must exhibit adaptations and behaviours that allow them to:
- Secure nutrients and water.
- Avoid being predated.
- Reproduce successfully.
- Disperse to find new space to occupy.
Of course plants are at one major disadvantage when compared to most animals, in
that grown individuals are rooted to the spot. So plants have to have very particular
strategies to overcome this.
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So, let's step back and have some basic plant ecology.
Here's a model - the RSC triangle - which describes plant survival strategies.
In this respect, grazing can be considered as both a disturbance - which the
original approach considered it - but also a stress, in that it provides an ongoing
restriction on the ability of competitive plants to dominate.
So, a fast growing plant will find that it rapidly loses a large amount of material in
which it has invested a lot of material.
Plants associated with grazed grassland, therefore, tend to have growing points
close, at or below ground level, and to be able to spread laterally. This is part of
their ability to tolerate stress.
Stressing the vegetation can lead to increased diversity, as the ability of
individual species to grow, spread and compete is limited.
Of course, increase the grazing pressure sufficiently, and it becomes real
disturbance. Conservation practice has traditionally shied away from disturbance
in grassland as being damaging to the sward. And it is the case that continued
high grazing pressure can shift the balance so far towards the ruderal element of
the flora that there is a serious reduction in diversity.
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But it is also the case that many threatened grassland plants require repeated
disturbance for survival. For some, it is keeping a low, open sward which provides
reduced shade & competition for low-growing plants, but perhaps crucially also makes
for easier germination.
Some species, like Ground-pine and Basil-thyme (left), are grassland annuals, which
can only grow and flower if the ground is well disturbed - effectively dug over. Some of
these plants are associated with arable, but look most at home in grassland.
A few genuinely do best where grazing is really heavy. Hound's-tongue (right) is
unpalatable and a biennial, and often found in greatest profusion immediately around
rabbit warrens.
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Red Star-thistle (left) is another biennial. The first-year rosettes are flat to the ground to
avoid grazing, and are resistant to trampling. The second-year plants are astonishingly
tough and prickly and so it thrives where grazing pressure is so high that the
surrounding vegetation is kept very short with an abundance of bare ground.
And Small Fleabane (right) a once widespread but now very rare annual of grazed
commons and similar areas thrives best in what would be considered the very worst of
pasture management, with heavy grazing and substantial amounts of poaching.
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Far less extreme, so perhaps more instructive, is Meadow Clary.
Meadow Clary is a long-lived (30-40 years) perennial of grassland. It's listed as Near
Threatened as its distribution is fairly stable, but it still only has a population of maybe
8,000 individuals. At Ranscombe, we've been studying it as we have small population
on the edge of a wood. This population appeared to have been static for some while,
and this was a cause for concern, as an apparently healthy population can hold an
extinction debt – i.e. Plants may continue to flower, but, without any seedling
recruitment, there will be a gradual decline in population size as individual plants reach
the ends of their lives.
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We sought to remedy this by the simple exercise of creating bare ground where
seedlings might germinate. This took just a few hours of work in July, after the flowers
had set seed.
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It was a very successful exercise with more than 100 seedlings being produced in the
first year.
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By plotting the position of existing and new plants each year, we have been able to
follow the demographics of the population.
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This graph show the change in Meadow Clary life stages (from seedlings up to flowering
adults) recorded for all the plants present at Ranscombe. It is noticeable that this shows
that more than 2 years are needed for plants to grow to flowering size.
The non-flowering rosettes are resistant to grazing and trampling, so will survive and
grow even under fairly heavy grazing. However, any flower-heads are grazed off, and so
no recruitment can occur under such conditions.
This suggests that Meadow Clary would do best where there is heavy grazing, taking off
any flowers but producing lots of bare ground which will last into the following year,
followed by a year when grazing is relaxed and seed can be set.
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Meadow Clary is a plant where conservation efforts have struggled in the past, and I
think this may be because we tend to favour management systems which are effectively
the same each year.
However, grassland as a more natural habitat is likely to be more dynamic, going
through cycles of succession, so that species have adapted to exploit this. One of the
challenges of grassland conservation may be to try and establish this sort of dynamism
within it.
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Of course, having a dynamic grassland system does presuppose that plants can move
to new habitat.
The other major challenge is to understand how plants get around. One of the
noticeable things about the Meadow Clary work is that almost all seeds fell within about
a metre of the parent plant. And this kind of thing is true of most plants which don't have
seeds specifically designed to dance off through the air. Even tiny orchid seeds, which
are like dust, almost all fall within a short distance of the parent.
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How plants move about is still a mystery, but it is important to recognise that vectors
may be present for more species than we think. We have been managing the 23ha
Brockles Field at Ranscombe since 2010. It is former set-aside dating back to the late
1980s.
Plants like the Ox-eye Daisies in the photo, Marjoram, Red Clover and others have all
colonised the field naturally (despite all these having quite large seeds), and species are
still arriving.
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For example, An Eyebright species (left) arrived in some deliberately created bare
patches some 3 years after the patches were created, but once present, quickly spread,
while the first Cowslip (right) in the field was seen in 2015. It is notable that neither
species occurs anywhere else on the reserve, so how they arrived is a complete
mystery.
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Studies in Europe have shown that deer and boar are important vectors of open habitat
plants. This paper found 55 species on the feet and fur of 25 shot roe deer and nine wild
boar, and concluded that “hoofed game play a particular role in the dispersal of ruderal
and grassland species in the agricultural landscape of Central Europe.”
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Likewise, we have noted that the seed of Broad-leaved Cudweed at Ranscombe
appears to spread on the wheels of vehicles and the feet of people and/or wild animals.
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Plantlife’s Joe Costley has also published a paper on the colonisation of meadows at
our Joan's Hill reserve.
This showed that ten plant species colonised a relatively species-poor hay meadow in
an eleven year period, during which time animals and machinery moved between that
meadow and other more species-rich grassland on the same site.
However, some species remained limited to older fields: these include green-winged
orchid Anacamptis morio, common milkwort Polygala vulgaris, pepper-saxifrage Silaum
silaus, cowslip Primula veris, betony Stachys officinalis, lady’s bedstraw Galium verum
and dyer’s greenweed Genista tinctoria. Pepper-saxifrage, common milkwort and
betony are mainly confined to those fields on the farm where evidence suggests they
have been grassland for at least 88 years. Similarly, established colonies of greenwinged orchid and dyer’s greenweed are confined to those fields on the farm that we
believe could have been grassland for at least 170 years. This clearly suggests
differences in the ability of different plant species to spread through the landscape, with
implications for how we look to restore re recreate grasslands in the most natural way
possible.
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Clearly grazing means all sorts of different things to a wild plant – stress, disturbance,
germination opportunities, and a free lift to new places – and these are perhaps very
different to the way we see grazing impacting on vegetation.
Though how we go forward in the light of all this information is a challenge we have yet
to meet fully.
Costley, J. 2015. Meadow management increased plant species diversity in a speciespoor, neutral grassland in Herefordshire, UK. Conservation Evidence 12: 40-42 .
Heinken, T. & Raudnitschka, D. (2002) Do Wild Ungulates Contribute to the Dispersal of
Vascular Plants in Central European Forests by epizoochory? A Case Study in NE
Germany. Forstw. Cbl. 121: 179−194.
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