河合塾】第３回全統記述模試 ※ネタバレ２
A weed is any plant that is growing where it is not wanted.
Unfortunately for farmers, weeds flourish quickly in freshly cultivated
areas and compete with crops for water, sunlight, and nutrients.
In addition, they are difficult to get rid of and their seeds,
which remain dormant for many years, can spread over long distances.
So why do weeds exist? Before answering this question,
we have to consider where weeds lived before humans began cultivating the ground.
Towards the end of the last ice age in Britain, about 12,000 years ago,
there was a time when the glacial ice was disappearing.
This left large areas of bare, open, treeless soils.
Pollen and seed fossils show that many plants now called weeds were present at the time.
They must have been growing on nutrient-rich, open soils left by the melting
glaciers and permanent ice. Such soils were probably quite similar to the
cultivated land they now occupy.
By about 10,000 years ago, Britain was invaded by trees and soon most of the
country was covered in forest. This, of course, meant the end of the large areas
of ideal habitats for weeds. So where did all the weeds go between then and the
reopening of the land by human agriculture? For about 5,000 years, they must have
survived in the few treeless spaces left among the woodlands ― places like sea-shores,
dried-up lakes, cliffs areas of landslip, treeless mountaintops, and so on.
Most of these possible site are small and soon disappeared.
Open soils caused by landslips, uprooted trees, drought or fire are quickly overgrown
or re-flooded and then no longer offer opportunity for colonization.
The weeds would have to invade and grow quickly in the available space so that they
could flower and set seed before the gap closed. The seed would need to be widely dispersed
and able to remain dormant for long periods so that it could take advantage of the next
landslip or bare river bank.
Thus, for many thousands of years, these weed species grew in situations where
the conditions were less than ideal. Then along came humans who destroyed the
forest and cultivated the land. By doing this, humans provided the weed species
with large areas to colonize. In other words, ironically, we have allowed plants
which were disappearing from the natural environment to flourish again.
Unfortunately for farmers, weeds flourish quickly in freshly cultivated
areas and compete with crops for water, sunlight, and nutrients.
In addition, they are difficult to get rid of and their seeds,
which remain dormant for many years, can spread over long distances.
So why do weeds exist? Before answering this question,
we have to consider where weeds lived before humans began cultivating the ground.
Towards the end of the last ice age in Britain, about 12,000 years ago,
there was a time when the glacial ice was disappearing.
This left large areas of bare, open, treeless soils.
Pollen and seed fossils show that many plants now called weeds were present at the time.
They must have been growing on nutrient-rich, open soils left by the melting
glaciers and permanent ice. Such soils were probably quite similar to the
cultivated land they now occupy.
By about 10,000 years ago, Britain was invaded by trees and soon most of the
country was covered in forest. This, of course, meant the end of the large areas
of ideal habitats for weeds. So where did all the weeds go between then and the
reopening of the land by human agriculture? For about 5,000 years, they must have
survived in the few treeless spaces left among the woodlands ― places like sea-shores,
dried-up lakes, cliffs areas of landslip, treeless mountaintops, and so on.
Most of these possible site are small and soon disappeared.
Open soils caused by landslips, uprooted trees, drought or fire are quickly overgrown
or re-flooded and then no longer offer opportunity for colonization.
The weeds would have to invade and grow quickly in the available space so that they
could flower and set seed before the gap closed. The seed would need to be widely dispersed
and able to remain dormant for long periods so that it could take advantage of the next
landslip or bare river bank.
Thus, for many thousands of years, these weed species grew in situations where
the conditions were less than ideal. Then along came humans who destroyed the
forest and cultivated the land. By doing this, humans provided the weed species
with large areas to colonize. In other words, ironically, we have allowed plants
which were disappearing from the natural environment to flourish again.
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