large herbivores, trees and flowers: an Irish and Scottish perspective 🐂🌳🌼(thread, a bit detailed).
outside of cities, our surroundings are massively shaped by the actions of large herbivores - cattle, horses, sheep and deer - alongside our efforts to manage or exploit them
outside of cities, our surroundings are massively shaped by the actions of large herbivores - cattle, horses, sheep and deer - alongside our efforts to manage or exploit them
in the lowlands, our efforts to exploit cattle primarily determines how the landscape looks (intensively managed grass fields), except in surviving woods, wetlands and meadows.
in the uplands the actions of the herbivores themselves are more important (the focus of this thread)
in the uplands the actions of the herbivores themselves are more important (the focus of this thread)
large herbivores mainly influence vegetation by feeding. when they eat trees and other woody plants we call this browsing, and when they eat grasses, wildflowers and other non-woody plants we call this grazing.
the rate of browsing/grazing is how much they eat over time
the rate of browsing/grazing is how much they eat over time
rate is one of the key parameters of browsing/grazing.
eg. if the browsing rate matches or exceeds the rate of tree/shrub growth, new trees/shrubs can't establish and those within reach become stunted. if this continues for long enough any tree cover present will be lost
eg. if the browsing rate matches or exceeds the rate of tree/shrub growth, new trees/shrubs can't establish and those within reach become stunted. if this continues for long enough any tree cover present will be lost
selectivity is another. some herbivores prefer to eat certain plants (they're tastier or more nutritious), and so browsing/grazing rates can vary between plant species. this is part of the reason you get fields like this- sheep prefer eating the grasses and herbs over the rushes
different combinations of these parameters create different vegetation over time:
1) low browsing rate -> tends to woodland with many tree and shrub species
2) medium browsing rate, high selectivity -> tends to woodland dominated by the least tasty trees and shrubs
1) low browsing rate -> tends to woodland with many tree and shrub species
2) medium browsing rate, high selectivity -> tends to woodland dominated by the least tasty trees and shrubs
3) high browsing rate -> tends to open vegetation/loss of woody plants
4) low grazing rate -> ground covered in tall herbs/shrubs
5) med grazing rate, low selectivity - ground with high % wildflowers
6) med grazing rate, high selectivity - ground with low % wildflowers
4) low grazing rate -> ground covered in tall herbs/shrubs
5) med grazing rate, low selectivity - ground with high % wildflowers
6) med grazing rate, high selectivity - ground with low % wildflowers
7) high grazing rate, low selectivity - ground with high % wildflowers, vegetation short
8) high grazing rate, high selectivity - ground with low/no wildflowers, vegetation short
8) high grazing rate, high selectivity - ground with low/no wildflowers, vegetation short
different large herbivores browse and graze in different ways: cattle browse and graze less selectively, horses mostly graze, sheep and deer browse and graze selectively, goats mostly browse
most uplands in Ireland and Scotland are grazed year round by significant numbers of sheep or deer, so you get scenario 3 + 6/8 -> no trees and few wildflowers. this is the worst possible outcome for most wildlife, which relies on diverse woodland, scrub or flower rich pasture
you also get a fair bit of scenario 2 + 6 (low diversity woodland) inside deer fences. these start off as scenario 1 + 4 (diverse woodland) but deer get inside and change the course of vegetation development before long
how browsing/grazing rates and selectivity vary through time can also be key to understanding vegetation.
eg. evergreen trees/shrubs are relatively more nutritious in winter, so get targeted; most perennial herbs retreat underground in winter, so can't be selectively grazed
eg. evergreen trees/shrubs are relatively more nutritious in winter, so get targeted; most perennial herbs retreat underground in winter, so can't be selectively grazed
browsing/grazing rates can also vary across landscapes:
-if herbivore numbers are low, they can concentrate activity in certain areas, creating a patchwork of vegetation types
-some areas may be inaccessible to certain herbivores (eg. boulderfields and ravines to cattle/horses)
-if herbivore numbers are low, they can concentrate activity in certain areas, creating a patchwork of vegetation types
-some areas may be inaccessible to certain herbivores (eg. boulderfields and ravines to cattle/horses)
-and in natural ecosystems, the presence of predators influences where and when browsing/grazing takes place.
our present upland landscapes, with significant sheep/deer numbers, usually only retain trees and certain flowers on cliffs and ledges. these can be threatened by goats
our present upland landscapes, with significant sheep/deer numbers, usually only retain trees and certain flowers on cliffs and ledges. these can be threatened by goats
the key to restoring more wildlife to the uplands is better herbivore management.
want woodland?- reduce the browsing rate.
want wildflowers?- reduce selective grazing, or only graze in winter.
want woodland?- reduce the browsing rate.
want wildflowers?- reduce selective grazing, or only graze in winter.
note: soil type, hydrology and available seed/propagule sources also determine which kinds of plants can grow where- but the principles of more trees with low browsing and more wildflowers with less selective grazing generally hold on non-intensively managed land
