Appalachian balds - mountain top grassland ecosystems that are anomalous under current climate regimes. They cause has been a long debate. Some have been created or modified by humans, but he argues that many of these have a megafaunal origin.
Many of the plants found there are Pleistocene relics (e.g. Greenland stitchwort). Lots of endemic plants also that are found only in these ecosystems. Many of these are light demanding plants that do not survive under trees - a botanical signature of bald antiquity
Variety of ideas to cause of balds (climate, insect attack, soils, fire) but none of these factors are different on other surrounding peaks. Human causes are also unlikely given their antiquity
Now there is a lot of woody encroachment of these bales.
Additional case studies of Oregon Coast Range Balds, Poloninas (or poloninys) in East Carpathians.
There are several features in common: they are sub-alpine, grass dominated communities, richly diverse shade intolerant communities, south of glacial maximum extent, and all had history of pastoral grazing after human settlement.
Some work shows that these sites corresponding to a climate-imposed treeline during the peak ice age. This is the origin proposed. But then he argues that megafaunal browsing maintained these grasslands after their origination
Owen-Smith’s “keystone megaherbivirore” hypothesis. Abundant evidence of effects of contemporary herbivores today in altering vegetation structure. Elephants breaking trees.
How were the balds maintained after megafaunal extinction? There was a chain of herbivores. The successors were bison, elk, deer that maintained these until they were taken out by European hunters, then maintained by pastoral grazing. Today the only bales persisting are those actively managed. They are missing their natural disturbance regime of grazing animals.
These balds represent ghost ecosystems; remnants of larger open expanses in a disturbance-maintained non-equilibrium state.
Weigl and Knowles Biological Reviews summarises this argument - is available online.
Frans Vera: why are the successors of a megafauna not able to keep areas open. You don’t need elephants to keep out a tree, just a deer to take out the seedlings.
Many of the plants found there are Pleistocene relics (e.g. Greenland stitchwort). Lots of endemic plants also that are found only in these ecosystems. Many of these are light demanding plants that do not survive under trees - a botanical signature of bald antiquity
Variety of ideas to cause of balds (climate, insect attack, soils, fire) but none of these factors are different on other surrounding peaks. Human causes are also unlikely given their antiquity
Now there is a lot of woody encroachment of these bales.
Additional case studies of Oregon Coast Range Balds, Poloninas (or poloninys) in East Carpathians.
There are several features in common: they are sub-alpine, grass dominated communities, richly diverse shade intolerant communities, south of glacial maximum extent, and all had history of pastoral grazing after human settlement.
Some work shows that these sites corresponding to a climate-imposed treeline during the peak ice age. This is the origin proposed. But then he argues that megafaunal browsing maintained these grasslands after their origination
Owen-Smith’s “keystone megaherbivirore” hypothesis. Abundant evidence of effects of contemporary herbivores today in altering vegetation structure. Elephants breaking trees.
How were the balds maintained after megafaunal extinction? There was a chain of herbivores. The successors were bison, elk, deer that maintained these until they were taken out by European hunters, then maintained by pastoral grazing. Today the only bales persisting are those actively managed. They are missing their natural disturbance regime of grazing animals.
These balds represent ghost ecosystems; remnants of larger open expanses in a disturbance-maintained non-equilibrium state.
Weigl and Knowles Biological Reviews summarises this argument - is available online.
Frans Vera: why are the successors of a megafauna not able to keep areas open. You don’t need elephants to keep out a tree, just a deer to take out the seedlings.