In a previous blog entry I already hinted at a new species endangering rare and protected plants like orchids (but also feather grass and many more) especially on the hot lands of Lobau (the dry lands with poor soil - sandy, mostly limestone-rich earth with little nutrient value). Now here the hard facts.
As far as Lobau is concerned black locust (Robinie - Robinia pseudoacacia; native of Northern America) already is endangering the north-eastern hotlands of Lower Lobau; with the technics of 'ringing' the national park rangers try to fight the tree spreading into the hot lands. Black locusts are especially problematic as they enrichen the soil with nitrogen and thus change the character of the hot lands forewer: they are, after a while, no more poor soil, and the endangered species now growing there would vanish. These here are ringed black locusts, all of them now dead already:
Now if you think that this is cruel (because technically of course it is 'tree killing' - and this in a national park) then try the Darwinist viewpoint, the survival of the fittest: it would mean letting black locusts occupy whatever area they can which would lead to the extinction of many species here in Europe. Black locusts are extremely vital pioneer plants, they not only sow their seeds but also grow new shoots from dead tree's roots; therefore it would be no use to cut them, ringing them seems to be the only option to keep them at bay.
The really strange thing however is that the park foresters only did ring some of them; however, right behind these dead ringed trees there are a lot non-ringed ones, producing more seeds and root-shoots each year. I can't really see a strategy behind the ringing - probably they only recently tried out if it would work, and probably they'll expand it to other trees soon.
But apart from black locusts there's also another new species endagering this biotope: the tree of haven (Götterbaum - Ailanthus altissima), also a very energetic pioneer tree even though it is not (like black locusts) one enrichening the soil with nitrogen. It is a native of East Asia and especially China where it was and is cultivated for silkworm growing, and introduced a few hundred years ago here in and around Vienna to try and found a silk industry of our own (which failed, by the way, even though the tree of haven as well as the silkworm are now natives of our landscape - successful immigrants in the warmer regions of the Pannonian climate). With trees of haven ringing does not work quite as well as with black locusts - while with the latter this is a secure method to prevent root sprouts it is not so with the tree of heaven, they even grow new sprouts on the stem of the tree, just below the ring, as you can see here:
Admittedly, the hot lands always were kind of a 'temporary landscape': here in Europe we have our own pioneer trees - such as (especially here in Lobau) hawthorn, and many more. But the European pioneers grow much slower and take much longer to overgrow a hot land area; they give nature time to form another hot land elsewhere - at least in former times when the Danube river still was free to float in the swamplands and changed its course continually, with new dry lands with poor soil emerging.
So what do the national camp rangers to prevent hot lands from disappearing in Lobau, now that the Danube river is tamed? (That is, in areas where black locusts and tree of haven still are no problem - yet.) For once there are plans to again let the Danube float free in Lower Lobau (but not in Upper Lobau which is too much of a recreation area for the citizens to do that) when water levels are high, and let so nature take its course. And as this project still may take years before it could be realised there's another strategy for now - a simple one: sheep.
This is the orchis meadow in Upper Lobau where each year, at the beginning of summer when most hot land orchids aren't flowering any more, they let sheep graze. (Well, you can only see the fence; I'm sorry for that ... for some reason the sheep always stay in the truck standing a few metres outside the picture which works for a shed for them; I guess they don't like being photographed. Or probably they're just shy.) Sheep not only eat grass but also new sprouts of trees; thus they keep trees and bushes short, the hot lands are kept relatively free of tree growth.
Black locust and tree of haven are endangering the natural balance in this sensible biotope. The situation even is much worse in Hungary where the climate is even warmer and 'more Pannonian' than here in and around Vienna - and Pannonian climate is exactly what these two new species like (rather warm, and with no longer periods of strong winter frosts). There are also a great many dry areas in Hungary which are similar to the hot lands of Lobau. For me the ringing is fully justified and justifyable. I just love the hot lands; they must not die.
The strange thing really is that I got curious about this ringing only now - I already wondered about it last year but I didn't take the pains to find out more about it.
