http://www.euronet.nl/users/mbleeker/diemer_e.html -- Lawrence F. London, Jr. - Venaura Farm - Chapel Hill, NC, USA mailto:london@sunSITE.unc.edu http://sunSITE.unc.edu/london mailto:london@mercury.interpath.net http://www.interpath.net/~london Piedmont Online http://sunSITE.unc.edu/piedmont piedmont@sunSITE.unc.eduTitle: The Diemerzeedijk
Introduction | Navigation Centre | |||
History | ||||
Dioxin | Botany Education | |||
Vegetation types | ||||
The "Savanna" | Species list | |||
Epilog | Flowering in July/Aug |
Unless otherwise stated, the below links are photos (JPG, ± 35 Kb)
Imagine: a savanna. Hills, with scattered bushes and also some larger thickets. The shrubs are mostly Willows / [R] and Elder (Sambucus) / [R], plus large patches of Bramble (Rubus fruticosus) / [R]. In high summer it is mainly Buddleja / [R] that gets all the attention - from butterflies mainly. Between those bushes is not so much grassland, but rather all kinds of flowering herbs. In July and the first half of August they are at their best, displaying wave after wave of bright colours. The opening act is done by the modest Sedum acre (Biting Stonecrop) / [R], soon followed by the many tall herbs, like Brassica nigra (Black Mustard) / [R] and Chamerion angustifolium (Rosebay Willowherb) / [R]. All this time the star performer was quietly preparing for the main act: Dipsacus fullonum (Wild Teasel) / [R] forms whole 'forests' that turn mauve.
And there are many more colourful plants in this landscape: here's a complete species list, or look at this flowering list for the months July and August. It's exemplary for other such ruderal vegetations in this part of Europe as well I suppose. More about the flora further down.
Animal life is not bad either. Lots and lots of rabbits are all around. In winter they eat the bark off many shrubs, and those shrubs that get 'ringed' this way will die. The whole aspect of the landscape might be largely determined by the rabbits. But foremost they are the basis of the ecological pyramid: there are 3 couples of foxes, I've seen weasels and there's even a Goshawk (Accipiter gentilis) nesting and fouraging here. Talking about birds: many small song birds and plenty waterfowl, enough to please birdwatchers from all around. The Bearded Tit (Panurus biarmicus)* is a specialty here, and you can see Cormorants (Phalacrocorax carbo)* resting, while drying their feathers with spreaded wings. Going down the taxonomical hierarchy: there's a population of ring-snakes, and in spring you'll hear the frog's concerts. Many insects as well: dragon-flies, bumble bees and butterflies to mention just a few groups.
* Both sound files courtesy of ETI (CD-ROM "Birds of Europe") |
The zee-dijk part of the name Diemerzeedijk means 'sea-dike'. And yes, this dike once protected us from a real sea, called the Zuiderzee, or Southern Sea. In 1932 a large dam was built between the provincies North-Holland and Frysland, which closed this sea off from the North Sea (the Afsluitdijk). The water gradually became sweet, and the coastral vegetation also changed, but there are still quite a few relicts I believe.
Human interference has been the main theme since then. On the land-side a canal was dug out, connecting Amsterdam with the river Rhine. So there is water on both sides of the dike now, and it's only accessable from either Amsterdam, or the other end about 5 km south-east (as the Cormorant flies). The canal was dug right through two inland waters (one of them called the Diem), so it has always been a real wetland / [R].
During the 'Rebuilding Period' after the war, a large part of this strip of land became a dump for industrial waste. This explains the hills I mentioned above: big piles of rubble, but now covered up with a sedimentary layer and a rich vegetation, because the dump has not been used as such anymore for about 25 years. Sometimes however, the subterrain does emerge, and you might have holes in the ground giving access to real dungeons... At he coastline, if you can reach it cutting yourself a way through brambles, stinging nettles etc, you might find yourself on top of a real cliff, enjoying a beautiful view over the former sea, now a large lake (IJmeer). Apart from this 'survivalist' aspect, this dumpsite (about 2½ km long and on average 500 m wide) became a unique piece of nature, perhaps not so much for the rarity of the species, but just the whole layout, the fields of colourful blooming flowers and shrubs are just magnificent. However...
Dioxin is a dangerous poison, and was part of 'Agent Orange', the defoliant used in Vietnam. It is one of the most poisonous chemicals we know: 10 milligrams is enough to kill a human. Luckily it hardly ever occurs in such lethal concentrations: it is mostly an inadvertent and much diluted side-product. Prolonged exposure to very low concentrations can also be dangerous however. The first symptomes of a dioxin poisoning typically show a few weeks after the fact. They include a skin-rash (chlorine acne) and neurological problems, resulting in depression or apathy. In a further stage the liver and the thyroid gland may be affected, and the victim will loose weight. Dioxin interacts with DNA (the heriditary material), which may lead to cancer or reduced fertility... The rabbits on the Diemerzeedijk seem to have no problem here tho...
During the 70-s and 80-s, dioxin was more notorious in the form of air pollution. It may come free with refuse incineration, especially when certain synthetics are being burned. This may rain out again, perhaps in grassland where it might be eaten by cattle. This way it comes back to man, not so much in the meat, but rather in the milk. A mother may also pass it on to her child with brest feeding. However, this problem has been largely solved in Holland now, with regulations (norms) and smoke filters on incineration ovens. Pollution of the soil is a larger problem. It is virtually impossible to clean it up. In the Volgermeer it was attempted with a strain of bacteria that could break the stuff down. It was not very effective. For the Diemerzeedijk there was talk about heating the soil with large electrodes, thereby capturing the chemicals in a sort of glazing process. Too expensive I presume. The plan is now to just isolate the polluted area by covering it up with plastic foil, and put a 2 meter thick layer of clean soil on top of it. This way, the area would not be fit for housing: they want to build a new residential area right next to it (IJburg), and the Diemerzeedijk would become a park. At the expense of the current flora and fauna of course.
A small bright spot is perhaps, that dioxin is hardly or not being absorbed by plants. Personally I did taste some of the many fruits you can find here (bramble, apples, cherries, berries), but I would not eat much of them. And this remains of course anybody's own responsibility. The real danger is more in the soil itself: children might get it in the mouth with dirty hands.
The Dutch version of this text deals more with the hazards, in case you're actually going to visit this area. It is more of a guided (survival) tour.
Introduction | Navigation Centre | |||
History | ||||
Dioxin | Botany Education | |||
Vegetation types | ||||
The "Savanna" | Species list | |||
Epilog | Flowering in July/Aug |
Then there are the real marshes, mainly reedlands / [R]. Also very important for the birds, but again rather poor in plant species. Typha latifolia, the Bulrush is quite common here, and of course the Reed (Phragmites australis) / [R] itself. Looking down from the dike on these reedlands with small lakes between them, there's a lot to appreciate. It is in essence as Dutch as can be. And it has something for every season: in spring and autumn migrating waterfowl, in summer the marsh warblers and other singers. In September the reed starts to bloom, with beautiful dark purple plumes. Later in the season they die off, but the dead stalks remain upright, and keep on propagating the feathered seeds, right through winter, into next spring. And winter can be the most beautiful of all: imagine a little snow or glazed frost on the reed, a pale sun on it, preferably in contrejour... splendid! A little bit higher up the dike, but also rather wet, you can find Petasites hybridus (Butterbur) / [R]. It flowers in March, but has no leaves then. These come later, and in summer they reach giant proportions. Whole fields full of larger-than-life umbrellas: you can almost walk underneith them, and imagine you're in a tropical jungle. Very characteristic is also the Yellow Iris / [R], that blooms end May and June.
The flanks of the dike are in fact a gradient from the waterside to the dryer verges of the road on top. It is mostly a grassland vegetation, not much different from other road-sides and polders in Holland, except that it's left alone here. Heracleum spondylium (Hogweed) is quite common here, different kinds of Vicia (Vetch), and much more. A bit less common perhaps are Convolvulus arvensis (Bindweed) / [R] and kinds of Silene (Campion). And don't underestimate the common Thistle (Carduus crispus) / [R]: the flower-head is really beautiful and much appreciated by butterflies.
The fourth terrain type is a very recent one: the place where mud from the canal was dumped. This happened in 1994. Spring '95 it was a desert-like bare sandy plain. But the next summer it was already covered with a yellow jungle of Brassica nigra (Black Mustard) / [R]. There are many yellow Crucifers, and this one is recognizable by the fruits, that are pressed against the stem. That year, there was some work done in the area, something related to drainage, and a kind of 'natural' creecks were grinded out in the muddy/sandy soil. A whole new vegetation is starting to settle now in these gradients (wet/dry, sun/shade). Last autumn I counted 5 new species for the area, like Senecio inaequidens (Broom Ragwort), a recent invader from South Africa, by way of Belgium (it has been known in Belgium since the beginning of this century, but somehow it decided to wait with its invasion of Holland till the years 60 and 70). Another peculiar species here is Atriplex patula bracteata (Common Orache) with its large, a bit fleshy bracts. Short, it's very interesting to see this pioneer vegetation develop and reclaim the bare soil. A fast succession of vegetations rather. I wonder what this year will bring (if not bulldozers).
Let me just put forward some botanical arguments. Point is, I've never seen a vegetation like this. It is a climax of a ruderal vegetation (if that's not a contradiction in terminis), with elements, perhaps relicts, of a coastral (dune) vegetation, and species that have 'escaped' from cultivation. When you think of it, a sort of a mix, not unlike the cultural diversity of people in the nearby urban area's :-), anyway, it's quite a unique ecosystem, and beautiful, so one should think twice before destroying it. Although Dipsacus is a protected plant, and Verbascum nigrum is rare, it is not so much the individual species that make this area of interest, it is more the combination of them, the dynamics, also in relation to the poison in the ground. How is this vegetation evolving? Are species adapting? Are species of the genus Salix hybridising here? What's the long term effect of dioxin poisoning? These questions could be studied here. And to have such a beautiful piece of real rough and wild nature just near town, is a value on its own. Perhaps we could think of an alternative kind of recreational use instead of a park... Fishing, hunting, survival tours, botany and ornithology education, ...
Introduction | Navigation Centre | |||
History | ||||
Dioxin | Botany Education | |||
Vegetation types | ||||
The "Savanna" | Species list | |||
Epilog | Flowering in July/Aug |