Expanding wilderness

 

 

 

 

 

 

 

Soon the well-managed woods, plantations, and fields began looking less well-managed. Wind-fallen trees were left where they fell, and draining ditches and field tracks were soon overgrown by herbs and bushes.

This description of the vegetation succession on the former arable land is for the major part based on surveys of the vegetation of the island, undertaken during the 1950s by Professor Knud Jessen (Jessen 1968), and by myself in 1991-92 (Halberg 1996), and in 2006 (Halberg 2006). These surveys are presented in figs. 4-6, at the bottom of this page.

The vegetation succession in the forests and plantations on the island is described by Dal & Fabricius (2013).

When you encounter names of localities in the text, see fig. 1.

 

 

 

 

 

 

As early as 1933, most of these species had been replaced by various grasses, e.g. Agrostis capillaris, Dactylis glomerata, and Holcus lanatus, together with Cirsium arvense, Rubus idaeus, and others.

The grass cover was slowly replaced by communities of taller plants, dominated by Chamaenerion angustifolium and Rubus idaeus, and, to a lesser extent, Cirsium arvense and Urtica dioica. After 1955, however, Chamaenerion quickly began to expel the other species. Aerial photographs show that many of the growths were circular, indicating spreading by subterraneous runners. This explosive spreading was also caused by the fact that Chamaenerion is very competitive. It is tall, and its withered foliage contains chemicals, which inhibit growth of other species. The rich soil on Vorsø was also beneficial to the species.

In 1962, the distribution of grassy areas and the Chamaenerion-Rubus community on the fields was about equal, namely 45% each, while young woods and bushes covered 10%.

Since then, young woods and shrubs have been steadily spreading, and today only small areas with grass cover, Chamaenerion-Rubus community, and meadows with tall perennials remain on Vestermark. During the 1980s, in the south-eastern part of this field, several grassy areas were taken over by Dryopteris filix-mas and a few Athyrium filix-femina, the former today covering large areas. The only remaining larger area with grass cover is found south of Vestre Remise, and it is obvious that grazing roe deer have delayed the succession.

 

 

 

 

 

 

 

Acer pseudoplatanus quickly took over most of this area, covering an area of c. 8 hectares (fig. 6). Initially, Fraxinus, Ulmus, Acer platanoides, and Abies alba took part in the competition, but only a few specimens of the former three were able to reach the crown layer.

During the 1990s, Dutch elm disease (see page Dutch elm disease on Vorsø) killed all larger Ulmus in the young wood on Østermark, but to this day, new specimens sprout constantly. Various shrubs formerly grew on the forest floor, including Rosa canina, Corylus avellana, Viburnum opulus, Crataegus laevigata and C. monogyna, and Sambucus nigra. Today, the forest floor here is very dark due to the dense foliage of Acer pseudoplatanus, and no bushes grow here, apart from Sambucus, which forms brushwood here and there, and a few Crataegus.

The grass cover soon disappeared from this young wood, and, since around 1980, the forest floor has been partly covered by dense growths of shadow-tolerant herbs, predominantly Circaea lutetiana, Geranium robertianum, and Geum urbanum. Near a former clay pit in the north-eastern corner of the field, Sanicula europaea and Brachypodium sylvaticum are numerous.

Other places on the island, formation of forest initially only took place near the edges of the old forests. Today, these young woods are dominated by Fraxinus and Acer pseudoplatanus, with species like Corylus, Salix caprea, and Crataegus laevigata in the bush layer.

In a small area of Østermark, between Østerskov and the road, a dense growth of Alnus glutinosa was established shortly after 1928, and by 1936 the trees were already 4 m tall. Later, Fraxinus invaded this area, and today almost all Alnus have disappeared.

During the 1970s and 1980s, huge thickets of Prunus spinosa, P. cerasifera, Rosa canina, Crataegus monogyna, Sambucus, and Salix cinerea were established many places on the old fields, often being so dense that they were impenetrable. In the same period, small groups of young trees were established here and there on the fields, dominated by Fraxinus and Acer pseudoplatanus, mixed with Ulmus, Quercus robur, Corylus, Salix caprea, and Betula pendula.

From the plantation Vestre Remise (see caption Swamp like in the 1700s below), Populus x canescens spread into the surrounding field by root shoots, forming a young wood, which, however, was soon severely damaged by breeding cormorants. Beneath this young wood, very dense Sambucus shrubs were formed. Humulus lupulus, which grew in Vestre Remise, soon spread to the surrounding areas of Vestermark, and today bushes in a larger area near the plantation are completely overgrown by this vigorous vine.

By 2006, on the old fields, young forest had almost completely replaced the former grassy areas, as well as the Chamaenerion-Rubus community, and shrubs were also slightly declining. The forest floor in these young woods was still quite open, and a large number of various herbs grew here, especially Circaea lutetiana, Geum urbanum, and Mercurialis perennis, besides many others, including Dryopteris filix-mas, D. dilatata, Allium ursinum, Galium aparine, Polygonatum multiflorum, Silene dioica, Geranium robertianum, and Ajuga reptans. In young woods near the northern coast, species like Anthriscus sylvestris, Sanicula, Polygonatum multiflorum, and Alliaria petiolata dominated.

During the 2010s, many of the thickets on the old fields, consisting of Prunus spinosa, P. cerasifera, Rosa canina, Crataegus monogyna, Sambucus, and Salix cinerea, broke down from old age, and in these areas, lots of Fraxinus and Acer pseudoplatanus are sprouting.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Similar to the development on the old protected fields around 1930, the new protected fields, for a few years, were completely dominated by annuals and biennials, in particular Matricaria perforata and Elymus repens. The latter, which had been a common weed on the arable land, soon took over large areas of the ploughed fields, together with Taraxacum and others. Elymus repens is able to withstand ploughing, as even a tiny part of its rhizome can sprout into a new plant.

In 1979, on the stubble field, seeds of Chamaenerion were at once able to sprout, spread from a dense growth of this species on Vestermark. On the ploughed fields, the cover of Elymus was already so dense that germination of Chamaenerion seeds was inhibited. However, those Chamaenerion plants, which had been able to establish themselves here, soon began spreading by subterraneous runners, and as early as 1984 this species had taken over Nordmark and the western part of Sydmark, together with Cirsium arvense, Rubus idaeus, and Urtica dioica.

Far fewer Chamaenerion seeds had been spread to the eastern part of Sydmark and Centralmark, and the grass cover, dominated by Elymus, Dactylis glomerata, and Holcus lanatus, endured for many years.

By 2006, most of the grassy areas and the Chamaenerion growths on the Nordmark and Sydmark had been replaced by huge shrubs of Rubus idaeus, mixed with Rubus caesius, Urtica, Cirsium arvense, Galium aparine, and others. In some areas, Hypericum hirsutum and H. maculatum were common.

Grass cover was still found in small areas of the fields, mainly along the coast. In 2006, many species, which are rather rare on Vorsø, were growing here, including Centaurium erythraea, Crepis capillaris, Trifolium dubium, T. striatum, Erigeron acer, Pilosella officinarum, Senecio jacobaea, and Angelica sylvestris. In 2022, all these species, apart from Angelica, had disappeared.

In a gravel-dominated area on the southern field, northwest of Tepotten, Chamaenerion never managed to dominate. In 1991, this area somewhat resembled a grazing pasture, housing an abundance of species, dominated by Arrhenatherum elatius and Holcus lanatus, and with a number of rarer species, including Pilosella aurantiaca, Tussilago farfara, Allium oleraceum, and Trifolium campestre. In 2006, Rubus idaeus and R. caesius had taken over much of this area, and only Fragaria vesca was of some interest.

Today, dense shrubs of Prunus spinosa, P. cerasifera, and Crataegus have been established here and there on Nordmark and Sydmark, especially on the former. Salix cinerea and S. caprea form growths along Vesterskov, on the central part of Sydmark, and along a hedge of P. cerasifera on Nordmark.

During the 1980s, along the southern and north-eastern edges of Vesterskov, a young wood sprung up, dominated by Ulmus, mixed with Fraxinus, Betula pendula, Alnus glutinosa, and Populus tremula. When the elms have reached a certain height, they are attacked by Dutch elm disease and die, but new young trees soon sprout (see page Dutch elm disease on Vorsø). Today, the herb layer in these young woods is dominated by Urtica, mixed with Dryopteris filix-mas, Geranium robertianum, Geum urbanum, and others.

Immediately after the protection in 1978, many Alnus sprouted in the north-western corner of Sydmark, spread from a single tree in the south-western corner of Vesterskov. Today, these alders form a young wood.

At the same time, thousands of seeds, originating from a few large Acer pseudoplatanus in Tepotten, were spread into the field, and in the following years a rather large area (except on the previously mentioned gravel strip) was covered by young trees. By 1993, a dense young wood had been established, in which the highest trees measured 8-9 m. By 2006, this young forest had further spread, the tallest trees by now measuring over 15 m. The succession here closely corresponds to the one, which took place 50 years earlier on Østermark north-east of Østerskov.

By 2006, in the south-eastern corner of Sydmark, a young wood had sprung up, dominated by Fraxinus, Ulmus, and Acer pseudoplatanus. Since then, the former two have somewhat declined. In 2022, Pulmonaria officinalis was very common in this wood.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Following the protection in 1978, the major part of Centralmark was quickly covered by various grasses, dominated by Elymus repens, which had largely been replaced by Holcus lanatus by 1991. A depression in the southern part of the field, along the road, is very humid, and until the mid-1980s, a dense carpet of Ranunculus repens was found here, later largely replaced by Elymus.

A young wood of Alnus glutinosa was established here at an early stage, today forming a dense young wood. The forest floor here is still very wet, covered by vegetation of grasses. Around 2000, Mentha aquatica and Ranunculus auricomus, were also noted here, but the latter has since disappeared.

In 1991, Centralmark was one of the most interesting botanical areas on the island, displaying a large number of rarer herbs, including Dactylorhiza majalis, Carex ovalis, C. flacca, Luzula campestris, Senecio jacobaea, Gnaphalium sylvaticum, and Veronica officinalis. Of these, only Carex flacca and Senecio jacobaea could be found again in 2006, but there were many other interesting herbs, including Agrimonia eupatorium, Hypericum hirsutum, H. maculatum, Carex pallescens, and

Ajuga reptans. Beneath the hedges, Sanicula europaea was abundant, and four small growths of Epipactis helleborine were also found here.

As opposed to the development on Nordmark and Sydmark, thorny shrubs were quickly established on Centralmark, today forming dense, almost impenetrable thickets, similar to the ones that were formerly present on the old fields.

In the late 1970s, countless seeds of Fraxinus were spread from the eastern edge of Vesterskov onto the field, and during the 1980s thousands of tiny ash trees sprouted here. For several years, these small trees were severely set back by roe deer, which ate the major part of the buds during winter. By 1991, however, some of the trees had been able to grow tall. The rest were only 30-40 cm high, and the growth was so dense that it was difficult to enter the area.

By 2006, many of these low ash trees had managed to reach a height of 10 m, but a remarkably large number of them had a dent on their trunk, 30-40 cm above the ground – exactly where the roe deer had previously bitten off the top shoots. The growth was still very dense, in some areas up to 25 trees per m². Since the 1990s, a young ash forest has also been established in the south-eastern corner of Centralmark.

In later years, most of the ash trees in the field have been killed by ash dieback, a disease caused by an ascomycete fungus, Hymenoscyphus fraxineus. In 2022, parts of the field was a jumble of living and dead ash trees, with a few Populus tremula in between.

Today, in the few remaining open parts of the field, Rubus caesius has become very common, and Holcus lanatus has almost disappeared.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Numerous species thrived here, including Bolboschoenus maritimus, Sparganium erectum, Scutellaria galericulata, Carex pseudocyperus, Solanum dulcamara, Bidens tripartita, Ranunculus sceleratus, Agrostis stolonifera, and Mentha arvensis.

During the following 30 years, a dramatic change of the vegetation in this plantation took place. After some years with rising groundwater level in the area, the two original ponds and the depression were, for the major part of the year, transformed into one larger pond, named Vesterdam (‘western pond’).

Those trees in the plantation, which were now standing in water most of the year, died, becoming the perfect breeding place for cormorants, which emigrated here from Vesterskov. When the cormorants were protected on the island in 1971, their numbers quickly increased significantly. They spread to the remaining part of the plantation, causing all trees to die. Only Populus x canescens survived, spreading by root shoots. In areas with many cormorants, the vegetation cover on the ground also perished. Those areas that were no longer used by the cormorants, were quickly invaded by Sambucus nigra, and small areas with grasses were also established.

The swamp vegetation changed due to the strong influence of the guano. In 1991, Phragmites australis and Bolboschoenus maritimus dominated, together with Typha latifolia, which had spread to this area around 1980 (fig. 2, centre). Other common species were Bidens tripartita, Persicaria amphibia, Atriplex prostrata, and Oxybasis rubra. Late in the summer, when the pond started drying out, the latter species covered large areas. Shrubs of Salix cinerea had spread significantly, now also covering a former meadow of tall perennials.

By 2006, Phragmites australis had spread to most of the depression, and north of the former road Bolboschoenus maritimus was dominant, together with Phalaris arundinacea and Typha latifolia (fig. 2, bottom). Oxybasis rubra had almost disappeared, whereas Rumex maritimus had appeared. Around the pond, many of the elders had disappeared and had been replaced by a community of high perennials, dominated by Epilobium hirsutum.

Today, the same species as in 2006 dominate, but Rumex maritimus has disappeared again. Distribution of the various species may vary significantly from year to year.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Following the destruction of the drainage pipes in 1980, the groundwater level rose, and the field once again turned into a meadow. Every spring, during the 1980s, the vegetation here was completely dominated by Ranunculus repens, which is still very common here. In the 1990s, various grasses began to dominate, especially Agrostis stolonifera and Alopecurus geniculatus, with large growths of Phalaris arundinacea, Persicaria amphibia, Mentha aquatica, Solanum dulcamara, Alopecurus pratensis, Bidens tripartita, Potentilla anserina, and Deschampsia cespitosa. Most of these plants are still present, and Carex pseudocyperus displays several fine tussocks.

During the 1990s, cormorants were breeding in large numbers right out to the western edge of Østerskov. At this time, several guano-tolerant species grew along the forest edge, including Oxybasis rubra, Chenopodium polyspermum, Persicaria lapathifolium ssp. pallidum, and Atriplex prostrata. In 2006, there were not nearly as many cormorants, and the above-mentioned plants had disappeared, except Oxybasis, which has since also vanished.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Prior to the destruction of the drainage pipes in 1980, tall perennials had taken over the depression, dominated by Phalaris arundinacea, Urtica dioica, and Filipendula ulmaria. With the rising groundwater level, a small pond, called Østerdam (‘eastern pond’), was present here for the major part of the year.

During the first half of the 1980s, this pond was almost covered by a huge growth of Ranunculus peltatus, but by 1991 this species had been replaced by Phalaris arundinacea, Sparganium erectum, Typha latifolia, Bolboschoenus maritimus, Schoenoplectus tabernaemontani, Persicaria amphibia, Bidens tripartita, and Solanum dulcamara (fig 3a).

Eleocharis palustris and Rorippa palustris were scarce, and along the northern edge of the pond was a growth of Oxybasis rubra, which benefitted from guano of breeding cormorants. The pond had spread into a growth of Populus x canescens, and the rising water level caused many of these to topple.

In 2006, the pond had about the same distribution as in 1991, but the vegetation had changed dramatically (fig 3b). Around the edge of the pond, Phalaris arundinacea still formed a zone, but in the pond proper, Typha latifolia and Bolboschoenus maritimus had increased. Sparganium erectum, Eleocharis palustris, and Rorippa palustris had disappeared, whereas Mentha aquatica, Rumex maritimus, and Veronica catenata were new to the area.

In 2022, Bolboschoenus maritimus had increased dramatically, now covering almost the entire pond, together with a dense tangle of Solanum dulcamara. Typha latifolia was now restricted to a small area in the northern part, and Phalaris arundinacea had also decreased significantly. As early as 2018, Schoenoplectus tabernaemontani, Rumex maritimus, and Veronica catenata had disappeared, and in 2022 Mentha aquatica could not be found. The pond is now completely covered by vegetation, and a pond proper is only formed during the winter months.