Tag Archives: frogs

The nature reserve “The big and the white bog”- “Großes und Weißes Moor”

The nature reserve “The big and the white moor” (Fig. 1) is located in the Lower Saxony, in the district of Rotenburg (Wümme). Even though it used to be almost dry, it has been recovered and naturalised due to the drainages made for agricultural purposes. Today, it is among the best preserved raised bogs in the North-West Germany.

Raised bogs are acidic, wet habitats, poor in mineral nutrients, populated by plants adapted to live in such extreme conditions (Fig. 2). In north Germany they can develop only under ideal climate conditions – wet with a balanced distribution of precipitations over the year.

The development of the bog started around 4000 years ago. At first a flat bog developed thanks to sand deposition and accumulation of water. Slow acidification of the trapped water allowed the accumulation of partially decomposed plant material under low oxygen levels, which developed into peatland. At this stage, the inhabiting plants were sedges, rushes, deergrasses, Phragmites and alders. In the transition stage, other plant species folowed – bushes, trees, peat mosses and cotton-grasses. The rised bog developed very slowly, in a period of many centuries, along with strong rainfalls.

The peat, accumulating over time, traps CO2 gasses by reducing their amount in the atmosphere. Therefore bogs are important for the climate and by protecting them, we protect the climate.

About 60% of plants of the german bogs are threatened. Among them, the heather (Calluna vulgaris, Fig. 3), and the cross-leaved heath (Erica tetralix, Fig. 4) are very common. Both are low growing perennial shrubs, easily found in the heathland and moorland, growing in acidic soils in sunny or partially shady places, adapted to live in low nutrient conditions. Cross-leaved heath is particularly vulnerable because the increased drainage creates drier conditions, where it is quickly replaced by the moor grass Molinia. However, gradual naturalisation is essential for the survival of this plant in this protected area.

Increased drainage permits the growth of Molinia, birch and pine trees (Fig. 5). As the forest develops, it absorbs more water so that the typical conditions for bog plants survival are quickly lost.

Fig. 5 As the conditions get drier, Molinia, birches and pine trees are slowly replacing the typical bog plants. Constant management via irrigation is necessary for the recovery of the raised bog.

Among animals, we can find the slow worm (Anguis fragilis), the moor frog (Rana arvalis), the common water frog (Fig.6), the Araneus spider (Fig. 7) etc.

However, last summer (2016) was extremely hot and dry, the precipitations were not well distributed and the temperatures were well above the average. While in July everything looked fine, in September the picture was a bit different. The pond where the frog from the Fig. 5 has been found become almost dry in September (Fig. 8 and 9), even the blueberries were flaccid or dry. The conditions worsened in the next weeks, with temperatures above 30°C and no rain.

I like to think that it was just an exceptional year and that it will only rarely happen to have such extreme conditions in Northern Europe, but I´m not that optimistic for the future of this peculiar biotope.

Photos by Ingrid Ugussi Vukman


The island of Cres: Tramuntana

The island of Cres (Fig. 1) lies in the Kvarner Gulf, at the Croatian side of the Adriatic sea. Along with Krk, it is the largest Croatian island – both have an area of about 406 km2 . Rich in biodiversity, it hosts about 1300 plant species, many bird and reptilian species, among them various endangered and protected, of which many endemisms.

Fig. 1 The view of the island of Cres early in the morning, seen from Tramuntana.

Tramuntana is the name given to the northern half of Cres; it is also known as the “head of the island” (or, in Latin, “Caput Insulae”). Situated just slightly above the 45th parallel, Tramuntana is widely covered by a dense forest of deciduous trees such as oaks (Quercus pubescens, Qurcus cerris), ashes, hornbeams, elks and chestnuts. Such abundance of trees is favoured by the peculiar climatic conditions, a mixture of continental and Mediterranean – known also as the submediterranean climate.

This area was once mainly used as a pasture and this activity had an important impact in the architecture of the landscape and in the creation of new components of the ecosystem with peculiar microclimates that enriched the primary biodiversity.  The inhabitants of Tramuntana practiced agriculture, raised olive trees and forest harvesting in a sustainable way, which ensured an adequate balance between plant and animal species. Sheep (Fig. 2) were important members of the ecosystem because they ensured the maintenance of the grassland in a natural way, and their carcasses were an important food source for the griffon vulture (Gyps fulvus), which inhabits the nearby cliffs. In the last few decades, the amount of sheep drastically decreased, and this led to the decrease of the number of griffon vultures in the island, since sheep are a crucial component of their food chain.

Fig 2. In the island of Cres, sheep are free grazers. Since there are various sheep owners, they cut their ears so that they could be easily recognised. The only task of the owner is to ensure that they have enough water. During bad weather conditions, they find shelters in abandoned houses, caves or in the cavity of old trees.

In the same time, the abandonment of the practice of sheep breeding has caused many changes in the vegetation landscape, since the absence of the grazers has allowed the regrowth of the underbrush, made prevalently of Juniperus oxycedrus, Paliurus spina-christi and Crataegus monogyna.

The interior of Tramuntana is mainly covered by forests, however it is possible to see many scattered open patches with small ponds that are an important source of water for the wildlife; there are also many small areas delimited by dry walls where olive trees and old fruit trees still grow; these are excellent pastures for sheep (Fig. 3 and 4).

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What caugt my attention is the strong scent that in the whole island begins to spread starting from March, that is released by a big euphorbian species which starts to flower in this period, the Euphorbia characias subsp. Wulfenii (Fig. 5). Typical of the Mediterranean vegetation, this plant can grow up to 180 cm in height. Even though their flowers attract various insect species (Fig. 6 and 7), like all the members of the Euphorbia species, they produce a toxic white sticky sap, which has been used for treating skin excrescences since ancient times.

Fig. 5 Euphorbia characias subsp. Wulfenii in the foreground. In the background it is possible to see the rocky coast and the spectacular cliffs. Sheep are often forced to climb the cliffs in search for food. Frequently they fall and injure themselves, and when they die, they become food for the griffon vultures.

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The following pictures (Fig. 8, 9, and 11) are just an example of the rich biodiversity of Tramuntana. Starting from early spring, a rich bird concert makes a journey in the area particulary pleasent. The forest is espeically rich in song bird species, owls, the hoopoe, the european nightjar, swifts etc. According to curren estimates, of the 136 bird species present in the island of Cres, 65 of them nest in this area. In the whole island there are 32 autochtonous amphibian and reptilian species, among them the common toad (Bufo bufo), the blue-throated keeled lizard (Algyroides nigropunctatus), the common newt (Triturus vulgaris meridionalis), the yellow-bellied toad (Bombina variegata), the agile frog (Rana dalmatina) and the slow worm (Anguis fragilis). One curios thing is that, in the island of Cres and Losinj there are no venomous snakes and still nobody knows the exact reason.

Text and photos by Ingrid Ugussi Vukman 

The twin lakes of the Lower Saxony in Germany (Die Bullenseen)

The twin lakes (Großer and Kleiner Bullenseen) are situated in the Wümme depression that was covered by ice during the Ice Age. As the ice retired, the two depressions filled with water remaind and today they are replenished by the Wümme´s branches. The small lake is since 1938 part of the nature reserve “The big and the white moor” (“Großes und Weißes Moor”).

Since the water of the big lake (Fig. 1) is surrounded by a bog, it is rich in humic substances, therefore very acid  (pH 4.5-5) and not suitable for fish. However many other animals can thrive in such conditions – so here we can find various water bird species, snakes, like the grass snake Natrix natrix, frogs (Fig. 2), dragonflies and even bats in the evenings.

Fig. 1 The big lake (Großer Bullensee)
Fig. 2 A frog captured at the border of the big lake

Typical plant species found near the shore are the bulrush or Typha latifolia, the water-dropwort (genus Oenanthe), Fig. 3a,  the bog arum or Calla palustris, Fig. 3b and the carnivorous plant Drosera anglica.

Fig. 3a The bulrush and the water-dropworth; Fig. 3b The bog arum.

The small lake (Fig. 4a and b) is accessible by a trail with informative panels made by the Nabu association. It is positioned north of the big lake, surrounded by a pine forest and blueberry bushes which densely grow at the forest floor (FIg. 5a and b).

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The lake can be observed only by a certain distance since this environment is very vulnerable and the soil is muddy and soft, so it can easily trap you.

Various water bird species can be found, the most common are the tufted duck Aythyla fuligula, the mallard Anas platyrhynchos and the Eurasian teal Anas crecca.

Photos by Ingrid Ugussi Vukman