Despite the fact that nature has been explored for thousands of years, until know we do not know everything about natural phenomena. Scientists have described less than 2 million species – both existing and extinct - while there most probably are more then 10 million (and maybe 50 million) species. That means that at least 80 % of them do not even have a name! This thousands and millions help to realize how diversified nature is.

Biological diversity is the expression of nature’s adjustment to the constantly changing environment. Thanks to its diversity nature can face all the occurring changes. Even though some specimens, species, and ecosystems are damaged, they are diversified to such an extent that at least some of them survive and pass their dominating features to future generations. In the process of evolution nature constantly produces diversity and sustains it – new species appear and adapt to the changing conditions in many various ways, in order to survive every possible change in the environment.

Nature creates diversity and diversity guarantees natural stability – homeostasis on the level of specimens, species and ecosystems. All systems built out of greater number of elements are more stable (more resistant, better adjusted, more effectively reacting to changes) compared to those made of smaller number of co-existing elements.

Biological diversity (also called biodiversity) is a special value of living nature and it can be described as:

• all forms of living matter,
• all creatures together with all their specific features and adaptations, as well as all their interactions.

Threats to biological diversity
Extinction of species is a natural process, which takes place due to constant changes in natural environment. Extinction concerns every single species. However, nowadays humans transform natural environment so quickly and to such an extent, that natural process of extinction has taken a catastrophic size.

It has been estimated that if the process of deforestation continues, within the next 30 years 50 to 100 thousand plant and animal species shall disappear every year – it amounts to 137 species daily and 8 species every hour! If the effects of global warming become more severe, within the next dozens of years the extinction of many marine species shall begin. The catastrophe of this size has not taken place since the era of dinosaurs, which is 65 million years ago. The main cause of such rapid extinction of species is economic activity of humans.

What is the cause of such a rapid extinction of species?
The most important cause is the loss of habitats, which means the destruction of conditions appropriate for species to live in. Humans begin to inhabit larger and larger areas of land, they transform natural environment in their “civilized world”. Many species cannot live in this transformed conditions – they cannot hide, they cannot find food or procreate – so they die. Extinction due to the loss of habitats concerns about half of the number of species which become extinct.

Second important factor causing extinction of spices is introduction of non-indigenous species from different geographic regions – these new species  displace indigenous species or simply eat them. This problem can be easily seen in Australia and Oceania, where animals introduces by humans: goats, sheep, hares, rats, dogs and cats quickly started to reign the environment eating out the food of indigenous species.

Third place on the list of factors which cause extinction of species is killing by fishing, poaching , hunting or cutting down  natural forests (mainly tropical rainforests).

Most endangered are species of small range
Birds are the example of species of small range. Over ¼ of all bird species (2623 out of 7100 species) have small ranges, which means that they live on areas smaller than 50,000 km2 – more or less the size of one Polish province. In the group of small range species there are 816 species endangered by extinction, which is 74 % of all threatened species. 80% out of 62 bird species which have become extinct within the last 200 years have also been species of small range.

When we learn more about living nature and its actions we discover that every single element and mechanism has its meaning and is important for our existence, development, health or convenience. For example species like rice, wheat, sheep or yeast have been important for human economy for thousands of years. However, other species may appear important for humans in the future. For example "bread mold" produced Penicillium for millions of years, but man discovered it and used in medicine, as late as dozens of years ago.

Many plant and animal species, as well as bacteria and fungi nowadays seem to be worthless and useless, for we cannot see the benefits of using it. They have not been researched thoroughly or we simply do not know how to make use of their features. This is why thoughtless destruction of these “useless” and unknown species, starting from microscopic bacteria and fungi, finishing with huge trees, means acting to our own harm, and doing harm to the future generations.

Protection of biological diversity
Since 1920s people understand that, it is vital to preserve biological diversity in all ecosystems. It must be protected to:

• Sustain the mechanisms of working nature;
• Preserve nature’s ability to survive changes in environment;
• No to lose natural values, which we cannot discover and use, and which may become the basis for development for future generations.

Protection of biological diversity has become an important element in a number of international conventions concerning the protection of nature, development programmes of the European Union as well as laws of many countries. Agriculture and forestry are the first to protect biodiversity.

The main tasks of modern agriculture and forestry is to keep alive many diversified natural systems with all their typical species.

Biological diversity in Poland
There are about 72-75 thousand species. There are over 39 thousand micro-organisms and fungi. There are about 2750 Vascular plant species and sub-species. There are about 33-45 thousand animal species. Scientists in Poland have singled out 360 kinds of ecosystems.

The number of species registered in Poland (from Andrzejewski, Weigle, 1991 “Polskie stadium roznorodności biologicznej.