Croatia is a country at the crossroads of Central and Southeast Europe. It shares a coastline along the Adriatic Sea, and borders Slovenia to the northwest, Hungary to the northeast, Serbia to the east, Bosnia and Herzegovina and Montenegro to the southeast, and shares a maritime border with Italy to the west and southwest. The country spans an area of 56,594 square kilometres, with a population of nearly 3.9 million.
Croatia can be subdivided between several ecoregions because of its climate and geomorphology. The country is consequently one of the richest in Europe in terms of biodiversity. There are four types of biogeographical regions in Croatia—the Mediterranean along the coast and in its immediate hinterland, Alpine in most of Lika and Gorski Kotar, Pannonian along Drava and Danube, and Continental in the remaining areas. The most significant are karst habitats which include submerged karst, such as Zrmanja and Krka canyons and tufa barriers, as well as underground habitats. The country contains three ecoregions: Dinaric Mountains mixed forests, Pannonian mixed forests, and Illyrian deciduous forests.
The karst geology harbours approximately 7,000 caves and pits, some of which are the habitat of the only known aquatic cave vertebrate—the olm. Forests are also significantly present in the country, as they cover 2,490,000 hectares representing 44% of Croatian land area. Other habitat types include wetlands, grasslands, bogs, fens, scrub habitats, coastal and marine habitats.
In terms of phytogeography, Croatia is a part of the Boreal Kingdom and is a part of Illyrian and Central European provinces of the Circumboreal Region and the Adriatic province of the Mediterranean Region. The World Wide Fund for Nature divides Croatia between three ecoregions—Pannonian mixed forests, Dinaric Mountains mixed forests and Illyrian deciduous forests.
There are 37,000 known species in Croatia, but their actual number is estimated to be between 50,000 and 100,000. The claim is supported by nearly 400 new taxa of invertebrates discovered in Croatia in the first half of the 2000s alone. There are more than a thousand endemic species, especially in Velebit and Biokovo mountains, Adriatic islands and karst rivers. Legislation protects 1,131 species.The most serious threat to species is the loss and degradation of habitats. A further problem is presented by invasive alien species, especially Caulerpa taxifolia algae. Croatia had a 2018 Forest Landscape Integrity Index mean score of 4.92/10, ranking it 113th globally out of 172 countries.
The invasive algae are regularly monitored and removed to protect the benthic habitat. Indigenous sorts of cultivated plants and breeds of domesticated animals are also numerous. Those include five breeds of horses, five breeds of cattle, eight breeds of sheep, two breeds of pigs, and a poultry breed. The indigenous breeds include nine endangered or critically endangered ones. There are 444 protected areas of Croatia, encompassing 9% of the country. Those include eight national parks, two strict reserves, and ten nature parks. The most famous protected area and the oldest national park in Croatia is the Plitvice Lakes National Park, a UNESCO World Heritage Site. Velebit Nature Park is a part of the UNESCO Man and the Biosphere Programme. The strict and special reserves, as well as the national and nature parks, are managed and protected by the central government, while other protected areas are managed by counties. In 2005, the National Ecological Network was set up, as the first step in the preparation of the EU accession and joining of the Natura 2000 network.