of outstanding features", 61 nature reserves, and 281 natural monuments. With 29.1% of its territory covered by forest, Serbia is considered to be a middle-forested country, compared on a global scale to world forest coverage at 30%, and European average of 35%. The total forest area in Serbia is 2,252,000 ha (1,194,000 ha or 53% are state-owned, and 1,058,387 ha or 47% are privately owned) or 0.3 ha per inhabitant. It had a 2019 Forest Landscape Integrity Index mean score of 5.29/10, ranking it 105th globally out of 172 countries. The most common trees are oak, beech, pines, and firs. Air pollution is a significant problem in Bor area, due to work of large copper mining and smelting complex, and Pančevo where oil and petrochemical industry is based. Some cities suffer from water supply problems, due to mismanagement and low investments in the past, as well as water pollution (like the pollution of the Ibar River from the Trepča zinc-lead combinate, affecting the city of Kraljevo, or the presence of natural arsenic in underground waters in Zrenjanin). Poor waste management has been identified as one of the most important environmental problems in Serbia and the recycling is a fledgling activity, with only 15% of its waste being turned back for reuse. The 1999 NATO bombing caused serious damage to the environment, with several thousand tonnes of toxic chemicals stored in targeted factories and refineries released into the soil and water basins. Politics Serbia is a parliamentary republic, with the government divided into legislative, executive, and judiciary branches. Serbia had one of the first modern constitutions in Europe, the 1835 Constitution (known as the Sretenje Constitution), which was at the time considered among the most progressive and liberal constitutions in Europe. Since then it has adopted 10 different constitutions. The current constitution was adopted in 2006 in the aftermath of the Montenegro independence referendum which by consequence renewed the independence of Serbia itself. The Constitutional Court rules on matters regarding the Constitution. The President of the Republic (Predsednik Republike) is the head of state, is elected by popular vote to a five-year term and is limited by the Constitution to a maximum of two terms. In addition to being the commander in chief of the armed forces, the president has the procedural duty of appointing the prime minister with the consent of the parliament, and has some influence on foreign policy.