This gives the region high humidity and precipitation, with rainfall averaging 1,000–2,000 mm each year. Precipitation is highest in the southernmost portions and diminishes toward the north. Temperatures are fairly steady, averaging 24˚ for the entire region except for the northwestern portions of Mbam division, where they fall to 23˚. The Centre also experiences equatorial seasons, alternating between rainy and dry periods. The long dry season begins the year, running from December to May. After this comes the short rainy season, which lasts from May to June. The short dry season comes next, from July to October. The year ends in the long rainy season from October to November. North of 5˚, the dry periods last up to four months. Plant and animal life The Centre is forested except for the valleys of the Djérem, Mbam, and Noun rivers (most of the Mbam division) and the northern border region. These areas are woodland savanna and Sudano-Guinea savanna, respectively. The woodland savanna is characterised by large expanses of grass punctuated by small copses of trees from the forested zones farther south. The Sudano-Guinea portion is similar, only the grass grows more thinly, and trees are both evergreen and deciduous. The region was once much more heavily forested, but exploitation of species such as ebony and iroko has thinned out the woodlands and allowed dense undergrowth to appear. This has also pushed the savanna farther south over time. Today there remains very little virgin land in the province. The Mfou Reserve (Réserve du Mfou) is one such area, recently created by the WWF and the GTZ to protect various bird, monkey, and snake species. Cameroonian wildlife also lives in the Mvog Betsi Zoo in Yaoundé. In April 2019, 2 lions were discovered in Mpem and Djim National Park. Demographics Settlement patterns With a population of more than 4 million, the Centre is one of the more densely populated of Cameroon's provinces. The area has been an important population center for the Beti-Pahuin people for over a century, but it has since experienced a great amount of immigration due to the placement of Cameroon's seat of government there in colonial times. Yaoundé's presence has prompted the construction of a large and well-maintained road system, and this has contributed to the area's boom. Another factor in the area's growth is its multiple plantations, particularly in the cocoa-growing centre between the Sanaga and Nyong rivers