Niassa Reserve is one of the most pristine wildernesses in Africa. The vegetation is mostly Brachystegia (miombo) woodland (50%) – characteristically low productivity woodland, occurring on poor soils, where 95% of the biomass is found in herbaceous vegetation. This Miombo Woodland is interspersed with open savanna (40%), and wetlands (5%) - grassy depressions where water collects. Of particular interest biologically are the small isolated forest communities that occur on the mountains and inselbergs (3%) found throughout the Reserve, and the riparian forests along the perennial rivers (2%). There are 21 vegetation types and the preliminary surveys indicated 191 species of trees and shrubs.
Despite years of human conflict it supports a remarkably rich and diverse collection of wildlife. The results of an aerial census carried out in October 2002, the third one since 1998, estimated an elephant population of 12 000 with evidence of an increasing trend in numbers. The Reserve also has over 9000 of the sable antelope and several thousands each of Cape buffalo, Lichtensteins hartebeest, eland, and zebra. There are smaller populations of kudu, bushbuck, impala, wildebeest, waterbuck, reedbuck, and hippo. Duiker and warthogs abound. Lion, leopard and spotted hyena are common. The endangered Cape hunting dog (African wild dog) occurs with an estimated population exceeding 200 animals, which makes the Niassa Reserve one of the last best refugees for this species. Of particular interest are three endemic subspecies, which exist in Niassa but are rare elsewhere, namely: Niassa wildebeest (Connochaetes taurinus johnstoni), Boehms zebra (Equus burchelli boehmi), and Johnstons impala (Aepyceros melampus johnstoni).
The Reserve has a rich birdlife including the rare Angola pitta (Pitta angolensis), Pel’s fishing owl (Scotopelia peli), and abundant raptor population. Rovuma River is an Important Bird Area and over 370 bird species have been identified already.