Allen campaigns for the Mau Forests Complex (MFC), which forms the largest closed-canopy forest ecosystem in Kenya, the largest indigenous montane forest in East Africa. It is the most important water catchment in the Kenyan Rift Valley and Western Kenya. The forests provide critical environmental services to the country: freshwater, river flow regulation, flood mitigation, recharge of ground water, erosion control, water purification, biodiversity conservation and micro-climate regulation.

The ecosystem services provided by the Mau Forests support a range of economic sectors including agriculture and tourism. The market value of the goods and services generated annually in the tea and tourism sectors alone, to which the forest complex contributes, is estimated in excess of Ksh20 billion (US$ 229 million). Recent investigations show that the Mau Forest has been affected by widespread unplanned settlements, irregular forest land allocation and illegal extraction of forest resources. In addition, over 10% has been impacted by forest plantations by subsistence and cash crop farming and unregulated logging concessions. Scientists predict that further destruction of the forest will cause an environmental disaster in Kenya and significantly reduce river flows and lake levels.