**1. Introduction**

Usambara Mountains are famous Mountains ranges located at the Northeastern part of Tanzania. These are Block Mountains forming a series of 12 separate mountains described as the Eastern Arc Mountains (EAM). The EAMS stretches from Kenya the Taita hills through Udzungwa Mountains in southern highlands of Tanzania [1]. Most of the EAMs 11 separates mountains are found in Tanzania namely: North Pare, South Pare, West Usambara, East Usambara, Nguu, Nguru, Uluguru, Malundwe, Ukaguru, Rubeho, and Udzungwa [2]. The name 'Eastern Arc Mountains' (EAM) was coined as a suitable way of defining unique forests areas that comprises many rarely found plants' and animals' species [3].

Literature shows existence of intensive and extensive studies since 1800s that targeted flora and fauna throughout the individual mountains of the Eastern Arc. There are discoveries made on biological diversity for small mammals [4–7], larger mammals such as primates [8], carnivores [9], invertebrates [10], reptiles and amphibians [11], and birds [12–14]. The literature also indicates rich diversity of plants like angiosperms [15, 16]. So, far research works indicated the existence of over 100 species of birds, mammals, amphibians and reptiles, and also over 500 plants, and vast numbers of butterflies and millipedes [17].

These long-time research efforts that were made on the biodiversity treasures of the EAMs have led to the global recognition of EAMs as a very important global biological rich heritage [18], therefore, the EAMs have been designated as the 25th world's biodiversity hotspots [19, 20] and one of the World Wild Fund's Global 200 priority ecoregions [2]. Furthermore, the EAMs are not only important as the global biodiversity hotspots, but in Tanzania, the Eastern Arc forests are the source of 90% of water flowing for the hydroelectric power of the country. The forests are also the source of water for major cities including Dar es Salaam, Morogoro and Tanga all of which with human population of over 10 million people. The EAMs watersheds in Tanzania are also flowing waters through some of the National Parks including Udzungwa, Mikumi, Mkomazi, Saadani and Selous Game Reserve. In general, the EAMs are crucial for both as an ecological haven and also as socio-economic treasure of the country.

The Usambara Mountains are formed by two separate land massifs, the 'east' and 'west Usambara' Mountains, that are separated by a 4 km wide Lwengera River Valley. These Mountains share the uniqueness of the EAM characterised by the myriads of endemic flora and fauna: a rich biodiversity, and perhaps the most studied in the EAMs [19, 21, 22]. The biologists and ecologists studied well and established factors that governed high proportion of endemism and biodiversity in the Usambara Mountains and the entire EAMs series, linking biodiversity with long periods of tropical forest cover attributed to reliable rainfall onsets and patterns [21, 23]. However, the studies on abiotic factors influencing biotic forest dwellers were limited in the EAMs. The abiotic factors including climate, geology, soils, and landform characteristics are strong determinants of plants and animal distribution [24, 25].

The organism presence is expressed in the theory of the 'ecological niche of a species', defined by Hutchinson [26] to be 'a sum of all the environmental factors acting on the organism, in a region of n-dimensional hyperspace' of which each factor acting on the organism is one dimension within which a species can theoretically maintain a viable population. The multiple dimensions [26] include factors such as physical, chemical and biological parameters which set-up a niche with a range of prevailing conditions (landform, soils, temperature, rainfall) and resources (food, water, breeding sites, safe refuge) within which a species can persist. Knowing factors making the ecological niche are important because conservationists get to know the effects environment has on species and vice versa the effects species has on the environment. Previous studies [18–20] mainly covered species in their niche with little coverage how the environmental (abiotic) factors impact survival of the species. Lack of knowledge consequences is that endemic species of plants and animal in West Usambara Mountains and EAMs maybe threatened as abiotic factors are degrading to irreversible levels due to human interventions.

The aim of this study is to contribute the understanding of the influences the abiotic factors have on the biodiversity of West Usambara Mountains. It is expected that this will shed light to various actors on what ought be done to conserve the devastated rich biodiversity in west Usambara Mountains due changing abiotic factors including human activities such forest deforestation.
