ABSTRACT. – Spatial patterns of species richness and abundance were studied on a local scale (alpha-diversity) along an elevational gradient (540-1550 m a.s.l.) within a Mediterranean mountain in the Montseny Natural Park and Biosphere Reserve (NE Spain). Eight sampling stations consisting of 49 Sherman trap plots were sampled 11 times between 1995 and 1997. Values of cumulative species density, and species richness estimates (interpolated and extrapolated), were calculated to ascertain alpha diversity patterns. Species richness showed no consistent patterns along elevation, since patterns changed depending on the diversity measure used. Species richness (the number of species once controlling for the number of individuals sampled) showed a moderate increase with elevation, whereas a richness estimator (Jack 2) showed that alpha diversity peaked at middle elevations (1000-1200 m a.s.l.). Interpolation of species ranges suggested a mid-elevation peak in species diversity. Further, a null model provided moderate evidence of the influence of the geometrical constraints of species’ ranges on the observed pattern, lending weight to a hump-shaped pattern of diversity with elevation. Nonetheless, the most consistent pattern observed was the strong decrease of small mammal abundance with elevation. Structural equation modeling confirmed that species density and species richness were associated with the mean climatic features of the plots, although vegetation structure profiles were also seen to influence patterns (cover and plant height). Species richness increased from the warm and relatively dry lowlands to the colder and moister uplands, with the highest levels of species richness being found at the divide between the Mediterranean and Eurosiberian climatic zones and plant communities. However, patterns of species richness were not related to patterns of vegetation richness at plot level, which decreased significantly with elevation. The abundance of small mammals also decreased with elevation due to climatic harshness and possibly also to the decreasing productivity associated with greater elevations. We hypothesized that the combined effects of geographical (mid-domain effect), abiotic (climatic), and biotic (vegetation composition and structure, density of small mammal individuals, interdigitation of biotic communities) factors would seem to be responsible for the mid-elevation peak in small mammal alpha diversity in the Montseny mountain.