Ultrabasic forest is the most species rich forest type for trees but this forest type has lower bird and

bat species richness compared to lowland dipterocarp forest and montane forest. Bird and bat species richness are much stronger correlated across the four forest types. Our results on ambiguous cross-taxon congruence in species richness at finer levels of spatial scales add Selleck Etomoxir to the reservation on this issue in other studies (Prendergast et al. 1993; Lawton et al. 1998; Part and Soderstrom 1999; Ricketts et al. 1999; Heino 2010) although Mac Nally et al. (2002) found strong similarities in the diversity of birds, mammals and trees in one hectare blocks in Australia. Species richness congruence between species groups is likely to be linked through functional relationships, for example by trophic interactions or ecological similarity (Negi and Gadgil 2002; Rodrigues and Brooks 2007) or structural complexity (Kissling et al. 2008). Lowland dipterocarp forest, with its high canopy, complex structure and food resources for other taxa has the highest species richness of birds

and bats. Ultrabasic forest in our study is idiosyncratic in its high tree species richness. The extreme richness of ultrabasic forest in the NSMNP in tree species is further Selleckchem Batimastat supported by the findings of Aspartate Co et al. (2004) who identified 335 tree species in a 16 ha plot in lowland dipterocarp forest in the NSMNP compared to the 409 tree species found in the total of two ha in our study in ultrabasic forest. Little is known about

ultrabasic forests in the tropical Far East where some are very species poor and some exceptionally rich in plant species (Proctor 2003). Forest on ultrabasic soils in the Northern Sierra Madre clearly belongs to the latter category. The low bird species richness in ultrabasic forest in the NSMNP that we found is in concordance with avifaunal diversity studies in this forest type on other Southeast Asian islands (e.g. Poulsen and Lambert 2000) although ultrabasic forest on Borneo has several habitat specialist birds (Sheldon et al. 2009). The decrease in tree species richness with elevation that we found in the NSMNP, and a floristic ecotone at about 800 m where dipterocarp dominated forest is replaced by oak-laurel forest, has been well described on wet tropical mountain areas (e.g. Ashton 2003). The lower bird species richness in montane forest in the NSMNP compared to lowland dipterocarp forest reflects the general higher species richness of Philippine birds at lower elevations: 61% of resident species are restricted to lowlands, 15% to montane areas over 1,000 m and the remainder of 24% occurs al all elevations (Kennedy et al. 2000).