Question: Our study aimed at testing to what extent water and/or nutrients affect community composition in sub-alpine heath. We hypothesized that nutrient addition will have an overall positive effect on heath vegetation but water addition will have greater effects and will probably reinforce the effects of fertilization in drier habitat conditions.

Location: Monte Rondinaio, northern Apennines, Italy (44°08′ N; 10°35′ E, ca. 1850-1930 m a.s.l.).

Methods: Nutrients and water were added during five growing seasons in two communities (HV community, moister; EV community, drier) and the biomass of all species was estimated non-destructively by the point-quadrat method.

Results: Total above-ground biomass increased in both communities with fertilization due to increased graminoid biomass and decreased moss biomass, but was unaffected by irrigation. In the HV community species richness decreased as an effect of fertilization while in the EV community species richness was raised by irrigation.

Conclusions: Our study partly supported our hypothesis since water addition had a stronger effect in the drier community. However, this effect was not revealed by changes in above-ground biomass but rather by differing responses of individual species in the two communities.

Nomenclature: Aeschimann et al. (2004) for vascular plants with the exceptions of Vaccinium uliginosum ssp. microphyllum, henceforth called V. uliginosum (instead of Vaccinium gaultherioides Bigelow) and Festuca rubra L. ssp. commutata Gaudin, henceforth called F. rubra (instead of Festuca nigrescens Lam.); Frahm & Frey (1987) for bryophytes with the exception of Polytrichastrum alpinum (Hedw.) G.L. Smith instead of Polytrichum alpinum Hedw.