Impact of disturbance on above-ground water storage capacity of bryophytes in New Zealand indigenous tussock grassland ecosystems

Bryophytes are widespread in many plant communities and can attain cover and biomass levels that influence ecosystem processes. We investigated the impact of disturbance (fire, topsoil removal) on the composition, biomass, and water storage capacity of bryophytes in indigenous temperate tall-tussock grasslands managed to sustain an ecosystem service (regular provision of water) to nearby urban areas. We surveyed bryophyte composition, structure and water-related traits 9 years after experimental fires and topsoil removal. Total water storage capacity of non-epiphytic bryophytes in control grassland sites was estimated at 4.3 mm, a value similar to that found in temperate New Zealand forests. Total biomass, species composition, and waterrelated traits were the main drivers of water storage potential from bryophytes. A major shift in bryophyte species composition following disturbances reduced this potential by over 80%. Bryophyte community changed from a dense ground cover (71%) of the pleurocarpous moss Hypnum cupressiforme with high water holding capacity (c. 1400% of dry mass) in control plots, to low frequency of the colonist moss Polytrichum juniperinum in burned plots, and two Campylopus species in areas with topsoil removed for firebreaks (all three displaying a low water holding capacity of less than 800% dry mass). We concluded that despite their low species diversity (12 species in total in undisturbed sites), bryophytes form a major, previously unrecognised, component of indigenous tall-tussock grasslands in New Zealand, and contribute towards sustaining the valued water holding capacity of these systems. Like the tussock dominants, bryophytes and their associated ecological functions are highly susceptible to long-term impacts from burning and vegetation clearance. It is therefore critical to account for the recovery of bryophytes in the management of indigenous tall-tussock grasslands to maintain healthy ecosystems.