In New Zealand, concern has been expressed at the detrimental effects of burning snow tussock (e.g. Chionochloa rigida and C.macra) dominated grasslands, especially at higher altitudes. The present paper follows on from earlier results on short-term effects of fire on growth and flowering of narrow-leaved snow tussock C.rigida, from a study undertaken at 1,220 m on the Old Man Range in Otago (South Island). Here, results over 14 years after spring burning are summarised.
Measurements were first carried out on snow tussocks burned in extensive spring fires in 1959 and 1961, and on nearby plants unburned since at least 1945. In spring 1964, small areas previously burned in 1959-1961 were reburned and fenced to exclude livestock (mainly sheep).
Monthly leaf elongation, leaf production and tillers were measured on three mature tillers for each of 10 tussocks per treatment. Flowering was recorded for 50 permanently tagged tussocks per treatment until 1971, when unfortunately a prescribed spring fire over-burned part of the previously burned study area. This reduced the number of 1959-64 burned tussocks tagged to measure flowering to 20.
During 1972-73, leaf and stem samples from five tussocks from each treatment were analysed for non-structural carbohydrate reserves.
Growth (leaf elongation), increased significantly during the two growing seasons after burning (30-48 cm/year), but then declined ( to around 20 cm/year) i.e. below that of nearby unburnt tussocks (average over 14 years 28 cm/year). Leaf and tiller production also increased significantly in the two seasons after fire.
Flowering was prolific in the first season after burning (a trait usual for the species), but then fell below that of unburnt tussocks, over the next 13 years.
Average seasonal levels of non-structural carbohydrate reserves were significantly reduced in the year after burning. Thereafter, there was a small increase in average carbohydrate levels over those in unburnt tussocks.
Recovery of above-ground biomass of burned tussocks was slow, taking around 14 years to approach that of unburned tussocks. Reburning produced responses similar to that of the initial fire, but the magnitude was reduced.
C.rigida is a very long lived and slow growing species (especially in alpine environments) and these results highlight that burnt areas may take many years to recover after fire.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.royalsociety.org.nz/Site/publish/Journals/nzjb/1979/6.aspx