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The Influence of Disturbance Type on Precipitation - Use Efficiency at Functional Group and Species Scales in an Arid Habitat

Busso C. A., Montenegro O. A., Torres Y. A., Giorgetti H. D., Rodriguez G. D.

Polish Journal of Ecology

2016

Vol. 64, nr 2

143--164

We used long-term datasets (1984–1992) to contrast precipitation-use efficiency estimates between various disturbance kinds at a functional group and/or a species scale. Effects of varying amounts of precipitation and plant cover on PUE were also examined. Field studies were conducted at northeastern, arid Patagonia, Argentina (40°39′49″S, 62°53′6.4″W). Within each management kind, biomass was sampled in 0.5 × 0.5m permanent plots (n = 30) over 9 years after defoliation at 5 cm stubble at the end of each growing season, and it was separated into species. Biomass sampling allowed determination of annual net primary production. Thereafter, species were grouped into each of three functional groups. Precipitation-use efficiency (PUE) was calculated as the total dry matter produced per unit surface area on any given year divided by the total rainfall in that year. Plant cover on 20 out of those 30 plots was determined to study the relationship between plant cover and PUE. The contribution of cool-season perennial grasses to total PUE was higher (P <0.05) than that found for the other two functional groups in all management kinds and years. PUE was similar (P> 0.05) in wet than dry years, and it was greater (P <0.05) or similar (P> 0.05), but not lower, on the more than less competitive perennial grass species in all management kinds. The relationship between plant cover and PUE was positive, linear (P <0.0000) and management-kind dependent.

Can Potentilla fruticosa Linn. shrubs facilitate the herb layer of heavily grazed pasture on the eastern Tibetan Plateau

Li P., Krusi B., Li S., Cai X., Yu F.

Polish Journal of Ecology

2011

Vol. 59, nr 1

129-140

The facilitative and competitive effects of shrubs on herbaceous species have been extensively studied, but little is known about the roles of the shrub distribution patterns in such effects. On a heavily grazed pasture on the Tibetan Plateau, we investigated the effects of Potentilla fruticosa Linn. shrubs of different distribution patterns on the small-scale vegetation pattern of the herb layer. We made same-sized releves at five micro-site types, i.e., beneath and outside the canopies of solitary Potentilla individuals, beneath and outside the canopies of edge-of-patch individuals and at the central openings of torusshaped large Potentilla patches. Shrubs protected certain species by increasing their frequencies of occurrence or flowering. However, only few species benefited from shrubs and more occurred or flowered more frequently outside. The data at community level indicated that species richness and diversity index were higher outside. The patch openings did not benefit species richness, pooled cover, diversity index or evenness of central vegetations. No special species was found growing beneath shrubs exclusively and few species were found with higher occurrences beneath shrubs. Furthermore, no significant difference was found between the two different distribution patterns at either community or species level. Vegetation ordinations confirmed this and vegetations beneath and outside the shrubs were distinguished merely. In conclusion, Potentilla facilitated some species in the herb layer and the patch openings did not show large protective effects. Also, distribution patterns of Potentilla did not affect the difference between vegetations beneath and outside shrub canopies.