Grass seed production in the central Monte desert during successive wet and dry years

Abstract

In desert regions, water availability triggers primary production, which determines seed production, the composition and size of soil seed reserves and the abundance and behaviour of seed-eating animals. In the central Monte desert, large precipitation events (≥10 mm) account for a high proportion of growing season's rainfall. Our first objective here was to assess whether and how timing and amount of seed production of C3 and C4 perennial grasses are linked to spring and summer precipitation pulses and to estimate the seasonal and year-to-year variability in seed production. Our second aim was to calculate grass seed production and compare it with seed requirements by granivorous animals to infer whether the animals can exert top-down effects on plant populations. Seed production of C3 and C4 species was triggered by significant spring and summer rainfall, respectively. Such distinct response may be associated with the effect of precipitation during flower development and seed set in both functional groups. In all species, seed production varied among years. Rainfall pulses in the summer triggered and positively affected the magnitude of seed production in most C4 grasses. However, all perennial grasses were able to produce high amount of seeds even during a year subjected to extreme drought, suggesting that perenniality would allow these species to make large reproductive investment despite harsh environmental conditions. The comparative assessment of seed production and consumer demands suggests that it is unlikely that granivory exerts a top-down control on grasses in the Monte desert.