EFFECTS OF CATTLE INGESTION ON VIABILITY AND GERMINATION RATE OF CALDEN (PROSOPIS-CALDENIA) SEEDS

Calden (Prosopis caldenia Burkart) is the dominant tree of the xerophytic open forest in the semiarid pampa of Argentina. Calden has gradually increased its distribution throughout the region during the past century as a result of livestock grazing in the pampa forest. Calden has an indehiscent legume fruit that is consumed by livestock during the February-April fruit shedding period (FSP). Both free seeds and pod segments (1 seed inside the endocarp) can be found in cattle dung. Free seeds and pod segments coming from fruits (uningested) and dung (excreted) were collected during the fruit shedding period on 22 February (D1), 7 March (D2) and 27 March (D3) to compare viability and germination rate. Viabilities of uningested free seeds and pod segments averaged 95% and 65%, respectively, and were unaffected (P less than or equal to 0.01) by date of collection. Excreted free seed from D1 was 37% viable, which was lower (P less than or equal to 0.01) than the 72% viable for D2 and D3. Excreted pod segments averaged only 10% viable seeds. Ingestion increased (P less than or equal to 0.01) germination rate of free seed for DI and D3. However, excreted seed displayed a range of delayed germination response. This diversity would increase the probability of seed germination for a variety of environmental and site conditions.