JOBBAGY GAMPEL Esteban Gabriel
Forage production in natural and afforested grasslands of the Pampas: ecological complementarity and management opportunities
NORDENSTAHL, M; CLAVIJO, MP; GUNDEL, PE; JOBBAGY EG
Año: 2011 vol. 83 p. 201 - 211
In managed rangelands periods of lowprimary productivity determine troughs of forageavailability, constraining animal production yearround.Although alternative tools to increase forageavailability during critical seasons exists, most ofthem are unaffordable and short-lived in marginalareas. We explore the potential benefits of deciduoustree plantations favoring winter forage productivityby comparing aboveground net primary productivity(ANPP) patterns in herbaceous understory to treeplantations and natural grasslands in the Pampas(Argentina). These temperate subhumid grasslandsare characterized by the coexistence of winterspecies, mainly C3 grasses of the native generaStipa, Piptochaetium, and Bromus and the exoticgenera Lolium and Festuca) and summer species(mainly C4 grasses of the native genera Paspalum,Bothriochloa, and Stenotaphrum) that replace eachother throughout the seasons, with domination of thelatter. We hypothesize that the natural decoupling ofgrowing seasons between winter deciduous trees andwinter grasses could provide the basis for thesustainable promotion of winter forage. We measuredANPP on two 23-year-old Populus deltoides plantationsand their understory and compared them withadjacent open grasslands. Afforested stands had5575% higher annual ANPP than their non-afforestedneighbors, with trees contributing *70% tototal ANPP. Herbaceous canopies beneath plantationsachieved about half of the ANPP observed in nonafforestedsituations with a contrasting seasonaldistribution associated with shifts from C4 to C3grass dominance. Winter ANPP, the most criticalsource of forage in these grazing systems, was similaror higher in the herbaceous understory of treeplantations to that on their non-afforested counterparts,suggesting that mixed systems involvingdeciduous trees and understory pastures are a validand viable option in the region.