Ferrante, D.

Humano, G.

Oliva, Gabriel E.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 21st International Grassland Congress / 8th International Rangeland Congress Long-Time Effects of Grazing on Patagonian Rangelands (Argentina) Gabriel E. Oliva INTA, Argentina G. Humano INTA, Argentina D. Ferrante INTA, Argentina Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/21/3-1/48 The 21st International Grassland Congress / 8th International Rangeland Congress took place in Hohhot, China from June 29 through July 5, 2008. Proceedings edited by Organizing Committee of 2008 IGC/IRC Conference Published by Guangdong People's Publishing House This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅰ 　 瞯 ]471　 瞯Grasslands/Rangelands Resources and Ecology ——— Soil‐Plant‐Animal InterrelationshipsLong‐time effects of grazing on Patagonian rangelands (Argentina)Oliva , G . , H umano , G . , and FerranteD . IN TA EEA Santa Cruz (Convenio IN TA‐UNPA‐CA P) . E‐mail : Chacra 45‐A . Río Gallegos .goliv a＠ correo .inta .gov .arKey words : sheep , grazing , soils , nutrients , erosionIntroduction Rangelands in the area of the Magellan Strait , southern Patagonia , are dominated by tussock grasslands of Festucagracillima . The Open Tussock Grassland State seems stable , and may endure grazing with little physiognomic changes , but atsome step irreversible transitions to dwarf‐shrub steppes of Nardophyllum brioides take place .Materials and methods A tussock grassland ( Moy Aike Chico , Santa Cruz , １７０ mm rainfall ) was subjected to １１ years ofcontrolled grazing in an experiment with two ４０‐ha paddocks at stocking rates of ０ .６０ ( high) , ０ .２０ ewes/ ha/ year ( moderate)and a ２ ha exclosure ( equivalent to １ .５６ AUM ha‐１ , ０ .５０ AUM ha‐１ and ０ AUM ha‐１) starting in １９８７ . In １９９９ , fences wereremoved and the area returned to normal production grazing regime ( ０ .５０ ewes/ ha ) . Six ４００ m‐２ monitoring plots wereestablished per treatement , and three of them were randomly selected to be fenced off . Vegetation and soil differences betweenthese areas were monitored in years ２０００ , ２００２ and ２００６ . Vegetation was sampled with point‐intercept method (５００ points) ,and composite samples of topsoil ( １０ cm) were drawn for physical and chemical analysis . One‐way Analysis of Variance andDuncan contrasts were performed . Letters in Results section indicate significant differences for treatments in ２００６ ( P ＜ ０ .０５ ) .Results and discussion Most grazing effects generated in the １９８７‐１９９９ stocking treatment persisted af ter seven years of uniformtreatments . Grazed and ungrazed plots in the １９９９‐２００７ period did not differ significantly , so the results are reported jointly .Significant differences were still observed in ２００６ in percentage of Bare Soil (３０ .９a high stocking , ２４畅２b moderate and ２１畅３b inexclosure) , Litter (１３畅６b , １６畅１b and ２２畅１a respectively ) , Short Grasses ( １６畅２b , ２３畅４a and ２２畅６a) , Dwarf Shrubs (２１畅３a ,１６畅８ab and １２畅６b) and Shannon‐Wiener diversity index (‐１畅３３b ,‐１畅４７a , and‐１畅３９ab) . Cover of dominant tussock grasses andherbs were not significantly different in １９９９ . Soils in the grazed treatments still showed in ２００６ lower percentages of fineparticles such as Clay (１３ .１a , １１ .２b and １０ .３b) , Fine Silt (１３ .５b , １４ .２ab and １５ .３a) , Coarse Silt (５ .４c , ７ .８b and １０ .６a)and Very Fine Sand ( １５畅０b , １７畅４a , １７畅６a) , but were enriched in coarse particles including Fine Sand ( ２５畅３a , ２５畅４a and２３畅２b) , Medium Sand (１６畅９a , １４畅８b and １４畅８b) , Coarse sand ( ７畅９a , ６畅４b and ６畅４b) , and Very Coarse Sand ( ３畅０a , ２畅９aand １畅８b) . The lower levels of organic carbon in grazed treatments that were evident in ２０００ no longer differed significantly in２００６ (１畅４７ , １畅４６ and １畅６０％ ) , but significantly different contents of Total Nitrogen ( ０畅１４b , ０畅１５b and ０畅１７a ) and P(１５畅５b , ２４畅２a and １８畅７b) were observed .Conclusions The １１ year period of high stocking rates did not generate physiognomic changes in the Magellanic steppes , as thesesystems seem to persist in Stable States ( Oliva et al . ,１９９８) , but subtle effects such as a reduction in palatable grass cover anddiversity , the increase in dwarf shrubs , reduced soil fertility ( N and P ) and coarser soil textures ( probably because intensewinds eroded fine particles away from unstable grazed soil surface ) were evident after ７ years , regardless of the grazingmanagement in the recovery period . The results indicate the importance of gradual processes with long‐lasting and cumulativeeffects on vegetation and soil of these perennial‐dominated tussock grasslands , and underline the importance of careful long‐timemanagement in order to assure sustainable sheep grazing .ReferencesOliva , G . , Collantes , M . , Humano , G . , ( ２００５ ) . Demography of Grazed Tussock Grass Populations in Patagonia .Rangeland Ecology and Management . ５８ :４６６‐４７３ .Oliva , G . , Cibils , A . , Borrelli , P . , Humano , G . , ( １９９８ ) . Stable States in Relation to Grazing in Patagonia : A １０‐yearexperimental trial . Journal o f A rid Env ironments . ４０ : １１３‐１３１ .

Long-Time Effects of Grazing on Patagonian Rangelands (Argentina)

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Long-Time Effects of Grazing on Patagonian Rangelands (Argentina)

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