O\u27Reagain, Peter J.

Orr, David M.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 21st International Grassland Congress / 8th International Rangeland Congress Grazing Impacts on the Dynamics of Two Long Lived Perennial Grasses in Tropical Australia David M. Orr Department of Primary Industries and Fisheries, Australia Peter J. O'Reagain Department of Primary Industries and Fisheries, Australia 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/21/3-1/41 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. 瞯 ]472　 瞯 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅰ 　Grasslands/Rangelands Resources and Ecology ——— Soil‐Plant‐Animal InterrelationshipsGrazing impacts on the dynamics of two long lived perennial grasses in tropical AustraliaD . M . Orr and P . J . O摧ReagainDep t . Primary Industries and Fisheries , PO Box 6014 , Rockhamp ton Mail Centre , Queensland 4702 , A ustralia . E‐mail :dav id .orr＠ dp i . gld .gov .au .Key words : Bothriochloa ewartiana , Chrysopogon f allax , demographyIntroduction Bothriochloa ewartiana ( desert bluegrass ) is a long lived perennial grass which is important for the northernAustralian pastoral industry , however , little is known of its basic population demography . Interim results from an extensivegrazing study indicated that rainfall had a greater impact than grazing pressure on the dynamics of B . ewartiana ( Orr andO摧Reagain ２００５) but suggested that a more pronounced grazing impact may emerge with time . This paper reports further dataon the continuing impacts of rainfall and grazing on B . ewartiana and also on another long lived perennial grass Chrysopogonf allax ( golden beard grass) .Materials and methods A large grazing study was established in １９９７ in open Eucaly p tus savanna at Wambiana , ChartersTowers (２０°３４′S , １４６°０７′E) , northern Australia to asses the impacts of ５ grazing strategies on animal production and resourcecondition . In １９９８ , ２０ permanent quadrats ( ５０ × ５０ cm ) delineated ４０ B . ewartiana and a variable number of C . f allaxplants to examine their persistence under constant light ８ ha/ Animal Equivalent ( AE) and heavy stocking ( ４ ha/ AE ) androtational wet season resting ( ６ ha/ AE) with３３％ of the pasture rested annually . ( The rotational stocking treatment waschanged to ９ ha/ AE in ２００３ and the heavy grazing treatment to ６ ha/ AE in ２００５ ) . The dynamics of B . ewartiana and C .f allax are charted annually by charting the survival of original plants along with that of recruited seedlings ( Orr and O摧Reagain２００５) . Plant survival was analysed using a proportional hazards survival model ( Cox １９７２) .Results and discussion Seasonal rainfall ( October‐March) between １９９８‐１９９９ and ２０００‐２００１ was above the long term mean (５１３mm) while rainfall since ２００１‐２００２ has been below the long term mean ( Figure １ ) . Seedling recruitment of both speciesbetween １９９８ and ２００７ has been minimal such that the persistence of both species is due almost entirely to the presence of theoriginal plants . Survival of the original B . ew artiana plants has been reduced ( P ＜ ０ .０５ ) by heavy grazing particularly after２００５ ( Figure １a) while survival of the original C . f allax plants has been reduced ( P ＜ ０ .０５ ) by light and rotational grazingparticularly af ter ２００２ ( Figure １b) .Figure 1 Changes in the surv iv al (number o f p lants) o f ( a) B . ewartiana and (b) C . fallax in relation to seasonal rain f all(October‐March) (mm) between １９９８ and ２００７ under ３ graz ing strategy at W ambiana .Conclusions Contrary to previous findings , these results indicate a clear impact of grazing pressure with increasing grazingpressure reducing the survival of B . ewartiana but increasing that of C . f allax . These current results also emphasise theimportance of long term research in drawing valid management conclusions .ReferencesCox , D . R . (１９７２ ) . Regression and life tables . Journal Royal Stat . Soc . , Series B ３４ , １８７‐２２０ .Orr , D . M . and O摧Reagain , P . J . (２００５ ) . Rainfall and grazing impacts on the population dynamics of Bothriochloa ewartianain tropical Australia . XX International G rassland Congress , pp . ５２６ .(a) 40 ~ 30 C: OS a. o 20 .s 1 -~ 10 :::, en 800 600 400 ---- Rotational -.-Heavy 200 --Rainfall 0 +----,-......--.....----,-....... - ............. - ....... -.....---+ 0 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 (b) 25 800 20 600 15 I 400 ;;' 10 J!! C: ·ca 5 200 c::: 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 

Grazing Impacts on the Dynamics of Two Long Lived Perennial Grasses in Tropical Australia

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Grazing Impacts on the Dynamics of Two Long Lived Perennial Grasses in Tropical Australia

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