Leonard, E. D.

Monaco, Tom A.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 21st International Grassland Congress / 8th International Rangeland Congress Does Disturbance Similarly Facilitate Weed Invasion within Grass, Forb, and Shrub Plots? Tom A. Monaco U.S. Department of Agriculture E. D. Leonard U.S. Department of Agriculture 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/21/1-3/9 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 ]108　 瞯 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅰ 　Grasslands/Rangelands Resources and Ecology ——— Ecology of Grasslands/RangelandsDoes disturbance similarly facilitate weed invasion within grass , forb , and shrub plots ?T .A . Monaco and E .D . LeonardUSDA‐ARS Forage and Range Research L ab . Utah State University , Logan , Utah 84322 , U .S .A . , E‐mail :tom .monaco＠ars .usda .govKey words : grow th form , soil resources , safe sites , Bromus tectorum , Isatis tinctoriaIntroduction Big sagebrush communities ( A rtemisia tridentata Nutt .) in the Great Basin have been degraded by the synergisticconsequences of chronic disturbance and annual weed invasion ( Young and Evans １９７８ ) . Repairing ecosystem function is anoverarching goal of restoration efforts , but it remains unclear which species most effectively resist weed invasion and howdisturbance mediates weed invasion . We evaluated whether disturbance similarly facilitates invasion in single‐species grass ,forb , and shrub plots .Materials and methods Experiments were conducted at Millville , UT ( ４１°３９ .４４′N , １１１°４８ .８８′W , １４０２ m ) . The soil is agravelly loam series . Plots (１ .５ m × １ .５ m , １ m aisles) were established in May ２００３ f rom transplants reared in a greenhouse ,and consisted of ２４ plants in a ５ × ５ square arrangement equally spaced (３０ cm apart) , w ith the center plant absent . Three plot‐types were randomly located with ３０ replicates : grass ( A gropy ron cristatum [ L .] ) , forb ( A chillea lanulosa [ Nutt .] Piper) ,and shrub ( A rtemisia tridentata var .wyomingensis [Beetle & A . Young] Welsh) . A disturbance treatment was applied in midNovember ２００４ to １５ replications by removing four plants from the １ m２ center of plots with a shovel to potentially increaseabove and below‐ground resources and create safe seed sites for the two invasive species . Plots were seeded an invasive annualgrass ( Bromus tectorum L .) and an invasive forb ( Isatis tinctoria L .) autumn ２００４ and ２００５ ( ４００ seeds per species) . Totalweed seedling density was determined in summer ２００５ and ２００６ . Total ( non‐weed ) shoot dry mass , soil nitrate and solarradiation (４００‐７００ nm) at the soil surface was determined for plots in summer ２００６ .　 　 　 Figure 1 Mean ( ＋ １ SE) weed density in autumn .( Lowercase letters indicate di f f erences ( P ＜ ０畅０１ ) .Results Disturbance significantly increased weed density for allthree grow th forms except for A gropy ron in ２００６ ( Figure１) . Within a treatment , weed density was less variable in２００５ than ２００６ . Weed density also sharply increased between２００５ and ２００６ in all plots except A gropy ron . In fact , weeddensity declined within disturbed A gropy ron plots during thestudy . In contrast , A chillea and A rtemisia plots had ２‐３ foldgreater weed density than A gropy ron . Total plot non‐weedshoot dry mass ( g ) of A chillea ( １９５７ ± ５４２ ) was lower ( P＜ ０ .０１) than A gropy ron (４６０８ ± ５４２ ) , which was lower ( P＜ ０畅０１ ) than A rtemisia ( １４ ,５９４ ± ５４２ ) . The disturbancetreatment did not consistently increase soil nitrate ( mg kg‐１soil) or solar radiation at the soil surface ( mol m２ s‐１ ) .However , A chillea plots had significantly greater ( P＜ ０畅０１)mean soil nitrate and solar radiation ( ５ .２ ± ０ .０５ and ３８２ ±５０) than A gropy ron ( １ . ３ ± ０ . ０５ and ３５５ ± ５０ ) andA rtemisia (０ .９ ± ０ .０５ and １５５ ± ５０) plots , respectively .Conclusions The importance of disturbance to mediate weed invasion is clearly corroborated by our results . The capability of thelong‐lived perennial grass ( A gropy ron) to resist invasion appears to be associated with greater biomass productivity . Incontrast , high susceptibility to weed invasion of A chillea plots was due to significantly greater amounts of underutilized aboveand belowground resources (Davis et al . , ２０００) . Our results agree with the general contention that disturbance events increaseavailable resources or safe sites for weed invasion . Perennial grasses appear to be a necessary component of minimizingunderutilized resources . Our results also emphasize that managerial efforts to reduce the recurrence of disturbance events shouldbe a primary goal to reduce the impacts and prevent continual dominance of invasive annual species in the sagebrush‐steppeecosystems of the Great Basin .ReferencesYoung , J . A . , Evans , R . A . , １９７８ . Population dynamics after wildfires in sagebrush grasslands . Journal o f RangeManagement ３１ :２８３‐２８９ .Davis , M .A . , Grime , J . P . , Thompson , K . , ２０００ . Fluctuating resources in plant communities : a general theory ofinvisibility . Journal o f Ecology ８８ :５２８‐５３４ .700 €J □ intact E ■ disturbed a (/) CJ) 525 C '5 Q) Q) !:E, ~ 350 b "iii C Q) C ""Cl ""Cl Q) 175 d Q) s 0 Agropyron Achillea Artemisia Agropyron Achillea Artemisia 2005 2006 

Does Disturbance Similarly Facilitate Weed Invasion within Grass, Forb, and Shrub Plots?

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Does Disturbance Similarly Facilitate Weed Invasion within Grass, Forb, and Shrub Plots?

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