The  Impact  of  Ambrosia  trifida  (giant  ragweed)  on  Native  Prairie  Species   in  an  Early  Prairie  Restoration  Project.       An  Honors  Thesis   Presented  to   The  Department  of  Earth  and  Environmental  Sciences   of  the  University  of  New  Orleans     In  Partial  Fulfillment     of  the  Requirements  for  the  Degree  of     Bachelor  of  Science,  with  University  Honors   and  Honors  in  Earth  and  Environmental  Sciences     by   Krisztian  Megyeri   December  2011 ACKNOWLEDGEMENTS     I  wish  to  thank  my  major  professor,  Dr.  Martin  O’Connell,  for  his  guidance  not   only  through  this  project,  but  throughout  my  undergraduate  experience.  I  would   also  like  to  thank  Dr.  Ioannis  Georgiou  for  offering  up  the  use  of  his  lab  space  and   drying  ovens.  For  all  of  their  continuous  and  enthusiastic  help  with  species   identification  and  insight  into  prairie  ecology,  I  would  like  to  thank  Dr.  Charles  M.   Allen,  Marc  Pastorek,  and  Brian  Early.  Additionally,  I  wish  to  thank  Wes  Michaels  for   integrating  ecological  research  into  the  Couturie  Forest  restoration  project.  Finally,   for  her  invaluable  help  with  all  fieldwork  throughout  the  hot,  humid  summer,  I   thank  Wendy  Hounsel.                                                ii TABLE  OF  CONTENTS     Section     Page         Acknowledgement     ................................................................................................................   ii     Table  of  Contents   ................................................................................................................   iii     List  of  Tables     ................................................................................................................   iv     List  of  Figures   ................................................................................................................   v     Abstract   ................................................................................................................   vi     Literature  Review   ................................................................................................................   1       Introduction   ................................................................................................................   16     Methods   ................................................................................................................   23     Results   ................................................................................................................   29     Discussion   ................................................................................................................   37     Conclusion   ................................................................................................................   41     References   ................................................................................................................   46                          iii LIST  OF  TABLES           Table     Page         Table  1   Results  showing  initial  cover  estimates  for  all  plots   30     Table  2   Survey  data  of  all  species  collected  in  all  sites   32     Table  3   Total  biomass  data  in  grams  for  all  30  plots   35     Table  4   List  of  species  by  botanical  and  common  names   42                                                  iv LIST  OF  FIGURES               Figure     Page         Figure  1   The  Couturie  Forest  and  Scout  Island  restoration  plan   22     Figure  2   Location  of  the  study  plots   25     Figure  3   MDS  plot  showing  the  (dis)similarity  within  and  between   36     treatments     Figure  4   Location  of  study  site  within  City  Park,  New  Orleans,  LA.     44       Figure  5   Frame  used  for  estimating  cover  percentage   44     Figure  6   Study  plot  with  sampling  plots  shown   45                                 v ABSTRACT       As  the  ecological  importance  of  prairies  is  becoming  more  recognized,  the   number  of  prairie  restoration  projects  is  increasing  worldwide.  One  of  the  major   challenges  in  restoring  any  disturbed  ecosystem  is  the  successful  establishment  of   native  species  at  the  expense  of  invasive  species.  While  some  weedy  species  are   gradually  replaced  as  other,  more  desired,  species  become  established,  there  are   invasive  species  that,  due  to  their  level  of  dominance,  may  out-­‐compete  native   species  indefinitely.  The  objectives  of  this  study  were  1)  to  quantify  the  impact  of   Ambrosia  trifida  (giant  ragweed)  on  the  plant  community  of  a  newly  established   prairie,  2)  to  assess  any  difference  in  effectiveness  between  management  practices   (cutting  versus  pulling)  of  A.  trifida,  and  3)  to  establish  a  baseline  vegetation  survey   to  be  used  in  future  evaluations  and  research  of  the  prairie.  In  March  of  2011,  30   plots  (each  3  m2)  were  established  within  the  20  acre  prairie  including  10  control   plots  [C],  10  plots  where  A.  trifida  was  selectively  cut  approximately  10  cm  above   ground  level  [Rc],  and  10  plots  where  A.  trifida  was  selectively  pulled  [Rp].   Treatment  (cutting/pulling)  was  applied  three  times  (April,  June,  and  August)   during  the  study,  and  in  order  to  compare  the  effectiveness  of  the  treatments,  the   number  of  removed  A.  trifida  was  recorded  for  the  first  two  applications.  Between   April  and  June,  the  number  of  A.  trifida  decreased  by  a  mean  of  34.9  individuals  in   the  cut  plots,  and  increased  by  a  mean  of  12.4  individuals  in  the  pulled  plots   suggesting  (albeit,  not  significantly)  that  pulling  may  disturb  the  ground  and    vi promote  the  germination  of  more  seeds  from  the  seedbed.  Final  biomass  data   collection  was  conducted  in  mid  August  by  removing  the  above  ground  biomass  of   all  plants  excluding  A.  trifida  from  four  subplots  within  each  of  the  30  main  plots,   followed  by  drying  and  weighing  of  all  biomass.  A  total  of  172  plants  from  39   species  were  removed  for  a  total  biomass  of  1735.10  grams.  In  the  control  plots,  the   mean  biomass  was  6.73g  and  the  species  diversity  (H’)  was  0.037.  In  the  treatment   plots,  the  corresponding  values  were  83.39g,  and  2.093.  This  twelve-­‐fold  difference   in  biomass  suggests  that  the  presence  of  A.  trifida  has  a  remarkable  impact  on  the   overall  community  of  this  newly  established  prairie  and  that  the  correct   management  of  A.  trifida  could  expediate  the  restoration  process.                                               Keywords:  Restoration,  Ecology,  Invasive,  Prairie,  Amborsia  trifida,  ragweed  vii 1   LITERATURE  REVIEW         The  Prairie       There  are  numerous  definitions  of  a  prairie  depending  on  the  specific  climate,   region,  and  the  array  of  plants  in  the  community.  In  its  basic  definition,  a  prairie  is   simply  a  grassland  characterized  by  a  dominance  of  herbaceous  plants,  especially   grasses,  some  shrubs,  and  an  absence  of  trees.  Furthermore,  one  can  add  that  this   ecosystem  depends  on  certain  natural  forces  with  which  it  has  evolved  over  time.   While  most  people  think  of  prairies  as  arid,  rainfall  can  and  does  vary  greatly.  In   North  America,  for  instance,  the  Great  Plains  varies  in  precipitation  from  West  to   East  and  thus,  has  both  shortgrass  steppes  as  well  as  tallgrass  prairies.  The  coastal   prairie  of  Louisiana  is  similar  in  community  composition  to  the  midwestern   tallgrass  prairies,  but  there  are  certain  differences  between  the  two.  For  instance,   because  of  the  higher  rainfall  and  the  potential  for  the  coastal  prairie  to  turn  into   marshland,  plants  like  Panicum  virgatum  (switchgrass)  are  more  common  in  a   coastal  prairie  (Allain  et  al.  1999).  Some  of  the  other  species  more  common  in   coastal  prairies  are  Solidago  odora  (sweet  goldenrod),  Asclepias  rubra  (red   milkweed)  and  the  grasses  Dichanthium  tenue  (slender  bluestem)  and  Paspalum   plicatulum  (brown-­‐seed  paspalum)  (Allain  et  al.  1999).  Native  Americans  and   European  settlers  used  numerous  plant  species  of  the  coastal  prairie  for  food,   spices,  dyes,  textiles  and  medicines  (Allain  et  al.  1999). 2   The  history  of  the  prairie     The  majority  of  the  grassland  biome  of  North  America  stretches  West  to  East   from  the  eastern  edge  of  the  Rocky  Mountains  to  Illinois-­‐Indiana,  and  North  to  South   from  Saskatchewan,  Alberta  to  central  Mexico.  This  great  expanse  of  grassland   developed  and  was  maintained  due  to  several  geological,  ecological  and  climatic   factors.  The  latest  retreat  of  the  North  American  ice  sheets  (approximately  10,000-­‐ 12,000  BP)  caused  the  warming  of  the  climate  as  well  as  the  leveling  of  topography,   both  factors  favoring  the  formation  of  the  grasslands  of  central  North  America   (Axelrod,  1985).  Floral  and  faunal  fossils  suggest  the  increasing  aridity  during  the   Miocene  and  Pliocene  restricted  the  forests  that  once  dominated  the  Great  Plains,   thereby  aiding  in  the  explosive  evolution  and  dominance  of  grassland  species   (Axelrod,  1985).  This  aridity  aided  the  grasses  by  means  of  a  feedback  system   described  by  Keeley  &  Rundel  (2005):     Critical  elements  [of  the  expansion  of  grasslands]  were  seasonality  that   sustained  high  biomass  production  part  of  year,  followed  by  a  dry  season   that  greatly  reduced  fuel  moisture,  coupled  with  a  monsoon  climate  that   generated  abundant  lightning-­‐igniting  fires.  As  woodlands  became  more   open  from  burning,  the  high  light  conditions  favoured  C4  grasses  over  C3   grasses,  and  in  a  feedback  process,  the  elevated  productivity  of  C4  grasses   increased  highly  combustible  fuel  loads  that  further  increased  fire  activity.     The  essential  difference  between  C and  C  plants  is  their  respective  photosynthesis   3   4 process,  and  C  plants  photosynthesize  faster  under  high  light  and  temperature   4 conditions  due  their  specific  enzyme  pathways.  Coupled  with  their  more  efficient 3   use  of  water,  C  plants  are  more  suited  to  grassland  environments  than  their   4 counterparts.     Another  important  factor  in  the  expansion  and  maintenance  of  grasslands  is   the  coevolution  of  grasses  and  herbivores.  Throughout  history  there  were  cycles  of   the  type  (grazers,  browsers),  and  abundance  of  herbivores.  In  North  America,  the   diversity  of  ungulates,  (including  horses,  camels,  pronghorns,  hogs,  rhinos,  and   elephant-­‐like  animals)  as  well  as  rodents,  peaked  during  the  Miocene  to  a  degree   that  is  comparable  to  the  savannas  of  contemporary  Africa  (Webb,  1977).  This  rise   in  diversity  was  partially  due  to  the  increased  migration  of  savanna  species  between   North  and  South  America  by  way  of  the  newly  formed  Isthmus  (land  bridge)  of   Panama  (Webb,  1977).  One  of  the  latest  of  the  herbivorous  species  to  have  greatly   contributed  to  the  grassland  ecosystem  is  the  bison.  It  is  believed  that  bison  arrived   from  Eurasia  during  the  Pleistocene,  and  that  their  presence  greatly  altered  the   herbivore  fauna,  possibly  due  to  their  high  fecundity  and  aggressive  grazing   (Stebbins,  1981).  Many  of  the  previously  dominant  herbivores  became  extinct  while   the  bison  numbers  continued  to  increase  (Stebbins,  1981).  While  bison  may  have   adversely  affected  their  herbivorous  counterparts  to  some  degree,  the  late   Pleistocene  extinction  of  a  large  number  of  mega  fauna  is  believed  to  be  attributed   to  climate  change,  as  well  as  hunting  pressures  from  humans  (Barnosky,  et  al.  2004).   What  is  known  is  that  by  the  Holocene,  bison  became  one  of  the  few  dominant   herbivorous  species  of  the  North  American  prairie.  According  to  the  earliest   estimates  in  the  mid-­‐late  1800’s,  bison  may  have  numbered  between  30  million  and   60  million  (Knapp  et  al.  1999).  These  vast  numbers,  however,  would  plummet  to