01955nas a2200253   4500008004100000245010600041210006900147300001300216490000700229520114300236653000901379653001501388653001201403653002201415653002101437100001901458700002001477700002001497700001801517700001501535700001501550700001901565856011701584       2005                        eng d00aAn ecosystem in transition: causes and consequences of the conversion of mesic grassland to shrubland0 aecosystem in transition causes and consequences of the conversio  a243 -2540 v553 aWoody plant expansion is one of the greatest contemporary threats to mesic grasslands of the central United States. In this article, we synthesize more than 20 years of research to elucidate the causes and consequences of the ongoing transition of C4-dominated grasslands to savanna-like ecosystems codominated by grasses and woody plants. This transition is contingent on fire-free intervals, which provide the opportunity for recruitment both of new individuals and of additional shrub and tree species into this grassland. Once shrubs establish, their cover increases regardless of fire frequency, and infrequent fires accelerate the spread of some shrub species. This process has resulted in a new dynamic state of shrub–grass coexistence in the mesic grasslands of North America. Important consequences of this shift in plant life-form abundance include alterations in plant productivity, species diversity, and carbon storage. Without drastic measures such as mechanical removal of shrubs, it is unlikely that management of fire and grazing regimes alone will be sufficient to restore historic grass dominance in these ecosystems.10afire10aGrasslands10aGrazing10atallgrass prairie10awoody vegetation1 aBriggs, J., M.1 aKnapp, Alan, K.1 aBlair, John, M.1 aHeisler, J.L.1 aHoch, G.A.1 aLett, M.S.1 aMcCarron, J.K.  uhttp://knz.lternet.edu/content/ecosystem-transition-causes-and-consequences-conversion-mesic-grassland-shrubland