02741nas a2200229   4500008004100000245010100041210006900142300001500211490000700226520198700233653000702220653000702227653002202234653000902256653001002265653002202275653003202297653002002329100001902349700002002368856012302388       2003                        eng d00aC3 shrub expansion in a C4 grassland: positive post-fire responses in resources and shoot growth0 aC3 shrub expansion in a C4 grassland positive postfire responses  a1496 -15010 v903 aChanges in land management and reductions in fire frequency have enabled woody species to increase in grasslands worldwide. Nevertheless, fire is rarely eliminated from grasslands, and for shrubs to survive, they must be able cope with fire and replace aboveground structures. Because new shoots may have more available solar radiation, greater root : shoot ratios, and thus more resources available belowground after fire compared to undisturbed shrub communities, we hypothesized that carbon, nutrient, and water relations may be enhanced in stems compared to those in an undisturbed grassland. However, this same post-fire resource pulse stimulates the grasses and may intensify competitive interactions between shrubs and grasses. To test these predictions, we measured seasonal patterns in net photosynthesis (A), predawn xylem pressure potentials (XPP), leaf nitrogen (N) content, and productivity of Cornus drummondii shoots from shrub patches (islands) of different sizes in mesic grasslands burned annually, burned infrequently, and protected from fire. Seasonal average A was 20% higher (P = 0.016) in burned than in unburned shrubs, regardless of island size. Shrubs in burned sites also produced shoots with higher leaf N than unburned shrubs, and N content was higher in leaves from small islands compared to large islands (P < 0.0001). Burning caused a decrease in late summer predawn XPP in small islands (−3.1 MPa), whereas burned large islands did not differ from unburned shrubs. Post-fire productivity of new shoots was significantly greater compared to shoots in unburned sites. These results indicate that a transient period of high resource availability after fire allows for increased growth and rapid recovery of grassland shrubs. Thus, although fire has a negative effect on aboveground biomass of shrubs, the post-fire increases in resource availability, which enhance growth in the dominant grasses, are also important for recovery of woody species.10aC310aC410aCornus drummondii10afire10ashrub10atallgrass prairie10atransient maxima hypothesis10awoody expansion1 aMcCarron, J.K.1 aKnapp, Alan, K.  uhttp://knz.lternet.edu/content/c3-shrub-expansion-c4-grassland-positive-post-fire-responses-resources-and-shoot-growth