The effects of neighbors and grazing on the growth of Helianthus paradoxus

Helianthus paradoxus (puzzle sunflower) is a rare species of annual sunflower (Compositae) that grows in inland saline marshes in four locations world-wide. One location is the Diamond-Y Springs Preserve, north of Fort Stockton, Texas (31 degrees 10'N, 102 degrees 45'W) and three locations are in central and southeastern New Mexico. The importance of neighbors (competitors) and the impact of grazing on X. paradoxus are unknown. In this experiment, the effects of neighbor removal (clipping and herbiciding) on Helianthus paradoxus were evaluated within salt marsh plots that were grazed or ungrazed by large ungulates. Analysis of variance indicated significant effects of neighbors. The presence of grazers did not have a significant effect on plant stem length, but did cause a 32% reduction. The number of flowers (heads) was reduced 22 to 54% and basal diameter was reduced 3 to 21% when grazers were present, but the magnitude was dependent on the neighbors. Overall, with neighbors present, the mean number of flowers was reduced 57% and basal diameter was reduced 39% compared to removal. The presence of grazers caused a reduction in flower, leaf and stem dry mass by 49%, 39% and 25% respectively. Flower, leaf and stem dry mass were all significantly affected by the presence of neighbors and increased 2.38, 2.61 and 2.75 times respectively with neighbor removal. Thus, grazing by large ungulates will reduce various indicators of Helianthus paradoxus growth and reproduction, but the presence of neighbors caused the greatest reduction.