The composition and dynamics of local plant communities are strongly affected by increasing densities of this juniper species. Several aspects of this process and its effects are being currently being studied by members of Fowler's group, including competition, fire, and the dynamics of the encroachment process itself.
"Understanding the juniper juggernaut: patterns and mechanisms of shrub encroachment in central Texas" (Fowler and Batchelor 2005) powerpoint from talk given at the 2005 ESA meeting
Ana Gonzalez is studying the dynamics of woody plant encroachment in central Texas savannas by analyzing sequential aerial photographs.
Peggy Batchelor found that adult junipers facilitate the survival of seedling junipers, but slow their growth; Quercus fusiformis (live oak) does not facilitate juniper seedlings. Facilitation is probably due to amelioration of water stress.
The pronounced clustering of J. ashei commonly observed in central Texas savannas is apparently mostly due to to bird dispersal and to many seeds remaining under maternal plants.
As Juniperus ashei and other woody plants increase in size and abundance in a site, they reduce the habitat available for herbaceous species that cannot live under woody plant canopies. They also increase the fragmentation of the habitat for these herbaceous species. Karen Alofs is studying the effects of habitat fragmentation on these species. She has found that fragmentation reduces native species richness but may also block the spread of B. ischaemum.
Jill Noel studied the effects of fire on J. ashei. Fire survival rates increase with plant size, but even the smallest plants (<0.5m tall) are likely to survive a winter fire. It may be, however, that summer fires, if they were allowed, would kill more junipers and therefore maintain savannas.
Bothriochloa ischaemum, an invasive Eurasian grass, can form near-monocultures. It is more common along roads, but its distribution is unrelated to fire or grazing. In a garden experiment it out-competed the largest common native grass, Schizachyrium scoparium.
