Growth of Prosopis glandulosa in response to changes in aboveground and belowground interference

Recent increases in woody plant density have occurred in grasslands worldwide, but both the cause and mechanisms involved in these changes have been elusive. Changes in grass biomass mediated by high levels of constant herbivory seem to be the pivotal reason. In this field study in central Texas, USA, effects of aboveground and belowground interference on the growth of seedlings of a deep-rooted, woody heliophyte, Prosopis glandulosa, were tested. The effects of two positions (gap or Bouteloua curtipendula grassland), two levels of aboveground interference (high or low light), and three levels of grass root interference (2, 20, and 40 cm deep root excluders) on P. glandulosa aboveground, belowground, and total dry mass were measured. The exclusion of belowground interference significantly increased aboveground, belowground, and total P. glandulosa dry mass, with the reduction of belowground interference to a depth of 20 cm maximizing P. glandulosa dry mass. Aboveground, belowground, and total dry mass of P. glandulosa were not significantly different when grown in gaps compared to grasslands, nor were there any significant differences when aboveground interference (shade) was imposed. However, the trend was for greater dry mass in gaps and high light. Data indicate that belowground interference from grass roots significantly reduces the dry mass of P. glandulosa, while aboveground interference has a lesser effect.