The effect of shrub clearing on the control of the fire-prone species Ulex parviflorus

Vegetation clearing is a fuel control technique used to reduce the risk of fires in fire-prone shrublands (e.g. Ulex parviflorus (gorse) shrublands). Nonetheless, its efficacy can be undermined as much by the reproductive strategies of the different species as by the structural organization of their phytomass. In our research we tested the hypothesis that effective control of Ulex parviflorus could be limited by the vertical dead/live shoot distribution and that this distribution could affect posterior growth. We applied clearing as a fuel-control technique in three juvenile shrublands. For the following 4 years, we studied the effects of this clearing application by measuring several structural variables of the individuals involved. At the end of the study we compared the structure of treated individuals with that of untreated ones. The clearing treatment eliminated only 46% of the population. The large dependence shown between cutting height and dead shoot height in relation to treatment effectiveness (individual mortality) suggests that applying the clearing treatment below the dead shoot level rather than above it would increase effectiveness considerably. In response to the loss of phytomass, the individuals that survived the clearing treatment increased their weight by a factor of 5 in the second year. This would explain the rapid re-establishment of the relation between phytomass and basal diameter after 2 years. Significantly larger values of phytomass and basal diameter showed a compensatory growth by the fourth year. These results show that clearing is not effective in young shrublands since it generates Ulex parviflorus-dominated shrublands in a short period of time. Temporal changes in the vertical dead/live shoot distribution are seen as a key morphological variable in the effectiveness of using clearing to control this species.