Mechanical control of invasive Pyracantha shrubs under three felling frequencies

Abstract

Mechanical control is widely used to reduce the invasion of exotic shrubs and the effort must persist until regrowth is almost nil. A regime of frequent felling implies more intense short term effort, but should weaken the plant faster and could imply a lower long term effort. Here we propose to find the best felling frequency. In the mountains of Córdoba, Argentina, we selected 192 shrubs of Pyracantha angustifolia and P. aff. atalantioides, we measured their sizes, felled them at the base, applied three treatments of regrowth felling frequencies: annual, biennial and at year 4, and measured all felling times. Shrub survival in year 5 was 36, 83 and 91% for the annual, biennial and at year 4 felling treatments, respectively. The average height before felling the shrubs was 323±13 cm, and after a year, the regrowth measured almost half. For the annual felling treatment, regrowth height was successively lower. For the treatment of biennial felling, the height of regrowth reached 84 and 88% of the original height in years 2 and 4, respectively. For the felling treatment in year 4, the shrubs reached a height of 351±13 cm, exceeding their pre-felling height by 20 cm. The number of fruits for annual and biennial felling treatment was 0 and 33 fruits.shrub^-1.year^-1, respectively, and in the felling treatment in year 4, fruiting increased from 0 to 565±85 fruits.shrub^-1.year^-1 from year 1 to year 4. Only the annual felling treatment presented a year-to-year reduction in felling time. We conclude that the mechanical control of Pyracantha should consider frequent regrowth felling.