ABSTRACT
Summary Detached joints or pads of plains pricklypear cactus (Opuntia polyacantha) can root and form new plants. However, few data exist to quantify this phenomenon or to describe conditions under which rooting takes place. A severe hailstorm at the Central Plains Experimental Range in northeastern Colorado on 31 July 1978 broke segments from plants of plains pricklypear. This occurrence provided an opportunity to determine the amount of joint dispersal and rooting from a natural destructive event. Cactus joints detached and scattered by the force of the hail were counted on permanent belt transects established in two pastures having different pricklypear populations. One year later, the transects were sampled again to determine the number and proportion of joints that had successfully rooted and become established. In one pasture, where the average ground cover of pricklypear was approximately 1.2%, the hail detached 4,100 cactus segments/ha. In the other pasture, pricklypear totaled about 3.3% of ground cover and hail detached 19,100 segments/ha. In the pasture with less pricklypear, 34% of the segments had rooted by August 1979, while only 13% of the segments had rooted in the other pasture. However, the population of rooted segments was equivalent to 1,400 and 2,400 new plants/ha in the pastures with less and more pricklypear, respectively. Precipitation from the 1978 hailstorm through the first 4 months of 1979 was less than 100 mm (67% of the long-term average). Some joints had short roots on the underside in late winter of 1978-1979, but no roots reaching the soil were found in April. In May and June, more than 200 mm of precipitation fell, almost twice the average for that period. The detached pricklypear joints that eventually rooted survived 9 months of unfavorable moisture conditions and then were able to root successfully after moisture became available. This remarkable adaptability may be one of the reasons why pricklypear is so prevalent on the Great Plains.
