Results
Average animal stocking rate in 1983-1985 was 0.98 AU/ha/yr (AU = animal units = 350 kg live weight). However, the frequency distribution of this variable is asymmetric (skew = + 1.72), indicating that the median (0.67 AU/ha/yr) is a better measure of the central tendency of the data. The age of the stand at the first grazing changed over the years. Grazing was first experimentally introduced in 1979 in a 3 yr old plantation. In 1982 only stands >~ 4yr old were grazed, but by the end of 1984 stands as young as 2.5 yr were grazed. Grazing took place in stands 2.5-9.0 yr old. However, a dramatic increase in broadleaved species severely reduces animal carrying capacity in stands > 8 yr. Per cycle stocking rates in any given paddock varied between 0.10- 3.39 AU/ha/yr. This large variability is an expected outcome since pasture growth responds to short term events such as dry spells, periods with excessive rain and/or cloudiness (which further reduce the amount of light reaching the ground), unbalances between forage availability and grazing pressure in the previous cycle (which affects pasture recovery), etc. Analyses were thus conducted using annual averages of stocking rate per paddock. Annual stocking rate (S) per paddock over the whole measurement period (1983-1985) was low in plantations 3-4yr (0.85-0.88), increased in plan- tations 5-6 yr old (1.09), and then declined in older plantations (0.52-0.90 (Table 1). Data from 1984 show the same pattern (Fig. 1). In 1984, S for pine stands 3-8 yr old was 0.93 AU/ha/yr; a maximum of 1.38 AU/ha/yr was reached at plantation age 5 yr. A quadratic equation was fitted to the 1984 data (R 2 --- 0.75; p < 0.0009;