Indices of interspecific plant competition for Pinus radiata in the central north island of New Zealand

Abstract

Pinus radiata D. Don was grown on its own and with a range of densities of either buddleia (Buddleja davidii Franchet) or broom (Cytisus scoparius L.), two important forest weed species, in a field trial at Rotorua, New Zealand. Tree growth from the time of planting to age 3 was modelled as a function of tree size and a competition modifier. The competition modifier is, in effect, a multiplier that reduces tree growth according to the degree of competition defined by a competition index (CI). A range of CIs, with some sensitivity to both weed and tree growth and development over time, were individually incorporated into the modifier and evaluated. The "best" CI combined measures of weed height relative to tree height, proximity of the weed to the tree, and weed abundance, and was negatively correlated with an index of light availability. For a given value of CI, the effect on tree growth was independent of weed species. For diameter growth, the effect of CI was independent of tree age. However, for height growth the negative effect of a given CI value was much higher in year 3 than in years 1 and 2. This suggest that competition has an immediate effect on diameter but a delayed effect on height growth.

Neighbour‐regulated mortality: the influence of positive and negative density dependence on tree populations in species‐rich tropical forests

“…The effects of spacing and neighbour identity on the growth and survival of larger trees have been reasonably well studied in temperate forest plantations (e.g. Martin & Ek 1984; Richardson et al. 1999; Cao et al.…”

Effects of overtopping on growth of white spruce in Alaska

“…where y 0 and y 1 are volume at the beginning and end of the time period (year), respectively; CI is a competition index; and a, b, and m 1 are model parameters to be estimated, as presented in Richardson et al (1999). Volume was derived using the formula for a cone (one-third height × basal area at 15 cm).…”

Relative persistence of commonly used forestry herbicides for preventing the establishment of broom (Cytisus scoparius) seedlings in New Zealand plantations

“…Studies carried out on both moist (Richardson et al 1996;Richardson et al 1999) and dry sites (Clinton et al 1995;Richardson et al 1997;Richardson and Whitehead 2002;Watt et al, 2003) have shown that broom can have a large negative influence on radiata pine growth during the establishment phase. These effects persist in stands that are slow to close canopy.…”