Insights from full-rotation Nelder spacing trials with <i>Eucalyptus</i> in São Paulo, Brazil

Abstract

The choice of spacing among trees for operational plantations is typically based on one or more experimental plantations that test for the response of tree and stand growth to a range of tree-to-tree distances. The most common design for spacing experiments entails rectangular plots that test different distances between rows, and between trees within rows, and with replication of plots covering one to several hectares within a single stand. Other designs may offer more information with simpler layouts, and we examined the insights that could be obtained from a Nelder (fan-shape) design, where spacing among trees varies with the radial distance from a central point. The response of Eucalyptus dunnii seed-origin trees to spacing was essentially similar between a classic plot design replicated in four blocks (tree spacing from 4.5 to 9.2 m² tree^-1, covering 1.4 ha of land), and a  Nelder design (tree spacing from 2.1 to 44.0 m² tree^-1, covering 0.6 ha of land). The Nelder design showed slightly higher volume increment  through 10 years of stand development than the block design (for the  range of overlap in spacing), but the treatment effect of spacing was essentially identical between the designs at the level of both trees and stands. A second Nelder experiment used clonal-origin trees from six clones, testing for differences in responses to spacing among clones. In all three spacing experiments and for all clones, individual-tree growth was greatest at the widest spacing and stand-level growth was highest at the tightest spacing. These trends were much clearer across the wider range of spacing tested in the Nelder plots (228 to 4 760 trees ha^-1) than in the narrower range of spacing tested in the block design (1 111 to 2 222 trees ha^-1). Current annual increment reached a higher, earlier peak at narrow spacing. At 8.5 years, the light use efficiency (stem volume growth per unit of light intercepted) was about twice as great for trees at narrow spacing than at wider spacing. Overall, the Nelder designs provided the same information on responses to spacing as the classic block design. The simplicity and small size of Nelder designs provide valuable insights for basic decisions on spacing for operational plantations, particularly when forestry extends into new geographic areas, new genotypes, and new silvicultural techniques.

Keywords: Eucalyptus clones, Eucalyptus dunnii, forest growth and yield, leaf area, light use efficiency, sawlog production

Southern Forests 2010, 72(2): 90–97