Effects of a low-cost crate-based tree-propagation system on the field performance of framework species when initiating lowland tropical forest restoration

The need for cost-effective nursery techniques that maximize planted tree performance is growing, to meet surging demand from forest-ecosystem restoration projects around the tropics. We tested the hypothesis that propagating trees in polybags in bottle-crates promotes air root-pruning, thus stimulating root development and improving 1^st-year performance of trees, planted to restore tropical forest. Working with five framework tree species (those that catalyse forest-ecosystem restoration), in a small-scale nursery in southern Thailand, we compared: 1) saplings in polybags in crates on the ground (COG) and 2) the same, raised on wire benches (COB), with 3) a control: non-crated polybags on the ground (CON). Sapling growth and survival were recorded monthly for 358 days, after which root dry weight and architecture were assessed. Saplings were then planted in a restoration plot, and their survival and growth monitored over the first growing season. In the nursery, crating substantially reduced shoot:root ratios (on average by 59.4 %, with COG). In the field, crating significantly increased mean height growth of almost all species, by up to 71.0 % and crown expansion by up to 32.5 %. The COB and COG treatments increased mean sapling performance index (combined growth & survival, across species), from the control value of 56.5 to 81.8 and 82.6 respectively (P=0.017 and 0.005), with COG being the most cost-effective method (saving 4-5 cents per tree). Crating is recommended for producing saplings for forest restoration and potentially for agroforestry, community forestry etc. The system repurposes a commonplace resource (discarded crates)—a more environmentally-friendly solution than importing purpose-made root-trainers.