Planting orientation of Portulacaria afra cuttings for thicket restoration: vertical versus horizontal

Abstract

Aim. The re-establishment of Portulacaria afra in the landscape-scale Subtropical Thicket Restoration Programme has exclusively used vertically-orientated truncheons (i.e. large cuttings with the main stem planted 10-20 cm into the ground). Despite the planting of millions of truncheons, the rates of survival, growth and restoration are low. This may be driven by browsing pressure and/or drought conditions during the truncheon establishment phase. Here we conduct a common garden experiment to explore the establishment of horizontal versus vertically orientated truncheons. Horizontal truncheons have their main stem buried in the soil and only a few side branches exposed above ground — these truncheons may experience reduced water stress. Here we compared the levels of water stress during the establishment phase of truncheons with different orientation. Location. Eastern Cape, South Africa Methods. Our experiment involved three planting treatments for truncheons: vertical orientation, horizontal orientation, and horizontal orientation with exposed side branches clipped. Truncheons were grown for two months and plants were well-watered. On two occasions during the experiment, photosynthetic efficiency was measured on all plants to ascertain levels of plant stress. After the experiment, the root, stem and leaf dry mass were recorded for each replicate, as well as leaf moisture. Results. The root mass proportion (of the total plant) was not significantly different among treatments. Despite this, leaf-level photosynthetic efficiency was recorded as significantly lower in vertical truncheons versus horizontal truncheons. Main conclusions. Smaller horizontally-orientated truncheons do not grow roots at a faster rate (relative to their total size) than the larger vertically-orientated truncheons that have more leaf material to support. Nonetheless, under well-watered conditions, the larger truncheons experienced stress evidenced by lowered leaf photosynthetic efficiency values. Thus, we suggest that horizontal buried truncheons may have a higher likelihood of survival under seasonal drought-stress conditions. It remains to be tested whether horizontally-orientated truncheons (with less above-ground biomass) experience lower rates of herbivory than the standard vertical cuttings. 9 10 11 12 13 14 15 16 17 18 19