Can productivity and post-pruning growth of Jatropha curcas in silvopastoral systems be regulated by manipulating tree spacing/arrangement without changing tree density?

摘要

The potential of tree spacing/arrangement to alleviate effects of interspecific competitionof hedgerow intercropping systems on productivity and response to pruning of Jatrophacurcas (Jatropha) was investigated using a Jatropha e Pennisetum clandestinum (kikuyu) silvopastoralsystem at Ukulinga (KwaZulu Natal, South Africa). Treatments were differentiatedby presence/absence of kikuyu and arrangement/spacing of Jatropha trees (one, twoand three tree hedgerows on either side of the alley) and had the same tree density(1110 ha 1). When high water availability and kikuyu dormancy coincided, tree growthrates did not significantly differ across treatments. Trees of the treatment without interspecificcompetition (tree-only) were the tallest. Even when rainfall was high, post-pruningtree height growth rate was affected by belowground (BG) interspecific competition andtree spacing/arrangement. Treatment with a single tree hedgerow between alleys had themost frequent maximum stem growth rate and was the most efficient during limited wateravailability. Its trees showed slow initial response to pruning due to a high tree-grassinterface, followed by compensatory growth when competition for water with grass waslow. Generally, length of tree-grass interfaces affected yield inversely especially as treesmatured toward their maximum-yield age (4e5 years). BG competition reduced tree yieldmore than tree biomass, while tree spacing/arrangement did not affect tree harvest index.Manipulation of tree arrangement/spacing without changing tree density had no consistenteffects on tree productivity.