Biomass allocation in five semi-arid afforestation species is driven mainly by ontogeny rather than resource availability

Abstract

& Key message The changes in the relative biomass allocation to roots in juvenile stands of fast-growing (Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L.) and slow-growing (Anacardium occidentale L. and Parkia biglobosa Jacq.) afforestation species are driven mainly by ontogeny rather than resource availability. However, silvicultural management aiming at increasing availability of water and particularly nutrients enhances biomass production in all species. & Context Understanding the patterns of biomass allocation among tree species in response to ontogeny and to variation in resource availability is key to the successful restoration of degraded land using forest plantations. & Aims This study assessed the effects of resource availability and ontogeny on biomass accumulation and partitioning in five semi-arid afforestation species. & Methods The aboveground and belowground biomass production of fast-growing Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L. and slow-growing Anacardium occidentale L. and Parkia biglobosa Jacq. was monitored following the application of manure (1 kg plant −1) and/or supplemental irrigation (0.5 L per sapling daily) during the first two rainy seasons and the intervening dry season on degraded cropland in Northern Benin. & Results Biomass accumulation in the fast-growing species was positively impacted by fertilization and irrigation during both rainy seasons. The slow-growing species responded positively to the silvicultural treatments during the dry and second rainy season. The application of fertilizer alone increased the biomass of P. biglobosa by up to 335% during the dry season. Fifteen months after planting, manure-treated L. leucocephala accumulated the most biomass (2.9 kg tree −1). The root fraction decreased with increasing tree size in all species. The comparison of root versus shoot allocation in trees of equal size indicated that the treatment-induced shifts in biomass partitioning were controlled by ontogeny, which explained 86-95% of the variation in root-shoot biomass relationships. & Conclusion While ontogeny was the main driver of biomass partitioning, increased resource availability induced a larger production of biomass, overall leading to greater aboveground production in all species.

Climate Change Sensitivity of Multi-Species Afforestation in Semi-Arid Benin

“…Data for parametrization, validation, and simulations stemmed from a field experiment conducted during 2014-2015 at Pouri village (10 • 54 8.4" N, 1 • 4 47.4" E), Atacora region, northern Benin [18,20]. The region has been significantly affected by land degradation driven by deforestation and soil nutrient mining, which threatens the sustainability of forest and farming systems [18,46,47].…”

“…(drumstick tree, Moringaceae), were germinated in a local nursery. Seedlings were planted in monospecific plots at the experimental site in July 2014 after 2.5-4 months, and were monitored over 15 months [18,20,26]. These local species were selected based on the fast growth rate of their shoots and roots in response to water and nutrient supply, as well as their socio-economic importance and increasing recent efforts to expand their plantation acreage in West Africa [18,26].…”

“…If drought occurrences are exacerbated by global warming, it stands to reason that the sustainability of forests and plantations will largely depend on the physiological adaptations and changes in silvicultural management [18,20]. For example, Abdulai et al [14] revealed drought vulnerability in a cocoa-based system in the forest-savanna transition zones of West Africa, despite the availability of subsoil water below a depth of 75 cm.…”

“…Our study may be the first to test explicitly this generic approach to assess climate change risks for newly established dryland afforestation sites. The datasets stem from a site in a semi-arid zone of West Africa, where tree-based land restoration is high on the agenda and existing information is not sufficient to assess the robustness of afforestation option for a range of tree species [18,20,26].…”

“…The aim of our research was to assess the climate sensitivity of two afforestation species-Jatropha curcas L. and Moringa oleifera Lam.-in the early stages of their development (i.e., the first two years of growth), decisive for the future growth [42] and also when plants are most sensitive to changes in water availability [43][44][45]. The two species have been subjects of silvicultural trials on degraded cropland in northern Benin [18,20,26]. The specific objectives were to (i) compare different indicators calculated from climate records to identify those with the greatest predictive power for the first two years of tree growth; (ii) quantify the climate-growth relationships of tree growth over the first two years, and (iii) test possible adaptation strategies to reduce the sensitivity of saplings to extreme climate events.…”