Tree to 10 or more metres high, the branchlets usually tomentose when young. Leaves moderately large, an average leaf about 20-foliolate;petiole short, pubescent, eglandular;rachis usually about 2 dm. long, eglandular and otherwise like the petiole;leaflets several to many pairs, lanceolate, 3-8 cm. long and usually about 2 cm. wide, acute apically, obtuse basally, pubescent below, especially along the veins, puberulent to subglabrous above and less dull than below, opposite on the rachis, with 10 or more pairs of prominent lateral veins;petiolules 2-3 mm. long, pubescent. Inflorescence of several terminal or subterminal several-flowered racemes;bracts lanceolate, a few mm. long, caducous. Flowers yellow;sepals 5, obovate-orbicular, markedly unequal, up to 1 cm. long and broad, glabrous to lightly puberulent;petals 5, mostly obovate, markedly unequal, up to 2.5 cm. long and 1.5 cm. broad, subglabrous, venose, short-clawed;stamens 10, 3-morphic;the 3 lowermost the largest, their anthers oblong, about 7 mm. long, short-rostrate apically and dehiscent by terminal pores, the loculi somewhat converging terminally;anthers of 4 median stamens 5-6 mm. long, similar to the 3 lowermost except the rostrum reflexed and the loculi divergent terminally;3 uppermost stamens markedly dissimilar, more or less rudimentary, the anthers distinctly bilobed, each lobe reniform and dehiscent the length of its outer margin;ovary linear, glabrous. Legume linear, turgid-quadrangular, up to 2 dm. long and 1 cm. wide, transversely multiseptate, tardily dehiscent along one margin (Missouri Botanical Garden, 2014).
S. spectabilis is a medium to large tree from tropical America, listed in the Global Compendium of Weeds as an ‘environmental weed’, ‘garden thug’, and ‘naturalised weed’ (Randall, 2012). The species is extremely fast-growing, flowers and sets seed profusely, and re-sprouts readily when cut (Mungatana and Ahimbisibwe, 2010). In Australia it is considered naturalized, has been recorded as a weed of the natural environment and an escape from cultivation, and is labelled an invasive species, indicating its high negative impact on the environment due to its ability to spread rapidly and often create monocultures (Randall, 2007). In Uganda, the species is considered an invasive alien species with high risk to the native flora (Mungatana and Ahimbisibwe, 2010). In Singapore S. spectabilis has been identified as a casual, spontaneous exotic species that survives outside cultivation but does not form self-replacing populations, and relies on repeated introductions or limited asexual reproduction for persistence (Chong et al., 2009). The species is a cultivation escape in Trinidad and Tobago (Irwin and Barneby, 1982) and is considered an invasive species in Cuba (Oviedo-Prieto et al., 2012).
Agroforestry experiments in Kenya showed that while S. spectabilis is useful as hedges for cropping systems, if grown in semi-arid conditions S. spectabilis will out-compete crops for water uptake and suppress crop yields;in the cases recorded, grain yields of maize grown with S. spectabilis or Leucaena leucocephala were reduced by between 39% and 95% (Noordwijk et al., 2004).
Agroforestry is a land use management system in which trees or shrubs are grown around or among crops or pastureland. This diversification of the farming system initiates an agroecological succession, like that in natural ecosystems, and so starts a chain of events that enhance the functionality and sustainability of the farming system. Trees also produce a wide range of useful and marketable products from fruits/nuts, medicines, wood products, etc. This intentional combination of agriculture and forestry has multiple benefits, such as greatly enhanced yields from staple food crops, enhanced farmer livelihoods from income generation, increased biodiversity, improved soil structure and health, reduced erosion, and carbon sequestration. Agroforestry practices are highly beneficial in the tropics, especially in subsistence smallholdings in sub-Saharan Africa and have been found to be beneficial in Europe and the United States.
Agroforestry shares principles with intercropping but can also involve much more complex multi-strata agroforests containing hundreds of species. Agroforestry can also utilise nitrogen-fixing plants such as legumes to restore soil nitrogen fertility. The nitrogen-fixing plants can be planted either sequentially or simultaneously.
Agroforestry is a collective name for land-use systems and technologies where woody perennials (trees, shrubs, palms, bamboos, etc.) are deliberately used on the same land management unit as agricultural crops and/or animals, in some form of spatial arrangement or temporal sequence. In agroforestry systems there are both ecological and economic interactions between the different components.