The indigenous agroforestry systems of the south-eastern Rift Valley escarpment, Ethiopia : Their biodiversity, carbon stocks, and litterfall

Agroforestry systems integrate trees into agricultural landscapes and provide a number of ecosystem services. Studies on agroforestry systems have so far mainly focused on their spatial design, food production, soil fertility management and system interactions, and little attention has been given to their ecosystem services, such as biodiversity conservation and carbon sequestration. The objectives of the study were to determine and evaluate the floristic diversity, the above- and below-ground biomass carbon (C) and soil organic carbon (SOC) stocks, and the litterfall production and associated C and nitrogen (N) fluxes of three indigenous agroforestry systems in south-eastern Rift valley escarpments, in Gedeo, Ethiopia. Three indigenous agroforestry systems studied were Enset (Ensete ventricosum (Welw.) Cheesman), Enset-coffee, and Fruit-coffee. C stocks in biomass and soil (0 60 cm layer) (Mg C ha-1) were determined for each agroforestry system, and litterfall collected for seven woody species for a period of 12 months. Allometric equations were derived to estimate the biomass of enset and coffee while published allometric equations were used to determine the biomass of other tree and shrub species. The biomass values were then converted into C stocks. A total of 58 woody species, belonging to 49 genera and 30 families were recorded. Of all woody species identified, 86% were native. The Enset and Enset-coffee systems contained the highest proportion native woody species (92% and 89%, respectively). In all, 22 native woody species were recorded as of interesLyhennelmät for conservation using International Union for Conservation of Nature (IUCN) Red lists and local criteria. The square power equation using stump diameter at 40 cm (d40), Y = b1d402 (R2 > 0.80) and the power equation using d10 (diameter at 10 cm height) and height, Y=b1d10b2hb3 (R2 > 0.90) were found to be the best for predicting aboveground biomass of coffee (Coffea arabica L.) and total biomass of enset, respectively. The agroforestry C stock (biomass C plus SOC) was the highest for the Enset-coffee system (293 Mg C ha-1) and the lowest for the Enset (235 Mg C ha-1) system. Biomass (above- and belowground) C stocks were the highest for the Enset-coffee system (116 ±65 Mg C ha-1), followed by Fruit-coffee (79 ±24) and Enset (49 ±44) systems. Trees (fruit and non-fruit) formed 81, 89 and 80% of total biomass C stocks for Enset, Enset-coffee and Fruit-coffee agroforestry systems, respectively; the remainder being coffee, enset, litter, herbaceous plants, and fine root biomass. SOC to biomass C ratios were 4:1 for the Enset system, 2:1 for Fruit-coffee system, and 1.5:1 for the Enset-coffee system. Monthly litterfall production per unit crown area decreased in the order: Croton macrostachyus Del. > Erythrina brucei Schweinf. > Cordia africana Lam. > Persea americana Mill. > Mangifera indica L. > Coffea arabica L. > Millettia ferruginea (Hochst.) Bak. The annual litterfall production (sum of seven species) averaged 7430 kg ha-1(land area) for the Enset system, 10187 for the Enset-coffee system and 12938 for the Fruit-coffee system. The associated annual C fluxes (kg ha-1) were 2803 (Enset system), 3928 (Enset-coffee system) and 5145 (Fruit-coffee system) and the corresponding N fluxes were 190 (kg ha-1), 257 and 278. This research shows that the native woody species and C stocks observed in the three indigenous agroforestry systems were among the highest reported for tropical agroforestry systems. Thus, it should be given more attention, to counteract the local threat of these species from the wild and offset greenhouse gases (GHGs) emission. The indigenous agroforestry systems of the south-eastern Rift Valley escarpment in Ethiopia form a win-win opportunity by supporting livelihoods and providing food for a dense human population while also maintaining native floristic diversity and mitigating climate change through carbon sequestration. Key words Biomass, Carbon sequestration, Coffee, Enset, Floristic diversity, Gedeo, Indigenous agroforestry system, Litterfall fluxes, South-eastern Ethiopia

Peltometsäjärjestelmät turvaavat puiden säilymisen maatalousalueilla ja tarjoavat monia ekosysteemipalveluja. Näiden järjestelmien tutkimus on tähän saakka painottunut eri osakomponenttien yhdistelyvaihtoehtoihin ja keskinäiseen vuorovaikutukseen, ruoantuotannon lisäämisen mahdollisuuksiin sekä maaperän ravinnetalouteen. Sen sijaan vain vähän huomiota on kiinnitetty peltometsäviljelyn tuottamiin ekosysteemipalveluihin. Tämän tutkimuksen tavoitteena oli mitata perinteisissä peltometsäjärjestelmissä kasvilajiston monimuotoisuutta, maanpäällisen ja maanalaisen biomassan hiilen määrää, maaperän orgaanisen hiilen määrää sekä karikkeen muodostumista ja siihen liittyvää hiilen ja typen kiertoa. Tutkimuspaikkana oli Suuren hautavajoamalaakson reunajyrkänne Gedeon lähellä Etiopiassa. Tulokset osoittavat, että puulajistoltaan rikkaimpia olivat paikallisen kotoperäisen, banaanikasvien heimoon kuuluvan enset-ravintokasvin vallitsemat peltometsäjärjestelmät. Enemmän kaupalliseen tuotantoon keskittyvät järjestelmät olivat puulajistoltaan köyhempiä, ja niissä esiintyi yleisesti vieraita viljelypuulajeja. Kolmessa erilaisessa perinteisessä peltometsäjärjestelmässä nyt mitattu hiilen määrä oli korkeimpia mitä yleensä on tavattu trooppisessa peltometsäviljelyssä. Johtopäätöksenä oli että nämä Hautavajoamalaakson rinteiden perinteiset peltometsäjärjestelmät Etiopiassa tuottavat moninkertaisen hyödyn. Ne turvaavat viljelijöiden ruoantuotannon ja toimeentulon alueella, jolla väestön tiheys on suuri, samalla kun ne toimivat paikallisen kasvilajiston monimuotoisuuden turvaajina ja hillitsevät, suuren hiilensidontakykynsä vuoksi, myös ilmastonmuutosta. Avainsanat: Biomassa, Hiilen sidonta, Kahvi, Enset, Gedeo, Perinteinen peltometsäviljely, Karikkeen ravinnekierto, Alkuperäislajit, Kaakkois-Etiopia

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