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Frontiers in Forests and Global Change 01 frontiersin.org
Salient features and ecosystem
services of tree species in
mountainous indigenous
agroforestry systems of
North-Eastern Tanzania
OforoDidasKimaro
1,2*, EllenDesie
2, Didas NahumKimaro
3,
KarenVancampenhout
2† and Karl-HeinzFeger
1†
1 Institute of Soil Science and Site Ecology, Department of Forest Sciences, Faculty of Environmental
Sciences, TU Dresden, Tharandt, Germany, 2 Department of Earth and Environmental Sciences, KU
Leuven, Geel, Belgium, 3 Department of Agriculture, Earth and Environmental Sciences, Mwenge
Catholic University, Moshi, Tanzania
Indigenous agroforestry systems in tropical mountainous environments
provide crucial ecosystem services, but these ecosystems are also facing some
challenges. A loss of diversity and native tree species in the overstory layer has
been a growing concern in agroforestry worldwide, yet the drivers behind it
remain inadequately understood. Wehypothesize that the choice of overstory
tree species is closely linked to the ecosystem services required by farmers,
their livelihood strategy, and the salient features of each system. We, therefore,
investigated four dierent farming systems in the mountains of northeastern
Tanzania, i.e., the Kihamba on Mt. Kilimanjaro, Ginger agroforestry in the South
Pare mountains, and Miraba and Mixed spices agroforestry in the West and
East Usambara. In 82 farms, we collected data on the structure, tree species
composition (both native and non-native), diversity, and associated provisioning
ecosystem services as identified by smallholder farmers. Our results indicate that
although all studied systems are multi-layered with three or four vertical layers,
they have notable dierences in their salient features concerning structure,
composition, and diversity. The unique climate, landscape setting, soil, historical
background, and economic opportunities that exist in each region contribute
to those dierences. Our findings indicate that the Kihamba system had the
highest number of native tree species, and the largest diversity in species used
for provisioning services, followed by Ginger agroforestry. No native species
were used in Miraba or Mixed spices agroforestry, where a limited number of
non-native tree species are planted mainly for fuel and timber or as a crop,
respectively. Our findings regarding reported provisioning ES corroborate our
hypothesis and imply that policies to increase resilience and restore the native
tree species cover of the agroforestry systems of Tanzania can only besuccessful
if knowledge of the ES potential of native species is increased, and interventions
are tailored to each system’s ES needs for conservation as well as livelihood.
KEYWORDS
smallholder indigenous farming systems, agroforestry systems, Kihamba,
homegardens, vernacular names tree species, ecosystem services, mountain
ecosystems, Tanzania
OPEN ACCESS
EDITED BY
Geertje M. F. Van Der Heijden,
University of Nottingham, UnitedKingdom
REVIEWED BY
Gopal Shankar Singh,
Banaras Hindu University, India
Marion Pfeifer,
Newcastle University, UnitedKingdom
Eleanor Moore,
Newcastle University, UnitedKingdom,
in collaboration with reviewer MP
*CORRESPONDENCE
Oforo Didas Kimaro
didas.oforo_kimaro@mailbox.tu-dresden.de
†These authors share last authorship
RECEIVED 28 October 2022
ACCEPTED 20 December 2023
PUBLISHED 13 February 2024
CITATION
Kimaro OD, Desie E, Kimaro DN,
Vancampenhout K and Feger K-H (2024)
Salient features and ecosystem services of
tree species in mountainous indigenous
agroforestry systems of North-Eastern
Tanzania.
Front. For. Glob. Change 6:1082864.
doi: 10.3389/gc.2023.1082864
COPYRIGHT
© 2024 Kimaro, Desie, Kimaro,
Vancampenhout and Feger. This is an open-
access article distributed under the terms of
the Creative Commons Attribution License
(CC BY). The use, distribution or reproduction
in other forums is permitted, provided the
original author(s) and the copyright owner(s)
are credited and that the original publication
in this journal is cited, in accordance with
accepted academic practice. No use,
distribution or reproduction is permitted
which does not comply with these terms.
TYPE Original Research
PUBLISHED 13 February 2024
DOI 10.3389/gc.2023.1082864
Kimaro et al. 10.3389/gc.2023.1082864
Frontiers in Forests and Global Change 02 frontiersin.org
1 Introduction
Mountain ecosystems in the tropics are important for the
provision of ecosystem services, both on-site as to regions that are
downhill (Grêt-Regamey etal., 2012; IPBES, 2019). Trees and forests
are essential to those ecosystem services, given their positive eects
on erosion control and slope stabilization, biodiversity, water
buering, nutrient cycling, carbon sequestration, microclimate and
supporting other biodiversity, as well as harboring culturally
important sites (e.g., Padilla etal., 2010; Hirschi etal., 2013; Pătru-
Stupariu etal., 2020). In northeastern Tanzania, mountain ecosystems
contain important conservation landscapes, including forest reserves
and national parks with high species diversity and of international
importance (Lovett and Wasser, 1993; Lovett, 1998; Burgess etal.,
2007; Heckmann, 2011).
However, tropical mountain ecosystems are also facing growing
environmental, social, and economic challenges as short-term needs
in terms of livelihood and food security may conict with
conservation goals despite a local understanding that these goals
benet the community in the long run (Hamilton and Bensted-
Smith, 1989; Kimaro etal., 2018; Glushkova etal., 2020; Kimaro and
Chidodo, 2021). Indigenous agroforestry systems have been praised
as a promising avenue for balancing those needs and as a model for
climate-smart agriculture (Negash etal., 2012; FAO, 2022; Kassa,
2022). If properly managed, these ecosystems can play an important
role in conservation eorts and simultaneously provide regulating,
supporting, and cultural as well as provisioning ecosystem services
(ES; Kuyah etal., 2016, 2017). In Tanzania, indigenous agroforestry
systems support regions with large population densities (ranging
from 150 to 350 persons/km
2
(URT, 2013); 90% of them being
smallholder farmers; Mattee et al., 2015). On the other hand,
agroforestry systems are also at risk of environmental degradation
associated with poverty and are vulnerable to the eects of climate
change (FAO and UNCCD, 2019). Recent studies about the
mountains of northeastern Tanzania have focused on specic aspects,
such as soil organic carbon (Winowiecki etal., 2016; Kirsten etal.,
2019), erosion (Wickama etal., 2014), dynamics of land use change
(Hall etal., 2011), and land management and livelihoods (Lundgren,
1980; Reyes, 2008). Nevertheless, the term ‘agroforestry’ as a
collective name for ‘land-use systems where woody perennials are
deliberately used on the same land-management units as agricultural
crops and/or animals (FAO, 2015)’ holds danger for generalization:
In northeastern Tanzania, indigenous agroforestry systems
considerably dier in their farming traditions, livelihood strategies,
structural arrangement and choice of crops, animals or overstory
species as well as in soils, rainfall, and landforms. Few studies have
considered the interaction between those dierences in salient
features and the delivery of ecosystem services (Michon etal., 1983,
1986; Abebe etal., 2013).
e overstory layer is one of the important features in multi-layer
agroforestry systems due to its inuence on multiple ES (Soini, 2005;
Graham etal., 2022). Nonetheless, the overstory layer is undergoing
many changes in agroforestry systems around the globe (Pantera
etal., 2021). In Africa, many homegardens are being transformed and
native tree species are being replaced by non-natives for timber
production (Yakob etal., 2014; Endale etal., 2017; Wagner etal.,
2019; Gemechu et al., 2021). e increasing dominance of
agroforestry canopies by fast-growing non-native tree species is a
consequence of colonial governance in the period of 1900–1970 (von
Hellermann, 2016), a bias toward production services and a focus in
research and extension on species providing fodder or xing nitrogen
(Atangana etal., 2014; Franzel et al., 2014). Non-native species
provide fewer ES because they score lower in terms of
multifunctionality (van der Plas etal., 2016; Castro-Díez etal., 2019,
2021). eir increased share in agroforestry canopies is considered a
signal of indigenous agroforestry degradation (Oginosako et al.,
2006; Lelamo, 2021). Examples of non-native species with a negative
eect include Eucalyptus spp. (acidication, water reserve, and
nutrient depletion; Castro-Díez etal., 2012; Silva etal., 2017); Acacia
mearnsii, Leucaena leucocephala, and Persea americana (biodiversity
decline; Vilà etal., 2011; Sharma etal., 2022); and Cedrela odorata
(native tree suppression; FORCONSULT, 2006). In Tanzania,
common examples of non-native trees in homegardens include
Eucalyptus saligna, Pinus patula, Cedrela odorata, Acacia mearnsii,
Grevillea robusta, Persea americana, and Leucaena spp. (Lyimo etal.,
2009). ese species are promoted for provisional services, i.e.,
timber provision, fuel, food, and fodder, yet minimally contribute to
regulating (water regulations, pollination, climate), cultural (esthetic
values, heritage, recreation, and ecotourism), or supporting (nutrient
cycling or soil formation) ES (Munishi etal., 2008; Lyimo etal., 2009;
Negash etal., 2012; Abebe etal., 2013).
Despite the growing concern about this loss of native species and
their services, governments in developing countries lack strategies for
restoring native tree species in agroforestry systems at the landscape
scale (FAO, 2013). Furthermore, such strategies have little chance of
success if they are not tailored to the specic livelihood strategies and
salient features of dierent types of agroforestry systems in dierent
regions, nor to the drivers and ES requirements that are behind the
choices that people make for their homegardens and elds. Hence, in
this study, wefocus on the internationally renowned (Kitalyi etal.,
2013; FAO, 2022) yet rapidly transforming indigenous agroforestry
systems in the mountains of northeastern Tanzania, i.e., in the
Kilimanjaro, South Pare, and West and East Usambara region (cf.
Munishi etal., 2008; Hall etal., 2011; Molla and Kewessa, 2015; Brus
etal., 2019). Wehypothesize that the choice of overstory tree species
is closely linked to farmers ES needs, livelihood strategy, and the
salient features of each system. To assess that hypothesis, wevisited 82
smallholder farms to identify the structure and dierent components,
i.e., crops, animals, and perennials, and discuss their roles in the
livelihood strategy of the farmers. Next, wequantied the identity and
diversity of the dierent trees in the canopy of each system. Finally,
wediscussed the dierent perceived ES services farmers require from
those trees and how they relate to the salient features of each system.
is information can guide future policies and campaigns to improve
the canopy biodiversity to bein sync with the needs and preferences
of the farmers in each region.
2 Materials and methods
2.1 Study area
Agroforestry in northeastern Tanzania is practiced on Mount
Kilimanjaro, in South Pare, and in the West and East Usambara
Mountains, each occupying an agricultural area of approximately
8,000 km
2
(Figure 1; Burgess et al., 2007; Heckmann, 2011;
Kimaro et al. 10.3389/gc.2023.1082864
Frontiers in Forests and Global Change 03 frontiersin.org
Zech etal., 2014) with elevations ranging from 800 to 2,000 m asl. e
climate is humid and monsoonal. Annual rainfall has a bimodal
distribution with the main rainy season occurring between March and
June (locally called Masika) and a shorter rainy season from October
to December (Vul i). Each mountain range has its own unique
indigenous agroforestry system (Akinnifesi etal., 2008; Reetsch etal.,
2020a,b). ese mountain ranges are referred to as ‘Kihamba’ or
‘Chagga homegardens’ on the southern slopes of Mount Kilimanjaro
(Hemp and Hemp, 2008; Banzi and Kalisa, 2021), ‘Ginger agroforestry’
in South Pare (Ndaki, 2014; Mmbando, 2015), ‘Miraba’ in West
Usambara (Msita, 2013), and ‘Mixed spices agroforestry’ in East
Usambara (Hall etal., 2011; Patel etal., 2022).
2.2 Data collection
2.2.1 Site selection
For each mountain range, an area of ca. 200 km
2
was demarcated
(Figure1), comprising six representative administrative wards (local
government areas; Figure2). In each ward, plots of 0.2–0.5 ha were
demarcated in randomly selected household farms. In total, 82 plots
were selected, i.e., 35in Kihamba, 18in Ginger agroforestry, 20in
Miraba, and 9in Mixed spices agroforestry. For each area, mean annual
rainfall and temperature were derived using Modern-Era Retrospective
Analysis for Research and Applications (MERRA-2) and Geodetic Earth
Orbiting Satellite GEOS 5.12.4 from the Prediction of Worldwide Energy
FIGURE1
Location of the studied areas (top) and selected wards (bottom) in the northeastern mountains of Tanzania.
Kimaro et al. 10.3389/gc.2023.1082864
Frontiers in Forests and Global Change 04 frontiersin.org
Resources (POWER) database [Global Modeling and Assimilation
Oce (GMAO), 2015]. Landform and soil information were derived
from the Harmonized World Soil and SOTER Databases (FAO, 2016)
and the WoSIS database in SoilGrids (ISRIC, 2023), complemented by
own eld observations. e data are presented in Table1.
2.2.2 System structure and tree species
composition in the indigenous agroforestry
systems
We conducted a eld survey from July to September 2021,
collecting data on salient features of each agroforestry system (i.e.,
vertical structure (number of layers and canopy depth), horizontal
arrangement, mixing patterns and management aspects, and species
composition; cf. Michon et al., 1983; Hemp and Hemp, 2008;
Dhanya etal., 2014). e canopy depth was assessed by a tape
measure and clinometer (cf. Leonard etal., 2010; Kanmegne-Tamga
etal., 2023), and photographs of farm plots were taken at the eye
level during the daytime to document structure and arrangement.
All photographs were taken at 50 m from the predominant
agroforestry layers. Tree species (both vernacular and botanical
names) were identied with the help of plot owners, botanists from
Tanzania Forest Research Institute, digital photo interpretation
[PlantNet] app, 2021 (Goëau et al., 2013), and vegetation
identication guides (Mbuya etal., 1994; Maundu and Tengnäs,
2005; NAFORMA, 2010; ijs et al., 2014).
To verify livelihood strategies and management aspects,
weconsulted with four key people from each ward in a focus group
discussion, including a village executive ocer, a ward executive
ocer, an agricultural extension ocer, and senior/experienced
smallholder farmers (Appendices 1, 2). In addition, wecomplemented
that information with 82 household interviews (see section 2.2.2;
interviews and open-ended questionnaires) where farmers were asked
about local management techniques carried out on their farm plots,
such as indigenous irrigation, application of farmyard manure, green
manure, mulches, opening the tree canopy, lopping, and spacing out
the banana stools (cf. Sabbath, 2015; Reetsch etal., 2020a,b).
2.2.3 Ecosystem services in the indigenous
agroforestry systems
At each farm plot, a household representative was interviewed
using a semi-structured questionnaire to identify farmers’ perceptions
and needs regarding ES provided by the canopy layer in the system.
is study focused on ES relevant for production (food, fodder, fuel
wood, timber, and shade) as most essential to the livelihood strategies
of smallholder farmers (Fisher and Turner, 2008; Kuyah etal., 2016,
2017; Mkonda and He, 2017; Wagner etal., 2019). Each ES was ranked
by smallholder farmers using the 3-point Likert ordinal scale (1 = not
important, 2 = important, 3 = most important) for each of the trees
identied on their plot (Munishi etal., 2008).
2.3 Data analysis
2.3.1 Stand structure and species composition in
the indigenous agroforestry systems
We developed schematic prole representations of the canopy
depth of the dominant multi-layer agroforestry systems based on the
eld photographs using Adobe Photoshop with the aim to better
visualize layers and distinguish tree species and canopy depth (cf.
Reetsch etal., 2020a,b).
FIGURE2
Detailed boundaries and location of administrative wards within each study landscape: (A) Mount Kilimanjaro; (B) South Pare Mountains; (C) West
Usambara Mountains; (D) East Usambara Mountains. Boundaries and location of administrative wards were generated using QGIS 3.16.6 with GRASS
7.8.5 software.
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Frontiers in Forests and Global Change 05 frontiersin.org
We used descriptive statistical analyses from R soware (3.6.3
version, R Core Team, 2021) and data visualization packages psych
and ggplot2 (Nordmann etal., 2022) to explore the distribution of tree
identity (native and non-native) and their provisioning of multiple ES
within and across the studied systems. We excluded Mixed spices
agroforestry because the upper canopy only consists of one non-native
tree species (clove, see also Pungar etal., 2021).
2.3.2 Tree species diversity
For each smallholder farm, wecalculated tree species diversity,
richness, and evenness using the Shannon and Weaver (1963) index
of diversity (Eq.1; Admas and Yihune, 2016; Patel etal., 2022) and
Shannon’s equitability (EH) index (Eq.2),
Shannon index (H′):
( ) ( )
H Pi ln pi= −∑
'
(Eq.1)
Shannon equitability index EH:
H
E H / Hmax H / ln S= =
''
(Eq.2)
where H' is index of species diversity, pi is proportion of total sample
belonging to i-th species, lnS is (S = number of species encountered),
and Hmax is the highest possible species diversity value.
We also used Sorenson’s coecient index to determine similarities
between the identied tree species in two adjacent systems with
similar characteristics in terms of multi-layer vegetation composition
and local management (McCune and Grace, 2002; Eq.3),
( )
’
Sorenson s coefficient CC 2= C / L1 L2+ (Eq.3)
where C is the number of tree composition the two AGF landscapes
have in common, L1 is the total number of tree composition found in
a system/area1, and L2 is the total number of tree composition in
system/area 2.
Sorenson’s coecient gives a value between 0 and 1, and the closer
the value is to 1, the more the systems have in common, with the value of
1 indicating complete overlap in species and a value of 0 indicating two
systems are completely dierent in species composition (Clarito
etal., 2020).
2.3.3 Ecosystem services in the indigenous
agroforestry systems
We used descriptive and non-metric multi-dimensional scaling
(NMDS) approaches in R (Dexter etal., 2018) to analyze the perceived ES
oered by the dierent tree species (Kenkel and Orloci, 1986; Ampoorter
etal., 2015). In the NMDS plot, the closer the points are together in the
ordination space, the more the similar are their ecosystem communities
(Lefcheck, 2012; Buttigieg and Ramette, 2014). e function metaMDS
command from the vegan package (Oksanen etal., 2020) in R, coupled
with Bray–Curtis similarity and dissimilarity metric calculation between
samples (Bray and Curtis, 1957), was deployed for suitable ordination to
run the NMDS and check for the homogeneity of the variances (i.e., tree
species), respectively (Pot etal., 2022). Weused R package ggplot2 to plot
the ordination graph. Weassessed dierences in the ES oered by the
dierent tree species using the permutation test (PERMANOVA) to assess
whether dierences were signicant.
3 Results
3.1 Salient features and livelihood
strategies of the indigenous agroforestry
systems in the study areas
3.1.1 Kihamba (Chagga homegardens) on the
southern slopes of Mount Kilimanjaro
Agroforestry farms at Mt. Kilimanjaro are managed according
to the traditional homegarden system of the Chagga tribe, known as
TABLE1 Climatic and topographic characteristics of the areas included in the study.
Mt. Kilimanjaro South Pare Mountains West Usambara East Usambara
Studied area 212 km2252 km2243 km2209 km2
Agroforestry type Kihamba Ginger agroforestry Miraba Mixed spices agroforestry
Altitude 800–2,000 m asl 1,200–1,800 m asl 1,300–1,800 m asl 800–900 m asl
Mean annual rainfall 1,890 mm 1,000 mm 1,700 mm 1,920 mm
Mean annual
temperature range
16–19°C 15–20°C 17–18°C 17–24°C
Landform Foot ridges and very steep riverside
valley slopes
Dissected plateau, rolling to hilly
relief, slopes ranging from 10 to
40%
Ridges, steep to very steep
slopes, narrow and broad
U-shaped valley bottoms
Ridges, steep to very steep slopes,
narrow V-shaped valley bottoms
Soils Nitisols and Cambisols on volcanic
material
Acrisols and Leptosols on old
precambrian basement rocks
Acrisols and Alisols on old
precambrian basement rocks
Acrisols and Alisols on old
precambrian basement rocks
Selected wards Uru North & South; Mbokomu;
Kilema central; Marangu West & East
Bombo Mvaa & Mjema; Mtii;
Lugulu & Kanza; Chome
Lukozi, ndabwa; Manolo;
Mwangoi; Shume; Kwai
Amani shebomeza, Magoda &
mlesa; Kisiwani; Mbomole; Misalai
Number of selected
household farm plots
35 18 20 9
Field/homegarden size
range (ha)
0.2–0.5 0.2–1 0.2–0.5 0.2–1
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‘Kihamba.’ e plots in our study typically consisted of a complex,
four-layered system (Figure3): e rst layer is a canopy of trees
with a canopy depth ranging from 12 to ≥30 m. In the plots in our
study, the most common native tree species in the tree layer include
Maragaritaria discoidea, Bridelia micrantha, Albizia schimperiana,
Cusonia holstii; Rauvola cara, Ficus natalensis, Cordia africana,
and Croton macrostachyus (Table2; Figure3; Supplementary Table S1).
Common non-native species include Grevillea robusta, Magnifera
indica (mango), Persea americana (avocado), Artocarpus
heterophyllus (jackfruit), and Eriobotrya japonica (loquat). Some
evergreen climbing species, such as oysternut (Telfairia pedata) and
vanilla (Vanilla planifolia/polylepis), are grown with the trees
as support.
e second layer is a dense upper perennial herb layer, mainly
comprising banana varieties (Musa sp.) with a canopy depth of
2.5–5 m. e third layer mainly comprises coee (Coea arabica) with
a few young trees, shrubs, and taller herbs making a canopy depth of
1–2.5 m, and the fourth layer consists of annual food crops, mainly
beans (Phaseolus vulgaris L.), cassava (Manihot esculenta), maize (Zea
mays), cocoyam (Colocasia esculenta), and potato (Ipomoea batatas
(L.) Lam. and Solanum tuberosum). ese are complemented by nduu
(Dioscorea bulbifera), shia (Dioscorea alata), and biringanya (Solanum
melongena). Herbs, shrubs (Dracaena steudneri; afromontana and
fragrans), and grasses (Drymaria cordata, Setaria splendida) are grown
in fallow gaps. e canopy depth of this last layer ranged from 0.2 to
1 m. e spatial arrangement of the components has no clear pattern
FIGURE3
Overview of dierent homegarden agroforestry systems in mountain regions of Tanzania: Kihamba (left), Ginger (center), and Mixed spices agroforestry
(right). For each agroforestry system, the main vertical layers are illustrated; for example, for the Ginger agroforestry: A = Trees (first layer); B = Banana
(second layer); C=Sugarcane (third layer); D = Ginger (fourth layer; photographs by O. D. Kimaro, August 2021). The structure of Miraba, which is not a
homegarden system, is depicted in Figure4.
FIGURE4
Miraba agroforestry in the West Usambara Mountains: A = trees (first layer); B = banana and cassava patches near settlements (second layer); C = strips
of Guatemala or elephant grass, maize, and beans inside the square (third layer; photograph by O. D. Kimaro).
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TABLE2 Scientific and vernacular names of tree species recorded in the studied agroforestry systems for the Kilimanjaro (Kihamba, Chagga language),
Pare Mountains (Ginger agroforestry, Pare language), and Usambara Mountains Miraba and Mixed spices agroforestry (Sambaa language).
Vernacular names
Tree species Chagga Pare Sambaa
Native species
Albizia schimperiana Oliv Mfuruanje, Mruka Mririgwi, Mshai, Mruka
Bridelia micrantha (Hochst.) Baill. Mmarie Mwira
Cordia africana Lam. (C. abyssinica R. Br.) Mringaringa Mringaringa
Commiphora zimmermannii (C. Zimmermann) Mna
Croton macrostachyus Hochst. ex Delile Mfurufuru
Croton megalocarpus Hutch. Muhande, Irisa, Mfurufuru
Cussonia holstii Harms ex Engl. Mnengere
Ficus Vallis-Choudae Del. Mkuu Mkuu
Ficus natalensis Hochst. Mfumu
–Ihoko
Lannea schweinfurthii (Engl.) Engl. Mshishina
Maragaritaria discoidea (Baill.) G.L. Webster Mshamana
Markhamia lutea (Benth.) K. Schum. Mtalawanda Mtaanda
–Mhodo
Mitragyna rubrostipulata (K. Schum.) Havil. Mkundukundu
Newtonia buchananii (Baker) Gilbert & Boutique Mririgwi, Mhashita
Olea capensis L. Mloliondo/Mchiio
Pterocarpus angolensis DC. Mninga wa kipare
Rauvola cara Sonder Msesewe, Mwembemwitu,
Mku
Syzigium guineense (Willd.) DC Mlama
Tarenna pavettoides (Harv.) Sim Kitundu
Telfairia pedata (Sims) Hook. Oysternut, Kweme Oysternut, Kweme
Trichilia dregeana Sond. Mgolimazi wa mzitui,
Nduruma, Mtimaji
Vangueria madagascariensis J.F.Gmel. Ndowiro
Non-native species
Annona senegalensis Pers. Mtopetope
Acacia mearnsii De Wild. (black wattle) Miwati, Mgamadume,
Mblakiwato
Mhache
Artocarpus heterophyllus Lam. (Jackfruit) Mfenesi Mfenesi
Calliandra calothyrsus Meissner –
Callistemon citrinus (Curtis) Skeels Lemon, Bottle brush
Calotropis procera (Ait.) Ait. F. Mkaburi, Jatropha
Carica papaya L. (papaya) Mpapai
Cedrela odorata L. (Spanish cedar) Mvuje, Mwerezi, Mtikunuka
Cedrus libani A. Rich. (Libanon cedar) Mierezi
Cinnamon zeylanicum Bl. (cinnamon) Mdalasini
Citrus limon (L.) Burm. f. (lemon) Mlimau, Ndimu
Citrus sinensis (L.) Osbeck (orange) Mchungwa, Ichungwa
Cupressus lusitánica Mill. (cypress) Mtarakwa, Mkrisimasi
(Continued)
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and is irregularly spaced, with trees, shrubs, and arable crops closely
intermixed (Figure3). Most farms have a livestock component in the
homegarden, consisting of only a few animals. ese farms include
typically 2–3 dairy cows and other animals, including pigs, goats, or
local poultry and African stingless bees.
For their livelihoods, farmers traditionally depend mainly on
coee and bananas for cash, but due to low coee prices, the sale of
fruits, milk, or honey has become more important. e bananas and
arable crops are grown for subsistence, while herbs, grasses, and some
woody species are used for fodder or as medicinal plants. Farm
management includes lopping the canopy for rewood or for
increasing light to the lower layers (e.g., for ensuring better fruiting of
the coee) and spacing out banana stools. Irrigation is also common,
where each homegarden is connected to a network of indigenous
irrigation furrows. e application of cattle manure as a mulching
material to improve soil fertility also was a common practice for many
smallholder farmers.
3.1.2 Ginger agroforestry in South Pare
Mountains
Ginger agroforestry, practiced in South Pare Mountains (as shown
in Figure3), also consists of four layers, but, as compared to Kihamba,
the upper canopies are much less dense (as seen in Figure3). e rst
layer consists of trees with a canopy depth ranging from 10 m to over
40 m. e common native tree species in this layer include Trichilia
dregeana, Syzigium guineense, Mguthuru, Newtonia buchananii,
Tarenna pavettoides, Markhamia lutea, Croton megalocarpus, Cordia
africana, Albizia schimperiana, and Ficus Vallis-Choudae (Table2;
Supplementary Table S1). Common non-native tree species include
jackfruit, avocado, mango, loquat, and Grevillia robusta.
The second layer consists of sparsely scattered bananas
(canopy depth of 2.5–5 m), followed by a third layer with a
canopy depth of 1–2.5 m is characterized by mixed shrubs,
(Dracaena spp. and Vernonia subligera). Sugarcane (Saccharum
officinarum) and maize (Zea mays) are also part of this layer. Few
smallholder farmers (< 5%) integrate shade coffee into this layer.
Our observations showed that the spatial arrangement of the
components is irregular, haphazard, and sparsely intermingled.
The lowest layer, with a canopy depth of 0.5–1 m, is densely
occupied with ginger (Zingiber officinale), an underground stem
herb plant rotated with arable crops, such as maize and dry beans
(Phaseolus vulgaris). Few farmers include a few animals, such as
a cow (low zero grazing and extensive grazing on fallow gaps) and
local chicken breeds.
For their livelihoods, farmers mainly depend on the cultivation of
ginger for cash, which was introduced in the area in the 1980s as an
alternative for coee on the dryer and more acidic soils of the Pare
mountains, following the collapse of coee prices and growing disease
pressure. e yield is complemented by fruits, sugarcane, and arables.
Farm management includes local pipe irrigation. Manure is in short
supply and sometimes bought from the lowlands.
3.1.3 Miraba agroforestry in West Usambara
Mountains
e West Usambara Mountains have a very dierent cultural
tradition as compared to the Kilimanjaro and South Pare areas. A
cultural heritage system called ‘Miraba’ (literally meaning ‘squares’)
is a farming system that integrates grassy hedges in the landscape
(see Figure4). Originally practiced by women in gaps in the forest,
it was later reintroduced in soil and water conservation programs
to control erosion that also promoted the use of nitrogen-xing
species, such as Grevillia. Miraba can beconsidered as a three-
layer system with a very sparse, scattered, and linear rst layer,
consisting of trees with a canopy depth ranging from 20 m to 40 m.
TABLE2 (Continued)
Vernacular names
Tree species Chagga Pare Sambaa
Eriobotrya japonica Lindl. (loquat) Sambia, Loquat Sambia, Loquat Msambia
Eucalyptus spp Mkaratusi
Eucalyptus camadulensis Dehnh., Cat. Pl. Hort. Mkaratusi/Opani
Eucalyptus saligna Smith Mkaratusi
Grevillea robusta A. Cunn. ex R. Br. Mkawilia, Mkerewila,
Mweresi
Mgrevillea, Mieresi Mkarela/Mgrevillea
Leucaena leucocephala (Lam.) de Wit Mlusina
Malus domestica (Suckow) Borkh. (apple) Apple
Mangifera indica L. (mango) Mwembe Mwembe Mwe mbe
Passiora edulis Sims. (passion fruit) Isapiku/Ikungu
Persea americana Mill. (avocado) I, Mparachichi Embe, mafuta
Pinus patula Schldl. Et Cham. (pine) Msonobari, msindano Msindano
Prunus persica (L.) Batsch. (peach) Mpichi Mfyoski
Psidium cattleianum Sabine (cattly guava) Mpera wa kizungu/Ng’ombe
Psidium guajava L. (guava) Mpera Mpera
Sechium edule (Jacq.) Sw. (chayote) Chayote/Chocho
Syzygium aromaticum (L.) Merr. & Perr. (clove) Mkarafuu
"-" denotes not encountered.
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Only non-native tree species were encountered including Grevillea
robusta, cypress (Cupressus spp.), pine (Pinus patula), loquat
(Eriobotrya japonica), black wattle (Acacia mearnsii), and
Eucalyptus spp. (see Tables 2, 3). e second layer of patches of
bananas and cassava (Manihot esculenta) is only present near or
around settlements. e third layer consists of squares of low,
grassy hedges of Guatemala and Elephant grass (Tri ps acu m
andersonii and Pennisetum purpureum). In between the hedges,
maize (Zea mays), dry beans (Phaseolus vulgaris L.), and Irish
potatoes (Solanum tuberosum) are the most common arable crops.
Contrary to the Kihamba, Ginger, and Mixed spices
agroforestry, Miraba is not a system of homegardens. Due to lower
rainfall, acidic soils, and connections to the vegetable markets of
Tanga, Dar es Salam, and Kenya, households rely mainly on
vegetables grown in valley bottoms for cash and on the Miraba on
the slopes for subsistence foods. Animal husbandry is not common,
and grasses from the hedges are oen sold. Some farmers use shrub
leaves, such as Tithonia diversifolia (Alizeti Pori) and Vern onia
myriantha (Tughutu) as mulching materials in the Miraba
eld plots.
3.1.4 Mixed spices agroforestry in the East
Usambara Mountains
e ‘Mixed spices’ agroforestry system of the East Usambara
Mountains is a smallholder farming system targeted at growing
clove (Syzygium aromaticum), cinnamon (Cinnamomum verum),
cardamom (Elettaria cardamomum), and black pepper (Piper
nigrum). Our study found a dense three-layered system (Figure3)
with an irregular layout of components closely intermingled in
space. e rst layer consists of clove trees with a canopy depth
ranging from 8 to 30 m. Black pepper is growing as a woody
climber around the clove trees. e second layer consists of
cinnamon trees with a canopy depth ranging from 8 to 17 m. e
use of other trees besides clove and cinnamon was not observed.
e third layer comprises mainly cardamom with a canopy depth
of 1 to 2 m. is layer covers more than 80% of the eld plot. Other
vegetation integrated in the patches of cardamom are shrubs such
as Lantana camara, Vernonia spp., Clidemia hirta, Stachytarpheta
jamaicensis and herbs (Justicia spp., Polygala spp., Impatiens spp.,
ferns, Commelina spp., Mimosa pudica, Senencio spp., Ipomea
batata, Rubus rosifolis, Afromomum corrorima, and Afromomum
melegueta). e incorporation of animals in the system is rare.
Management includes tending to the trees and minimal weeding.
As the soils are very strongly leached due to the Precambrian
parent material and very high rainfall, coee and arable crops in
general do very poorly. Hence, farmers grow mainly spices
requiring warm and humid conditions for cash and rely on market
purchases for food.
3.2 Composition and diversity of tree
species in the study landscapes
3.2.1 Tree species composition, occurrence, and
diversity
A total of 73 tree species native and non-native were identied
across the four study areas (Table2; Supplementary Figure S2). e
most common native tree species identied were Albizia
schimperiana, Maragaritaria discoidea, Cordia africana (abyssinica),
Ficus Vallis-Choudae, Croton macrostachyus/megalocarpus, Olea
capensis, Markhamia lutea, and Telfairia pedata. e most common
non-native tree species were Syzygium aromaticum and
Cinnamomum zeylanicum (dominant in Mixed spices agroforestry)
and Grevillea robusta, Persea americana, Psidium guajava,
Mangifera indica, Eucalyptus spp., Pinus patula, cypress (Cupressus
spp), and Acacia mearnsii dominant in the Miraba and
Ginger agroforestry.
Our results show that Kihamba agroforestry has more native
tree species per plot, i.e., 2.77 ± 0.28 as compared to Ginger
agroforestry 1.83 ± 0.33. Miraba and Mixed spices agroforestry do
not have native species in farm plots (Tables 2, 4;
Supplementary Figure S2). We found a similar pattern for
non-native tree species where Kihamba agroforestry scored a mean
of 2.54 ± 0.18 followed by Ginger agroforestry 2.22 ± 0.33 and
Miraba agroforestry 1.95 ± 0.17 (Table4). Mixed spices agroforestry
only has clove trees in the upper canopy (Syzygium aromaticum)
and cinnamon trees in the second layer (Cinnamon zeylanicum).
Kihamba and Ginger agroforestry have the highest Shannon–
Weaver Index diversity, with scores of 2.82 and 3.03, respectively,
while that of Miraba is 1.66 and of Mixed spices agroforestry is 1.45
(Table4).
3.2.2 Tree species similarity between
agroforestry systems
Similarities and dissimilarities of tree species communities in
the studied systems are presented in Tables 3, 5,
Supplementary Table S2, and Supplementary Figure S1. e two
agroforestry systems with native trees (i.e., Kihamba and Ginger
agroforestry) were investigated for tree species similarity and
dissimilarity (Sorenson’s coecient indices; Sébastien, 2010;
International Coee Organization, 2018; Ichinose etal., 2020). A
total of 12 tree species (Tables 3, 5; Supplementary Table S1)
common in both systems were identied for coecient index
analysis. According to Sorenson’s coecient, Kihamba and Ginger
agroforestry do not have much overlap or similarity in their tree
species composition (Sorenson’s Coecient (CC) = 0.38)
(Supplementary Table S2).
3.3 Tree species and ecosystem services
e contribution of native and non-native tree species to ES
diered among the studied areas (as shown in Tables 3, 5 and
Figure5). Native tree species are perceived as important for food
and fodder very commonly in Kihamba (80% of native tree species)
and Ginger agroforestry (75%). Shade also was an important
service of native trees in those systems (70%, as compared to ≤20%
for non-native species). Non-native trees are also used for food or
fodder but much less for shade. In the Usambara, no native trees
were encountered. Non-native trees were mostly valued as
important for fuel and timber in Miraba and food (clove and
cinnamon; data not shown) in Mixed Spices agroforestry (Figure5).
When split according to species (Tables 3, 5; Figure 6;
Supplementary Figure S3), it becomes evident that farmers have
dierent requirements in dierent systems and use dierent trees
to meet them. Moreover, a tree can have a dierent function in
dierent agroforestry systems. In Kihamba, the largest share of
trees was reported to beplanted for food and fodder, and they
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belonged to a wide range of species (with Margaritaria and
Rauvola being the main native species, and avocado as an
important non-native). e second largest group was planted for
shade, most of them being natives (Albizia, Cordia, Croton, and a
variety of other species). Albizia is also important for fuel in
Kihamba, and Grevillea is found to bean important non-native
used for fuel and timber in the system. In Ginger agroforestry, trees
were mainly planted for food and fodder (with fruit trees having
the largest share) and shade (Albizia and a range of other native
species). Few trees were encountered in Miraba, and fuel and
timber were the most sought-aer ES, with large shares for
Grevillea, Acacia, and pine. Fruit trees are relatively rare (loquat,
apple, and mango). Grevillea and pine are used for shade although
farmers in the West Usambara use the term ‘shade’ also to denote
soil and water conservation.
A PERMANOVA (Table 6) and NMDS ordination plot of
Bray–Curtis community dissimilarities (Figure7) conrmed that
there is a signicant dierence between the identied tree species
in the studied systems and the smallholder farmers reported most
important ES (p < 0.001) across the study areas. is implies that
the identied tree species have a most signicant inuence on the
smallholder farmers who reported multiple ES (food/fodder,
fuelwood, timber, and shade) at p of <0.05 across the studied
agroforestry systems.
TABLE3 Non-native tree species in indigenous agroforestry systems and the farmers’ reported provisioning ecosystem services.
Reported ecosystem service
Non-native tree species Kihamba Ginger agroforestry Miraba Mixed
spices
Acacia mearnsii – – Fuel, timber –
**Artocarpus heterophyllus Food – – –
Annona senegalensis Food
**Artocarpus heterophyllus – Food, fodder ––
Calliandra calothyrsus Fodder – – –
Callistemon citrinus Forage, Fuel – – –
Calotropis procera – Shade, Fuelwood ––
Carica papaya L. Food – – –
Cedrela odorata – Timber ––
Cedrus libani Timber – – –
Cinnamon zeylanicum –Food –Food (spice)
Citrus limon –Food ––
Citrus sinensis –Food ––
Cupressus lusitanica – – Fuel, timber –
**Eriobotrya japonica Food, fodder,shade Food Food –
Eucalyptus spp – – Timber –
Eucalyptus camadulensis Timber – – –
Eucalyptus saligna – Timber ––
**Grevillea robusta Fuelwood, timber, shade Fuel, timber Fuel, timber soil
conservation, shade
–
Leucaena leucocephala Fodder – – –
Malus domestica Food –
**Mangifera indica Food Food Food –
Passiora edulis Food, fodder – – –
**Persea americana Food, fodder Food/fodder – –
Pinus patula Timber – Fuel, soil conservation,
shade, timber
–
Prunus persica Food Food, shade – –
Psidium cattleianum –Food – –
**Psidium guajava Food Food, fodder – –
Sechium edule (Jacq.) Food, fodder – – –
Syzygium aromaticum – – Food (spice)
** Denotes tree species common in both Kihamba and Ginger agroforestry. "-" denotes not encountered.
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Moreover, our results generated by multipatt command from
indicator species analysis (Supplementary Table S6) show statistically
signicant native tree species abundance (p < 0.04) for Maragaritaria
discoidea and (p < 0.02) for Albizia schimperiana associated with
Kihamba. ese tree species have high relative abundance in the
provision of food/fodder and shade. Locally native tree species Mguthuru
(p < 0.03) and Newtonia buchananii (p < 0.05) were found statistically
signicant associated with Ginger agroforestry (Supplementary Table S7).
TABLE4 Diversity, evenness, and equitability of tree species (native and non-native) in the indigenous agroforestry systems.
System Tree species Total number of
species
encountered
Average
number of
species per plot
s.e. nShannon
index (H′)
Equitability
Kihamba Native 16 2.77 0.28 35 2.82 0.81
Non-native 16 2.54 0.18
Ginger Native 15 1.83 0.33 18 3.03 0.89
Non-native 16 2.22 0.33
Miraba Native – 0.00 – 20 1.66 0.80
Non-native 8 1.95 0.17
Mixed spices Native – 0.00 – 9 1.45 0.70
Non-native 2 2 –
s.e = standard error, n = number of observed plots. "-" denotes not encountered.
TABLE5 Native tree species in the agroforestry systems and their reported provisioning ecosystem services (no native tree species were identified in
Miraba and Mixed spices).
Native tree species Reported ecosystem services
Kihamba Ginger agroforestry
**Albizia schimperiana Fodder, fuelwood, shade Fodder, fuelwood, shade
**Bridelia micrantha Fodder Shade
**Cordia africana Food, fodder, fuelwood, shade Shade
Commiphora zimmermannii Fodder, shade –
Croton macrostachyus Food, fodder, shade –
Croton megalocarpus – Shade
Cussonia holstii Fodder –
**Ficus Vallis-Choudae Shade Shade
Ficus natalensis Shade
–Food, fodder
Lannea schweinfurthii Food, fodder, shade –
Maragaritaria discoidea Food, fodder, fuelwood, shade –
**Markhamia lutea Timber Food, fodder, shade
–– Food, fodder
–– Food, fodder
Mitragyna rubrostipulata Food (medicinal) –
Newtonia buchananii – Fodder, fuelwood, shade
Olea capensis Food, fodder
Pterocarpus angolensis Timber, shade
Rauvola cara Food, fodder, shade –
Syzigium guineense – Food, fodder, shade
Tarenna pavettoides – Food (medicinal)
**Telfairia pedata Food, fodder, shade Food, fodder
Trichilia dregeana – Fuelwood, timber
Vangueria madagascariensis Food, fodder –
"-" denotes not encountered.
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4 Discussion
4.1 Structure and species composition of
the indigenous agroforestry systems in the
studied areas
e agroforestry systems studied, i.e., Kihamba, Ginger
agroforestry, and Miraba and Mixed spices agroforestry, are unique to
Tanzania and East Africa (O'kting'ati and Mongi, 1986; Rugalema et
al., 1994; Hemp and Hemp, 2008; Namwata etal., 2012; Kinyili etal.,
2019). Although all studied systems are multi-layered with three or
four vertical layers, our study shows that they have notable dierences
in their salient features mainly because of the unique climate,
landscape setting, soils, historical background, habitat, and species
adaptation that exists in this region (Table1; Figures3, 4; Namwata
etal., 2012). erefore, understanding the salient features of these
systems including arrangements and patterns in space and the
composition of their components will beof paramount importance in
conserving these important agricultural heritage systems (cf. Charles,
2015; Reetsch etal., 2020a,b).
Kihamba homegardens have existed for over 800 years and most
closely mimic a tropical montane forest, oen containing mature tree
species with a canopy layer height of more than 40 m and a large
variety of native and non-native species (Figure3; Tables 2, 4). is
layout oers optimal growing conditions for coee and banana on the
volcanic soils of Kilimanjaro, while an important integration of cattle
in the homegardens keeps soil fertility up to par for those demanding
crops. Nevertheless, a crash in coee prices has induced a shi in tree
species toward other cash crops, notably avocado. e Ginger
agroforestry in the South Pare mountains has a cultural link to the
Kihamba on Kilimanjaro (Kitalyi etal., 2013; Ndaki, 2014), but as
coee and banana income declined even faster on the poorer,
Precambrian soils, a boom of pests and coee diseases motivated
farmers to switch to growing ginger (70% of production in Tanzania)
and sugarcane (Ndaki, 2014). As ginger is a root crop requiring a
dappled shade, farmers kept the shade trees that are also common in
Kihamba, but with a fewer dense canopy lowering light and root
competition (Table4; Figure3). e introduction of ginger, hence,
escalated the deforestation of the native tree species in the Pare
mountains (Ndaki, 2014; Mmasa and Mhagama, 2017), while the
lower nutrient requirements also contributed to a reduction in heads
of cattle and fodder trees. is concurs with the increasing importance
of non-native trees, mainly fruits, in the overstory layer (Figure5;
Table3), consistent with earlier ndings of Nath etal. (2016).
In Miraba, the culture of maize and vegetables requires ample
sunlight, so farmers only plant scattered trees among the Miraba
hedge lines (Figure 4). ere was no culture of traditional
homegardens as in Kilimanjaro and Pare, yet the use of Miraba
(hedges) around elds was traditionally practiced mainly by women
(Msita etal., 2010, 2012). e use of trees native to the area in farming
was not part of the tradition. Historically, the Usambara mountains
were covered by native forest tree species, such as Albizia gummifera,
FIGURE5
Percentage contribution of native and non-native tree species in smallholder systems reported as most important for provisioning of the ecosystem
services food or fodder, fuel, timber, and shade. Mixed spices agroforestry is omitted as the trees in this system were exclusively used for the
production of spices.
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Prunus africana, Catha edulis, Ocotea usambarensis, Podocarpus
usambarensis, Parinari excelsa, and Milicia excelsa (Msuya etal.,
2008). However, much of the forest tree species were logged for timber
before the logging ban of 1984 (MNRT, 2001; FAO, 2005). Increasing
population densities expanded community activities, i.e., cultivation
of maize, beans, and Irish potatoes on slopes and vegetables on valley
bottoms. e intensication in land use led to severe soil erosion on
the mountain slopes and ash oods in the valley bottoms (Haruyama
and Toko, 2005; Msuya etal., 2008). Due to these challenges, Miraba
was promoted as a soil conservation measure. Other interventions in
the landscape, for example, the Gesellscha für Technische
Zusammenarbeit (GTZ) project on Soil Erosion Control and
Agroforestry (SECAP) in collaboration with other institutions
including the Tanzania Forestry Research Institute (TAFORI),
introduced non-native tree species, such as Grevillea, pine, and
eucalyptus for curbing soil erosion and to reduce logging (Johansson,
2001; Msuya etal., 2008). Hence, these species remain important in
the landscape (Table3; Figure6).
East Usambara receives very high amounts of rain from the Indian
Ocean. Combined with the Precambrian, easily leachable soils, it
makes it dicult to get good yields of arable crops, banana, or coee.
As the region has cultural ties to Zanzibar, Madagascar, and India, a
system of spice crops that thrive in high humidity and on well-
draining soils has been practiced here for over 50 years (Figure3; Hall
etal., 2011). is type of agroforestry starts with the thinning of
canopy trees to create 50% shade and the complete clearance of the
lower strata of a once natural forest (Reyes etal., 2005; Hall etal.,
2011). ose authors noticed an absence of young native tree species
in two-thirds of the active agroforest sites, questioning the ability of
the Mixed spices agroforestry to contribute to the conservation goals
FIGURE6
Use of species for dierent ecosystem services across the dierent agroforestry systems. Numbers denote the number of trees encountered in the
plots that farmers indicated as planted primarily for that ecosystem service, and charts denote the relative share of tree species. Species with a low
share were grouped under ‘other species.’ Mixed spices is omitted as the overstory only consists of clove.
TABLE6 Permutational multivariate analysis of variance (PERMANOVA) of multi-layer agroforestry systems tree species on the smallholder farmers
reported ecosystem services.
Df Sums of sqs Mean sqs F.Model R2Pr(>F)
Tree spp. AGF 3 1.6034 0.53446 3.0803 0.42913 0.001 ***
Area ES 2 1.0919 0.54594 3.1465 0.29224 0.003 **
Residuals 6 1.0411 0.17351 0.27863
Tot a l 11 3.7363 1
Signicance codes: 0 ‘***’ 0.001; ‘**’ 0.01; ‘*’ 0.05; ‘.’ 0.1; ‘’ 1.
AFG, agroforestry system; ES, ecosystem service.
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of the East Usambara Mountains (Reyes etal., 2010; Hall etal., 2011).
During our eld campaign in 2021, native trees were absent from the
canopy. Mature clove trees are most productive in full sunlight, and
their conical–cylindrical shape allows ample sunlight for the
cinnamon trees below. Land scarcity may push to a further clearing of
the original canopy to prevent competition for light and space with
clove and cinnamon trees. Black pepper and cardamom require partial
to full shade underneath the trees, and pepper uses the clove trees
for support.
4.2 Provisioning ecosystem services
required by farmers in the dierent systems
Consistent with the farming strategies described above, farmers
have dierent ES requirements for trees in the dierent systems
(Tables 3, 5), providing a more diversied image as compared to
earlier studies stressing the importance of on-farm tree resources for
the provision of food, fodder, shade, timber, and fuel (Munishi etal.,
2008; Charles, 2015; Wagner etal., 2019).
Moreover, our analysis shows that tree species are used in dierent
ways in the dierent agroforestry systems (Figures6, 7).
e identication of dominant native tree species, such as Albizia
schimperiana, Maragaritaria discoidea, Rauvola cara, and Cordia
africana, in the studied agroforestry systems holds signicant
implications for ecosystem services provisioning. ese trees play a
pivotal role in the sustainability and multifunctionality of the
agroecosystems in northeastern Tanzania. Notably, they serve as
crucial shade providers for coee cultivation, contribute to fodder
production, serve as a source of fuelwood, and in some instances, are
employed for medicinal purposes. As such, native species are mainly
valued in systems requiring shading of coee, banana, or ginger, and
in systems with an important cattle component, notably in Kihamba
(Banzi and Kalisa, 2021). In Ginger agroforestry, Albizia schimperiana
remains as a shade tree but fodder trees are being replaced by fruits
(Figure6).
e ndings of this study align with prior research in the same
study area, reinforcing the importance of Albizia schimperiana as a
primary choice for shading coee in both smallholder farms and
large-scale commercial coee plantations (Hundera, 2016). Findings
in our study revealed that native species in the Kihamba remain
important for communities in accessing ES, such as food, fodder, fuel,
and timber, and in providing shade for the production of coee,
banana, rewood, roots, and tuber crops as well as vegetables
(Figure5; Table5). In this system, farmers have accumulated wide
indigenous knowledge and use a wide range of trees and shrubs
(Figure6; Akinnifesi etal., 2008; Hemp and Hemp, 2008; Reetsch
etal., 2020a,b).
However, wedemonstrated that the proportions of non-native
tree species are becoming competitive with native tree species in the
studied areas, and native species are not or no longer used in farming
in the Usambara Mountains. For example, Grevillea robusta, Persea
americana, and Eucalyptus camadulensis have been introduced for the
timber market and have replaced part of the native trees used for fuel
and timber in Kihamba and Ginger agroforestry (Table3; Figures5, 6).
Fruit trees are replacing native food and fodder trees most notably not
only in Ginger agroforestry but also in Kihamba. In systems with no
shade requirements (Miraba) or where native tree species would
compete with tree crops (Mixed spices agroforestry), native trees are
now absent from elds and homegardens.
4.3 Prospects for conservation
e tree component of agroforestry systems is important not only
for provisioning services but also for supporting, regulating, and
FIGURE7
Represent non-metric multidimensional scaling (NMDS) ordination plot of Bray–Curtis community dissimilarities index showing homogeneity of the
variances and relationship between tree species community distribution and the oered multiple provisioning ES in dierent mountainous AGF.
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cultural ES important for conservation and ecosystem resilience
(Soini, 2005; Graham etal., 2022). Mature, native trees in Kihamba
have been reported as important for biodiversity conservation and
carbon sequestration (Fernandes etal., 1984; Gupta etal., 2009). e
taller canopy provides a diverse range of habitats and niches,
supporting a greater variety of ora and fauna, contributing to overall
biodiversity in the agroforestry system (Hemp, 2006). e Kihamba
native tree layer has, moreover, been shown ecient in controlling
landslides, in reducing soil erosion, in improving soil fertility, and in
protecting sources of water for local and downstream users (Kitalyi
and Soini, 2004; Hemp and Hemp, 2008; Mbeyale, 2010; Santoro etal.,
2020; Reetsch etal., 2020a,b; Banzi and Kalisa, 2021; Mbeyale and
Mcharo, 2022). In the North Pare Mountains, agroforestry tree species
help to improve the resilience of smallholder farmers against
environmental extremes by modifying temperatures (Charles, 2015).
e absence of native tree species has, moreover, changed the outlook
of the landscapes in terms of their pristineness, cultural history, and
land use/cover arrangements. Restoration eorts and re-introduction
of native species have, thus, been proposed to improve the resilience
of the studied systems and are advocated as an avenue to minimize
conicts and encroachment into the protected areas (Johansson, 2001;
Kueer etal., 2013; López etal., 2017).
Over the past 100 years, farming systems in the northeastern
Mountains of Tanzania have undergone several transformations due
to colonial and post-colonial policies, land scarcity, migration of
younger generations to urban areas, crop pests and diseases, and
collapse in coee prices (Chuhila, 2016; von Hellermann, 2016). e
results of our study corroborate the importance of livelihood strategies
on the tree component of agroforestry systems (Figures 3–7),
corroborating the statement that these challenges have led the
smallholder farmers in the area to diversify their sources of income to
accommodate external changes and market dynamics (Namwata etal.,
2012). e majority of smallholder farmers have adopted the
introduced non-native tree species, sometimes for conservation value
but more so for their economic benets (von Hellermann, 2016;
Figures5, 6). Hence, dierences in the context of smallholder farming
conditions and ES requirements, as evidenced in our study, should
betaken into consideration for restoration eorts to besuccessful.
von Hellermann (2016) stressed the importance of an increased
sale of coee for agroforestry during the 1940s. Our study corroborates
that shade ES required for coee farming promotes the use native tree
species (Figure5) and supports the hypothesis that a collapse in coee
prices since has led to a gradual abandonment of the coee crop and
diversication of crop production in Kilimanjaro and Pare (Ndaki,
2014), leading to a deforestation of the native tree species (Ndaki,
2014; Mmasa and Mhagama, 2017; Table 4). If native trees are to
be restored in this region, additional research and supporting
measures are needed to help farmers build alternative value chains for
products that can benet from the ES from native species, such as the
sale of milk or honey from (stingless) bees (Eersels, 2022;
Tersago, 2022).
In the East Usambara mountains, protecting habitat for endemic
species is one of the most important conservation objectives (Burgess
etal., 2007; Hall etal., 2011). In Mixed spices agroforestry, the strata
of a once natural forest (Reyes etal., 2005; Hall etal., 2011) have now
completely disappeared (Table4). Several authors, therefore, question
the contribution of Mixed spices agroforestry to conservation goals
(Reyes etal., 2010; Hall etal., 2011). Although such a tree-covered
agricultural system may provide additional ecological services
compared to sun-grown agriculture, a lower compositional and
structural diversity will aect the ES not related to food production as
compared to natural forests. Furthermore, a more protable
cardamom market could bebenecial to local farmers, which may
encourage agroforestry establishment in currently deforested areas but
could also lead to the expansion of cultivation into protected areas
(Reyes etal., 2010). Some previous studies suggest that sustainable
cultivation of spice is possible (Kumar and Nair, 2004; Reyes etal.,
2006; Swallow etal., 2006) and that some farmers are already adopting
ecologically sound intensication practices in homegardens (Reyes,
2008; Reyes etal., 2010). erefore, any eorts to encourage integrated
Mixed spices agroforestry with other native agroforestry tree species
should beexplored. Nevertheless, as all farms in our study do not have
productive ES requirements for trees other than clove and cinnamon
(Tables 3, 5), these eorts will not bestraightforward to realize for
farmers from a livelihood perspective without anking measures. e
protection of native vegetation in forest reserves, therefore, also
remains an urgent priority.
e role of policy and knowledge bias in agroforestry tree
composition has been highlighted by several authors. Worboys (1979)
and Sheridan (2001) mentioned the role of policy and mass promotion
by government regimes with a motive to produce timber for export
and also restore previously cleared forests. Interventions to control
erosion and reduce logging introduced non-native species, such as
Grevillea, pine, and eucalyptus, as these are well studied in the
international literature on soil and water conservation, as compared
to species native to the Usambara (Johansson, 2001; Msuya etal.,
2008). Policies to restore the native tree cover can, therefore, only
besuccessful if underpinned by a better knowledge of local species
and their potential to bealigned with the diverse ES needs of local
communities (Figures5–7). Kihamba agroforestry can serve as an
inspiration as it shows a kind of resilience in terms of available native
tree species that are the remnants of the forest tree species (Table5;
Figure6) and has been shown very ecient in the provisioning of ES
for conservation purposes (Hemp and Hemp, 2008; Reetsch etal.,
2020a,b). e fact that Kihamba farmers still use native tree species
for ES that are also required in systems without native species
(Figures 6, 7) indicates potential for the exchange of indigenous
knowledge between distant communities as well as for driving
scientic research toward the potential of these trees.
5 Conclusion
Our study has highlighted the dierences in salient features
between the agroforestry systems of Mt. Kilimanjaro (Kihamba), the
South Pare Mountains (Ginger agroforestry), and the West and East
Usambara (Miraba and Mixed spices agroforestry, respectively). All
systems are multi-layered with an important tree component, but they
considerably dier in terms of structure, tree species composition
(both native and non-native), and diversity. Our ndings reported
provisioning ES corroborates our hypothesis that the choice of
overstory tree species is closely linked to farmers’ ES needs, livelihood
strategies, and the salient features of each system. e Kihamba system
has retained higher proportions of native trees and uses more native
tree species for provisioning ES as compared to the other systems. e
higher proportions of non-native tree species in Miraba and Mixed
Kimaro et al. 10.3389/gc.2023.1082864
Frontiers in Forests and Global Change 16 frontiersin.org
spices agroforestry are dictated by economical needs for timber, fuel,
and sun-requiring cash crops. Policies to increase resilience and
restore the native tree species cover, therefore, can only besuccessful
based on the knowledge of native species, their traits, and ES potential.
Furthermore, they should balance conservation and livelihood,
acknowledge the complex mix of pressures on farmers’ livelihoods,
and propose measures tailored to the areas’ salient features and
specic challenges.
Data availability statement
e original contributions presented in the study are included in
the article/Supplementary material, further inquiries can bedirected
to the corresponding author.
Author contributions
OK, KV, and K-HF: conceptualization and methodology. OK, DK,
KV, and K-HF: investigation. OK, DK, KV, ED, and K-HF: validation,
data curation, reviewing, and editing. OK: formal analysis and
writing—original dra preparation. All authors have read and agreed
to the published version of the manuscript.
Acknowledgments
e authors appreciate nancial support by the Deutscher
Akademischer Austauschdienst (DAAD; 57507871), Germany through
a PhD scholarship to the rst author and the South Initiative
(SI)-VLIR-UOS (Livelablink; TZ2020SIN312A101) project funded by
the Flemish Interuniversity Council (VLIR), Belgium. Furthermore,
wereceived support from the Mwenge Catholic University (MWECAU).
e authors appreciate mentioning and thank all our interview
individual smallholder farmers of northeastern mountain landscape in
Tanzania practicing the dominant agroforestry ecosystems for
dedicating their time, resources, collaboration, and information. It is of
the same weight worth it to mention sta and management of TAFORI,
Lushoto Centre, northeastern Tanzania regions Rural District Council,
and the whole team of extension sta for their devotion and
dedicated support.
Conflict of interest
e authors declare that the research was conducted in the
absence of any commercial or nancial relationships that could
beconstrued as a potential conict of interest.
Publisher’s note
All claims expressed in this article are solely those of the authors
and do not necessarily represent those of their aliated organizations,
or those of the publisher, the editors and the reviewers. Any product
that may be evaluated in this article, or claim that may be made by its
manufacturer, is not guaranteed or endorsed by the publisher.
Supplementary material
e Supplementary material for this article can befound online
at: https://www.frontiersin.org/articles/10.3389/gc.2023.1082864/
full#supplementary-material
SUPPLEMENTARY FIGURE S1
Schematic example showing tree species distribution and evenness in AGF
farm plots (Similarities and dissimilarities) (Allison, 2019).
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