Smart agroforestry for sustaining soil fertility and community livelihood

Abstract

Smart Agroforestry (SAF) is believed to be one of the alternative solutions in implementing sustainable forest management to achieve the community welfare. SAF provides agricultural and silvicultural knowledge and practices that aims not only for recovering the environmental attributes but also for increasing farmers resilience. However, the benefits of agroforestry related to soil fertility in optimizing the land productivity and governing the community livelihood are often overlooked and have not been well discussed. This review aims to describe how smart agroforestry practices in various regions in Indonesia and several other countries have significantly contributed to maintaining soil fertility and increasing crop production while assuring profitable benefits for the community. This review paper focuses on discussing the role of SAF in sustaining soil fertility and community livelihood in tropical and non-tropical regions. The review article was based on a synoptic review approach to SAF and Soil Fertility-related relevant publications and nationwide experiences. The review compiled and analyzed information from national and international research papers in various online scientific journals, conference proceedings and relevant books, to gain a comprehensive understanding of the topic being discussed. The study utilized a qualitative approach and drew upon primary and secondary sources based on a systematic review. Agroforestry has a significant role in recycling soil nutrients from the materials in the surrounding environment. SAF influences soil fertility physically, chemically and biologically. SAF practices in both wet and dry lands can contribute significantly to the community’s income. This review unveils the latent potential and the role of SAF in sustaining soil fertility that supports the community's livelihood and can serve as impetus for future research.

Keywords:

• Mixed tree-crop planting
• soil physical fertility
• soil chemical fertility
• soil biological fertility
• land equivalent ratio

1. Introduction

The conversion of forest area into agricultural land or other purposes has caused several environmental problems and deforestation (FAO, 2021) which become a reflection of the pressure on the forest due to the community’s dependence on the forest to meet their needs. Agroforestry is an alternative solution to address the challenges in performing sustainable forest management, especially in forest areas adjacent to community settlements (Singh et al., 2021), and enhancing communities’ resilience (Sanudin et al., 2023).

Agroforestry is defined as a planting technique that combines long-lived tree crops with seasonal agricultural crops, livestock, or fisheries within or outside forest areas (FAO, 2022), through spatial and temporal arrangements, either simultaneously or alternately. Nair et al. (2021) mentioned there are three major categories of agroforestry system (AFS) identified namely agrisilvicultural, silvopastoral, and agrosilvopastoral systems. The good practice of agroforestry called Smart Agroforestry (SAF) is a set of agriculture and silvicultural knowledge and practices that are aimed not only at improving environmental parameters, including climate change mitigation and adaptation, biodiversity enhancement, and soil and water conservation but also increasing profits and resilience for farmers (Octavia et al., 2022).

In Indonesia, recent data show an increase in the number of villages that closely interact with the surrounding forest amounted 39,147 villages (46.76%) located on the edge of forest areas and 3,324 villages (3.97%) located within forest areas (BPS, 2020). The population of these villages was estimated at 37.2 million people, of which around 1.7 million were categorized as poor (MoEF, 2020).

Much evidence points to the potential of trees to provide multiple benefits and multiple ecosystem services (Iñamagua-Uyaguari et al., 2023). Some of them are its potential in landscape restoration by enhancing physical, chemical and biological soil characteristics (Arruda et al., 2023), generating farmer income and alleviating poverty, providing housing, health, energy, and environmental sustainability in agricultural landscapes (Duffy et al, 2021). This has rendered the presence of trees as a major component of "evergreen agriculture" (Octavia et al., 2022; Sopacua et al., 2021). Inclusion of trees in farming systems significantly optimize the nutrient cycle of the soil (Nugroho, 2020). This significant role is particularly crucial in tropical soils, where the high level of weathering have created deep, leached soils that are poor in nutrient.

Various efforts have been done by the Indonesian Government to accommodate the interests and needs of the community on the one hand and the need to preserve forests on the other. This requires proper strategy in managing forest resources, one of which is done by enabling the community to participate in cultivating forest land through agroforestry (Parhusip et al., 2019; Murniati et al., 2022a). However, de Sousa et al. (2020) emphasized that despite of its potential benefits of agroforestry, it is important to note that agroforestry is not a total panacea against food insecurity and environmental degradation. To be effective and sustainable, agroforestry needs improved integration: not only agriculture with trees but also trees with people, considering the suitability of technical, economic and social condition (Khatri et al, 2023).

Therefore, there is a need to develop a good agroforestry practices (SAF) which has many goals both ecologically help to sustain soil fertility and mitigate climate change for ensuring sustainable landscape management and economically to increase farmer’s income and the resilience of communities to various social and economic shocks including drought and food shortages. This review aims to describe how smart agroforestry practices in various regions in Indonesia and several other countries have significantly contributed to maintain soil fertility and increasing crop production while assuring the maximum benefits for the community.

2. Material and Methods

This article was based on a synoptic review approach to SAF and Soil Fertility-related relevant publications and nationwide experiences. The review compiled and analyzed information from national and international research papers in various online scientific journals, conference proceedings and relevant books, to gain a comprehensive understanding of the topic being discussed. The study utilized a qualitative approach and drew upon primary and secondary sources based on systematic review. Some terms such as “smart agroforestry”,“agroforestry and soil fertility”, “agroforestry and land productivity”, “agroforestry and livelihood”, and “land equivalent ratio” were employed to search research articles. Once the appropriate literatures were gathered, they were organized and synthesized.

3. Result and Discussion

3.1. Smart agroforestry contributions in maintaining soil fertility to support plant growth

The increasing pressure to boost food production has resulted a heavy burden on soil resources (Mosier et al., 2021). Agroforestry is an agricultural technique that integrates trees into the farming system and focuses on diversifying various agro-ecosystem production commodities such as wood producers, crops, palms and forages for cattle (Rosati et al., 2021) so as to produce food diversity and increase soil fertility (Puškarić et al., 2021), improve environmental quality and encourage the biodiversity conservation (Amaral et al., 2019). Agroforestry can be an economical and climate-smart farming technique that can assist smallholder farmers to deal with the climate-related extremes of dry land areas by diversifying food sources, improving and protecting soil, and reducing wind erosion (Fahad et al., 2022). Combining trees on farms through agroforestry can be an excellent approach to increase soil fertility, even though managing soil fertility can be challenging (Fahad et al., 2022).

Trees play a significant role in the nutrient cycle by recapturing and pumping back leached soil nutrients via deep roots and has function as a 'safety net' against the loss of nutrients in the nutrient cycle (Fahad et al., 2022) (Figure 1). In AFS, the woody perennial plants take up a large quantity of nutrients from the soil for their growth. Most of these nutrients are stored in their organs (e.g. roots, trunk, branches and shoots) which are later pruned or turned into litter (Kaba et al., 2021) that have great potential as organic fertilizer, especially for annual crops. This organic fertilizer can be a solution to the limited mineral fertilizer that is often unaffordable by the farmers (Dori et al., 2022). Perennialization in the AFS has significant potential for restoring soil fertility of degraded croplands and serving to meet food security needs in the future (Mosier et al., 2021). Soil fertility is divided into three components, namely soil physical, chemical and biological fertility. Soil fertility is the main factor affecting crop productivity. Addressing the soil fertility problem has a direct impact on farm yields since soil fertility and farm production are directly correlated (Tsufac et al., 2021).

Figure 1. Nutrient pumping and cycling in agroforestry system (Adapted from: Fahad et al., 2022).

3.1.1. Smart agroforestry contribution in maintaining soil physical fertility

Important soil physical properties for determining the level of soil fertility consist of solum, texture, structure, consistency, porosity, permeability, infiltration, bulk density, water content, soil moisture, temperature, and soil colour. Their role in supporting plant growth is interrelated (Tripathi et al., 2020). Therefore, it is important to improve soil physics to secure food, energy, water (FEW) and ecosystem services (Shang et al., 2018). Alletto et al. (2022) stated that the physical properties of soil are related to the dynamics of water and air and are also related to aspects of soil conservation and land management. Furthermore, they proved that agroforestry practices affect various soil physical properties, such as changes in soil retention, circulation, and available water capacity. Tree roots can improve soil structure and porosity where dead tree roots produce pore holes, thereby increasing infiltration and reducing run-off (Tsufac et al., 2021). The physical soil properties are related to soil erosion that occurs in upland and sloping land caused by a lower infiltration capacity of the soil, a higher runoff, and reduced of fine particles which function to support the stability of soil aggregates (Dori et al., 2022). Conversion from native forest to low-input pasture intensively degraded soil physical quality compared with conversion to agroforestry system which improves soil physical quality in areas previously occupied with pasture. It indicates greater potential for soil reclamation through more diversified planting systems (Cherubin et al., 2018).

Agroforestry practices significantly improve the soil cation exchange capacity (CEC) through the accumulation of crop residues. CEC is the capacity of clay to adsorb and exchange cations which is influenced by clay content, clay type, and organic matter content (Dori et al., 2022). Integrating no tillage-agroforestry at dry land agroecosystem in Kenya revealed that conservation agriculture by combining trees and crops resulted in a significant rise of CEC compared to treeless farming system. Higher CEC in this case, is resulted from the accumulation of crop residues and green biomass produced and retained by trees within the cropping fields (Kisaka et al., 2023). A study from Macedo et al. (2023) in Northeastern Brazilian highland reveals that agroforestry improved the soils’ ability as soil organic carbon (SOC) sinks in microaggregates, implying greater long-term SOC storage and stabilization. SOC and irones oxide had substantial (p < 0.05) effects on the stability of soil macroaggregates and microaggregates under agroforestry, respectively.

Agroforestry practices on upland and sloping lands are not only related to soil fertility but also protect the soil from erosion and degradation (Wawire et al., 2021). Combined fruit and coffee plantations with grass and maize crops can significantly overcome erosion and land degradation (Do et al., 2023). The physical soil quality of complex agroforestry is similar with natural forest which has better structure, bulk density and porosity (Purnama et al., 2022). Agroforestry systems with greater structural complexity and botanical composition enhancing soil physical quality by improving the soil aggregation and porosity processes (Duran-Bautista et al. 2023).

3.1.2. Smart agroforestry contribution in maintaining soil chemical fertility

Soil chemical properties are some of the main parameters of soil fertility having an important role in supporting plant growth and development. This parameter is mainly expressed by the amount of nutrient availability in soil, such as Nitrogen (N), Phosphorous (P), Potassium (K), etc. The chemical properties of the soil are dynamic and are significantly affected by soil formation factors, i.e., parent material, climate, biota/organisms/vegetation, time, and topography (University of Hawaii, 2023). Some soil chemical variables which affect nutrient availability are soil reaction (pH), soil organic matter/carbon (SOM/SOC), and cation exchange capacity (CEC) (Khaleel et al., 2020). Soil organic matter is a crucial soil component that significantly influences soil fertility (Widyati et al., 2022). Among those soil formation factors, the most relatively easy to human adjustment is organisms. Through the appropriate organism management, the desired soil chemical properties can be achieved and will drive good plant growth and productivity. Hence, agroforestry can manage organisms well to increase soil fertility (including soil chemical fertility), growth, productivity, and land sustainability as shown in Figure 2.

Figure 2. Agroforestry influences on soil fertility, growth and productivity of the plant and land sustainability

Agroforestry is a natural resource management system that is developed based on the organisms (tree, crop, shrub, cattle, etc.) arrangement. In agroforestry, trees, crops, and cattle are purposely selected, placed and grown in certain landscape patterns. This means that agroforestry is one of the tools having a huge possibility to influence soil formation and soil chemical properties as the results of interaction among organisms and between organisms and other soil formation factors (climate, parent material, topography, and time) (Figure 2). Some evidences of agroforestry practices can improve soil chemical fertility are presented in Table 1.

Table 1. Soil chemical fertility improvement due to agroforestry practices (in %).

Soil chemical fertility improvement (%)
N	P	K	SOM/SOC	pH	Locations	References
117.9	327.1	240.8	156.9	3.15	Garut, West Java, Indonesia	Gunawan et al., 2019
–	–	–	88.8	4.8	Kuningan, West Java, Indonesia	Purnama et al, 2022
138.1	–	–	133	4.7	Malang, East Java, Indonesia	Khalif et al., 2014
14.3	0	–	26.3	−1.2	South of France	D’Hervilly et al., 2021
−7.7	60.0	7.6	6.9	−6.4	Dang, Nepal	Panday et al., 2019
46	11	–	21	2	Humid & sub humid tropic	Muchane et al., 2020
14			6.5	5.2	Narsingdi, Bangladesh	Riyadh et al., 2018
−4.8	401.1	−18.75	–	4.3	Peatland, Central Kalimantan, Indonesia	Agus et al., 2020
52.5	64.1	–	20	–	Tanzania	Vyamana et al., 2021
−6.9	113.6	279.7	11.5	17.5	Gedeo, Southeastern Ethiopia	Dori et al., 2022
48.1	119.5	158.3	7.8	6.4	Sahelian Niger	Diallo et al., 2019
18.6	16.3	6.1	30.1	15	Deli Serdang, North Sumatra, Indonesia	Rizwan et al., 2020
231	39.3	−16.7	286	2.5	Bogor, West Java, Indonesia	Parjono et al., 2021
–	–	–	128	–	Pangalengan, West Java, Indonesia	Aji et al., 2021

These interactions can be positive (mutual support) or negative (competitive) depending on the selection of species, land types and management applied (Octavia et al., 2022). However, in general, a lot of studies have shown that agroforestry gives advantages in improving soil chemical properties. Based on the agroforestry practiced worldwide, the increase of soil N, P, K, organic carbon and pH could reach 117.9%, 401.1%, 240.8%, 286%, and 17.5%, respectively (Table 1). Since chemical properties are generally correlated with plant growth and production (Mindawati et al., 2019), there is a lot of evidence about the increasing crop production in agroforestry system such as millet, cowpea, and ziziphus (Bado et al., 2021). The presence of the tree in agroforestry provides a significant positive impact on improving soil fertility and productivity of the land. The high nutrient will be returned to the floor through high litterfall and then through decomposition will be released to the soil and available for the plant (Junaedi et al., 2020; 2022). The tree also has root exudates that also play a significant role in soil fertility due to its capability to act as an organic carbon and energy source for microbiology and determine nutrient P solubilization (Pantigoso et al., 2020).

3.1.3. Smart agroforestry contribution in maintaining soil biological fertility

Contribution of Smart Agroforestry in maintaining soil biological fertility can be seen from its positive impacts on the population and biomass of the organisms living in soil (microorganisms, fauna and roots). Soil organism is defined as any organism inhabiting the soil during part or all its life cycle and could associate and adapt with soil environment (Husamah et al., 2017). Soil biota (soil microorganism) is a crucial part of the soil ecosystem (Chamorro-Martínez et al., 2022). Fungi and/or bacteria, are beneficial in agriculture as substitutes for chemical pesticides and mineral fertilizers because they are environmentally friendly (Ortiz & Sansinenea, 2022). In fact, a variety of products have been commercially manufactured that contain one or more species of bacteria or fungi in the form of biofertilizers aiming to enhance plant growth and sustainability (Hakim et al., 2021). The soil macrofauna plays a key role in optimizing soil fertility and supporting sustainable soil use in fruit orchard agrosystems (Sofo et al., 2020), while soil mesofauna contributes to soil reclamation (Bhaduri et al., 2022).

Mycorrhizas are mutualistic associations between the plants roots and certain soil fungi, which can be grouped into four types: ectomycorrhiza, orchid mycorrhiza, ericoid mycorrhiza, and arbuscular mycorrhiza (Soudzilovskaia et al., 2020). In tropical agroforestry systems, the arbuscular mycorrhizal fungi (AMF) form is the most important group (Qiao et al., 2022). AMF form symbiotic associations with the majority of land plants, receive organic carbon from the host plant, and in return deliver mineral nutrients, particularly inorganic phosphate (P), to the host (Soudzilovskaia et al., 2020). AM fungi influence nutrient availability and uptake, increase the photosynthetic rate, improve antioxidant activities, and increase tolerance against environmental stress, as well as have a positive impact on both the primary and secondary metabolites and also increase growth, yield, and productivity (Khan et al., 2022). Therefore, understanding the mechanisms of phosphate acquisition and delivery in the fungi is very important for full appreciation of the mutualism in the association (Ezawa & Saito, 2018). The use of AMF, phosphate–solubilizing bacteria (PSB), and the addition of silicon (Si) can be an effective and economical way to improve the availability and efficacy of P (Etesami et al., 2021). In agriculture, P nutrition is an essential nutrient for plant development, which promotes root development and is a fundamental component of plant energy and organic tissues (Timacagro, 2023). This is way P called as ‘key of sustainable agriculture’ that ensuring soil fertility and enhancing crop yields.

Araújo et al.(2019) reported that soil under agroforestry system in Northern Brazil had the highest AMF species richness compared to the other land use types (monoculture soybean, monoculture corn, native forest). They also concluded that soil organic matter (SOM) attributes in the agroforestry system had influence in AMF species richness. Other study by Dobo et al. (2018) found that agroforestry practices with leguminous trees used as shade tree species for perennial crops like Coffea arabica and Ensete ventricosum had higher AMF abundance and diversity than the other shade tree species. This indicates that AMF show tendency of being affected by group of plants.

Rhizosphere bacteria are essential for plant growth and nutrition (Ortiz & Sansinenea, 2022), they contribute significantly to the functioning of stable soil ecosystems (Puskaric et al., 2021; Khmelevtsova et al., 2022).The other report revealed that agroforestry of walnut and an agricultural crop has positive effect on the bacteria (Puskaric et al., 2021). Moreover, endophytic bacteria supports plant growth and health through an increase of nutrient availability and the ability of nitrogen fixation from the atmosphere (Wemheuer et al., 2019).

Winara (2020) stated that the soil macrofauna diversity is higher in agroforestry systems. He found that the value of soil macrofauna diversity in teak (Tectona grandis) and kimpul (Xanthosoma sagittifolium) agroforestry is higher than that in teak and kimpul monocultures. Duran - Bautista et al. (2023) reported that agroforestry systems promote richness and diversity of edaphic macrofauna. An agroforestry system influences the soil fauna community through the soil physical (temperature, humidity, water content, aeration) and chemical (pH) aspects, as well as soil organic matter. Soil fauna generally prefer more moist soil (Ertiban, 2019) that can be accommodated by agroforestry systems. Agroforestry could increase in the biomass and abundance of soil invertebrates (Asfaw & Zewudie, 2021).

3.1.4. Smart agroforestry contribution in enhancing land productivity

The benefits of implementing agroforestry pattern are increasingly felt in dry areas because its ability to maintain the plant performance against water deficit impacts during drought (Temani et al., 2021). In Africa, intercropping trees in rice fields can increase the rice yields compared to monoculture on non-fertilization treatment (Rodenburg et al., 2022). Increased production of agroforestry-managed crops can occur through mechanisms which improve the health of cropping system. Compared to monoculture, cacao grown in agroforestry has fewer pests and diseases, resulting in higher yields (Armengot et al., 2020). Agroforestry also improves the environment for the habitat of pollinator insects, increasing the success of plant fertilization (Varah et al., 2020).

Karki et al. (2021) found strong evidence that the nutrient input and vegetation composition in southern-pine silvopasture led to changes in soil physiochemical properties which further caused a shift in soil microbial community composition. Compared to woodland, silvopasture of loblolly pines with small ruminants produces higher plant growth and soil chemical. Karki et al. (2022) found that silvopastures offer a better environment for a faster growth of southern pine trees versus woodlands, when the understory vegetation present in both systems is managed with small ruminants. The sylvopasture pattern can increase the success of planting Abies hickelii trees because grazing sheep eat herbaceous plants which have the potential to be weeds (Aparicio-Lechuga et al., 2021). Poudel et al. (2022) revealed that soil under silvopasture system with black walnut (Juglans nigra) and honeylocust (Gleditsia triacanthos) had about 45% to 60% greater (p < 0.05) microbial biomass than soil under open pasture. They concluded that silvopastures system with proper management can improve certain soil health parameters over time depending on tree characteristics and the age of the system.The combination of species in an agroforestry system can reduce one species' production while compensating for another's production. Although agroforestry of jackfruit-papaya-eggplant reduced the yields of papaya by 22.8% and eggplant by 17.4%, the total production calculated from the economic value of the pattern is still higher than monoculture system (Miah et al., 2018). Several factors contribute to the increase of the economic value of agroforestry: a) the use of empty space under the shade trees, b) the increase in tree growth due to the fertilization effect on understory crops, c) the efficiency of soil nutrient derived from the increase of organic material originating from trees, and d) the higher quality of farm commodities obtained by implementing organic agriculture system (Das et al., 2022). Land Equivalent Ratio (LER) is a land equivalence value to estimate the effect of crop competition and the value of profit derived from the land, that can be used to evaluate the productivity of agroforestry systems (Ceunfin et al., 2017). Some LER values from several agroforestry planting patterns are presented in Table 2.

Table 2. The value of Land Equivalent Ratio on several agroforestry patterns.

Crop Combination	Country	LER Value	Reference
Tectona grandis+Xanthosoma sagittifolium	Indonesia	1.61-1.85	Winara et al., 2022
T.grandis+Maranta arundinacea / T.grandis+Canna edulis / T.grandis+Dioscorea esculenta	Indonesia	1.65, 2.65, 1.27	Maharani et al., 2022
Zizyphus jujuba+Gossypium hirsutum	China	1.565-1.527	Wang et al., 2022
Citrus sinensis+Brassica oleracea/Pisum sativum+ Zingiber officinale+Curcuma longa	Bangladesh	2.01	Das et al., 2020
Talun (forest garden) dominated by bamboo and Fatsia japonica/mixed garden dominated by Carica papaya, Mangifera indica, Nephelium lappaceum / home garden dominated by ornamental trees	Indonesia	1.40, 1.81, 0.96	Prastiyo et al., 2018, 2020
Alley cropping of hybrid poplars+Triticum aestivum (1^strotation)+Hordeum vulgare (2^nd rotation)	Germany	2.0–2.9	Seserman et al., 2018
Acacia auriculiformis+ Zea mays (2^nd & 3^rd rotation) A. auriculiformis+Glycine max (1^st, 2^nd, 3^rd rotation)	Indonesia	1.71, 1.36 2.22, 1.99, 1.36	Figyantika et al., 2020
T. grandis+Arachis hypogaea+Z. mays	Indonesia	1.2-1.36	Karimuna et al., 2022
Dimocarpus longan + Z. mays + Panicum maximum	Northwest Vietnam	1.1-1.9	Do et al., 2020
Melaleuca leucadendra+Zea mays + Glycine max	Indonesia	1.49-1.77	Elonard & Lusianingsih, 2018
Dyera polyphylla+Elaeis quineensis	Indonesia	1.4	Nasamsir & Usman, 2019
Trees (willow, alder, hazelnut, beech, apple, olive)	Denmark, U.K, Poland, Romania	1.36-2.00	Lehman et al., 2020

Annual LER provides only a temporary view of productivity. Assessing the fluctuation of LER on a yearly basis would be beneficial to evaluate the changes in productivity. These changes could be derived from the effect of species competition, the light intensity and the nutrient sharing. The fluctuation in LER value provides additional information about how land management should be adjusted with several options such as silvicultural treatments (pruning, thinning, fertilizing) or alternate the understory crops. Modern silvoarable agroforestry systems by short rotation coppice strips also are considered as a potential way to increase and promote biodiversity while simultaneously producing arable crops and woody biomass (Zitzmann & Langhof, 2023). Another study in Indonesia on diversified plantation as a strategy in oil palm management through ‘Jangka Benah Policy’ (Octavia et al., 2022) in Jambi Province revealed that the birds’ diversity in oil palm agroforestry plot was higher than that in oil palm monoculture plot (Ridho et al., 2023).

3.2. Smart agroforestry and its contribution to local community’s livelihood

The worldwide challenges of poverty, hunger and climate change require a proper strategy to tackle. Many studies have revealed that agroforestry, a natural resources management system that integrates trees on farms in the agricultural landscape has the capacity to provide multiple benefits and therefore has become a viable option for overcoming those challenges. Over a long period, agroforestry practices have evolved as an effort in adaption to dynamics that involve interactions between available resources, market demand, agroecological conditions and plant diversity (Burgess et al., 2022).

In addition to the combination of various types of tree-crop plants, complex systems based on crop-livestock-fruit/forest integration, namely silvopastoral has been practiced for centuries. Silvopastoral can also provide a wider variety of goods (e.g. food, feed, fiber, firewood, and timber) and greater access to livelihood capitals (Birhane), as additional ecosystem services (e.g. control soil erosion and biodiversity conservation) and maintains forage cover and prevents weed outbreaks. Apart from its environmental and economic relevance, silvopastoral can help in the preservation of traditional landscapes as well (Munaro et al 2023). The study on agrosilvopastoral practice reveals that it provides a possibility for rural community development by meeting the growing demand for high-quality animal products, maintain a high degree of animal welfare, and can cope with climate change through both adaptation and mitigation techniques (Mele et al. 2019).

In the context of social-economic and cultural aspects, many studies revealed that livelihood was the most important driving factor for developing agroforestry in Indonesia (Parhusip et al., 2019; Octavia & Rachmat, 2020). Practicing agroforestry enables farmers to have the chance to work and earn from various plant species throughout the year on a daily, monthly, yearly basis for their families, from fruits, cash crops, food, wood and other by-products (Murniati et al., 2022a, Octavia et al., 2022;).

In many cases, SAF is practiced on dry land and on community land. Common development of SAF on community-owned land then would raise a question on how the economic contribution of agroforestry if it is practiced on state forest/government-owned land with some restrictions such as no logging and no intensive farming on protected areas that have specific function as biodiversity conservation sites. Furthermore, it is also interesting to study how agroforestry practice on wetlands. Techniques and implementation strategies are certainly different from agroforestry practice on dry land.

3.2.1. SAF practices on dry land

Some examples of SAF practices on state forests can be found in Wan Abdul Rachman Grand Forest Park, Lampung Province, Indonesia. SAF practices in the area have made a significant contribution to household income, amounting to 45.96% of total household income (Riani et al., 2017). Other research on similar site also confirmed that SAF practices contributed to 75.63% of total farmers’ household income (Murniati et al., 2022b) in addition to several other benefits that farmers took advantage of, such as increased production of food crops, ownership of luxury goods, and access to information and finance (Murniati et al., 2022a). SAF practices developed by farmers in the buffer zone of Lore Lindu National Park, Central Sulawesi Province also verified that the highest revenue optimization was obtained through diversification pattern of sweet potato and cocoa plants with an increase of IDR. 28,382,068 or 25.1% to total farmer’s income (Pribadi et al., 2021).

The practices of SAF in customary land were developed by local people in Paru Village Forest, West Sumatra Province. It provided substantial income and encouraged the development of new business opportunities with forward and backward linkages such as the business of providing agricultural production inputs and post-harvest processing businesses into end products such as rattan furniture and household appliances having higher economic value (Octavia & Nugroho, 2020; Yeny et al., 2021).

In Java Island, agroforestry is commonly developed on community’s homegarden. Local culture and traditions between generations are some of factors that influence the composition of agroforestry component species (Hakim et al., 2018). Subsequently, agroforestry developed in home-garden can symbolize ethnic identity in Indonesia hence it has different patterns and values ​​(Wakhidah et al., 2020). Agroforestry development on land far from community settlement is mostly in the form of mixed gardens consisting of wood, fruit and plantation crop species with less intensive management (Parikesit et al., 2021). Growing tree as the main component of agroforestry aims to produce timber, as land boundaries and understory shade trees, to prevent land erosion and to secure the availability of necessary basic commodities (Sabastian et al., 2019). Descriptions of various patterns of agroforestry development on dry land both in state forest areas and on community-owned land in Indonesia are presented in Table 3.

Table 3. Descriptions of various patterns of agroforestry development on dry land in Indonesia

	Species Composition
Location (Source)	Forest Tree	Estate Crop	Fruit Tree	Food Crop	CTI (%)
Wan Abdul Rachman Grand Forest Park, Lampung Province (Murniati et al., 2022b)	Swietenia mahagoni, Litsea spp, Dalbergia latifolia, Aleurites moluccana	Theobroma cacao, Syzygium aromaticum, Hevea brasiliensis, Ceiba pentandra, Areca catechu	Durio zibethinus, Parkia speciosa, Archidendron pauciflorum, Artocarpus heterophyllus	Vanilla planivolia, Colocasia esculenta, Zingiber officinale, Piper retrofractum	75.63
Paru Village Forest, West Sumatra Province (Yeny et al., 2021)	Calamus spp, Cinnamomum verum	T. cacao, H. brasiliensis	P. speciosa, A. catechu, Lansium domesticum, Mangifera indica, Artocapus integer, Citrus spp. , D. zibethinus, Garcinia mangostana	–	25-50
Community-owned land in South Sulawesi (Jumiyati et al., 2018)	Palaquium spp, Heritiera javanica	T. cacao	–	–	46.7
Karang Siri Village, Soe Sub District, East Nusa Tenggara (Liwu et al., 2021)	Gmelina arborea, S. mahagoni, Senna siamea	–	Musa paradisiaca, Cocos nucifera, Carica papaya, Syzygium malaccense	Zea mays, Capsicum frutescens, Manihot utilissima	31.31
Lampung (Kholifah et al., 2017)	–	H. brasiliensis, Cofea robusta	D. zibethinus	Vegetables	98.47
South Kalimantan (Syamsudin et al., 2020)	–	H. brasiliensis	L. domesticum, A. heterophyllus	–	77
South Sulawesi (Zaman et al., 2020)	–	Z. aromaticum, Piper nigrum, Myristica fragrans	Nephelium lappaceum, D. zibethinus, L. domesticum	Z. officinale, C. esculenta, Capsicum sp	78.69
Maluku (Latue et al., 2018)	–	T. cacao, Z. aromaticum	Salacca zalacca, M. paradisiaca, D. zibethinus,	Manihot esculenta, Z. mays, C. esculenta , Cucurbita moschata	97.02
West Nusa Tenggara (Iqbal et al., 2021)	–	–	D. zibethinus, N. lappaceum	Arachis hypogaea, Z. mays,	88.31
East Nusa Tenggara (Agu & Neonbeni, 2019)	Eucaliptus pellita, S. mahogany, T. indica, Casuarina junghuhniana , Hibiscus macrophylus, Santalum album	C. robusta, A. catechu, Piper betle	M. paradisiaca, Anacardium occidentale	Oryza sativa, Amorphophallus muelleri, C. esculenta, C. moschata, M. esculenta, Cucumis sativus, Z. mays, Ipomea batatas, Arachis hypogaea	59-67

Note: CTI = Contribution to farmers’ total income.

3.2.2. SAF practices on wetland

Tropical wetland is one of the most productive ecosystems with high biodiversity. Establishing agroforestry as a conservation effort in the buffer zones can protect the wetland ecosystem (Dewanto et al., 2021). In mangrove forest areas, deforestation and conversion to ponds, settlements, and agricultural land have resulted in the loss of some ecosystem services that have negative impacts on people's lives (Rahman & Mahmud, 2018). One of the options to develop agroforestry in wetlands is through silvofishery development, which is an alternative to utilize mangroves and to increase people's income by cultivating both fish and shrimp ponds.

Studies verified that the contribution of silvofishery development to people's livelihood is significant. Kusuma (2019) found that there was an increase in community income of 36.5% from IDR 25,964,624.5 per hectare (non silvofishery) to become IDR 40,875,702.5 per hectare with the silvofishery pattern. The increase in community income does not only come from selling products gained from fish and shrimp cultivation, but also from selling mangrove by-products including shrimp, firewood, and crabs. Meanwhile for non-silvofishery farmers, the community's income only relies on the sales of milkfish and tiger shrimp. Similar to the development of SAF on dry land, silvofishery in mangrove forest areas has also indirectly created new job opportunities with the emergence of various follow-up businesses having forward and backward linkages (Andriani, 2019).

Agroforestry patterns have also been developed on peatland by its surrounding community. One example is the agroforestry model developed in Jambi with a combination among other: (a) oil palm-corn (Elaeis guineensis – Zea mays); (b) Areca-corn (Areca catechu – Z. mays); (c) oil palm-Areca-corn (E. guineensis – A. catechu – .Z. mays) and (d) Areca-coffee (A. catechu – Coffea liberica) (Yuniati et al., 2018). Meanwhile in Kampar, Siak and Kepulauan Meranti Regency of Riau Province, agroforestry patterns are also developed on peatlands through a combination of various tree crops such as geronggang (Cratoxylum arborescens), balangeran (Shorea balangeran), gelam (Melaleuca cajuputi), coconut (Cocos nucifera), mango (Mangifera indica), rambutan (Nephelium lappaceum), cassava (Manihot utilissima), oil palm (E. guineensis), long beans (Vigna unguiculata), longan (Dimocarpus longan), red chilli (Capsicum annum), jackfruit (Arthocarpus integra), papaya (Carica papaya), sago (Metroxylon sago), and rubber (Hevea brasiliensis). This agroforestry system does not only contribute to increase people's income, but also opens new jobs for the local community and could be selected as a tool to overcome social conflict around forest area (Junaedi et al., 2021).

3.3. Challenges for further development

SAF has been practiced not only in Indonesia, but also in other parts of the world and has proven to increase community’s income (Kiyani et al., 2017) and community’s resilience (Sanudin et al., 2023), in facing dynamics due to some changes involving interactions between available resources, market demand, agroecological conditions and plant diversity (Santiago-Freijanes et al., 2021), including various NTFP species that provide significant contribution to rural household (Derebe & Alemu, 2023). However, apart from its great potential, there are still some challenges for further development due to relatively small land holdings coupled with limited farmer's access to funding and resource availability (Achmad et al., 2022; Tega & Bojago, 2023). In addition, some studies reported that, the younger generation seems less interested in activities in the agricultural sector, causing the farmers who develop agroforestry to be relatively old, which affects land productivity and decreases the contribution of agriculture to the farmer's economy (15.8-29%) (Race et al., 2022).

In addition, limited labour and skills related to post-harvest processing, especially for perishable agricultural products, are other obstacles need to be handled. Policy makers and development practitioners need to anticipate the various obstacles and try to eliminate possible barriers to adoption. Increase community access to funding source and provision of production inputs and various necessary trainings are strategic actions to overcome the various above challenges. Another option for increasing investment into agroforestry could be financial compensation for environmentally friendly practices. Finally, an attractive marketing opportunity is needed to ensure fair price for products from the farmers (Rahman & Neena, 2018).

4. Conclusions

The ideal form of SAF can be achieved by the right selection of plant species and planting pattern configurations that can bring benefits by addressing aspects of productivity, sustainability, and adoptability. SAF should also be developed by making the best use of local resources and use of knowledge both modern and indigenous for effective and efficient agricultural practices to gain environmental benefits and high economic profits. Hence ideal form of SAF is also a type of smart landscape and land-use management that plays important roles in soil and water conservation, bioenergy, climate change responses, and enhanced biodiversity conservation.

Incorporating trees on farms through agroforestry practices can be the best approach to improve soil fertility. Meanwhile, diversifying various agro-ecosystem production commodities in agroforestry such as wood producer, crops, palms, forages for cattle, can also be an appropriate approach to enhance community livelihood. SAF contributes significantly for sustaining soil fertility, through improving cation exchange capacity, bulk density, structure, pH, SOM, C-organic, N total, available P and K of soil, as well as sustaining community’s livelihood through the increase of farming production while assuring the benefits for local community. SAF can affect various soil physical properties, such as changing soil retention and available water capacity. With regard to soil chemical properties, the increase of soil N, P, K, and C organic could reach more than 100% and increase soil pH amounting to 17.5%. The contribution of SAF in maintaining soil biological fertility is shown by the increasing population of soil organisms and its biomass as well as the population of soil fauna.

The significant contributions of SAF practices to community livelihoods were achieved both on dry land and wetlands. It reached 98.47% of total household income and being able to meet almost all of livelihood needs. It is important to note that agroforestry is not a total panacea against food insecurity and environmental degradation. To be effective and sustainable, agroforestry needs improved integration: not only agriculture with trees but also trees with people considering the suitability of technical, economic and social condition. Therefore, there is a need to develop further good agroforestry practices through smart agroforestry (SAF). The multi-benefit of smart agroforestry has been widely proven, but its implementation in larger scale still requires awareness and collaboration of multistakeholder involved in realizing sustainable forest and land management. Further study is needed tp formulate strategy for the betterment of SAF implementation.

Author Contributions

All authors had an equal contribution to the conceptualization, methodology, the literature reviews, as well as writing, reviewing and finalizing the manuscript. All authors have read and agreed to the published version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).