1.1. Social and economic benefits from walnut forests Walnut forests provided important environmental benefits, such as the equalization of seasonal variations of water flows, slope stabilization and soil protection, biodiversity conservation, and carbon sequestration (Rao et al. 1999; Vahdati et al. 2018). In addition, numerous products and services originated from these forests that were used by the local populations, such as timber, firewood, and a variety of non-timber forest products (NTFP) ranging from wild fruits and nuts to feed. These forest products contributed in various ways to rural livelihoods, e.g. in terms of employment and income (Bourne 2012), opportunities for processing enterprises (Bourne 2012; Ozolin 1990), food security and nutrition (Aryal et al. 2009; Ghanbari et al. 2014; Abbasi et al. 2016; (FFI 2016), medicine (Kunwar et al. 2006; Pala et al. 2010; Ganie Aijaz Hassan et al. 2013), support of social networks (Fisher et al. 2004; Schmidt 2007; Rubinov 2016), and in-kind remittances (Rubinov 2016). In addition, they also contributed to foreign exchange earnings at the national level (Zarra-nezhad et al. 2013; Qammer & Baba 2016). Timber J. regia was widely appreciated for its attractive, high-quality and valuable timber, in particular the walnut burls. Local craftsmen in Kyrgyzstan, Afghanistan, China or Iran were famous for the different items they made from walnut wood, such as horse saddles, agricultural tools and music instruments (Knowles 2016; Wüthrich 1999; FFI 2016 ). In Pakistan’s Swat district, J. regia was still widely used for making cabinetry such as beds, chairs and tables (Sher et al. 2010). However, with a few exceptions, timber production primarily concerned natural forests and was less common from walnut plantations, which might be related to the poor trunk shapes prevalent in walnut and its susceptibility to late frost. Given the increasing pressure on the remaining natural walnut forests, timber utilization for commercial purposes has been prohibited in the Central Asian countries, China and Georgia (Bobokashvili et al. 2016). Exceptions only existed for sanitary interventions and to induce forest regeneration, as well as the local population’s entitlements to collect limited amounts of dry wood for home consumption (Rehnus et al. 2013). Also in Nepal, the collection, sale, transportation and export of J. regia, even from private plantations, was not permitted (Ghimire and Nepal 2007; Acharya et al. 2008). While walnut was widely grown in farm orchards and plantations in China, its timber was of relatively limited importance as more commonly, the timber of the Manchurian walnut (J. mandshurica M.) was used for furniture production and other purposes. Nutrition It is widely recognized that the natural walnut forests harbor a number of wild fruits and plants, which are rich in nutrients, vitamins, macro- and microelements and traditionally important for human food consumption (Vira et al. 2015; Smanalieva et al. 2019; (Smanalieva et al. 2020). Forest food can contribute to food security during particular periods of the year and increase dietary diversity, which is important for nutritionally-balanced diets both of rural and urban inhabitants (Samant and Dhar 1997). Despite their apparent importance, official statistics in most Silk Road countries do currently not provide a detailed account of the contribution of forest plants to food consumption. Of all forest fruits, walnut kernels were and still are the most important and commonly used product for human nutrition and highly commercialized in many Silk Road countries for the domestic and export markets (Samant & Dhar 1997; Sundriyal et al. 1998; Hamayun et al. 2006; Pala et al. 2010; Khan 2011; Chatrabnous et al. 2018). They were mostly consumed raw, roasted and/or salted as snacks or further processed for use in confectionary, biscuits, cakes, salads, as ingredient in breakfast cereals, honey, cheese, energy bars, etc. The segment of salted snacks, in which walnuts hold a share of 80%, was expected to reach a volume of USD 75 billion per annum by 2020 in China alone (Lavrinenko 2018). Green walnuts were used in Kyrgyzstan and Georgia to produce a locally popular jam (FFI 2016) Bobokashvili et al. 2016). The kernels were widely processed into walnut oil, which forms a common ingredient of local dishes in many Silk Road countries. For example, in the eastern Himalayas of China, villagers consumed walnut oil and mush as a substitute for butter (Weckerle and Huber 2005). In China walnut milk and walnut powder were also common (Yan et al. 2017). The walnut pellicle was added as an ingredient to produce a strong alcoholic beverage in Georgia (Bobokashvili et al. 2016). Numerous other wild fruits of the walnut forests were locally consumed in raw or processed forms (Ozolin 1990; Bobokashvili et al. 2016; FFI 2016) . For example, wild apples (Malus sieversii) were collected by locals in Kyrgyzstan and consumed fresh or processed at household level into various products such as ‘Chelpek’ (sweet pastille) or ‘Talkan’ (dried powder), which was used to produce compote or sweets (FFI 2016). The fruits of Crataegus pontica were locally processed into jams, and fresh and dried leaves were used for teas in South Kyrgyzstan (FFI 2016). Fruits of Rosa spp. and Berberis spp. were consumed raw as snack in Nepal (Bhattarai et al. 2009). Morels (Morchella esculenta and Morchella conica) were perceived as very valuable and nutritious plants by locals in Afghanistan, China, Kyrgyzstan and Pakistan, because they were rich in proteins and minerals and contained low amounts of calories (FFI 2016). Yet, despite the fact that many of the plant species of the walnut forests possess some potential for human nutrition and have traditionally been used to complement diets, reports of their actual use were generally rare in the reviewed literature. In addition to home consumption, some of these forest products like walnuts or mushrooms were traditionally also sold or exchanged in markets to fulfill other needs. For example, in some remote places of Nepal walnuts were exchanged for cereals and other food grown in lower areas (Ghimire and Nepal 2007). Reports from Kyrgyzstan and Pakistan (Schmidt 2007; Ahmad et al. 2017) pointed out that forest products with high market value such as walnut kernels or morels were not typically consumed by the rural people who collected them but rather sold to traders and finally consumed in urban areas. As described by Samant and Dhar (1997), the morels collected by locals from the walnut forests in Pakistan were sold in Karachi, Lahore, Islamabad and other major cities and consumed by urban dwellers and tourists. High market value of forest products leading to their excessive commercialization has been described as one major cause of overutilization and degradation of natural walnut forests in nearly all of the Silk Road countries (Latif & Shinwari 2005; Akhmadov 2008; Orozumbekov et al. 2014; Butkov & Turdieva 2017). In addition, as walnut kernels were in great demand during the festival season in autumn, early and premature harvesting of walnuts was common in China (Yan et al. 2017). However, premature harvest of walnuts led to much lower nutrient and oil contents ((Yan et al. 2017). Walnut imports from areas with earlier harvests, such as Chile, could partially alleviate the pressure on the walnut forests (USDA 2016b). Medicine Apart from their nutritional value, some of the wild fruits and plants from the walnut forests also possessed significant health and medicinal benefits, albeit the distinction between food and medicinal values of these products was not always clear (Samant and Dhar 1997). These benefits were of particular importance in places in which forest products served as substitutes for costly synthetic medicine that was not always easily available, such as the rural areas of China, India, Nepal, and Pakistan. Though the reviewed literature reported some traditional medicinal uses of these species, these reports might only be an incomplete reflection of traditional practices in the Silk Road countries. J. regia is a species often used in traditional medicine (Dobriyal 2014). Due to the antioxidant, antihypercholesterolemic, antidiabetic, anti-inflammatory, antiamyloidogenic, antimutagenic, antiviral and antimicrobial activity of some of its phytochemical components (Lim 2012; Jahanbani et al. 2016;), consumption of walnuts was recommended for a variety of health benefits, such as to reduce cholesterol, improve brain health, and lower the risks of diabetes and cancer ( USDA 2016a; USDA 2017b; Yan et al. 2017). The nuts and bark of the tree were used to treat skin disorders in Nepal (Kunwar et al. 2006). In Turkey, walnut leaves were considered a remedy against hair loss, pimples, parasites and in skin care, and teas made from the leaves were used for reducing triglyceride and cholesterol levels (Doldur 2017). In Kyrgyzstan walnut leaves were a treatment for livestock indigestion. The fruits, flowers and bark of Crataegus turkestanica and C. songarica were used against diarrhea, while its flowers were used to treat sleeplessness and anxiety in northern Iran (Talebi et al. 2014). In Uzbekistan C. turkestanica was used to treat diabetes, liver disorders and gastrointestinal diseases (Egamberdieva et al. 2012). C. pontica was used against heart diseases, hypertonia, nervous system disorders, depression, and as an antioxidant food supplement (Egamberdieva et al. 2012). Morels (Morchella esculenta and Morchella conica) also had medicinal value in Pakistan. For example, Sher et al. (2010) described that local people in the Shishi valley used morels to treat mouth and eye diseases and infections. In Swat valley however morels were traditionally used to stop extensive bleeding, enterogastritis, indigestion and poor appetite (Sher and Hussain 2009). Rural employment and incomes Natural walnut forests as well as walnut plantations provided significant employment and income opportunities in rural areas. While the collection, processing and trade of walnuts and other NTFPs such fruits, berries and mushrooms from the natural forests was often an informal economic activity, the expansion of walnut plantations has led to the establishment of formal employment in plantation management, nut processing and trade in some Silk Road countries. In Kyrgyzstan, more than one million people lived within and around the walnut-fruit forests and directly or indirectly benefited from the collection of walnuts and other non-timber forest products (Undeland 2012). Among them, approximately 16,000 rural inhabitants were directly employed in the walnut value chain as collectors, crackers, traders or as temporal employees of the 20 processing enterprises in the area (Bourne 2012). Women were of great importance in these activities (Messerli 2000; Marti 2000; Neudert and Köppen 2005). While such employment was typically seasonal and part-time, detailed time budget analyses on the households’ involvement in walnut collection, processing and sale were not reported in the reviewed literature. On average, households had leased 3-5 ha of State forest land for a period of up to 59 years to acquire the right of walnut collection. Walnut collection contributed on average 1,129 EUR annually or 46.3% to the total household budget in a productive year for these households (Agrolead 2016). For the other countries that still possess significant areas of natural walnut forest such as Tajikistan and Uzbekistan, the reviewed literature did not provide accounts of similar detail. Walnut and fruit processing for local markets was common in two mountain communities in Tajikistan (Novikova 2017), however the number of households involved in the collection and processing activities and the respective incomes were not reported. Evidence from 18 household case studies from Uzbekistan showed that of the walnuts collected almost 80% were sold while only 20% were consumed (Gotor et al. 2018), yet the contribution to household income was not provided. Similarly, despite the significance of the walnut plantation sector in China, a systematic account of its socio-economic importance was not provided in the reviewed literature. Yan et al. (2017) estimated that approximately 90% or 2.5 million smallscale farmers were engaged in walnut production in Yunnan province in 2010, which contributed 22.4 % to total Chinese walnut production. These farmers on average derived between 15-50% of their total annual incomes from walnut cultivation (Yan et al. 2017). Apart from small-scale walnut farming, the commercial walnut processing sector in China was also discussed in the reviewed literature. Chengzhong et al. (2014) described Fenyang city as a national center of walnut processing recognized by the Chinese National Forestry Bureau in 2001. The city harbored five walnut-processing corporations and 60 small to medium-scale processing facilities, which together had an annual processing capacity of 35,000 t of walnuts, produced 15,000 t of walnut kernels and generated USD 20 million of export revenues. Unfortunately, information on the number of people employed in these operations was not provided. In India’s Jammu and Kashmir states approximately 50,000 people were engaged in walnut cultivation (Ganie et al. 2013) and derived an annual income of Rs 15,00050,000 (corresponding to USD 242-806) from these activities. The walnut wood carving sector provided employment for 3,000 workers in Kashmir (Saraf 1987). In Pakistan, approximately 35,000 families were involved in walnut production (Samant and Dhar 1997). Each of these families owned five walnut trees on average, resulting in approximately 575 kg of annual walnut production and an corresponding farm income of RS 5,750 (USD 449) (Sabra & Walter 2001). Information on the contribution of walnut orchards to rural employment and incomes in Turkey and Iran was not available in the reviewed literature despite their considerable importance in these countries. Apart from the rural employment and income effects of the fruits and timber of J. regia, only few further forest species were analyzed in the reviewed literature. Wild apples and morels were of considerable importance in this regard in Kyrgyzstan and contributed EUR 260 and 171 annually to household incomes in the walnut forest area, respectively (Agrolead 2016). Morels were widely gathered by men, women and children in the temperate forests of Afghanistan, China, India and Pakistan and traded internationally in large quantities. For example, morels were collected by 150,000 forest dwellers in Pakistan and contributed on average one third to their annual household incomes (Sabra and Walter 2001). The overall annual contribution of morels commercialization to the national economy was estimated at Rs 14.57 Mill. (USD 500,000) (Hamayun et al. 2006a; Ajmal et al. 2015). While generally only very few of the reviewed studies investigated the contribution of the walnut forests to rural livelihoods or the role of forest products in the household budgets, these studies showed that the forests alone could not provide sufficient income, as many of the species showed significant yield fluctuations and seasonality. The majority of households therefore relied on a combination of various income sources and livelihood strategies, including livestock husbandry, crop cultivation, offfarm employment, use of NTFPs and (temporal or permanent) migration (Schmidt 2007; Gerstenberg & Langeheine 2014; Gerstenberg and Langeheine 2014; Ghanbari et al. 2014; Larsen et al 2014; Fulwider 2018;). NTFPs therefore were important gapfillers in times of instability or scarcity (Fisher et al. 2004; Schmidt 2005; Asanbaeva 2006; Baumann 2006). Consequently, households that mainly depended on NTFPs were very vulnerable and often caught in poverty. Schmidt (2007) described that poor families in Kyrgyzstan suffered from food insecurity in years of low walnut harvest, as forest income was hardly sufficient to cover food and other basic expenditures. While other households tried to make more incomes from livestock, crop production or off-farm activities, poor households did not have such opportunities (Fisher et al. 2004; Schmidt 2007). Cultural importance Walnut forests and the various tree species they harbor traditionally were and often still are important elements of rural life, as reflected in folklore, legends, traditions, rituals as well as location names in China, Georgia, Kyrgyzstan and Turkey (Weckerle and Huber 2005; (Bobokashvili et al. 2016; FFI 2016). For example, in the Shuiluo valley in Sichuan, China, members of the Shuhi ethnical group offered walnuts to the local gods as an essential part of their morning, healing and funeral rituals. While of ancient origin, these rituals were kept alive until presently (Weckerle and Huber 2005). Religious norms also effectively prevented the cutting of walnut trees, which were considered sacred. Ignoring these norms was believed to have negative consequences for family members (Weckerle and Huber 2005). In addition, various tree parts possessed aesthetic, cultural or spiritual importance in this area, such as walnut leaves used as decoration during harvest feasts and walnut oil used for altar lamps (Weckerle and Huber 2005). Walnut pigments had also been used for the religious statues of Bamiyan in Afghanistan (Knowles 2016). In Kyrgyzstan, hawthorn (Crataegus spp.) wood was commonly used for making amulets (FFI [Fauna and Flora International] 2016). Nuts and items made from walnut wood were considered a valuable gift in China (Weckerle and Huber 2005). In countries where labor migration was common, such as Kyrgyzstan, Nepal and Tajikistan, fruits and nuts from the walnut forest were often sent as in-kind remittance to the family and were important complements to food rations and cash income of migrants (Rubinov 2016).