Introduction

Multifunctional forests provide several ecosystem services that are important for people’s health and well-being. These include wood and non-wood forest products, climate change mitigation through carbon sequestration, renewal and purification of water resources, and social benefits such as recreational opportunities and aesthetic values (Juutinen et al. 2021). However, forestry sector is currently facing various problems, such as climate change and environmental degradation. In order to preserve the natural environment and reduce the vulnerability of forests around the world, countries are constantly adopting a series of ambitious policies that use nature-based solutions to address these challenges (Lier et al. 2021). In recent years, a legally binding treaty on climate change, the Paris Agreement (2015), has been adopted at the international level, while the European Union (hereafter EU) has adopted, for example, the Renewable Energy Directive (2018), the European Green Deal (2019), the European Climate Act (2021), the Biodiversity Strategy for 2030 (2020), and the new European Forest Strategy for 2030 (2021). These policy documents introduce a new policy narrative and direction by setting clear targets for all policy areas and show that current forest management faces numerous challenges. These challenges are constantly opening up new opportunities and highlight that the responsibility for sustainable forest management (hereafter SFM) is increasingly being transferred to numerous private forest owners (hereafter PFOs) (Wilkes-Allemann et al. 2021). It is therefore obvious that PFOs can make an important contribution to the achievement of policy objective and the provision of forest ecosystem services, as the decisions concerning how to manage the forest are in their hands (Takala et al. 2022).

The distribution of forest ownership categories varies by regions and countries (UNECE 2020). In the EU, 56% of forest land is privately owned (ranging from 11% in Bulgaria to 93% in Portugal) (Živojinović et al. 2015), of which a majority (76.8%) is owned by individuals and families (Weiss et al. 2019; UNECE 2020). Similar ownership structures exists in other parts of the world, for example in the Unites States of America (UNECE 2020).

Previous research has shown that forest ownership has been constantly changing due to various social and political developments (UNECE 2020), such as e.g., structural change in agriculture sector (Hogl et al. 2005; Ficko et al. 2019; Butler et al. 2023), changes in lifestyle (Ziegenspeck et al. 2004; Feliciano et al. 2017; Weiss et al. 2019; Westin et al. 2023), privatisation and restitution (Sarvašová et al. 2015; Dobšinská et al. 2020). As a result, there is great heterogeneity among PFOs, which is reflected in a variety of values (Richnau et al. 2013; Muttilaninen et al. 2022; Westin et al. 2023), motivations, objectives (Urquhart and Courtney 2011; Kuhlman et al. 2022; Lidestav and Westin 2023), and management strategies (Kurttila et al. 2001; Snyder and Kilgore 2017; Feliciano et al. 2017; Ficko 2019; Eriksson and Fries 2020). Therefore, PFOs have a significant impact on forest management outcomes and the fulfilment of various forest and forest-related policy objectives (Arnould et al. 2022; Lidestav and Westin 2023).

In order to ensure and balance all (often conflicting) policy objectives and societal demands in relation to forests, many countries have opted for more collaborative forms of forest management or ensured a certain levels of government intervention (Mizaraitė and Mizaras 2014). For many years, policy makers and practitioners in forest sector have recognized cooperation between and joint action by PFOs, especially in countries with small and fragmented private forest ownership, as a key policy instrument to support SFM, to secure forest ecosystem service provision, to mobilise resources and implement policy objectives (Kittredge 2005; Stern et al. 2013; Sarvašová et al. 2015; Põllumäe et al. 2016; Lawrence et al. 2020; Arnould et al. 2022). Various forms of PFOs cooperation are known in many countries, called forest owners’ organisations (FOOs) (Kittredge 2005; UNECE 2020), which have been established for different purposes, e.g. to strengthen the political power of forest owners, to improve market position through joint marketing of timber, to obtain financial incentives, to organise training, to share information and improve forest operation through joint work in the forest and joint purchase/use of forest machinery (UNECE 2020). Consequently, these cooperation improve the PFOs capacity to implement sustainable and multifunctional forest management and provide timber and other forest ecosystem services on the one hand and improve the profitability and income of PFOs on the other (Schwarzbauer et al. 2010).

Cooperation between PFOs has been one of the important topics in forest policy research over the last three decades, not only in Europe but around the world. Many studies have focused on cooperation between PFOs (e.g., Kittredge 2005; Finley et al. 2006; Rauch 2007; Pezdevšek Malovrh 2010; Põllumäe et al. 2016; Pezdevšek Malovrh et al. 2017; Fischer et al. 2019; Górriz-Mifsud et al. 2019) and analysed their cooperation mostly with the aim of understanding the influence of different factors on the willingness of PFOs to cooperate (Pezdevšek Malovrh et al. 2010), the reasons for the establishment of different organisational forms (Schraml 2005; Sarvašová et al. 2015), the factors influencing the establishment, development, professionalism and efficiency of organisational forms (Glück et al. 2010; Leban 2014; Lönnstedt 2014; Fabra-Crespo and Rojas-Briales 2015; Sarvašová et al. 2015; Kronholm 2016; Pezdevšek Malovrh and Laktić 2017; Černač and Pezdevšek Malovrh 2020), the motives of PFOs and their benefits for joining (Pezdevšek Malovrh et al. 2011; Põllumäe et al. 2014; Hrib et al. 2018), the effects of cooperation on SFM (Seeland et al. 2011; Hansmann et al. 2016), and the role of stakeholders (Šálka et al. 2016; Aurenhammer 2017; Aurenhammer et al. 2017). After decades of development of PFOs cooperation, there is a great amount of research on this topic that provides important insights into the state of PFOs cooperation, but mostly focuses on only one organisational form (e.g. PFOs associations or cooperatives), one country, cross-national comparisons or regions. To our knowledge, none of the studies address the evolution of PFOs cooperation in a global context and in a long-term perspective. Therefore, there is a considerable research gap in this area. Considering the fact that it is very difficult to effectively organise, summarise, and quantitatively analyse the development of a specific field in a large number of studies over a long period of time in traditional review articles, a bibliometric network analysis (hereafter BNA) is needed to provide a comprehensive overview which is complemented with a literature review. BNA is a quantitative review technique that uses data mining, statistics and mathematics to unveil emerging trends in a particular area of research (Donthu et al. 2021). According to Otte and Rousseau (2002), BNA is a useful tool for assessing trends and patterns in the scientific literature. It has now become a popular method and is applied to various research topics. For example, in recent years, many environment and natural resources studies have used BNA to analyse the scientific literature on various topics, such as: natural capital (Buonocore et al. 2018), ecosystem services (Pauna et al. 2018, 2019), food security (Skaf et al. 2020), private land conservation (Gooden and ‘t Sas-Rolfes 2020), forest entrepreneurship (Mourao and Martinho 2020), forest carbon sequestration (Huang et al. 2020), bioeconomy (Biancolillo et al. 2020; Mougenot and Doussoulin 2022), and circular economy (Türkeli et al. 2018).

Based on the above considerations, this study uses a BNA complemented with a literature review to examine the international scientific publication on PFOs’ cooperation and provide an overview of the patterns of research topic and changing trends in research hotspots over time. The results are important to provide a comprehensive overview of PFOs cooperation, that helps policy makers to improve their forest policy measures and scientist to decide where to focus their research.

Materials and Methods

The review of the international scientific literature on PFOs’ cooperation was conducted by a BNA complemented with a literature review to identify and analyse peer-reviewed publications – e.g. books, chapters, articles and papers published in international proceedings on the following two main topics:

  • “Reasons for joining FOO”: the decision of PFOs to join FOO is based on their own values and the services FOO offers and the benefits they can receive;

  • “Factors influencing cooperation of PFOs”: several factors (individual and structural) are related to the willingness of PFOs’ to cooperate in the FOO.

As the institutional and political background frameworks in each country and the general development of FOOs vary, it is useful to analyse the reasons why PFOs have decided to join FOOs, as they are offered different services (e.g. market support, information and knowledge exchange, representation of PFOs’ interests in policy processes, advocating their interest). Previous research has also shown, that the services offered by FOOs are closely related to the PFOs’ main reason for joining (Weiss et al. 2012). In addition, PFOs’ decision and behaviour are influenced by individual factors such as their own values and beliefs, the social groups they belong to, their awareness and perceptions, as well as external (structural) factors from the operational environment. Therefore, these factors were also considered as important drivers that influence PFOs decisions for cooperation.

The peer-reviewed publications were retrieved from Scopus database (https://www.scopus.com) on 28th January 2023 using two queries, one for each topic:

  • Reasons for joining FOO: (“forest owner*” OR “non-industrial forest owner*” OR “small-scale forest owner*”) AND (“reason*”) AND (“cooperative*” OR “association*” OR “society*” OR “machinery ring*” OR “organization*” OR “chamber*” OR “legal form*” OR “umbrella organization*” OR “forms of cooperation*” OR “leasing”).

  • Factors influencing cooperation of PFOs: (“private forest owner*” OR “non-industrial forest owner*” OR “small-scale forest owner*”) AND (“precondition*” OR “formation” OR “driver*” OR “change*” OR “barrier*” OR “problem*” OR “constraint*” OR “challenge*” OR “factor*” OR “establishment*” OR “development*” OR “good practice*” OR “motive*” OR “incentive*” OR “initiative*” OR “decision making*” OR “legislation*” OR “policy*” OR “instrument*”).

The keywords used in the BNA were searched for in the titles, abstracts and keywords of the individual peer-reviewed publications, using the last two decades as a time frame (reference period: 2000–2021). All data were then exported as “comma-separated values” (CSV) files and processed by a BNA using VOSviewer software (version 1.6.11). The VOSviewer software developed by Van Eck and Waltman (2014) is an open-access software aimed to create, visualise, and explore maps combining bibliometric review and Social Network Analysis (hereafter SNA) approaches. On the one hand, the bibliometric review approach is a scientific, computer-assisted review method used to analyse scientific productivity on a specific topic (Han et al. 2020). In particular, the bibliometric approach is based on three main indicators: quantity indicators to measure the productivity of a researcher, quality indicators to measure the performance of a researcher’s output and structural indicators to measure connections between publications, authors and research field. On the other hand, SNA is generally applied to understand the relationships among all components (e.g. concepts, words, social actors, authors, organisations, countries) of a system and to identify the key role of some components in the system (Wasserman and Faust 1994). From a practical point of view, the main output of SNA is a network modelled using a graph formed by a set of nodes (e.g. keywords or countries) denoting the issues being studied, and a set of links reflecting the relationships between the issues (Majeed and Ibtisan 2020). The outputs provided by SNA are presented in clusters – defined as a set of elementary contexts characterised by a pattern of keywords and described by the most representative lexical unit (Moretti et al. 2016) – capable of visualizing the existing connections among the bibliometric data.

The BNA was conducted in this study to highlight the hot spots concerning the PFOs’ cooperation addressed in the international scientific literature. For this purpose, two types of analyses were conducted: co-occurrence and co-authorship.

The co-occurrence analysis was performed to create semantic network maps over the keywords used in the two topics related to the PFOs cooperation. The co-occurrence analysis is a method for investigating the collective interconnection of terms/concepts (e.g. keywords) based on their paired presence in the international scientific literature (e.g., title, abstract, list of keywords of peer-review publications) on a specific topic. For this reason, the results of the co-occurrence analysis can be useful to identify the most important concepts investigated in the scientific literature (Pauna et al. 2019). In the present study, a minimum number of 10 occurrences was set to be included in the co-occurrence network.

The co-authorship analysis was conducted to create network maps of the authors’ countries (and not the countries where the research was carried out) based on the number of publications they co-authored. The results of the co-authorship analysis can be useful to highlight the most active countries in studies and research/or researchers in the field of PFOs cooperation. To interpret these results, it is important to emphasise that they refer to the country where the institution of the authors of the publications are located, and not to the countries where the research was carried out. For this analysis, a minimum number of 5 documents per country was set as a threshold.

The role of keywords and countries in the networks was quantified through some indicators. For the keywords, the co-occurrence (O) – defined as the number of co-occurrences of two keywords is the number of publications in which both keywords appear together in the title, abstract or list of keywords (Van Eck and Waltman 2014) – and the total link strength (TLS) – the cumulative strength of the links of an item with other items (Van Eck and Waltman 2018) – were calculated and used to interpret the data. For the countries, the number of documents (D), the number of citations (C), the TLS, and the ratio between citations and documents (R) were applied to understand the importance of each country in the network. According to Biancolillo et al. (2020), the ratio R is a synthetic indicator of the impact of publications on the international scientific community and it can be calculated in the following way:

$$R = \frac{{\sum\nolimits_{i = 1}^n {\frac{{{C_i}}}{{{D_i}}}} }}{n}$$

where:

n is the total number of documents on a specific topic published in the period 2000–2021;

Di is the document i;

Ci is the total number of citations received by document i.

In order to provide a general picture on PFOs cooperation, the BNA was complemented by an overview synthesis of the scientific literature results, whereby 103 core scientific literature were considered. The selection of core scientific literature was based on the screening of identified results (abstract and title) and eligibility criteria. We considered the scientific literature dealing with the functioning of FOOs and their purposes and activities. The synthesis focuses on the content of the articles in terms of key findings, including the nature of PFOs cooperation, level of cooperation, membership, origin, legal forms and services provided by FOOs.

Results

General Overview on PFOs Cooperation

The review synthesis of the selected scientific literature identified in Scopus database shows that almost two third of published publications (63.1%) in the period of 2000–2021, studied PFOs business cooperation and only around one third PFOs interest cooperation (36.9%). The analysed publications showed that PFOs are the most likely to engage in FOO, regardless of their forest property size. The most frequently, analysed publications studied PFOs cooperation at the local level (57.7% of the analysed articles), followed by national and regional/federal level (19.3% respectively). In almost half of the analysed publications, FOOs were formed from the top-down approach (52.94%), mainly based on the government initiative, while quite often initiative to form the FOOs came from the bottom-up (most often from PFOs, public forestry service and a company). Given the results that in a good half of the analysed publications, the FOOs were established by governmental initiative, it is not surprising that the government has provided support, either through monetary incentives or supportive regulations. In addition to that, private capital and EU RDP funds were also important source of support. Among the forms of business cooperation, the cooperative was the most frequently analysed form of business cooperation of private forest owners (33.9%), followed by business partnerships (16.1%), associations of private forest owners with an established private company (12.5%), companies owned by private forest owners (8.9%), joint forest management (8.9%) and forest leasing (7.2%). Among the forms of interest cooperation, the most frequently analysed were private forest owner’s society, private forest owner’s association and forest groups. FOOs were established to provide a variety of services to their members. In the analysed publications, FOOs established for business cooperation most often provide services such as timber marketing (23.3%), timber harvesting (20.5%), forest management planning (12.5%) or provide overall forest management services (so-called “all inclusive” services) (11.7%). Less frequently, forms of business cooperation offer services related to the marketing of firewood and biomass (10.8%), the marketing of non-timber forest products (9.1%), the joint use of machinery (5.7%) and the construction and maintenance of forest infrastructure (2.3%). FOOs established for interest cooperation most frequently provide services such as providing advice to PFOs (21.2%), followed by education, training (15.4%), information sharing (12.5%), consultation with other organisations and government (10.6%), representation of their members’ interests in the political process (9.6%), socialising/networking (8.7%), lobbying of their members’ interests in the policy arena (7,7%), and forest certification (5.5%).

Bibliometric Analysis Outcomes

The database contains 1,012 peer-reviewed publications that were distributed by two topics related to PFOs cooperation: 532 peer-reviewed publications on the “Reasons for joining FOO” (on average 24.2±9.1 documents per year) and 480 peer-reviewed publications on the “Factors influencing cooperation of PFOs” (on average 21.8±10.4 documents per year). The overlap rate between these two databases is quite low, as only 10 peer-reviewed publications are included in both databases, which correspond to 1.1% of the total documents. Therefore, the two databases were analysed separately in order to identify the main keywords and country clusters in both networks.

Regarding the publication trend (Fig. 1), the results show a steady, albeit gradual, growth in publications on both topics from 2000 to 2021. In particular, the average growth trend (%) year by year for “Reasons for joining FOO” is + 0.16±0.62%, while the average growth trend (%) for “Factors influencing cooperation of PFOs” is + 0.13±0.32%. For both topics, the most productive year was 2019 with 39 documents on reasons for joining FOO and 44 documents on factors influencing cooperation of PFOs.

Fig. 1
figure 1

Trend of publications concerning “Reasons for joining FOO” and “Factors influencing cooperation of PFOs”

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Reasons for Joining FOO Analysis

The analysis of the keywords related to “Reasons for joining FOO” showed a total of 3,477 results. Of these, only 255 met the threshold of at least five co-occurrences, and 112 the threshold of at least ten co-occurrences. The five most important keywords are “forestry”, “forest management”, “forests”, “timber”, and “ownerships” (Table 1). However, it is interesting to highlight the importance of several keywords related to private ownership in the context of cooperation such as: “private forest owners” (O = 39; TLS = 358), “private ownership” (O = 37; TLS = 407), “private land” (O = 23; TLS = 361), “non-industrial private forest owners” (O = 22; TLS = 246), “nonindustrial private forests” (O = 15; TLS = 141), “nonindustrial private forest owners” (O = 13; TLS = 133), “private forests” (O = 12; TLS = 154), “private sector” (O = 12; TLS = 171), “privatization” (O = 10; TLS = 117). Focusing specifically on the reasons for joining FOO, the results show that the main reasons are timber harvesting (main keywords used: “harvesting” O = 28; TLS = 283, “timber harvesting” O = 17; TLS = 199, “logging” O = 15; TLS = 134), followed by marketing and trade of wood products (main keywords used: “marketing” O = 23; TLS = 194, “commerce” O = 20; TLS = 230) and forest certification (main keywords used: “forest certification” O = 20; TLS = 140, “certification” O = 15; TLS = 160).

In terms of geographical context, the results show that the most frequently occurring country is the United States of America (O = 56, TLS = 694), followed by Sweden (O = 28; TLS = 242), Finland (O = 24; TLS = 220), Japan (O = 15; TLS = 114), and Germany (O = 12; TLS = 70).

Table 1 Top ten keywords related to the reasons for joining FOO, ranked by co-occurrence
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Observing the network of keywords used in the publications related to “Reasons for joining FOO” (Fig. 2), the results show three topic-orientated clusters (blue, red, and green), a small cluster (yellow), and a transitional cluster (purple). The most important cluster 1 is the red one formed by 38 keywords, named “Economic cluster” which emphasises the logistic and economic aspects of cooperation along the wood supply chain. The most important specific keywords used in this cluster are: “timber”, “industrial economics”, “optimization”, “logging”, “harvesting”, “commerce”, “wood products”. Cluster 2 is the blue one formed by 29 keywords, named “Environmental cluster” It focuses on the PFOs’ cooperation to improve the provision of forest ecosystem services and climate change mitigation such as “biodiversity”, “environmental/natural resources conservation”, “climate change”. However, it is important to note that the keyword “ecosystem services” is in an intermediate position between the blue and green clusters. Cluster 3 (green cluster formed by 29 keywords), named “Forest management cluster” focuses more on sustainable, multifunctional forest management and planning as a result of cooperation between PFOs, including also “ecosystem services” among the benefits provided. This cluster also includes many case studies examples from many European countries (e.g. Germany, Switzerland, Slovenia) and Japan. The small cluster 4 (yellow cluster formed by 12 keywords) considers the cooperation between small-scale PFOs, such as individual and family forest owners. The last transitional cluster (purple cluster formed by only four keywords) identified some studies related to questionnaire surveys conducted with private forest owners to investigate their needs, expectations, and preferences related to forest management.

The complete list of keywords used in the publications related to “Reasons for joining FOO” can be found in Annex 1, organised by clusters.

Fig. 2
figure 2

Network map of most used keywords related to the “Reasons for joining FOO” (10 co-occurrences threshold)

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The results regarding the trend of the keywords used over time show important changes from 2000 to 2021 (Fig. 3). In the early 2000s, the main keywords used in the issue related to reasons for joining the FOO, were related to the forest-wood supply chain and the timber, paper, and pulp industries (keywords in purple on the left side of Fig. 2). In other words, in a first period, PFOs join FOOs to supply the raw material for the wood processing industry. This fact is evidenced by an important role of some keywords such as “timber” (O = 101, TLS = 905), “logging” (O = 15, TLS = 134), “harvesting” (O = 28, TLS = 283), “wood products” (O = 12, TLS = 95), “pulp and paper industry” (O = 10, TLS = 73) in the network. After 2015, the use of keywords related to environmental and climate change mitigation issues of forests were increasingly used in the scientific literature (keywords in yellow on the right side of Fig. 2). The most recent keywords used in the scientific literature are the following: “ecosystem services” (O = 18, TLS = 212), “climate change” (O = 29, TLS = 262), “conservation of natural resources” (O = 23, TLS = 437), “environmental protection” (O = 39, TLS = 567).

Fig. 3
figure 3

Network map of time evolution of most used keywords related to the “Reasons for joining FOO” (10 co-occurrences threshold)

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Factors Influencing Cooperation of PFOs Analysis

The analysis of the keywords in the publications related to “Factors influencing cooperation of PFOs” shown a total of 3,091 results. Of them, only 266 met the threshold of at least five co-occurrences and 111 met the threshold of at least ten co-occurrences. The most frequent keywords (Table 2) in this network includes both general terms (e.g., “forestry”, “forest management”, “timber”, “forests”) and more specific terms that relate to the context of private ownership – e.g., “private forest owners” (O = 116, TLS = 1091), “private land” (O = 37, TLS = 503), “private ownership” (O = 31, TLS = 383), “private forests” (O = 28, TLS = 250), “nonindustrial private forest owners” (O = 26, TLS = 250), or the keywords related to the influence of forest-related policies on PFOs cooperation, e.g., “forestry policy” (O = 55, TLS = 500), “forest policy” (O = 40, TLS = 317), “public policy” (O = 26, TLS = 266), “incentives” (O = 12, TLS = 110), “policy instruments” (O = 12, TLS = 107).

Table 2 Top ten keywords related to the “Factors influencing cooperation of PFOs”, ranked by co-occurrence
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Considering the network of keywords used in the publications related to “Factors influencing cooperation of PFOs” (Fig. 4), the results show three important clusters (yellow, green and red), and two transitional clusters (purple and blue). Cluster 1, the yellow one – named “Timber/bioenergy production and marketing cluster” and formed by 17 keywords – focuses on influence of timber production-oriented policy objectives and marketing of timber and woody biomass for bioenergy production on PFOs cooperation. Cluster 2 (green one formed by 29 keywords), named “Land and policy interaction cluster” investigated the role of rural development and national governments support on PFOs’ cooperation. This cluster also includes publications dealing with policy instruments/public policy support to stimulate cooperation between private (and small-scale) forest owners for SFM, as-well-as the publications on the restitution of public forests in Eastern and South-Eastern European countries. Cluster 3, the red one – named “Nature conservation cluster” and is formed by 31 keywords focussing on the influence of biodiversity conservation and environmental/nature protection policy objectives on PFOs cooperation. The transitional cluster 4 (purple one formed by 7 keywords) is focused on the role of PFOs’ cooperation in the implementation of adaptive forest management, while the transitional cluster 5 (blue one formed by 27 keywords) includes research on small-scale PFOs cooperation for SFM and forest certification.

The complete list of keywords used in the publications related to “Factors influencing cooperation of PFOs” can be found in Annex 2, organised by cluster.

Fig. 4
figure 4

Network map of most used keywords related to the “Factors influencing cooperation of PFOs” (10 co-occurrences threshold)

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The results concerning the trend of keywords used in the publications on “Factors influencing cooperation of PFOs” show a shift in forest policy from economic objectives to environmental one (Fig. 5). In the early 2000s, most studies focusses on economic-oriented driving factors that influence cooperation of PFOs along the forest-wood supply chain (keywords in purple). These aspects were highlighted by using keywords such as “timber” (O = 96; TLS = 979), “harvesting” (O = 39; TLS = 398), “timber market” (O = 12; TLS = 99), “timber supply” (O = 13; TLS = 155), “forest certification” (O = 10; TLS = 84) or “certification” (O = 9; TLS = 97). From a geographical perspective, these studies mainly concerned on countries of Northern Europe (Sweden with O = 44 and TLS = 380, Finland with O = 35 and TLS = 318, Norway with O = 7 and TLS = 68) and North America (United States of America with O = 54 and TLS = 602, and individual United States of America states such as Oregon with O = 9 and TLS = 141, Michigan with O = 5 and TLS = 54). After 2015, the studies shift to environmental objectives (e.g. climate change, carbon sequestration, biodiversity conservation, ecosystem services) as highlighted in the yellow keywords in Fig. 5.

Fig. 5
figure 5

Network map of time evolution of most used keywords related to the “Factors influencing cooperation of PFOs” (10 co-occurrences threshold)

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Co-Authorship Analysis

The analysis of co-authorship by countries provided 59 results (corresponding to the countries) for the topic of “Reasons for joining FOO” and 56 results for the “Factors influencing cooperation of PFOs”. The five most productive countries with regard to the “Reasons for joining FOO” are as follows (Table 3): United States of America (21.3% of all studies, TLS = 36), Finland (9.1%, TLS = 44), Sweden (8.2%, TLS = 49), Germany (6.3%, TLS = 33), and Japan (4.9%, TLS = 10). It is also interesting to emphasize the great interest shown by the authors from Central and Northern European countries such as: Austria (3.3% of all documents, TLS = 47), Switzerland (3.0%, TLS = 13), Norway (3.0%, TLS = 38). The four most productive countries in the “Factors influencing cooperation of PFOs” topic are the same as for the “Reasons for joining FOO” topic: United States of America (18.0%, TLS = 14), Finland (13.8%, TLS = 63), Sweden (11.0%, TLS = 58), and Germany (6.2%, TLS = 39). However, the authors from the South-East European countries (Slovenia with 4.3% of total studies, Croatia with 3.3%, Serbia with 2.5%, and Bosnia and Herzegovina with 1.6%) and Baltic and Eastern European countries (Lithuania with 2.1% of total studies, Czech Republic and Latvia with 1.7% respectively, Estonia and Slovakia with 1.6%, and Poland with 0.8%) show increased interest in this topic.

Table 3 Top ten countries related to the “Reasons for joining FOO” and “Factors influencing cooperation of PFOs”, ranked by number of publications
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Considering the ratio between citations and published documents, the results show that for “Reasons for joining FOO” the highest values are found for Australia (46.5), Denmark (44.0), China (32.5), and the United Kingdom (30.8), while for “Factors influencing cooperation of PFOs” the highest values are found for Portugal (34.4), the United States of America (24.7), Switzerland (24.6), and Belgium (23.9) (Fig. 6). These results show that research teams from some countries, have had a considerable scientific impact on the international scientific community despite having published a small number of articles.

Fig. 6
figure 6

Ratio between citations and documents published for the two topics considered: (a) “Reasons for joining FOO” and (b) Factors influencing cooperation of PFOs.

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Observing the co-authorship network map of countries in “Reasons for joining FOO” (Fig. 7), it can be seen that there is a collaboration (green) cluster between authors from Baltic and Eastern European countries (i.e. Slovakia, Czech Republic, Estonia, Latvia, and Lithuania) and a collaboration (purple) cluster between authors from Western Balkan countries (i.e. Serbia, Slovenia, Croatia, Bosnia and Herzegovina). The most important cluster is the red one in which authors from the United States of America collaborated closely with authors from Canada, New Zealand, Japan, Indonesia and the United Kingdom. In the other two clusters (blue and yellow) many European countries are represented from Northern Europe (Finland and Norway in the blue cluster and Sweden in the yellow cluster) to Southern Europe (Portugal, France, and Spain in the blue cluster). In terms of the authors’ institutions, the results show that the most active universities and research centres on this topic in Europe are the Czech University of Life Sciences Prague in the Czech Republic, Høyskolen Kristiania in Norway, the University of Ljubljana in Slovenia and the Technical University in Zvolen in Slovakia, while in North America the Oregon State University and the USDA Forest Service.

Fig. 7
figure 7

Co-authorship network map of countries that have published on “Reasons for joining FOO”, based on number of documents (5 co-occurrences threshold)

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In the co-authorship network map of countries concerning the “Factors influencing cooperation of PFOs” (Fig. 8), it is possible to identify the same clusters among Wester Balkan countries (purple one) already identified in the “Reasons for joining FOO” network. In addition, there are three further clusters that include only European countries (blue, yellow and green clusters) and another international cluster (red culster) that includes six countries: United States of America, Canada, Japan, United Kingdom, Norway, and Germany. Observing the data by the authors’ institutions, it is interesting to emphasize that the most active institutions on this topic are the Swedish University of Agricultural Sciences (Sweden), the University of Ljubljana (Slovenia), and the Latvian University of Life Sciences and Technologies (Latvia) in Europe, while Oregon State University and the University of Minnesota are in the United States.

Fig. 8
figure 8

Co-authorship network map of countries that have published on “Factors influencing PFOs cooperation”, based on number of documents (5 co-occurrences threshold)

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Finally, the comparison between the countries of the authors of publications and those of the case studies shows that there is a high correspondence. The Spearman correlation test between the number of publications in the co-authorship analysis by country and the occurrences in the keyword analysis shows that the two variables are correlated for both topics: Reasons for joining FOO (α = 0.01, p < 0.0001) and Factors influencing cooperation of PFOs (α = 0.01, p < 0.0001).

Discussion

With the growing international concern about climate change and environmental degradation, forests play an important and irreplaceable role in adapting and mitigating the negative effects through SFM (IPBES 2019). In regions with predominantly private forest ownership, PFOs play an inevitably role in achieving different policy objectives and forest ecosystem services provisioning. Therefore, PFOs cooperation has been recognised by policy decision-makers and practitioners as a key policy instrument to achieve desired outcomes. Given the importance of PFOs cooperation, the aim of this paper was to systematically examine the international scientific literature on PFOs’ cooperation in order to tackle its evolution over the last two decades and to track where the trend has moved. The BNA, which was complemented with a literature review, focusses on the two topics “Reasons to join FOOs” and “Factors influencing PFOs cooperation”.

General Observation from a Bibliometric Analysis

In the 2000s, most published articles on both topics were published in the United States of America, followed by the Nordic countries (Finland, Sweden, Norway) and Central European countries (Germany, Austria, Switzerland). It can be observed that authors in countries where private ownership is predominant (Nichiforel et al. 2018; UNECE 2020) and where there is a long tradition of PFOs cooperation show a greater scientific interest for that topic. In addition, an increased interest in the topic of “Factors influencing cooperation of PFOs” can be observed among from South-East European countries (i.e. Slovenia, Croatian, Serbia and Bosnia and Herzegovina), Baltic (i.e. Lithuania, Latvia, Estonia) and Eastern European countries (i.e. Slovakia, Czech Republic and Poland). This is not surprising, as ownership structures in these countries have changed significantly following the privatisation and restitution processes that began in the 1990s. The emergence of FOOs after the restitution and privatisation process and the “new” PFOs gained increasing interest not only from researchers, but also from research funding organisation such as the Food and Agriculture Organisation of the United Nations and the European Forest Institute, which support joint research activities (e.g. the PRIFORT project - Research into the Organisation of Private Forest Owners in the Western Balkan Region and the Forest Policy and Institutions Working Paper - Review of forest owners’ organizations in selected Eastern European countries). In addition, joint research activities of these authors were also observed in the co-authorship network maps for both topics. The co-authorship network maps also show that authors from the same regions collaborate and publish research articles together. As expected, the results of the Spearman correlation test show that most authors from one country have conducted research in case studies for the same country. However, there are some exceptions due to authors collaborating with research teams from other countries or being involved in large international research teams.

Major Issues in Research Related to Reasons for Joining FOO

The results of the network related to the “Reasons to joining FOO” show that there are three important topic-orientated clusters. These clusters are related to the services that FOOs offer to their members. Mendes et al. (2011) and Weiss et al. (2012) report that FOOs were mainly established for the joint marketing of timber, the coordination of joint forest management and investment activities or the representation of forest owners’ interests. Therefore, it is not surprising that the “Economic cluster” was the most important one, focusing on the logistic and economic aspects of cooperation along the wood supply chain. This shows that the reason why PFOs cooperate in the FOO are related to the main objective of PFOs, namely the commodity provision (timber, woody biomass and other marketable forest ecosystem services), generally with the aim of achieving economic benefits. As the nature of forest management freedom varies widely across countries (Nichiforel et al. 2018; UNECE 2020), from a hierarchical implementation of governmental designed technical norms to a space for negotiation or learning guided by the “freedom with responsibility” principles, one cluster has been associated with “Sustainable and multifunctional forest management” as a reason for PFOs cooperation in FOOs. PFOs cooperate in FOOs because FOOs facilitate access to forest management services, provide information on forest management practices and jointly develop forest management plans. Higher political priorities of the EU, such as biodiversity conservation and the transition towards a carbon-neutral economy, contributed towards changed values system of forest use. In fact, the “Environmental cluster” focussed on PFOs’ cooperation to improve the provision of ecosystem services, biodiversity conservation and climate change mitigation. Recent studies on PFOs’ behaviour have confirmed that timber production is not necessarily at the forefront of the PFOs’ objectives; PFOs are primarily interested in preserving the forest for future generations, protecting nature and wildlife, and aesthetics that forests provide (Feliciano et al. 2017; Juutinen et al. 2020, 2021; Westin et al. 2023). In addition, recent studies show that the conservation perspectives of PFOs are crucially influenced by social-ecological drivers (Tiebel et al., 2022) and that although PFOs are willing to manage their forest for biodiversity, there is a huge heterogeneity among them (Husa and Kosenius 2021; Takala et al. 2022).

The results concerning the trend of the keywords over time, related to the “Reasons for joining FOOs”, highlight important changes over the last twenty years. In the early 2000s, the reasons for joining FOOs were mainly related to the supplying of timber for forest-wood supply chain as-well-as timber, paper, and pulp industry, while after 2015, reasons related to the environmental aspects of forests prevail. These results show a change in perspective in the reasons why PFOs’ cooperate: from cooperation for “timber production and supply to the market” to cooperation for “multifunctional and sustainable forest management”, “biodiversity conservation” and “climate change mitigation”. These findings are in line with the general trend in forest-related policies as in the last two decades the emerging political agendas of agriculture and rural development, environmental and nature protection, renewable energy and climate change have increased the political attention for sustainable and multifunctional forest management and nature conservation (Winkel 2017; Deuffic et al. 2018). Even though some of the policy objectives may be incoherent in their practical implementation in the ground, they offer a syncretic vision of what role forestry should play in our society and what objectives PFOs should achieve (Sotirov and Storch 2018). It appears than, not only forest policy has responded to the integration pressure, but also FOOs have also undergone a transformation that has led to in new services offerings for PFOs (Matilainen et al. 2023).

Major Issues in Research Related to Factors Influencing Cooperation of PFOs

The results when observing the network related to the “Factors influencing cooperation of PFOs” show that there are three topic-orientated clusters, which indicate PFOs’ decision-making related to cooperation is based on the interplay between individual and structural factors, where motives of PFOs to cooperate are mainly driven by changes in the social, economic and political environment (UNECE 2020). The analysis of EU forest policy done by Elomina and Pülzl (2021) revealed that the most dominant frames in the forest-related policy documents are those related to the “forests as providers of wood and non-wood forest products”, “forests as contributors to the bioenergy”, “forest as a climate change solution” and “forest as providers, hosts and protectors of biodiversity”, which legitimizes the influence of forest policy on PFO cooperation (the keywords related to the influence of forest-related policies on PFOs cooperation had a high co-occurrence). From the cluster “Timber or bioenergy production and marketing cluster”, it can be concluded that PFOs cooperation is a response to the challenges related to forest-based sectors, where economic objectives of forest policy (timber and bioenergy production) influence the PFOs willingness for cooperation. Therefore, FOOs have been established mainly for joint marketing of timber, coordination of joint forest management and investment activities. The members of these FOOs aim to improve their forest management and marketing, to make it easier to sell their products and to obtain better conditions on the market (Weiss et al. 2012). In the recent past, forest policy has changed as response to absorb pressure to integrate other policy sectors such as energy, biodiversity conservation and climate change (Sotirov and Stoch 2018). The growing pressure to integrate biodiversity conservation into forest policy has also triggered a shift in PFOs cooperation. In fact, the “Nature conservation cluster” refers to the changing preferences of PFOs in forest management and their willingness to adopt forest management practices that promote biodiversity conservation. To improve and support forest management, the EU has implemented a variety of financial instruments (Feliciano et al. 2017; Weiss et al. 2012). One of these is the EU Rural Development framework, which was an important factor affecting the establishment of the FOO (Mendes et al., 2006). In addition, national governments also support the establishment of FOOs and provide some financial support for their operation and management, but this support has generally not continued (Weiss et al. 2012). Therefore, in the “Land and policy interaction cluster”, the main factor behind the establishment of FOOs was the institutional change that followed the collapse of communism and the reintroduction of private ownership in the Baltic, Central European and South-East European countries in the 1990s. Liberalization involved the privatisation and restitution of forest land and led to heterogeneous forest ownership structures (UNECE 2020). In these countries, “new” PFOs have joined together and organized themselves into FOO to improve the management of fragmented and small-scaled properties, or to advocate for their own interest’s vis-a-vis the state. Initially aimed at resolving specific problems related to the restitution process.

The results concerning the trend of keywords used in the publications on “Factors influencing cooperation of PFOs” confirm the shift in forest policy from economic objectives (sustained yield) to climate and environmental objectives.

Methodological Point of view and Limitation of the Study

From a methodological point of view, a BNA complemented with complemented with a literature review provides an overview of the main aspects of PFOs cooperation, investigating the relationship occurring among keywords and countries. The main advantage of the proposed method is that the integration of a SNA and a bibliometric review is a useful approach capable of capturing the multidimensional nature of the different topics - in our study PFOs cooperation - by analysing a large scientific literature database, such as Scopus. The main disadvantage of the proposed method is that only peer-reviewed publication in Scopus database are included, without being able to include grey literature (e.g., technical and project reports, working papers, Bachelor’s and Master’s theses). Furthermore, our study is certainly missing some publications related to PFOs cooperation because they do not explicitly use the selected search terms in the title, abstract or keywords or were published before 2000 or after 2021. However, the results of this study are based on objective data and are stable, reliable and by and large not influenced by empiricism. For a more in-depth analysis of the individual clusters, a further step of systematic literature review would be necessary.

Conclusion

This paper employed the BNA complemented with a literature review to examine the PFOs cooperation in international scientific publications, which included two topics: “Reasons for joining FOO” and “Factors influencing cooperation of PFOs”. Based on the analysis of 1,012 per-review publications from Scopus databases, the study found that PFOs cooperation as a research topic has been steady, albeit gradually, growing from 2000 to 2021, confirming that the research community has recognized the importance of PFOs cooperation to achieve SFM. For both topic, 2019 was the most productive year, which shows the influence of different projects, such as FACESMAPE “Forest Land Ownership Changes in Europe: Significance for Management and Policy” or PRIFORT “Research into the Organization of Private Forest Owners in the Western Balkan Region and Forest Policy” on the productivity of researchers.

The country analysis revealed that the research effort related to PFOs cooperation was higher in countries where private forest ownership is predominant or where there is a long tradition of PFOs cooperation, but also in countries in transition as a result of the restitution and privatisation processes in the 1990s.

Based on a keyword clustering analysis, the three main topic-oriented clusters related to “Reasons for joining FOO” were identified. “Economic cluster”, which focuses on the logistic and economic aspects of cooperation along the wood supply chain; “Environmental cluster”, which focuses on PFOs’ cooperation to improve the provision of forest ecosystem services and climate change mitigation and “Forest management cluster”, which focuses on sustainable, multifunctional forest management and planning as a result of PFOs cooperation, including also “ecosystem services” among the service provided. In the analysis of the keywords connected to “Factors influencing PFOs cooperation” also three main topic-oriented clusters were also identified. “Timber/bioenergy production and marketing cluster” focuses on the influences of timber production-oriented policy objectives and marketing of timber and woody biomass for bioenergy production on PFO cooperation, the cluster “Land and policy interaction cluster” examines the role of rural development and national government support on PFOs’ cooperation, while the “Nature conservation cluster” focused on the influence of biodiversity conservation and environmental/nature protection policy objectives on PFO cooperation. The results concerning the trend of keywords over time related to both topics, show that the research hotspots have changed in the last two decades, from economic (sustained yield production) ones to climate and environmental issues.

Although this study has identified the main research hotspots and their evolution in PFOs cooperation, deeper information on each research topic hotspots, such as the methodologies employed, theoretical frameworks and what are the policy recommendations, is still needed in the future work. Harmonisation across studies could increase comparability and allow for more comprehensive conclusions. Furthermore, we suggest analysing the strengths and weaknesses of the various forms of PFOs cooperation in order to identify best practices and transfer them to other contexts. We also suggest to explor the dynamics of the authors/co-authors’ networks by studying them in different time periods/years. Such an analysis would give us insight into the different rhythms of collaboration in the scientific fields studied. In any case, the results obtained here are a promising contribution for the several stakeholders around the world working on promoting PFOs cooperation and for policy decision makers to design more effective policy instruments to support the development of PFOs cooperation.