Global biodiversity is under pressure from human activities, and the effort for nature conservation and restoration and the allocation of economic resources for biodiversity policies remain insufficient. In such a context, volunteers can play an important role as a resource in nature conservation projects if their recreational activities interact with the objectives of nature management. Ensuring that volunteers remain motivated and engaged is crucial for the success of conservation projects. Five motivational factors determine the engagement of the volunteers, namely social, nature value, instrumental, identification, and personal benefit.
Global biodiversity is under huge pressure from human activities, and nature is declining globally at rates not seen before in human history . The IPBES global assessment  reveals that more than a third of the world surface is devoted to crop or livestock production in 2019. Despite an increase in the numbers of protected areas  and global spending on nature restoration and preservation , funding and efforts on existing protected areas are still considered insufficient , and the lack of financial resources is one of the main barriers. One way of addressing the lack of resources is to increase attention to non-financial and voluntary activities to enhance biodiversity and to improve human livelihood . Especially in areas close by urban settlements, urban conservation efforts matter and can be a solution to the lack of resources for nature conservation, as it offers possibilities for rerouting volunteers who devote their time and other resources to restore and conserve biodiversity for altruistic reasons and to gain socio-psychological benefits .
Research in sustainable nature management has mainly focused on investigating landowners’ motivation or willingness to contribute to nature and landscape conservation  as well as the factors that motivate volunteers to participate in citizen science projects , conservation tourism, or conservation and wildlife initiatives . Environmental volunteers were studied in various contexts, such as the conservation of forests , freshwater , grasslands, and rangelands , but few studies have focused on the diversity of motivations for volunteering. Understanding what motivates individuals to participate in volunteering could play a significant role in ensuring the success of conservation projects and empower the role of volunteers in nature conservation. Therefore, citizens’ motivation for participating in practical nature management in public and private areas still needs to be understood  and additionally understanding why they continue to volunteer .
Volunteers’ commitment and engagement are explained by various motivational processes (see Table 1). Therefore, forming a universal theory for volunteer motivation is a significant challenge . Clary et al.  applied a volunteer functions inventory (VFI) to identify six socio-psychological benefit of volunteering: (1) understanding, (2) strengthened social ties, (3) expressed altruistic values, (4) protecting the ego from negative feelings, (5) enhancing psychological growth, and (6) career-related experience. This inventory has been used in many studies to investigate volunteers’ motivation , as it offers both a guide to stakeholders and managers who need to understand what volunteers can offer, and how to create the most effective and generative network of collaboration among volunteers.
Table 1. Summary of findings regarding the link between demographic and motivational in volunteer research.
|Factor||Summary of Findings||Reference|
|Age||People with low social capital (e.g., lower education and poorer health) are more prone to volunteer for social reasons.||Clary et al. |
|For those of ages above 60, the chance of volunteering increases.||Einolf and Chambré |
|As age increases, motivation changes, as learning and career becomes less important.||Dávila and Díaz-Morales , Alender |
|Gender||Males and females generally volunteer the same number of hours, but females volunteer slightly more than males at the global level.||Wilson 
Bussel and Forbes 
|In Europe, no differences in volunteering are found between males and females.||Wilson |
|Females generally put more importance into various motivational factors, while males see volunteering more as completing a task.||Papadakis and Frater , Wuthnow |
|Education||The level of education is the most influential predictor of volunteering, as it is a reflection of more awareness and resources.||Wilson |
|The level of education were correlated to to volunteering as well as to value reasons, social reasons, and for reducing negative feelings (e.g., loneliness).||Principi et al. |
|Children||Parents with children living at home were more likely to volunteer, but people with young children volunteer fewer hours.||Wilson |
|Adults who can involve children in voluntary work are often motivated by transmitting values, the opportunity to be a role model, having fun, and spending time together with the children.||Littlepage et. al. |
|Friends||Having friends involved in volunteering positively affects an individual’s own involvement.||Wymer ,
Einolf and Chambré 
|People already having friends involved in voluntary work may be motivated by the social opportunity to spend time with these friends.||Ryan et. al. |
Although motives for volunteering are likely to show various patterns between countries due to differences in culture and institutions, the literature review discloses some general patterns, which we summarize in the following.
Volunteering is often more attractive to resource-rich individuals, who already have the capital and/or knowledge required for participation . In general, volunteers have a job, are well educated, are wealthier and healthier, and have a large social network than non-volunteers . Thus, the level of education is the most consistent predictor of volunteering. The higher a volunteer’s level of education, the more likely they are to volunteer. This may be due to having a larger network and therefore a greater likelihood of being encouraged to volunteer; this may also be because well-educated people are more likely to be aware of problems that need attention . High levels of education were found to be associated with volunteering for altruistic reasons but also to reduce negative feelings, such as guilt and loneliness . The presence of children, especially if living at home, may affect the degree of volunteering, depending on the type of volunteer work, the civil and employment status of the parents, and the age of the children and parents. Parents with children living at home are more likely to volunteer but likely for fewer hours if the children are young . If children can be involved in the volunteer activity, the parents are motivated by a desire to transmit values, be a role model, and have fun and spend time together . Friends, social roles, and social networks are key factors that influence behavior and opportunities in a person’s life. Having friends involved in volunteering has a positive effect on an individual’s volunteer involvement . Most volunteers have been encouraged to join a cause, which is why social ties are important for volunteer involvement . Such individuals may be motivated to volunteer by the social opportunity of spending time with their friends .
Ethical and moral values are often a major motivational factor among volunteers . Age has been linked to volunteering as it expresses a measure for stock of resources, which changes over a lifetime. Volunteering occurs at all ages, but certain life stages are particularly associated with volunteering. Middle-aged people between 35 and 44 years show the highest rates of volunteering , while people above 60 years are more likely to volunteer and continue volunteering compared to younger generations . Younger people are more motivated for education and forging a career, while life existence goals become more important later in life, especially generative goals where “taking responsibility for future generations” becomes stronger . However, the frequency of volunteering may decrease with age, which can be caused by decreasing social capital, poor health, or becoming widowed . Gender may have an influence on volunteering, but the results are ambiguous. In some geographical settings, it was found that women volunteer more than men, and in other settings there is no difference . It is generally found that females volunteer more when they are young, while males volunteer more when they become older . It was also found that females attach more importance to the six VFI motivations than males do .
The results from the work by Strzelecka et al. from 2017  suggested that environmental volunteering (travelers/tourism) is mainly driven by a belief that participation in ecological restoration is a worthwhile activity. The motivations to participate in an ecological restoration project can be strengthened or weakened depending on the promise of a pleasurable experience. This also indicated that there may be a difference between initial motivation and the motivation for long-term continuation in volunteering.
In general, the motivation of volunteers can be connected to one or more of the key elements of the VFI . However, this may not always be sufficiently comprehensive to capture all the motivations for volunteering among environmental volunteers. Schroeder  found improved environmental outcomes to be the primary motivator for individuals becoming involved in restoring degraded habitats, preserving wilderness areas, or improving natural resources. Environmental motivations were also found to be linked to, or associated with, desired social outcomes such as a desire to be social or to fulfil economic, health, physical, or cultural needs . In other words, through participation in conservation initiatives, the volunteers gain both pleasure as well as a sense that their actions are needed to defeat the increasing global environmental degradation . Jacobson et al.  found that years of volunteering was negatively correlated with the advancement of career goals or experience but positively correlated with a motive to help the environment. Environmental volunteers’ long-term commitment was, in general, more closely associated with a motivation to protect the environment (nature values), whereas episodic volunteers were more motivated by a need to reduce negative feelings or to develop themselves personally.
Ryan et al.  added five factors that are important for the commitment and motivation of volunteers in environmental stewardship programs: (1) learning, which involves using the volunteer opportunity to learn new things about the environment; (2) helping the environment, which entails an opportunity to do something good for the environment; (3) social, which involves meeting new people or spending time with family and old friends; (4) reflection, with which an individual uses the volunteer experience to reflect on themselves, and; (5) project organization, which is the opportunity to participate in a well-organized project, where time is used efficiently.
Motivation among environmental volunteers may also be associated with attachment to a local environment and sensing a need to contribute to the local community . This can be seen in the work by Selinske et al. . Here the willingness of private landowners to voluntarily participate in the conservation of their land were investigated and it reviled that the environmental or conservation values were the strongest motivator, closely followed by place attachment to their land.