Job reservation, or affirmative action, for Scheduled Tribes (STs) in India is a constitutional provision aimed at addressing historical injustices, promoting social equality, and ensuring their adequate representation in public employment and educational institutions. While it has had a significant positive impact, its effectiveness in fully alleviating unemployment among the tribal population is a complex issue with both successes and limitations.

Positive Effects in Alleviating Unemployment:

1. Increased Representation and Economic Upliftment: Reservations have undeniably led to a substantial increase in the number of tribal individuals securing government jobs, positions in public sector undertakings, and admissions to higher educational institutions. This has provided economic security, stable incomes, and upward mobility for many tribal families, lifting them out of poverty and improving their living standards.
2. Social Mobility and Empowerment: Access to education and employment through reservations has enabled tribal individuals to break traditional barriers, achieve higher social status, and gain respect within society. It has fostered a sense of empowerment and participation in the mainstream economy and administration, challenging historical marginalization.
3. Reduced Disparity (for a segment): For the beneficiaries, reservations have helped in reducing the wide disparities in employment rates and income levels between tribal and non-tribal populations, particularly in the organized sector.
4. Role Models and Aspiration: Successful tribal individuals who have benefited from reservations serve as crucial role models, inspiring younger generations within their communities to pursue education and aspire for better career opportunities.
5. Access to Quality Education: Reservations in educational institutions, particularly in professional courses, have opened doors for tribal students to acquire skills and qualifications that make them eligible for a wider range of jobs.

Limitations and Challenges in Fully Alleviating Unemployment:

1. Limited Reach and Uneven Benefits: Reservations primarily benefit a relatively small segment of the tribal population, mainly those with some access to education and awareness. The vast majority of tribal people, especially those in remote, forest-dwelling, or particularly vulnerable groups, remain largely untouched by these benefits due to lack of basic education and awareness.
2. Quality of Education and Skill Gap: Many tribal individuals lack access to quality primary and secondary education, which is a prerequisite for competing for reserved seats in higher education or government jobs. This results in a significant skill gap, making them less competitive even for reserved positions, leading to a backlog of vacant posts.
3. Focus on Public Sector: Reservations are largely confined to government jobs and public sector undertakings. The private sector, which is a major employer in the growing Indian economy, has limited or no reservation policies, thus restricting the overall employment opportunities for tribal people.
4. Underutilization and Backlog: Despite reservations, many reserved posts remain vacant due to a lack of eligible candidates or inadequate implementation of the policy. This 'backlog' indicates that the policy's full potential is not being realized.
5. 'Creamy Layer' Concerns: While not officially applied to STs, there are concerns that the benefits of reservation might disproportionately accrue to relatively better-off tribal families who are already socio-economically advanced, leaving the most marginalized within the community behind.
6. Stigma and Discrimination: Some beneficiaries of reservation may face subtle discrimination or a sense of stigma in the workplace, impacting their career progression and overall well-being.
7. Broader Economic Issues: Unemployment is a complex, economy-wide issue. Reservations alone cannot solve the massive problem of unemployment, which is influenced by economic growth rates, industrial development, and overall job creation across all sectors.

Conclusion:

Job reservation has been an indispensable tool for promoting social justice and providing crucial opportunities for a segment of the tribal population, significantly alleviating unemployment for those who can access its benefits. However, it is not a panacea for the widespread unemployment among tribal people. To comprehensively address this challenge, reservations must be complemented by robust measures such as improving access to quality education from the foundational level, targeted skill development programs, promoting entrepreneurship, ensuring land and forest rights, and fostering inclusive economic growth that creates diverse employment opportunities beyond the public sector. Only a multi-faceted approach can truly empower tribal communities and alleviate their unemployment effectively.