In order to work at this level, you will need specialist training. This is likely to involve technical or scientific skills, which you could learn as you are working.
You might learn to use special equipment to help with environmental monitoring or you might need people skills to deal with the public. Volunteering with a conservation project will help you meet people with similar interests and find out about the career. Short courses in topics such as dry stone walling, species identification and surveying can help increase your chances of promotion.