Pg. 178 of the PHB describes the Nature proficiency as "Your Nature check measures your ability to recall lore about terrain, plants, animals, the weather, and natural cycles". That said, players, even with a high intelligence are not omniscient. Knowledge of the natural word comes through experience, study, and learning. A character who grew up in a city is not likely to know the difference between breeds of cow, recognize a rare forest herb, or the effects of mountain terrain on travel. However, a character may choose to pursue knowledge of the natural world through travel, exploration, talking with experts, collecting books of natural lore, and many other means. After achieving a basic education in such things, the character can be referred to as a Naturalist.
Naturalists can be classified into the following categories, depending on experience. These categories are awarded by the DM once sufficient effort has been made, etc.
Novice
Naturalist
Master
Specialist
Game Mechanics
There is no change to the Nature Proficiency. Any characters may attempt a Nature check. If they are proficient, they will have advantage in the roll. However, the results of a successful roll will be determined on the basis of the character's knowledge and experience of the natural world. Consider searching through a pile of pebbles found in the corner of a dungeon room, perhaps looking for stones of possible value. A character with a farming background might notice that one or two stones look different than the others. One with high born background, might recognize a possible gemstone. A character with jeweler tools and some experience might be able to tell the difference between a garnet and a ruby. A character who has made a deep study into geology could tell you that this is not only a ruby, but that it is not native to this area.
During play, a player might make this statement to the DM, "Baldur is a dwarf and a novice naturalist with mining experience wants to make a Nature check to see if this stone might be valuable." He rolls well and the DM announces that the stone is a dark emerald, very rare in these parts. There is no requirement to add this additional information. The player might assume that the DM already knows that the characters is an expert naturalist with a specialty in healing herbs. The player can also add, "My character has a book titled Recognizing Raw Gemstones" to get more information, if available.
Nolaria has a long game tradition of encouraging characters to acquire knowledge in various forms. Academics often build their own library. Rangers accumulate experience during their travels, sometimes going out of their way to see new sights. A weaponsmith might spend some time working with a renowned smith to learn new techniques. All of this is intended to add more depth and flavor to the game, as well as creating useful differences in characters.