Knows general principles of how climate, terrain, and life forms interact. Can identify problems, but can only guess at causes.(The topsoil has eroded away.) Can determine causes of problems. (Heavy rainfall washed away the topsoil and leached away the nutrients.) Can suggest solutions to problems. (Add fertilizer to the remaining soil. To prevent further erosion, keep land covered with grasses or trees.)
If the DM is stumped as to whether a ranger knows a particular piece of information, he may require the ranger to make a Wisdom check, adding bonuses or penalties to the roll depending on the relative difficulty of the question. For instance, knowing if a particular substance will work as a fertilizer is a relatively easy question, requiring no penalty to the roll. Knowing which specific crops the fertilizer will nourish is a more difficult question, and a penalty to the roll may be in order. In all cases, the DM should use common sense. A ranger who's never been out of the desert won't know much about the effects of a hurricane on a coastal environment, regardless of his level.
The ranger is exceptionally skilled at surviving harsh conditions associated with his primary terrain. In game terms, the ranger is considered to automatically have the Survival proficiency in his primary terrain. This skill costs no proficiency slots. A ranger can spend slots in the Survival pro iciency to acquire survival skills in environments other than his primary terrain.
The ranger's survival skill helps in the following ways, all of which apply only in the primary terrain. In certain cases, the DM may require a Survival check (which is equivalent to an Intelligence check). A ranger rolling less than or equal to his Intelligence score on 1d20 succeeds in the check.
The ranger knows the basic precautions necessary to enhance the chances of survival, and can instruct and assist any companions accordingly. For example, a ranger whose primary terrain is Mountains realizes that physical exertion in high altitudes may result in headaches and fatigue (due to low air pressure). A Desert ranger knows that in arid climates, it's better to rest in the still air than exposed to a strong wind (wind promotes evaporation from the skin, increasing the degree of dehydration). An Aquatic ranger understands that saltwater can't be used for drinking. An Arctic ranger realizes that temporary protection can be had from a bitter wind by tunneling inside a snow drift. This knowledge doesn't guarantee survival by any means; it merely improves the odds. If the ranger wonders about any particular piece of information, the DM will decide if he knows it, requiring a Survival check if necessary.
The ranger can stave off starvation by finding small amounts of food. A successful Survival check locates enough food to feed himself or one other character. He can locate food in this way once per day.
The ranger can find enough water to keep himself or another character alive for one day by making a successful Survival check. This assumes that the water is