Once the rainy season is over, the branches all shed their leaves in a very short time. For large stretches of the year, the trees all lose their leaves, giving the appearance of a dead or "winter" forest, despite it being tropical and warm. Leaves are lost, and photosynthesis halted, because both are the major causes of a tree to "waste" or expend water. Then, when the rains start again, the forest explodes into life, transforming significantly overnight.
A few species of tree have specifically adapted to the dryness in other, unique, ways. Plants in a Seasonal Dry forest may have evolved to take advantage of one or more of the following possible mutations:
- Dark green tree bark that can engage in limited photosynthesis without wasting or leaking water.
- Leaves that fold or close up at night (like some flower species) to reduce water loss. This process is called nyctinasty.
- Thick waxy leaves that are more resistant to evaporation.
- Water storage tissues in their roots or trunks similar to a cactus.
Likewise, animals living in the Seasonal Dry Forest are also adapted to the cycles.
- Burrowing deep, seeking water and/or cooler temperatures.
- Estivation is the summertime equivalent of Hibernation.
- Migratory patterns, and dry season denizens live off a much larger expanse of territory than equivalent animals in more temperate climes. There's just not much food per acre during the dry times.
- Seasonal social behavior. Otherwise aggressively territorial animals might be cooperative or tolerant during the dry seasons, sharing the limited resources or crowding in tightly to riverbank and coastal areas where water is still plentiful.
Seasonal dry forest often gives way into Savanna at its edges.
Game and Story Use
- Like Miombo, the Seasonal Dry Forest can be used to disorient or alienate PCs (and Players) from far into the Northern Hemisphere.
- Give your Ranger-types a workout. Wilderness Surival and Nature Lore could help you gather precious water in these dry times, but probably at a a bit of a penalty if the character comes from lusher climes.
- Especially if abducted, transported without explanation, or if the change in locations is accompanied by some other unexplained phenomenon, the appearance of the forest where they arrive may confuse them about what time of year it is. If done with enough panache or mystery, the PCs might assume they aren't even in the same year. "Well, it was spring when the aliens abducted us, and now it's clearly either a unseasonably dry autumn, or after the end of the world…"
- If you and your players live in the tropics, the inverse could work just as easily. Use cold, icy winters instead of hot, dry summers.
- Another planet can be made to seem all the more alien if the local wildlife doesn't follow the patterns you're used to. One easy way to model that without having to invent a lot of spurious alien biochemistry is to base it off something foreign, but still existing in the real world (and thus well documented). A seasonal dry forest could serve as "alien" if the players are all familiar with other climates. To make it a bit more alien, see Non-Green Photosynthesizers.
- The contrast of forest types could provide a thematic differentiation between two nations in your campaign world. A mountain range could have jungle or rainforest on one side, and Seasonal Dry Forest on the other. It's all about the way the wind blows, and where the storms fall.