A whale fall occurs when the carcass of a whale has fallen onto the ocean floor at a depth greater than 1,000 m (3,300 ft), in the bathyal or abyssal zones.[1] On the sea floor, these carcasses can create complex localized ecosystems that supply sustenance to deep-sea organisms for decades.
D&D isn’t required to follow real-world ecologies. But they are amazing sources of inspiration because their complexity and natural logic creates verisimilitude without requiring that we build complex working systems from scratch. How could we use this shortcut for a D&D game?
Dragons are among the largest creatures in a typical fantasy world, and already have the most cultural cachet; it makes sense to make them similarly central to the life of the fantasy world in question. The dragon is more than just a monster to be fought. It can be set dressing, a hazard, and even an adventuring site.
Whale falls happen because of the particular environmental conditions in very deep parts of the ocean. When whales die in shallow water, they decompose normally. But in the ocean depths, their death radically changes the local environment.
So how is a dragon dying different from any other large animal dying? Dragons are unusual creatures. They are inherently magical. They change the land around their lairs during their life, reshaping it to more closely match their chromatic type. Why not also in death?
Green dragon by Better Legends (betterlegends.com)
When a dragon dies outside its lair*, it changes the land around the site of its death for a period of time equal to the dragon’s lifespan. The change corresponds to the type of dragon.
Black Dragons: It gets into the air first, like a crummy gray haze that the wind can't disperse. It’s really noticeable when the first storm hits, and acid rain falls; it will be the only kind of rain in the region for years, maybe decades. Plants turn into monstrous, sickly mockeries of themselves. The water table’s PH level gradually sinks below 7.0. Most creatures shelter bitterly or flee, but purple worms burrow unerringly toward the site, and oozes and other toxic things follow. These conditions do eventually fade, but even centuries later, it’s still possible to identify the site of a black dragon’s death by the pitted patterns on even the toughest exposed rock.
Green Dragons: The location of a green dragon’s death is a superfund site that will someday grow into a horrible, mutant forest. A miasma of toxins fill the water, the air, the very earth. Creatures adapted to such environments are like clownfish hiding in a stinging anemone.
White Dragons: A frozen bomb goes off, like a snowglobe dropped from a great height. An already-cold region turns into a desolate wasteland. A temperate or warm locale gains a localized forever-winter, spinning off tornados and other weather phenomena due to the drastic temperature differences along its borders. Cold-loving creatures sojourn to this place to bask in its frostiness.
Blue Dragons: Perhaps the least obvious of the draconic death-sites, at least at first glance. The effects are subtler, but just as pronounced in their own way. Animals that use magnetic fields for navigation and migration are lost. Metal objects are constantly conveying electric charges, sometimes dangerously powerful. Water tastes metallic. The air is perpetually dry, and people in the area experience frequent static shocks and nosebleeds. Lightning mephits and conduit demons spawn with every thunderstorm.
Red Dragons: Bro, have you ever even been to the elemental plane of fire? You think it is just a hot place? Wait until you see fire so hot that it can burn rock. Fire that flows like water. Fire that sets other fires on fire. This environment is obviously dangerous and deadly to creatures not native to the elemental plane of fire, but the hardiest and greediest dwarven smiths will seek out these locations, because a red dragon’s grave is also a furnace capable of forging the most epic creations.
*A dragon’s lair is not just its home. It also serves as an environmental safety measure to minimize the blast radius of the dragon’s detrimental death. Woe to the creatures of the land when a dragon dies outside its lair!