Science Mystery Pix
Stomatal pores under a leaf? Sand dunes on Mars? Clams clamoring to be fed? Hint: the image illustrates an evolutionary adaptation. Take a guess, then read on!
Secret of Serotiny: In 1961, a fire destroyed 28,000 acres of forest in Montana. Since then, the lodgepole pine has established dominance over this vast acreage, with a density of tens of thousands of trees per acre. Yet, this pine normally does not spread its seed beyond a range of some 200 meters. How did the lodgepole pine achieve this remarkable biotic potential?
Its secret was serotiny: millions of seeds per acre were stored inside cones, high up at the canopy top of mature stands, for just this scenario. The heat of the fire melted the resin that kept the cones closed, releasing seeds to be carried by wind or gravity over several days, to land on burned but cooling ground. With little competition, more light, warmth and nutrients from ash, the seedlings flourished, making this pine an aggressive pioneer species.
Serotiny is the adaptation by some plants that hold on to their seeds for decades after they are mature, releasing them only in response to a specific environmental trigger. The trigger could be dryness, water, or fire. Some desert plants have adapted to release seeds after rainfall, when the chances of successful germination are high. Other plants release seeds only after they die, a feature known as necriscence. Oddly, fire-survival strategies may be paired with fire-embracing adaptations, such as retaining dead (and flammable) branches instead of the more common practice of self pruning . Known as niche construction, this double strategy ensures removal of poorly adapted plants in regions susceptible to natural fires.
The Fiery Cretaceous: Fire has been an effective agent of natural selection for at least 125 million years and possibly longer! The high oxygen levels (23-29% compared to today’s 21%) in Earth’s paleoatmosphere of the early Cretaceous fueled frequent fires, captured as charcoal in the fossil records. Since then, fire adapting traits in plants arose independently, many times. Our Mystery Pix can now be revealed as the cone of a Banksia tree, endemic to Australia, with open seed pods after a bushfire. Photo via PinkRockAus’s Fotothing http://goo.gl/ZEfDHm