Final answer:
Fire is required to open some pine cones because of serotiny, an adaptive trait in which high temperatures from forest fires melt the resinous bond protecting seeds, allowing them to germinate in conditions with ample sunlight and reduced competition.
Step-by-step explanation:
One reason fire is needed to open some pine cones, such as those of the jack pine (Pinus banksiana), is due to a phenomenon known as serotiny. Serotiny is an adaptive trait where the cones protect their seeds under a resinous bond that requires high temperatures to melt. This usually occurs during a forest fire, which consequently reduces competition by clearing out underbrush and adds nutrients like nitrogen to the soil, fostering a better environment for the new seedlings to thrive.
The jack pine, among other fire-adapted pines like the long-leaf pine and the ponderosa pine, exhibits this behavior. Their seeds, once released post-fire, find an advantageous setting for germination due to the abundance of sunlight and reduced competition. Cones opening only in high temperatures ensure that seedlings emerge at a time when their chances of survival are improved.