Sometimes forest fires can have important effects that are not obvious to an observer. Kirtland's warbler is a blueish grey bird with a yellow abdomen. It nests only in the lower peninsula of Michigan in a forest dominated by short, bushy jack pines. The Kirtland's warbler makes its nest in the soil near jack pine trunks. But only jack pines with bushy lower branches provide the warbler with sufficient cover.
Young pines have branches that are too widely spaced to offer sufficient protection.
Older jack pines lose their lower branches because the higher branches cast too much shade. Only jack pines between 1.5 and 5.5 metres tall provide suitable habitat for the Kirtland's warbler. Starting in the 1960's, foresters burnt off the organic litter with small, controlled fires. Wild, uncontrolled fires were almost completely eliminated. Without wildfire, the jack pines began to grow too tall for the warbler.