Spring brings trees covered in white blossoms, but this display is accompanied by a distinctly unpleasant odor. Many people describe this smell as similar to decaying fish, rotting meat, or sometimes a more acrid scent. This powerful, disagreeable aroma is a common experience in urban and suburban areas across the United States during the brief flowering period. The source of this highly recognizable fragrance is a widely planted ornamental tree.
Identifying the Main Offender
The tree responsible for the pervasive odor is the Callery Pear (Pyrus calleryana). Native to China and Vietnam, it was introduced to the U.S. in the early 1900s for its resistance to fire blight, a destructive bacterial disease affecting common pear orchards. The most infamous variety, and the one most commonly associated with the odor issue, is the ‘Bradford Pear’ cultivar.
The ‘Bradford Pear’ gained immense popularity as a landscaping tree in the mid-20th century due to its uniform shape, tolerance for urban conditions, and striking white flowers. The foul smell is exclusively produced by the dense clusters of five-petaled white flowers, which emerge before the leaves in early spring. This short, intense blooming period is the only time the tree releases its signature scent, which dissipates once the petals drop.
The Science Behind the Foul Odor
The offensive smell results from chemical compounds released by the flowers, which are organic molecules known as amines. The primary compound causing the fishy smell is trimethylamine, a volatile organic compound (VOC). This same compound is naturally present in decaying fish and seafood, resulting from the breakdown of trimethylamine oxide by bacteria.
The tree produces this scent as a biological strategy for reproduction. While many flowering trees use sweet fragrances to attract bees and butterflies, the Callery Pear’s putrid aroma is designed to attract different types of pollinators. The odor mimics decaying matter to lure carrion-loving insects, such as flies and beetles, which then transfer pollen between flowers. This method ensures pollination despite the tree not producing the nectar rewards common in other species.
Physical Characteristics and Visual Identification
When not in bloom, the Callery Pear can be identified by several visual features. Young trees typically exhibit a narrow, symmetrical, and pyramidal shape, which contributed to their initial appeal as landscape trees. The leaves are a glossy, dark green color with a finely toothed margin and an oval to heart shape.
The tree is known for its vibrant fall foliage, which turns shades of deep red, purple, and orange before dropping. However, the tree’s structure is a significant weakness, as the branches grow at tight, upright angles that create weak unions. This weak branching makes mature Callery Pears highly susceptible to splitting and failure during strong winds or heavy ice and snow events.
Management and Ecological Concerns
The Callery Pear’s history as a popular ornamental tree has led to it becoming a significant ecological problem in many regions. Although the original ‘Bradford Pear’ cultivar was thought to be sterile, it can cross-pollinate with other Callery Pear varieties, including newer cultivars like ‘Cleveland Select’ and ‘Aristocrat.’ This cross-pollination results in viable seeds that are then widely dispersed by birds and small animals that eat the small, hard fruit.
The species has since escaped cultivation and is now classified as a highly invasive species in many parts of the U.S. In natural areas, the Callery Pear forms dense, thorny thickets that aggressively out-compete and shade out native plant species. As a non-native species, it provides little food source for native insects and wildlife, which disrupts the local ecosystem. Due to these environmental concerns, many state and local governments now recommend or mandate the removal of Callery Pears and their replacement with native, non-invasive alternatives.