The appearance of an unexpected tree seedling in a yard is a common experience for property owners. These spontaneous seedlings, often referred to as volunteer trees, are self-sown plants that germinate and begin to grow without any human intervention. The discovery of these young trees prompts the question of whether they should be nurtured or removed. Understanding their biological nature and potential impact on structures is the first step in deciding their fate.
Defining the Volunteer Tree
A volunteer tree is a plant that has grown entirely on its own, sprouting from a seed that arrived naturally. This term distinguishes them from trees deliberately planted or those arising from an existing root system, known as suckers. The volunteer’s origin is always a seed that germinated where it landed, often from an established tree nearby. While sometimes welcomed, these self-seeded plants are frequently viewed as weeds when they appear in inconvenient spots.
The seeds are carried from a parent plant by various external agents. This process, called seed dispersal, is an adaptive mechanism that ensures offspring can colonize new areas away from the original tree. Successful establishment requires the seed to find a suitable site for growth, often including disturbed soil or cracks where moisture and nutrients collect.
Mechanisms of Seed Dispersal
One effective way seeds travel is through wind dispersal, or anemochory, which utilizes specialized structures to catch air currents. Maple trees produce samaras, often called “helicopter seeds,” which spin and float through the air. Other trees, such as willows or cottonwoods, release lightweight, fluffy seeds that ride the breeze over long distances. This mechanism allows seeds to land far from the parent tree, including on rooftops, in gutters, or in pavement cracks.
Animals are another significant vector for spreading seeds, a process known as zoochory. Birds and mammals consume fruits, and the seeds are then excreted in their droppings. Squirrels and jays also contribute by burying nuts and acorns for winter caches, inevitably forgetting some that then sprout. Some seeds have evolved hooks or barbs, allowing them to attach to the fur or feathers of passing animals.
Water dispersal, or hydrochory, is a less common but effective method, especially for plants near water bodies. Seeds from trees like alder have air pockets that keep them buoyant, allowing them to float on water. Runoff and drainage can also carry seeds into pipes, along driveways, and into other unexpected urban locations.
Locations of Concern
The most significant problems arise when volunteer trees sprout in locations that compromise infrastructure. Tree roots exert pressure, known as turgor pressure, which enables a root tip to displace concrete or masonry. If a volunteer establishes itself in a crack in a building foundation or paved driveway, its expanding roots will widen that fracture over time, causing structural damage. Root systems may also contribute to foundation instability by extracting moisture from the soil, leading to soil shrinkage and uneven settlement.
Volunteer seedlings often take root in gutters, downspouts, and on chimney crowns where debris and moisture accumulate. As the tree grows, its roots trap organic matter, creating clogs that lead to water backup and overflow. This moisture exposure can damage fascia boards, soffits, and the roofline, potentially causing costly repairs. The invasive Tree of Heaven (Ailanthus altissima) is notorious for growing out of pavement cracks and structurally compromising walls and asphalt.
Deciding Whether to Keep or Remove
The first step in deciding the fate of a volunteer tree is to accurately identify its species and determine its ultimate size potential. If the seedling is a native species with desirable characteristics and is growing in a suitable location, it may be possible to transplant it. However, fast-growing or non-native invasive species should be removed immediately upon identification.
The Tree of Heaven is a problematic volunteer because it is highly aggressive and releases chemicals that inhibit the growth of nearby plants. This species is also the preferred host for the spotted lanternfly, a destructive agricultural pest. Removal is easiest when the plant is a small seedling, as it can typically be pulled out by hand, ensuring the entire root system is extracted. If a significant taproot develops rapidly, the difficulty and cost of removal increase substantially, often requiring herbicides to prevent aggressive root-sprouting.