The tree of heaven, also known as Ailanthus altissima, is a deciduous tree native to China that has become invasive in many parts of the world. This fast-growing tree is known for its ability to thrive in challenging urban environments and its prolific seed production. But one of the most distinctive features of the tree of heaven is its vibrant foliage that provides a splash of color in the summer and fall. So what exactly is the color of the tree of heaven’s leaves?
The Tree of Heaven
The tree of heaven (Ailanthus altissima) is a medium to large deciduous tree that can grow up to 80 feet tall. It has smooth gray bark and large, odd-pinnate compound leaves with 10-41 leaflets. The leaflets are ovate-lanceolate in shape with entire margins. The foliage of the tree turns a bright yellow in the fall. The tree produces an abundance of small yellowish-green flowers in large terminal panicles in the spring. These give way to clusters of papery samaras or winged seeds. The tree is dioecious, meaning individual trees are either male or female. The tree of heaven is native to northern and central China and Taiwan but has become a common invasive species across much of Europe, North America, Australia, and New Zealand. It was first introduced into Europe and the United States in the late 18th century for ornamental and medicinal purposes. It has now naturalized in urban and disturbed areas due to its rapid growth, abundant seed production, and ability to regenerate from roots. The tree is considered an invasive pest in many areas due to its prolific spread and potential to dominate native ecosystems. It is also known to emit chemicals that prevent the growth of nearby plants. For these reasons, the management and removal of the tree of heaven is often necessary, especially in conservation areas.
Foliage Color
The most striking feature of the tree of heaven is its lush, bright green compound leaves that emerge in late spring. The leaves provide welcome shade under the dense canopy throughout the summer. In autumn, the foliage transforms into a showy display of various brilliant yellow hues. This is one of the characteristics that led to the tree’s common name, since its vibrant autumn coloring seems heavenly.
The progression of color change begins in early fall as the leaves start turning a clear lemon yellow. By mid-autumn, the leaves graduate into more intense shades of golden yellow. In late autumn, just before the leaves drop, the foliage approaches a saturated yellow-orange hue in some specimens that is quite dramatic. Throughout this process, the foliage retains its bright vitality before dropping to mulch around the base of the tree.
The variability in autumn leaf color on different specimens of tree of heaven likely has to do with genetic differences between trees. Soil conditions, moisture, sun exposure, and other environmental factors can also affect the timing and vividness of the fall display. Some trees may take on ruddy or orange hues mixed in with the predominant golden yellow colors.
Leaf Structure
The green and yellow color palette of the tree of heaven comes from pigments located within the leaves themselves. The various shades result from the types and amounts of these leaf pigments during different seasons.
During the spring and summer when the tree is actively growing, the leaves contain high levels of chlorophyll. This green pigment is essential for photosynthesis, the process by which plants convert sunlight into food. Chlorophyll absorbs blue and red light most strongly, causing it to appear green.
In addition to chlorophyll, tree of heaven leaves contain carotenoid pigments. Carotenoids absorb blue and green light, leading to a yellowish color. During the growing season, the green chlorophyll mostly masks the underlying yellow carotenoids.
As autumn approaches, the chlorophyll in the leaves begins to degrade. The green fades away, revealing the bright yellow and orange hues provided by carotenoids. The proportions of different carotenoids present in the tree’s genetics and growing conditions impact the exact autumn color each year.
The vibrant pigments are eventually transported from the leaves back into the tree before they fall. This ensures valuable nutrients are conserved and not lost. The used up leaves then become brown and brittle once the color is gone.
Factors Influencing Color
Although tree of heaven reliably turns a golden yellow in autumn, several environmental factors can impact the timing and intensity of the fall foliage display.
Sunlight: The amount of direct sunlight exposure affects chemical reactions and pigment production in the leaves. More sun usually results in brighter fall colors. Shaded trees tend to reach peak coloration later.
Temperature: Cool autumn nights and warm sunny days intensify the autumn display. Sustained frost and freezing leads to quicker leaf drop without reaching peak color.
Water: Adequate moisture ensures leaves remain vital and intensely colorful before falling. Drought stress can lower vibrancy and cause early leaf drop.
Soil: Fertile, slightly acidic soil provides ideal nutrition for lush foliage and bright pigments. Poor soils can impair foliage color and health.
Damage: Leaf damage from insects, diseases, pollution, or storm winds can weaken color intensity. Damaged leaves often turn brown and fall sooner.
Genetics: Some trees have more pigments and turn much brighter colors through certain gene variants. This natural genetic variation leads to diversity.
Location: Northern regions with distinct fall seasons tend to produce better color than warmer southern climates. Elevation and latitude impact timing.
Typical Timing
In locations with four distinct seasons, the foliage of the tree of heaven generally starts changing color in mid-late autumn and reaches peak color in early-mid autumn before dropping. Some variations in timing occur based on weather patterns each year and between different regions and individual trees.
Here is an approximate timeline for the fall color stages:
Early autumn: Leaves begin changing from green to light yellow, starting at the tips and edges.
Mid-autumn: Color deepens to golden yellow, moving inward from leaf edges.
Early-mid autumn: Foliage reaches full vibrant yellow or orange-yellow color.
Mid-late autumn: Color starts to fade, leaves begin falling or turn brown.
Late autumn: Nearly all leaves dropped, branches are bare.
The duration of peak fall color for an individual tree lasts only about 1-2 weeks. Leaf drop typically occurs rapidly shortly after peak color is reached. The window for the most vibrant display is therefore fairly short. The precise timing shifts yearly with seasonal variations.
Influence of Climate Change
As global climate patterns continue shifting in response to increased atmospheric carbon dioxide and warming trends, the fall foliage cycle of trees like the tree of heaven may be affected. Certain consequences of climate change that could impact the autumn display include:
– Warmer fall temperatures may delay onset of leaf color change.
– Hotter drought conditions may lessen intensity of fall colors.
– Increased severe weather events can strip leaves before color peaks.
– Milder winters and springs may alter chemical signaling for fall dormancy.
– Rising carbon dioxide levels can cause leaves to drop sooner.
– Increasing precipitation may leach nutrients from leaves.
– Earlier spring bud burst may affect later autumn leaf processes.
The interactions between trees and climate are complex. Increased monitoring and research will further reveal how fall foliage cycles respond and adapt to a changing climate in the coming decades.
Conclusion
With its cascading, deeply lobed foliage that transforms from bright green to brilliant yellows and oranges, the tree of heaven provides a dramatic fall display. The color results from the pigments produced in the tree’s leaves that change with the seasons. Chlorophyll gives way to carotenoids as the greens fade and yellows emerge. A mix of genetic and environmental factors influence the timing and vibrancy of autumn color each year. Appreciating the radiant seasonal change in a tree of heaven’s foliage allows us to connect with nature’s cycles and consider our changing climate’s impact on these processes. Tracking and sustaining fall foliage diversity will be an increasingly important task in the future.
