Green has an explanation
Many leaves look green because of chlorophyll, a pigment involved in capturing light energy for photosynthesis. Leaves contain other pigments, but chlorophyll can dominate the colour we see. This helps explain why a change in appearance need not begin with a completely new substance arriving. Sometimes a colour already present becomes more visible as the green fades.
The change is more than a switch
In many deciduous trees, declining chlorophyll as leaves age allows yellow and orange pigments to stand out. Red and purple shades are associated with other pigments, such as anthocyanins. Not every species follows the same pattern. Day length and weather conditions contribute to the transition, so there is no identical colour calendar for every tree or every year.
Not all trees put on the same display
A street can have green trees beside others with yellow leaves or almost no foliage. Before interpreting this as a problem, identify the species and observe local conditions. Trees with different strategies need not change at the same pace. A photograph of a leaf is also insufficient to diagnose a plant’s health. Colour, the distribution of changes, season and context must be considered together.
Create a repeat observation route
Choose three or four trees visible from a public path. Photograph each from a similar point over several weeks. Record the date and general canopy condition without picking leaves or damaging branches. Add a short description of colours and leaves on the ground if useful. Comparison is valuable: a simple series reveals changes that can go unnoticed when every visit is left only to memory.
What photography may change
Early morning light, shade and camera white balance influence colour appearance. Try keeping conditions similar when comparing pictures and avoid filters that automatically intensify tones. If photographs differ substantially, note that limitation rather than treating the difference as evidence of biological change. A small observation notebook need not be perfect, but should distinguish what you saw from what equipment may have transformed.
