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The environment surrounding the tulip poplar changes through the course of a year. The daily cycles of temperature swing between 5 and 10 °C, while the coldest and warmest day of the year may differ by 25 °C or more (Figure 1.3). Incoming sunlight in winter averages about half the level experienced in summer, as a result of shorter days, lower sun angles, and fewer clouds. These environmental changes lead to regular, predictable patterns in the phenology of the tree.

The tulip poplar begins an annual cycle of flowering and growth with the initiation of root growth late in the winter, followed by flowering in April and May. The tulip‐shaped flowers are pollinated by bees and other insects, with 10 000 seeds raining from the crown in autumn. The leaves of the crown also expand in April and May, from expanding buds that were set the previous year. The initial burst of leaf growth depends on stored sugar, but the leaves rapidly provide new sugar for their own growth, and for the growth of all parts of the tree. The growth of a new leaf requires only about one‐week's production of sugar; the rest of the span of the leaf's existence contributes to the growth and maintenance of other tissues.

Over the course of the growing season, the tulip poplar may produce 50 kg of sugar. Respiration would consume half, and the growth of short‐lived roots and leaves might consume another quarter. Less than 25% of the annual production from the tree's leaves would be found in new stem wood, increasing the diameter and height of the tree. The annual growth of the tree might use more than 8000 liters of water.

Dry periods during the summer lower the rate of photosynthesis in two ways. Low supplies of water in the soil lead to closure of leaf stomata, restricting both the gain of CO₂ and the loss of water. The tulip poplar might also respond directly to the dryness of the atmosphere, and days with very high vapor pressure deficits may have low rates of photosynthesis, even if the soil is moist.