Deciduous trees only hold leaves for a portion of the year so they must store up the food created from photosynthesis as quickly and as excessively as possible while they do have leaves. This is in order to create a ready food reserve so the supply will not run out when the leaves are absent plus being in sufficient supply to regrow the entire canopy.
Basic life support or basal respiration continues year round in trees that under go ectodormancy (climate triggered dormancy) or endodormancy (internally clocked dormancy). Without chloroplasts they may not photosynthesize but cellular respiration continues in their mitochondria throughout the sapwood volume of the plant. The maintenance respiration rate continues depending on the temperature in the woody tissue. Stem respiration increases with spring bud break over several weeks but the bole respiration is only slightly increased over winter levels. There is no above ground growth during dormancy but the plant continues basic metabolic functions and minimal below ground growth/repair in their root zone.
During the course of the year plants produce more photosynthate (carbohydrate) than they need for immediate use. They store this excess in plastids (leucoplasts) that are located primarily below ground to ensure the plant has enough reserves to support life over the dormant period and ensure spring bud break when it can resume photosynthesis.
Conifers that do not drop their leaves so have no need to compensate for regrowth in spring. Thus conifers have a lower photosynthetic rate during the year and store less for their winter dormancy.