Climate conditions are the first of many variables that influence how trees produce wood, resulting in the annual wood-forming rhythm [9]. Temperature and photoperiod influence cambium reactivation and secondary xylem production [19,20]. In Japanese cedar (Cryptomeria japonica), the shoot and young needle sense temperature and photoperiodic signal and show seasonal transcriptome changes [21]. Photosynthesis produces C compounds for cell wall formation, and rainfall supplies water to create the right turgor pressure on the cell wall, which results in cell expansion [22,23].

Warmer temperatures after a cold winter are thought to be one of the main factors in determining when cambium resumes at the start of the growing season (early spring) [13,19,24,25]. The earliest cambium activity of the year is recorded at 10 °C in Chinese red pine (Pinus massoniana Lamb.) and Scots pine (Pinus sylvestris), and 5.6–9 °C for European larch (Larix decidua), Swiss pine (Pinus cembra), Norway spruce (Picea abies), Balsam fir (Abies balsamea), Bosnian pine (Pinus leucodermis), and Mountain pine (Pinus uncinate) [19,25,26]. Threshold temperature depends on the species and age [24,25]. Three to four weeks after cambium reactivation, cambium cells are actively dividing, and xylem differentiation occurs through cell expansion, SCW formation, and PCD [7,25]. Temperatures favorable for cambium activity are about 17 °C for Scots pine and about 25 °C for Chinese red pine [19,26]. When the air temperature decreases in the fall (about 15 °C for Chinese red pine and 8–10 °C for Chamaecyparis obtuse), cambium enters dormancy and the wood formation process ceases [19,24].

During the long days of spring and summer, photosynthesis is active, providing a constant source of carbon for cell wall formation [19,21,23]. Prolonged photosynthesis provides sufficient ingredients for cell wall formation during the beginning of the active season, when cambium cells divide rapidly and xylem cells expand as much [20,26]. As a result, earlywood is formed, which has a large area, thin cell wall, and brilliant color [26]. The constant supply of sucrose produced from starch reserves may promote cambium cell division and xylem formation [19]. The inducing soluble sugar that changes the osmotic pressure may contribute to turgor pressure necessary for cell expansion, so it parallel with the activity of cambium cell [24,26]. During mid to late summer (July to September) in the Northern Hemisphere, day length is very long. It may suggest that the abundant source of carbon at this time provides for cells in SCW formation progress, leading to thick cell-walled latewood. At the half end of the active season, when conditions are no longer favorable, cambium activity decreases and xylem cells do not expand [24,26].

Precipitation strongly influences cambium activity and xylem differentiation because they require turgor pressure during cell expansion [19,27]. In the beginning of the growing season, abundant rainfall increases cambium division, resulting in the formation of many layers of xylem cells with a large cell area called earlywood. Conversely, in the second half of the growing season, drought reduces cambium division, resulting in the formation of a few layers of xylem cells with a small cell area called latewood [26,27]. Latewood formation is strictly influenced by environmental conditions [24]. Cambium is known to rest in the cold weather of fall [24,26]. In fact, though, drought is considered to be the major factor that leads to cambium inactivation. Growth is enhanced and the latewood ring is thin under ideal conditions, whereas latewood formation is high under low precipitation and low temperature in Douglas-fir (Pseudotsuga menziesii) [28]. In Scots pine, cambium rest and latewood forms in the hottest time of summer (around 27 °C), under low precipitation, due to the limitation of cell expansion [26]. However, cambium division, cell expansion, and SCW formation have two peaks in the subtropical forest: one during the rainy season (middle of April) and another during the dry season (early October, by the time of long sunshine duration) [19].

Dormancy is crucial for the growth of wood since it enables the tree to preserve energy and resources during the winter. When a tree goes dormant, it diverts energy and nutrients from growth activities to other survival-related processes. This enables the plants to shield the meristems from unfavorable environmental circumstances and coordinate the time of their growth cycle for favorable environmental factors [29]. Cold temperature is thought to be the key factor in dormancy induction. In Hinoki cypress (Chamaecyparis obtusa), a decrease of temperature from 25 °C to 8–10 °C inhibits cambium cell division [24]. However, this effect is still not well understood.

At the beginning of dormancy, the ‘rest’ phase (endodormancy or physiological dormancy) is the time after the cambium becomes inactive, which takes 2–4 weeks and is influenced by endogenous factors, so the cambium is unable to divide even under favorable conditions. The ‘quiescence’ phase (ecodormancy or environment dormancy), on the other hand, occurs after that and is the result of environmental factors, so it can stop when climatic conditions become favorable [19,24,25,29]. The difference between the rest and quiescence was shown in the study of vacuoles in Lodgepole pine (Pinus contorta). Cambium cells in the rest phase have many small and elongated vacuoles, whereas cambium cells in the quiescence phase have fewer rounded big vacuoles [29]. Vacuoles play an important role in the storage of reserves in cell activity. Thus, the change in vacuole status relates to the change in cell activation [29]. Until now, the genetic and hormone regulation in the transition from rest to quiescence is still unknown in gymnosperm, but chilling in the winter is required for the onset of quiescence [29]. In angiosperm, it has been suggested that, after 4 weeks of short-day treatment, cambium stops dividing and goes to the quiescence phase with the decline of histone H1 kinase activity in A- and B-type cyclin kinase (CDKA/B) kinase complex, which regulates cell cycle. However, longer short-day treatment (6 weeks) leads to the rest phase, which reduces and inhibits CDKA/B, followed by the reduction of retinoblastoma (Rb) phosphorylation activity from CDKA protein complex. Thus, G1 to S phase in cell cycle is blocked [30].

In summary, the transition from active growth to rest phase of dormancy can be caused by a decrease in day length, precipitation, and temperature. The transition from rest to quiescence phase is affected by chilling, which leads to structural, histochemical, and functional changes in cambial cells. The transition from quiescence to reactivation phase depends on temperature and day length.