sivukasvuun

Sivukasvuun, or secondary growth, refers to the increase in thickness or girth of woody plants, such as trees and shrubs, as opposed to primary growth, which involves elongation. This process occurs in dicotyledonous plants and gymnosperms and is driven by specialized tissues known as the vascular cambium and cork cambium (phellogen).

The vascular cambium is a layer of meristematic cells located between the xylem and phloem in the stem and roots. It produces new xylem cells inward, contributing to the plant’s conductive tissue, and new phloem cells outward, aiding in nutrient transport. Over time, the accumulation of these cells increases the plant’s diameter. The cork cambium, on the other hand, generates protective outer layers called cork (phellem) and phelloderm, forming the bark that shields the plant from physical damage and pathogens.

Secondary growth is regulated by environmental factors such as light, temperature, and water availability, as well as hormonal signals like auxins and gibberellins. In temperate climates, growth rings—visible as alternating bands of light and dark wood—form annually, reflecting seasonal variations in growth rates. These rings can be analyzed to determine a tree’s age and historical environmental conditions.

While secondary growth enhances structural stability and resource transport efficiency, it also requires significant energy and nutrients. Some plants, particularly monocots like grasses, lack vascular cambium and thus do not exhibit secondary growth, relying instead on fibrous root systems for support. The study of sivukasvuun is important in forestry, dendrochronology, and plant physiology, offering insights into plant development, ecological dynamics, and climate history.