The bald cypress, common in the wetlands of the southeastern United States, is defined by peculiar wooden protrusions emerging from the soil. These structures, commonly called cypress knees, give the tree an almost prehistoric appearance. They are a unique biological feature, and their fate is often questioned when the main tree is removed. This centers on whether these woody growths remain permanent landscape fixtures once their parent tree is gone.
What Are Cypress Knees and Their Purpose?
Cypress knees are outgrowths of the tree’s shallow, horizontal root system, technically classified as pneumatophores. They are formed by the vascular cambium, the living tissue layer in the root that produces wood and bark. These are living root tissues that grow vertically upward, emerging above the water level or soil surface.
The exact biological reason the bald cypress produces these knees remains debated. One long-standing theory suggested they act as “air roots” to help the submerged root system obtain oxygen in waterlogged soils. However, modern research largely unsupported this idea, as knees often lack the specialized internal air-transporting tissue found in true pneumatophores.
A more accepted theory proposes that the knees primarily provide mechanical support and stabilization. They act as anchors or buttresses, helping the massive tree remain upright in soft, unstable, or saturated soil. Their existence is intimately tied to the tree’s overall root structure and its ability to thrive in wetland environments.
The Biological Outcome After the Tree is Felled
When the main cypress tree is cut down, the entire underground root system, including the knees, is effectively condemned. This process is certain because the roots lose their only source of food. A tree’s leaves produce carbohydrates through photosynthesis, which are transported downward via the phloem to feed the roots.
Felling the trunk immediately halts this nourishment supply, causing the underground system to starve. Since cypress knees are direct extensions of the shallow, horizontal roots, they cease growth and begin dying along with the rest of the root mass. Without the energy from the canopy, the living cells composing the knees cannot survive.
The knees will remain physically present in the landscape for a time but are no longer biologically active. Over the following months, the knees stop growing and harden as the living tissue within them dies. The dead root system underground will slowly begin to decay, leading to the eventual decomposition of the knees themselves.
Managing the Remaining Knees and Stump
Once the tree is gone and the knees have died, the challenge shifts to dealing with the remaining dead wood. Cypress wood is notably resistant to decay, especially in wet environments where the knees are found. This means the decomposition process is extremely slow. Property owners should expect the dead knees to remain structurally sound for many years, possibly decades, before they naturally rot away completely.
Mechanical Removal
For those who do not wish to wait for natural decay, the dead knees and the main stump can be addressed through mechanical removal. The most common method involves using a stump grinder to chip away the main stump down to below ground level. This equipment can also be used to grind down the dead knees to a manageable height or below the soil line, eliminating them as tripping hazards.
Chemical Acceleration and Cutting
Chemical treatments can be applied to the freshly cut stump to accelerate the decomposition of the dead wood. These treatments often involve high-nitrogen compounds that feed naturally occurring decay fungi. Since the knees are already dead, they can be cut off below the soil surface with a saw or other cutting tool. This is a simpler task than removing them when they were actively growing, and the resulting dead root fragments can then be covered with soil or mulch.