Like all living beings, trees have a limited life cycle with phases of youth, maturity and senescence. In their early stages they provide shade, freshness, environmental quality and an indisputable aesthetic value to the urban space. However, as they age they undergo weakening processes that affect their stability. Old age leads to internal rotting, hollows in the trunk, fungal and bacterial invasions, and an increasing risk of breakage or fall.

In the natural environment, dead specimens are integrated into the ecological cycle and provide refuge for specialized fauna. In cities, however, where human safety is a priority, these same processes represent a danger that cannot be ignored.

Extensive damage that the human eye cannot see

Urban treemanagement requires responsibility and foresight. One of the main problems is that degradation is not always visible to the naked eye. A tree can have a lush green canopy while its interior is hollow or weakened.

Xylophagous fungi, for example, those that attack wood to feed, decompose the cellulose or lignin that make up the wood, making the structure fragile.

Among the most common types of this rotting process, two can be distinguished. On the one hand, brown rot, when organisms such as Paenibacillus glucanolyticus or Serpula lacrymans degrade cellulose and hemicellulose. On the other hand, the white one, in which lignin is degraded by the fungus Trametes versicolor.

In both cases the outcome is the same: the tree loses strength irreversibly. Despite the seriousness involved, it is often only possible to check the extent of the damage caused after felling, confirming (or not) whether the removal of the tree was necessary. Other times it is possible to identify if there is a mismatch between the external appearance and the real state by using resistographs, equipment that assesses the integrity and density of the wood by means of a minimal perforation.

Logging times according to species

Not all tree species have the same life cycle. Fast-growing trees, such as poplars and poplars, live shorter lives than others. When they reach about fifty years of age, they tend to enter accelerated senescence: their trunks hollow out, the roots lose firmness and the risk of collapse multiplies.

Although they have served a valuable function for decades, there comes a point when they must be replaced by younger, safer specimens. Keeping them beyond their vital limit unnecessarily exposes park users to the danger of unexpected falls.

It is understandable that the felling of a tree causes regret among neighbors, as many trees are linked to memories and are part of the identity of the place. However, management cannot be guided by nostalgia alone, but by the safety of all and a vision for the future.

Delaying felling (i.e. felling a tree at its base in order to fell it) when a tree is already in the final phase of its life compromises safety. And the consequences can be serious, ranging from heavy falling branches to complete collapse of specimens, with risk of personal injury and material damage.
 

Preserve hollow logs as shelter for birds and bats.

The removal of aged trees must be accompanied by new plantings, preferably of native or adapted species. In this way, the green heritage is not diminished, but renewed and even increased, while biodiversity is enriched. In this way, future generations will inherit healthier and safer parks.

Treemanager also includes sanitary pruning, height reductions in at-risk specimens and, in some cases, the temporary conservation of hollow trunks as shelter for birds, bats and insects. Where there is no direct danger, old wood can continue to be useful for wildlife. But in areas of intensive use, the safety of people must be paramount.

Explain to the public the function of trees.

Urban trees are not just ornaments. They regulate temperature, filter pollutants, muffle noise and beautify the landscape. They are an essential factor in the well-being of citizens. Renouncing them is not an option, but neither is maintaining specimens that have exceeded their useful life and represent an unacceptable risk. Hence the importance of proper treemanagement .

In this context, transparency is essential. Explaining to the public why certain trees are being felled and what criteria have been applied reduces mistrust. When it is explained that an apparently healthy tree is in fact very deteriorated and poses a danger, the need to act is better understood. And if the decision is accompanied by a replacement policy with a larger issue of trees and a greater diversity of species, social support is strengthened.
 

Citizens and nature in harmony

The life cycle of trees forces us to recognize that they are not eternal. They are born, grow, age and die. And in that process, particular challenges arise in urban public spaces.

Serious management must anticipate decrepitude, assess hidden risks, plan for pruning when necessary, and guarantee replacement with new plantings. Only in this way will city parks remain safe, beautiful and lively places, where nature and citizens live in balance.

This article was originally published in The Conversation. Read the original.