Wood Quality and Climatic drivers of Chestnut Tree Growth (Castanea sativa Mill.) and Canopy Stress in Central Italian Coppices

Trees are not merely static pillars of a forest; they are living systems that constantly negotiate with their environment, drawing water from the soil and light from the sky to build wood and leaves. When these systems face pressure from extreme heat, prolonged drought, or invading pests, they often show signs of distress long before they collapse. In the forests of central Italy, where the sweet chestnut tree has shaped the landscape for centuries, scientists are watching closely to see how these ancient giants are faring. The chestnut is a vital resource, providing timber and food, but it faces a complex web of threats. Some come from living enemies like fungi that rot the wood from the inside or insects that damage the leaves. Others come from the changing climate, where hotter, drier summers strain the trees' ability to survive. Understanding how these factors interact is crucial, not just for the health of the forest, but for the economic value of the wood it produces. If a tree looks healthy from the outside but is rotting inside, or if it grows slowly because the weather is too harsh, the quality of the timber drops, affecting the livelihoods of those who depend on it.

In a specific chestnut forest near the town of Lariano, a team of researchers set out to investigate these hidden challenges. They focused on a stand of trees that had been left to grow for 37 years, a period longer than the usual harvest cycle for this type of forest management. The team wanted to know if the wood at the base of these trees was deteriorating, what role the weather played in their growth, and whether the trees showed visible signs of stress from space. To find the answers, they combined several methods: they cut down trees to inspect the wood, measured the rings inside the trunks to see how fast the trees grew year by year, watched the trees' leaves and buds in the field, and even looked at the forest through satellite images.

The investigation began with a look at the wood itself. After the trees were felled, the researchers examined the base of the trunks, the part that sits closest to the ground. They found that some of the wood was discolored, turning a dark brown, and in some cases, it was actually rotting. This decay was caused by a fungus that attacks the roots and the lower stem. When these trees were taken to a sawmill to be processed, the workers had to cut off the damaged bottom sections. On average, they had to remove about 0.87 meters of wood from the base of each affected tree. While this might sound like a lot, the total volume of wood thrown away was actually quite small, representing only about 2.4 percent of the entire harvest. This suggests that while the problem exists, it has not yet caused a massive loss of usable timber. Interestingly, the researchers noticed that this rot was not limited to the large, single trees left standing in the forest; it was also found in the smaller shoots that sprout from the stumps of cut trees. This was a new finding, as previous studies in the area had mostly focused on the larger trees.

To understand why the trees were growing the way they were, the scientists turned to dendrochronology, the study of tree rings. By measuring the width of the rings in the wood, they could see a history of the tree's life. They found that the trees grew very fast when they were young, a typical trait for chestnuts that have the energy reserves of a large root system to draw from. However, the rings told a story of struggle during specific years. The trees grew very little during 2017 and 2023, which were exceptionally hot and dry years. The data showed a clear link between the amount of rain in August and how much the trees grew that year. When August was dry, the trees grew less. This indicates that even though the trees have deep roots, they are still very sensitive to water shortages during the late summer. The study also looked at the impact of the Asian chestnut gall wasp, an invasive insect that appeared in the region around 2008. The tree rings showed a sharp drop in growth when the wasp infestation peaked, followed by a recovery a few years later, likely because a natural enemy of the wasp was introduced to control it.

The researchers also kept a close eye on the trees' leaves and buds, watching how they developed from winter dormancy to full summer growth. They found that the wood inside the tree started to form new cells before the leaves had fully opened. This means the tree begins its work on building its trunk while it is still waking up from winter, a process that is triggered by rising temperatures in early spring. By June, the wood formation was well underway, and the leaves were fully expanded. This timing helps scientists understand exactly when the tree is most vulnerable to weather changes.

Finally, the team looked at the forest from above using satellite images. They compared pictures taken in June 2024 and June 2025 to see if the canopy looked different, which would indicate widespread sickness or death. Surprisingly, the satellite images did not show any obvious signs that the forest was in trouble. The trees looked green and healthy from space. However, the researchers noted that this does not mean everything is fine. They did spot a few dead trees standing in the forest, likely victims of the severe droughts of the past. The lack of a clear signal in the satellite images suggests that the stress these trees are feeling is subtle and internal, not yet visible as a general browning of the forest. It is like looking at a person who feels unwell but still appears healthy on the outside; the problem is happening beneath the surface.

The study concludes that while the chestnut trees in this area are showing some signs of stress, they are currently holding their own. The rot at the base of the trees is present but not yet devastating to the timber supply. The trees are resilient, able to bounce back from pest attacks and buffer short-term weather shocks thanks to their large root systems. However, the researchers warn that this resilience has limits. The forest is older than usual, and the trees are facing increasingly frequent and intense heatwaves and droughts. If the dry spells in late summer continue to get worse, or if the trees are left to grow too old without proper management, their ability to recover could fade. The findings suggest that forest managers need to be proactive, perhaps by thinning the trees to reduce competition for water or by harvesting them at the right time to ensure the wood remains high quality. For now, the chestnut forests of central Italy are a mix of resilience and hidden vulnerability, a reminder that even the strongest trees need careful attention in a changing world.