Effects of Thinning Intensity on Wild Berry Cover, Height, and Yield in Scots Pine Stands
In Latvian Scots pine stands, moderate thinning significantly enhances lingonberry cover and yield within a few years without altering soil chemistry or affecting bilberry production, indicating that distinct silvicultural strategies are needed to optimize these two non-timber forest products.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
In the forests of northern and eastern Europe, the ground is often carpeted with small, hardy shrubs that produce wild berries. Two of the most common are the bilberry, a dark blue fruit, and the lingonberry, a bright red one. These plants are not just snacks for hikers; they are a vital part of the local economy and culture, harvested by millions of people for food and income. For decades, forest managers have focused primarily on growing timber, cutting trees to make wood for construction and paper. However, modern forest policy is shifting toward a more balanced approach that values the forest for many things at once, including the berries that grow beneath the trees. A central question for foresters is how the way they manage the trees affects the berries. Specifically, does cutting down some trees to let more light in help the berry bushes grow, or does it hurt them? The answer is not simple, because different berry species have different needs, and the effects of cutting trees can take years to show up.
Researchers in Latvia set out to find the answer by studying twenty different stands of Scots pine trees. They wanted to see how the intensity of thinning—the process of removing some trees to reduce crowding—changed the amount of berry bushes on the forest floor, how tall they grew, and how many berries they produced. To do this, they established a long-term experiment. In each forest stand, they created three different groups of plots. One group was left completely untouched to serve as a control. A second group was thinned moderately, leaving a moderate amount of tree density. The third group was thinned heavily, removing many more trees to create a very open canopy. The researchers then visited these plots every year for four years, from 2019 to 2022, to measure the berries. They counted how much ground the bushes covered, measured their height, and carefully counted and weighed the berries to estimate the total harvest per hectare. They also dug up soil samples to check if the cutting of trees had changed the chemistry of the ground, such as its acidity or nutrient levels.
The results revealed a striking difference between the two types of berries. The lingonberry responded clearly and positively to the heavy thinning. In the plots where the most trees were removed, the lingonberry bushes began to cover more ground starting in the third year of the study. More importantly, the amount of berries produced increased significantly in these heavily thinned areas compared to the uncut forests. The researchers found that the relationship between how much ground the bushes covered and how many berries they produced also changed; in the open plots, the bushes seemed to produce more fruit per unit of ground covered. This suggests that the extra sunlight allowed the individual plants to fruit more heavily, not just that there were more plants.
In contrast, the bilberry showed no significant reaction to the thinning. Even though the data hinted that bilberry might be growing slightly better in the thinned areas, the differences were not large enough to be considered real or reliable. The bilberry bushes did not grow taller, cover more ground, or produce more berries in the thinned plots compared to the uncut ones. This lack of response happened even though the two species often grow side by side. The study also found that the thinning did not change the soil chemistry in any measurable way. The acidity and nutrient levels of the soil remained the same across all the different groups, regardless of how many trees were cut. This indicates that the changes in the berries were driven by the amount of light reaching the forest floor, not by changes in the soil itself.
The study also highlighted the importance of timing and weather. In 2021, a year with a very cold winter and a wet spring, the berry harvest dropped dramatically across all the plots, regardless of how many trees were cut. This suggests that weather conditions can have a massive impact on berry production, sometimes overwhelming the effects of forest management. However, when the weather was normal, the pattern was clear: heavy thinning helped the lingonberry thrive, while the bilberry remained largely unaffected.
These findings offer a practical guide for forest managers who want to support both timber and berry production. If the goal is to increase the harvest of lingonberries, cutting more trees to create an open canopy is an effective strategy that works within just a few years. However, managers cannot assume that the same treatment will boost bilberry production in the same timeframe. Because the two species react so differently, they cannot be treated as a single group when planning forest management. To truly understand how to support both, foresters will need to continue watching these forests over a longer period and perhaps try different levels of thinning, but for now, the evidence shows that what is good for the red berry is not necessarily good for the blue one.
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