Why unmanaged forests are crucial for understanding long-term forest dynamics


Yannek Käber discusses his recent article: Sheltered or suppressed? Tree regeneration in unmanaged European forests. Find out how the intricate relationships between tree species, competition, and stress responses are vital for devising effective conservation and management strategies in the face of climate change:

Logo of the EuFoRIa Network

Forest regeneration is a complex process influenced by a multitude of factors, making it challenging to understand and study comprehensively. Many conditions must be met for the initial establishment of forest regeneration, such as successful seed production and dispersal, as well as appropriate climate and soil conditions. However, this is only the first step, the completion of this process can span several decades. To gain meaningful insights into these dynamics, researchers need extensive data covering large temporal and spatial scales. This is where the European Forest Research Initiative (EuFoRIa) steps in, aiming to unravel the processes of natural forest ecosystems on a large scale. Here we delve into a study conducted by the EuFoRIa network, focusing on tree regeneration dynamics in unmanaged forests of Europe.

Our study on tree regeneration dynamics “Sheltered or suppressed? Tree regeneration in unmanaged European forests” is the result of several generations of scientists meticulously measuring trees in forest reserves across Europe. What began as individual monitoring projects has now evolved into a collaborative effort, utilising the full potential of analysing these vast observations as a group. The EuFoRIa network gathered a collection of over 1 million tree measurements from more than 6000 forest inventory plots in 299 forest reserves. These reserves have remained unmanaged for an extended period, some with no known history of human influence, an uncommon feature for European forests. Remarkably, certain time series date back over a century, as in the case of Białowieża National Park.

Insights into forest regeneration dynamics

The study has revealed fascinating findings regarding changes in tree species composition along environmental gradients. Patterns of forest regeneration are driven by a complex interplay of species properties, forest density, disturbances, and climate:

Quantification of competition with the example of Abies alba showing tree recruitment per ha and 10 years (N.recr) for high stand density (highLAI; solid line) vs. low stand density (lowLAI; dashed line) along a gradient of seasonal site water balance. Competition is shown in red and positive interaction in blue

1. Competition prevails

In forest ecosystems, competition is the prevailing influence, and positive interactions between trees are less common than some ecological theories suggest. However, our study has shed light on how species properties and the type of stress, be it low temperature or drought, can modulate these patterns.

2. Different regeneration patterns under low temperature vs. drought

Notably, our study highlights differences in tree regeneration responses to various stresses. Trees appear to find more shelter and support from their peers under low-temperature stress compared to drought conditions. This phenomenon may be attributed to the fact that temperature is not a limited resource that leads to direct competition among trees. In contrast, under dry conditions, the scarcity of water triggers fierce competition, resulting in the potential suppression of smaller trees.

3. Species regeneration strategies

We gained insights into regeneration of tree species in dense forests that provide shelter for smaller trees during stressful climatic conditions. On the other hand, some tree species consistently face suppression by neighbouring trees and instead wait for disturbances to exploit new opportunities for growing fast, provided enough light becomes available. The diverse combinations of these strategies give rise to complex tree communities, unique to protected forest reserves.

Paving the way for future research

The EuFoRIa network remains committed to expanding their efforts in understanding natural forest dynamics and developing a basis for projecting forest development under the influence of climate change. Our study on forest regeneration serves as a starting point for their continued exploration and collaboration in future projects throughout Europe.

Unmanaged forest reserves provide invaluable insights into the long-term dynamics of forest ecosystems. Understanding the intricate relationships between tree species, competition, and stress responses is vital for devising effective conservation and management strategies in the face of climate change. By harnessing the collective efforts of researchers within the EuFoRIa network, this study serves as a stepping stone for a better understanding of the complexities of nature and the future of our forests.

Yannek Käber, ETH Zürich, Switzerland

Read the full article online: Sheltered or suppressed? Tree regeneration in unmanaged European forests

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