The Role of Monumental Trees in Carbon Storage
Authors: Oktan Ercan , Atar Neslihan 
Published: November 2023

Forest ecosystems are an important component of the global carbon cycle. Changes in the forest carbon cycle were determined by considering the biological structures at the leaf and stand level. However, there is no consensus on the nature of productivity at the individual tree scale. The mass growth rate of trees, and thus carbon deposition, differs depending on the size and age of the trees. In this study, the role of old monumental trees, which provide a wide variety of ecological functions and environmental benefits, in carbon storage was investigated. Because nowadays, the importance of monumental trees in carbon sequestration and protection of biological diversity in forest management has been better understood and accordingly, monumental old trees have become a significant research subject. Although monumental trees make up a small proportion of the number of stems in a given stand or vegetation, they contribute greatly to carbon biomass and help reduce global warming. Monument trees have special structures that allow long-term carbon accumulation to be sustained. Features such as slow growth, stress tolerances, mosaic structure, phenotypic plasticity, and rejuvenation potential allow for sustained age-related increases in growth, allowing for long-term carbon accumulation. In addition, changes in available resources due to global warming may be an indicator of increases in the biomass of these trees. However, these issues are still under discussion. The slow but continuous growth abilities of these trees in order to achieve longevity contribute significantly to the total carbon stock and wood production. In addition, when these trees are evaluated at the stand scale, they also make a significant contribution in terms of annual carbon sequestration. Monument trees are not just aging carbon stores. They are unique beings that can hold large amounts of carbon compared to young trees. Depending on the growth and development status, the carbon sequestration capacities show a high increase, although disproportionately. In some forest types, the largest and oldest trees continue to accumulate large amounts of biomass even though they are at the end of their natural life stages. On the other hand, there are many different opinions. These views are generally based on an assumption that older individuals have reduced biomass accumulation. Therefore, it is argued that younger trees can sequester more carbon. In line with the same view, there is a widespread opinion that carbon accumulation obtained by photosynthesis is lost by respiration due to stand development in old forests. This situation suggested that old forests are negligible as carbon sinks. There are studies showing that old forests can continue to accumulate carbon contrary to the long held view that they are carbon neutral. Numerous hypotheses have been developed to explain age- and size-related changes in biomass. In this context, the change in biomass; It has been attributed to the changing balance between photosynthesis and respiration, increased hydraulic resistance, decreased nutrient supply, differences in the access rates of resources necessary for growth, and genetic changes due to meristem age. However, these hypotheses expressing the change in growth may not be consistent as they vary depending on the species, vegetation period and growing environment. This situation falls short of explaining the physiological basis of the changes in the biomass size of these trees. The fact that the ecological role of these trees, which are rare in the world and disappear for various reasons, cannot be fulfilled by any other living thing, requires increasing the studies on these trees. In this context, when the average annual increase in diameter of a 2 m-diameter Oriental beech (Fagus orientalis) tree is assumed to be 0.5 cm, its annual increase is calculated as 0.182 m3. The fact that this value is not to be underestimated shows that these trees can be considered as carbon storage areas. Therefore, the role of monumental trees in carbon storage should be re-evaluated.