Assessing Biodiversity Associated with Four Monumental Trees in Madrid Region (Spain)

Abstract Background A tree is supposed to be an ecosystem in itself by storing and supporting a large number of organisms who live, feed, nest, take shelter, or interact with it. However, there are no full diversity studies within a single tree. Monumental trees are suitable field-based laboratories to explore niche biodiversity richness as a holobiont. Methods Four ancient trees from different genera ( Populus , Pinus , Quercus , and Platanus ) were selected in the Madrid region (Spain) to analyze their species richness. We used field and molecular techniques during a single year (April to November). Results About 300 taxa were found in each tree, including vertebrates, invertebrates, plants, fungi, bryophytes, lichens, bacteria, and myxomycetes with some chorological novelties. The ecological roles of the organisms found were explored. Conclusions The high biodiversity found in these 4 trees is a compelling argument to consider old trees as a supporting ecosystem. Pruning and access to trees should be carefully considered to preserve ecological niches and therefore associated biodiversity.