Habitat trees are a crucial element in maintaining the biodiversity of forests. These trees, either standing or dead, provide microhabitats or ecological niches that are essential for a variety of species including vertebrates, invertebrates, plants, and fungi.

1. Habitat trees provide ecological niches, or microhabitats, that are vital for the survival of many forest species.
2. At least 25% of forest species depend on or benefit from habitat trees and deadwood.
3. Veteran, ancient, or monumental trees are especially important because of their age or size and the fact that they can provide habitat for many endangered species.
4. The ecological value of a tree increases with its age and habitat, trees with a diameter of over 70 cm are typically less abundant in managed forests than in unmanaged forests.
5. Microhabitats, such as cavities, cracks and loose bark, fruit-bodies of saproxylic fungi, and other microhabitats, are important for a variety of species including vertebrates and invertebrates, plants, and saproxylic fungi.
6. Changes in management practices in the 19th century led to a decline in the number of habitat trees and microhabitats in forests.
7. Habitat trees are often removed during tending and harvesting operations and are generally considered to have low economic value but high ecological value.
8. To conserve habitat trees, specific measures should be taken during forest operations, such as retaining at least 5-10 per hectare and selecting non-vigorous low quality trees or those with the potential to develop microhabitats.
9. Set-asides or old-growth islands can be used to protect complete forest stands and allow trees to complete their natural cycle, including senescence and decomposition.
10. Habitat trees play a vital role in maintaining important ecosystem functions, such as nutrient cycling, through their decay and incorporation into the forest soil.

Forests are vital ecosystems that provide numerous ecological, economic, and social benefits. Habitat trees, which are standing live or dead trees that provide ecological niches or microhabitats, are a crucial component of healthy forests and play a vital role in the conservation of forest biodiversity. Foresters, or forest engineers, are responsible for managing forests and ensuring that they are sustainably and responsibly managed. In order to effectively conserve habitat trees, it is important for forest engineers to consider their ecological value and integrate strategies for their protection into forest management plans. Ultimately, the conservation of habitat trees is essential for the long-term health and biodiversity of forests, and the role of forest engineers in this process is crucial.