Definitions according to the book Developmental Dynamics of Virgin Forest Reserves in the Czech Republic I (Tomáš Vrška et al.) Academia 2002:

Bent - Heavily bent stems, e.g. due to the slope displacement, etc.

Breakage - A still living tree with a part of the main stem missing. Its height is measured from 1.5 m upwards.

Burr - Any unnatural formation of tumorous, myomatic, etc. origin on the stem.

Dead standing tree - An entirely dead standing tree with the preserved main stem.

Five-stem tree - An individual with five stems.

Four-stem tree - An individual with four stems.

Lying stem - A lying main tree stem or its part without the root system. There are three stages of disintegration distinguished in the lying stems as follows:

• hard (the species is still recognizable, usually with bark and relatively healthy, hard wood);
• touchwood (the species usually still can be idetified, the wood is not compact along entire stem length; either the core or outer mantle (in trees that fell down healthy by for example wind and are in the contact with the soil environment) are rotting, falling rough bark);
• disintegrated (the wood at an advanced stage of rottening, the species cannot be identified, a kick into the stem results in stem breakage, often only just "little graves" with the patch vegetation).

Natural forest - A forest developed through natural processes but influenced by man in the past (especially by selective cutting and by grazing, not by planting or sowing). Its species composition and spatial structure usually correspond to the site conditions and might also differ at sporadic places, e.g. due to the spontaneous development under modified conditions (e.g. after some parts of the forests were stumped in the medieval times and then left to their further long-term spontaneous development).

Near-natural forest - A forest whose species composition usually corresponds to the site conditions but whose spatial structure is simpler than that of the original natural forest. These stands developed under the influence of man and their condition could have been deliberately achieved by man. The spontaneous development was being controlled for a long time and traces of this control are still visible (extraction of dead wood, logging, tending measures, etc.).

Original (virgin) forest - A forest which is - in a more free and more frequently used conception - more or less not influenced by man, in which the species composition and spatial structure correspond to the site conditions. The original forest can also be a stand which was influenced by man in the past but the measures did not result in the distortion of the natural developmental trajectory and the traces of intervention are for long time not recognizable - e.g. the selection cutting of individual trees more than a hundred years ago, the clearing of dead trees from the stand edges more than fifty years ago, etc.

Prop roots - are usually formed in Norway spruce on water-impacted sites at the regeneration on fallen stems which gradually rot out.

Stub - A dead standing tree with a missing part of the main stem. The stub is considered a stem reminder higher than 1.5 m.

Stump - A stem base part with roots, left after the tree fall, max. height 1.5 m. In virgin forest stands with some tree fellings in the past, there are cutting surfaces to be seen on stumps at some places.

Triple-stem tree - An individual with three stems.

Twin-stem tree - An individual with two stems.

Virgin forest - A general definition for stands of the original, natural and near-natural forest, whose common denominator is the site-corresponding species composition, at least a partly differentiated stand structure and the higher percentage of the dead wood than it is usual in the current commercial forest.

Windthrow - A fallen uprooted tree. The stages of disintegration are identical as in the Lying stems.