Composition and structure of English yew forest stands (Taxus baccata L.) in different conservation systems of Arasbaran forests, Iran

One of the most important conservation actions that can be taken in disturbed forests is the development of enclosed areas that can substantially impact the structure and composition of vegetation. The main goal of forest management plans is to maintain the natural structure of stands. Yew is one of the most important and threatened tree species in the Arasbaran region in northwestern Iran.

In this research, we assessed the structural characteristics and composition of yew forest communities using the nearest neighbor and full callipering methods at three sites with different management histories. Within a one-hectare sampling area, tree species identity, diameter, height, and crown diameter were measured. In each of these sampling areas, 56 sample points were surveyed in a 25 m × 25 m grid for trees species identity, diameter, height, and distance from reference to neighbor trees. To quantify the structural characteristics in areas of different conservation status, some indices calculated including mingling, distance to neighbor, diameter and height differentiation, uniform angle, and Clark Evans.

The average height of yew trees at the long-term sites SKA and SVA was 5.1 and 4.8 m respectively. These trees were located in the lower layer. In the short-term site (SKU), however, yew trees (4.04 m) had approximately the same height as other trees (4.3 m). Results revealed that four species – hornbeam (68%), maple (8%), yew (7%), and oak (5.2%) composed 88% of tree species. The majority of trees had a low distance (2–3 m) between neighbors. Due to the high density of trees in the sites with a long-term conservation period (SKA and SVA), a low percentage of trees had mean distance more than 5 meters. Mean of distance to neighbor (Di) index for long-term and short-term sites were 3.8 and 5.14, respectively. The mean TDi for long-term and short-term conservation areas was 0.59 and 0.06, respectively. The uniform angle index showed that there was no class value 1 at all three sites. In the long-term enclosed area, Clark Evans index was 1.18. In short term-enclosed areas, it was less than 1 (0.82). At all sites, yew trees were in the least vital class.

Reducing tree density and basal area of other species will lend strength to yew trees in the studied sites. However, because yew trees need moderate light conditions, excessive decreases in the tree density can be detrimental. In order to optimize the management of forest resources, it is essential to get the correct information about the structure of forest stands. It is important to obtain enough information about the forest stand structure and changes in various indicators of stand to offer new approaches to forest management. The results of this research can show the conservation effects on yew stands in long-term and short-term conservation periods. It helps provide effective and useful conservation solutions.