Original Paper Journal of Forest Science, 65, 2019 (7): 272–282 https://doi.org/10.17221/45/2019-JFS Impact of long and short-term conservation periods on structure of English yew (Taxus baccata L.) in Arasbaran forests, Iran Sajad Ghanbari1*, Kiomars Sefidi2, Matthew M. Aghai3 1Department of Forestry, Ahar Faculty of Agriculture and Natural Resources, University of Tabriz, Iran 2Department of of Natural Resources, Faculty of Agriculture and Natural Resources Technology, University of Mohaghegh Ardabili, Ardabil, Iran 3Center for Sustainable Forestry at Pack Forest, School of Environmental and Forest Science, University of Washington, United States *Corresponding author: [email protected] Citation: Ghanbari S., Sefidi K., Aghai M.M. (2019):Impact of long and short-term conservation periods on structure of English yew (Taxus baccata L.) in Arasbaran forests, Iran. J. For. Sci., 65: 272–282. Abstract: Yew (Taxus baccata L.) is one of the most important and threatened tree species in the Arasbaran region of northwestern Iran. To understand the natural stand structure of yew forests to inform forest management, we assessed the structural characteristics and composition of yew communities using the nearest neighbour and full callipering method at three sites with different conservation 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 tree species identity, diameter, height, and distance from reference to neighbour trees. To quantify the structural characteristics in areas of different conservation status, some indices were calculated including mingling, distance between reference tree and its nearest neighbouring trees, diameter and height differentiation, uniform angle, and Clark-Evans index. Results revealed that four species – hornbeam (68%), maple (8%), yew (7%), and oak (5.2%) – composed 88% of the tree species. The majority of trees had a short distance (2–3 m) between neighbours. The mean diameter differentiation index 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. We conclude that enclosing affects the yew stand structure, specifically in long-term periods of enclosure. Keywords: conservation-based management; diameter differentiation; forest structure; nearest neighbour Forest management plans aim to conserve the natu- The structure of forest stands can be defined using ral stand structure through a range of management three metrics: the shape, size, and spatial distribution and conservation activities. Forest structure is neces- of trees (Sefidi et al. 2015). There are different mea- sary in the formation and maintenance of many forest surement and computational methods for quantify- ecosystem functions. Investigating the pattern of spa- ing the structural indices of the stand. The study of tial structure can inform about ecological and forest- stand structure using the nearest neighbour indica- ry issues (Karimi et al. 2012). High species diversity tor is one of the most suitable methods (Nouri et al. and ecological stability of a stand are often related to 2015; Pommerening 2002). The nearest neighbour increased heterogeneity in the horizontal and vertical indicators are used to quantify the distance between a stand structure (Pommerening 2002). Silvicultural reference tree of a target species in relation to neigh- operations can help to improve the stand structure bouring trees. These indicators are accurate, low cost, and sustainability, and maintain species diversity in a easy to measure, and are sufficient to describe forest stand (Pommerening 2002). stands (Nouri et al. 2015; Sefidi et al. 2015). 272 Journal of Forest Science, 65, 2019 (7): 272–282 Original Paper https://doi.org/10.17221/45/2019-JFS Arasbaran broadleaved forests, found in north- order to develop prescriptive management method- western Iran, have an outstanding conservation ologies, a good understanding of the original forest value because of their high levels of biodiversity (Sa- stand structure is necessary. Therefore, the main aim gheb-Talebi et al. 2014). More than half of these of this study was to understand the structural charac- forests were designated as a UNESCO biosphere teristics and composition of yew forest communities reserve in 1976. Yew, an endangered, slow-growing, in Arasbaran forests by assessing the distance by the long-lived species (e.g. trees up to 1,500 years of age neighbour method and tree diameters of trees across have been reported) is one of the key tree species three sites. This research highlights the implications found in Arasbaran forests. As a shade tolerant spe- of the short- and long-term use of forest enclosures cies, yews occur in the understorey of humid forest for the stand structure of these forests. (Yazdani et al. 2005; Dhar et al. 2007). While they are able to tolerate low light conditions, higher light conditions can facilitate their better growth (Do- MATERiaL AND METHODS browolska et al. 2017). To better manage yew stands, an understanding of Study area the natural stand structure of this species in forests is critical. In the Hyrcanian region of Iran, Esmail- Three sites in the Ilghanachay and Horand water- zadeh and Hosseini (2007) described yew com- sheds of Arasbaran, Iran, where yew is naturally distrib- munities that are co-dominated by European (Car- uted were selected for this study. Across all three sites, pinus betulus) and Oriental hornbeam (Carpinus yew distribution ranges from approximately 800 to orientalis). In Arasbaran forests yew can also occur 1,600 m above sea level (Ebady, Omidvar 2011). The in stands with oak (Quercus) and maple (Acer) spe- average annual rainfall is between 300–500 mm and cies (Ghanbari Sharafeh et al. 2010). In the past, average temperature varies from 5°C to 14°C at differ- yew had been removed from these forests. There has ent altitudes (Sagheb-Talebi et al. 2004). been regeneration of yew since then, estimated at The three sites differed in conservation back- 520 saplings per hectare, and these seedlings show ground and short- and long-term enclosure peri- high vitality (Ghanbari Sharafeh et al. 2010). ods (Table 1; Ebady, Omidvar 2011; Ghanbari et The structure of yew forests have been investi- al. 2010). Although all three areas were protected, gated throughout the world, using different indices they differed in access and protection status: Kala- (Dhar et al. 2006; Ruprecht et al. 2010). The vari- leh (SKA) site and Vaygan site (SVA) were protected ation of habitat conditions has led to differences 42 years ago, and experienced a low human impact in various structural indices such as diameter and due to their distance from the village. The third site, height differentiation, mingling, and vitality. The Kuran (SKU), was protected eight years ago and is spatial pattern of tree species has been studied by easily accessible by rural communities because of its the uniform angle index, the mingling index, and proximity to the village. the differentiation index in beech forests of Den- mark. In the Hyrcanian forests Golbaian et al. Sampling method and data analysis (2016) found that the diameter distribution curve of yew trees was composed of even-aged stand with After determining the distribution area of this spe- a two-layer structure. In these stands, yew trees cies at all three sites, three one-hectare sample plots reached a maximum height of 30 m, a maximum from each site, for a total of nine hectares, were se- diameter of 2 m, and accounted for 100 m3·ha–1 lected and inventoried (Akhavan et al. 2012). The stand volume. inventory was done in each sample plot using two Interest in yew conservation has been prevalent methods: full callipering and nearest neighbour throughout Europe in recent years (Devaney et (Wadt et al. 2005). For the full callipering method, al. 2014; Casals et al. 2015; Dobrowolska et al. we measured tree characteristics (at 1.3 m height, di- 2017). Conservation-based management practices ameter at breast height (DBH) ≥ 7.5 cm) such as type like selective stand thinning to reduce the basal area of species, tree height with DBH ≥ 7.5 cm, distance of other species is one approach that may be effec- and azimuth of each tree from the reference point, tive at increasing yew prevalence throughout forest DBH, and average crown diameter. Distance and azi- systems (Dobrowolska et al. 2017). However, in muth of each tree from the previous tree (as a refer- 273 Original Paper Journal of Forest Science, 65, 2019 (7): 272–282 https://doi.org/10.17221/45/2019-JFS Table 1. Geographic position and characteristics of studied sites in Arasbaran forests, Iran (site names are defined as: SKA – Kalaleh, SKU – Kuran, SVA – Vaygan Conservation history Site Latitude/longitude Dominant tree species Forest origin and distance from village SKA 38°56'14''N, 46°45'30''E 42 years (< 1 km) hornbeam, oak, yew coppice with standards SKU 38°56'41''N, 47°26'19''E 8 years (< 1 km) oak, hornbeam, yew coppice SVA 38°55'22''N, 46°44'57''E 42 years (> 1 km) hornbeam, yew coppice with standards ence point for the next tree) were recorded. Distances index (CE) has different values. The value of CE = 1 and azimuths were later converted to the Cartesian indicates random distribution of trees, CE > 1 – regu- coordinates (X, Y). This coordinate was added to the lar and CE < 1 – clustering of individuals in the pop- coordinate of the first tree (as a reference tree). All of ulation (Szmyt, Korzeniewicz 2014). Unlike the the trees had a UTM coordinate system (Akhavan et CE index, uniform angle index is a single tree vari- al.