The study was conducted in the Ayllón Mountain Range, located at the eastern end of the Central System Range of the Iberian Peninsula, Spain. Topographic heterogeneity and altitudinal variations (from 1000m up to 2272m) act as climatic diversification factors, causing numerous microclimatic conditions where Atlantic species can grow. The survey was carried out on three yew groves: Arroyo de la Tejera (41.247ºN- 3.416ºO, Rio frío de Riaza municipality, Segovia province); Acebeda de Becerril (41.262ºN-3.371ºO, Riaza municipality, Segovia province); Arroyo del Ermito (41.146ºN-3.497ºO, El Cardoso de la Sierra municipality, Guadalajara province).

Localization and survey has taken 17 field work days between September 2017 and May 2018. At first, each population was characterized by the substrate type, altitude, orientation, dominant vegetation and companion woody species. Then, each tree was surveyed taking data of UTM coordinates (Garmin GPS-map 62st), height, trunk perimeter (circumference at breast height, 120cm) and sex. Less than 5cm high seedlings were excluded due to their high mortality rates. Finally, according to Fernández et al. (2015), individuals were classified in four age groups considering height and trunk perimeter: 1) AgeGroup1, Seedling: Lignified plants between 5cm and 150cm tall; 2) AgeGroup2, Juvenile: Trees taller than 150cm and with a trunk perimeter up to 50cm; 3) AgeGroup3, Adult: Trees with trunk perimeter above 50cm and less than 300cm 4) AgeGroup4, Old: Trees with trunk perimeters above 300 cm.

According to Serra (2007), Recruitment rate can be defined as (Equation 1):

“Arroyo de la Tejera” is a mountain creek which runs inside a north oriented Pyrenean oak forest and heath shrubs. The core yew grove is located between 1552m and 1562m of altitude, grown on siluric slates and quartzite. Woody companion species are: Quercus pyrenaica Willd., Juniperus communis L., Fagus sylvatica, Corylus avellana, Erica arborea L., Crataegus monogyna Jacq., Ilex aquifolium, Vaccinum myrtillus, Frangula alnus Mill., Sorbus aucuparia L., Fraxinus excelsior, Betula alba, Sorbus aria (L.) Crantz., Salix atrocinerea Brot., Cytisus scoparius (L.) Link., Arctostaphylos uva-ursi and Quercus petraea. In all, 171 yew trees were counted (Fig. 1), with a Recruitment rate of Rr = 0.93

“Acebeda de Becerril” yew grove is located at the altitudinal limit of a north orientated mixed deciduous forest, grown on siluric slates. The main specimens are located between 1711m and 1717m of altitude. Woody companion species are: Fraxinus excelsior, Quercus pyrenaica, Quercus petrea, Fagus sylvatica, Acer monspessulanum L., Sorbus aria, Sorbus aucuparia, Juniperus communis, Rhamnus alpines L., Crataegus monogyna, Rosa canina L., Erica australis L., Calluna vulgaris (L.) Hull, Arctostaphylos uva-ursi, Cistus laurifolius L., Corylus avellana, Vaccinium myrtillus.A total of 974 yew trees were counted (Fig. 2), with a Recruitment rate of Rr = 0.81

“Arroyo del Ermito” is a mountain creek which runs inside a Pyrenean oak forest. It grows on siluric gneiss and it is western orientated. Yew grove is located between 1485m and 1489m of altitude. Woody companion species are: Quercus pyrenaica, Juniperus communis, Erica arborea, Adenocarpus hispanicus (Lam.) Dc., Sambucus nigra L., Ilex aquifolium, Betula alba, Cytisus scoparius, Rosa sp, Fagus sylvatica, Salix atrocinerea, Salix caprea L..Altogether, 459 yew trees were counted (Fig. 3), with a Recruitment rate of Rr = 0.71

All three populations show high recruitment rates as seedling and juvenile trees are more numerous than adult and old ones,and thus, surveyed yew populations show regeneration dynamics (Serra, 2007). This vigorous natural regeneration seems to be related with the last decades reduction of human pressure, particularly of domestic herbivorous (López, 1982). Even so, feral browsing pressure was recorded in “Acebeda de Becerril” and “Arroyo del Ermito” groves, as yew is an evergreen species integrated in deciduous forest, its foliage is the main herbivorous resource during the winter (Serra, 2007). However, browsing pressure was not recorded in “Arroyo de la Tejera” grove because most seedlings and juvenile trees are covered by a heather shrub layer which acts as nurse plants, reducing herbivorous trampling and browsing (Cortes et al., 2000, Serra, 2007).

These results lead us to partially reconsider the relictic character assigned to the species in the Iberian Mediterranean Mountains (Arroyo et al., 2004). Actually, scattered yew population’s presence is conditioned by humidity and precipitation. But the image of dense monospecific yew forests in regression, leading to isolated yew groves or solitary trees (Serra, 2007), is refuted by our data, as we observe vigorous natural regeneration. Yew presence in the Iberian Mediterranean Mountains is associated with areas where specific topographic characteristicsfavor forest diversity, leading to mixed forest where yews are integrated. And, it is in these areas where conditions such as the presence of nurse plants facilitating seedlings growth or the presence of fleshy fruit species increasing seed dispersal birds (Serra, 2009), favor yew natural regeneration.

In conclusion, yew populations are vigorously naturally regenerating. This make us reconsider the relictic character assigned to the species in the Iberian Mediterranean Mountains. Finally, the study of the facilitating elements for yew regeneration should be deepened, as well as survey and mapping the yew populations of the Central Iberian Mountain Range, currently poorly studied.