Age structure of Juniperus communis L. in the Iberian peninsula:
Conservation of remnant populations in Mediterranean mountains
Daniel Garcõ
Â
a*, Regino Zamora, Jose
Â
A. Ho
Â
dar, Jose
Â
M. Go
Â
mez
Departamento de Biologõ
Â
a Animal y Ecologõ
Â
a, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain
Received 10 November 1997; received in revised form 17 April 1998; accepted 29 April 1998
Abstract
We examined the demographic structure of Juniperus communis L. populations in the Mediterranean high mountains of southern
Spain in order to analyse its population viability. For this, we compared the age structure of these Mediterranean populations with
those of northern Spain (Atlantic), and, on a local scale, the populations of dierent habitats within the Sierra Nevada. The
populations from northern Spain showed age structures with high proportions at young stages. In contrast, the Mediterranean
populations proved to be dominated by adult and senescent individuals, except for the few habitats with higher water availability
during the summer, which have larger proportions of seedlings and juveniles. Dry habitats showed a lower seedling survival rate
than did wet ones, mainly due to summer drought. Both the dierence between Atlantic and Mediterranean categories, and the
dierence between habitats in Sierra Nevada re¯ect a serious limitation on recruitment of J. communis in Mediterranean mountains
due to climatic stress imposed by summer drought. The Mediterranean populations provide a clear example of remnant dynamics,
surviving for long periods due to great individual longevity which partially osets losses to unfavourable environmental conditions.
The low ability to recover after anthropic disturbances emphasizes the need for conservation of J. communis populations in south-
eastern Spain. # 1998 Elsevier Science Ltd. All rights reserved.
Keywords: Age structure; Iberian peninsula; Juniperus communis; Mediterranean high mountain; Remnant populations; Sierra Nevada
1. Introduction
The mountain areas of the Mediterranean Basin con-
tain the highest plant species diversity in Europe and
one of the greatest plant species richness on earth (Cox
and Moore, 1993; Castro-Parga et al., 1996; Cowling et
al., 1996). This diversity, related both to historical cau-
ses and to high local environmental heterogeneity, has
resulted in the coexistence of old taxa, from palaeo-
tropical and boreoalpine climates, with new taxa
appearing under the current Mediterranean climate
(Herrera, 1992; Cox and Moore, 1993; Greuter, 1994).
Consequently, Mediterranean mountains are equivalent
to ecological islands containing, in their coldest and
wettest habitats, species which were distributed in
southern Europe during the glacial periods, and which
currently are abundant in boreal areas (Bennett et al.,
1991). Juniper Juniperus communis L. (Cupressaceae), is
one of the gymnosperms with the widest distribution in
the Holarctic. It is a clear example of a plant species
abundant today in boreal and northern areas but iso-
lated in the mountain areas of Mediterranean Europe.
In the Iberian Peninsula, it covers a continuous area in
northern Spain but is increasingly fragmented south-
wards in mountain ranges (Castroviejo et al., 1986).
Although J. communis is still a common species in
Europe, its populations have suered serious regression
processes in certain insular areas (Ward, 1973, 1981;
Clifton et al., 1997). In the Mediterranean mountains,
such as the Sierra Nevada, juniper is a major species of
the xeroacanthic shrublands above the treeline (Vigo
and Ninot, 1987). These juniper shrublands have a high
ecological value, mainly in relation to their soil-retain-
ing ability, their associated endemic ¯ora and fauna,
and their traditional use as summer grazing areas
(Molero et al., 1992). Despite their ecological value, no
study has yet evaluated the conservation of juniper
populations in the Mediterranean area. The present
work was performed to determine the population viabi-
lity of juniper in the Spanish Mediterranean mountains,
in relation to the species status throughout the Iberian
BIOLOGICAL
CONSERVATION
Biological Conservation 87 (1999) 215±220
0006-3207/98/$Ðsee front matter # 1998 Elsevier Science Ltd. All rights reserved
PII: S0006-3207(98)00059-7
* Corresponding author. Fax: 0034-58-243238;
e-mail: dgarcia@ goliat.ugr.es