R. B. Elias T. Resendes E. Dias




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Contrasting phenology and female cone characteristics of the two Macaronesian island endemic cedars (Juniperus cedrus and J. brevifolia)

Beatriz Rumeu Æ Manuel Nogales Æ Rui B. Elias Æ

David P. Padilla Æ Tiago Resendes Æ Airam Rodr´ıguez Æ

Francisco Valde´s Æ Eduardo Dias




Abstract Phenology and female cone characteristics of the two endemic cedars (Juniperus cedrus and J. brevifo- lia) from the Macaronesian islands were studied. Despite their closely taxonomic affinity and their evolution under insular conditions, different trends were recorded. Mature J. cedrus female cones were present throughout the year, while those from J. brevifolia were only present in summer and autumn. J. cedrus female cone size was significantly larger than that of J. brevifolia, a trend consistent with the presence of larger vertebrates (lizards and birds) in the Canary Islands. However, water content was four times higher in J. brevifolia female cones, which can be related with the higher rainfall existing in the Azores. J. cedrus has two or three seeds per cone, whereas J. brevifolia

Communicated by R. Matyssek.
B. Rumeu (&) M. Nogales D. P. Padilla A. Rodr´ıguez Island Ecology and Evolution Research Group (IPNA-CSIC), C/Astrof´ısico Francisco Sa´nchez no 3, 38206 La Laguna, Tenerife, Canary Islands, Spain

e-mail: brumeu@ipna.csic.es


R. B. Elias T. Resendes E. Dias

Departamento de Cieˆncias Agra´rias, Centro do Clima, Meteorolog´ıa e Mudanc¸as Globais (C-CMMG)/Centro de

Investigac¸a˜o em Tecnologias Agra´rias dos Ac¸ores (CITAA), Universidade dos Ac¸ores, Angra do Hero´ısmo, Azores, Portugal
F. Valde´s

Applied Plant Biology Group, Plant Biology Department, University of La Laguna, La Laguna, Tenerife,

Canary Islands, Spain
Present Address:

A. Rodr´ıguez

Department of Evolutionary Ecology, Estacio´ n Biolo´ gica de Don˜ ana (CSIC),

Avda. Ame´rico Vespucio s/n, 41092 Seville, Spain

frequently had three. Seeds from J. cedrus were clearly larger and heavier, coinciding with the female cone size trend. However, tetrazolium tests revealed higher viability values in J. brevifolia. The relatively low percentage of filled seeds in J. cedrus could be a consequence of the climatic stress and limits to pollination due to fragmented populations as described for other Juniperus species. In summary, our results reveal that some environmental fac- tors such as the harsh conditions, high population frag- mentation and the dependence on large dispersers have compromised the fitness of J. cedrus in the Canary Islands.
Keywords Juniperus cedrus Juniperus brevifolia

Female cones Seasonality Island plants

Plant conservation

Introduction


The genus Juniperus (Cupressaceae) is the second largest of the conifers, with only Pinus L. containing more species (Arista et al. 1997). It consists of approximately 67 species and 28 varieties, and is divided into three sections: Cary- ocedrus (one species, Juniperus drupacea Labill.); Juni- perus (=Oxycedrus, with 12 species) and Sabina (with the remaining, 55 species approximately) (Adams 2008). All these species grow in the northern hemisphere except for J. procera Hochst. Ex. Endl., which grows southward along the Rift Mountains in east Africa into the southern hemi- sphere (Adams et al. 1993). J. cedrus Webb and Berthel. and J. brevifolia (Seub) Antoine are the two species from the Juniperus section represented in the Macaronesian Islands. Genetic analyses using RAPDs (Adams 2000) show a close proximity of J. cedrus and J. brevifolia, clearly separated from the other species from the section




Juniperus. They are both endangered (IUCN 2008), espe- cially J. cedrus, due to the drastic past deforestation. This species is endemic to Madeira and Canary Islands, being present in La Palma, La Gomera, Tenerife and Gran Canaria (Izquierdo et al. 2004). On the other hand, J. brevifolia is endemic to the Azores archipelago, where it is distributed in all the islands except Graciosa (Sjo¨ gren

2001; Adams 2008; Elias 2007); these two species are dioecious. As the rest of the species of the genus Juniperus, they produce fleshy female cones that act functionally as fleshy angiospermic fruits (Herrera 1992). In the case of J. cedrus, these cones are reddish in colour when mature, while in J. brevifolia the cones are copper (Adams 2008). Both cedars have evolved in two oceanic archipelagos under rather different ecological conditions, such as geo- graphical location, distance from mainland, geological age, climate, altitudes, soils or types of frugivore interactions. At this respect, female cones of J. cedrus have been interacting with large seed dispersal agents, such as the Raven Corvus corax (Nogales et al. 1999) and probably by different species of endemic giant lizards (genus Gallotia) present in the Canaries. Nowadays, in this archipelago, J. cedrus female cones are consumed by medium-sized lizards such us G. galloti (snout vent length: 10.7–14.5 cm; Herna´ndez et al. 2000) in Tenerife (Valido 1999), while all the dispersers known in the Azores are presumably smaller (warblers, Sylvia atricapilla) and medium-sized birds (blackbirds, Turdus merula).

Lastly, despite the delicate conservation status of these cedars (especially J. cedrus), little knowledge is available about certain ecological features. Therefore, the main aim of this contribution is to present the first data on some basic aspects of their reproductive biology, such as phenology and female cone characteristics, which may be of particular use for conservation purposes.

Methods
Study sites


The Canary Islands lie between 27° and 29°N and 13°–

18°W and consist of seven main volcanic islands. This archipelago is close to the northwest African coast, with only 96 km separating Fuerteventura and West-Sahara. The islands are of different ages, Fuerteventura (22 Ma) being the oldest one, and El Hierro (1.2 Ma) the most recent; Tenerife, the largest of the islands, emerged 12 Ma ago and is about 2,058 km2 in size (Carracedo and Day 2002). The study of J. cedrus was carried out in ‘‘Riscos de La Fort- aleza’’ (2,170 m a.s.l.), a craggy geological formation located in ‘‘El Teide’’ National Park in Tenerife. The area is influenced by a typical high-mountain climate, with great

thermal oscillations throughout the year (differences of about 10°C between maximum and minimum monthly average temperatures) and a mean annual temperature of

10.7°C. The site receives an annual precipitation of about

367.5 mm, most of which falls during the winter months (Bustos and Delgado 2004). The vegetation consists prin- cipally of endemic plants (e.g. Spartocytisus supranubius, Pterocephalus lasiospermus, Adenocarpus viscosus, etc.), many of them found only in this region of Tenerife (Wildpret de la Torre and Mart´ın Osorio 2004). In Riscos de La Fortaleza, we can distinguish two different areas or sub- populations where J. cedrus grows: (1) smaller cedar plants located at the top of the crag (hereafter ‘‘crag-top’’), which is an area exposed to relatively frequent NW winds and scarce soil development and (2) larger cedar plants placed at the base of the crag (hereafter ‘‘crag-base’’), which is more sheltered from the wind and presents better soil presence. These two areas were selected to evaluate the influence of the habitat conditions in the parameters studied.

The Azores Archipelago is located in the North Atlantic, between 36°–40°N and 24°–32°W. It is made up of nine main islands and some small islets aligned on a WNW–ESE direction. The distance between the Azores (Sa˜o Miguel) and the mainland is about 1,584 km, calculated from Cabo da Roca (the most westerly point of the European continent). The islands are divided into three groups: (1) western: Corvo and Flores; (2) central: Faial, Pico, Graciosa, Sa˜o Jorge and Terceira and (3) eastern: Sa˜o Miguel and Santa Mar´ıa, plus the Formigas islets (Borges and Brown 1999). They are all volcanic islands of recent origin; Santa Mar´ıa being the oldest island (6 Ma) and Pico the youngest (0.25 Ma). The study of J. brevifolia cones was carried out in Terceira, which has an area of 402.2 km2 and an estimated geological age of 3.52 Ma (Franc¸a et al. 2003). Although we studied one of the main populations of J. cedrus in Tenerife, whose distribution is rather limited, in Terceira it is still possible to find some well-preserved and widely distributed J. brevi- folia populations (Dias et al. 2004; Elias and Dias 2004,

2009). For this reason, the study was carried out at three different sites in the central and western parts of the island. The three populations studied were ‘‘Malha Grande’’, ‘‘Pico Alto’’ and ‘‘Santa Ba´rbara’’, which are located at 505, 685 and 974 m a.s.l., respectively. At these sites the mean annual temperatures are 14.0, 13.1 and 11.1°C and total annual rainfall is 2,168, 2,387 and 3,078 mm, respectively. The rainfall occurs mainly in autumn and winter (Elias 2007). Vegetation in Malha Grande is of a pioneer scrub dominated by J. brevifolia and Erica azorica; in Pico Alto the vege- tation is mainly composed of Juniperus–Laurus mature forests, dominated by J. brevifolia, Laurus azorica and Ilex azorica; Santa Ba´rbara is located at the top of a volcano of the same name, whose vegetation is dominated by J. brev- ifolia and Calluna vulgaris shrubs.



Table 1 Population structure of Juniperus cedrus and J. brevifolia in the studied localities


Island

Locality

Sex-ratio #:$

Ø max. of the

Max. height (m)

Population

Estimated age










crown (m)

Mean ± SD



Mean ± SD

size (no. of

individuals)



(adults:immat.)

Tenerife (Canaries) Riscos de La

Fortaleza

1:1 (n = 94) 4.21 ± 2.53 (n = 96) 2.91 ± 1.33 (n = 96) &170 1:0.75 (n = 170)


Terceira (Azores)

Malha Grande

1:0.67 (n = 15)

2.16 ± 0.96 (n = 15)

1.50 ± 0.42 (n = 15)

[500

0.85:1 (n = 41)

Terceira (Azores)

Pico Alto

1:0.89 (n = 15)

2.83 ± 1.04 (n = 15)

3.00 ± 0.75 (n = 15)

[500

1:0.43 (n = 40)

Terceira (Azores)

Santa Ba´rbara

1:0.89 (n = 15)

0.61 ± 0.28 (n = 15)

0.37 ± 0.16 (n = 15)

[500

1:0.69 (n = 99)




The main parameters of the different population struc- ture in the four localities studied are showed in Table 1. In general, trees of all these populations presented an external healthy appearance. However, only in ‘‘Riscos de la Fort- aleza’’ several individuals (3%) showed a low vitality (reduced lushness and lighter colour of the crown).
Procedures
To study the female cone phenology, 20 female plants of J. cedrus were selected from the population at Riscos de La Fortaleza. Ten of them were at the crag-top and ten at crag-base. Ten branches of each plant were marked with different coloured tags. For two consecutive years (between 2004 and 2006 in the same plants), ripe and unripe female cones were counted seasonally per branch. With regard to J. brevifolia on Terceira, where three pop- ulations were studied, the methodology used for the female cone phenology was slightly modified. In this case, 15 female plants were selected (between 2003 and 2004) from each of the three populations. However, the main param- eter (% of female cones of different types) was calculated for the two species in the four different seasons, which permitted different comparisons to be made. Female cones of the two endemic Macaronesian cedars mature in the second year (Adams 2008). Thus, at the same time, a sole individual could present small unripe receptive or aborted female cones, 1- or 2-year large unripe female cones, and

2-year fleshy mature cones. As this succession is complex, we focused the phenology follow-up on the presence of large female cones and especially the proportion of mature ones, due to the importance of their availability to seed dispersers. Since there is an obvious difference in cone size between the two species (smaller female cones in J. brevifolia), in J. cedrus, we considered female cones C8 mm diameter as large and \8 mm as small. In J. brevifolia, cones C6 mm were scored as large and\6 mm as small.

To characterise mature cones, 180 female cones were taken from the whole population of Riscos de la Fortaleza in Tenerife. These samples were collected from the same plants as in the female cone phenology. In 90 of the female

cones, we measured the diameter and water content, weighing them wet and then drying at 60°C in a heater until a constant weight was reached. The remaining 90 female cones were weighed and their seeds removed and counted per cone. From these seeds, 180 were randomly selected, measured for length and width, and weighed independently. In Terceira, 60 female cones were collected from each population, and the same procedure was followed.

To assess seed viability, a total of 40 female plants were selected, 20 at Riscos de la Fortaleza (Tenerife) and 20 at Malha Grande (Terceira). Twenty female cones from each plant were collected and all their seeds extracted, main- taining the identity of their mother plant to evaluate potential differences in seed viability among the plants. More than 800 seeds of each species were carefully opened using a small bench vice to determine the morphological state of each embryo (healthy: filled seeds, or unhealthy: empty or with a damaged embryo). These seeds were also measured and weighed to compare biometric data and viability. After they were opened, damaged embryos were directly considered as non-viable. Embryos that appeared healthy were immersed for 24 h in water and then for 6 h in gibberellic acid (GA3, 0.16 mg/ml; gibberellic acid treatment was used to enhance red stain patterns in viable embryos, allowing us to identified non-viable embryos from apparently healthy embryos). This process was fol- lowed to avoid false results in the viability test, because juniper embryos exhibit physiological dormancy, as they are unable to develop a radicle due to an inhibition mechanism (Baskin and Baskin 1998). Next, embryos were cut and immersed in 2,3,5-triphenyl-tetrazolium chloride solution (hereafter TTC) diluted to 0.1% for 24 h in the dark, and at room temperature (Scharpf 1970; Tanaka

1984). The TTC used was ‘‘TTC sterile solution 1%, Scharlau Microbiology’’. In this method, living cells stain red as the tetrazolium is reduced by dehydrogenase enzymes to form a stable red triphenyl formazan, which is insoluble in water (Tanaka 1984). To avoid any physical dormancy caused by the seminal cover (Cantos et al. 1998), the embryos were tested in a completely bare condition. To establish the viability state of the embryos, a total of 15 different patterns of red stains were considered, which were






then reduced to three categories: non-viable, potentially viable and viable. This method was very conservative. An embryo was only considered to be viable when nearly all the surface was stained red. Potentially viable embryos were those partially stained and always in areas critical for germination such as shoots and root apices (Donald and Cooke 1997; West and Harada 1993).
Statistical analyses
Categorical analyses (Likelihood ratio tests) were per- formed to compare number of ripe female cones in the two endemic cedar species and among the different seasons. This analysis was also used when comparisons in seed viability were carried out. Student and Mann–Whitney tests, for parametric and non-parametric data, respectively, were applied when the different traits were compared between the two cedars. All analyses were performed using the SPSS statistical package (version 14.0).

Results
Female cones phenology


Juniperus cedrus mature cones were present throughout all seasons (Fig. 1). Among the female cones, unripe ones were more abundant than ripe ones throughout the year (G3 = 100.34, P \ 0.001). However, ripe female cones were mainly present in summer, autumn and winter; few ripe cones were present in the spring (only 15.7% of the whole ripening process, P \ 0.001 for all comparisons). When the two main sub-populations from El Teide were compared, large mature cones were more abundant at the crag-base than at the crag-top (G1 = 205.42, P \ 0.001), although the seasonal pattern was rather similar to the whole population.

The female cone phenology of J. brevifolia showed a markedly seasonal pattern with respect to J. cedrus. Ripe



100
80
60
40
20
0

winter spring summer autumn
J. cedrus-unripe J. cedrus-ripe

J. brevifolia-unripe J. brevifolia-ripe


Fig. 1 Female cone phenology of Juniperus cedrus in El Teide National Park (Tenerife, Canary Islands), and J. brevifolia in three localities of Terceira (Azores)

female cones totally disappeared during winter and spring; they were only present during summer and autumn, being significantly more abundant in the summer (G1 = 174.39, P \ 0.001) (Fig. 1). In contrast, unripe female cones were more abundant in winter (likelihood ratio tests, P \ 0.001 for all comparisons). Considering all female cones, unripe ones were present throughout the year and they were highly abundant during winter and spring (likelihood ratio tests, P \ 0.001 for all comparisons).

Female cones and seed traits
There were significant differences neither in female cone and seed sizes, nor in pulp water content among the three J. brevifolia populations studied in Terceira (P [ 0.05 for all comparisons). Therefore, data analysis of these three populations was merged.

Female cones of J. cedrus were 21.4% larger than those of J. brevifolia (Table 2), showing a significantly greater diameter (t178 = -12.13, P \ 0.001) and weight (Z =

-3.44, P = 0.001). However, water content was four times

larger in J. brevifolia female cones than in those of J. cedrus (Z = -11.59, P \ 0.001). Comparing the two areas con- sidered in Riscos de La Fortaleza (El Teide), female cones at the crag-base were significantly larger than those at the crag- top (U = 23.0, P = 0.041). When seeds from the two sub- populations were compared, no differences were found either in number of seeds per cone or in their length or diameter.

J. brevifolia normally has three seeds per female cone while J. cedrus produces two or three seeds (G3 = 9.04, P = 0.029). These are longer (Z = -15.98, P \ 0.001), wider (Z = -15.56, P \ 0.001) and heavier (Z = -15.98, P \ 0.001) than those of J. brevifolia (Table 2).

Seed viability


A total of 41.5% of the J. cedrus seeds examined contained apparently healthy embryos. A TTC test of these embryos revealed that 26.5% of them were non-viable, 8.9% poten- tially viable and 64.6% viable. Applying these results to the total number of seeds opened (filled and empty seeds): 69.3% were non-viable, 3.7% potentially viable and 27% viable. No significant differences were found between the size (diam- eter) of viable and non-viable J. cedrus seeds (t143 = 0.84, P = 0.40). However, in this species, viable seeds were sig- nificantly heavier than non-viable seeds (Z = -4.38, P \

0.001). Furthermore, significant differences were also found in the two sub-populations considered in Riscos de la Fort- aleza, with plants at the crag-base having higher seed via- bility (25.3%) than those growing at the crag-top (5.4%) (G1 = 81.06; P \ 0.001).



Table 2 Female cones and seed traits of Juniperus cedrus (‘‘Riscos de La Fortaleza’’, El Teide National Park, Tenerife, Canary Islands) and



J. brevifolia (Malha Grande, Pico Alto and Santa Ba´rbara, Terceira Island, Azores)


Parameters

J. cedrus













J. brevifolia







Mean

SD

Range

n




Mean

SD

Range

n

Female cone diameter (mm)

9.94

1.29

7.67–13.79

90




7.81

1.06

4.00–10.00

90

Fresh weight (g)

0.35

0.13

0.12–0.82

90




0.28

0.10

0.11–0.54

90

Water (%)

15.39

9.75

5.86–43.34

90




59.78

4.07

50.00–71.88

90

Number of seeds per cone

2.41

0.69

1.00–4.00

90




2.47

0.82

1.00–4.00

90

Seed length (mm)

6.48

0.79

4.59–8.69

180




4.42

0.62

2.90–5.80

180

Seed width (mm)

4.50

0.77

2.11–6.43

180




2.57

0.63

1.00–4.00

180

Seed weight (mg) 53.16 24.64 12.60–138.40 180 12.81 10.25 2.10–128.00 180

87.1% of the J. brevifolia seeds were filled, containing visibly healthy embryos. After TTC testing, 27.8% were found to be non-viable, 27.5% potentially viable and 44.7% viable. Considering the total number of seeds opened (filled and empty seeds), 37.1% were non-viable, 23.9% poten- tially viable and 39.0% viable. In J. brevifolia, no signifi- cant differences were found in the size or weight of viable and non-viable seeds.

Comparing both species, seed viability of J. brevifolia was significantly higher than J. cedrus (G1 = 185.59, P \ 0.001) (Fig. 2). On the other hand, the intraspecific comparison between the seed viability of the different mother-plants in each species revealed significant differ- ences both in J. cedrus and in J. brevifolia (G19 = 296.93, P \ 0.001; G19 = 49.64, P \ 0.001, respectively). In all of these categorical analyses, viable and potentially viable seeds were merged in one single group.

Discussion


Female cone phenology
Clear differences were recorded between the female cone phenology of the two endemic cedars in the Macaronesian islands. The J. cedrus population had mature female cones throughout the year, whereas J. brevifolia had a visibly different pattern in which mature cones were only present during two seasons: summer and autumn. It is remarkable that ripe female cones disappear during winter and spring in J. brevifolia, which contrasts with the persistence on the plants, even for years, in other Juniperus species (Cham- bers et al. 1999). This process is related to removal rates of frugivores and natural abscission beneath the plants from the Azores, where many rot due to the high environmental humidity and also predated by introduced rats (R.B.E., personal observation).

Female cones from the Macaronesian cedars mature in the second year (Adams 2008) and the notable presence of





Fig. 2 Ternary plot of seed viability scores (viable, potentially viable and non-viable) of the two Macaronesian endemic cedars (J. cedrus and J. brevifolia). Each point corresponds with the seed viability score of a plant; filled and empty seeds were considered. Five J. cedrus plants share the same values of seed viability (100% of non- viable seeds) and their correspondent circles are superimposed. Circles, J. cedrus and black dots, J. brevifolia. Program used to create Fig. 1: excel 2003. Program used to create Fig. 2: JMP Statistical software
ripe cones in summer and autumn show that these seasons are the most important for female cone maturity. In northern temperate habitats, most species that are dispersed by vertebrates have their ripening peaks in late summer– autumn, whereas Mediterranean forest and shrublands fruits ripen in autumn–winter (see Herrera 2002). This fact is also in concordance with the phenology pattern observed in J. brevifolia, which is a temperate species with matu- ration peaking in summer–autumn. However, J. cedrus occurs at lower latitude and higher percentages of mature cones appear in summer–autumn, but also in winter.




In the mutualistic interaction between temperate fleshy fruits and birds, the timing of fruit ripening affects the probability of seed dispersal by birds in continental eco- systems (Thompson and Willson 1979). According to these authors, weekly removal rates of fruits are faster for autumn fruiting species than for summer and winter species but, the two latter strategies should be more profitable at lower temperate latitudes due to the greater year-round presence of frugivores. In the present study, both summer and autumn are the most important seasons for the seed dispersal sys- tems of these insular cedar species, because the highest percentages of mature cones occur then. However, in the case of J. cedrus (which grows at subtropical latitudes), the presence of mature female cones is also relatively important in winter, showing a greater availability for all year-round frugivores, as described above.
Female cone sizes and pulp water content
Size is an important factor in fruits, because it limits ingestion to relatively small-sized dispersers, such as birds, that swallow them whole (Howe and Westley 1990; Her- rera 2002). However, this factor is probably less important in consumption by large vertebrates with wide mouths (Herrera 2002), whereas small birds tend to consume small fruits (Howe and Westley 1990; Noma and Yumoto 1997). In a thorough investigation carried out by Jordano (1995), in which the fleshy fruit characteristics of 910 angiosperm species were analysed, it was observed that there is a strong relationship between fruit diameter and disperser type. Although J. cedrus and J. brevifolia are both insular spe- cies evolving under particular ecological conditions, dif- ferences in female cone characteristics indicate two different evolutionary histories in their respective seed dispersal systems. J. cedrus has evolved with large verte- brate dispersers such us the Raven Corvus corax (Nogales et al. 1999), now presumably extinct in the study area, and almost certainly by different species of the endemic giant lizards (genus Gallotia) present in the Canaries. Mature cones on Tenerife are currently consumed by the medium size lizard G. galloti (Valido 1999) and by some Turdus species that had been recorded in the surrounding area of the plants (B.R., personal observation). In this regard, it is interesting to note that with the exception of the extinct giant lizards, no frugivores that could have interacted with J. cedrus have been recorded in the palaeontological deposits studied in Tenerife. However, ravens and native lizards are absent in the Azores archipelago, where med- ium-sized blackbirds T. merula (R.B.E., personal obser- vation) and possibly small warblers S. atricapilla are the dispersers of J. brevifolia.

The high water content in the J. brevifolia female cones

(four times higher than J. cedrus) seems to be related to the

wet climate of the Azores archipelago, with an average rainfall of 3,000 mm/year (Marzol et al. 2006; Elias 2007). Pulp water content may also be a single phenotypic response to the different environmental setting. In plants, this parameter seems to be linked to climatic features noted during fruit development (Debussche et al. 1987).


Seed viability
Differences in the number of filled seeds (seeds with apparently healthy embryos) were observed between the two species of Juniperus present in the Macaronesian islands, with J. brevifolia having more potential for natural regeneration. Junipers bear a high proportion of externally well developed but empty seeds (see Chambers et al. 1999; Garc´ıa et al. 2000a; Thomas et al. 2007). In a study of J. communis throughout its range in Europe (Garc´ıa et al.

2000b), a strong correlation was found between seed production, population fragmentation, distance between populations and climatic stress. Consequently, the pro- duction of filled seeds declined gradually towards the limits of J. communis distribution and juniper seed viability strongly diminished in regions with harsher environments. So, the low percentage of filled seeds in J. cedrus could be a consequence of the high-mountain climatic stress and pollination constraints probably due to the low proportion of sexually mature individuals (Table 1) and the frag- mented population as described for other species of junipers (see Chambers et al. 1999; Wesche et al. 2005; Thomas et al. 2007). As it is shown in Table 1, despite the balanced condition of the sex-ratio, the number of indi- viduals in J. cedrus population is much lower than that found in populations of J. brevifolia, where, in addition, individuals are less dispersed and must suffer a minor pollination restriction. Furthermore, the strong reduction in the J. cedrus population as a result of excessive human exploitation for timber purposes could have involved certain genetic impoverishment caused by inbreeding depression.

As occurs with female cone size and in the two sub-populations considered at Riscos de La Fortaleza (El Teide), differences in seed viability were also found between these two areas, where female plants at the crag- base had higher values of seed viability. Furthermore, these plants also presented higher values of total crown cover (Z = -2.50, P \ 0.05). This fact seems to confirm the significant effect of the habitat conditions and the climatic stress on seed viability, even within a population and over a short spatial scale.

TTC results indicate values significantly lower in via- ble seeds of J. cedrus (27%) with respect to J. brevifolia (44.7%). Although the viability of J. cedrus seeds was relatively low, the percentage of filled seeds with viable






embryos (64.6%) was much higher than in a previous study with reforested trees in which the highest viability value was 21% (Jorda´n de Urr´ıes 1997). TTC tests were also used in other studies on different populations of the endangered J. oxycedrus ssp. macrocarpa (Juan et al.

2003, 2006), and always indicated low values of viable seeds (\12% of totally stained embryos). However, in an unthreatened species such as the Redberry juniper J. pinchotii (Adams 2008), TTC results yielded 100% viability in filled seeds (44% of the seeds analysed) (Warren 2001 in Petersen et al. 2005). These results suggest that the endemic Macaronesian cedars are in an intermediate status with regard to their seed viability, between a critical situation like the endangered cedar J. oxycedrus ssp. macrocarpa (classified as in danger of extinction; Blanca et al. 1999) and other juniper species in a better conservation status.

Significant differences between seed viability of the mother-plants analysed were found in J. cedrus (range 0–

77.6%) and also J. brevifolia (range 21.7–60.8%). These

intraspecific differences show the important effect of the seed source on their subsequent success. Similar wide variations in the percentage of filled seeds were found in different populations of J. oxycedrus (ranging from 0 to

60% in different individuals) (Ortiz et al. 1998). Therefore, the mother-plant effect must be considered an important ecological factor for upcoming interpretations in seed dis- persal studies, and also for conservation purposes.


Final considerations
This contribution, based on some reproductive biology aspects, such as female cone phenology, size, weight, pulp water content and seed viability, is the first to present basic information about the two endemic insular species, J. cedrus and J. brevifolia. Therefore, this paper provides support for future research, essential for promoting regen- eration of these endangered island species. Lastly, our results reveal that some environmental factors such as harsh conditions, high population fragmentation and the dependence on large dispersers have compromised the fitness of J. cedrus in the Canary Islands.
Acknowledgments The staff of El Teide National Park (Organismo Auto´ nomo de Parques Nacionales), particularly A´ ngel Ban˜ ares, Manuel Durba´n and Manuel Marrero, facilitated our work in this protected area. Jose´ Ma Ferna´ndez-Palacios and Robert P. Adams

revised an early version of this contribution. Pedro Jordano provided us with important comments and suggestions, and he also helped us with some analyses using the JMP statistical package. We thank Raquel Gutie´rrez for technical support. B.R. and A.R. were financed by two grants conceded by the Spanish National Research Council (CSIC). D.P.P. was funded by a PhD grant awarded by the Canary Islands Government. This work was partially financed by a Canary Islands Government project (PI2007/053), partially supported by FEDER funds from the European Union.

References
Adams RP (2000) Systematics of Juniperus section Juniperus based on leaf essential oils and random amplified polymorphic DNA’s (RAPDs). Biochem Syst Ecol 28:515–528

Adams RP (2008) Junipers of the world: the genus Juniperus.

Trafford Publishing, Vancouver

Adams RP, Demeke T, Abulfatih HA (1993) RAPD DNA fingerprints and terpenoids: clues to past migrations of Juniperus in Arabia and east Africa. Theor Appl Genet

87:22–26

Arista M, Ortiz PL, Talavera S (1997) Reproductive isolation of two sympatric subspecies of Juniperus phoenicea (Cupressaceae) in southern Spain. Plant Syst Evol 208:225–237

Baskin CC, Baskin JM (1998) Ecology, biogeography, and evolution of dormancy and germination. Academic Press, London

Blanca G, Cabezudo B, Herna´ndez-Bermejo JE, Herrera CM, Molero

J, Mun˜ oz J, Valde´s B (eds) (1999) Libro rojo de la flora silvestre amenazada de Andaluc´ıa. Tomo I: especies en peligro de extincio´ n. Consejer´ıa de Medio Ambiente, Sevilla

Borges PAV, Brown VK (1999) Effects of island geological age on

the arthropod species richness of Azorean pastures. Biol J Linn

Soc 66:373–410

Bustos JJ, Delgado FS (2004) Clima. In: Canseco (ed) Parque

Nacional del Teide. Talavera de la Reina, pp 73–96

Cantos M, Cueva J, Za´rate R, Troncoso A (1998) Embryo rescue and development of Juniperus oxycedrus subsp. oxycedrus and

macrocarpa. Seed Sci Tech 26:193–198

Carracedo JC, Day S (2002) Canary Islands. Terra Publishing, Hertfordshire

Chambers JC, Vander Wall SB, Schupp EW (1999) Seed and seedling ecology of pin˜ on and juniper species in the pygmy woodland of western North America. Bot Rev 65:1–38

Debussche M, Cortez J, Rimbault I (1987) Variation in fleshy fruit composition in the Mediterranean region: the importance of ripening season, life-form, fruit type and geographical distribu- tion. Oikos 49:244–252

Dias E, Elias RB, Nunes V (2004) Vegetation mapping and nature conservation: a case study in Terceira Island (Azores). Biodivers Conserv 13:1519–1539

Donald RK, Cooke TJ (1997) Fundamental concepts in the embryo- genesis of dicotyledons: a morphological interpretation of embryo mutants. Plant Cell 9:1903–1919

Elias RB (2007) Ecologia das florestas de Juniperus dos Ac¸ores. Ph.D. dissertation. Azores University, Angra do Hero´ısmo

Elias RB, Dias E (2004) Primary succession on lava domes on

Terceira (Azores). J Veg Sci 15:331–338

Elias RB, Dias E (2009) Gap dynamics and regeneration strategies in

Juniperus–Laurus forest of the Azores Islands. Plant Ecol

200:179–189

Franc¸a Z, Cruz JV, Nunes JC, Forjaz VH (2003) Geologia dos

Ac¸ores: uma perspectiva actual. Ac¸oreana 10:11–140

Garc´ıa D, Go´ mez JM, Zamora R, Ho´ dar JA (2000a) a Do empty Juniperus communis seeds defend filled seeds against predation by Apodemus sylvaticus? E´ coscience 7:214–221

Garc´ıa D, Zamora R, Go´ mez JM, Jordano P, Ho´ dar JA (2000b) Geographical variation in seed production, predation and

abortion in Juniperus communis throughout its range in Europe.

J Ecol 88:436–446

Herna´ndez E, Nogales M, Mart´ın A (2000) Discovery of a new lizard in the Canary Islands, with a multivariate analysis of Gallotia

(Reptilia: Lacertidae). Herpetologica 56:63–76

Herrera CM (1992) Interspecific variation in fruit shape: allometry, phylogeny, and adaptation to dispersal agents. Ecology 73:1832–

1841




Herrera CM (2002) Seed dispersal by vertebrates. In: Herrera CM, Pellmyr O (eds) Plant-animal interactions. An evolutionary approach. Blackwell Science, Oxford, pp 185–208

Howe HF, Westley LC (1990) Ecological relationships of plants and animals. Oxford University Press, New York

IUCN (2008) The IUCN Red List of threatened species. Available via http://www.iucnredlist.org. Accessed 25 Nov 2008

Izquierdo I, Mart´ın JL, Zurita N, Arechavaleta M (eds) (2004) Lista de especies silvestres de Canarias (hongos, plantas y animales

terrestres) 2004. Consejer´ıa de Medio Ambiente y Ordenacio´ n

Territorial, Gobierno de Canarias, Santa Cruz de Tenerife

Jorda´n de Urr´ıes F (1997) Aproximacio´ n a la viabilidad de las semillas de J. cedrus Webb & Berthelot de Canarias. Aplicacio´ n

y comparacio´ n con J. oxycedrus ssp badia Debaux del centro peninsular. In: Puertas F, Rivas M (eds) I Congreso Forestal Hispano Luso. II Congreso Forestal Espan˜ ol. Pamplona, Espan˜ a,

pp 331–336

Jordano P (1995) Angiosperm fleshy fruits and seed dispersers: a comparative analysis of adaptations and constraints in plant- animal interactions. Am Nat 145:163–191

Juan R, Pastor J, Ferna´ndez I, Diosdado JC (2003) Relationships

between mature cone traits and seed viability in Juniperus oxycedrus L. subsp. macrocarpa (Sm.) Ball (Cupressaceae). Acta Biol Cracov Bot 45:69–78

Juan R, Pastor J, Ferna´ndez I, Diosdado JC (2006) Seedling

emergence in the endangered Juniperus oxycedrus subsp. macrocarpa (Sm.) Ball in southwest Spain. Acta Biol Cracov Bot 48:49–58

Marzol MV, Yanes A, Romero C, Brito de Azevedo E, Prada S, Martins A (2006) Los riesgos de las lluvias torrenciales en las islas de la Macaronesia (Azores, Madeira, Canarias y Cabo Verde). In: Cuadrat JM, Saz MA, Vicente SM, Lanjeri S, de Luis Arrillaga M., Gonza´lez-Hidalgo JC (eds) Clima, Sociedad y Medio Ambiente. Publicaciones de la Asociacio´ n Espan˜ ola de Climatolog´ıa (AEC), Serie A, no 5, pp 443–452

Nogales M, Herna´ndez EC, Valde´s F (1999) Seed dispersal by common ravens Corvus corax among island habitats (Canarian Archipelago). E´ coscience 6:56–61

Noma N, Yumoto T (1997) Fruiting phenology of animal-dispersed plants in response to winter migration of frugivores in a warm temperate forest on Yakushima Island, Japan. Ecol Res 12:119–

129


Ortiz PL, Arista M, Talavera S (1998) Low reproductive success in two subspecies of Juniperus oxycedrus L. Int. J Plant Sci

159:843–847

Petersen JL, Ueckert DN, Taylor CA, Shaffer KR (2005) Germination of Redberry Juniper (Juniperus pinchotii) seed in western Texas. Texas J Agric Nat Res 18:28–30

Scharpf RF (1970) Seed viability, germination and radicle growth of dwarf mistletoe in California. USDA For Serv Res Paper PSW

59:1–3

Sjo¨ gren E (2001) Plants and flowers of the Azores. Os Montanheiros, Angra do Hero´ısmo



Tanaka Y (1984) Assuring seed quality for seedling production: cone collection and seed processing, testing, storage, and stratifica- tion. In: Duryea ML, Landis TD (eds) Forest, nursery manual: production of bareroot seedlings. Martinus Nijhoff/Dr W. Junk Publishers, Boston, pp 27–39

Thomas PA, El-Barghathi M, Polwart A (2007) Biological flora of the

British islets: Juniperus communis L. J Ecol 95:1404–1440

Thompson JN, Willson MF (1979) Evolution of temperate fruit/bird interactions: phenological strategies. Evolution 33:973–982

Valido A (1999) Ecolog´ıa de la dispersio´ n de semillas por los lagartos ende´micos canarios (g. Gallotia, Lacertidae). Ph.D. thesis. Universidad de La Laguna, La Laguna, Spain

Wesche K, Ronnenberg K, Hensen I (2005) Lack of sexual

reproduction within mountain steppe populations of the clonal shrub Juniperus sabina L. in semi-arid southern Mongolia. J Arid Environ 63:390–405

West MAL, Harada JJ (1993) Embryogenesis in higher plants: an overwiew. Plant Cell 5:1361–1369

Wildpret de la Torre W, Mart´ın Osorio VE (2004) Flora vascular y vegetacio´ n. In: Canseco (ed) Parque Nacional del Teide.

Talavera de la Reina, pp 97–142




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