Do secondary sexual dimorphism and female intolerance to drought influence the sex ratio and extinction risk of Taxus baccata?

Abstract

Sex ratio and sexual dimorphism were studied in the dioecious tree Taxus baccata. We examined five populations of T. baccata in Poland and Ukraine to identify the differences between male and female individuals. The sex of all individuals, height and diameter, needle length and area, specific leaf area (SLA), the number of stomata rows, stomatal density, and content of carbon and nitrogen were measured to identify the differences between male and female individuals. The relationship between sex ratio and climatic conditions, age and population size were analysed using data collected from the field and the literature. Female trees were shorter than males, but needles of females were longer and had larger area. Although there were no differences among sexes in SLA, nitrogen and carbon concentration, we found a positive correlation between nitrogen concentration and SLA among females. The sex ratio changed with tree height within populations, and taller height classes were biased in favour of males. Regardless of population age, the percentage of females within populations was positively correlated with precipitation. Probably high reproductive effort caused female trees to lose in competition with males, and this loss may also be enhanced by lower drought tolerance in females and could contribute to risk of extinction for T. baccata. The continental geographic range of T. baccata may be restricted by limited occurrence of females, which demand higher water resources than males.

Appendix 1

Population	Geographical position	Altitude (m)	Number of individuals in population	Sex ratio (% females)	Source
Denmark, Munkebjerg	N 55° 41′ E 9° 37′	44	2,000	67	Svenning and Magård (1999)
Poland, Czarne	N 53° 41′ E 16° 56′	135	428	47	Fałtynowicz and Markowski (unpublished data)
Poland, Rogów Arboretum	N 51° 49′ E 19° 52′	150	380	38	Tumiłowicz (1965)
Poland, Pommerania, Wierzchlas	N 53° 52′ E 18° 07′	105	3,500	33	Authors
Poland, Kórnik Arboretum	N 52° 25′ E 17° 06′	70	3,000	48	Authors
Poland, Huta Stara	E 50° 32′ E 19° 15′	350	51	41	Głowacka et al. (2004)
Poland, Sudety Mts., Cisy	N 50° 50′ E 16° 30′	410	1,035	46	Authors
Poland, Sudety Mts., Cisowa Góra	N 50° 50′ E 16° 30′	450	757	47	Authors
Poland, Wąwoz Myśliborski	N 51° 01′ E 16° 07′	340	73	39	Boratyński et al. (1997)
Poland, Sudety Mts. Nowy Waliszów	N 50° 18′ E 16° 44′	600	697	46	Boratyński et al. (1997)
Poland, Sudety Mts., Książ	N 50° 50′ E 16° 18′	400	300	24	Boratyński et al. (1997)
Poland, Carpathians, Dukla	N 49° 34′ E 21° 34′	550	1,585	48	Bodziarczyk and Zator (2004)
Ukraine, Carpathians, Kniazhdvir	N 48° 50′ E 24° 50′	400	15,000	46	Authors
Switzerland, Vorberg, Rüttenen	N 47° 13′ E 7° 31′	860	650	54	Hilfiker et al. (2004)
Switzerland, Dottenberg, Lostorf	N 47° 23′ E 7° 56′	870	700	55	Hilfiker et al. (2004)
Switzerland, Einolte, Oberhof	N 47° 26′ E 8° 01′	700	60	62	Hilfiker et al. (2004)
Switzerland, Uetliberg–Falätschen, Zürich	N 47° 22′ E 8° 32′	750	2,500	52	Hilfiker et al. (2004)
Switzerland, Scheren–Sihl, Schindellegi	N 47° 10′ E 8° 42′	800	300	56	Hilfiker et al. (2004)
Switzerland, Etzelwald, Feusisberg	N 47° 11′ E 8° 46′	810	47	68	Hilfiker et al. (2004)
Switzerland, Guegenhard, Elgg	N 47° 29′ E 8° 51′	570	1,600	50	Hilfiker et al. (2004)
Switzerland, Schneitberg–Affenberg, Elgg	N 47° 31′ E 8° 53′	650	68	60	Hilfiker et al. (2004)
Switzerland, Hagebuechtobel, Zuzwil–Wuppenau	N 47° 29′ E 9° 06′	610	550	55	Hilfiker et al. (2004)
Switzerland, Schoostobel, Oberbüren–Niederbüren	N 47° 24′ E 09° 13′	560	150	49	Hilfiker et al. (2004)
Switzerland, Unterer Darewald, Salgesch	N 46° 18′ E 7° 34′	1,080	500	55	Hilfiker et al. (2004)
Switzerland, Blindtal, Naters	N 46° 21′ E 8° 01′	1,200	35	51	Hilfiker et al. (2004)