Conserving Slow‐Growing, Long‐Lived Tree Species: Input from the Demography of a Rare Understory Conifer,Taxus floridana

Abstract

Although land preservation and promotion of successful regeneration are important conservation actions, their ability to increase population growth rates of slow-growing, long-lived trees is limited. We investigated the demography of Taxus floridana Nutt., a rare understory conifer, in three populations in different ravine forests spanning its entire geographic range along the Apalachicola River Bluffs in northern Florida (U.S.A.). We examined spatial and temporal patterns in demographic parameters and projected population growth rates by using four years of data on the recruitment and survival of seedlings and established stems, and on diameter growth from cross-sections of dead stems. All populations experienced a roughly 10-fold increase in seedling recruitment in 1996 compared with other years. The fates of seedlings and stems between 8 and 16 mm differed among populations. The fates of stems in two other size classes (the 2-to 4-mm class and the 4-to 8-mm class) differed among both populations and years. Individual stems in all populations exhibited similarly slow growth rates. Stochastic matrix models projected declines in all populations. Stochastic matrix analysis revealed the high elasticity of a measure of stochastic population growth rate to perturbations in the stasis of large reproductive stems for all populations. Additional analyses also indicated that occasional episodes of high recruitment do not greatly affect population growth rates. Conservation efforts directed at long-lived, slow-growing rare plants like Taxus floridana should both protect established reproductive individuals and further enhance survival of individuals in other life-history stages, such as juveniles, that often do not appear to contribute greatly to population growth rates.Resumen: Aunque la preservación de tierras y la promoción de regeneración exitosa son acciones de conservación importantes, su capacidad para incrementar las tasas de crecimiento poblacional deárboles longevos de crecimiento lento es limitada. Investigamos la demografía de Taxus floridana Nutt, una conífera de sotobosque rara, en tres poblaciones en diferentes bosques de cañada abarcando todo su rango de distribución a lo largo del Río Apalachicola en el norte de Florida, (E.U.A.). Examinamos los patrones espaciales y temporales de parámetros demográficos y las tasas de crecimiento poblacional proyectadas utilizando cuatro años de datos sobre reclutamiento y supervivencia de plántulas y tallos establecidos, y en el diámetro de crecimiento de secciones transversales de tallos muertos. Todas las poblaciones presentaron un incremento general de 10 veces en el reclutamiento de plántulas en 1996 en comparación con otros años. El destino de plántulas y tallos de 8 a 16 mm difirió entre las poblaciones. El destino de tallos en otras dos clases de tamaño (2-a 4-mm y 4-a 8-mm) fue diferente entre ambas poblaciones y entre años. Los tallos individuales en todas las ‡Current address: Savannah River Ecology Laboratory, Kwit et al. Demography of Taxus floridana 433 pob...

Natural regeneration and gender-specific spatial pattern of Taxus baccata in an old-growth population in Foresta Umbra (Italy)

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