Reproductive biology and population structures of Podocarpus falcatus and P. latifolius in southern Cape forests

Abstract

GELDENHUYS, C. J., 1993. Reproductive biology and population structures of Podocarpus falcatus and P. latifolius i n southern Cape forests This study concerns morphological differences of the fruit types of two Podocarpus species in relation to their different population recruitment rates. First, sampling data from the mixed evergreen forests of Gouna and Groenkop in the southern Cape, South Africa, were used to describe the population structures of the two species. Podocarpusfalcatus is widely scattered at low density and has a low recruitment rate. Podocarpus latifolius is widespread and common at high density and has a high recruitment rate. Second, the morphology of their fruits and seeds was studied in relation to seed dispersal, predation and germination. The species represent the two basic 'fruit' types of the genus. Podocarpusfalcatus produces a heavy fruit, but invests mostly in dispersal (with a yellow fleshy pulp or epimatium enclosing the seed) and protective tissue (stony shell or sclerotesta) and very little into endosperm food reserves for the embryo. Podocarpus latijolius produces a light fruit which is composed mainly of dispersal tissue (blackish-purple fleshy receptacle) with protective tissue (thin leathery epimatium without woody sclerotesta) and food reserves for the embryo. The structure of the P. falcatus fruit is related to adaptation for protection during seed dispersal by bats. The stony sclerotesta delays germination for about one year and thereby causes the exposure of the seed to high post-dispersal predation by rodents and bushpig. Seedling recruitment is low. In contrast birds and baboons eat the receptacle of the P. lutifolius fruit and discard the seed undamaged. Less protective tissue is required. Seeds germinate within two to four months and recruitment is high. The structural differences of the two fruit types also have predictive value for the relative success of the different sections of the genus. Section Afrocarpus (to which P. falcalus belongs) and related sections have relatively restricted geographic distributions. Section Eupodocarpus (to which P. latijoolius belongs) and related sections have wide distributions.

Podocarps in Africa: Temperate Zone Relicts or Rainforest Survivors?

“…The proposed long-term persistence of A. falcatus relative to P. latifolius may result from their contrasting reproductive biology and seed physiology. Afrocarpus falcatus is a dioecious masting species with a periodicity of six to seven years between reproductive events (Geldenhuys, 1993). Podocarpus latifolius, on the other hand, is an annual seeder, resulting in less episodic recruitment and lower vulnerability to climatic instability compared with A. falcatus, which may partly explain the wider and more continuous distribution of P. latifolius.…”

“…Being bird dispersed and capable of rapid germination (4-6 weeks, H. Adie and M. J. Lawes, unpublished data;Geldenhuys, 1993) in a variety of habitats, P. latifolius displays traits typical of a highly vagile species. Podocarpus latifolius, therefore, fits the model of a good disperser with a high probability of establishment within a grass-dominated environment, provided it can escape fire.…”

“…Dispersed by birds, bats, monkeys, and baboons (Geldenhuys, 1993;Teketay and Granstrom, 1997;Negash, 2003;Hitimana et al, 2004), the falcatus-gracilior group is unlikely to be dispersal limited, even across the open grass-dominated landscapes that characterize the Afrotemperate region. However, the hard sclerotesta of A. falcatus cones delays germination for a year or more and leads to high postdispersal damage by mammals, resulting in low recruitment rates (Geldenhuys, 1993). In addition, seed viability declines by more than 50% within 12 months of harvesting (Negash, 2003).…”

“…Reduced mate assurance leads to pollination failure (Pannell and Barrett, 1998), or reduced seed production limits the effective size of the breeding population (Heilbuth et al, 2001). Third, recruitment rates are generally low because of delayed germination and high postdispersal damage by mammals (Geldenhuys, 1993) and loss of seed viability (Negash, 2003). Finally, sustained harvesting of A. falcatus poles has a significant impact on regeneration success (Tesfaye et al, 2002;Lawes et al, 2007b).…”

Characterization ofCorynelia uberataFr., a putative fungal pathogen ofPodocarpus falcatusinEthiopian forests

“…Podocarpus falcatus is an extremely valuable tree, both ecologically and economically. Ecologically, its dense crown and massive evergreen plant body is suitable for protection against soil erosion (Negash 1995), and its fleshy fruit serves as a food source for many birds as well as bats and the Colobus monkey (Colobus guereza) (Geldenhuys 1993). Economically, P. falcatus is a multipurpose tree used for making excellent timber products, and for extracting edible oil (Negash 1995) that has a medicinal use against gonorrhoea (Breitenbach 1963;Negash 1995;Aerts 2008;Orwa et al 2009).…”