Revista de Biología Tropical ISSN: 0034-7744 [email protected] Universidad de Costa Rica Costa Rica Castellanos, Maria Clara; Stevenson, Pablo R. Phenology, seed dispersal and difficulties in natural recruitment of the canopy tree Pachira quinata (Malvaceae) Revista de Biología Tropical, vol. 59, núm. 2, junio, 2011, pp. 921-933 Universidad de Costa Rica San Pedro de Montes de Oca, Costa Rica Available in: http://www.redalyc.org/articulo.oa?id=44922367030 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Phenology, seed dispersal and difficulties in natural recruitment of the canopy tree Pachira quinata (Malvaceae) Maria Clara Castellanos1,2 & Pablo R. Stevenson1 1. Centro de Investigaciones Ecológicas La Macarena, Universidad de Los Andes. Cr. 1 no. 18ª-12. Bogotá, Colombia; [email protected] 2. Centro de Investigaciones sobre Desertificación (CSIC-UV-GV), Apartado Oficial, 46470 Albal, Valencia, Spain; [email protected] Received 17-VIII-2010. Corrected 10-XII-2010. Accepted 10-I-2011. Abstract: Life history and recruitment information of tropical trees in natural populations is scarce even for important commercial species. This study focused on a widely exploited Neotropical canopy species, Pachira quinata (Malvaceae), at the southernmost, wettest limit of its natural distribution, in the Colombian Amazonia. We studied phenological patterns, seed production and natural densities; assessed the importance of seed dis- persal and density-dependent effects on recruitment, using field experiments. At this seasonal forest P. quinata was overrepresented by large adult trees and had very low recruitment caused by the combination of low fruit production, high seed predation and very high seedling mortality under continuous canopies mostly due to damping off pathogens. There was no evidence of negative distance or density effects on recruitment, but a clear requirement of canopy gaps for seedling survival and growth, where pathogen incidence was drastically reduced. In spite of the strong dependence on light for survival of seedlings, seeds germinated readily in the dark. At the study site, the population of P. quinata appeared to be declining, likely because recruitment depended on the rare combination of large gap formation with the presence of reproductive trees nearby. The recruitment biology of this species makes it very vulnerable to any type of logging in natural populations. Rev. Biol. Trop. 59 (2): 921-933. Epub 2011 June 01. Key words: anemochory, damping off, density-dependence, emergent tree, Bombacopsis quinata, seedling survival, Tinigua National Park. Many tropical timber tree species get a and their overexploitation could have additio- particularly high share of damage, because in nal negative consequences to other plant and addition to the destruction of their habitats due animal species. to deforestation, they are selectively logged in In spite of their commercial and ecolo- areas where their native forests are still stan- gical importance, it is surprising how little is ding (Nepstad et al. 1999, Asner et al. 2005). known about the life history and requirements If the species are also cultivated, then they are for recruitment of many timber species in their not in risk of going extinct, strictly speaking. natural habitats, even if they are widely logged But extraction practices of highly valued spe- or cultivated (Guariguata & Pinard 1998, cies can seriously threaten wild populations, Schulze et al. 2008b). Tropical tree species or even lead to local extinction, and to the occur in low densities and recent studies show genetic impoverishment this entails (André et that some of them have stringent requirements al. 2008). Because target species are usually for recruitment in their native habitats, and are large and long-lived trees, they are likely to therefore very sensitive to disturbance (Lobo play important ecological roles in the forest et al. 2007, Schulze et al. 2008a, Schulze et al. Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 59 (2): 921-933, June 2011 921 2008b). This is likely the case for many other to the eastern slopes of the Andes. It does not species, but basic life history information in occur in the adjacent non-seasonal Amazonian wild populations is scarce. forests. It is a deciduous tree that produces In this study we report several aspects bat- and moth-pollinated flowers after leaf of the natural recruitment of Pachira qui- abscission. It presents a mixed mating system nata (Jacq.) W.S. Alverson (Malvaceae), an with outcrossing rates that depend on the num- endangered canopy tree species native to Cen- ber of available mates (Fuchs et al. 2003). The tral America and northern South America. fruits are loculicid capsules with small seeds Its populations have been extensively logged (ca. 4mm in length) surrounded by a kapok throughout its natural range (Kane et al. 1993, that favors dispersal by wind. In their natural Sandiford 1998, Pérez et al. 2004). The spe- forests, adults become large emergent trees. The cies is also cultivated for timber production in wood is strong, resistant to termite attacks and Colombia, Venezuela, and Central America, easy to handle (Kane et al. 1993, Pérez et al. and in some regions, it represents the most 2004); therefore, it is valuable for construction important timber species (Kammesheidt 1998, and for production of a variety of woodcrafts. Cordero & Boshier 2003). The requirements This study took place at the Centro de for growing this species are therefore well Investigaciones Ecológicas La Macarena (2º known (see Cordero & Boshier 2003 for a 40’ N, 74º 10’ W; 350-400m a.s.l), within Tini- recent monograph). A few studies have focu- gua National Park, a rain forest at the border sed on its biology in natural forests, covering between the upper Amazon and Orinoco basins phenological aspects, pollination and reproduc- of Colombia. Rainfall is seasonal with a dry tive efficiency, often in fragmented landscapes period between January and March and a mean (Quesada et al. 2001, Fuchs et al. 2003, Lobo et annual rainfall of 2 780mm (Stevenson et al. al. 2003). Other aspects remain mostly unstu- 2008). The study site includes both terra firme died in natural habitats. For a population at the and flooded forests (Stevenson et al. 2004). southern, wettest limit of its distribution, we Human intervention at the study site was limi- describe phenological patterns, seed production ted to two small patches of 4-6ha, which were and dispersal, germination, natural densities cleared and then abandoned and were mostly and assess the importance of seed dispersal and covered by grasses or secondary forest at the density-dependent effects on recruitment using time of this study. field experiments. Our results contribute to Phenology the knowledge of early recruitment of tropical canopy trees and potential density-dependence To describe phenological patterns, we effects, and highlight the sharp contrast bet- made biweekly observations on six marked ween the low recruitment of this species in trees during one year (August 1996-July 1997), native forests compared to the ease with which and recorded the presence (or absence) of it is cultivated for timber. flowers, fruits and leaves in each tree. In addition, we looked for intra-annual variabi- lity in phenology using 5.6 km of transects, MATERIALS AND METHODS which we revisited biweekly during three years Study species and site (August 1996-July 1997, January-December 2000, January-December 2001). We recorded Pachira quinata (=Bombacopsis quinata) the presence of flowers or fruits in all trees on inhabits dry forests of Central and South Ame- transects and then estimated among-individual rica, and extends to the south into moist, but synchronization following the vector method seasonal, forests at the lowland regions close adapted by Stevenson et al. (2008). 922 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 59 (2): 921-933, June 2011 Estimation of crop size dispersal distance and local density of parental trees. Seeds (with kapok) were placed on the To estimate fruit and seed production, we floor at five different distances from a parental made direct counts of fruits with binoculars tree: 2, 10, 20, 50 and 100m, in the down-wind in six adult trees (as in Chapman et al. 1994) direction. In each location the density of seeds in February 1996, right before fruit ripening, was 1, 2, 4, 16 or 50, according to the latin when trees have lost their leaves. Seed produc- square design. We chose these numbers becau- tion was estimated by multiplying the number se seeds can be dispersed individually or in of fruits in a crown by the average number of small groups, while high densities of seeds are seeds per fruit (51±37.6 seeds per fruit, n=35 also found in fruits that fall before dehiscence healthy undehisced fruits found on the floor, and open on the forest floor. We repeated this most likely knocked down by fruit predator experiment under four different trees varying birds). We also estimated flower production in the number of conspecific adult trees around indirectly from 16-24 traps with a basal area them. We chose one tree with no other P. qui- 2 of 0.08m installed on the floor underneath the nata trees around, one with one neighbor in crowns of three of the six adult trees, haphazar- a radius of 100m, a third surrounded by four dly distributed, for the whole reproductive sea- trees, and a last one that was part of a group son. We recorded floral buds and open flowers of 17 adult conspecific tress in one hectare. in the traps and from this and the approximate A fifth group of seeds was established in an crown cover, estimated the number of aborted area with no P.