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Effects of Forest Fragmentation on Stem Length, Age, and Reproduction on an Understory Palm Species Chamaedorea pinnatifrons (Arecaceae) Peter Werrell Department of Biology, Fordham University ABSTRACT Forest fragmentation has been shown to decrease re productive output for some species of dioecious plants. Chamaedorea pinnatifrons (Arecaceae) is a dioecious understory palm found in wet, tropical forests from Mexico to Bolivia. This study examined differences in ratios of fruiting to non fruiting indiv iduals of C. pinnatifrons in both continuous and fragmented forests in Monteverde, Puntarenas, Costa Rica, in order to as well as three plots of f ragmented forests were examined and compared. Stem length, presence of fruit, number of raceme branches, number of fruit, and number of annual rings were measured and related to ratios of fruiting to non fruiting individuals in continuous forests versus f ragmented forest. A higher ratio of fruiting to non fruiting palms was found in continuous forest, showing lower reproductive output in fragmented areas. Other trends observed included an older population of fruiting plants in fragments and an older popu lation of individuals in continuous forests. These trends indicate that females in fragments may be under environmental stresses that impede younger females from setting fruit. This study further supports previous studies showing decreased fitness of man y plant species in forest fragments. RESUMEN Se ha demostrado que la fragmentacin del bosque disminuye la reproducin de ciertas especies de plantas dioicas. Chamaedorea pinnatifrons (Arecaceae) es una palma dioica del sotobosque que se encuentra en l os bosques hmedos tropicales desde Mxico hasta Bolivia. Este estudio examin las diferencias en las tasas de los individuos con fruta a los individuos sin fruta en C. pinnatifrons en bosques continuos y fragmentados en Monteverde, Puntarenas, Costa Rica para examinar los efectos de la fragmentacin en la capacidad reproductiva de la especie. Se estudiaron tres parcelas de bosques continuos y tres de bosques fragmentados. Se midieron la longitud del tallo la presencia de la fruta, el nmero de los raci mos, el nmero de frutas, y el nmero de anillos anuales y se compararon con las tasas de individuos con fruta a los individuos sin fruta en bosques continuos y en bosques fragmentados. Se encontr una tasa ms alta de palmas con fruto a palmas sin fruto en el bosque continuo, lo que demostr que haba una reproducin ms baja en reas fragmentadas. Otras tendencias observadas incluyeron una poblacin ms vieja de plantas con fruto en fragmentos y una poblacin de individuos ms vieja en bosques continuos Estas tendencias indican que las plantas femeninas en fragmentos pueden estar bajo presiones ambientales que les impiden producir fruta a las plantas femeninas ms jvenes. Los resultados de este estudio apoyan a estudios anteriores que mostraron una d isminucin en la adaptivilidad de muchas especies de plantas en fragmentos de bosque.
INTRODUCTION Tropical forest fragmentation is one result of increased deforestation, and its effects on many biological processes have been studied. Effects on polli nation and reproductive health are factors that are interesting to look at considering species in fragments are separated from the continuous forest pollen bank. Differences in such factors such as the availability of pollen and pollinators may arise with population divisions and increased human disturbance caused by fragments. A dry forest study in Argentina found variance in responses in terms of seed set, fruit production, and pollen movement in 16 different species representing a wide range of pollina tion systems (Aizen and Feinsinger 1994). Some tropical dry forest trees have shown significant declines in fruit set in forest fragments due mainly to low densities and less gene flow (Cascante et al. 2002). The species Samanea saman (Mimosaceae) experi enced lower fruit set in forest fragments compared to individuals in continuous forest in Guanacaste National Park, Costa Rica (Cascante et al. 2002). An almost identical study conducted on Pachira quinata (Bombacaceae) also found that forest fragmentatio n resulted in decreased fruit production due to less pollen provided by fewer trees and fewer pollinators (Fuchs et al. 2003). Both of these species are hermaphroditic and have animal pollinators. Pollination and reproduction are as likely to decline wit h forest fragmentation in self incompatible species as they are with self compatible species (Aizen et al. 2002). A study conducted in a cloud forest in the Western Ghats of India found forest fragmentation caused reductions in insect visits and fruit out put in three dioecious species: Diospyros montana Diospyros sylvatica and Garcinia talbotii ( Somanathan and Borges 2000) These studies were done on plants with animal pollen vectors and these mutualistic relationships may increase plant susceptibility to fragmentation (Aizen et al. 2002). Not much has been done concerning the effects of forest fragmentation on wind pollinated species, which are generally thought to be more resistant to fragmentation effects. A comparison of multiple studies on wind pol linated species, however, indicates that pollen limitations caused by forest fragmentation may be playing an equally crucial role in determining reproductive output in wind pollinated species (Koenig and Ashley 2003). Another study on Enhalus acoroides a Southeast Asian species of seagrass, did show a negative affect in fruit output caused by fragmentation (Vermaat et al. 2004) though the type of environment in which this species is found is drastically different from a cloud forest. The genus Chamaedore a (Arecaceae) includes over 100 species of dioecious understory palms found mostly in tropical moist or wet rain forests from Mexico to Bolivia, reaching high concentrations of diversity in Costa Rica and Guatemala (Hodel 1997). In Chamaedorea, as well as other palms, age is positively correlated with stem length, and age can be determined based on annual rings made by leaf scars (Oyama 1993). Chamaedorea pinnatifrons is a slender and solitary palm with a pale green trunk that grows up to 4.5 m in height, exhibits sigmoid pinnae, and is shade tolerant similar to most Chamaedorea species (Jones 1994). It is one of the most widespread and variable palms both latitudinally and altitudinally in the Americas (Henderson et al. 1995) but is uncommon below 400 m o n the Atlantic slope and below 1000 m on the Pacific slope. Chamaedorea pinnatifrons displays orange elliptical fruits that turn black when ripe and are contrasted by a bright orange raceme, which attracts bird dispersers. The pollination mechanism is wi nd but also thought to be in some way induced by insects, which are
only found on male flowers but not on female flowers (Listabarth 1993). The effects of fragmentation on reproduction of wind pollinated, dioecious species are poorly known and no studies have been conducted specifically on C. pinnatifrons It is suggested that pollen limitation due to fragmentation may, however, negatively affect certain wind pollinated species to an equal extent as it has been determined to affect animal pollinated speci es (Koenig and Ashley 2003). Reproductive success in females of a close relative C. radicalis also wind pollinated, is not limited by differences in the availability of pollen (Berry and Gorchov 2004) though the limited amounts of pollen were based on di fferences in male density and sexual composition rather than fragmentation. Most studies on forest fragmentation and pollination systems are done on plants with animal pollen vectors. This study compared the reproductive success in C. pinnatifrons betwe en fragmented forests and continuous forests in terms of quantity of fruit, number of racemes, and ratio of fruiting plants to non fruiting plants. Relationships between fruit output and plant height and age were also determined. It was hypothesized that fruit output and ratios of fruiting plats to non fruiting plants would be lower in fragmented areas compared to continuous forests. MATERIALS AND METHODS Research was conducted in the greater Monteverde area of Costa Rica on the Pacific slope of the T ilarn mountain range, Costa Rica. The average rainfall at the site is about 2.5 m per year with a 25% addition in moisture from cloud mist. All areas studied fell between 1300 and 1450 m in altitude (Figure 1). Sampling of continuous and fragmented tra cts of forest was conducted between July 17 th and 28 th 2005. Three plots from each type of forest were sampled, and each continuous plot was paired with a nearby forest fragment. One set of plots was located on the property of Wilford Guindon and family another on the property of Eric Rockwell, and the third on the property of the Estacin Biolgica de Monteverde. In each area 300 m of transects were run using a 100 m measuring tape following straight compass lines. Transects were kept parallel unless environmental constraints made it impossible to run a transect in that area. Constraints included steep hills, cliffs, ravines, water, or impenetrable undergrowth. Each transect was then divided into twelve, 25 m sections, and the number of individuals of C. pinnatifrons and their measurements were recorded in each section. Chamaedorea pinnatifrons individuals that fell within 2.5 m of either side of the transect line were recorded creating a total sampled area of 1500 m 2 at each site. Data for each in dividual palm were taken as follows: height from the roots up to the newest growing leaf, number of annual leaf scars, presence or absence of an infructescence, number of infructescences, number of raceme branches per plant, and number of fruit remaining p er plant. Stem length was used to determine height rather than height from ground because a substantial amount of individuals were severely bent and or twisted, often growing upward from underneath a structure that had previously fallen on it. The number of raceme branches was used to determine the extent of fruit output because it was unknown how many fruit were taken or had fallen off prior to count. The individuals were mapped as to location along the transect along with observations on light intensit y, areas of disturbance (such as paths), and areas crossing
small streams in order to detect possible patterns between these factors and palm abundance. Areas of greater light intensity were not measured, only observed. Analyses were carried out betw een each of the three pairs of continuous and fragmented forest plots as well as between all individuals sampled in all continuous plots and all individuals sampled in all fragmented plots. Plant densities, frequency of distribution of fruiters, percent f ruiters, mean number of fruits, mean number of raceme branches, and raceme branches/fruiter were calculated. Frequency of distribution of fruiting individuals was determined by dividing the number of 25 m sections with fruiters by the twelve 25 m sections total per plot. Two way contingency tables were used to determine if the ratios of fruiters to non fruiters were significantly different between continuous and fragmented sites. Simple regressions were used to determine if a correlation existed between height and palm age (as determined by the number of leaf scars along the trunk). A regression was also used to look at the relationship between fruiting plants height and number of racemes per fruiting plant. Unpaired t tests were used to determine if di fferences existed in number of raceme branches per fruiting palms between the two types of forests, as well as to determine if differences existed between the stem lengths of the fruiters in both areas. T tests were also run to determine if differences e xisted between continuous forests and fragmented forests in terms of height or number of leaf scars. RESULTS A total of 498 Chamaedorea pinnatifrons individuals were sampled in all transects, 293 individuals in continuous forest plots and 205 individual s in fragmented forest plots. Densities varied substantially between plots in continuous and fragmented areas though the mean density was greater in continuous forests (D = 0.085 plants/m 2 ) than in fragmented forests (D = 0.046 plants/m 2 )(Table 1). A gre ater mean frequency of fruiters was also found within continuous forests (55.6 %) than in fragmented forests (27.8%)(Table 1). Greater numbers of fruit were found in all continuous forest sites compared with their forest fragment counterpart, with an over all mean in continuous plots of 790.3 fruits and 140.0 in fragmented areas. The same trend was observed with the number of raceme branches with a mean of 142.3 raceme branches in continuous compared to a mean of 32.0 raceme branches in fragmented areas. Overall, C. pinnatifrons stems were longer (Unpaired t test, t = 7.699, P < 0.0001; Figure 2) and older (Unpaired t test, t = 3.589, P = 0.0004; Figure 3) in continuous forest areas. This trend was not significant in comparisons between continuous fores ts and fragments in each of the three study sites. In the Guindon pair of plots, stems were significantly longer (Unpaired t test, t = 7.021, P < 0.0001) and older (Unpaired t test, t = 4.131, P < 0.0001) in continuous forest. In the Monteverde pair stem s were significantly longer (Unpaired t test, t = 4.658, P < 0.0001) but no trend was observed in terms of age. Individuals of C. pinnatifrons at the Rockwell site did not exhibit significant differences in stem length or age. In fruiting individuals, t he number of raceme branches was found to increase with an increase in stem length (Simple regression, R 2 = 0.118, P = 0.009)(Figure 4). The number of fruits produced by individuals was significantly positively correlated to the number of raceme branches (Simple regression, R 2 = 0.208, P = 0.0004)(Figure 5).
Fruiting plants were significantly older in fragmented areas compared to continuous areas (Unpaired t test, t = 2.951, P = 0.005)(Figure 6). No differences between fragmented and continuous forests were observed in terms of length of fruiting plants or the number of raceme branches per fruiting plants. A higher ratio of fruiting plants to non fruiting plants was found in continuous forests than fragmented forests overall (X 2 = 10.147, DF = 1, P = 0.001) although no significant differences were found between individual site comparisons (Guin: X 2 = 2.746, DF = 1, P = 0.0975, Roc: X 2 = 2.892, DF = 1, P = 0.0890, Mont: X 2 = 1.632, DF = 1, P = 0.2014). Chamaedorea pinnatifrons generally increased in he ight as they grew older based on a simple regressions done on all individuals sampled (R 2 = 0.682, P = <0.0001)( Figure 7). The same trend was significant for all three sites. DISCUSSION This study found that the reproductive health of Chamaedorea pinn atifrons is greater in continuous forests compared to fragmented forests. The greater total number and mean number of raceme branches is a good indicator of a higher abundance of fruit in continuous forests. Comparing standing crop of fruit is a weaker m easure of reproductive output because the number of fallen or removed fruit was not determined. They still indicated greater output in continuous forests, however, assuming a constant rate of fruit loss or removal between the two areas. In any case, high er number of fruit was significantly positively related to the number of raceme branches (Figure 5). The study also indicates, based on taller and older palms in continuous areas, that a higher amount of community fitness in continuous forests exists whic h leads to stability for growth and long life for C. pinnatifrons without human disturbance. This study also found that the ratio of fruiting plants to non fruiting plants of C. pinnatifrons was greater in continuous forest compared to fragmented forest. The higher percentage of fruiters in continuous forests and greater frequency of fruiters in continuous forests support the idea that conditions favor greater reproductive output in continuous forests. It is difficult to state with confidence differences in reproductive success are based on less pollen availability to individuals in fragmented areas, though this is a possibility. It makes sense that due to separations of populations of C. pinnatifrons from the larger more sustained populations in continuo us forests, less pollen would be available from the continuous forest population. Populations in forest fragments would also be more probable to have a skewed ratio of males to females based on smaller populations which could partially explain the lower f requency of fruiting individuals in the forest remnants. Without knowledge of sex ratios and male plant densities it is hard to tell whether there are fewer females around to fruit though they may be exposed to a more pollen from a larger number of male p lants, or whether a larger number of females are not being exposed to as much pollen from a lesser number of males present. You would expect a continuous forest to have closer to a 1:1 ratio of males to females in understory palms (Oyama 1990) which is t he optimum ratio in order to have the best probability for reproductive success. A study conducted on three Indian cloud forest species, D. montana D. sylvatica and G. talbotii, found a drastically smaller ratio of males to females in forest fragments w hich could have contributed to the lower fruit
output in fragments (Somanathan and Borges 2000). Other factors, could better explain why the ratio of fruiters to non fruiters was higher in continuous forests. Emphasis should also be placed on comparisons of plant fitness rather than on fragmentation alone (Aguilar and Galetto 2004). This study found that the number of fruit producing raceme branches increases with increased with an increase in height possibly due to a higher amount of energy available to taller, older individuals. Fruiting plants in fragmented forests were significantly older than fruiters in continuous forests, however, suggesting that environmental pressures in fragments limit reproduction in younger individuals. Since C. pinnatifrons individuals were significantly older in continuous areas, females in fragments may not have the resources or energy to produce fruit as young as those in continuous areas. A study conducted on Arabidopsis thaliana showed that plants fruited at a younger a ge when shaded by neighboring vegetation ( Callahan and Pigliucci 2002). It makes sense for pants to fruit as soon as possible in order to produce the most fruit it can within its lifetime and also to produce fruit before unexpected mortality. Continuous forest individuals may find it advantageous to fruit fast at a younger age instead of wasting time waiting. A higher availability of light in fragments could contribute to plants waiting longer to fruit. A higher availability of light in forest fragments capacities to handle, which helps to explain why plants were significantly shorter in fragments. The correlation between length and age supports past studies done on palms in general. C ertain older individuals were observed to be much shorter than younger individuals, which could be a result of position in a favorable growing area for the younger individuals in this case. Interestingly, clumps of individuals were observed around light p atches and pathways and especially seen near streams. Though not directly measured by this study, observations hint that C. pinnatifrons individuals do well in small areas of higher light concentrations and areas that are open such as man made trails, wat er drainages, and streams. Plant height also seemed to increase with increased availability of light though not directly measured. If this were true it could be because higher photosynthetic rates allow for faster growth rates, as long as the light avail able does not exceed the capacities of photosynthesis in a shade tolerant palm. A study that compiled data on palm diversity in an Andean rain forest fragment in Ecuador showed that C. pinnatifrons actually benefited from areas of moderate human disturban ce that forest fragmentation is only one factor in a wide range of ecological conditions, such as those mentioned above, that effects growth and reproduction in C. pin natifrons In order to improve this study greater numbers of samples need to be collected per area that is statistically normal in order to compare the three sites individually and not just grouped into fragmented areas and continuous areas. This would al low for comparisons of fruiting in fragments and continuous areas on a distance gradient from the continuous forest. In order to perfect this study data must be collected for at least a year in order to determine the actual ratios of males to females. Th is would give a better measure on pollen availability and distance between male and female plants. Further studies could test C. pinnatifrons fitness in relation to smaller areas of disturbance such as tree falls, trails, and streams. It would be interes ting to determine if a relationship exists between plant density and light intensity.
Forest fragmentation continues to happen worldwide, especially in tropical areas as one result of deforestation. Much more research needs to be done in order to better understand the effects fragmentation has on species and communities. It has been shown in many cases that fragmentation leads to the reduction in species diversity and stability in fragmented areas (Aguilar and Galetto 2004). Though this study showed t hat reproductive fitness decreases for C. pinnatifrons with fragmentation, other aspects such as densities were not drastically affected and patterns of growth and reproduction may differentiate still depending on light intensity and smaller patches of hum an or natural disturbances within larger areas. Another key point to keep in mind is that palm fruit including the genus Chamaedorea provide an important food source mainly for birds but for other animals as well. A decrease in food production in fragmen ts may also lead to a decrease in bird populations. Overall, fragmentation is a growing problem in tropical areas and more research may shed light on exactly how forest fragmentation is affecting plants and animals. ACKNOWLEDGEMENTS I would like to th ank Carlos Guindon for his help in showing me around and locating good examples of forest fragments and continuous forest. I also thank Mr. And Mrs. Guindon, Eric Rockwell, and the Biological Station for letting me conduct my research on their properties. Special thanks to Mauricio Garca for the statistical run down, for help identifying the species, and for some background information on the Chamaedorea genus. Thank you Maria Jost and Nathaniel Talbot for your revisions and statistical help and other c ool stuff. Thank you Javier Mndez for making me laugh whenever I think about you looking exactly like Shrek. Thanks Elizabeth Hunter for letting me use the University of Wisconsin databases. Finally, thank you CIEE for giving me one of the most memorab le and educational experiences I have ever had and to Costa Rica for being so beautiful. LITERATURE CITED Aguilar, R. and L. Galetto. 2004. Effects of forest fragmentation on male and female reproductive success in Cestrum parqui (Solanaceae). Oecologia 138: 513 520 Aizen, M.A. and P. Finsinger. 1994. Forest fragmentation, pollination, and plant reproduction in a Chaco dry forest, Argentina. Ecology 75: 330 351 Aizen, M.A., L. Ashworth, and L. Galetto. 2002. Reproductive success in fragmented habitats : do compatibility systems and pollination specialization matter? Journal of Vegetation Science 13: 885 892 Berry, E.J. and D.L. Gorchov. 2004. Reproductive biology of the dioecious understory palm Chamaedorea radicalis in a Mexican cloud forest: pollinat ion vector, flowering phenology and female fecundity. Journal of Tropical Ecology 20: 369 367 Callahan, H.S. and M. Pigliucci. 2002. Shade induced plasticity and its ecological significance in wild populations of Arabidopsis thaliana Ecology 83: 1965 19 80 Cascante, A., M. Quesada, J.J. Lobo, and E.A. Fuchs. 2002. Effects of dry tropical forest fragmentation on the reproductive success and genetic structure of the tree Samanea saman Conservation Biology 16: 137 147
Fuchs, E. J., J.A. Lobo and M. Quesa da. 2003. Effects of forest fragmentation and flowering phenology on the reproductive success and mating patterns of the tropical dry forest tree Pachira quinata Conservation Biology 17: 149 157 Henderson, A., G. Galeano, and R. Bernail. 1995. Field guid e to the palms of the Americas. Princeton University Press, Princeton, New Jersey Hodel, D.R. 1997. Two new species of Chamaedorea (Arecaceae). Novon 7:35 37 Jones, D.L. 1995. Palms throughout the world. Smithsonian Institution Press, Washington, D.C. K Ecology and Evolution 18: 157 159 Listabarth, C. 1993. Insect induced wind pollination of the palm Chamaedorea pinnatifrons and pollination in the related W endlandiella spp. Biodiversity and Conservation 2: 39 50 Oyama, K. 1993. Area age and height correlated in Chamaedorea tepejilote (Palmae)? Journal of Tropical Ecology 9: 381 385 Oyama, K. 1990. Variation in growth and reproduction in the neotropical dio ecious palm Chamaedorea tepejilote Journal of Ecology 78: 648 663 Somanathan, H. and R.M. Borges. 2000. Influence of exploitation on population structure, spatial distribution, and reproductive success of dioecious species in a fragmented cloud forest in India. Biological Conservation 94: 243 256 Svenning, J.C. 1998. The effect of land use on the local distribution of palm species in an Andean rain forest fragment in northwestern Ecuador. Biodiversity and Conservation 7: 1529 1537 Vermaat, J.E., R.N. Ro llen, C.D.A. Lacap, C. Billot, F. Alberto, H.M.E. Nacorda, F. Wiegman, and J. Terrados. 2004. Meadow fragmentation and reproductive output of the SE Asian seagrass Enhalus acoroides Journal of Sea Research 52: 321 328
FIGURE 1 Map of Monteverde, Costa Rica area displaying the six individual sites in which Chamaedorea pinnatifrons individuals were sampled.
TABLE 1. Density and reproductive output of Chamaedorea pinnatifrons in three continuous forest and three fragmented forest sites. (2005) FIGURE 2 Relationship between mean Chamaedorea pinnatifrons height in three continuous fore st sites (N = 293, x = 121.181, +/ 69.007) compared to three forest fragment sites (N = 205, x = 75.000, +/ 61.117). C. pinnatifrons were significantly taller in continuous forest than in forest fragments (Unpaired t test t = 7.699, P < 0.0001). Plot Name Density (Plants/m 2 ) Frequency Distribution of Fruiters (%) % Fruiters # Fruits # Racemes Guin Cont 0.177 75.00 15.90 1195 261 Rock Cont 0.027 25.00 12.19 382 55 Station Cont 0.051 66.67 14.47 794 111 Mean 0.085 55.56 14.19 790.33 142.33 Guin Frag 0.037 16.67 7.14 71 34 Rock Frag 0.063 33.33 4.26 199 33 Station Frag 0.037 33.33 7.27 150 29 Mean 0.046 27.78 6. 22 140.00 32.00 M E A N H E I G H T
F IGURE 3 Relationship between mean Chamaedorea pinnatifrons age as measured by growth scars in three continuous forest sites (N = 295, x = 14.078, +/ 10.883) compared to three forest fragment sites (N = 203, x = 10.551, +/ 10.665). C. pinnatifrons were significantly older in continuous forest than in forest fragments. (Unpaired t test, t = 3.589, P = 0.0004). FIGURE 4 A simple regression of height vs. number of infructescence raceme branches for all fruiting individuals of Chamaedorea pinnatifrons i ndicating a significant positive correlation between height and number of raceme branches in fruiting plants. (N = 56, R 2 = 0.118, P = 0.004) M E A N A G E
FIGURE 5. Simple regression on number of fruits per number of raceme branches in Chamaedorea pinnatifrons indi cating a significant correlation between the number of fruits and number of raceme branches in fruiting individuals. (N = 56, N 2 = 0.208, P = 0.0004) FIGURE 6. Relationship between age measured by growth scars of fruiting individuals of Chamaedorea pi nnatifrons in three continuous forest sites (N = 44, x = 15.955, +/ 6.847) compared to three fragmented forest sites (N = 12, x = 23.583, +/ 11.229). C. Pinnatifrons were significantly older in continuous forest than fragments. (Unpaired t test, t = 2 .951, P = 0.005) M E A N # S C A R S
FIGURE 7 A simple regression of height vs. number of scars for all individuals on Chamaedorea pinnatifrons sampled. Number of scars was used as a measure of age suggesting a positive correlation for length vs. age in all individuals sampled. (N = 498, R 2 = .682, P < 0.0001)
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Efectos de la fragmentacin del bosque en la longitud del tallo, la edad, y la reproduccin en una especie de palma Chamaedorea pinnatifrons (Arecaceae)
Effects of forest fragmentation on stem length, age, and reproduction on an understory palm species Chamaedorea pinnatifrons (Arecaceae)
Forest fragmentation has been shown to decrease reproductive output for some species of dioecious plants. Chamaedorea pinnatifrons (Arecaceae) is a dioecious understory palm found in wet, tropical forests from Mexico to Bolivia. This study examined differences in ratios of fruiting to non-fruiting individuals of C.
pinnatifrons in both continuous and fragmented forests in Monteverde, Puntarenas, Costa Rica, in order to examine the effects of fragmentation on the species reproductive ability. Three plots of continuous forests as well as three plots of fragmented forests were examined and compared. Stem length, presence of fruit,
number of raceme branches, number of fruit, and number of annual rings were measured and related to ratios of fruiting to non-fruiting individuals in continuous forests versus fragmented forest. A higher ratio of fruiting to non-fruiting palms was found in continuous forest, showing lower reproductive output in fragmented areas. Other trends observed included an older population of fruiting plants in fragments and an older population of individuals in continuous forests. These trends indicate that females in fragments may be under environmental stresses that impede younger females from setting fruit. This study further supports previous studies showing decreased fitness of many plant species in forest fragments.
Se ha demostrado que la fragmentacin del bosque disminuye la reproducin de ciertas especies de plantas dioicas. Chamaedorea pinnatifrons (Arecaceae) es una palma dioica del sotobosque que se encuentra en los bosques hmedos tropicales desde Mxico hasta Bolivia. Este estudio examin las diferencias en las tasas de los individuos con fruta a los individuos sin fruta en C. pinnatifrons en bosques continuos y fragmentados en Monteverde, Puntarenas, Costa Rica, para examinar los efectos de la fragmentacin en la capacidad reproductiva de la especie. Se estudiaron tres parcelas de bosques continuos y tres de bosques fragmentados. Se midieron la longitud del tallo, la presencia de la fruta, el nmero de los racimos, el nmero de frutas, y el nmero de anillos anuales y se compararon con las tasas de individuos con fruta a los individuos sin fruta en bosques continuos y en bosques fragmentados. Se encontr una tasa ms alta de palmas con fruto a palmas sin fruto en el bosque continuo, lo que demostr que haba una reproduccin ms baja en reas fragmentadas. Otras tendencias observadas incluyeron una poblacin ms vieja de plantas con fruto en fragmentos y una poblacin de individuos ms viejos en bosques continuos. Estas tendencias indican que las plantas femeninas en fragmentos pueden estar bajo presiones ambientales que les impiden producir fruta a las plantas femeninas ms jvenes. Los resultados de este estudio apoyan a los estudios anteriores que mostraron una disminucin en la adaptabilidad de muchas especies de plantas en fragmentos de bosque.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone
Plantas del sotobosque
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Summer 2005
Ecologia Tropical Verano 2005
t Monteverde Institute : Tropical Ecology