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Revista de Biología Tropical

On-line version ISSN 0034-7744Print version ISSN 0034-7744

Rev. biol. trop vol.61 n.1 San José Mar. 2013


The effect of highly variable topography on the spatial distribution of Aniba perutilis (Lauraceae) in the Colombian Andes

José C. Fagua1*, Edersson Cabrera2*  & Victor H. Gonzalez3*

*Dirección para correspondencia:

Topography is a factor that can significantly affect the diversity and the distribution of trees species in tropical forests. Aniba perutilis, a timber species listed as vulnerable to extinction, is widely distributed in Andean forest fragments, especially in those with highly variable topography. Based on field surveys and logistic regression analyses, we studied the population structure and the effect of highly variable topography on the spatial distribution of this tree in three protected forest fragments in the central Andes of Colombia. Individuals of A. perutilis were mainly found on mountain ridges and hills with gentle slopes; no individuals were found in valleys. Using a species distribution model with presence/absence data, we showed that the available habitat for A. perutilis is significantly smaller than the extension of the fragments and much smaller than the extension of the currently protected areas. Our results have important implications for the conservation of A. perutilis and likely for other threatened Andean tree species, which can also have locally restricted distributions due to highly variable local topography.

Key words: conservation biology, forest fragments, logistic regression, species distribution models, population structure.


La topografía es un factor que puede afectar considerablemente la diversidad y la distribución de las especies de árboles tropicales. Aniba perutilis, una especie de árbol maderable  vulnerable  a  la  extinción,  está  ampliamente distribuida en fragmentos  de bosques andinos, especialmente en  aquellos con topografía altamente variable.  A partir de trabajo de campo y análisis de regresión logística, estudiamos la estructura  de la población y los efectos de la topografía  sobre la distribución espacial de este árbol en  tres fragmentos de bosque en la  cordillera  central de Colombia que actualmente se encuentran protegidos. Los individuos de A. perutilis se encontraron principalmente en los filos de montaña y colinas con gradientes topográficos suaves; no se encontraron individuos en los valles. A partir de un modelo de distribución de especies usando datos de presencia/ausencia,  mostramos que el hábitat disponible para A. perutilis es considerablemente más pequeño que la extensión de los fragmentos y mucho más reducido que la extensión actual de las áreas protegidas. Nuestros resultados tienen implicaciones importantes para la conservación de A. perutilis y probablemente otras especies de árboles andinos amenazados, los cuales pueden estar restringidos de forma similar debido a la variabilidad topográfica local.

Palabras  clave: biología de la conservación,  fragmentos de bosque, regresión logística, modelos de distribución de especies, estructura poblacional.

The tropical Andes are one of the most diverse areas in the world, containing about one-sixth of all plant life in less than 1% of the world’s  land  area  (Kattan  et  al.  2004). This ecosystem reaches its maximum physical complexity and biological diversity in Colombia, where it is divided into three main mountain ranges: the Western, Central, and Eastern Cordilleras (Kattan et al. 2004). Because of its diversity of climates and ecosystems, that allow the production of a wide variety of food, about 70% of Colombian population (~31 million of people) is concentrated in the Andes, which has strongly transformed native forests during the last century. Today, it is estimated that nearly 64.5% of the native Andean forests have been deforested during the past 40 years, especially in the central Andes (Cabrera et al. 2011). Most of the remaining native forest is sparsely found in patches or relicts along the Andes, especially in areas with highly variable topography where it is difficult to establish crops and grazing pastures for cattle ranching, the principal economic activities of this region.

Topography at the local scale is a factor that significantly affects the diversity and distribution of trees species in tropical and sub tropical forests (Oliveira-Filho et al. 1994, Clark et al. 1998, Oliveira et al. 1998, Gale 2000, Harms et al. 2001, Kubota et al. 2004). Topographic changes (i.e., variation of topographic units and topography gradient) produce discontinuities in edaphic conditions, thus affecting the establishment of trees (Clark et al. 1998). The effects of topography on the distribution of trees at the local scale and their consequences on the landscape scale have not been evaluated in any tree species of forest fragments in the tropical Andes. Such studies are relevant to promote the conservation of threatened tree species that are currently restricted to forest fragments with highly variable topography, such as those of the Colombian Andes.

Aniba  perutilis  Hemsley  (Lauraceae)  is a good example of a tree species restricted to such Andean forest fragments that is currently listed as a species vulnerable to extinction due to habitat loss and overexploitation (PRVCAB 1994,  UICN  2001, Vargas  2002). This  timber species, commonly  known as “comino” or “comino laurel”, is greatly esteemed for high-grade furniture, interior trim, durable construction,  and  resistance  to  the  attack of termites (Bernal 1994). This species is widely distributed in the Neotropical region, occurring  from  lowlands  to  mid  elevations (0-2 600m)  from  Colombia  to  Bolivia.  The species  becomes  more  abundant  in Andean forests, and although it was one of the most common trees in the “Cordillera Central” of Colombia. Today it is rarely found (PRVCAB 1994,  UICN  2001,  Vargas  2002).  Populations of A. perutilis in Colombia have been identified in three forest fragments along the Western flank of the Central Cordillera. These fragments (Bremen Forest Reserve, Otún- Quimbaya Natural National Park, and the Canyon of the Barbas River) are characterized by highly variable topography and by being surrounded by plantations of exotic trees and grazing pastures. To preserve these forest fragments, the state and federal governments of Colombia have established protected areas around them under the System of Protected Areas of Colombia (SINAP).

In this study, we sought to determine if topography could affect the distribution of A. perutilis inside these forest remnants. If this is the case, it would seem likely to find A. perutilis restricted to certain areas within the fragments, thus suggesting that the available habitat to A. perutilis would be significantly smaller than the extension of the fragment and much smaller than the extension of the protected area. To achieve this goal, we studied the relationship among several independent environmental variables and the probability of finding A. perutilis within the fragments using field data and logistic regression analyses. We then modeled the potential distribution of A. perutilis to estimate its available habitat using field data and Geographic Information Systems (GIS) tools.

Materials and methods

Study site and species: This study was conducted from June 2005 to May 2006 on three large forest relicts and the protected areas that  enclose  them  on  the  Western  slope  of the Cordillera Central of Colombia (4°38-42’ N - 75°32-38’ W): The Canyon of the Barbas River (CB), the Bremen Forest Reserve (BFR), and the National Natural Park Otún-Quimbaya (NNPO). These three areas are located between the departments of  Risaralda  and  Quindío, at  1 600-2 000m  (Fig.  1), are  characterized by their abrupt canyon formations, and are surrounded  by  plantations  of  exotic  grasses and trees (Pinus patula, Cupressus sp. and Eucalyptus sp.). The rainy season is bimodal, with a maximum from April to May and another from October to November. The mean annual rainfall is 2 817mm and the mean monthly temperature is 16-24°C. The vegetation is classified as subandean forest (sensu Cuatrecasas 1958) or premontane moist forest, bmh-PM (sensu Holdridge 1947). Numerous threatened animal species inhabit these forest fragments, such as Alouatta seniculus (Red howler monkey), Aotus lemurinus (Lemurine owl monkey), Dinomys branicki (Pacarana), Penelope perspicax (Cauca guan), Aburria aburri (Wattled guan), and Odontophorus hyperythrus (Chestnut wood-quail) (PNNC 2007). Due to the biological importance of these forest fragments, the Humboldt Institute and other Colombian institutions are trying to develop biological corridors that connect these three fragments.

Aniba perutilis is a large, evergreen canopy tree that reaches over 30m in height and 2m in diameter at maturity. The leaves are simple, coriaceous, lanceolate, and are arranged alternately  on  the  stems. The  flowers  are  small, bisexual, and brown to reddish-brown in color. The fruit is a fleshy, oil-rich, pear-shaped drupe (PRVCAB  1994,  Vargas  2002).  The  blooming  peak  occurs  through  the  drier  months and fruiting occurs through the rainy season (Alzate 1987). Seeds are primarily dispersed by Oilbirds (Steatornis caripensis) and several species of Toucans (Ramphastidae).

Preliminary GIS analysis and field methods: A map  of  vegetation  cover  types in the study area was generated using Ikonos Imagine (spatial resolution 1m2); field checks were done to improve the accuracy of these maps. We identified and digitized the following  vegetation  types:  1) Andean  forests,  2) introduced grasslands, 3) plantations of exotic trees, 4) high shrubs, 5) intermediate shrubs, 6) low shrubs, 7), isolated trees, 8) cultivated lands, 9) rivers, and 10) roads. Using the Digital Elevation Model (DEM) STRM (Shuttle Radar Topography Mission) at 30m2 of spatial resolution,  and  our  mapping  of  vegetation, we superimposed a grid of 300m2   cells over these layers and chose the cells that met two criteria: i) Andean forest cover of at least 70% of cell because A. perutilis is a canopy tree that grows inside mature forest, and ii) gentle topographic gradient (<30º) of at least 30% within each cell because areas with such a gradient are uncommon in these forest fragments and our preliminary field data showed that A. perutilis is predominantly found in areas with gentle topography. We found 85 cells with these two criteria (37 in NNPO, 39 in FRB, and 9 in CB).

We randomly selected 27 of the 85 cells (nine in each one of three fragments) and established a 10m wide transect in each cell in the field using a GPS. The length of the transect ranged from 60 to 100m due to canyon formations in the fragments. Such transects were oriented perpendicular to the topographic gradient lines and were divided every 5m into 5x10m2 plots. In each plot, we recorded the topographic gradient, topographical units (valley, hillside, and ridge), and altitude. In each 5x10m2 plot, a census of all A. perutilis individuals taller than 35cm was taken, whereas individuals shorter than 35cm were taken in 1x10m  plot nested within the 5x10m2  plot. The diameter at breast height (DBH) and height of each individual was recorded in all plots. Based on the DBH and Sturges’ (1926) equation, individuals were grouped in the following  size classes: Class 1 (0-0.4cm), Class 2 (0.4-3cm), Class 3 (3-6cm), Class 4 (6-9cm), Class 5 (9-12cm), Class 6 (12-15cm), Class 7 (15-18cm), Class 8 (18-21cm), Class 9 (21-24cm), Class 10 (25-40cm), Class 11 (40-55cm), and Class 12 (>55cm).

Analysis of field data: We used multiple logistic regression (MLR) to estimate the relationships between topographic gradient, topographical units (valley, hillside, and ridge), and altitude (explanatory variables) with the probability of finding A. perutilis in the forest fragments (response variable). MLR estimates the probability of presence, P (y=1), of A. perutilis based on n explanatory variables.

MLR is a special case of a generalized linear model that has suitable characteristics to analyze our data: 1) the response variable is binary (present/absent), which reduces effects of spatial autocorrelation (Lichstein et al. 2002) and pseudoreplication, 2) the explanatory variables can be numerical, categorical, binary or a mix of all them as in our case, and 3) the MLR model can be implemented into GIS to construct a map of potential distribution of the species. We applied two MLR analyses: 1) one to relate the probability of finding individuals taller than 35cm in the 454 plots (5x10m2) and 2) the other to relate the probability of finding individuals shorter than 35cm in height in the 454 nesting plots (5x1m2). Statistical analyses were done using Statistica 9.3 and SPSS 13.

Spatial Model of potential distribution: We constructed four raster maps corresponding to the explanatory variables mentioned before (topographic gradients, valleys, hillsides, and ridges) in forest fragments areas. Topographic gradients, valleys, and ridges rasters were obtained from STRM DEM using ArcGIS 9.3; specifically we used the following tools: Slope for topographic gradients, Arc Hydro (Version 1.0 Beta 2; Maidment 2002) for valleys, and Raster Surface for ridges. Areas which were not classified as valleys or ridges were classified as hillside because forest fragments are canyons with highly variable topography and without flat areas. Maps were projected in Magna-Sirgas Datum of Colombia, region VI (scale 1:10 000). Subsequently, we constructed a map of potential distribution of A. perutilis (raster of probability of finding A. perutilis) using a MLR model that takes into account the parameters of MLR of field data as follows:

Maps were projected in WGS 84 (World Geodetic System 84) Datum and UTM (Universal Transverse Mercator) projection (scale 1:10 000).


The explanatory variable topographic gradient was highly correlated with the probability of finding A. perutilis inside the forest fragments. The relationship was negative, and its magnitude was greater in individuals taller than 35cm (Wald=55.2, p<0.0001) than in individuals shorter than 35cm (Wald=31.8, p<0.0001) (Fig. 2); however, it was not statistically significantly different (X2=1.4, p=1.0). The topographical units, ridge and hillside, showed a significant relationship to the probability of finding A. perutilis in both individuals shorter than 35cm (Wald=21.3, p<0.0001; Wald=30.9, p<0.0001, respectively) and individuals taller than 35cm (Wald =43.4, p<0.0001; Wald=54.2, p<0.0001). The remaining explanatory variables (valley and altitude) did not have a significant relationship. When  forest  fragments  are  treated  in  the  analysis as  explanatory  variables,  we  found  that  CB and  NNPO  have  a  significant  relationship to  the  probability  of  finding  A.  perutilis  in both, short (CB: Wald=22.4, p=0.0001; NNPO: Wald=40.7, p=0.0001) and tall individuals (CB: Wald=22, p=0.0001; NNPO: Wald=24.7, p=0.0001), whereas FRB did not show a significant relationship. The distribution of size classes was not significantly different between NNPO and  BF  (X2=16.5,  p=0.12),  but  they both were significantly different from BFR (BFR vs. BF: X2=904, p=0.000001; BFR vs. NNPO  X2=775,  p=0.000001).  Individuals of the first five classes (DBH<12cm) and last two size classes (DBH>40cm) were found in similar proportions in NNPO and BF; individuals of the five intermediate classes were not found. Individuals of the first two classes (DBH<3cm) were found only in BFR (Fig. 3).

The model of spatial distribution of A. perutilis showed that suitable habitat for this tree species (areas inside the fragments with a probability  of  finding  A.  perutilis  greater than  0.7)  is  less  than  half  of  the  current  extension of the three protected areas combined, corresponding to 69%, 52%, and 47% of Andean forest covers of BFR, CB and NNPO, respectively (Table 1; Fig. 4). This result was expected given that ridges and hillsides with gentle topography and Andean forest cover (suitable habitat for A. perutilis) are uncommon in the area.


Species distribution models have been widely used at large regional scales (1:100 000 to 1:500 000) to predict the potential distribution of tree species based on presence only data (i.e., museum specimens), climatic variables, altitude, and soil type (Montiel 2008, Phillips & Dudík 2008, Soria-Auzaa et al. 2010). Our study predicted the spatial distribution of A.  perutilis at a fine local scale (1:10 000), based on presence/absence data as well as topographic variables measured in situ. This hierarchical approach allowed us to integrate information from different spatial scales to show how topographic heterogeneity at a very fine scale affects the distribution of A. perutilis in a local scale inside the studied forest fragments. Our analysis reveals that the available habitat for A. perutilis is significantly smaller than the extension of the fragment and much smaller than the extension of the currently protected areas. Our results have important implications for the conservation of A. perutilis, and likely for other threatened Andean tree species, if they are similarly restricted in distribution by topographic heterogeneity.

A spatial distribution limited by topographic  heterogeneity  at  a  local  scale,  such as  that  of  A.  perutilis,  suggests  preference or susceptibility to particular soil conditions, such as moisture (Ohsawa & Ozaki 1992, Wenny 2000, Kubota et al. 2004). The studied populations of A. perutilis showed a strong preference for ridges and slope habitats with slope angles lower than 36°. Despite the high precipitation of the studied areas (mean annual rainfall:  2 870mm),  seedlings  of  A.  perutilis occurred in soils that seemed relatively drier than  those  in  the  valleys,  where  we  found no seedlings of this species. Thus, seedlings might be susceptible to excessive moisture as previously suggested for other tropical tree species (Matelson et al. 1995, Clark et al. 1998, Oliveira et al. 1998, Harms et al. 2001, Kubota et  al.  2004). Another  factor  that  could  also influence the spatial distribution of A. perutilis in the studied areas is soil stability (Gale 2000). Soils at high gradients are structurally unstable and plants are more susceptible to fall to the ground due to height, weight, and strong winds. Aniba perutilis trees do not have morphological adaptations for growth in steep areas, such as buttress roots or tabular roots that provide extra anchorage and support. Given the preference of A. perutilis for areas with moderate gradient and the high topographic gradient that characterized the great majority of the land cover on each forest fragment, it is clear that most of the original habitat suitable for this species, the areas outside the forest fragments, has been transformed.

A population structure with a small number of individuals in several intermediate reproductive size classes, such as that of A. perutilis, suggests a gap in the successful reproduction of this species (Harper & White 1974, Roff 1992, Stearns 1992, Akçakaya et al. 1999). This may have been caused by the absence or low presence of reproductive trees as a consequence of selective extraction, which occurred 50 or 60 years ago, according to local informants. Aniba perutilis was one of the most common trees locally extracted for lumber, especially individuals with DBH>40cm. Because selective extraction of A. perutilis abruptly decreased about 40 years ago, the few large individuals currently  present are those that, scaped harvesting;  they  could not be used because they did not  have a suitable diameter at the time, or for some other reasons. It also suggests that those  are the progenitors of most of the current  seedlings. Although the breeding system of A. perutilis is unknown, it is probable that current populations of A. perutilis have some levels of endogamy because the progenitors are few and sparse.


We thank S. Giraldo, P. Garnica, J. Alzate and L.J. Rojas Valencia for their outstanding logistical support during the field work, and W. Vargas for assistance in plant identification; Amy Comfort de Gonzalez, James Ackerman, Jonathan Koch, and anonymous reviewers for their considerable input, insightful comments and suggestions that improved this work. We would like to thank UMATA of Filandia, Quindio. Support from the Instituto Alexander von Humboldt, Colombia, to the senior author to conduct field study is greatly appreciated. Partial support to V.H.G. was provided by the Department of Biological Sciences, Southwestern Oklahoma State University.


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José C. Fagua: Grupo de investigación en Percepción Remota, Centro de Investigación y Desarrollo en  Información Geográfica- CIAF, Instituto Geográfico Agustín Codazzi-IGAC, Carrera 30 No. 48-51, Bogotá D.C., Colombia.
Edersson Cabrera:  Instituto de Hidrología, Meteorología y Estudios Ambientales-IDEAM-, Bogotá, Colombia.
Victor H. Gonzalez: Department of Biological Sciences, Southwestern Oklahoma State University, 100  Campus Drive, Weatherford, Oklahoma, 73096, USA, & Division of Entomology, Natural History Museum, 1501 Crestline Drive – Suite 140, University of Kansas, Lawrence, Kansas 66045, USA.
1. Grupo de investigación en Percepción Remota, Centro de Investigación y Desarrollo en  Información Geográfica- CIAF, Instituto Geográfico Agustín Codazzi-IGAC, Carrera 30 No. 48-51, Bogotá D.C., Colombia;
2. Instituto de Hidrología, Meteorología y Estudios Ambientales-IDEAM-, Bogotá, Colombia;
3. Department of Biological Sciences, Southwestern Oklahoma State University, 100  Campus Drive, Weatherford, Oklahoma, 73096, USA, & Division of Entomology, Natural History Museum, 1501 Crestline Drive – Suite 140, University of Kansas, Lawrence, Kansas 66045, USA;

Received 13-XII-2011.    Corrected 27-V-2012.    Accepted 27-VI-2012.

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