Tree Diversity, Forest Structure and Productivity along Altitudinal and Topographical Gradients in a Species‐Rich Ecuadorian Montane Rain Forest

Abstract

We studied the spatial heterogeneity of tree diversity, and of forest structure and productivity in a highly diverse tropical mountain area in southern Ecuador with the aim of understanding the causes of the large variation in these parameters. Two major environmental gradients, elevation and topography, representing a broad range of climatic and edaphic site conditions, were analyzed. We found the highest species richness of trees in valleys o 2100 m. Valleys showed highest values of basal area, leaf area index and tree basal area increment as well. Tree diversity also increased from ridges to valleys, while canopy openness decreased. Significant relationships existed between tree diversity and soil parameters (pH, total contents of Mg, K, Ca, N and P), and between diversity and the spatial variability of pH and Ca and Mg contents suggesting a dependence of tree diversity on both absolute levels and on the small-scale heterogeneity of soil nutrient availability. Tree diversity and basal area increment were positively correlated, partly because both are similarly affected by soil conditions. We conclude that the extraordinarily high tree species richness in the area is primarily caused by three factors: (1) the existence of steep altitudinal and topographic gradients in a rather limited area creating a small-scale mosaic of edaphically different habitats; (2) the intermingling of Amazonian lowland plant species, that reach their upper distribution limits, and of montane forest species; and (3) the geographical position of the study area between the humid eastern Andean slope and the dry interandean forests of South Ecuador.

Comunidades forestales en bosques secundarios alto-andinos (Azuay, Ecuador)

“…Resultados sobre la influencia de la altitud y la temperatura en la composición florísti-ca y estructura han sido reportados históricamente, pero en las últimas décadas han sido descritos contundentemente bajo procedimientos, técnicos y científicos (Girardin et al 2014). Bajo la aplicación de estos procedimientos, los resultados difieren con los obtenidos en otros estudios en bosques andinos a nivel local (Homeier et al 2010) y regional (Girardin et al 2014, Báez et al 2015 en donde los mayores valores en riqueza de especies y área basal son registrados en sitios de menores altitudes.…”

“…En las vertientes occidentales forman parte de los puntos calientes o "hotspots" del planeta. Aquí, una gran cantidad de micro-hábitats y la accidentada topografía favorecen la existencia y adaptaciones biológicas incluyendo diferentes comunidades de plantas (Homeier et al 2010).…”

“…Para entender ecológicamente la magnitud y variación en los parámetros de composición, diversidad y estructura de la vegetación, se han descrito relaciones con variables ambientales. Por ejemplo, a nivel local en Zamora Chinchipe se reporta que la composición florística y riqueza de especies es influenciada por la altitud (Homeier et al 2010). Este resultado también es evidenciado a nivel regional, en amplias gradientes andinas de Perú y Bolivia (Girardin et al 2014).…”

Contribution of Topography and Incident Solar Radiation to Variation of Soil and Plant Litter at an Area with Heterogeneous Terrain

“…furthermore, this introduCtion Tropical forests are one of the richest and most complex natural systems on the planet (Brummit and Nic Lughadha, 2003;Leigh et al, 2004). Their great richness of species has repeatedly been linked to accelerated dynamics of natural processes and high availability of natural resources (Pinto et al, 2006;Homeier et al, 2010;Putten et al, 2013). A frequent approach is to use the relationships between plants and soil to evaluate the variation in richness of tropical forests, operating under the assumption that soil is a main plant resource (Chen et al, 1997;Oliveira-Filho et al, 2001;Budke et al, 2007;John et al, 2007;Gleason et al, 2010;Laurance et al, 2010;Aponte et al, 2013;Brandt et al, 2013).…”

Floristic Comparison Between Two Tree Communities Associated With Habitat Descriptor Variables

“…Nevertheless, altitudinal variations comprise a complex set of variables related to temperature, air humidity, water availability, wind exposure, in addition to soil depth and drainage classes HOMEIER et al, 2010;BLUNDO et al, 2012).…”