Effects of altitude and livestock on the regeneration of two tree line forming <Emphasis Type="Italic">Polylepis</Emphasis> species in Ecuador |
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Authors: | Arne Cierjacks Nadine Katrin Rühr Karsten Wesche Isabell Hensen |
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Institution: | (1) Institute of Biology/Geobotany and Botanical Garden, Martin-Luther-University Halle-Wittenberg, Am Kirchtor 1, 06108 Halle, Germany |
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Abstract: | Regeneration is known to be limited at many temperate tree lines, but very little data is available on the impacts of altitude
and anthropogenic disturbance on regeneration patterns along tropical tree lines. The study focused on the reproductive traits
of two Polylepis species in the Páramo de Papallacta in Ecuador along an altitudinal gradient, and involved different intensities of cattle
trampling within subsequent altitudinal ranges. We analyzed flowering, fruit set, seed viability, germination, and seedling
establishment as well as stand structure of Polylepis incana and P. pauta. The numbers of P. incana inflorescences and seedlings per m2 showed a marginally significant decrease with increasing altitude. Mean tree height was
significantly lower at higher altitudes, while stem number increased. The number of P. pauta inflorescences also decreased significantly upslope. In both forest types, trampling was found to have a positive impact
on seedling abundance, presumably due to the removal of the litter layer. Thus, there was no evidence of negative effects
of moderate cattle grazing on both tree line species. However, sapling establishment was minimal inside the forest stands
at all altitudes and grazing levels, and we consequently observed a low proportion of narrow stems within all investigated
forests. Our results show that, along with vegetative growth limitations of adult trees, important regeneration traits such
as seedling and inflorescence numbers are also influenced by altitude, which might contribute to the formation of the upper
tree line. Nevertheless, recruitment in the forest interior was low overall indicating that further factors, such as light
conditions, affect regeneration of the studied species. |
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Keywords: | Anthropogenic impact Herbivory Polylepis Reproduction Trampling Tree line |
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