High litterfall in old-growth and secondary upper montane forest of Costa Rica |
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Authors: | Lars Köhler Dirk Hölscher Christoph Leuschner |
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Institution: | 1.Plant Ecology, Albrecht-von-Haller-Institute for Plant Sciences,University of G?ttingen,G?ttingen,Germany;2.Tropical Silviculture and Forest Ecology, Burckhardt-Institute,University of G?ttingen,G?ttingen,Germany |
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Abstract: | Tropical upper montane forests usually comprise trees of small stature with a relatively low aboveground productivity. In
contrast to this rule, in the Cordillera de Talamanca (Costa Rica), tall trees (>35 m in height and more than 60 cm in diameter)
are characteristic for the upper montane old-growth oak forests which are growing at an altitude of almost 3,000 m close to
the alpine timberline. For these exceptional forests, productivity data are not yet available. In this study, we analyzed
litterfall and its components (tree leaves, litter of epiphytic vascular and non-vascular plants, mistletoes, twigs and other
canopy debris) in three forest stands belonging to different successional stages and related seasonal changes in litterfall
to micrometeorological variables. The studied stands were early-successional forest (10–15-year-old), mid-successional forest
(40-year-old), and old-growth forest. The stands are dominated by Quercus copeyensis and are located at 2,900-m altitude. Total litterfall was highest in the mid-successional forest (1,720 g m−2 y−1), and reached 1,288 g m−2 y−1 in the old-growth forest and 934 g m−2 y−1 in the early-successional forest. Litter mass was dominated by leaves in all stages (56–84% of total litterfall). In the old-growth
forest, however, twigs and small canopy debris particles (33%), epiphytes (6%), and mistletoes (5%) also contributed substantially
to litter mass. Leaf litterfall showed a clear seasonal pattern with a negative correlation to monthly precipitation and highest
values in the dry season (January–April). However, the strongest correlation existed with minimum air temperature (negative),
probably because temperatures already dropped at the end of the rainy season, when precipitation had not yet declined and
leaf shedding already increased. In contrast, litterfall of epiphyte mass, and twigs and other debris was mostly dependent
on occasional strong winds. We conclude that the upper montane oak forests of the Cordillera de Talamanca are exceptional
with respect to the large tree size and the relatively high productivity as indicated by litterfall. Litter mass was especially
high in the mid-successional and old-growth forests, where the observed annual totals are among the highest recorded for tropical
forests so far. |
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