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Over a period of 44 years, we observed the vegetation changes in the western part of the lagoon system of the Cienaga Grande de Santa Marta, which is situated on the Caribbean coast of Colombia and is separated from the sea by a sandy barrier. Since the construction of the Barranquilla-Cienaga Road between 1956 and 1960, the lagoon system has been exposed to different interventions in its hydrological make-up, as well as changes to the vegetation. During the time of our investigations, four periods with different plant cover were distinguished. In 1965, the road was bordered by dense mangrove forests. The low surface water salinity and the presence of freshwater plants indicated the influence of the Magdalena River. At the beginning of the seventies, the second period was marked by a decrease in the freshwater in-flow from the river, which led to an increase in salinity and a gradual decay of vegetation. In 1988, the areas formerly covered by mangroves had converted into salt flats. The third period began with the reconstruction of several channels (1995–1998) which renewed the freshwater in-flow from the river to the lagoons. The subsequent vegetation development was characterized by the establishment of Typha domingensis Pers. In 1999, a year with an unusually high amount of rainfall, this species covered most of the former mangrove area in the western part of the lagoon system. The very low surface water salinity favored its spread. The last period began in 2001/2002, when growth conditions for T. domingensis became unfavorable due to an increase in salinity. Instead, conditions for mangrove regeneration improved. This process was slower than expected and is still ongoing. The striking vegetation changes indicate the sensitivity of the coastal lagoon system to hydrological variability.

Background: Data on below-ground production of tropical montane forests along elevation gradients are scarce. Aims: To determine fine, coarse and large root biomass and productivity along a 2000 m elevation transect. Methods: In five south Ecuadorian mountain forests along a transect from 1000 to 3000 m above sea level, fine ( 50 mm) were analysed by soil coring and excavation of soil pits. Fine root production was estimated synchronously by three different approaches (sequential soil coring, the ingrowth core method, and the mini-rhizotron technique). Coarse and large root production was estimated by recording diameter increment using dendrometer tapes. Results: Fine root biomass increased four-fold between 1000 and 3000 m; coarse and large root biomass doubled. The three approaches for estimating fine root production yielded highly divergent results, with the mini-rhizotron approach giving the most reliable data, and indicating a significant in...

Summary Tropical rain forests decrease in tree height and aboveground biomass (AGB) with increasing elevation. The causes of this phenomenon remain insufficiently understood despite a number of explanations proposed including direct or indirect effects of low temperature on carbon acquisition and carbon investment, adverse soil conditions and impaired nutrient supply. For analysing altitudinal patterns of aboveground/belowground carbon partitioning, we measured fine (

Litter production from above-ground (leaves, twigs, fruits, flowers) and below-ground (roots) plant organs is an important component of the cycling of carbon and nutrients in forests. Tropical montane forests possess comparatively large quantities of fine-root biomass, suggesting that litter production by dying fine roots may represent a major component of total litter production. In a comparative study in three tropical montane forests of southern Ecuador at 1890, 2380 and 3060 m elevation, we measured leaf-fall by litter trapping and fine-root litter production by sequential soil coring and fine-root biomass and necromass analysis for about 1 y with the objectives (1) to quantify annual above- and below-ground litter production, and (2) to investigate elevational differences in litter production. Leaf litter mass decreased to less than a third (862 to 263 g m−2 y−1) with increasing elevation (1890 m to 3060 m), whereas fine-root litter production increased by a factor of about four (506 to 2084 g m−2 y−1). Thus, the ratio of leaf to fine-root litter shifted by an order of magnitude in favour of fine-root litter production between 1890 to 3060 m. Fine-root litter production was not synchronized with leaf litterfall and was seasonal only at 3060 m with mortality peaks in the drier and the wetter periods. We conclude that dying fine roots represent a very important fraction of total litterfall in tropical montane forests that can exceed the quantity of leaf litter. At 3060 m, the largest part of the organic material on top of the soil must originate from dying fine roots but not from fallen leaves.

Not much is known about the role of tropical mountain forests in the global carbon cycle. This chapter summarises a decade of research on C pools and C fluxes in Andean mountain forests of the San Francisco region along an elevation transect from 1,000 m to 3,000 m a.s.l. based on measurements in 5 (3) intensively studied stands at five elevations and supplementary data collected in additional 54 forest plots at three elevations covering different topographic positions at these altitudes. With ecosystem C pools in the range of 320–370 Mg C ha−1, these forests store equally large, or even larger, amounts of C than neotropical lowland forests, despite the decrease in aboveground biomass with elevation. Gross and net primary production (NPP) and net ecosystem production all decrease largely with elevation while fine root production seems to increase. Our results show that tropical mountain forests are playing an important, yet underestimated, role as C stores.

In tropical montane forests, the decline of tree size with increasing elevation is a well recognized phenomenon (Lieberman et al. 1996; Raich et al. 1997). The decrease aligns with a continuous species shift from lowland forests, to lower, middle and upper montane forests (Gentry et al. 1995). Leaf area index (LAI) also decreases with elevation from lowland to upper montane forest (Kitayama and Aiba 2002). With respect to other structural and functional parameters such as plant biomass and productivity, however, only very limited data exist from tropical montane forests. Altitudinal changes in aboveground biomass and productivity were studied in transects in Malaysia (Kitayama and Aiba 2002), Hawaii (Raich et al. 1997), Puerto Rico (Weaver and Murphy 1990) and Jamaica (Tanner 1980), some of them covering only a few hundred meters of altitudinal distance. The data base is even more limited if belowground biomass is considered: for example, a combined assessment of aboveand belowground biomass in neotropical montane forests has been conducted in not more than 16 different stands so far, and only exceptionally included altitudinal transects. A better understanding of the causes of tree size reduction with elevation in tropical mountains is closely linked to information on altitudinal changes in biomass, carbon allocation and productivity of montane forests. Although numerous hypotheses focusing on climatic or edaphic constraints of tree growth have been formulated in order to explain this phenomenon (e.g. Bruijnzeel and Proctor 1995; Flenley 1995), all of them are eventually linked to carbon gain and allocation of the trees and their control by the environment. Thus, tree biomass and productivity data (see Chapter 17 in this volume) are of paramount importance. In this chapter, we present detailed aboveand belowground biomass data of an altitudinal transect study in the Ecuadorian Andes. Study aim was to analyze altitudinal changes in forest biomass and tree root/shoot ratio , and to relate them to possible underlying climatic and edaphic factors.