Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

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 <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.

Abstract:

Since 1998, members of the DFG investigation group 402 (Since 2003 DFG investigation group 816) devoted themselves to the analysis of a local mountainous rainforest system in the Cordillera Real in southern Ecuador. The ?upper treeline? was subject to a closer study because of the atypical lowering of the local treeline ecotone at 2600 to 3350 m a.s.l. and the missing scientific findings on this topic. Within this thesis, methods of vegetation research as well as climatologic and pedologic analysis were used. Vegetation was taken up at ten different treeline sites ranging from the northern boundary of the Andes Depression near Cuenca in southern Ecuador to Huancabamba in the north of Peru. At each investigation area, eight vegetation transects (100 m2 each) were analysed and trees with a trunk diameter of >5 cm were recorded to species lists. The coverage of climatic parameters was carried out following the North-South-gradient at six sites. Three of them were analysed in detail by means of comparative micro-climatic measurements between forest and Páramo. The pedologic research was carried out at three lower-located sites of the upper treeline ecotone in the centre of the investigation area. The chapter of results is ordered into three sections, namely, structures of vegetation and its characteristics, climate and soil. In the chapter of botanical geography, syntaxonomic similarity of each transect and site was calculated by means of statistical classification methods and forest species with their particular populations were presented in detail. Results show that the upper treeline of the Andes Depression is completely different from the outer areas of the Depression in floristic terms. In the centre of the Andean Depression, which is rich in endemic species, up to 66 tree species form part of the forest border line (concerning an area of only 800 m2!). This number falls drastically at the northern edge of the area of examination, where the upper treeline rises to barely more than 4000 m a.s.l. Apart from the reduction of species with rising sea level, this fact can be postulated by distribution of Polylepis and different treeline structures. Monotypic Polylepis forests containing less species only exist at the northern edge of the Andes Depression and at the most southern study site in the West of Huancabamba. At all other sites, polytypic forests containing many different species are characteristic of the local treeline ecotone. The sites? taxonomic differences can be confirmed by ordination methods, which allow a clear floristic separation between Polylepis-free areas with populations of lowland taxa and Polylepis-forests. The different combinations of species are mainly due to variations in altitude, temperature, the number of humid months, and latitude. Nevertheless, the existence of an enormous range of species itself builds the precondition for a huge potential and a variable mixture of available taxa. The analysis of climate data shows that soil as well as air temperatures in the centre of the study area are clearly above 5.5° C, the postulated threshold value for tree growth. Therefore, temperature cannot be considered to cause the lowering of the local treeline ecotone of the Andean Depression compared to the Northern and Central Andes. Instead, quasi-permanent East winds, high amounts of precipitation throughout the year and maybe even extreme incidents of radiation lead to the depression of the local treeline ecotone system. While high global radiation leads to radiation stress especially for tree seedlings situated outside closed forest stands, strong East winds additionally constrain the establishment of forests in the higher-located ridge areas of Páramo formations. High precipitation leads to a shortage of nutrients in the more gently inclined ridges where the interflow is lower compared to steeper slopes. The results of chemical soil analysis show clearly that the three examined sites are characterized by low pH-values as well as a lack of nutrients. Furthermore, the upper soil layers of the Páramo areas show higher aluminium toxicity due to the type of litter decomposed by Páramo plants, a fact hindering the settling of young trees. Among the natural factors which prevent the growth of forests in higher areas are high rates of radiation, an extreme wind speed, as well as enormous rainfalls. Other sites restricted in forest growth are caused by human influence. The high diversity of species is remarkable in the upper treeline ecotone in the centre of the Andes Depression, a fact that can be ascribed to the lack of nutrients (strongly competitive species are locked out, cf. soil nutrient hypothesis) on the one hand. On the other hand, high precipitation amounts are also responsible for the lowering of the treeline. The result is the combination of a clearly marked forest treeline depression combined with an astonishing treeline complexity which is still an almost unknown paradox.

Abstract:

The leaves of Caladium steudneriifolium (Araceae) of the understorey of a submontane rainforest in the Podocarpus National Park (South East Ecuador, 1,060 m a.s.l.) are plain green or patterned with whitish variegation. Of the 3,413 individual leaves randomly chosen and examined in April 2003, two-thirds were plain green, whereas one third were variegated (i.e., whitish due to absence of chloroplasts). Leaves of both morphs are frequently attacked by mining moth caterpillars. Our BLAST analysis based on Cytochrome-c-Oxidase-subunit-1 sequences suggests that the moth is possibly a member of the Pyraloidea or another microlepidopteran group. It was observed that the variegated leaf zones strongly resemble recent damages caused by mining larvae and therefore may mimic an attack by moth larvae. Infestation was significantly 4?12 times higher for green leaves than for variegated leaves. To test the hypothesis that variegation can be interpreted as mimicry to deter ovipositing moths, we first ruled out the possibility that variegation is a function of canopy density (i.e., that the moths might be attracted or deterred by factors unrelated to the plant). Then plain green leaves were artificially variegated and the number of mining larvae counted after 3 months. The results on infestation rate (7.88% of green leaves, 1.61% of the variegated leaves, 0.41% of white manipulated leaves and 9.12% of uncoloured manipulated leaves) suggest that ovipositing moths are deterred by the minerinfestation mimicry. Thus, variegation might be beneficial for the plants despite the implicated loss of photosynthetically active surface.

Abstract:

This study confirms that the unique Purdiaea nutans forest in the upper montane belt of the Reserva Biologíca San Francisco in southern Ecuador is an azonal ridge vegetation type. Our assumption that the mass occurrence of Purdiaea may be caused by extremely poor soils was not confirmed. From our point of view the development of this monodominant forest was more likely triggered by historical fire events and a combination of site specific abiotic factors, related to topography, geology, pedology, and macroclimate. Neither the terrestrial nor the epiphytic bryophyte and macrolichen species richness or composition were affected by the unusual tree species composition, but instead represent typical upper montane ridge communities of the region. Distribution of bryophytes and Macrolichens is primarily determined by differences in microclimatic conditions. Habitat differences between slope forest and ridge forest, and small scale habitat heterogeneity within ridges, define microclimatic conditions and are therefore responsible for the variability of terrestrial bryophyte and Macrolichen assemblages in upper montane forests in southern Ecuador. In the epiphytic habitat, microclimatic conditions follow a vertical gradient rather than a horizontal one. Accordingly, different species assemblages, indicator species and life forms are observed in different positions within the tree. Tree crowns are inhabited by rather small, desiccation-tolerant and wind-approved bryophytes and Macrolichens, whereas on trunks taller, shade tolerant bryophytes predominate. The higher species richness recorded from other Neotropical upper montane forests is mostly due to high species numbers of mosses and Macrolichens; liverworts are relatively more pronounced in our study sites. The extremely high precipitation of the area favours liverworts and strong winds constrain the growth of projecting or hanging species such as Meteoriaceae and macrolichens typical for outer canopies elsewhere. A taxonomic comparison of alpha and beta diversities reveals no universally valid pattern for lichens, liverworts, mosses, and ferns. The results indicate that diversity patterns for epiphytic and terrestrial species are distinct and should be treated separately. Among the 92 studied taxonomic groups, ferns and liverworts show most similar patterns of alpha and beta diversity and therefore are most likely to work as surrogates for one another.