Lianenverjüngung in Primär- und Sekundärwäldern Zentralamazoniens

Lianas are an important component of tropical forests. Despite their moderate contribution to forest biomass and diversity, they have a strong influence on forest dynamics. Lianas are particularly abundant in disturbed forest areas such as forest edges and small fragments, tree-fall gaps, and secondary forests. Because old growth forests are becoming more fragmented and the area covered by secondary forests is increasing, the importance of lianas is expected to increase. Studies of liana communities in forests mainly focus on stem densities of mature ascending plants. Data on liana seeds, seedlings, saplings and sprouts are scarce, but regeneration is implicated in ecological processes of all scales and may indicate future vegetation. Thus, knowledge about liana regeneration can be useful in forest management and conservation.The objectives of the research were:Field work was conducted in a primary forest and in two regionally dominant secondary forests in Amazonia near Manaus, Brazil. The primary forest was a non-inundated tropical evergreen lowland forest. The secondary forests were the Vismia forest, established after formerly clear cut land was used for pasture and intensively burned, and the Cecropia forest, established on formerly clear cut land but without pasture usage or intensive fires. Liana regeneration, which includes seedlings, saplings and sprouts ≤ 1.7m in length, was assessed in 8 10 plots per forest type, with a total of 27 plots used. The distance of the secondary forest plots to the next primary forest edges ranged between 0.03 and 1.2 km. Stand characteristics, such as canopy cover based on analyses of hemispherical photos, basal areas of trees and stem density of other growth forms, were investigated in each plot. The first study investigated the density and species richness of liana regeneration in the three different forest types. The density of liana regeneration was 50% lower in the secondary forests than in the primary forests; whereas, the share of lianas on woody regeneration was similar in all forest types. Species richness was highest in the primary forest and lowest in the Vismia forest. Accumulated species richness in the Cecropia forest was similar to that in the primary forest. With increasing distance from the primary forest, species richness and the proportion of lianas on woody regeneration in the secondary forests decreased; however, distance did not explain all variations between secondary forests. These results indicate that secondary forest types influenced species richness of liana regeneration but not liana density. The second study focused on leaf and plant traits of the 26 most abundant species from the survey of the first part. Growth rate during one year and plant traits, that include specific leaf area, leaf size and shape, plant length, leaves per length, ratio of stem slenderness, and herbivory, were assessed at species and at community (plot) level. A principal component analysis suggested that most of the primary forest liana species exhibited similar plant and leaf traits and were characterized by short shoots and small, round leaves with low specific leaf area; whereas, secondary forest species had a broad range of trait characteristics. At the plot-level, separation of primary and secondary forest communities was confirmed. Plant size of lianas varied more within the secondary than within the primary forest plots. With increasing canopy cover, herbivory increased and variability of leaf size and plant length per plot decreased. The relative growth rate of lianas increased with decreasing canopy cover and was highest in Vismia forest plots. We concluded that plant functional characteristics of liana regeneration were more converged in the primary forest and differed substantially from secondary forests, yet canopy cover explained only partly the observed differences. The third study presents seed and germination characteristics of 20 liana species. Biometrical data of seeds (mass, moisture content, longest and shortest axes, desiccation tolerance calculated by seed-coat-ratio) were collected and the seedling type was classified. Germination trials for desiccation tolerance and light dependence were conducted at constant 25 °C. For a subsample of species the influence of 12/12h alternating temperatures (20/30 °C and 15/35 °C, 12 h light) on germination was tested. Dry seed mass differed 1000 fold between species (0.009 10.7 g). Species with desiccation sensitive seeds all had above 0.27 g dry seed mass. In five species desiccation sensitive seeds were found where so far only desiccation tolerant seeds have been reported in the same genus or family. Light depending germination was found in three small seeded species (0.01 0.015 g) and was first described for two of these species; however, it has to be noted that the results are based on seeds of only one mother plant per species. Further studies should validate these findings. Alternating temperature influenced germination of four out of the nine species. Compared to constant temperature of 25 °C, daily alternations between 15/35 °C always decreased the germination rate for these four species; alternations of 20/30 °C increased, decreased, or did not affect germination rate, depending on the species. The seed and germination characteristics of the studied species ranged from pioneer to climax traits, indicating that liana species could succeed in a range of environments.In conclusion, the growth form liana comprised a range of leaf, plant and seed traits what emphazises the functional diversity of the group. The success of liana regeneration in disturbed habitats depends on species identity and environmental factors; thus, it is difficult to identify when, where and how lianas will benefit during forest succession.