Effect of shade and precipitation on germination and seedling establishment of dominant plant species in an Andean arid region, the Bolivian Prepuna

Germination and seedling establishment are two critical processes in the life cycle of plants. Seeds and seedlings must pass through a series of abiotic and biotic filters in order to recruit as members of their communities. These processes are part of the regeneration niche of the species. In arid regions, the regeneration niche is frequently associated to facilitation by shade. Facilitation is a positive interaction between plants, in which one of them acts as a benefactor (the nurse) of the other (the beneficiary). The result of this interaction can be reflected in the increased growth, survival, and/or reproduction of the beneficiary plant. In this study, we determined experimentally the effect of shade and irrigation on the germination and early survival of dominant species of a semi-arid Andean region, the Bolivian Prepuna. An experiment with Acacia feddeana, Prosopis ferox, Cercidium andicola (woody species), Parodia maassii, and Oreocereus celsianus (cactus species) was carried out at an experimental garden in La Paz, Bolivia, with a bifactorial design, considering shaded and unshaded pots, subjected to two irrigation treatments (≈50 and 80 mm of rainfall during the whole study period). Microenvironmental conditions did not affect the seed germination of the woody species. However, they showed differences in seedling survival: A. feddeana survived better under shade, whereas P. ferox and C. andicola survived better without shade. Cercidium andicola, compared to P. ferox, was more affected by shade and low irrigation. Although germination success of cacti was low, both species germinated better under shade and with high irrigation. These results showed differences in the regeneration niche of dominant species of the Prepuna which may favor their coexistence and which may be characteristic of other dry Andean regions.

Plant traits and ecological dynamics

This chapter examines the multiple facets of trait variation and ecological dynamics in the contemporary Mediterranean landscape. Climatic constraints and transitions are paramount here. Diverse functional traits and strategies have evolved to avoid or tolerate the summer drought and the irregularity of spring rainfall. Annual plants do their best to avoid such constraints, and the role of functional traits in the regeneration niche and life-history strategy is undeniable. Perennial plants face the challenge of surviving their first summer and from then on illustrate a demographic persistence strategy. Dispersal and establishment generate interactions among species across a mosaic landscape where transitions between positive and negative interactions characterize successional dynamics. The study of two main features of the Mediterranean flora, its response to fire, and the diversity of aromatic plants illustrate well the importance of plant traits in the ecological dynamics of populations and communities in the mosaic landscape.

Germination requirements of the subordinate fen meadow species Valeriana dioica L

Plant species of the intermediate life strategy type are characteristic for species-rich grasslands, which are sensitive to changes in the level of disturbance. Germination and early establishment of seedlings is expected to be the most crucial stage, limiting the successful colonization of appropriate sites. Valeriana dioica is a typical plant of calcareous fens, which are dependent on regular suppression of strong competitors by means of moderate land use. It is endangered in many parts of Central Europe, including Lower Austria. We studied the effects of light, temperature and pre-treatment (cold stratification) on the germination success of V. dioica seeds and the role of litter produced by different competitors on the early establishment of seedlings. We tested seeds from five populations differing in the level of competition for light and considered also the morphological variability of propagules and maternal plants. We found that V. dioica is able to germinate without light. It showed high germination percentages both under high summer temperatures independent of cold stratification and at low temperatures, but only after the stratification. Litter produced by dicotyledonous forbs was less hampering for the seedlings than that of small sedges or grasses. Valeriana dioica possesses a broad regeneration niche and is able to use gaps for germination and establishment both in spring and in summer. It reproduces successfully in herb-dominated fen meadow vegetation but disappears from reed communities. This study demonstrates the significant plasticity of the regeneration niche for a species with an intermediate life strategy and also stresses the importance of gaps for its reproduction.

Supervivencia de una cohorte de plántulas de Abies religiosa bajo diferentes condiciones postincendio

The survival of a cohort of <em>Abies religiosa </em> seedlings was investigated during eight years in an intact forest (NAF) and forest patches affected by: shallow fi res (SUPAF), intermediate canopy fi res (ICAF), and full canopy fi res (FCAF). The objective of this paper was to provide a better understanding on the natural regeneration processes of <em>A. religiosa </em>. In each patch eight 1m2 plots were established and all rooted seedlings within each plot from the 1998 cohort were tagged. Seedling mortality and type of associated damage were recorded throughout censuses from 1998 to 2006. Fallen branches and desiccation of seedlings were the two most important factors associated with their death. Survival probabilities were the lowest in SUPAF and none in NAF. The highest survival probabilities were under ICAF condition, and it suggests that this type of fi re is an important component of the <em>A. religiosa </em> regeneration niche.