Karina Piermarteri

Evidence of Facilitation Cascade Processes as Drivers of Successional Patterns of Ecosystem Engineers at the Upper Altitudinal Limit of the Dry Puna

Facilitation processes constitute basic elements of vegetation dynamics in harsh systems. Recent studies in tropical alpine environments demonstrated how pioneer plant species defined as “ecosystem engineers” are capable of enhancing landscape-level richness by adding new species to the community through the modification of microhabitats, and also provided hints about the alternation of different ecosystem engineers over time. Nevertheless, most of the existing works analysed different ecosystem engineers separately, without considering the interaction of different ecosystem engineers. Focusing on the altitudinal limit of Peruvian Dry Puna vegetation, we hypothesized that positive interactions structure plant communities by facilitation cascades involving different ecosystem engineers, determining the evolution of the microhabitat patches in terms of abiotic resources and beneficiary species hosted. To analyze successional mechanisms, we used a “space-for-time” substitution to account for changes over time, and analyzed data on soil texture, composition, and temperature, facilitated species and their interaction with nurse species, and surface area of engineered patches by means of chemical analyses, indicator species analysis, and rarefaction curves. A successional process, resulting from the dynamic interaction of different ecosystem engineers, which determined a progressive amelioration of soil conditions (e.g. nitrogen and organic matter content, and temperature), was the main driver of species assemblage at the community scale, enhancing species richness. Cushion plants act as pioneers, by starting the successional processes that continue with shrubs and tussocks. Tussock grasses have sometimes been found to be capable of creating microhabitat patches independently. The dynamics of species assemblage seem to follow the nested assemblage mechanism, in which the first foundation species to colonize a habitat provides a novel substrate for colonization by other foundation species through a facilitation cascade process.

Filtering effect of temporal niche fluctuation and amplitude of environmental variations on the trait-related flowering patterns: lesson from sub-Mediterranean grasslands

Timing of flowering is a critical component of community assembly, but how plant traits respond to heterogeneity of resources has been identified mostly through observations of spatial variations. Thus, we performed a trait-based phenological study in sub-Mediterranean grasslands to assess the importance of temporal variation of resources in the species assemblage processes. We found that early flowering species have traits allowing for slow resource acquisition and storage but rapid growth rate. Instead, mid- and late-flowering species exhibited sets of strategies devoted to minimizing water loss by evapotranspiration or aimed at maximizing the species’ competitive ability, thanks to slow growth rate and more efficient resource acquisition, conservation and use. Our findings were consistent with the fluctuation niche theory. We observed that the amplitude of the environmental fluctuations influences the type and number of strategies positively filtered by the system. In fact, in the most productive grasslands, we observed the highest number of indicator trait states reflecting strategies devoted to the storage of resources and competition for light. Results seem also indicate that temporal variation of resources plays a role in trait differentiation and richness within a plant community, filtering traits composition of grasslands in the same direction, as formerly proved for spatial heterogeneity of resources.

Distribution of the Nurse Species Pycnophyllum molle J. Rémy and P. weberbaueri Muschl. in the Andean Dry Puna (Arequipa District — Southern Peru): Role of Topographic/Soil Variability and Disturbance Regime

ABSTRACT: The dry Puna is the widest pastoral ecosystem of the tropical alpine Andes, characterized by harsh environmental conditions (long and intense drought stress periods and unfertile soils) and grazed by wild and domestic camelids. In these conditions, facilitation is of key importance in plant diversity conservation. Indeed, facilitation is a positive plant-plant interaction by which the so called nurse species provide environmental amelioration of harsh conditions and/or refuge to other plants (beneficiary species), which otherwise might fail to establish. The research aims were to understand which ecological variables affect the distribution of the potential nurse cushion species Pycnophyllum molle J. Rémy and P. weberbaueri Muschl., and if these species are affected by grazing disturbance. The study area (4000–4900 m a.s.l.) is located in the southern Peruvian Andes. Data of species cover, topographic and soil features, besides type of disturbance were collected along transects. We used canonical redundancy analysis to understand the relations between the cover of the two Pycnophyllum species and the above mentioned constraining variables. Results indicate that both the Pycnophyllum species grow on sandy loam, moderately acid soils, with low organic matter and very poor nitrogen content, and avoid high disturbance intensities. P. molle is more sensitive than P. weberbaueri to disturbance, and grows on relatively more fertile soils, also at higher altitudes and on steeper slopes characterized by greater rockiness.