Yolanda Caceres

Doktorandin

Background

 

I am a very open and enthusiastic person and love to work in the field, in collaboration with teams, exchanging and communicating new ideas and questions within group discussions.

I joined iDiv because…

My graduate project represents a big challenge for me. I am trying to answer big questions, working with a multiplicity of factors and dealing with a complex ecosystem. Attending to iDiv’s graduate school I will have the chance to train creative and critical thinking skills needed during the entire process of my research.

On the other hand, discussing and reflecting my work, interacting with new people and establishing a working rhythm on campus is also an important part to assure successful work completion. This international graduate school has a great potential to accompany students, promote co-operation, enrich knowledge as well as in helping in career planning and in networking.

Background

As a plant ecologist my research interests have been mainly oriented to the study of biological interactions, biodiversity patterns and climate change effects on mountain ecosystems exploring diverse disciplines and their methods as complementary tools.

Research focus/interest/current research

Since my undergrad studies I have been interested on different aspects linking applied and theoretical ecology. During my bachelor thesis I worked with treeline ecophysiology in Venezuelan Andes.

More recently, during my master studies I emphasized on issues such as changes in the diversity and community structure along spatial and temporal gradients, adaptive strategies in plant species to extreme environments, also in tropical alpine ecosystems.

As a Humboldt Foundation Fellow (2012-2013) I had an enriching stay in Tübingen University researching on scale the dependence of plant-plant and plant-pollinator interactions and the operating mechanisms behind them.

Research Project

 

"Combined effects of altitude, fire and biotic interactions on the regeneration of subtropical mountain forest species in Central Argentina"

The subtropical forests ecosystems of South America and their species are currently one of the major global conservation priorities given their extraordinary endemism and the great antiquity of its biogeographic relationships (Villagrán & Hinojosa 1997). Nevertheless, climate change together with land use dynamics are expected to have serious consequences for landscape in the whole region, especially for agricultural activities, tourism and particularly for biodiversity conservation.

The knowledge gap

The restoration of subtropical mountain forests is currently serious concern; but unfortunately the current lack of understanding of the post-fire regeneration ecology of native mountain forest species subjected to grazing is one the main limiting factors to promote natural regeneration of degraded areas and also improve resilience facing climate change threats.

My PhD research - inserted in a bigger GFD binational project between MLU-Halle and Universidad Nacional de Córdoba - seeks to make a significant contribution on this topic

Research question / Hypotheses

(Q1)   What relative contributions do the different regeneration modes (sexual vs. vegetative) of subtropical mountain forest species make to post-fire recovery?

(H1) We expect that regeneration by seed is relatively more important at intermediate elevations, while vegetative reproduction is more prominent at the altitudinal extremes as a strategy to cope mainly with harsher abiotic conditions at the upper extreme and harsher biotic conditions at the lower.

(Q2)   How do altitude, grazing and the most important post-fire vegetation (through competition vs. facilitation) affect germination, seedling survival and growth of our study species?

(H2) We expect that all types of tall accompanying vegetation that provide freezing protection will facilitate establishment with increasing altitude. At lower altitudes, competition will be prevalent and facilitation will occur only by life forms providing shade and using water from deeper soil layers (shrubs as opposed to forbs and grasses, which use surface water).

Nurse plants will differ in their capacity to protect seedlings/saplings against browsing, and we expect a negative relationship between regeneration and grazing intensity.

(Q3)   Does local adaptation to climatic conditions of populations from different altitudes affect seed longevity, germination, seedling survival and growth of our study species?

(H3) We expect that local adaptation will be more pronounced in species with short seed dispersal distances (gravity dispersed, as in Polylepis australis), and less important for species with larger seed dispersal distances (e.g. seeds dispersed by birds, as in Maytenus boaria).

Methods to be used

1.      Observational studies of natural regeneration after fire

Along four altitudinal transects established in the burned forest (elevational gradient ranging from 900 to 2500 m), patterns of vegetative and sexual post-fire regeneration will be evaluated.

      1a. Post-fire regeneration types along environmental gradients

We will establish study plots of 5 m radius centred among scorched crown trees/scrubs (n=20) at elevation intervals of 200 m. Thus, for species distributed across the entire altitudinal range, this will imply sampling a maximum of 640 living individuals (20 x 8 x 4 transects). We will estimate pre-fire crown height and width, as judged by the remnant stems.

To determine the influence of pre-fire individual size and abiotic site characteristics on post-fire regeneration, we will measure numbers of browsed and non-browsed resprouts, their basal diameters and lengths and overall survival as proxies for resprout success and influence of grazing. We will also evaluate the presence/absence of seed production. Density will be inferred by measuring the distance to the six closest individuals of the same species.

Regeneration by seed will be quantified by searching for the presence of seedlings and saplings in 20 square quadrats (0.25 m2) randomly placed within our study. We will record their height and width in the same way as for the woody seeders, thereby permitting the calculation of the relative contribution to tree/scrub volume that recovers two years after the fire through vegetative and sexual reproduction (resprout and seedling/sapling volume).

We will also record site characteristics such as slope, solar incidence and proportion of rock, and temperature/atmospheric humidity.

Livestock intensity will be estimated by randomly placing a 30 x 30 cm quadrat 25 times around each of the study trees and scrubs to register dung, and by calculating a density index based on this data (Cingolani et al. 2003).

2.      Experimental studies

Sowing and planting experiments will be carried out along two elevational gradients.

         2a. Importance of biotic interactions for forest species regeneration

Our experiments will be focused along the unburned elevational gradient within four livestock exclosures (20 ha) (one livestock exclosure per 500/600 m of elevation. These exclosures provide established post-fire vegetation types that we will use as neighbors. Livestock density outside the exclosures will be assessed.

Seeds will be collected from at least 20 individuals per species and at the altitudinal level of the respective exclosure. Saplings will be established in local greenhouses. Half a year old saplings will be planted within and outside our exclosures across four microhabitats: 1) Under individuals of unpalatable spiny shrubs (at 1200 m Condalia montana, Rhamnaceae, at 1800 and 2300 m Berberis hieronymi, Berberidaceae); 2) among groups of unpalatable tussock grasses (at 1200 and 1800 m Festuca hieronymi, at 2300 m Poa stuckertii); 3) within typical grazing lawns composed of over 40 species of short grasses; and 4) on bare ground (control sites cleared of vegetation).

The experiment will be set up using a split-plot design: The study design will include the two grazing treatments (grazed/ungrazed) at each of the four altitudes (2 to 3 altitudes per species) and will constitute the main plot level (2 x 4 = 8 plots).

Within each exclosure and each grazed plot, we will establish 25 blocks containing several subplots of 1 m², which will be randomly assigned to one replicate of each factorial combination of study species and microhabitat. Depending on whether there are only two study species or all four study species present at a given altitude, each block will contain either eight subplots (2 species x 4 microhabitats) or 16 subplots (4 species x 4 microhabitats).

Within each study subplot we will sow 200 seeds and plant one sapling of each of the respective study species, resulting in a total of 120,000 seeds and 600 saplings per species for Polylepis australis and Maytenus boaria (studied at 1200, 1800 and 2300 m)

            2b. Elevational transplantation experiment on the importance of local adaptation

Our transplantation experiments will be focused along a burned elevational gradient where seven livestock exclosures measuring 20 x 20 m each will be established (one livestock exclosure per 300 m of elevation; 900-2700 m; we will use additional 40 x 40 cm cages (outside existing exclosures) to increase the number of site plots per elevation).

For each study species, seeds will be collected from at least 5 maternal trees/shrubs in each of 5 local populations per altitude (three altitudinal provenances per species: lower, intermediate and upper distribution limit). Saplings will be produced in local greenhouses. To identify important functional traits (Cornelissen et al. 2003), seed mass, seed sizes and initial seed viability will be determined per individual (Win Seedle). At each of the three altitudes per species (Polylepis australis and Maytenus boaria 1200/1800/2300 m), we will establish 8 site subplots within the exclosures, where we will sow 200 seeds of each of the altitudinal provenances per species (40 seeds of each local population). Site subplots and cages will be cleared of aboveground vegetation. In each of the 25 cages, we will plant one sapling from each altitudinal provenance (1 offspring from each of the 5 seed families of each of the 5 local populations). This will result in a total of 4800 seeds and 25 saplings per elevation (3) and per species (4). We are aware that using a single offspring per seed family limits the precision of estimates of within-population variation. However, as we are interested in general altitudinal effects across species.

Seedling emergence will be checked half yearly during the first year and sapling survival and growth height will be measured one and two years after planting. We will assess key functional traits of all saplings, including growth height, relative growth rate, several leaf traits reflecting the leaf economics spectrum (leaf dry matter content, leaf mass per area, leaf size and thickness; Richardson et al. 2013; using Win Folia), chlorophyll content (as a proxy of N-content; SPAD measurement device) and leaf C/N ratio (on exported leaves in the lab in Halle, Germany) following the protocols for standardized trait measurements (Cornelissen et al. 2003).

To analyze seed longevity in the soil and possible influences of local adaptation and elevational gradient, seed burial experiments using seeds of our two study species will be set up within the three exclosures. In each exclosure, 10 replicates of 50 seeds from each of the three elevational provenances will be buried at 5 cm depth in mesh envelopes for a maximum of 3 years. Seed viability will be determined yearly (end of wet season) on a portion of the seeds.

3.      Statistical Analysis

Both observation and experimental studies will be analyzed using generalized linear mixed effect models. Resprouting and seedling/sapling abundance will be tested against altitude and grazing effects, also testing for microsite conditions as interacting variables. In a second approach, proportions of resprouting individuals and seedlings will be tested using binomial models.

Seedling and sapling survival, growth and relative growth rates will be analyzed using mixed linear models according to the split plot design of the field experiment: Elevation and grazing will be considered as fixed effects and tested against the 'elevation x grazing interaction' as a random effect; species, microhabitat and their interactions with grazing and elevation will be fixed effects tested against the residuals after controlling for the block effect. Effects of species will be tested based on survival, relative growth rates and the trait analyses, while accounting for initial height as a covariate. Mixed models will be calculated with species, altitudinal provenance, altitude of transplantation site, and their interactions as fixed effects, and population nested within species and altitudinal provenance as a random effect. The interaction 'altitudinal provenance x altitude of transplantation site' will be used as criterion for local adaptation (i.e. the “local vs. foreign” criterion).

Scientific Activities

 

Publications

Cáceres Y., Llambí LD. and Rada Fermín. 2015. Shrubs as foundation species in a high tropical mountain ecosystem: a multi-scale analysis of plant spatial interactions. Plant ecology and Diversity 8 (2): 147-161

Cáceres, Y. and F. Rada. 2011. ¿How does the woody species Vaccinum Meridionale respond to temperature in its altitudinal limit of distribution in the tropical Andes? Ecotrópicos 24(1):80-91

Conference Contributions

Bonn, GERMANY 2014. International DAAD Alumni-Seminar “Reflecting Biodiversity – Holistic approaches and regional adaptation” 12– 15 September 2014. (Seminar scheduled in the run-up to the international BION conference “Biodiversity Today for Tomorrow” (17 – 19 September 2014).

London, ENGLAND 2013. Y. Cáceres, L. Llambí and F. Rada. Effect of a Dominant Shrub on Community Organization in a Tropical Alpine Ecosystem: a multi-scale analysis of plant spatial interactions. INTECOL 2013

Bonn, GERMANY 2012. Global Climate Change – Approaches to international cooperation. 3° International Symposium on climate protection and resource conservation for Young academics. Alexander von Humboldt Foundation

Tübingen, GERMANY 2012. Y. Cáceres  and M. Seifan. Developing a conceptual approach to assess the role of shared pollination in fragmented landscapes: a multiscale view. STEVE the Meeting of Students in Evolution in Ecology

Buenos Aires, ARGENTINA 2010. Garcia C., Y. Cáceres and M. León. Facilitative effect from Baccharis magellanica and Acaena intergerrima within a biotic gradient of Nothofagus antarctica in the Chilean Patagonia. IV Ecology Binational Meeting Chile-Argentina.

Loja, ECUADOR 2009. Cáceres Y. and F. Rada. Ecophysiological features of Vaccinium meridionale near its upper altitudinal limit in the tropical Andes. II World Congress of Paramos (PARAMUNDI).

Memberships 

British Ecological Society

Sociedad Venezolana de Ecología

iDiv-Publikationen

 

Schrieber, K., Caceres, Y., Engelmann, A., Marcora, P., Renison, D., Hensen, I., Muller, C.

(2020): Elevational differentiation in metabolic cold stress responses of an endemic mountain tree. Environmental and Experimental Botany 171 *

Caceres, Y., K. Schrieber, S. Lachmuth, H. Auge, D. Argibay, D. Renison, I. Hensen

(2019): Effects of altitude, land use and microsites on early life performance of a high mountain tree: Insights from an in situ sowing experiment. Diversity and Distributions 25(10), 1537-1550 *
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Institut für Biologie/ Geobotanik und Botanischer Garten
Am Kirchtor 1
06108 Halle

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+49 345 5526211
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Affiliation

Martin-Luther-Universität Halle-Wittenberg

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