Melisa A. Giorgis

Factors associated with woody alien species distribution in a newly invaded mountain system of central Argentina

To help determine the major factors associated with alien plant in a newly invaded mountain range; we analyzed the distribution patterns of woody alien species along the altitudinal gradient of the Córdoba mountains, in relation to biotic, abiotic and anthropogenic factors. We selected 303 plots using a Geographic Information System (GIS) covering all the variability of these factors. In the field we registered woody alien occurrence in these 303 and in 303 additional neighbor plots. We used 12 biotic, abiotic and anthropogenic variables from the GIS to predict the probability of presence of alien species through a logistic model. Then, we analyzed if neighbor alien occurrences could explain some additional variance. We created a probability map with 4 categories of alien occurrence which was then validated by new field sampling. Occurrence of woody aliens was highest in the eastern slope (with longer history of species introduction), at low altitudes, near sources of propagule pressure (human settlements, roads and neighbor sites with established alien plants), and associated to sheltered topographies. In the upper belt of the Córdoba Mountains woody invasion is incipient and thus in a transient stage. Accordingly, propagule pressure seems to be the major factor at play, while the relevance of disturbance and biotic interactions is less clear.

Evidence of shift in C4 species range in central Argentina during the late Holocene

AimMillennial-scale biogeographic changes are well understood in many parts of the world, but little is known about long-term vegetation dynamics in subtropical regions. Here we investigate shifts in C3/C4 plant abundance occurred in central Argentina during the past few millenniaMethodsWe determined present day soil organic matter δ13C signatures of grasslands, shrublands and woodlands, containing different mixtures of C3 and C4 plants. We measured past changes in the relative cover of C3/C4 plants by comparing δ13C values in soil profiles with present day δ13C signatures. We analyzed 14C activity in soil depths that showed major changes in vegetation.ResultsPresent day relative cover of C3/C4 plants determines whole ecosystem δ13C signatures integrated as litter and superficial soil organic matter (R2 = 0.78; p < 0.01). Deeper soils show a consistent shift in δ13C, indicating a continuous replacement of C4 by C3 plants since 3,870 (±210) YBP. During this period, the relative abundance of C3 plants increased 32% (average across sites) with significant changes being observed in all studied ecosystems.ConclusionsOur results show that C4 species were more abundant in the past, but C3 species became dominant during the late Holocene. We identified increases in the relative C3/C4 cover in grasslands, shrublands and woodlands, suggesting a physiological basis for changes in vegetation. The replacement of C4 by C3 plants coincided with changes in climate towards colder and wetter conditions and could represent a climatically driven shift in the C4 species optimum range.

Germination Characteristics of Four Argentinean Endemic Gymnocalycium (Cactaceae) Species With Different Flowering Phenologies

Abstract We analyzed germination percentages and germination rates at four temperature treatments (5/15, 10/20, 15/25 and 20/35 °C) and in light or darkness in four endemic species of the genus Gymnocalycium with different flowering phenologies from the Córdoba Mountains (Argentina). Gymnocalycium bruchii flowered and dispersed its seeds very early in the season in comparison to the other three species. No seeds germinated in darkness or at the coldest temperature regime. For all species except G. bruchii, germination was higher at the two warmest treatments. Gymnocalycium bruchii germination was maximum at the second warmest temperature (15/25 °C) and did not germinate at all at the highest temperature treatment (20/35 °C). Germination varied strongly among species, from about 80% in G. quehliaum to 20% in G. monvillei. Germination rate (t50) varied more strongly among temperature treatments (from 15 to 7 days in the coldest and warmest treatments respectively) than among species. The lack of germination of G. bruchii at 20–35 °C could be related to its early flowering phenology.

The diverse globose cactus community of Argentina's Sierras Chicas Ecology and conservation

Fil: Gurvich, Diego Ezequiel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto Multidisciplinario de Biologia Vegetal. Universidad Nacional de Cordoba. Facultad de Ciencias Exactas Fisicas y Naturales. Instituto Multidisciplinario de Biologia Vegetal; Argentina

Flowering phenology, fruit set and seed mass and number of five coexisting Gymnocalycium (Cactaceae) species from Córdoba mountain, Argentina1

Abstract Flowering phenology may play a critical role in plant coexistence, allowing not only a temporal partitioning of resources but also conditioning the relationship between seed mass and number in these species. We analyzed how flowering phenology was related to seed mass and number, and how these seed traits were related in five coexisting Gymnocalycium (Cactaceae) species in two consecutive flowering seasons. The flowering phenology of each species was characterized in terms of timing (onset and peak), duration, and flowering synchronicity. Although species showed differences in duration and synchronicity, the earliest flowering species tend to have higher reproductive success than species flowering later. However, we did not find a clear relationship between the flowering time and seed traits. A trade-off between seed mass and number in these species was highlighted, as species with higher seed mass were those producing a lower number of seeds per fruit and individual, whereas species with lower seed mass had a higher number of seeds. Our results showed a temporal resource partitioning associated with differences in flowering timing among species, which may lead to differences in reproductive success (number of mature fruits and fruit set) and highlight the importance of the trade-off between colonization vs competitive ability in promoting plant coexistence.

Changes in floristic composition and physiognomy are decoupled along elevation gradients in central Argentina

Question(s) Most vegetation descriptions tacitly assume that floristic composition and physiognomy are tightly linked. However, both vegetation properties may not respond in a similar way to environmental and disturbance gradients, leading to uninformed management planning and difficulties when attempting to restore degraded ecosystems. In this context, we addressed two main questions: how close are relations between floristic and physiognomic types as defined by numerical vegetation classification in mountain ecosystems? How are floristic and physiognomic types distributed along the elevation gradient?. Location Central mountains of Argentina, 31° 27′, 64° 54′, between 500 and 1700 m a.s. l. Methods We selected 437 sites where we performed complete floristic and physiognomic releves. We classified eight physiognomic and eight floristic types. We tested the relationship between both classifications through a chi2 analysis. We tested the association between elevation and each physiognomic and floristic type performing random permutations. Results In general, floristic types were significantly and positively associated with more than one physiognomic type and vice versa. Physiognomic and floristic types responded differently to the elevation gradient. Floristic types were restricted to different sections of the gradient, though having large overlap among them. In contrast, seven out of the eight physiognomic types did not show elevation restriction, being distributed along the complete elevation gradient. The open low woodland with shrubs was the only restricted physiognomy, significantly absent from the upper part of the gradient. Conclusions We highlight the importance of considering both vegetation properties independently when characterizing vegetation patterns in heterogeneous systems, since they show decoupled responses to environmental gradients. We notice that the assumption of a direct link between floristic composition and physiognomy may induce bias into the understanding of vegetation patterns and processes. For that reason, we encourage managers and restoration practitioners to consider the complete range of possible physiognomic types under each floristic type. This article is protected by copyright. All rights reserved.

Testing alien plant distribution and habitat invasibility in mountain ecosystems: growth form matters

Most studies focused on understanding habitat invasibility use the current levels of invasion as a direct proxy of habitat invasibility. This has shown to be biased by the influence of propagule pressure and climate. We suggest that plant growth forms need to be considered as an extra factor, as habitat preferences might not be equal for all potential invaders. We test the influence of propagule pressure, climate and habitat characteristics on the current level of invasion and habitat invasibility, specifically addressing whether an analysis focused on growth forms evidence different patterns than the total pool of alien species. We used 499 floristic vegetation plots located in Córdoba Mountains. We used proportional alien richness of the total pool and for each growth form as response variables. We identified models that best explained current levels of invasion. We used the residuals of the models with propagule pressure and climate as the response variable. Then, we performed linear models to test the relationship between habitat characteristics and the residuals of the models. We found different drivers of current alien distribution patterns for the total pool and each growth form. Habitat invasibility was not equal when quantified for the total pool or growth forms. Shrublands and outcrops were recorded as less susceptible to woody invasion, while grasslands and native woodlands were resistant to the invasion of grasses and none habitat type was resistant to the invasion of forbs. We highlight that the current level of invasion and habitat invasibility are highly growth form dependent.

Impact of Ligustrum lucidum on the soil seed bank in invaded subtropical seasonally dry woodlands (Córdoba, Argentina)

The impact of invasive species on below ground flora may differ from that on the above ground vegetation. Recent reviews of invaded and native communities emphasize the need for more comprehensive information on the impacts of plant invasion on soil seed banks. Ligustrum lucidum is one of the most important invasive woody species in several ecosystems of Argentina; however, its impact on soil seed bank communities has not been studied. Here we analyzed differences in species richness, total seed density and species composition (total, native and exotic species) in the soil seed bank of native and invaded woodlands, in two different seasons. We also analyzed differences in similarity between standing vegetation and soil seed banks of both woodland types. The study was carried out in the Chaco Serrano woodlands of Córdoba, central Argentina. Our main results indicate differences in L. lucidum woodland composition and a reduction in both richness and total density of species in the soil seed bank compared to the native woodlands, independently of the sampling season. Moreover, a higher abundance of certain exotic species in the soil seed bank was observed in L. lucidum woodlands, particularly in spring. Finally, low similarity between soil seed bank and the established vegetation was observed in both woodland types. From a management perspective, it seems that passive restoration from soil seed banks of L. lucidum might be coupled with active addition of some native woody species and control of other exotic species.

Functional strategies and distribution of climbing plant communities in different vegetation patches in a subtropical dry forest, central Argentina

Fil: Ferrero, Maria Cecilia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto Multidisciplinario de Biologia Vegetal. Universidad Nacional de Cordoba. Facultad de Ciencias Exactas Fisicas y Naturales. Instituto Multidisciplinario de Biologia Vegetal; Argentina