Phenology and phylogeny of animal-dispersed plants in a Dry Chaco forest (Argentina)

doi:10.1006/jare.2002.0976

Journal of Arid Environments

Volume 52, Issue 1, September 2002, Pages 1-16

https://doi.org/10.1006/jare.2002.0976 Get rights and content

Abstract

Phenological patterns of dry tropical forests have been related to environmental factors, mainly rainfall and insolation, and to plant endogenous rhythms inherent to trees as large, perennial plants. Superimposed to these environmental (‘external hypothesis’) and intrinsic (‘endogenous hypothesis’) explanations, there may be phylogenetic constraints contributing to shape phenology.

The phenology of tree and shrub species with fleshy fruits in a Dry Chaco forest in Argentina was studied addressing these hypotheses and following two approaches, with the species average values taken as independent data points, and removing phylogenetic effects.

The hypotheses addressed are largely complementary to one another. Strong environmental restrictions conditioned general flowering patterns with species endogenous characteristics acting secondarily. Phylogenetic patterns were also masked by climatic variables. When considering fruiting phenology, however, phylogeny, representing a set of species shared traits, predominated over environmental restrictions.

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The study was conducted in the Dry Chaco of central Argentina, assessing the seed dispersal role of Black-legged seriemas (Chunga burmeisteri). We collected 42 faeces of C. burmeisteri and found that all of them contained seeds from at least three woody plant species: algarrobo dulce (Neltuma flexuosa), tintitaco (Strombocarpa torquata) and mistol (Sarcomphalus mistol). We were able to compare the germination rates of seeds found in the faeces of C. burmeisteri with control seeds that did not undergo endozoochory only for N. flexuosa. The percentage of germinated seeds was slightly higher in the seeds that were ingested by C. burmeisteri compared to the control group. This study provides the first evidence of C. burmeisteri ‘s role as a seed disperser for dominant trees in the Dry Chaco forest. The discovery is surprising because C. burmeisteri was previously known only for its predatory behaviour. These findings highlight the need for further research on tree dispersal by vertebrates in the Chaco region, considering that dry forests, like the Chaco, are among the most threatened ecosystems worldwide.
Reproductive phenology of cacti species in the Brazilian Chaco
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In an area of dry Chaco in Argentina, flowering and fruiting activities intensified during sunnier periods (Marco and Paéz, 2002). According to Marco and Paez (2002), the seasonal patterns of solar irradiation and rainfall, which are positively correlated, provide conditions that trigger the phenological activities of the species studied. Nevertheless, different results were observed for Harrisia portoricensis Britton on Mona Island (Rojas-Sandoval and Meléndez-Ackerman, 2011), which displayed reproductive phenological patterns that did not correlate with day length.
In this study, we made monthly assessments of the reproductive phenology of ten cacti species that are widely distributed in the Brazilian Chaco over a 2-year period. We tested whether different climatic regimes in this region promoted the evolution of different reproductive strategies among cacti species. We applied circular statistics and the Rayleigh test to determine whether flowering and fruiting were seasonal and to detect significant periodic patterns. Multiple linear regressions were used to determine the influence climatic variables had on the number of flowers and fruits produced by each species. The flowering and fruiting periods began during the rainy season and peaked in November and January, respectively. Annual and continuous patterns were observed, which presented extended durations. The timing of flowering and fruiting was positively associated with day length and temperature. Rainfall was not significant in any of the models. In the Brazilian Chaco, the cacti reproductive phenophases were triggered by changes in day length and temperature. The similarity in flowering and fruiting patterns among the cacti species with extended durations generated a significant amount of overlap in flowering and fruiting, which may be a strategy to maintain pollinator and seed disperser populations in this environment.
Mapping continuous fields of tree and shrub cover across the Gran Chaco using Landsat 8 and Sentinel-1 data
2018, Remote Sensing of Environment
Citation Excerpt :
Contrary, when only using Sentinel-1 data, shrub cover showed better model performances than tree cover (Fig. 4). Several factors explain this: first, larger trees in the Chaco have a stronger phenological cycle compared to shrubs (Marco and Páez, 2002). This phenology was picked up stronger by the Landsat metrics than the Sentinel-1 metrics, because more Landsat observations per pixel were available than from Sentinel-1.
Tropical dry forests and savannas provide important ecosystem services and harbor high biodiversity, yet are globally under pressure from land-use change. Mapping changes in the condition of dry forests and savannas is therefore critical. This can be challenging given that these ecosystems are characterized by continuous gradients of tree and shrub cover, resulting in considerable structural complexity. We developed a novel approach to map, separately, continuous fields of tree cover and shrub cover across the South American Gran Chaco (1,100,000 km²), making full use of the Landsat-8 optical and Sentinel-1 synthetic aperture radar (SAR) image archives. We gathered a large training dataset digitized from very-high resolution imagery and used a gradient-boosting framework to model continuous fields of tree cover and shrub cover at 30-m resolution. Our regression models had high to moderate predictive power (85.5% for tree cover, and 68.5% for shrub cover) and resulted in reliable tree and shrub cover maps (mean squared error of 4.4% and 6.4% for tree- and shrub cover respectively). Models jointly using optical and SAR imagery performed substantially better than models using single-sensor imagery, and model predictors differed strongly in some regions, especially in areas of dense vegetation cover. Mapping tree and shrub cover separately allowed identifying distinct vegetation formations, with shrub-dominated systems mainly in the very dry Chaco, woodlands with large trees mainly in the dry Chaco, and tree-dominated savannas in the wet Chaco. Our tree and shrub cover layers also revealed considerable edge effects in terms of woody cover away from agricultural fields (edge effects extending about 2 km), smallholder ranches (about 1.2 km), and roads and railways (about 1.4 and 0.9 km, respectively). Our analyses highlight both the substantial footprint of land-use on remaining natural vegetation in the Chaco, and the potential of multi-sensoral approaches to monitor forest degradation. More broadly, our approach shows that mapping canopy structure and distinct layers of woody vegetation in dry forest and savannas is possible across large areas, and highlights the value of the growing Landsat and Sentinel archives for doing so.
Fruiting phenology and implications of fruit availability in the fragmented Ngele Forest Complex, KwaZulu-Natal, South Africa
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Citation Excerpt :
Phenological cycles of trees are established in order to maximize reproductive success (Anderson et al., 2005). Several factors have been shown to influence fruiting phenology, including: phylogeny, environmental conditions, and biogeographic history (Griffiths and Lawes, 2006; Marco and Paez, 2002). In areas where there are strong annual climatic cues, phenology is mostly predictable (Haugaasen and Peres, 2005).
Fragmented forests are under threat worldwide. Understanding fruiting phenology of these is important in terms of food supply to frugivores, particularly avifauna, which can move varying distances between forest fragments. Fragmentation can affect tree species' diversity, which in turn determines fruit availability and quality. Many forest types have predictable, synchronous fruiting which is often linked to climatic cues. However, some forest types show no seasonality in fruiting and have varying fruit outputs between years. We investigated the fruiting phenology of four forest fragments in the Ngele Mistbelt Forest complex, which forms part of the Eastern Mistbelt Forests in KwaZulu-Natal, using fruit-fall traps. We hypothesized that fruit availability would vary with forest fragment size and with season. Fruiting in three of the forest fragments did not show seasonal fruiting trends and had increased fruiting in late summer and autumn months. Middlebrook showed trends. Fruiting varied significantly between months for all fragments, and where annual variation was observed trends were insignificant. The number of fruiting species per fragment varied significantly and numbers of fruiting species per fragment per month were generally low. Tree species varied in their fruiting patterns between fragments and fruiting of Afrocarpus/Podocarpus trees and the implications for endemic, endangered Cape Parrots are discussed as an example. In summary, these forests have variable and unpredictable fruiting between fragments. These results highlight the need to conserve forest fragments of varying sizes as a network to provide a year round supply of fruits to frugivores.
Plant species richness in the Chaco Serrano Woodland from central Argentina: Ecological traits and habitat fragmentation effects
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Citation Excerpt :
Plant species were also classified according to their life form (trees, shrubs, herbs, grasses, vines, epiphytes, ferns and Cactaceae) and to their origin (native and exotics) after consulting the Flora Argentina Catalogue (Instituto Darwinion, 1997). Pollination and dispersal mode were derived from literature (Abraham de Noir et al., 2002; Aizen et al., 2002; Marco and Páez, 2002) and the observation of flower and fruit structures that represent an attraction or reward to animals. Data from the two sampling plots from each site were pooled in order to estimate remnant species richness (total and for each category).
The Chaco Serrano Woodland from central Argentina has been dramatically reduced during the past 30 years, and is currently confined to several isolates of different size. In this study, we evaluated the effects of forest size, isolation and edge formation on plant species richness. Furthermore, we tested whether plants species with particular ecological traits were differentially affected by habitat fragmentation. Habitat area showed the highest explanatory value for plant species richness in stepwise multiple regressions. The effect of area was most pronounced for rare species, suggesting that large forests are necessary to preserve species with low local or regional abundance. Differences between edge and interior of Chaco Serrano were more pronounced for native and shrub species richness. The analysis of individual species cover revealed that native and biotically pollinated plants were less abundant in woodland edges. Our results showed that forest transformation into smaller remnants has lead to an impoverishment of plant communities, with particular subsets of species defined by ecological traits (rarity, origin and pollination mode) being more susceptible.
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^*: Corresponding author. Present address: Fleming 48, Salsipuedes, CP X5113BPB, Córdoba, Argentina. E-mail: [email protected]

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Regular ArticlePhenology and phylogeny of animal-dispersed plants in a Dry Chaco forest (Argentina)

Abstract

Journal of Theoretical Biology

Journal of Arid Environments

Journal of Arid Environments

Herbivory as selective agent on the timing of leaf production in a tropical understory community

Nature

Forest fragmentation, pollination, and plant reproduction in a Chaco dry forest, Argentina

Ecology

Drought, diastrophism, and quantum evolution

Evolution

Phenology and control of flowering in tropical trees

Biotropica

Growth periodicity

Computer simulation of tree growth hydroperiodicity in tropical forests

Biotropica

Phylogenetic analysis of trait evolution and species diversity variation among angiosperm families

Evolution

Phylogenies and the comparative method

American Naturalist

Comparative phenological studies of trees in tropical wet and dry forests in the lowlands of Costa Rica

Journal of Ecology

The Comparative Method in Evolutionary Biology

Comparative methods for explaining adaptations

Nature

Why ecologists need to be phyllogenetically challenged

Journal of Ecology

Fruit variation and competition for dispersers in natural populations of Smilax aspera

Oikos

Synchronization of sexual reproduction of trees within the dry season in Central America

Evolution

Constraints and competition in the evolution of flowering phenology

Ecological Monographs

Seasonality and phenology in a dry tropical forest in Ghana

Journal of Ecology

Regular Article
Phenology and phylogeny of animal-dispersed plants in a Dry Chaco forest (Argentina)