Grassland-forest Mosaic Research Articles

Palynology of sedimentary soils in the Pampa biome: Grassland-forest mosaics and landscape-soil-pollen relationships

Pampa biome vegetation is characterized by extensive areas of native grassland, interspersed with forests close to water courses. An understanding is been searched on how grassland and forest dynamics to contribute for the conservation and management practices suitable for the biome. The objective of this study was to asses if landscape-soil-pollen relationships are determinant of grassland-forest mosaics, by analyzing summit, footslope and toeslope positions in the landscape, in the Campanha region of the Pampa biome. We collected 32 samples in three soil profiles in topossequence under natural grassland of the Pampa biome, in southern Brazil. These samples were treated following standard methodology used in palynology studies. The pollen percentage diagrams were generated to represent the identified pollen set, while cluster analysis was used to define the paleoecological zones. The results found were supported by radiocarbon dating (age of subsurface soil varying from 3,460 to 4,090 calibrated years before present), and particle-size analysis. The paleoecological zones, for each soil profile, indicate a predominance of grassland vegetation, especially Poaceae pollen, whereas Fabaceae and Piper were predominant in forest sites. The pollen set obtained in the three soil profiles indicates hegemony of the sites, even under climatic conditions of increased moisture. Rare pollen grains from forest taxa suggests that trees and shrubs existed in isolated form. The presence of bryophyte spores and taxa associated with soil wetness indicates that the region was once dominated by extensive wetlands and moist landscapes. Our findings enhance the comprehension of the Pampa flora, and are applicable in restoration of degraded areas. The preservation of pollen grains in soil profiles shows the potential of minerals soils to reconstitute Pampa biome vegetation, representing a site for palynological research advance, and demonstrate grassland formations maintain their supremacy even under unfavorable climatic conditions. Thus, this study expands the frontier of palynological work, encompassing new sites and new opportunities to evaluate land use/land cover changes.

Variability in leaf traits reveals contrasting strategies between forest and grassland woody communities across southern Brazil

Forests and grasslands often form mosaics in subtropical regions such as in southern Brazil. Currently, we observe the processes of woody species encroachment and forest expansion over grasslands due to changes in climate conditions and disturbance regimes. Woody plants occurring across such mosaics can be specialists from one habitat type (forest or grassland) or a generalist species (those occurring in both of these contrasting habitats). Here, we explore if their occurrence in distinct habitats is coordinated by functional traits, considering both intra- and interspecific variability and phylogenetic relatedness between species, thereby assessing changes between habitats from the individual to the community scale. We surveyed forest and grassland vegetation forming mosaics in nine sites in southern Brazil. We found that grassland-forest communities do not differ in phylogenetic diversity, irrespective of considering or not the gymnosperms of the communities. Furthermore, forests presented lower diversity in leaf area than grasslands, with a predominance of large leaves but higher diversity of specific leaf area and leaf dry matter content, with leaves predominantly with an acquisitive resource strategy. When considering species with different habitat preferences, forest-specialist species showed traits related to resource acquisition, while grassland-specialist species showed trait values associated with resource conservation. Generalist species have trait values according to habitat occurrence, showing high intraspecific variability and trait plasticity to establish on both forest and grassland habitats. Assessing the trait variability from woody individuals is important to understanding the contrasting strategies used by different species in grassland-forest mosaics and can be essential to predict the dynamics of these ecosystems, given the changes in climate and disturbances regimes.

First year woody survival supports feasibility of forest-steppe reconstruction as an alternative to landscaping in industrial areas

Urban-industrial restoration of complex native vegetation, such as grassland-forest mosaics could counteract land degradation and help develop methodology for larger scale complex restorations. We have studied the impact of grassland reconstruction techniques, the resulting biotic conditions, plus abiotic conditions on early woody survival in a forest-steppe reconstruction at an urban-industrial site. The study area is situated at the factory of the LEGO Group, Nyíregyháza in the acidic inland sand dune region of Nyírség, NE Hungary, Europe. Over 10,000 undercut 1-2-year-old saplings of 16 tree and shrub species were planted in patches of various size in November 2015 at ca. 20% of the restoration area. Specific plans were developed for each woody patch within the restored grassland. Tree and shrub survival was counted for all saplings in all patches in the summer of 2016. Vegetation height, cover of herb-layer, and elevation a.m.s.l. were estimated for each woody patch and soils were characterized for each restoration parcel. First year woody survival rates ranged between 4 and 66% for the different species. Only vegetation height had an overall negative impact on woody survival and seven species reflected some (often contradictory) impacts of the studied environmental variables. In our interpretation this shows that woody survival was basically independent of the grassland reconstruction techniques, but also that the management of the herb-layer of new woody plantations can be crucial in long-term maintenance. Our results support that the reconstruction of complex native habitats with a park-like appearance is a viable alternative to landscaping in industrial areas that can counteract land degradation and increase green infrastructure connectivity. The methods applied can be transferred to larger-scale restoration with modifications.

Loss of Generalist Plant Species and Functional Diversity Decreases the Robustness of a Seed Dispersal Network

SummaryUnderstanding cascading effects of species loss is a major challenge for ecologists. Traditionally, the robustness of ecological networks has been evaluated based on simulation studies where primary extinctions occur at random or as a function of species specialization, ignoring other important biological factors. Here, we estimate the robustness of a seed dispersal network from a grassland–forest mosaic in southern Brazil, simulating distinct scenarios of woody plant species extinction, including scenarios where species are eliminated based on their evolutionary and functional distinctiveness. Our results suggest that the network is more robust when species are eliminated based on their evolutionary uniqueness, followed by random extinctions, the extinction of the most specialist species, functional distinctiveness and, at last, when the most generalist species are sequentially eliminated. Our results provide important information for grassland–forest mosaic management, as they indicate that loss of generalist species and functional diversity makes the system more likely to collapse.

Moving from forest vs. grassland perspectives to an integrated view towards the conservation of forest–grassland mosaics

In this paper, we discuss some key aspects for the maintenance of biological diversity in grassland–forest mosaics in southern Brazil (Campos Sulinos) not explored yet. Campos Sulinos are grasslands distributed throughout the Pampa and the Atlantic Forest biomes. Since these grasslands remain from past dryer and colder climatic conditions, they are acknowledged as native rather than anthropogenic ecosystems (Pillar and Velez, 2010). The grasslands form mosaics with shrubby and forest physiognomies belonging to Araucaria and seasonal forests in southern Brazil, owing to climatic conditions suitable for forest expansion (Oliveira and Pillar, 2004). Thus, these ecosystems compete for spatial representativeness and resources in mosaics (Innes et al., 2013). Grasslands need specific attention and policies to proper management, conservation and sustainable use, since the ecological processes maintaining their biodiversity greatly differ from those driving diversity in forest ecosystems (Pillar and Velez, 2010; Overbeck et al., 2013). In ecosystems where climate favors woody vegetation, ecological disturbances are important for the temporal and spatial maintenance of grassy physiognomies (Bond and Parr, 2010; Pillar and Velez, 2010).

Plant diaspore traits as indicators of mutualistic interactions in woody vegetation patches developing into a grassland-forest mosaic

We evaluated the functional relevance of diaspore traits related to disperser attraction (DAT) of woody plants as indicators of plant-disperser mutualisms in the colonization of Araucaria forest patches in southern Brazil. Diaspores of colonizer plant genera were characterized in relation to DAT (diaspore type, size and color). We discriminated the influences of phylogenetic relationships among plant genera, forest patch size and interaction records with frugivorous birds on DAT by using variation partitioning based on Redundancy Analysis (RDA). DAT variation was poorly explained by each factor separately. Nonetheless, variation explanation shared between phylogeny and interactions was considerably high, indicating that the influence of interactions with frugivorous birds on DAT tended to be phylogenetically conserved. Furthermore, the variation related to patch size was high only when shared with phylogeny and interactions. Large, red, orange or brown diaspores, mainly berries and figs were related to more developed patches, while small to medium, violet or black drupes were related to small patches. Patch colonization is likely to result from a balance between plant responses to habitat conditions and plant diaspore traits, which is expected to influence seed deposition patterns depending on habitat use and diaspore handling by dispersers. Although phylogenetic habitat filtering is commonly thought to reflect ecophysiological plant traits, our results suggest that interactions with dispersers could also explain phylogenetic habitat filtering in plants.

Paradise burnt: How colonizing humans transform landscapes with fire

A striking feature of Southern Hemisphere landscapes is the occurrence of grasslands in regions that are climatically suitable for forests (Fig. 1). Ecologists and biogeographers working in these southern lands have developed a range of theories to account for the biogeographic anomaly of grassland–forest mosaics (1–7). Broadly speaking, these theories divide into those that privilege the importance of an ensemble of environmental factors, including fire, or those that stress the legacy of human landscape burning. The report by McWethy et al. in PNAS (8) provides incontrovertible evidence that anthropogenic burning transformed temperate forested landscapes on the South Island of New Zealand. They show that Polynesian (Māori) firing commenced shortly after colonization around A.D. 1280 and transformed 40% of the original forest cover of the island to grassland and fern-shrubland. There is little room for doubting their findings given the elegant integration of a range of paleoecological methodologies, very precise dating, and a high level of replication across the island. This report will spark renewed interest in the relative importance of fire, humans, and climate in shaping forest–grassland landscape mosaics worldwide (9).

Edge effects on epigeic ant assemblages in a grassland–forest mosaic in southern Brazil

This study analyzed the influence of vegetation structure variation along a natural vegetation mosaic formed by Araucaria forest and Campos grassland in the southern Brazilian highlands, on the species richness and composition of epigeic ants. The study site consisted of two different grassland–forest ecotones, where 76 pitfall traps were installed. We estimated the area covered by canopy vegetation by hemispherical photographs, and the structure of the understory vegetation by counting the number of vegetation touches, using a graduated stick. We collected 31 species or morphospecies of epigeic ants belonging to 17 genera and 6 subfamilies. Cluster analysis defined three habitat groups (grassland, edge, and forest) with different ant species composition as revealed by ordination analysis. The highest richness was observed at the forest edge, and decreased towards the grassland and the forest interior. Variation in the richness and composition of epigeic ant species was significantly explained by the factor of distance from the forest. The relationship between species richness and understory density was negative. On the other hand, species composition of epigeic ant assemblages was significantly explained by canopy cover. This finding indicates that the ecological responses of ant assemblages resulted predominantly from edge effects mediated by changes in vegetation structure.

Agricultural management, vegetation traits and landscape drive orthopteran and butterfly diversity in a grassland–forest mosaic: a multi‐scale approach

Abstract. 1. Most ecological processes at the population and community level act on multiple spatial scales. We identified the influence of grassland management, vegetation traits and landscape on orthopteran and butterfly diversity in 44 meadows located in a forest‐dominated region in the Italian Alps. The meadows were sampled in landscapes characterised by different proportions of woody vegetation and grasslands quantified at 11 spatial scales (95–3000 m).2. We applied a multi‐scale approach to investigate the scale‐dependent effects of landscape. Then, we built generalised linear models (Poisson and log‐link function) to test simultaneously vegetation traits and landscape variables on insect species richness.3. High fertilisation and cutting frequency created tall, species‐poor plant communities. This change reduced orthopteran diversity by providing an unsuitable sward structure, and butterfly diversity by creating disturbed plant communities with low species richness and abundance of flowering forbs and host plants.4. The proportion of woody vegetation had a strong positive effect on the richness of both groups at the smallest spatial scale (95 m), indicating the importance of undisturbed vegetation in the surrounding of mown meadows. The effect tended to disappear with increasing spatial extent.5. A multi‐scale approach was necessary to identify the effects of landscape factors in this study system. Conservation measures should endorse the maintenance of species‐rich, sparse and short plant communities by reducing organic fertilisation and cutting frequency. However, these schemes should also promote the presence of undisturbed woody vegetation in the immediate surrounding landscape or at least should prevent the complete mowing of large areas.

Plant dispersal strategies and the colonization of Araucaria forest patches in a grassland-forest mosaic

Questions: In a natural grassland-forest mosaic: What is the influence of phylogeny and diaspore traits related to disperser attraction (DAT) on (1) seed size/number trade-off (SSNT) in woody species colonizing forest patches; (2) on the frequency of the species? 3. What is the influence of forest patch area on mean seed size and number. 4. Do phylogeny and DAT expressed at the species level affect this relationship? Location: Campos grassland and Araucaria forest in Sao Francisco de Paula, RS, Brazil, at ca. 29°28' S; 50°13' W. Methods: Forest patches of different sizes in a grassland site recovering for ten years since human disturbances were surveyed by the relative abundance of vertebrate-dispersed woody saplings. We described colonizer species according to taxonomic phylogenetic relationships and diaspore type, size and color. We analyzed with a variation partitioning method their influence on SSNT and on species frequency in the patches. At the community level we regressed mean seed size and number on forest patch area and evaluated how these relation ships were affected by phylogeny and DAT at the species level. Results: 1. Phylogeny and DAT mostly explained seed size and seed number per diaspore variation. 2. By controlling phylogeny and DAT influence the frequency of species in forest patches was positively associated with their seed number in the diaspores, and negatively associated with their seed size. 3. Mean seed size and seed number at the community level were positively associated with patch area. 4. When phylogeny and DAT influences on seed size were removed this relationship was stronger for seed size and weaker for seed number. Conclusions: 1. Energy allocation to dispersal in detriment of offspring survival increased the successful establishment of colonizer species in forest patches, despite phylogenetic relationships and DAT variation in their diaspores. 2. Although patch area exerted a selective pressure on seed size, habitat preferences of dispersers may also influence patch colonization.

Land-use history and fragmentation of traditionally managed grasslands in Scandinavia

Abstract Plants associated with traditional agricultural landscapes in northern Europe and Scandinavia are subjected to drastic habitat fragmentation. In this paper we discuss species response to fragmentation, against a background of vegetation and land-use history. Recent evidence suggests that grassland-forest mosaics have been prevalent long before the onset of human agriculture. We suggest that the creation of infield meadows and outland grazing (during the Iron Age) increased the amount and spatial predictability of grasslands, resulting in plant communities with exceptionally high species densities. Thus, distribution of plant species in the present-day landscape reflects historical land-use. This holds also when traditional management has ceased, due to a slow response by many species to abandonment and fragmentation. The distribution patterns are thus not in equilibrium with the present habitat distribution. Fragmentation influences remaining semi-natural grasslands such that species density is l...