Search

Despite growing recognition of the conservation values of grassy biomes, our understanding of how to maintain and restore biodiverse tropical grasslands (including savannas and open-canopy grassy woodlands) remains limited. To incorporate grasslands into large-scale restoration efforts, we synthesised existing ecological knowledge of tropical grassland resilience and approaches to plant community restoration. Tropical grassland plant communities are resilient to, and often dependent on, the endogenous disturbances with which they evolved - frequent fires and native megafaunal herbivory. In stark contrast, tropical grasslands are extremely vulnerable to human-caused exogenous disturbances, particularly those that alter soils and destroy belowground biomass (e.g. tillage agriculture, surface mining); tropical grassland restoration after severe soil disturbances is expensive and rarely achieves management targets. Where grasslands have been degraded by altered disturbance regimes (e.g. fire exclusion), exotic plant invasions, or afforestation, restoration efforts can recreate vegetation structure (i.e. historical tree density and herbaceous ground cover), but species-diverse plant communities, including endemic species, are slow to recover. Complicating plant-community restoration efforts, many tropical grassland species, particularly those that invest in underground storage organs, are difficult to propagate and re-establish. To guide restoration decisions, we draw on the old-growth grassland concept, the novel ecosystem concept, and theory regarding tree cover along resource gradients in savannas to propose a conceptual framework that classifies tropical grasslands into three broad ecosystem states. These states are: (1) old-growth grasslands (i.e. ancient, biodiverse grassy ecosystems), where management should focus on the maintenance of disturbance regimes; (2) hybrid grasslands, where restoration should emphasise a return towards the old-growth state; and (3) novel ecosystems, where the magnitude of environmental change (i.e. a shift to an alternative ecosystem state) or the socioecological context preclude a return to historical conditions.

Understanding how land use and management practices affect biodiversity is essential for developing effective restoration and conservation strategies. Here, we used ant communities to evaluate the effects of historical land uses (former agriculture or tree plantation) and current management (grazing, burning, mowing, and fertilizing) in subtropical grasslands. We also examined how ant species richness and composition are affected through changes in resource diversity and habitat structure. We classified 80 study sites in southern Brazil into two groups: permanent and secondary grasslands. Permanent grasslands presented high, medium or low management intensities that had never been under other land use. Secondary grasslands are former grasslands that were used for agriculture or pine plantations in the past, followed by passive restoration. We sampled ant communities with D-Vac suction in three multiplots per site in 2013–2015. We found that secondary grasslands had lower ant species diversity and different community composition than permanent grasslands. Ant diversity did not differ among permanent grasslands, but composition was markedly different, especially when comparing medium and high management intensities with low. Additionally, ant richness in secondary grasslands was mainly mediated by a decreased resource diversity (i.e., plant species richness) and grass cover, while burning and mowing management increased ant richness by increasing resource diversity. Our results indicate that passive recovery of grasslands in early successional stages after other land uses leads to incomplete recovery of ant communities, as important resource and structure-related drivers of ant species remain altered. In contrast, traditional management practices promote ant diversity.

Bastin et al.’s estimate (Reports, 5 July 2019, p. 76) that tree planting for climate change mitigation could sequester 205 gigatonnes of carbon is approximately five times too large. Their analysis inflated soil organic carbon gains, failed to safeguard against warming from trees at high latitudes and elevations, and considered afforestation of savannas, grasslands, and shrublands to be restoration., Funding: Supported by the Texas A&M Sid Kyle Global Savanna Research Initiative (T.W.B.); Swiss National Science Foundation (20FI20_173691) (N.B.); Centre National pour la Recherche Scientifique CNRS PICS 2018-2020 (RESIGRASS) (E.B.); CNPq (Brazil, 303179/2016-3) (G.D.); CNPq (Brazil) (G.W.F.); CNPq (Brazil, 303988/2018-5) (A.F.); NASA award NNX17AK14G (F.F.); NSF award 1354943 (W.A.H.); Fundação de Amparo à Pesquisa do Estado de Minas Gerais (Brazil, 2016/13232-5) (S.L.S.); the Office of the Royal Society (IC170015) (C.E.R.L.); CNPq (Brazil, 310345/2018-9) (G.E.O.); the Spanish Government (FIROTIC, PGC2018-096569-B-I00) (J.G.P.); the National Research Foundation (ACCESS, 114695) (N.S.); CNPq (Brazil, 303568/2017-8) (F.A.O.S.); NSF awards 1342703 and 1926431 (C.J.S. and D.M.G.); NSF award EAR-1253713 (C.A.E.S.); Deutsche Forschungsgemeinschaft grant 5579 POEM (V.M.T.); and USDA-NIFA Sustainable Agricultural Systems Grant 12726253 (J.W.V.)

Summary Ecological restoration of grasslands is increasingly based on regional seeds derived from predefined seed transfer zones. However, the degree and spatial pattern of genetic differentiation among provenances of different seed transfer zones is largely unknown. We assessed the genetic differentiation among eight out of 22 German seed transfer zones for seven common grassland species (Arrhenatherum elatius, Centaurea jacea, Daucus carota, Galium album, Hypochaeris radicata, Knautia arvensis and Lychnis flos-cuculi) using AFLP markers. We analysed genetic population structure with AMOVA and Bayesian cluster analysis and tested for isolation by distance and isolation by environment. In all of the investigated species, almost all pairs of provenances were genetically differentiated. Bayesian cluster analysis revealed species-specific numbers and spatial patterns of gene pools, with between two (Arrhenatherum) and eight clusters (Lychnis). Most investigated seed transfer zones represented a unique gene pool in the majority of the species. We found isolation by distance in four species, isolation by environment, driven by climatic seasonality, in three species, and a lack of both in three species. Thus, the observed genetic differentiation appears to be caused by both neutral and adaptive processes. Synthesis and applications. Our study shows that grassland plants are indeed strongly genetically differentiated across Germany supporting the strategy of seed transfer zones for ecological restoration. Although the predefined seed transfer zones are unlikely to match the exact genetic structure of many species, they serve their purpose by capturing a substantial amount of intraspecific genetic variation across species.

Summary One of the key questions in ecosystem restoration is the choice of seed material for restoring plant communities. More and more scientists and practitioners are currently advocating the use of regional seed sources, based on the argument that plants are often adapted to local or regional environmental conditions, and thus, regional seed sources should provide the best restoration success. However, there is still substantial debate about this approach, partly because of a lack of solid empirical data. We conducted a multispecies transplant experiment in which we compared the performance of eight seed origins of seven plant species frequently used in grassland restoration in four common gardens across Germany. We found that, on average, plants of regional origins produced 10% more inflorescences and 7% more biomass than those of foreign origins. There were substantial differences among species in the strength of these effects, but in the majority of the study species fitness decreased with increasing geographical distance of seed origins or with increasing climatic differences between plant origins and experimental sites. In addition to these effects on plant fitness, increasing geographical or climatic distances of origin were often also correlated with increasing differences in plant phenology. Since phenology is important for biotic interactions, especially with pollinators and seed predators, using foreign seed sources may have cascading effects on local ecosystems. Synthesis and applications. Genetic differentiation is widespread in grassland species and often shows the patterns of regional adaptation. Our study thus supports the use of regional seed sources in restoration. Moreover, using non-regional seed sources in grassland restoration may not only decrease the performance of plants, but it will likely also affect their biotic interactions.

Despite growing recognition of the conservation values of grassy biomes, our understanding of how to maintain and restore biodiverse tropical grasslands (including savannas and open-canopy grassy woodlands) remains limited. To incorporate grasslands into large-scale restoration efforts, we synthesised existing ecological knowledge of tropical grassland resilience and approaches to plant community restoration. Tropical grassland plant communities are resilient to, and often dependent on, the endogenous disturbances with which they evolved - frequent fires and native megafaunal herbivory. In stark contrast, tropical grasslands are extremely vulnerable to human-caused exogenous disturbances, particularly those that alter soils and destroy belowground biomass (e.g. tillage agriculture, surface mining); tropical grassland restoration after severe soil disturbances is expensive and rarely achieves management targets. Where grasslands have been degraded by altered disturbance regimes (e.g. fire exclusion), exotic plant invasions, or afforestation, restoration efforts can recreate vegetation structure (i.e. historical tree density and herbaceous ground cover), but species-diverse plant communities, including endemic species, are slow to recover. Complicating plant-community restoration efforts, many tropical grassland species, particularly those that invest in underground storage organs, are difficult to propagate and re-establish. To guide restoration decisions, we draw on the old-growth grassland concept, the novel ecosystem concept, and theory regarding tree cover along resource gradients in savannas to propose a conceptual framework that classifies tropical grasslands into three broad ecosystem states. These states are: (1) old-growth grasslands (i.e. ancient, biodiverse grassy ecosystems), where management should focus on the maintenance of disturbance regimes; (2) hybrid grasslands, where restoration should emphasise a return towards the old-growth state; and (3) novel ecosystems, where the magnitude of environmental change (i.e. a shift to an alternative ecosystem state) or the socioecological context preclude a return to historical conditions.

Land degradation is a complex concept that integrates different aspects, including changes in soil conditions, biodiversity, productivity and socio-economic implications, compared to a reference state. We propose a new conceptual framework to analyze degradation stages and restoration thresholds in species-rich natural grasslands. The framework integrates different degradation stages with their respective thresholds and describes key processes of land-use change that lead to certain stages and thresholds. Specifically, we discuss two scenarios of grassland degradation, i.e. unsuitable grassland management and complete change of land use, sometimes followed by spontaneous recovery. We illustrate the framework with the case of south Brazilian grasslands, which are rich in biodiversity, but suffer from a series of degradation processes and are poorly considered from a conservation perspective. The conceptual framework can be applied by studies on degradation and restorability of tropical and subtropical grasslands after changes in management or transition to other land use; it will facilitate decisions on alternative management and conservation.

Native grasslands in the Campos de Cima da Serra, Brazil, are being converted at speed for exotic tree plantations and cropland. The impact of modified and novel soil conditions on the establishment of native grassland species is unknown; establishment of non-native species, deliberately or accidentally introduced, could be favoured. In a common garden composed of fully randomized replicate samples of soils collected from remnant grassland, former cropland and pine plantations, we tested emergence and establishment of five cold-season species: Native low-tussock grass Piptochaetium montevidense (Spreng.) Parodi; native legume Trifolium riograndense Burkart; naturalized low-tussock grass Vulpia bromoides (L.) Gray; low-tussock grass Holcus lanatus L., cultivated and naturalized in Brazil; and a cultivar of non-native Trifolium repens. Other than expected, soil type and species*soil type interactions had no significant effect on seedling emergence after 132 days in the field. Species effect on seedling emergence, however, was highly significant. Vulpia bromoides emergence was significantly highest in all soil types. Holcus lanatus and Trifolium riograndense both achieved second highest emergence rates and did not differ significantly from each other. Lowest overall emergence rates were found in the non-native clover cultivar. Lab germination tests failed for Piptochaetium, although it showed reasonable emergence in the field. Good performance of the native clover is encouraging for future grassland restoration, but the value of highly germinable Vulpia as a forage remains to be tested. Holcus tolerates a wide range of soil conditions and its life history traits may promote naturalization, or even invasiveness. Native grasslands of the region should be monitored for this species. Studies like these, but set up on a larger geographical scale and with a wider array of native species, will be essential in developing ecological restoration methods for southern Brazilian grasslands. Resumo Uma acelerada conversão do campo nativo em plantações de espécies florestais exóticas e lavouras tem ocorrido nos Campos de Cima da Serra, Sul do Brasil. Ainda é desconhecido o impacto que as condições edáficas, em solos alterados ou preservados, exercem no estabelecimento de espécies nativas do campo; as espécies exóticas, introduzidas deliberada ou acidentalmente, talvez sejam favorecidas. Em um common garden composto por repetições aleatórias de amostras de solo, coletadas em áreas de antigas plantações de pinus, de antigas lavouras ou em áreas com campo nativo preservado, foram testados a emergência e o estabelecimento de cinco espécies hibernais: Piptochaetium montevidense (Spreng.) Parodi, gramínea cespitosa nativa; Trifolium riograndense Burkart, leguminosa nativa; Vulpia bromoides (L.) Gray, gramínea cespitosa naturalizada no sul do Brasil; Holcus lanatus L., gramínea cespitosa exótica, cultivada e disseminada no Brasil; e um cultivar de Trifolium repens, leguminosa exótica largamente utilizada. Diferentemente do esperado, o tipo de solo e interações espécie*tipo de solo não tiveram efeito significativo na emergência de plântulas após 132 dias de teste a campo. O efeito da espécie na emergência das plântulas, entretanto, foi altamente significativo. A emergência de Vulpia bromoides foi significativamente superior em qualquer tipo de solo. Ambos Holcus lanatus e Trifolium riograndense apresentaram as segundas maiores taxas de emergência, não diferindo significativamente entre si; as taxas mais baixas foram apresentadas pelo cultivar de trevo não nativo. O Teste de Germinação em laboratório falhou para o Piptochaetium, apesar de este ter demonstrado razoável emergência a campo. O bom desempenho do trevo nativo é encorajador para futuras restaurações de pastagens nativas; o valor forrageiro de Vulpia, que apresentou alta germinação, ainda precisa ser testado. Holcus tolera uma ampla faixa de condições de solo, e suas características adaptativas podem vir a torná-lo naturalizado ou mesmo invasivo. Os campos da região devem ser monitorados em função dessa espécie. Estudos como esse, mas configurados em escala geográfica maior e com maior variedade de espécies nativas, serão essenciais no desenvolvimento de métodos de restauração para os Campos Sulinos Brasileiros.

Question What is the relative significance of seed source, growth form and seeding density in contributing to restoration of calcareous grasslands? Location Experimental field site on calcareous gravel in the lowlands north of Munich (S Germany). Methods The research question was investigated using a dominant grass (Festuca rubra) and three subordinate forbs (Buphthalmum salicifolium, Dianthus carthusianorum, Linum perenne). A randomized split-block design consisting of six blocks was established with two growth forms of F. rubra (rhizomatous, tussock) from two sources (cultivars, ‘regional’ plants from the region of the field experiment) seeded at two densities (800, 1600 seed·m−2) and inter-seeded with forbs from cultivar and regional sources (100 seed·m−2). Each combination of plant source, growth form and seeding density of the dominant species was replicated six times. Individual numbers of F. rubra (Year 1), the subordinate species (Year 1 and Year 2) and the spontaneously invading alien plant Erigeron annuus (Year 2) were counted, and total cover of vascular plants in each subplot and average number of flowers per area were recorded in Year 2. Results Regional seed generally had higher establishment than the cultivar counterpart in both the dominant and subordinate species. Growth form and seeding density of F. rubra differed little in their effects on establishment of the forbs, but fewer E. annuus invaded subplots with regional F. rubra, and subplots with the tussock growth form. Only in D. carthusianorum did regional rather than cultivar subordinates produce more flowers. Conclusions Seed source and growth form are the most significant factors for designing seed mixtures for restoration of calcareous grasslands.

Intra- and interspecific trait variation express the response of plants dealing with different environmental conditions. We measured root and leaf traits on 14 species of calcareous grasslands in a restoration experiment. We aimed at identifying intraspecific differences in biomass allocation and functional plant traits under contrasting soil conditions by comparing plants growing in ancient grassland and two restored grasslands on ex-arable land, one of them with topsoil removal. Relative importance of trait variation within and among species, and among site was assessed by variance partitioning. Interspecific variation was more important than intraspecific variation, but the contribution of the latter to total variation was considerable, especially for specific leaf area. Changes in soil properties due to topsoil removal resulted in lower values of plant height, specific leaf area and specific root length compared to the control (ancient grassland). Soil fertility found in the treatment without top soil removal did not affect plant plasticity compared to the control. The study species showed two allocation strategies in relation to resource stress, while the responses of individual traits to the soil treatments were consistent across species. We conclude that caution must be taken when using mean trait values for plastic species or when working with environmental gradients.

Agricultural expansion on pristine woodlands and grasslands in Brazil usually causes major changes in soil organic C (SOC) stocks. Quantitative assessment of these stocks, their regional distribution and variability in rural landscapes are key scientific issues related to the Brazilian commitment to pursue climate-friendly agriculture. The aim of this research was to refine existing SOC stocks estimates in the Campos de Cima da Serra (temperate highlands) of Rio Grande do Sul state. Our approach included soil sampling campaigns to obtain primary SOC data, complemented by secondary data sources (published surveys and research projects). The field study sampled surface soil layers (to 30 cm depth) stratified by the predominant soil classes and agricultural land uses: primary grasslands with and without fire management, grasslands overseeded with legume forages, and fields fallowed after intensive annual horticultural crops or Pinus plantations (secondary grasslands). Large SOC stocks (0–30 cm depth) were measured in Ultisols (244.4 Mg C ha−1) and Inceptisols (191.1 Mg C ha−1) under grasslands without burning, whereas lower stocks were found in Inceptisols under agricultural crops. SOC stocks in this study were generally larger than those calculated using IPCC global reference SOC stocks, those estimated in SOC maps of Brazil − 70% higher in Inceptisols and 120% higher in Ultisols. Our estimates were 75% higher than those estimated for the study region in a state SOC map. Soils in this region store large C stocks, which had been generally underestimated in previous smaller scale inventory. Additionally, the SOC stock map obtained allows more detailed visualization of the spatial distribution of SOC than previously possible. This information can be used to define public policies for conservation agriculture and support the update and refinement of national inventories of SOC greenhouse gases.

1 Departamento de Botânica, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brazil 2 Restoration Ecology, Center of Life and Food Sciences Weihenstephan, Technische Universitat Munchen – TUM, Freising, Germany 3 Programa de Pos-graduacao em Botânica, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brazil 4 Faculty of Agricultural Sciences and Landscape Architecture, Hochschule Osnabruck – University of Applied Sciences, Osnabruck, Germany 5 Department of Nature Conservation and Landscape Planning, Anhalt University of Applied Sciences, Bernburg, Germany 6 Terrestrial Ecology, Center of Life and Food Sciences Weihenstephan, Technische Universitat Munchen – TUM, Freising, Germany 7 Departamento de Ecologia, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brazil 8 Departamento de Plantas Forrageiras e Agrometeorologia, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brazil 9 EMBRAPA Pecuaria Sul, Bage, RS, Brazil 10Programa de Pos-graduacao em Ecologia, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brazil 11Parque Nacional Aparados da Serra, ICMBio, Cambara do Sul, RS, Brazil

We report extent and rate of land use/land cover change in a forest–grassland mosaic of Rio Grande do Sul, Brazil, during a recent period of increasing conflicts between native habitat protection and conversion. The area is part of the Atlantic rain forest biome, a Global Biodiversity Hotspot. Analyzing Landsat and Google Earth imagery, and calculating an effective conservation risk index () as ratio of converted to remnant area, we specifically compared the effectiveness of designated fully protected areas (-s) and Sustainable Use areas (-s) in preventing conversion of native forest and grassland habitats for agri- and silviculture, relative to areas outside. Grassland area decreased by 17%, corresponding to a net loss of 59,671 ha, in the entire area. Forest gains exceeded losses, and was zero inside Full Protection s. Non-native tree plantation area increased by 94% over the entire study area; cropland increased by 7%. Conversion for silviculture predominated outside the designated s and conversion for agriculture predominated inside the designated s. was generally higher for grassland than forest, and in -s, grassland was several times higher than in areas without any protection status. These developments are in stark contrast to the high standards of the Brazilian protected area system and corresponding International Union for Conservation of Nature and Natural Resources categories. They are due to protracted regularization of land conversion and establishment of designated protection areas. Furthermore, they reveal the dilemma of previously managed grasslands in strictly protected areas being eventually succeeded by forest, and the hazards of broad interpretation of the term “sustainable development”.

Questions We investigated the effects of grassland management intensity and temporary conversion to other land uses on abiotic and biotic properties of subtropical grasslands. We used species-rich permanent grasslands of medium management intensity (PG-M) as a reference, and asked the following questions: (1) do permanent grasslands with low and high management intensities (PG-L and PG-H, respectively) have different plant diversity and species composition than reference grasslands; and (2) do secondary grasslands recovering from conversion to arable fields (SG-A) or pine plantations (SG-P) differ from permanent grasslands in their plant species composition and abiotic conditions? Location Highland grasslands, Campos de Cima da Serra, Rio Grande do Sul (RS), Brazil. Methods We analysed variation in plant species composition and diversity among 80 grassland sites, including three types of permanent grassland and two types of secondary grassland. An indicator species analysis was used to identify characteristic species for the different land-use types. We used a linear discriminant analysis to investigate differences in soil conditions among land-use types. Results Both PG-L and PG-H differed from PG-M regarding plant species composition. Although PG-L shared many typical grassland species with PG-M, their communities were generally less diverse. PG-H, on the other hand, not only had fewer species but also deviated from PG-M in species composition. Secondary grasslands on former arable fields and plantations differed from PG-M in species composition and showed lower diversity. Soil conditions of SG-P were similar to those of PG-L and PG-M, but they were distinct from those of PG-H and SG-A. Conclusions All land-use types showed deviations from reference grasslands (PG-M). The decrease in the number of species in PG-L may be reversed if traditional management intensity is re-introduced, whereas strong compositional changes in SG-P may require the re-introduction of grassland species. This is also true for PG-H and SG-A: both showed marked deviations from reference grasslands in biotic and abiotic components. Overall, restoration of altered land-use types to near-natural subtropical grassland seems feasible, but suitable techniques have to be developed.

Resprouting of trees and shrubs in forest-grassland ecotones is a key process to understand the dynamics of these systems under different disturbance regimes. This study integrates resprouting of grassland shrubs and pioneer forest trees (‘gullivers’), burned in subtropical lowland grassland and cut in temperate highland grassland of Rio Grande do Sul, Brazil. Per grassland site, 20 individuals each of 1–2 grassland shrub species (Asteraceae) and two forest tree species (Myrsinaceae, Myrtaceae) were tagged, and post-disturbance survival and growth monitored for 1 year at 2–4 month intervals. Differences in resprouting vigour (summed-up basal area of resprouted shoots per pre-disturbance summed-up area of basal stems), and in density and allometry of resprouted shoots (allocation mode) were compared between tree and shrub species by linear mixed effects modelling and multiple comparisons, using the Tukey test. All grassland shrub individuals resprouted and regained 73–142 % (species average) of pre-disturbance basal area within one year, as opposed to 14–24 % in trees. All Myrtaceae ‘gullivers’ resprouted, but up to two-thirds of Myrsine individuals did not survive disturbance. Tree species tended to produce either many slender or few stout shoots, while shrub species were intermediate between these extremes. Forest trees regained 22–46 % of pre-disturbance height, independent of allocation mode, and grassland shrubs up to 73 %. This suggests that grassland fires allow grassland shrubs but not forest trees to persist and to grow to reproductive size. Differing sprout allocation modes may reflect allometric constraints rather than strategies to outgrow the fire-prone grass matrix.