Restoration Of Plant Diversity Research Articles

Increasing plant species richness by seeding has marginal effects on ecosystem functioning in agricultural grasslands

Abstract Experimental evidence shows that grassland plant diversity enhances ecosystem functioning. Yet, the transfer of results from controlled biodiversity experiments to naturally assembled ‘real world’ ecosystems remains challenging due to environmental variation among sites, confounding biodiversity ecosystem functioning relations in observational studies. To bridge the gap between classical biodiversity‐ecosystem functioning experiments and observational studies of naturally assembled and managed ecosystems, we created regionally replicated, within‐site gradients of species richness by seeding across agricultural grasslands differing in land‐use intensity (LUI) and abiotic site conditions. Within each of 73 grassland sites, we established a full‐factorial experiment with high‐diversity seeding and topsoil disturbance and measured 12 ecosystem functions related to productivity, and carbon and nutrient cycling after 4 years. We then analysed the effects of plant diversity (seeded richness as well as realized richness), functional community composition, land use and abiotic conditions on the ecosystem functions within (local scale) as well as among grassland sites (landscape scale). Despite the successful creation of a within‐site gradient in plant diversity (average increase in species richness in seeding treatments by 10%–35%), we found that only one to two of the 12 ecosystem functions responded to realized species richness, resulting in more closed nitrogen cycles in more diverse plant communities. Similar results were found when analysing the effect of the seeding treatment instead of realized species richness. Among sites, ecosystem functioning was mostly driven by environmental conditions and LUI. Also here, the only functions related to plant species richness were those associated with a more closed nitrogen cycle under increased diversity. The minor effects of species enrichment we found suggest that the functionally‐relevant niche space is largely saturated in naturally assembled grasslands, and that competitive, high‐functioning species are already present. Synthesis: While nature conservation and cultural ecosystem services can certainly benefit from plant species enrichment, our study indicates that restoration of plant diversity in naturally assembled communities may deliver only relatively weak increases in ecosystem functioning, such as a more closed nitrogen cycle, within the extensively to moderate intensively managed agricultural grasslands of our study.

Floristic diversity in agroforestry systems in the state of Rio de Janeiro

The present article brings together existing plant diversity in agroforestry systems (AFS) in the state of Rio de Janeiro. The survey was carried out with digital databases, using terms in Portuguese and English, such as: ‘‘sistemas agroflorestais RJ’’, ‘‘agrofloresta RJ’’, ‘‘agroforestry RJ’’, and ‘‘agroforestry systems RJ’’, with fourteen AFSs being verified. The species present in the agroforests of Rio de Janeiro were listed when present in at least five of the fourteen AFSs found (35.71%). Fifteen species (8.82%) were among the most common, out of a total of 170 different species found, demonstrating the diversity of AFSs. Plant species are located in the following cities in the state of Rio de Janeiro: Seropédica, Rio de Janeiro, Três Rios, Paraty and Nova Friburgo. The most mentioned species were papaya (Carica papaya L.) and annatto (Bixa orellana L.). More AFSs were analyzed in the Metropolitan Region within the state of Rio de Janeiro, highlighting the municipality of Seropédica. Agroforests can contribute to the conservation or restoration of plant diversity, while promoting food and nutritional sovereignty and security, community subsistence, and local commercialization, among other benefits.

The effects of the aggressive species Pteridium caudatum on the vegetation of Socorro Island: Restoration challenges and opportunities

Humans’ impacts on natural environments have become pervasive, and natural regeneration is often hampered by extreme soil degradation. This situation is exacerbated in insular habitats where introductions of non-native grazing mammals have left behind completely barren areas. Once mammals are removed, aggressive native or non-native plant species can grow vigorously. This leads to the question of whether biodiversity can return through native succession, or if other actions are needed to prevent invading pioneer species from causing successional arrest. This occurs on the remote Socorro Island, in the UNESCO World-Heritage Revillagigedo Archipelago, Mexico. To understand whether native plants are establishing at sites invaded by Pteridium caudatum, we evaluated natural regeneration in sites with different Pteridium cover in two contrasting zones of the island (dry and mesic). We also calculated plant stress indicators (midday leaf water potential, chlorophyl content and maximum quantum yield) for two native species—Dodonea viscosa and Psidium socorrense—growing in open areas and under Pteridium. Our results showed that Pteridium is a significant barrier to seedling establishment. Thus, restoration actions such as seeding and/or plantings should focus on areas without Pteridium cover. Certain local species can be used to restore degraded areas: P. socorrese and Waltheria americana could be used in dry zones, while D. viscosa could be sown in either dry or mesic zones. For adult plants of the two dominant shrubs, Pteridium cover neither imposes or ameliorates stress. Our results suggest that the restoration of plant diversity in the vast Pteridium-invaded areas of Socorro Island will require management actions, including progressive physical removal of Pteridium cover to activate natural regeneration. Pteridium removal can be accelerated by nucleation, planting adults of native shrubs to generate shading. This strategy could be viable if restoration programs involve conservation institutions and government agencies, who currently have critical human and technological resources on the Island.

Restoration of plant diversity in permanent grassland by seeding: Assessing the limiting factors along land‐use gradients

Abstract Land‐use intensification has caused dramatic declines in grassland biodiversity, and in Europe this decline has not yet been halted. Therefore, a major challenge in ecological restoration is to effectively restore plant diversity in permanent grasslands, that is, long‐term managed grassland not being used as cropland. As species richness is often limited by seed dispersal, introducing locally absent species is crucial. Seeding diverse seed mixtures is an appropriate tool, but restoration outcomes are highly variable. Considering constraints by land‐use intensity and plant functional traits during restoration could improve the efficacy of restoration efforts. We established a full‐factorial experiment with high‐diversity seeding and topsoil disturbance in 73 grasslands along land‐use intensity and productivity gradients and evaluated the restoration success over 5 years. In addition, after 5 years we assessed the number of established species and tested whether specific traits promoted the establishment of sown species in interaction with productivity. Plant diversity increased considerably when seeding and disturbance were combined while seeding alone only slightly increased species richness. Along land‐use gradients, we found no direct effects of grazing or mowing on the establishment of sown species, but fertilization indirectly limited establishment in the combined treatment via a negative effect of productivity. Functional traits structured the establishment of sown species, especially in the combined treatments, but effects varied with productivity. Species with low seed mass and low specific leaf area had greater establishment success in low‐productivity grasslands, whereas species with high seed mass had greater establishment in high‐productivity grasslands. Synthesis and applications. Our results highlight the potential of using diverse seed mixtures for biodiversity restoration in a wide range of permanent grasslands, especially when combined with topsoil disturbance. However, productivity both limited restoration success and affected establishment via an interaction with plant functional traits. As productivity is a major constraint in grassland restoration, we strongly recommend to first stop fertilization and reduce soil nutrient loads in highly productive grasslands. Restoration by seeding, with or without disturbance, should only be applied when productivity is reduced and the local environment should be considered to compile site‐specific seed mixtures to maximize restoration success. ​

Grassland biodiversity restoration increases resistance of carbon fluxes to drought

Abstract Evidence suggests that the restoration of plant diversity in grasslands not only brings benefits for biodiversity conservation, but also the delivery of ecosystem services. While biodiversity‐function experiments show that greater plant diversity increases resistance of plant productivity to climate extremes, it is not known whether real‐world management options for grassland restoration likewise stabilize ecosystem responses to extreme climate events. We used a long‐term (23 year) field experiment in northern England to test the hypothesis that management aimed at biodiversity restoration increases the resistance and recovery of ecosystem carbon (C) fluxes to short‐term summer drought. This was tested by measuring plant, soil and microbial responses to a simulated drought in experimental grassland plots where fertilizer application and seed addition have been managed to enhance plant species diversity. The cessation of fertilizer application brought about small increases in plant species richness. Additionally, cessation of fertilizer application reduced overall plant productivity and promoted hemi‐parasitic plants at the expense of grasses and forbs. Resistance of CO2 fluxes to drought, measured as ecosystem respiration, was greater in non‐fertilized plots, as lower plant biomass reduced water demand, likely aided by proportionally more hemi‐parasitic plants further reducing plant biomass. Additionally, legumes increased under drought, thereby contributing to overall resistance of plant productivity. Recovery of soil microbial C and nitrogen was more rapid after rewetting than soil microbial community composition, irrespective of restoration treatment, suggesting high resilience of soil microbial communities to drought. Synthesis and applications. This study shows that while grassland diversity restoration management increases the resistance of carbon fluxes to drought, it also reduces agricultural yields, revealing a trade‐off for land managers. Furthermore legumes, promoted through long‐term restoration treatments, can help to maintain plant community productivity under drought by increasing their biomass. As such, grassland management strategies not only have consequences for ecosystem processes, but also the capacity to withstand extreme weather events.

Ground layer plant species turnover and beta diversity in southern-European old-growth forests.

Different assembly processes may simultaneously affect local-scale variation of species composition in temperate old-growth forests. Ground layer species diversity reflects chance colonization and persistence of low-dispersal species, as well as fine-scale environmental heterogeneity. The latter depends on both purely abiotic factors, such as soil properties and topography, and factors primarily determined by overstorey structure, such as light availability. Understanding the degree to which plant diversity in old-growth forests is associated with structural heterogeneity and/or to dispersal limitation will help assessing the effectiveness of silvicultural practices that recreate old-growth patterns and structures for the conservation or restoration of plant diversity. We used a nested sampling design to assess fine-scale species turnover, i.e. the proportion of species composition that changes among sampling units, across 11 beech-dominated old-growth forests in Southern Europe. For each stand, we also measured a wide range of environmental and structural variables that might explain ground layer species turnover. Our aim was to quantify the relative importance of dispersal limitation in comparison to that of stand structural heterogeneity while controlling for other sources of environmental heterogeneity. For this purpose, we used multiple regression on distance matrices at the within-stand extent, and mixed effect models at the extent of the whole dataset. Species turnover was best predicted by structural and environmental heterogeneity, especially by differences in light availability and in topsoil nutrient concentration and texture. Spatial distances were significant only in four out of eleven stands with a relatively low explanatory power. This suggests that structural heterogeneity is a more important driver of local-scale ground layer species turnover than dispersal limitation in southern European old-growth beech forests.

Fire, Defoliation, and Competing Species Alter Aristida purpurea Biomass, Tiller, and Axillary Bud Production

Aristida purpurea (purple threeawn) is a competitive native perennial grass with monoculturistic tendencies and poor palatability. We examined effects of fire, defoliation, and interspecific/intraspecific planting for 1) threeawn responses in the presence of threeawn, Bouteloua gracilis, or Pascopyrum smithii, and 2) B. gracilis and P. smithii response with threeawn. Biomass, aboveground production, tillers, and axillary buds were analyzed following two fire and four clipping treatments applied to three species–pair combinations in a completely randomized factorial design with nine replications. Fire killed 36% of threeawn. Fire reduced surviving threeawn biomass 61% and reduced production 27%. Threeawn production was greatest when neither plant was clipped and least when competing species were moderately clipped, or when both plants were severely clipped. Tiller counts of burned threeawn were similar among clipping treatments, and less than non-clipped or moderately clipped plants not burned. Fire decreased threeawn axillary buds on average by 25%. Moderately clipped plants had greater production than those from other clipping treatments across species. Average threeawn percentage of pot biomass was greater with B. gracilis (46±3% SE) than P. smithii (38±3% SE). Fire reduced threeawn from 60±3% to 23±3% of pot biomass, indicating good potential for rapid reductions in threeawn dominance and restoration of plant diversity with fire.

Restoration of plant diversity on ditch banks: Seed and site limitation in response to agri-environment schemes

Recently it has become clear that seed limitation is probably a much more important factor in plant recovery than has often been recognized. However, in practice, restoration measures that are focussed on decreasing site limitation may actually increase seed limitation. We tried to determine whether the effects of restoration measures affect site or seed limitation or both. An experiment was set up on ditch banks in the Netherlands which applied agri-environment schemes (AES). To investigate whether nature reserves (seed source) can improve species diversity on the surroundings and to what extent AES is improving this function, we studied the plant diversity (presence of individual species and species richness) of ditch bank vegetations in relation to increasing distance from nature reserves. The presence or absence and species richness of 25 target plants were assessed in 26 ditch banks with AES and 36 non-AES at 15 plots each differing in distance to a nature reserve. Data were analyzed using a Hierarchical Generalized Linear Model (HGLM) with species richness and presence of individual species as response variables and distance to nature reserve and application of AES as factors, controlling for possible confounding factors. Results were interpreted as the effects of AES on seed and site limitation of the species. The results showed that plant diversity decreased significantly with distance from source populations. There were considerable differences in species diversity between AES and non-AES ditch banks, with the former showing greater plant diversity especially in the first 200 m from nature reserves. Presences of all individual species decreased with distance to nature reserve, but the strength of this relationship and the AES effects differed among species. AES ditch banks had lower site limitations for most plant species, but did not have lower seed limitation.

The role of area enclosures and fallow age in the restoration of plant diversity in northern Ethiopia

AbstractThis study investigated the roles played by area enclosures and fallow age in the restoration of plant species richness and soil seed bank species richness in degraded mountain rangelands in northern Ethiopia. Management types (enclosures versus grazed) influenced woody and herbaceous species richness, while fallow age showed no effect on the woody species. Management, age and the doubling of fallow age influenced the herbaceous species richness and species diversity. Management showed no effect on soil seed bank species richness. Fallow age and the doubling of fallow time also showed no influence on the soil seed bank of grass species, but they were influential on the forbs species soil seed bank. The trends for restoration of plant species richness and diversity and grass seed bank in response to fallow age were positive‐linear, but they declined when the fallow ages were doubled. The exception was the forbs seed bank showed linear trends when age of restoration was doubled. The data suggest that the restoration of degraded rangelands in the high mountain zones of northern Ethiopia was still in the weedy succession stages. Long‐term monitoring will be required to gain an informed understanding of the roles played by area enclosures and fallow age in the restoration of plant biodiversity.