Reduction In Plant Cover Research Articles

Toward an extreme world: The hyper‐arid ecosystem as a natural model

AbstractThe forecasted increased frequency and intensity of extreme climatic events may strongly affect ecosystem structure and function in the future. It is unclear how ecosystems will function in the long run over a large spatial scale under a new extreme water cycle. This open question calls for a conceptual framework as a fundamental basis for theoretical and experimental exploration of ecosystem function on a large scale driven by an extreme climate envelope. To assess the problem on a large scale, we investigated hyper‐arid ecosystems (HAEs) as natural tangible models that already function under an extreme climatic envelope. Our new assertion is that if extreme climate change drives arid lands to function under alternate extreme conditions, then arid land ecosystems will function like an HAE as an alternative state, rather than progress to desertification. To support our assertion, we developed a conceptual framework of HAEs that includes a geo‐hydrological “abiotic engine” that drives HAE function by soil moisture diversity and plant functional groups. Based on this conceptual framework, we suggest incorporating two new hypotheses in climate change studies to advance our understanding of responses of large‐scale, water‐limited ecosystems: (1) Hydro‐climatic extremes in water‐limited ecosystems will reduce the degree of resource conservation by slope ecosystems due to reduction in plant cover and soil. The decreased ecosystem function on the slope will be compensated for by increasing the effect of the abiotic engine on the ephemeral stream, thus enhancing meta‐ecosystem functioning in the ephemeral stream. (2) In water‐limited ecosystems, climate change toward hydro‐climatic extremes will rescale the dominant hydro‐ecological processes of pulse–reserve, source–sink, and connectivity along the semiarid, arid, and HA gradients in two ways: (i) shrinking of both spatial and temporal dimensions; and (ii) shrinking in the temporal dimension and expanding in the spatial dimensions. The first rescaling trajectory is related to biodiversity–ecosystem function and the second to the abiotic engine processes.

Pathways of glyphosate effects on litter decomposition in grasslands

AbstractGrasslands store a third of global terrestrial carbon but are vulnerable to carbon loss due to inappropriate livestock grazing. Grasslands management can be improved with a mechanistic understanding of biogeochemical processes that determine carbon storage, such as plant litter decomposition.Herbicides, such as glyphosate, are used to improve the quantity and quality of the forage. In the Flooding Pampa, the most extensive cattle grazed natural grassland and one of the few remnants' temperate grasslands in South America—glyphosate is applied to promoteLolium multiflorum, a forage grass associated with a fungal endophyte nontoxic for cattle.We studied five mechanistic pathways in which the application of glyphosate can alter litter decomposition. We grouped them into single application pathways, through effects on living plants (1), leaf litter (2) and bare soil (3), and repeated annual application pathways, through legacies on ecosystem properties (4) and through the growth of an annual forage grass with a fungal endophyte (5). Single application pathways were tested in a greenhouse experiment using leaf litter ofL. multiflorumand of a native dominant grass. Repeated annual application pathways were tested through a field experiment with 3‐year annual glyphosate application using leaf and root litter ofL. multiflorumwith and without endophyte association.Glyphosate application on living plants produced leaf litter with 70% higher nitrogen content and 140% higher decomposition constant than naturally senesced litter. In contrast, glyphosate application on naturally senesced leaf litter reduced decomposition constant by 20%. Glyphosate application on the soil did not affect the decomposition of naturally senesced leaf litter but accelerated the decomposition of the glyphosate‐killed plants even more.Legacies of repeated annual application of glyphosate resulted in a notable reduction in plant cover (45%) and potential soil respiration (57%), with a consistent acceleration of leaf (53%) and root (18%) litter decomposition. Furthermore, endophytes inL. multiflorumplants reduced leaf litter decomposition by 22%. On the contrary, endophytes did not alter root litter decomposition.Glyphosate application on living plants and legacies of repeated application on the ecosystem stimulate litter decomposition, which can result in a net carbon loss from grasslands. In other ecosystems, the net result on decomposition would depend on the relative cover of vegetation, above‐ground litter and bare soil. This study highlights that glyphosate application should be considered when evaluating sustainable management to preserve and enhance soil carbon storage in grasslands.Read the freePlain Language Summaryfor this article on the Journal blog.

Anthropogenic impacts on phytosociological features and soil microbial health of Colchicum luteum L. an endangered medicinal plant of North Western Himalaya

Colchicum luteum is currently a rare and threatened medicinal plant species in the Kashmir Himalaya. Due to the subsequent increase in anthropogenic pressure on medicinal plant species, it is imperative to understand the phytosociological and conservational status of the plant in its natural habitat. The objectives of this study were analysed in year 2018–2019 on the phytosociological data, viz. density, frequency, and abundance, as well as the rhizospheric soil microbial diversity of C. luteum in disturbed and undisturbed areas of the Kashmir Himalaya. We examined the distribution pattern, phytosociological data, and conservation status of C. luteum by analysing ecological features like abundance, frequency, and density in all three selected locations in Kashmir, Northern India and were found maximum values at Undisturbed areas. The highest values of density (3.24 ± 0.69 m2), frequency (57.77 ± 13.55%), and abundance (5.49 m2) were recorded at undisturbed site Harwan. The total bacterial count (CFU) and Vesicular Arbuscular Mycorrhiza (VAM) spore population from the rhizospheric soil of C. luteum were also analysed, with higher bacterial count i.e., Pseudomonas, Azatobacter, Rhizobium and PSB were (26.2 ± 0.648) (21.88 ± 0.675) (30.11 ± 0.576) and (14.11 ± 0.671) and VAM spore population (g−1) of soil recorded 6.36 ± 0.550 at undisturbed areas viz. Harwan. The bacteria and fungi are likely keystone organisms that form an interface between soils and plant roots. Mutualistic associations with host plants have been observed in various natural and agricultural ecosystems. The present findings could be helpful in formulating conservation strategies for C. Luteum threatened and endangered medicinal plant present in North western Himalayan regions. The plant in disturbed areas that are affected by anthropogenic activities like tourism, grazing, deforestation, urbanization, transport etc. impacts on phytosociological and soil microbial patterns in the area. Because of these abiotic pressures, causes a reduction in plant cover in forest regions, soils become exposed, affecting soil microbial health. Therefore, the study shows the necessity for best practices for medicinal plant and forest management that provide effective monitoring and regulation of human activities in the offshore forest regions and avoid the intrusion of existing reserves.

Effects of a large-scale, natural sediment deposition event on plant cover in a Massachusetts salt marsh.

In mid-winter 2018, an unprecedented sediment deposition event occurred throughout portions of the Great Marsh in Massachusetts. Evaluation of this event in distinct marsh areas spanning three towns (Essex, Ipswich, and Newbury) revealed deposition covering 29.2 hectares with an average thickness of 30.1±2.1 mm measured shortly after deposition. While sediment deposition helps marshes survive sea level rise by building elevation, effects of such a large-scale deposition on New England marshes are unknown. This natural event provided an opportunity to study effects of large-scale sediment addition on plant cover and soil chemistry, with implications for marsh resilience. Sediment thickness did not differ significantly between winter and summer, indicating sediment is not eroding or compacting. The deposited sediment at each site had similar characteristics to that of the adjacent mudflat (e.g., texture, bivalve shells), suggesting that deposited materials resulted from ice rafting from adjacent flats, a natural phenomenon noted by other authors. Vegetative cover was significantly lower in plots with rafted sediment (75.6±2.3%) than sediment-free controls (93.1±1.6%) after one growing season. When sorted by sediment thickness categories, the low thickness level (1–19 mm) had significantly greater percent cover than medium (20–39 mm) and high (40–90 mm) categories. Given that sediment accretion in the Great Marsh was found to average 2.7 mm per year, the sediment thickness documented herein represents ~11 years of sediment accretion with only a 25% reduction in plant cover, suggesting this natural sediment event will likely increase long-term marsh resilience to sea level rise.

Vegetation structure determines the spatial variability of soil biodiversity across biomes

The factors controlling the spatial variability of soil biodiversity remain largely undetermined. We conducted a global field survey to evaluate how and why the within-site spatial variability of soil biodiversity (i.e. richness and community composition) changes across global biomes with contrasting soil ages, climates and vegetation types. We found that the spatial variability of bacteria, fungi, protists, and invertebrates is positively correlated across ecosystems. We also show that the spatial variability of soil biodiversity is mainly controlled by changes in vegetation structure driven by soil age and aridity. Areas with high plant cover, but low spatial heterogeneity, were associated with low levels of spatial variability in soil biodiversity. Further, our work advances the existence of significant, undescribed links between the spatial variability of soil biodiversity and key ecosystem functions. Taken together, our findings indicate that reductions in plant cover (e.g., via desertification, increases in aridity, or deforestation), are likely to increase the spatial variability of multiple soil organisms and that such changes are likely to negatively impact ecosystem functioning across global biomes.

Rainfall pulses mediate long‐term plant community compositional dynamics in a semi‐arid rangeland

Abstract Semi‐arid rangelands, comprising more than 40% of the Earth's land surface, provide critical ecosystem services. Worldwide, these ecosystems are experiencing rapid degradation due to overgrazing and precipitation changes. However, how plants respond to these interacting factors remains relatively unexplored, and precisely which and how rainfall factors determine plant community dynamics in rangelands has not been well developed. We used a long‐term (1953‒2018) dataset from semi‐arid rangeland to investigate coupled effects of grazing intensity and rainfall intensity (the total amount of precipitation) on different groups of plant cover (herbaceous, woody and cacti plants) using linear mixed‐effects models, redundancy analysis and structural equation models. We examined how rainfall intensity influenced plant cover dynamics according to pulse size (intensity over time) categories, which we analysed at three scales: yearly, within the wet season only (June–September) and within the dry season only (October–May). Plant community cover showed a humpbacked trend in the last six decades, mostly through changes in woody plants. Although both grazing intensity and rainfall presented similar humpbacked trends with plant community cover, our models demonstrated that the reduction of plant cover from the 1990s has been mainly caused by a decrease of rainfall rather than grazing intensity, particularly due to profound reductions of the intensity of relatively small rainfall pulses (e.g. 5.1–15 mm/day) during the dry season. Specifically, these small rainfall pulses can increase plant cover of all subgroups of woody and herbaceous species, thereby increasing plant community cover. Moreover, rainfall pulses during the wet season had negative effects on herbaceous species and positive effects on woody plants. These results suggest a phenological niche partitioning between woody plants and herbaceous in subtropical rangelands. Synthesis and applications. Our results show how critical seasonal rainfall pulses are for regulating plant community compositional dynamics, which has significant implications for rangeland management and our ability to adapt and mitigate amplified climate influences in semi‐arid ecosystems.

Leaf litter of Bombax ceiba L. threatens plant cover and floristic diversity in a new urban ecosystem

Bombax ceiba L. (Bombacaceae) is a common deciduous tree introduced to Egypt for ornamental purposes. This study was conducted to describe the impact of B. ceiba leaf litter on plant cover and species diversity in a new urban ecosystem. In general, the sites under B. ceiba canopy attained lower species richness, diversity, plant cover and biomass than in adjacent open areas. Winter species were more adversely affected than summer ones. Both Amaranthus viridis and Trigonella hamosa were completely absent from the sites involving Bombax, whereas the cover of Euphorbia prostrata, Lolium temulentum and Paspalum dilatatum were stimulated. Moreover, the litter-affected soils were more abundant in organic matter and nutrients. Mulching with B. ceiba leaf litter in greenhouse reduced the emergence and growth of Amaranthus viridis, Melilotus indicus and Trifolium resupinatum, whereas the negative effect of litter amendment was pronounced for the former species only. The HPLC analysis confirmed the presence of some free phenolics and flavonoids. Gallic acid was abundant amongst phenolics (90.3 μg g−1 leaf dry weight) whereas quercetin and apigenin were common amongst flavonoids (8.7 and 6.7 μg g−1 leaf dry weight, respectively). In conclusion, the reduction in species diversity and plant cover in the understorey vegetation was attributed to the effects of the tree litter. The test due to litter amendment into soil denotes that allelopathy may have function at least for some species. Besides, the statistical differences between mulching and litter amendment indicate that reduction in plant cover and diversity could be related to the mechanical effect of the litter. These findings suggest that B. ceiba affects species diversity and plant cover and, therefore, represents a threat to the plant communities in the new urban areas. The severity of the litter impact was correlated with seed size, litter amount and the season coinciding with leaf abscission.

Soil surface complexity has a larger effect on food exploitation by ants than a change from grassland to shrubland

1. Changes in vegetation community composition, such as a transition from grassland to shrubland (woody encroachment), are associated with reductions in plant cover and increases in bare ground. Encroachment‐driven changes in surface cover at small spatial scales can alter ant community assemblages by changing their foraging behaviour and their ability to locate and monopolise resources.2. Artificial arenas with three levels of complexity were used to examine changes in ant foraging efficiency, body size and ability to monopolise food. The three levels of complexity included a control (no substrate), low‐complexity treatment (woody debris) and high‐complexity treatment (leaf litter).3. No difference was found in ant species composition within the complexity arenas between grassland and shrubland, but ant functional groups ‘generalised Myrmicinae’ and ‘subordinate Camponotini’ were more abundant in grassland arenas, whereas ‘opportunists’ were more abundant in shrubland arenas. Ants took twice as long to find baits in high‐complexity treatments, and 1.5 times as long in low‐complexity treatments, than in control treatments, which were bare arenas with no substrate. Ant body size declined with increasing surface complexity, suggesting that larger ants are discouraged from foraging in complex habitats.4. There was also significantly greater monopolisation of the protein bait (tuna) in low‐ and high‐complexity treatments, but there were no differences between tuna and carbohydrate (honey) in the control treatment. Consistently, no differences were found in ant behaviour between grasslands and shrublands.5. The present study shows that ants are more responsive to small‐scale alterations in soil surface complexity than to changes in vegetation community composition. Changes in soil surface complexity select for ants based on body size, which in turn influences their foraging success. Changes in vegetation complexity at small spatial scales are therefore likely to influence ant behaviour and abundance of some functional groups, potentially having an effect on the many ecosystem functions carried out by ants.

Modeling the effect of water level on the Nueces Delta marsh community

Water resource development has decreased water delivery to marshes in the Nueces Delta, Corpus Christi, Texas, USA by 45% since 1983, which has led to marsh degradation. Recent management actions will allow for partial hydrological restoration of the marsh, but there is a need to understand the dynamics and the interactive roles of climate and water cycle changes in order to predict changes in salt marshes in the future. In this study, a model of multi-species competition with respect to hydrological change was developed to perform modeling experiments of the effects of water elevation on development of marsh plant species. Nueces Delta plants were divided into two functional groups: (1) clonal stress tolerant plants (Batis maritima, Distichlis spicata, Monanthcloe littoralis, and Salicornia virginica), and (2) clonal dominants (Borrichia frutescens and Spartina alterniflora). Growth rates were calculated for three climate regimes (wet, moderate, and dry), and in three elevation locations (low, mid, and high marsh). The model predicts reductions in plant cover in both drought and moderate conditions. Marsh plant coverage increases only during wet conditions and when there is space available for plant expansion. It is concluded that changes in areal extent of the marsh largely depend on water flow and elevation, which in turn depends on the quantity of fresh water flowing into the marsh. However, under current climate and water management conditions, the marsh will degrade further.

Climate variability and community stability in Mediterranean shrublands: the role of functional diversity and soil environment

Summary Understanding how different factors mediate the resistance of communities to climatic variability is a question of considerable ecological interest that remains mostly unresolved. This is particularly remarkable to improve predictions about the impact of climate change on vegetation. Here, we used a trait‐based approach to analyse the sensitivity to climatic variability over 9 years of 19 Mediterranean shrubland communities located in southwest Spain. We evaluated the role of functional diversity (FD) and soil environment as drivers of community stability (assessed as changes in plant cover, species diversity and composition). The studied shrubland communities were strongly sensitive to inter‐annual variability in climate. First, colder and drier conditions caused remarkable decreases in total plant cover but increased FD, likely because the reduction of plant cover after harsh climatic conditions promoted the expansion of functionally dissimilar species in the new open microsites; although communities returned to their initial values of plant cover after nine years, changes in FD and structure persisted over time. Second, drier and colder conditions favoured the predominance of shrubs with a conservative resource‐use strategy (i.e. with higher dry matter content in leaves, stems and roots), bigger seeds and a more efficient use of water. The most functionally diverse communities were the most stable over time in terms of species diversity, likely because a higher number of functionally dissimilar species allowed compensatory dynamics among them. Communities inhabiting more acidic and resource‐limited environments were less variable over time, probably because they were mainly constituted by slow‐growth, stress‐tolerant species that are potentially better adapted to harsh climatic conditions. Synthesis. This study highlights the utility of a trait‐based approach to evaluate how plant communities respond to climatic variability. We could infer that the increased frequency of extreme climatic events predicted by climatic models will alter the functional structure of shrubland communities, with potential repercussions for ecosystem functioning. Our results also provide new insights into the role of FD and soil environment as buffers of the climate impact on woody communities, as well as potentially useful information to be applied in ecologically based management and restoration strategies.

Biological invasion by a benthivorous fish reduced the cover and species richness of aquatic plants in most lakes of a large North American ecoregion.

Biological invasions are projected to be the main driver of biodiversity and ecosystem function loss in lakes in the 21st century. However, the extent of these future losses is difficult to quantify because most invasions are recent and confounded by other stressors. In this study, we quantified the outcome of a century-old invasion, the introduction of common carp to North America, to illustrate potential consequences of introducing non-native ecosystem engineers to lakes worldwide. We used the decline in aquatic plant richness and cover as an index of ecological impact across three ecoregions: Great Plains, Eastern Temperate Forests and Northern Forests. Using whole-lake manipulations, we demonstrated that both submersed plant cover and richness declined exponentially as carp biomass increased such that plant cover was reduced to <10% and species richness was halved in lakes in which carp biomass exceeded 190kg ha-1 . Using catch rates amassed from 2000+ lakes, we showed that carp exceeded this biomass level in 70.6% of Great Plains lakes and 23.3% of Eastern Temperate Forests lakes, but 0% of Northern Forests lakes. Using model selection analysis, we showed that carp was a key driver of plant species richness along with Secchi depth, lake area and human development of lake watersheds. Model parameters showed that carp reduced species richness to a similar degree across lakes of various Secchi depths and surface areas. In regions dominated by carp (e.g., Great Plains), carp had a stronger impact on plant richness than human watershed development. Overall, our analysis shows that the introduction of common carp played a key role in driving a severe reduction in plant cover and richness in a majority of Great Plains lakes and a large portion of Eastern Temperate Forests lakes in North America.

Ecotone analysis: assessing the impact of vehicle transit on saltmarsh crab population and ecosystem.

The frequent transit of vehicles (recreational or not) through saltpans and saltmarsh fields has been recorded as one of the major causes of physical and ecological damage for these environments. While several studies have been carried out to assess the consequence of this anthropogenic activity on the different local plant species, little is known on its long-term impact on the faunal community. Invertebrates, such as crabs, provide several essential ecological services, and their presence and abundance are tightly connected to that of the saltmarsh plants. Decrease of vegetative cover due to vehicle transit is likely to cause alterations in the morphology and the composition of the saltmarsh ecosystem. In this study we evaluate presence and distribution of the main crustacean species in several impacted sites in Townsville area (Queensland, Australia), to determine possible correlation between vehicle tracks alterations and crab distribution, as well as investigate any possible habitat shift in the mid- and long-term. Results indicate that reduction of plant cover affects species composition and distribution, with different effects based on the unique characteristics of each crab species analysed, resulting in an overall alteration of the assemblage structure.

Non-equilibrium hillslope dynamics and irreversible landscape changes at a shifting pinyon–juniper woodland ecotone

Pinyon–juniper woodlands of the western United States frequently exist within topographically complex landscapes where varied slope aspect yields substantial, local microclimate variation. Vegetation composition and cover typically change markedly along the gradient of relatively mesic northern aspects to more xeric southern aspects. Ecohydrological processes including precipitation runoff, soil moisture storage, and erosion are strongly influenced by vegetation. In certain cases, reduction of plant cover may set self-enhancing feedbacks in motion that lead to further declines of both vegetation and soils, and in some cases, replacement of woodlands with more xerophytic vegetation. The first place such change is likely to occur is in the ecotone between the drier southern aspects and moister north aspects. We studied vegetation, soils, and soil erosion in two small (1–2ha) drainage basins in northeastern Arizona where pinyon–juniper woodlands occupy northern aspects, grading to shrub-dominated vegetation on more xeric southern aspects. Mapping of soil thickness, use of tree-root exposure to measure long-term soil erosion rates, and data on tree mortality and establishment indicate that the ecotone between woodland and more xerophytic vegetation has apparently been shifting for centuries, with a reduction in woodland vegetation. Erosion rates on xeric aspects ranged from 14 to 23cm per century in one basin and as much as 60cm per century in the other basin. In contrast, mesic aspects showed either no net soil losses over the last several centuries or rates significantly less than on the xeric aspects. Exposure of small roots (<5mm diameter) of cliff rose (Purshia stansburiana) directly overlying bare bedrock surfaces indicates that the process of denudation is ongoing and probably expanding in ecotonal areas. Mesic and xeric aspects exemplify “conserving” vs. “non-conserving” ecohydrologic systems in terms of their capacities to retain water and soils. The contrasting sets of self-enhancing feedback dynamics on xeric vs. mesic aspects not only produce different states in vegetation and soils, they also set in motion the production of pronounced geomorphic contrasts that probably require centuries to millennia to develop. The ongoing ecohydrological transitions in the more xeric aspects are in the process of transforming those hillslopes from smooth, curvilinear, soil-mantled, sediment transport-limited slopes to detachment-limited slopes characterized by an expanding area of bare bedrock steps and cliffs, and this transition is probably irreversible. Predicted temperature increases over the next century for the region are comparable to the present-day soil temperature differential on xeric vs. mesic aspects at the site. Soil temperature is the principal driver of soil water evapotranspirative losses, and because of the interdependent linkages between soil temperature, soil moisture, weathering, production and retention of soil, vegetation, and hydrological response, relatively small temperature increases will likely accelerate the ongoing environmental changes in this and similar areas.

Seed rain after a fire in a xerophytic shrubland

Fire causes a reduction of plant cover due to the death of several structures, especially of those that are not isolated from high temperatures; such as seeds and fruits. After a disturbance the availability of diaspores is crucial for the recovery of the community. This work studied the composition and abundance of the seed rain in the xerophytic shrubland of the Pedregal de San Angel Ecological Reserve, located at the Universidad Nacional Autonoma de Mexico campus in Mexico City, which was affected by a surface fire. In order to understand the role of diaspores in the natural regeneration of a burned site, seed traps were placed on 2 sites, one affected by the fire and the other in an unburned location. During 1 year the dispersed seeds and fruits were collected and identified. Results showed that species richness, life forms, and dispersal syndromes were different between sites. The highest abundance and richness values were observed in the burned site. This work offers basic data on the availability of species as diaspores, information which is useful for potential restoration strategies especially in those areas under constant anthropogenic disturbances.

Land degradation impact on soil carbon losses through water erosion and CO2 emissions

Worldwide concerns with global change and its effects on our future environment require an improved understanding of the impact of land cover changes on the global C cycle. Overgrazing causes a reduction in plant cover with accepted consequences on soil infiltration and soil erosion, yet the impact on the loss of soil organic carbon (SOC) and its associated processes remain unaccounted for. In this study performed in South Africa, our main objective was to evaluate the impact of plant cover reduction on (i) SOC erosion by water in both particulate (POC) and dissolved (DOC) forms, and (ii) soil CO2 emissions to the atmosphere. The study performed under sandy-loam Acrisols investigated three proportions of soil surface coverage by plants (Cov), from 100% (Cov100) for the “non-degraded” treatment to 25–50% (Cov50) and 0–5% (Cov5). POC and DOC losses were evaluated using an artificial rainfall of 30mmh−1 applied for a period of 30min on bounded 1×1m² microplots (n=3 per treatment). CO2 emissions from undisturbed soil samples (n=9) were evaluated continuously at the laboratory over a 6-month period. At the “non-degraded” treatment of Cov100, plant-C inputs to the soil profile were 1950±180gCm−2y−1 and SOC stocks in the 0–0.02m layer were 300.6±16.2gCm−2. While soil-C inputs by plants significantly (P<0.05 level) decreased by 38.5±3.5% at Cov50 and by 75.4±6.9% at Cov5, SOC, the losses by water erosion of 0.75gCm−2 at Cov100 increased from 66% at Cov50 (i.e. 3.76±1.8gCm−2) to a staggering 213% at Cov5 (i.e. 7.08±2.9gCm−2). These losses were for the most part in particulate form (from 88.0% for Cov100 to 98.7% for Cov5). Plant cover reduction significantly decreased both the cumulative C–CO2 emissions (by 68% at Cov50 and 69% at Cov5) and the mineralization rate of the soil organic matter (from 0.039 gC–CO2gC−1 at Cov100 to 0.031gC–CO2gC−1 at Cov5). These results are expected to increase our understanding of the impact of land degradation on the global C cycle. Further in-situ research studies, however, need to investigate whether or not grassland degradation induces net C-emissions to the atmosphere.

Chemical composition of dew and rain in an extreme desert (Negev): Cobbles serve as sink for nutrients

► Cobbles serve as sink for nutrients. ► Ion concentration of dew showed a substantial enrichment of 1.5–7.7 in comparison to rain. ► Total annual potential contribution was 2.5, 1.4 and 3.0 times for N, P, and K, respectively, in dew in comparison to rain. ► High nutrient input may explain lush plant cover and high species composition in the Negev Highlands. ► Global warming may result in a decrease in dew and hence in nutrients and plant cover. Dew is important source of water in the Negev Desert, yet little is known about the chemical composition of dew and consequently about its possible role in supplying nutrients to the ecosystem. Dew was collected in Sede Boqer (SB) in the central Negev Highlands and in Nizzana (NIZ) in the western Negev Desert ( P = 95 mm) during the fall of 1992 and analyzed for their main ion constituents. In addition, rain was also collected and analyzed. Dew composition was mainly of the Ca–SO 4 type and showed high total dissolved ions (TDIs) ranging between 88 and 758 mg/l, which decreased with an increase in dew precipitation. Contrarily, it increased with time since the previous dew event indicating that dissolution of dust particles may have a substantial contribution to the chemical composition of dew. When the ion concentration of dew per millimeter was compared to that of rain, all ions showed a substantial enrichment, of 1.5–7.7. High dew to rain ratios characterized the terrestrial ions and especially the major nutrients N (5.4–6.1), K (3.9–7.6), and P (3.5). When the annual contribution of dew nutrients was calculated for SB, total potential contribution was 2.5, 1.4 and 3.0 times that of rain for N, P, and K, respectively, albeit its low annual amount (∼38 mm). The findings highlight the role of substrates subjected to enhanced condensation such as cobbles and stones, implying that they may serve as sink for nutrients, and may provide an additional explanation for the relatively high plant cover and high species composition in the Negev Highlands. It also implies that a possible decrease in dew precipitation due to global warming may also result in nutrient depletion and subsequently in a reduction in plant cover.

Impacts on biodiversity at Baltic Sea beaches

Sandy and shingle beaches were investigated in 2009 and 2010 along the coast of the Baltic Sea in northern Germany with the purpose of assessing biodiversity gradients from shingle to sandy beaches, from beach to primary dunes, and the impacts of tourism on biodiversity. On nine beach sites, ranging between 100% shingle and 99% sand without shingle, Carabidae, Staphylinidae, and Araneae were studied. Two of the six sandy beaches were open and four were closed to tourists. Additionally, trampling effects from tourists, species richness of plants, and plant cover were investigated on sixteen beaches. According to results, primary dunes showed higher species richness in carabids and spiders, but not in staphylinds. Shingle beaches exhibited lower species richness in Staphylinidae and Araneae, but not in Carabidae. As estimated by the Jackknife II method, shingle beaches were the lowest in total species richness. Trampling intensity ranged from 0 footprints m−2 day−1 on closed beaches, up to a maximum of 30 footprints m−2 day−1. On “intensively” used beaches (12 footprints m−2 day−1, on average), reduction of plant cover was more pronounced than on “extensively” used beaches (7 footprints m−2 day−1, on average). Both plant cover and plant species richness were lower on intensively and extensively used beaches than on closed beaches. In arthropods, only staphylind and spider species richness was significantly lower on open beaches than on closed beaches, but no differences were found in carabids. Referring to our results, trampling effects from tourists have high impact on species richness of sandy beaches, on both intensively and extensively used sites.

Aboriginal settlements of arid Patagonia: Preserving bio- or sociodiversity? The case of the Mapuche pastoral Cushamen Reserve

Preservation of biodiversity can be at odds with preservation of sociodiversity, i.e., human groups with different cultures, social organization and economic activities coexisting within a region. We analyzed this problem in the Cushamen Reserve, a pastoralist Mapuche aboriginal settlement in Patagonia, Argentina. We found that the current stocking rate of domestic herbivores is twice the rangeland carrying capacity, and this overstocking has resulted in a 20–30% reduction in plant cover, productivity, floristic richness and pastoral value compared to similar sites located on neighboring capitalist farms. The potential economic income of a generic Cushamen farm (625 ha) under the current stocking rate (0.27 sheep units∙ha −1) and productive parameters (wool and number of lambs produced per sheep each year and the number of sheep that died or were discarded per year) is above the family poverty line, but this potential may be only rarely achieved due to interannual variability of productive parameters. However, under the carrying capacity, only an improbable combination of 0.84 lambs∙sheep −1 yr −1, 5.5 kg wool∙sheep −1 yr −1 and a 16% rate of annual sheep discarding would equal the present potential income. Active policies aimed at increasing carrying capacity of the Cushamen Reserve are needed to preserve both bio- and sociodiversity.

Impacts of woodchip amendments and soil nutrient availability on understory vegetation establishment following thinning of a ponderosa pine forest

Mechanical thinning for fire mitigation has become increasingly widespread in recent years throughout the western United States. A common practice in fire-mitigation procedures is the conversion of slash into chipped mulch (referred to as “woodchips”) that is spread on-site. Here, we investigated: (1) the effect of woodchip amendments on soil nitrogen availability, and (2) the influence of potential interactions between woodchip amendments and soil nitrogen availability on patterns of understory plant establishment in a thinned montane forest in the Front Range of Colorado. We created a gradient of soil nitrogen availability among experimental plots by applying sugar to reduce plant-available nitrogen and applying ammonium nitrate to increase plant-available nitrogen. Soil and resin bag analyses confirmed the effectiveness of the nitrogen manipulations. Nitrogen manipulations did not affect understory species richness or diversity, but increased nitrogen availability promoted a disproportionate increase in the cover of non-native forbs over the three-year post-treatment interval. Woodchips did not alter inorganic nitrogen availability at ambient levels of soil fertility during the first two years of the study, but were associated with increased soil N availability in the third growing season. Woodchip additions were associated with significantly lower species richness, diversity, and overall plant cover than found in unchipped plots. The observed reduction in plant cover affected native and non-native species similarly, although certain species had distinctive responses to woodchip amendments. On the whole, woodchips excluded more species than they promoted, and the physical effects of woodchips appeared to be more important than soil nitrogen status in influencing the understory composition of this area following thinning. At this site, approximately 60% of the plant cover in the three years following thinning operations was comprised of non-native plant species. Thus, the thinning activity, itself, promoted non-native understory plant species cover, but the application of woodchip mulch reduced vegetation cover and native species richness relative to the thinned areas that did not receive woodchips. This effect was largely independent of soil nitrogen availability during the first three years following thinning.

Livestock, soil compaction and water infiltration rate: Evaluating a potential desertification recovery mechanism

Models predict that desertification, the loss of perennial grasses in arid and semiarid environments, will be difficult to reverse due to the positive feedback between plant cover and water infiltration; reductions in plant cover concurrently reduce water infiltration to a level that is insufficient for grass growth and recruitment. Thus, a desertified state becomes stable. However, these models cannot account for recently reported perennial grass recovery in desertified habitats. Here, we suggest a novel mechanism to explain these observations: the natural increase in water infiltration rate associated with recovery from livestock-induced soil compaction. We empirically evaluate this mechanism by comparing vegetation, water infiltration rates and soil compaction at three nearby, desertified livestock exclosures that differ in time since livestock removal and perennial grass recovery; the oldest exclosure (54 years) has experienced a significant increase in perennial grasses, while there has been no such increase at the two younger exclosures (25 and 10 years). Across sites, relative differences (inside compared to outside) in water infiltration rate and soil compaction increased across each grazing fence with time since livestock removal. The relative difference in soil compaction and relative difference in water infiltration rate were significantly greatest at the sole exclosure in which perennial grasses have recovered. These data support a key aspect of desertification models: the importance of water infiltration rate for resilience of vegetation in desertified systems. Although water infiltration rate plays a critical role in understanding the stability of desertified systems, theoretical models of desertification have only incorporated plant cover as the key mechanism affecting infiltration rate. Our work suggests soil compaction may also be an important mechanism.