Effects of reindeer on boreal forest floor vegetation: Does grazing cause vegetation state transitions?

Intensive reindeer grazing has been hypothesized to drive vegetation shifts in the arctic tundra from a low-productive lichen dominated state to a more productive moss dominated state. Although the more productive state can potentially host more herbivores, it may still be less suitable as winter grazing grounds for reindeer, if lichens, the most preferred winter forage, are less abundant. Therefore, such a shift towards mosses may have severe consequences for reindeer husbandry if ground-growing lichens have difficulties to recover. We tested if reindeer cause this type of vegetation state shifts in boreal forest floor vegetation, by comparing plant species composition and major soil processes inside and outside of more than 40-year-old exclosures. Lichen biomass was more than twice as high inside exclosures than in grazed controls and almost 5 times higher than in heavily grazed patches. Contrary to our predictions, net N mineralization and plant production were higher in the exclosures than in the grazed controls. The lack of response of phytometer plants in a common garden bioassay indicated that changed soil moisture may drive effects of reindeer on plant productivity in these dry Pine forest ecosystems.     

Does aboveground vegetation composition resemble soil seed bank during succession in specialized vegetation on gypsum soil?

This paper evaluates the aboveground vegetation in relation to the soil seed bank throughout a 60-year succession process following agricultural abandonment in a semi-arid Mediterranean gypsum habitat. There is little information regarding the relationship between these two community components in the context of succession on semi-arid gypsum soils. Aboveground vegetation and the corresponding seed bank of gypsum plant communities were sampled through a chronosequence of 24 abandoned fields. Generalized linear models were used to model seed species richness and density, redundancy analyses to model the effect of time since abandonment and the effect of soil physicochemical parameters on seed bank species composition, and Mantel tests to analyze resemblance between above- and belowground species composition. In this last case, the effect of time since abandonment was controlled using a partial Mantel test. Mantel correlograms using time intervals instead of distances were used to describe the resemblance of above- to belowground species occurrence in different aged fields. No significant variability in seed species richness, seed density, or species composition due to time since abandonment was found. Differences in seed species composition were mainly due to small spatial scale predictors such as slope and soil calcium content. High correlations between species composition in the soil seed bank and the aboveground vegetation were detected during succession. The lack of a significant trend in aboveground species replacement over time was also reflected in seed bank composition. We concluded that the rapid establishment of strict gypsophyte species relied mainly on the long-term persistence of these species in the seed bank.     

Can vegetation indicate landfill cover features?

Generally, great efforts are made in measuring features of landfill covers. However, conventional physical or chemical parameters reach their limits in indicating the small scale changes of the habitats. Bio-indication is a proven tool to assess habitat conditions. The advantages of vegetation monitoring are obvious: cheap, easy, and integrating over time and space. Our study displays, how vegetation can indicate landfill cover features by adapting some common evaluation methods. Ellenberg's ecological indicator values were used, but ubiquitous species were excluded from multivariate data analysis of the Ellenberg values. Four groups of habitats were distinguished according to their cover material: (i) loamy substrates; (ii) wet hollows and areas with mature compost; (iii) fresh compost and mechanically biologically treated waste; (iv) slag from municipal solid waste incineration and leachate-influenced areas with fresh untreated waste or sewage sludge. The differences were assessed by ecological indices. The results give a promising impression of the potential vegetation monitoring has in the indication of landfill cover features.     

How reliable are our vegetation analyses?

Abstract. Two sets of 40 relevés, made independently by two observers on the same 5m x 5m sample plots, were compared to estimate the sampling error and to assess the effect of this sampling error on (1) estimates of species richness and diversity (2) results of multivariate analyses, and (3) estimation of species turnover in repeated sampling. The relevés were made according to the standard Braun-Blanquet method. The sampling error was estimated for (1) recording of species in sample plots and (2) visual estimation of the degree of cover (or of the general population size). Despite the fact that the sample plots were searched thoroughly for 30 - 40 min, the number of overlooked species was high with a discrepancy of 13% between corresponding relevés. Regarding multivariate analysis, the error caused by missing species was at least as important as the error in visual estimation of species cover. The estimates of degree of cover using the Braun-Blanquet scale are sufficiently reliable for use in multivariate analysis when they are subjected to ordinal transformation. When average cover values are used, the patterns detected are based solely on dominants. Species richness and species diversity could be reliably estimated from the relevés, but the estimates of equitability are very unreliable. The classical relevé method remains one of the most efficient survey methods for recognition of vegetation types on the macro-community and landscape scales.     

Sahelian woody vegetation in Sénégal

Structure and composition of woody vegetation in Sahelian forest types (not including riparian and riverine types) were studied in Sénégal. The application of classification and ordination resulted in the recognition of seven distinctive woody community types, related to soil and precipitation gradients. The described vegetation types only contained four strictly Saharan species, the rest being of Sahelian and Soudanean affinity, so a floristic change from savanna to desert vegetation after two decades of drought could not be confirmed. Tree density was lower in the northern part than earlier, possibly an indication of degradation. Rejuvenation was greatest at the northernmost arenosolic stations, but low in the southern, ferrouginous areas. This presumably demonstrates the resilience of North-Sahelian vegetation, at the moment being in a dynamic rejuvenation phase, after a period of adverse conditions.     

What are the organismic elements of vegetation science?

The recent inclusion of communities of planktonic algae and microbial crusts into the system of European vegetation types is critically discussed. It is argued that formal vegetation classification should be limited to plant taxa represented by macroscopic individuals within a plot, including all vascular plants, bryophytes, lichens, charophyta and macrophytic chlorophyta, rhodophyta or phaeophyta. In the interest of comparability and methodological stringency, all microscopic algae and all prokaryotes, including cyanobacteria, and the habitats dominated by such microorganisms (e.g. plankton, biofilms and crusts), should be excluded from vegetation classification.     

Human–vegetation interactions during the Holocene in North America

Vegetation History and Archaeobotany - Between the initial colonization of North America and the European settlement period, Indigenous American land use practices shaped North American landscapes...     

Increasing terrestrial vegetation activity in China, 1982—1999

Variations in vegetation activity during the past 18 years in China were investigated using the normalized difference vegetation index (NDVI) derived from the 3rd generation time series dataset of NOAA-AVHRR from 1982 to 1999. In order to eliminate the effects of non-vegetation factors, we characterized areas with NDVI < 0.1 as “sparsely vegetated areas” and areas with NDVI ≥ 0.1 as “vegetated areas”. The results showed that increasing NDVI trends were evident, to varying extents, in almost all regions in China in the 18 years, indicating that vegetation activity has been rising in recent years in these regions. Compared to the early 1980s, the vegetated area increased by 3.5% by the late 1990s, while the sparsely vegetated area declined by 18.1% in the same period. The national total mean annual NDVI increased by 7.4% during the study period. Extended growing seasons and increased plant growth rates accounted for the bulk of these increases, while increases in temperature and summer rainfall, and strengthening agricultural activity were also likely important factors. NDVI changes in China exhibited relatively large spatial heterogeneity; the eastern coastal regions experienced declining or indiscernibly rising trends, while agricultural regions and western China experienced marked increases. Such a pattern was due primarily to urbanization, agricultural activity, regional climate characteristics, and different vegetation responses to regional climate changes.     

Increasing terrestrial vegetation activity in China, 1982–1999

Variations in vegetation activity during the past 18 years in China were investigated using the normalized difference vegetation index (NDVI) derived from the 3rd generation time series dataset of NOAA-AVHRR from 1982 to 1999. In order to eliminate the effects of non-vegetation factors, we characterized areas with NDVI < 0.1 as “sparsely vegetated areas” and areas with NDVI ≥0.1 as “vegetated areas”. The results showed that increasing NDVI trends were evident, to varying extents, in almost all regions in China in the 18 years, indicating that vegetation activity has been rising in recent years in these regions. Compared to the early 1980s, the vegetated area increased by 3.5% by the late 1990s, while the sparsely vegetated area declined by 18.1% in the same period. The national total mean annual NDVI increased by 7.4% during the study period. Extended growing seasons and increased plant growth rates accounted for the bulk of these increases, while increases in temperature and summer rainfall, and strengthening agricultural activity were also likely important factors. NDVI changes in China exhibited relatively large spatial heterogeneity; the eastern coastal regions experienced declining or indiscernibly rising trends, while agricultural regions and western China experienced marked increases. Such a pattern was due primarily to urbanization, agricultural activity, regional climate characteristics, and different vegetation responses to regional climate changes.     

Increasing terrestrial vegetation activity in China, 1982—1999

The搊pening?policiesimplementedinChinainthepasttwodecadeshaveresultedinextensivechangesinlanduseandlandcover.Vegetationactivityhasincreasedthroughagriculturalpracticessuchasafforestation,irrigation,andintensiveagriculturalmanagement[1,2].Ontheotherhand,vegetationcover-agehasdecreasedduetorapidurbanization,industri-alization,andovergrazing[3,4].Thus,therearecon-flictingreportsregardingthestatusofChina抯vegeta-tion,asnointegrativeanalysisatthenationallevelhasyetbeenconducted.Thisstudyaimstoexpl…     

Soil–vegetation relationships in cerrados under different fire frequencies

Fire is an important ecological factor that structures savannas, such as the cerrado, by selecting plant species and altering soil nutrient content. In Emas National Park, central Brazil, we compared soils under three different fire regimes and their relationship to the cerrado species they support. We collected 25 soil and vegetation samples at each site. We found differences in soil characteristics (p?<?0.05), with fertility and fire frequency positively related: in the annually burned site we found higher values of organic matter, nitrogen, and clay, whereas in the protected site we detected lower values of pH and higher values of aluminum. We also observed differences in plant community structure, with distinct floristic compositions in each site. Floristic composition was more related to sand proportion (intra-set correlation?=?0.834). Different fire frequencies increase environmental heterogeneity and beta diversity in the Brazilian cerrado.     

The ‘salão’ vegetation of Southwestern Amazonia

This paper presents a first account of the salão vegetation of southwestern Amazonia, a frequent but poorly known formation and unusual in that it is a lowland moist tropical environment in which virtually all of the plant diversity is accounted for by herbs. The salões occur along canalized portions of the Purus and Juruá river basins, and their substrates consist of exposed parent materials that characterize much of this sector of Amazonia but are usually overlain by a relatively thin (<1 m) layer of soil. They are constantly moist seeps or ‘seepage banks,’ and the lower portions are seasonally submerged. Strata are recognizable in the vegetation, and the physiognomy and composition of each vegetation band of the salões is likely determined by the slope, the parent material, and (for lower bands) the duration of flooding. To date the salão flora has registered 66 species: 11 bryophytes, 12 ferns, and 43 angiosperms. Five of the bryophyte species, two ferns, and one grass, Arundinella berteroniana, are found in most if not all salões and can be considered indicators of this vegetation type, while most of the pteridophytes and other angiosperms occur more sporadically. None of the species is endemic to the formation and only four to the region; most are associated generally with the margins of rivers, lakes, and streams, often on rocky or sandy substrates. The floristic and conservation significance of this formation lie in its apparent affinities with montane regions, in the fact that 21 species and eight genera are recorded for the Acre flora only from the salões, and in its local value as a source of filtered potable water.     

Can the red palm mite threaten the Amazon vegetation?

The red palm mite Raoiella indica Hirst (Tenuipalpidae) was first reported in the New World in 2004, dispersing quickly and widely while adopting new plant species as hosts. Since then, it has caused severe damage in this region, especially to coconut (Cocos nucifera L.). It was first found in Brazil in 2009, in the northern Amazonian state of Roraima. In the present study, native and introduced plants were sampled between March 2010 and February 2011 in sites of the 15 Roraima municipalities, to estimate its distribution and the associated mite fauna. In addition, monthly samples were taken from a coconut plantation in Mucajaí throughout the same period, for an initial appraisal of the levels R. indica could reach. It was found in 10 municipalities, on 19 plant species of four families. Six species are reported for the first time as hosts. Among the associated predators, 89.1% were Phytoseiidae, most commonly Amblyseius largoensis (Muma), Iphiseiodes zuluagai Denmark & Muma and Euseius concordis (Chant). The highest densities of R. indica, 1.5 and 0.35 mites/cm² of leaflet (approx total of 331 and 77 mites/leaflet), were reached respectively in March 2010 and February 2011. The highest density of phytoseiids on coconut (0.009 mites/cm² or about 2 mites/leaflet) was reached in November 2010. The average densities of R. indica recorded for Roraima were comparable to those reported for countries in which the mite is reportedly economically damaging. The dispersal of R. indica through the Amazon forest may result in damage to cultivated and native palms, and plants of other families, if the projected increase in both the frequency and the severity of drought events occurs. Parts of the Amazon have undergone periods of low rainfall, a condition that appears to favour the biology of this mite. Its eventual arrival to northeastern Brazil may result in heavy economic and ecological losses.     

Are spring staging brent geese evicted by vegetation succession?

The number of spring staging brent geese on the salt marshes of the Dutch island of Schiermonnikoog increased from about 1500 individuals in the late 1960s to > 4000 in the late 1970s. Since then, numbers on Schiermonnikoog have levelled off, while the world population continued to increase. Although the extent of salt-marsh area on the island has dramatically increased over the past 20 yr, the number of brent geese on Schiermonnikoog was rather constant in this period. We hypothesise that the number of geese did not increase because of successional changes in the vegetation.
On the basis of 24 yr of counts, we show that geese had to give up older parts of the marsh. Over time, tall growing species like the shrub Atriplex portulacoides have invaded, making the marsh unsuitable for goose grazing. Newly developed marsh, however, was readily exploited by the geese. The area of older salt marsh lost due to succession was almost exactly compensated for by the development of new feeding grounds. Geese which persistently utilised the older marsh were faced with a high proportion of non-preferred species, although they still managed to assemble a diet largely composed of preferred plant species. In the older marsh, a significant reduction in the time spent foraging was also observed. We conclude that brent geese are largely excluded as vegetation succession progresses. Numbers on the island as a whole, however, are sustained due to the dynamic nature of the island. If development of new salt marshes were to be prevented, geese would be forced to abandon the salt marsh.     

The concept of potential natural vegetation: an epitaph?

We discuss the usefulness of the concept of Potential Natural Vegetation (PNV), which describes the expected state of mature vegetation in the absence of human intervention. We argue that it is impossible to model PNV because of (i) the methodological problems associated to its definition and (ii) the issues related to the ecosystems dynamics.We conclude that the approach to characterizing PNV is unrealistic and provides scenarios with limited predictive power. In places with a long‐term human history, interpretations of PNV need to be very cautious, and explicit acknowledgement made of the limitations inherent in available data.     

The role of vegetation in methane flux to the atmosphere: should vegetation be included as a distinct category in the global methane budget?

Currently, the global annual flux of methane (CH₄) to the atmosphere is fairly well constrained at ca. 645 Tg CH₄ year^?1. However, the relative magnitudes of the fluxes generated from different natural (e.g. wetlands, deep seepage, hydrates, ocean sediments) and anthropogenic sources remain poorly resolved. Of the identified natural sources, the contribution of vegetation to the global methane budget is arguably the least well understood. Historically, reviews of the contribution of vegetation to the global methane flux have focused on the role of plants as conduits for soil-borne methane emissions from wetlands, or the aerobic production of methane within plant tissues. Many recent global budgets only include the latter pathway (aerobic methane production) in estimating the importance of terrestrial vegetation to atmospheric CH₄ flux. However, recent experimental evidence suggests several novel pathways through which vegetation can contribute to the flux of this globally important, trace greenhouse gas (GHG), such as plant cisterns that act as cryptic wetlands, heartwood rot in trees, the degradation of coarse woody debris and litter, or methane transport through herbaceous and woody plants. Herein, we synthesize the existing literature to provide a comprehensive estimate of the role of modern vegetation in the global methane budget. This first, albeit uncertain, estimate indicates that vegetation may represent up to 22 % of the annual flux of methane to the atmosphere, contributing ca. 32–143 Tg CH₄ year^?1 to the global flux of this important trace GHG. Overall, our findings emphasize the need to better resolve the role of vegetation in the biogeochemical cycling of methane as an important component of closing the gap in the global methane budget.     

The influence of vegetation pattern on the productivity,diversity and stability of vegetation: The case of `brousse tigrée' in the Sahel

Sample sites of `brousse tigrée' and related vegetation types are described for Mali and Niger. Species composition and physical structure of the herbaceous layer as well as woody plant population were recorded at all sites together with data on soils and natural resource management. Herbage yield was measured whereas foliage yield and wood mass were calculated using allometry equation calibrated for each species. `Brousse tigrée' is characterized by the regularly alternating bare-soil stripes with dense linear thickets arranged perpendicularly to the slope. There was no clear superiority in total plant production of `brousse tigrée' when compared to neighbouring site with diffuse vegetation. However, the pattern of `brousse tigrée' tended to favour woody plant yield to the detriment of herbage yield. The number of herbaceous species recorded per site (22–26) was slightly above Sahelian vegetation average despite low number of species per 1-m² quadrat (6–9), bare soil excluded. This species richness reflects the diversity in edaphic niches resulting from the redistribution and local concentration of water resources and shade. The high spatial heterogeneity and species richness of the herbaceous layer in `brousse tigrée' did not attenuate the interannual variation in herbage yield despite low yields. Except for the herb layer, little evidence was found of grazing influence on the vegetation structure and yield a few hundred metres away from livestock concentration points. On the other hand, the clearing of thickets for cropping led to severe soil erosion which threaten the resilience of `brousse tigrée'. These observations and the well-defined climatic, soiland topographic situations under which the `brousse tigrée' occurs invalidate the hypothesis of an anthropic origin of that vegetationpattern.