Changes In Plant Cover Research Articles

Climatic events inducing die-off in Mediterranean shrublands: are species' responses related to their functional traits?

Extreme climatic episodes, likely associated with climate change, often result in profound alterations of ecosystems and, particularly, in drastic events of vegetation die-off. Species attributes are expected to explain different biological responses to these environmental alterations. Here we explored how changes in plant cover and recruitment in response to an extreme climatic episode of drought and low temperatures were related to a set of functional traits (of leaves, roots and seeds) in Mediterranean shrubland species of south-west Spain. Remaining aerial green cover 2 years after the climatic event was positively related to specific leaf area (SLA), and negatively to leaf water potential, stable carbon isotope ratio and leaf proline content. However, plant cover resilience, i.e. the ability to attain pre-event values, was positively related to a syndrome of traits distinguished by a higher efficiency of water use and uptake. Thus, higher SLA and lower water-use efficiency characterized species that were able to maintain green biomass for a longer period of time but were less resilient in the medium term. There was a negative relationship between such syndromes and the number of emerging seedlings. Species with small seeds produced more seedlings per adult. Overall, recruitment was positively correlated with species die-off. This study demonstrates the relationship between plant traits and strong environmental pulses related to climate change, providing a functional interpretation of the recently reported episodes of climate-induced vegetation die-off. Our findings reveal the importance of selecting meaningful traits to interpret post-event resilience processes, particularly when combined with demographic attributes.

Native versus non‐native invasions: similarities and differences in the biodiversity impacts of Pinus contorta in introduced and native ranges

AbstractAimTo determine whether one of the most invasive pine species introduced to the Southern Hemisphere, Pinus contorta, has changed plant species richness, composition, diversity, and litter depth where it has invaded into native open forest, shrub steppe and grassland communities and to assess whether changes were similar in its native and introduced ranges.LocationRío Negro Province, Argentina; Aysén and Araucanía Regions, Chile; Greater Yellowstone Ecosystem, USA.MethodsWe measured changes in plant species richness, species composition and cover, diversity, and litter depth associated with increasing P. contorta tree cover along the invasion front at three sites in the introduced range (Argentina and Chile) and one in the native range (Montana, USA).ResultsPlant species richness and cover generally declined with increasing P. contorta canopy cover, at similar rates in both the introduced and native ranges. However, plant cover was not affected by P. contorta in a forested setting in the introduced range. P. contorta invasion explained more of the decline in species richness in the introduced than native range. Native species composition changed more strongly across the invasion gradient in the introduced than native range. Litter depth increased more rapidly with P. contorta cover in the native than introduced range.Main conclusionsOur results highlight the potential of pines to alter plant communities whether encroaching from forests in the native range or from plantations in the introduced range. Species richness and plant cover declined in both settings; however, individual species abundance and species composition were more impacted in the introduced range than in the native range. We suggest that invading trees have a greater capacity to cause ecological impacts in their introduced than in their native range, particularly where they represent a novel life‐form.

Twenty-Five Year Record of Changes in Plant Cover on Tundra of Northeastern Alaska

Northern Alaska has warmed over recent decades and satellite data indicate that vegetation productivity has increased. To document vegetation changes in the Arctic National Wildlife Refuge, we monitored plant cover at 27 plots between 1984 and 2009. These are among the oldest permanently marked and continuously monitored vegetation plots in the Arctic. We quantified percent cover of all plant species by line-point intercept sampling and assessed change over time for seven plant growth forms. Cover of bryophytes and deciduous shrubs showed slight decreasing trends. Evergreen shrubs, horsetails, and depth of thawed soil above permafrost had no trends. For lichens, graminoids, and forbs, trends varied by plant community type. Overall, vegetation in the plots changed little over the study period, in contrast to results from other studies in northern Alaska. A few plots had dramatic changes, however, which we attributed to subsidence from melting ground ice or to floodplain dynamics. Our results demonstrate that vegetation change on the Arctic Refuge coastal plain over the past quarter century has been spatially heterogeneous and facilitated by disturbance. The findings highlight the need for greater work linking plotlevel and regional remote sensing measurements of change.

Herbivore preference drives plant community composition.

Herbivores are important drivers of plant species coexistence and community assembly. However, detailed mechanistic information on how herbivores affect dominance hierarchies between plant species is scarce. Here, we used data of a multi-site herbivore exclusion experiment in grasslands to assess changes in the cover of 28 plant species in response to aboveground pesticide. application. Moreover, we assessed species-specific values of plant defense of these 28 species measured as the performance of a generalist caterpillar, and the preference of the caterpillar and a slug species in no-choice and choice feeding experiments, respectively. We show that more preferred species in the feeding experiments were those that increased in cover after herbivore exclusion in the field, whereas less preferred ones decreased. Herbivore performance and several measured leaf traits were not related to the change in plant cover in the field in response to herbivore removal. Additionally, the generalist slug and the generalist caterpillar preferred and disliked the same plant species, indicating that they perceive the balance between defense and nutritional value similarly. We conclude that the growth-defense trade-off in grassland species acts via the preference of herbivores and that among-species variation in plant growth and preference to herbivores drives plant community composition.

A shady business: pine afforestation alters the primary controls on litter decomposition along a precipitation gradient in Patagonia, Argentina

SummaryOur understanding of the principal controls on litter decomposition is critical for our capacity to predict how global changes will impact terrestrial ecosystems. Although climate, litter quality and soil organisms clearly modulate carbon (C) and nutrient turnover, land‐use change affecting plant species composition and structure can alter the relative importance of such controls.We took advantage of prior land‐use changes of intentional planting of exotic forest species along a broad precipitation gradient [250–2200 mm mean annual precipitation (MAP)] in Patagonia, South America, where we established five paired sites in natural vegetation and adjacent 35‐year‐old pine plantations. We explored direct and interactive effects of precipitation and plant community structure on litter decomposition within situdecomposition, common litters and reciprocal transplants, in addition to an evaluation of microenvironmental changes.Surface litter decomposition in natural vegetation (NV) was similar in all sites along the gradient, independent of litter quality,MAPor soil characteristics, while mass loss demonstrated a significant positive linear relationship withMAPin pine plantations (PP).Decomposition of common litters inPPwas markedly reduced with respect toNV, which was > 50% faster at the arid extreme of the gradient. C:N ratios predicted decomposition only inPP, and differences in decomposition were highly correlated with impacts of vegetative cover on incident solar radiation.Synthesis. Concurrent changes in plant cover inNVwith increasingMAPresulted in reduced incident solar radiation at the soil surface and decreased the relative importance of photodegradation as a control on surface mass loss. These changes eclipsed direct effects of water availability, litter quality and soil nutrients. In contrast, increased shade and recalcitrant litter with afforestation inPPsites combined such that photodegradation was entirely eliminated as a control and biotic decomposition was much reduced. While afforestation projects are promoted as a strategy to mitigate increased atmospheric carbon dioxide due to human activity, our results highlight that primary controls of litter decomposition were substantially altered with unexpected consequences for the C balance of these ecosystems.

Nitrogen Critical Loads for an Alpine Meadow Ecosystem on the Tibetan Plateau.

Increasing atmospheric nitrogen (N) deposition has the potential to alter plant diversity and thus the function and stability of terrestrial ecosystems. N-limited alpine ecosystems are expected to be particularly susceptible to increasing N deposition. However, little is known about the critical loads and saturation thresholds of ecosystem responses to increasing N deposition on the Tibetan Plateau, despite its importance to ecosystem management. To evaluate the N critical loads and N saturation thresholds in an alpine ecosystem, in 2010, we treated an alpine meadow with five levels of N addition (0, 10, 20, 40, and 80 kg N ha(-1) year(-1)) and characterized plant and soil responses. The results showed that plant species richness and diversity index did not statistically vary with N addition treatments, but they both changed with years. N addition affected plant cover and aboveground productivity, especially for grasses, and soil chemical features. The N critical loads and saturation thresholds, in terms of plant cover and biomass change at the community level, were 8.8-12.7 and 50 kg N ha(-1) year(-1) (including the ambient N deposition rate), respectively. However, pronounced changes in soil inorganic N and net N mineralization occurred under the 20 and 40 kg N ha(-1) year(-1) treatments. Our results indicate that plant community cover and biomass are more sensitive than soil to increasing N inputs. The plant community composition in alpine ecosystems on the Qinghai-Tibetan Plateau may change under increasing N deposition in the future.

Human impact on the plant cover of four villages in SE Poland

The observation of the rapid rate of plant cover transformation caused by urbanization and agricul tural technology was the inspiration for undertaking the study in rural areas. The study was carried out in the Sandomierz Basin in four typical villages with varying degrees of the anthropogenic impact. The changes observed included: Koszyce Male – evident transformation of fields and meadows into building land; Kolbuszowa Dolna – intensive changes in land use, abandonment of fields and meadows, and river regulation; Roźwienica – emergence of new habitats for plant colo nization after reclamation of land previously occupied by a brick factory and a landfill; Krzeczowice – intensive crop cultivation and unchanged land use. In 2009–2010, floristic investigations with the patrol method were carried out in these areas. The historical-geographical classification and indices of the anthropogenic changes of the flora were employed in the analysis. Substantially, domination of synanthropic species over non-synanthropic spontaneophytes was noted in the analysed floras. In the synanthropic species group, the proportion of apophytes was 3-fold higher than that of anthropophytes. Archaeophytes were more abundant than kenophytes. The flora of Krzeczowice, an area af fected by long-term anthropopressure, was by approx. 30% less abundant than that in the other villages; it was also characterised by the highest synanthropization index, apophytization index, and index of apophytism of spontaneophytes. In turn, the flora found in Kolbuszowa Dolna was rich due to the presence of a wide variety of habitats; it was characterised by the lowest apophytization index accompanied by the highest anthropo phization index. KEy worDs: rural areas, Sandomierz Basin, anthropopressure, changes of plant cover, anthropogenic indices

Palynological Indication of Anthropogenic Plant Cover Changes in the Eastern-European Coniferous-Broadleaf Forests in the Late Holocene

The paper summarizes the current knowledge of palynological criteria which allow to reconstruct anthropogenic disturbances of plant cover in the late holocene. The case studies of modern and fossil pollen spectra of Central Forest State Reserve (Tver oblast, Russia) and forest reserve Osveisky in Belarus were discussed. Obtained results show that anthropogenic changes of plant cover could be reliable detected by general changes in composition of pollen spectra and by appearance of particular species – indicators.

Changes in soil aggregation and microbial community structure control carbon sequestration after afforestation of semiarid shrublands

Changes in plant cover after afforestation induce variations in litter inputs and soil microbial community structure and activity, which may promote the accrual and physical-chemical protection of soil organic carbon (SOC) within soil aggregates. In a long-term experiment (20 years) we have studied the effects, on soil aggregation and SOC stabilization, of two afforestation techniques: a) amended terraces with organic refuse (AT), and b) terraces without organic amendment (T). We used the adjacent shrubland (S) as control. Twenty years after stand establishment, aggregate distribution (including microaggregates within larger aggregates), sensitive and slow organic carbon (OC) fractions, basal respiration in macroaggregates, and microbial community structure were measured. The main changes occurred in the top layer (0–5 cm), where: i) both the sensitive and slow OC fractions were increased in AT compared to S and T, ii) the percentage and OC content of microaggregates within macroaggregates (Mm) were higher in AT than in S and T, iii) basal respiration in macroaggregates was also higher in AT, and iv) significant changes in the fungal (rather than bacterial) community structure were observed in the afforested soils (AT and T) – compared to the shrubland soil. These results suggest that the increase in OC pools linked to the changes in microbial activity and fungal community structure, after afforestation, promoted the formation of macroaggregates – which acted as the nucleus for the formation and stabilization of OC-enriched microaggregates.

Rainfall intensity modulates the interaction between the marsh cordgrass Spartina densiflora and the mouse Akodon azarae

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 523:71-80 (2015) - DOI: https://doi.org/10.3354/meps11119 Rainfall intensity modulates the interaction between the marsh cordgrass Spartina densiflora and the mouse Akodon azarae Jesús Pascual*, Alejandro D. Canepuccia, Juan Alberti, Pedro Daleo, Oscar Iribarne Instituto de Investigaciones Marinas y Costeras (IIMyC), CONICET - UNMDP, Lab. Ecología, Dpto. Biología, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, CC 573 Correo Central, B7600WAG, Mar del Plata, Argentina *Corresponding author: pascualjesu@gmail.com ABSTRACT: Changes in rainfall patterns caused by anthropogenic global climate change or planetary-scale events, such as the El Niño Southern Oscillation, can significantly affect the abundance and distribution of organisms. Despite the evidence of such effects on marine and terrestrial systems, ecological consequences of rainfall fluctuations in coastal marine ecosystems remain poorly understood. Here we evaluate the effects of rainfall intensity on the interaction between the cordgrass Spartina densiflora and Azara’s grass mouse Akodon azarae in a southwestern Atlantic salt marsh (Mar Chiquita coastal lagoon, Argentina). Field surveys showed that the abundance of A. azarae increased during rainy summers (i.e. El Niño 2005 and 2007) and had lowest values during dry summers (i.e. La Niña 2008). Salt content in sediment and plant tissue were negatively related with rainfall. In addition, field experiments showed that increased sediment salinity resulted in increased salt content in plant tissues. Elevated soil salinity also increased the proportion of senescent S. densiflora tissues and reduced plant growth. The consumption of S. densiflora leaves by A. azarae also decreased with increased soil salinity. The proportion of S. densiflora in feces collected during the driest summer was very small. Therefore, changes in the abundance of A. azarae could be mediated by plant-rodent trophic interaction or by plant cover changes. In conclusion, rainfall fluctuations changed the abiotic environment (i.e. salinity), decreasing primary production and indirectly modifying habitat use by the omnivore A. azarae and its trophic interaction with S. densiflora. The present study provides evidence that rainfall can modify ecological processes that affect the structure and dynamics of coastal marine ecosystems. KEY WORDS: Climate change · Rainfall changes · Spartina densiflora · Akodon azarae · Habitat use Full text in pdf format PreviousNextCite this article as: Pascual J, Canepuccia AD, Alberti J, Daleo P, Iribarne O (2015) Rainfall intensity modulates the interaction between the marsh cordgrass Spartina densiflora and the mouse Akodon azarae. Mar Ecol Prog Ser 523:71-80. https://doi.org/10.3354/meps11119 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 523. Online publication date: March 16, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Impacto de la erosión y escorrentía en laderas de agroecosistemas de montaña mediterránea

Duran, Z.V.H., Rodriguez, P.C.R., Cuadros, T.S., Francia, M.J.R. 2014. Impact of soil erosion and runoff on mountain slopes of Mediterranean agroecosystems. Ecosistemas 23(1):66-72. Doi.: 10.7818/ECOS.2014.23-1.12 Land degradation in Mediterranean agroecosystems implies the loss of current utility and reduction of its potential functions, by both natural processes and those specifically induced and intensified by human actions. The impact of erosion and runoff on different land-use types (LUT): farmland (olive, almond and cereal), forest ( Pinus halepensis and Pinus sylvestris ), shrubland, grassland and abandoned farmland in Sierra Nevada (SE Spain) have been assessed. The erosion plots twice replicated were located on the slopes for each land-use type, monitoring the erosion and runoff rates for 22 rainfall events. According to the results of the present study the LUT consisting in P. halepensis and P. sylvestris significantly minimized soil erosion and runoff, in contrast to the abandoned farmland. In relation to farmland activity important impact of erosion has been found in olive plots than in almond and cereal. The shrubland generated intermediate erosion and runoff rates between Pinus trees and agriculture-grassland plots. Consequently, plant cover change is crucial in interpreting the productivity degradation of soils, as well as in planning sustainable strategies to mitigate soil degradation processes in Mediterranean agroecosystems.

The influence of South Africa's post-apartheid land reform policies on bush encroachment and range condition: a case study of Fort Beaufort's municipal commonage

We examined the effect of changes in land use and land tenure on bush encroachment and vegetation condition. An analysis of aerial photographs from three time steps (1949, 1985 and 2004) was used to document changes in woody plant density in different vegetation types on commonage and an adjacent commercial farm in Fort Beaufort, South Africa. Rangeland condition was assessed in different vegetation units of the area and woody plant density was related to distance from urban settlement. Results showed that there has been an increase in woody plant cover in both commonage and commercial farming areas, particularly between 1949 and 1985. However, since 1985, increased rates of urbanisation have stabilised, and in some areas reduced, woody plant thickening, especially at locations closest to urban settlements. Bush encroachment is being controlled to some extent by fuelwood harvesting and goat browsing, resulting in a reduction in height of favoured woody species such as Acacia karroo (Vachellia karroo). There has been a shift to less palatable browse species on the commonage areas and the condition of the grass sward is poor. Change in woody plant cover is significantly influenced by changing patterns of land use and land tenure over time which, in turn, affect rangeland condition.

Spatial and temporal structuring of arbuscular mycorrhizal communities is differentially influenced by abiotic factors and host crop in a semi-arid prairie agroecosystem

Agroecosystems are dynamic systems that experience frequent chemical inputs and changes in plant cover. The objective of this study was to test whether abiotic (soil chemical properties and climate) and biotic (plant host identity) factors influence the spatial and temporal structuring of arbuscular mycorrhizal fungal (AMF) communities in a semi-arid prairie agroecosystem. 454 GS FLX+ high-throughput sequencing technology was successfully utilized to characterize the AMF communities based on long reads (mean length: 751.7 bp) and generated high-resolution data with excellent taxonomic coverage. The composition of the AMF community colonizing roots of the three crops (pea, lentil, and wheat) significantly differed, but plant host identity had a minimal effect on the composition of the AMF community in the soil. We observed a temporal shift in the composition of AMF communities in the roots and surrounding soil of the crops during the growing season. This temporal shift was particularly evident in the root-associated AMF community and was correlated with soil phosphate flux and climatic variables. In contrast, the spatial structuring of the AMF community in the site was correlated with soil pH and electrical conductivity. Individual AMF taxa were significantly correlated with pH, electrical conductivity, and phosphate flux, and these relationships were phylogenetically conserved at the genus level within the Glomeromycota.

Ретроспектива изучения растительного покрова Крайнего Севера в Ботаническом институте им. В. Л. Комарова РАН за полтора века и перспективы в XXI веке

Ретроспектива изучения растительного покрова Крайнего Севера в Ботаническом институте им. В. Л. Комарова РАН за полтора века и перспективы в XXI веке

Grazing impact on desert plants and soil seed banks: Implications for seed-eating animals

We assess whether the knowledge of livestock diet helps to link grazing effects with changes in plant cover and soil seed bank size, aiming at inferring the consequences of grazing on seed-eating animals. Specifically, we test whether continuous and heavy grazing reduce the cover, number of reproductive structures and seed reserves of the same grass species whose seeds are selected and preferred by granivorous animals in the central Monte desert, Argentina. Grass cover and the number of grass spikes usually diminished under grazing conditions in the two localities studied (Telteca and Ñacuñán), and soil seed bank was consistently reduced in all three years evaluated owing to a decline of perennial grass and forb seeds. In particular, the abundance of those seeds selected and preferred by birds and ants (in all cases grass species) declined 70–92% in Ñacuñán, and 52–72% in Telteca. Reduction of perennial grass cover and spike number in grazed sites reinforced the causal link between livestock grazing and the decline of grass soil seed reserves throughout failed plant reproduction. Grass seed bank depletion suggests that grazing may trigger a “cascade” of mechanisms that affect the abundance and persistence of valuable fodder species as well as the availability of seed resources for granivorous animals.

Vegetation changes and human activity around Lake Łańskie (Olsztyn Lake District, NE Poland) from the mid Holocene, based on palynological study

ABSTRACT Bottom sediments of Lake Łańskie in NE Poland (Olsztyn Lake District) were studied by pollen analysis, and vegetation changes from ca 4800 BC to modern times were reconstructed based on the results. Due to rapid sedimentation the changes in plant cover are recorded with high resolution. The variation of pollen spectra composition reflects changing shares of deciduous trees and the continuous dominance of pine forest. Nowadays the surroundings of Lake Łańskie are also heavily forested but as early as 1100 AD the deciduous trees began to be eliminated. On the basis of pollen data, five phases of increased human activity were distinguished. Based on the available archaeological chronology of local settlements, the first stage is connected with para-Neolithic groups of Ząbie-Szestno type and the Lusatian culture. They are followed by the West Baltic Barrow culture, Wielbark culture and Early Medieval Prussian tribes. The pollen record shows low intensity of exploitation of the terrain around Lake Łańskie, probably attributable to the brevity of episodes of human occupation in the near vicinity of the lake. The last phase, covering part of the Middle Ages (since ca 1000 AD) and modern times, is reflected in the most distinct vegetation changes on the pollen diagram, caused by increased intensity of settlement. In spite of the distinct diminution of forest cover around the lake the scale of deforestation was much lower than at other sites in NE Poland. The main aims of this paper were to describe the changes in the palaeoenvironment which took place around Lake Łańskie (Olsztyn Lake District) and to find those changes in the plant cover which were the effect of human activity, and to confirm whether the changes of palaeoenvironment around Lake Łańskie were noted at the same time in adjacent areas.

Changes in alpine snowbed‐wetland vegetation over three decades in northern Norway

We have quantified floristic changes in alpine snowbeds and wetland vegetation during three decades and analyzed to what extent these changes are related to initial variations in snow cover duration and distance to groundwater level. Vascular plant species richness and total plant cover were estimated along three transects in northern Norway. Three different vegetation zones were identified along the original transects: relatively dry snowbeds, wet snowbeds and wetlands. The resampling shows major changes in species richness and plant cover. In general, there was a net immigration of species and 13 new species were found. Five rare species with initial low cover were lost. In the dry and wet snowbeds, species richness and total plant cover increased, mostly because of invasion by shrubs, graminoids and herbs. A general trend was that species indicating high soil moisture were strongly reduced. In the wetland zones there were no significant floristic changes but hygrophilous species had decreased and were replaced by graminoids and shrub species with lower water requirements. These floristic changes were significantly related to snow and soil moisture conditions, important factors for rate and direction of change. Contrasting vegetation responses within very short distances demonstrate the importance of detailed knowledge of the actual microhabitats when effects of climate change in alpine habitats are considered.

Responses of aquatic macrophyte cover and productivity to flooding variability on the Amazon floodplain

Macrophyte net primary productivity (NPP) is a significant but understudied component of the carbon budget in large Amazonian floodplains. Annual NPP is determined by the interaction between stem elongation (vertical growth) and plant cover changes (horizontal expansion), each affected differently by flood duration and amplitude. Therefore, hydrological changes as predicted for the Amazon basin could result in significant changes in annual macrophyte NPP. This study investigates the responses of macrophyte horizontal expansion and vertical growth to flooding variability, and its possible effects on the contribution of macrophytes to the carbon budget of Amazonian floodplains. Monthly macrophyte cover was estimated using satellite imagery for the 2003-2004 and 2004-2005 hydrological years, and biomass was measured in situ between 2003 and 2004. Regression models between macrophyte variables and river-stage data were used to build a semiempirical model of macrophyte NPP as a function of water level. Historical river-stage records (1970-2011) were used to simulate variations in NPP, as a function of annual flooding. Vertical growth varied by a factor of ca. 2 over the simulated years, whereas minimum and maximum annual cover varied by ca. 3.5 and 1.5, respectively. Results suggest that these processes act in opposite directions to determine macrophyte NPP, with larger sensitivity to changes in vertical growth, and thus maximum flooding levels. Years with uncommonly large flooding amplitude resulted in the highest NPP values, as both horizontal expansion and vertical growth were enhanced under these conditions. Over the simulated period, annual NPP varied by ca. 1.5 (1.06-1.63 TgCyr(-1) ). A small increasing trend in flooding amplitude, and by extension NPP, was observed for the studied period. Variability in growth rates caused by local biotic and abiotic factors, and the lack of knowledge on macrophyte physiological responses to extreme hydrological conditions remain the major sources of uncertainty.

Climate and plant cover co-determine the elevational reduction in evapotranspiration in the Swiss Alps

Summary Atmospheric conditions and plant cover are the two main determinants of evapotranspiration (ET), and both strongly depend on elevation. The objective of this work was to separate the two effects across a 1 km elevation gradient and compare theoretical and experimental approaches in order to improve hydrological models for mountainous regions. We used the Penman–Monteith model (FAO-56 procedure) and atmometers (evaporimeters) in combination with grassland weighable lysimeters (WLs) and deep seepage collectors (DSCs) positioned at 1490, 1960 and 2440 m of elevation in the Swiss Alps to quantify climatic and vegetation effects on ET. Atmometers and the Penman–Monteith model were used to quantify atmospheric evaporative demand and WLs were employed to measure ET during clear days (WLET). DSCs were used to calculate ET rates from the water balance equation over longer time periods (DSCET) during summer in 2010 and 2011. During clear days, Penman–Monteith evapotranspiration (PMET) was reduced by 11% at the high site in comparison to the low site, atmometer evaporation (AE) was reduced by 23%, and daytime WLET rates decreased by 37%. Over longer time spans (close to three months), PMET decreased by an average of 10% (14% and 6% for 2010 and 2011) along the entire elevational gradient, and DSCET dropped by a mean 35% (45% and 25% during 2010 and 2011). The steeper elevational gradient in DSCET in 2010 was probably caused by the early onset of the growing season at low elevation during that year. Reductions in WLET and DSCET with elevation were thus consistently larger than the decline in both AE and PMET. Smaller vascular plant biomass at high elevation causes a reduction in ET that is approximately as large as the reduction in ET by reduced atmospheric forcing. These findings call for a revision of the view that evapotranspiration during the growing season is explained by season length only (assuming no effect of elevation on a daily basis). Solving the water balance by hydrological modelling in high elevation catchments needs to account for elevational changes in plant cover (amount of transpiring biomass, LAI), even within the same type of land cover as shown here for grassland.

Differences in plant cover and species composition of semiarid grassland communities of central Mexico and its effects on net ecosystem exchange

Abstract. Changes in land use across the semiarid grasslands of northern Mexico have driven a decline of plant cover and alteration of plant species composition. A number of different plant communities have resulted from these changes. Their implications, however, on the carbon (C) cycle and regional carbon balance are still poorly understood. Here, we examined the effects of plant cover loss and changes in species composition on net ecosystem CO2 exchange (NEE) and their biotic and abiotic controls. NEE was measured in five representative plant community types within a semiarid grassland by temporarily enclosing the entire aboveground ecosystem using a chamber method (i.e., geodesic dome). Sites included an oat crop (crop), a moderately grazed grassland (moderate grazing), a 28 yr-old grazing exclosure (exclosure), an overgrazed site with low perennial grass cover (overgrazed), and an overgrazed site presenting shrub encroachment (shrub encroachment). For natural vegetation, rates of standardized daytime NEE for sites with a high plant cover (exclosure and moderate grazing) were similar (P > 0.05) as compared to sites with low plant cover (overgrazed and shrub encroachment). However, yearly total nighttime NEE (carbon loss) was more than double (P < 0.05) for sites with high plant cover compared to sites with low cover, resulting to slight C sinks for the low plant cover sites, and neutral or sources for the high plant cover sites as accounted by daytime and nighttime NEE annual balance. Differences in plant cover and its associated biomass defined the sensitivity to environmental controls. Thus, daytime NEE in low plant cover sites reached light compensation points at lower photosynthetic photon flux density than those from high plant cover sites. Differences in species composition did not influence NEE rates even though there were transient or permanent changes in C3 vs. C4 functional groups. Our results allowed the detection of the large variability and contribution of different plant communities to regional C balance in patchy landscapes. Identification of the role of landscape patches in the regional C balance as either sinks or sources may provide tools allowing land use management strategies that could favor C uptake in patchy landscapes.