Dry Ecosystems Research Articles

Continental estimates of forest cover and forest cover changes in the dry ecosystems of Africa between 1990 and 2000

AimThis study provides regional estimates of forest cover in dry African ecoregions and the changes in forest cover that occurred there between 1990 and 2000, using a systematic sample of medium-resolution satellite imagery which was processed consistently across the continent.LocationThe study area corresponds to the dry forests and woodlands of Africa between the humid forests and the semi-arid regions. This area covers the Sudanian and Zambezian ecoregions.MethodsA systematic sample of 1600 Landsat satellite imagery subsets, each 20 km × 20 km in size, were analysed for two reference years: 1990 and 2000. At each sample site and for both years, dense tree cover, open tree cover, other wooded land and other vegetation cover were identified from the analysis of satellite imagery, which comprised multidate segmentation and automatic classification steps followed by visual control by national forestry experts.ResultsLand cover and land-cover changes were estimated at continental and ecoregion scales and compared with existing pan-continental, regional and local studies. The overall accuracy of our land-cover maps was estimated at 87%. Between 1990 and 2000, 3.3 million hectares (Mha) of dense tree cover, 5.8 Mha of open tree cover and 8.9 Mha of other wooded land were lost, with a further 3.9 Mha degraded from dense to open tree cover. These results are substantially lower than the 34 Mha of forest loss reported in the FAO's 2010 Global Forest Resources Assessment for the same period and area.Main conclusionsOur method generates the first consistent and robust estimates of forest cover and change in dry Africa with known statistical precision at continental and ecoregion scales. These results reduce the uncertainty regarding vegetation cover and its dynamics in these previously poorly studied ecosystems and provide crucial information for both science and environmental policies.

First record of Austroleon dispar Banks, 1909 (Neuroptera: Myrmeleontidae) from Brazil

The present note extends the geographic range of Austroleon dispar Banks, 1909 to Brazil based on the examination of three females and one male collected in the Estação Ecológica Jataí, Luiz Antônio, São Paulo. The present finding indicates that A. dispar is associated with dry ecosystems, at least in part of its geographic distribution.

Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grasslands

Most of the world's grasslands are managed for livestock production. A critical component of the long-term sustainability and profitability of rangelands (e.g., grazed grassland ecosystems) is the maintenance of plant production. Amending grassland soils with organic waste has been proposed as a means to increase net primary productivity (NPP) and ecosystem carbon (C) storage, while mitigating greenhouse gas emissions from waste management. Few studies have evaluated the effects of amendments on the C balance and greenhouse gas dynamics of grasslands. We used field manipulations replicated within and across two rangelands (a valley grassland and a coastal grassland) to determine the effects of a single application of composted green waste amendments on NPP and greenhouse gas emissions over three years. Amendments elevated total soil respiration by 18% +/- 4% at both sites but had no effect on nitrous oxide or methane emissions. Carbon losses were significantly offset by greater and sustained plant production. Amendments stimulated both above- and belowground NPP by 2.1 +/- 0.8 Mg C/ha to 4.7 +/- 0.7 Mg C/ha (mean +/- SE) over the three-year study period. Net ecosystem C storage increased by 25-70% without including the direct addition of compost C. The estimated magnitude of net ecosystem C storage was sensitive to estimates of heterotrophic soil respiration but was greater than controls in five out of six fields that received amendments. The sixth plot was the only one that exhibited lower soil moisture than the control, suggesting an important role of water limitation in these seasonally dry ecosystems. Treatment effects persisted over the course of the study, which were likely derived from increased water-holding capacity in most plots, and slow-release fertilization from compost decomposition. We conclude that a single application of composted organic matter can significantly increase grassland C storage, and that effects of a single application are likely to carry over in time.

A meta-analysis of observational epidemiological studies of Newcastle disease in African agro-systems, 1980-2009.

Newcastle disease (ND) is one of the most important and widespread avian pests. In Africa, backyard poultry production systems are an important source of protein and cash for poor rural livelihoods. ND mortality in these production systems is important and seriously disrupts benefits derived from it. This study undertook an African continental approach of ND epidemiology in backyard poultry. After a systematic literature review of studies published from 1980 to 2009, a meta-analysis of spatio-temporal patterns of serological prevalence and outbreak occurrence was performed. Average ND serological prevalence was estimated at 0·67 [95% confidence interval (CI) 0·58-0·75] in regions characterized by humid ecosystems, high human and poultry densities and low altitudes; 0·36 (95% CI 0·30-0·41) in dry ecosystems at intermediate altitude where human and poultry densities are low and 0·27 (95% CI 0·19-0·38) in mountain ecosystems where human and poultry densities are intermediate. In terms of seasonality, ND outbreaks occur mostly during the dry seasons in Africa, when environmental conditions are likely to be harshest for backyard poultry. In addition, a phylogeographical analysis revealed the regionalization of ND virus strains, their potential to evolve towards a higher pathogenicity from the local viral pool and suggests a risk for vaccine strains to provide new wild strains. These results present for the first time a continent-wide approach to ND epidemiology in Africa. More emphasis is needed for ND management and control in rural African poultry production systems.

First record of Leucospis signifera Bouček, 1974 (Insecta: Hymenoptera: Leucospidae) in the São Paulo state, Brazil

The present note extends the geographic range of Leucospis signifera Bouček, 1974 farther to the Northeast, reaching the State of São Paulo, based on the examination of four females collected at Jataí Ecological Station, municipality of Luiz Antônio, São Paulo State, Brazil. The present finding indicates that L. signifera is associated with dry ecosystems, at least in part of its geographic distribution.

Environmental and physical controls on northern terrestrial methane emissions across permafrost zones

Methane (CH4 ) emissions from the northern high-latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing-season CH4 emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on environmental and physical variables, including permafrost conditions, were used to assess controls on CH4 emissions. Water table position, soil temperature, and vegetation composition strongly influenced emissions and had interacting effects. Sites with a dense sedge cover had higher emissions than other sites at comparable water table positions, and this was an effect that was more pronounced at low soil temperatures. Sensitivity analysis suggested that CH4 emissions from ecosystems where the water table on average is at or above the soil surface (wet tundra, fen underlain by permafrost, and littoral ecosystems) are more sensitive to variability in soil temperature than drier ecosystems (palsa dry tundra, bog, and fen), whereas the latter ecosystems conversely are relatively more sensitive to changes of the water table position. Sites with near-surface permafrost had lower CH4 fluxes than sites without permafrost at comparable water table positions, a difference that was explained by lower soil temperatures. Neither the active layer depth nor the organic soil layer depth was related to CH4 emissions. Permafrost thaw in lowland regions is often associated with increased soil moisture, higher soil temperatures, and increased sedge cover. In our database, lowland thermokarst sites generally had higher emissions than adjacent sites with intact permafrost, but emissions from thermokarst sites were not statistically higher than emissions from permafrost-free sites with comparable environmental conditions. Overall, these results suggest that future changes to terrestrial high-latitude CH4 emissions will be more proximately related to changes in moisture, soil temperature, and vegetation composition than to increased availability of organic matter following permafrost thaw.

The resilience of annual vegetation primary production subjected to different climate change scenarios

We examined if climate change in two dry ecosystems—Mediterranean (DME) and Semiarid (SAE)—would cause substantial reduction in the production of annual vegetation. Field measurements and computer simulations were used to examine the following six climate change scenarios: (1) rainfall amount reduction; (2) increases of 10 % in annual evaporation rate and 5 % in annual temperature; (3) increase in magnitude of rainfall events, accompanied by reductions in frequency and seasonal variation; (4) postponement of the beginning of the first rainfall event of the growing season; (5) long dry spells during the growing season; and (6) early ending of the growing season. The results revealed the following outcomes. a) Reduction by 5–35 % in annual rainfall amount did not significantly affect productivity in the DME, but a large (25–35 %) decrease in rainfall would change vegetation productivity in the SAE and lead to a patchier environment. b) Similar results were observed: when temperature and evaporation rate were increased; when the magnitude of rainfall events increased but their frequency decreased; and during a long mid-season dry spell. c) In both ecosystems, changes in the temporal distribution of rainfall, especially at the beginning of the season, caused the largest reduction in productivity, accompanied by increased patchiness. d) Long-term data gathered during the last three decades indicated that both environments exhibited high resilience of productivity under rainfall variability. These results imply that the response of dry ecosystems to climate change is not characterized by a dramatic decrease in productivity. Moreover, these ecosystems are more resilient than expected, and their herbaceous productivity might undergo drastic changes only under more severe scenarios than those currently predicted in the literature.

Ethnoecological appraisal of Acacia modesta Wall. common tree of dry ecosystem in Pakistan

Ethnoecological studies on Acacia modesta Wall. (Mimosaceae) growing wild in Dargai area of Malakand District (Pakistan), demonstrated a great demand due to the medicinal value of its flowers oil, gum, resins and sticks for honey bee. The plant as a whole is also valuable as fuel-wood and as construction material for income. Locally, common folk used it as fodder, timber, fencing, and household items and as a source of honey bee production. The tree was found to be abundant in some villages of Dargai area. The frequency being: 35% in Jaban, 15% in Kot, 25% in Mehrdi, 10% in Wartair, and 15% in Qaldara villages of Dargai. Interestingly, a great variation was noticed in the local selling prices of the gum which were also found higher in national as well as international markets. Ecological studies showed that A. modesta trees growing on all ranges of soils including: dry to wet, sandy to calcareous and acidic soils along with association of Olea cuspidata, Ziziphus jujuba, Zizyphus nummularia, and Acacia arabica. Phonological studies revealed all the three stages of trees from juvenile, young and rare older trees, in the region under study. Market survey and interviews with local collectors showed that Dargai was the major trade route for medicinal plants. In general, there are locally well known centers where A. modesta is growing in abundance. Dargai is believed to be a regional herbal medicines market route where the transportation of A. modesta gum and other herbals to other areas, have well been recorded. During the current study, it was observed that major plant collectors in the area were local women and children, however, many workers were Afghan refugees. Local men were cornered from open field work, perhaps due to safety reasons. Men participate in cutting of bigger plants whenever demand arises. There is a need that, along with conservation of valuable timber by participatory approach, A. modesta must also be included in these efforts to make its availability in long term for poor local collectors whose one the major source of income is from gum and fuel wood collection. Key words: Acacia modesta Wall. (Mimosaceae), Dargai, Malakand, Pakistan, useful plants for humans.

"Applied Open -Web GIS Server based solution to develop the Web-Based Mapping Application using Open-Source Software Server (OSS)"

Wetlands are the transitional zones between permanently aquatic and dry terrestrial ecosystems. Wetland systems directly and indirectly support millions of people, providing goods and services to them. The use of remote sensing technology for the mapping, identification, inventory and classification of the wetlands has been a common application of satellite imagery. Remote sensing has provided a great mean to study various ecosystems of the earth including wetlands by providing cost and time effective data. For a country like India, with its vast biological and cultural diversity, a comprehensive use of remote sensing, GIS and other related technologies is of great use in their conservation. DOI: http://dx.doi.org/10.11591/ij-ict.v1i1.547

CATÁLOGO DE LAS PLANTAS VASCULARES DE RÁQUIRA (BOYACÁ), FLORA ANDINA EN UN ENCLAVE SECO DE COLOMBIA

La revista Colombia Forestal publica manuscritos originales en temáticas del campo forestal y diversos aspectos de los recursos naturales y del medio ambiente, los cuales se discriminan en las categorías de artículo de investigación, de revisión, de reflexión y notas técnicas de acuerdo con lo estipulado por COLCIENCIAS para las publicaciones científicas. De acuerdo a la clasificación de áreas científicas de la Organización para la Cooperación y el Desarrollo Económico (OCDE), la revista Colombia Forestal pertenece al gran área de Ciencias Agrícolas(4), área de Agricultura, Silvicultura y Pesca(4A) y a la disciplina Forestal (4A02).

New evidence that high potential nitrification rates occur in soils during dry seasons: Are microbial communities metabolically active during dry seasons?

Emerging research is challenging existing paradigms of nitrogen (N) cycling in arid and semiarid ecosystems that experience distinct seasonal patterns in precipitation. We measured equal or greater potential nitrification rates in the dry season than the wet season in chemically and physically distinct soils along a three million year substrate age gradient in Arizona. These surprising and counterintuitive results are supported by recently published work in California Mediterranean grasslands. Considered together, these studies call attention to the need to measure process rates during the dry, non-growing season of xeric ecosystems. Several mechanisms may be responsible for these patterns, but we highlight the importance of understanding the contribution of archaeal ammonia oxidizers to nitrification in these seasonally dry ecosystems.

Nitrogen compounds emission and deposition in West African ecosystems: comparison between wet and dry savanna

Abstract. Surface emission and deposition fluxes of reactive nitrogen compounds have been studied in five sites of West Africa during the period 2002 to 2007. Measurements of N deposition fluxes have been performed in IDAF sites representative of main west and central African ecosystems, i.e., 3 stations in dry savanna ecosystems (from 15° N to 12° N), and 2 stations in wet savanna ecosystems (from 9° N to 6° N). Dry deposition fluxes are calculated from surface measurements of NO2, HNO3 and NH3 concentrations and simulated deposition velocities, and wet deposition fluxes are calculated from NH4+ and NO3− concentration in samples of rain. Emission fluxes are evaluated including simulated NO biogenic emission from soils, emissions of NOx and NH3 from biomass burning and domestic fires, and volatilization of NH3 from animal excreta. This paper is a tentative to understand the eventual impact of the monsoon variability from year to year, with the natural variability of local sources, on the emission and deposition N fluxes, and to compare these evolutions between dry and wet savanna ecosystems. In dry savanna ecosystems where the rain season lasts mainly from June to September, the occurence of rain correlates with the beginning of emission and deposition fluxes. This link is less obvious in wet savanna ecosystems (wet season mainly from May to October), where the surface is less submitted to drastic changes in terms of water content. Whatever the location, the natural variability of rain from year to year does not exceed 15 %, and the variability of emission and deposition magnitude ranges between 15 % and 28 %. While quasi providing the same total N budget, and due to the presence of different types of soils and vegetation, wet and dry savanna do not present the same distribution in emission and deposition fluxes contributions: in dry savanna, the emission is dominated by ammonia volatilization, and the deposition is dominated by the dry contribution. In wet savanna, emission is equally distributed between ammonia volatilization, emissions from biomass burning and natural NO emissions from soils, and wet and dry deposition are equivalent. Due to the scarcity of available data on the African continent, and despite the numerous uncertainties resulting from the different calculations and assumptions, this work is a combination of data from different origins (surface measurements, satellite and modelling) to document the atmospheric Nitrogen cycle in tropical regions.

An international workshop: mycorrhiza, a biological tool for sustainable development in Africa

Althoughmycorrhizal symbiosis are well known on European, North American, South American, Southeast Asian, and Australian plant species from natural or anthropogenic ecosystems, data from Africa are still scarce and neglected. The international workshop on “Mycorrhiza: a biological tool for sustainable development in Africa” held in Dakar, Senegal, February 21–23, 2011, was therefore particularly timely. Eighty-seven participants from 23 countries attended theworkshop, which included oral presentations, poster sessions, excursion and many free-ranging discussions. Abstracts of all the talks and posters, and details of the participants can be found on the website http://www.ird.sn/web-mycorhizes2011/. The aim of the workshop was to present state of the knowledge and perspectives in mycorrhizal research on tropical and Mediterranean plant species in Africa. The contents addressed diversity and function of mycorrhiza associated with forest and agricultural plants, in Mediterranean and tropical, wet and seasonally dry ecosystems. Impacts of mycorrhiza on plant diversity and composition, regeneration and dynamics of ecosystems, and biomass production in forestry and agriculture, were topics for oral presentations and poster sessions. The workshop was also a pretext to put in concrete form the idea of creating of a scientific network that connects researchers working with mycorrhiza in Africa. In the opening lecture, A. Fortin (Canada) introduced mycorrhiza and their role in the evolution and functioning of plants and terrestrial ecosystems. Although symbiotic systems have provided a major impetus to plant speciation and to the development of soils and therefore to terrestrial ecosystems, all concepts at the base of modern agriculture have been developed and applied as if mycorrhiza did not exist. A. Fortin invited scientists working in the field ofmycorrhiza in tropical and Mediterranean ecosystems, political deciders, and partners for development to exchange experience and to set up new strategies on mycorrhizal research in Africa. There was a large discussion about the use of mycorrhiza in agriculture and forestry in Africa. A. Bâ (Senegal) opened a session on diversity and function of ectomycorrhizal (ECM) symbioses, illustrating that Russulales and Thelephorales dominate aboveand belowground ECM fungal communities in open and rain forests in tropical Africa. Following presentations covered the role of ECM in the regeneration and functioning of tropical African forests, their potential use for ecological restoration of sites contaminated by heavy metals and the rich occurrence of edible ECM fungi in these regions (N. Onguene Awana, Cameroon; G. Kudzo Atsu, Togo; K. Sanon, Burkina Faso; M. Ducousso, France). There followed much debate about the importance of ECM fungi in forest diversity, productivity, resilience, and restoration. V. Gianinazzi-Pearson (France) introduced a session on diversity and function of arbuscular mycorrhiza (AM) by emphasizing the ecosystem services they provide to plant productivity and survival, and the necessity, for their efficient exploitation in plant production systems, to reduce chemical inputs, evaluate in situ fungal potential and plant responsiveness A. Bâ (*) IRD/LCM/LSTM, BP. 1386, Dakar, Senegal e-mail: amadou.ba@ird.fr

Impact of Savannization on Nitrogen Mineralization in an Indian Tropical Forest

The effects of conversion of an Indian dry tropical forest ecosystem into savanna, on mineral nitrogen (N), net N-mineralization rate and microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP) in soil were studied for two years. There was a marked seasonal variation in all the above parameters at both (upper, 0-10 cm and lower, 10-20 cm) the soil depths of forest and savanna ecosystems. In forest ecosystems the mean annual values of mineral N, net nitrification rate, net N-mineralization rate, MBC, MBN and MBP at both depths were 17.41 and 13.2 µg g -1 , 18.76 and 10.96 µg g -1 mo -1 , 23.54 and 12.83 µg g -1 mo -1 , 623 and 195µg g -1 , 116 and 29µg g -1 , 16 and 9µg g -1 , respectively; while in savanna ecosystems the values were 20.15 and 15.73 µg g-1, 10.74 and 6.29 µg g-1mo-1, 16.59 and 10.11 µg g -1 mo -1 , 453 and 150µg g -1 , 79 and 21.7µg g -1 , 13 and 6µg g -1 , respectively. The soil microbial biomass was positively related to root biomass and total plant biomass (i.e., above- and below-ground biomass). Interestingly, seasonal soil moisture and temperature are reciprocally related to microbial biomass and mineral N and directly related to nitrification and N-mineralization. The microbial biomass, nitrification and N-mineralization are negatively related to clay content. Savannization caused significant loss of soil mean organic carbon (OC), total N (TN) total mean annual nitrification, N-mineralization, MBC, MBN and MBP by 40, 42, 27, 27, 29 and 7%, respectively at upper soil depth and 18, 21, 42, 29 and 22%, respectively at lower soil depth. The reflectances of soil microbial biomass to OC were 1.22 and 1.06 folds at upper and lower soil depths, respectively. Thus, conversion of dry tropical forests into savanna affects remarkably the soil N transformation; microbial biomass and loss of soil organic C which adds to the environmental pollution.

The aggregates stability indicator <ASItest> to evaluate soil spatiotemporal change in a tropical dry ecosystem

In this work, aggregate stability was evaluated as a quality indicator in soils of tropi- cal dry deciduous forests (TDF) with relation to land use, the sampling position in the hillslope and the sampling season. The study was done on a representative morpho-edaphological unit of the tropical dry ecosystems (hillslope on granite with eutric regosol) on the coast of the state of Jalisco, Mexico. The evaluated soil ag- gregation indexes were: Aggregate stability index (ASI)test, maximum stability, minimum stability, relative index of variability, and the index of quality of aggrega- tion change. These indexes showed differences in soil aggregation resulting from changes in land use (conserved TDF, grazed TDF, and cultivated pasture). The in- dexes showed that there is greater stability of the aggregates during the rainy season than in the dry season; as well as in the higher part of the slope than in the lower one. The relationship of the edaphic properties with the ASItest indicator was mainly with radical volume, and less so with exchangeable bases (calcium and magnesium), clay, and organic carbon. The proposed soil aggregation indexes allowed monitoring spatiotemporal changes in soil structure.

Spatial, Ontogenetic, and Sexual Effects on the Diet of a Teiid Lizard in Arid South America

Most lizard species feed on small arthropods, and although some are omnivorous, only a few species are strict herbivores. We studied the diet of Dicrodon guttulatum, a teiid lizard endemic to the arid coastal deserts and dry forests of northern Peru. Herbivory by this lizard has been identified as a potential limiting factor in the regeneration of plant communities in these dry ecosystems. We collected gastric and fecal samples of adult males, adult females, and juveniles of D. guttulatum in different plant communities. Based on the ontogenetic shift from insectivory to herbivory observed in other herbivorous lizards, we hypothesized that juvenile D. guttulatum would have an omnivorous or insectivorous diet. We found D. guttulatum to be almost exclusively herbivorous (78–100%) and to feed largely (12–95%) on mesquite (Prosopis pallida) leaves and flowers across all plant communities and locations. Contrary to our predictions, there was a large overlap in diet between adult males and juveniles, whereas adult females were most likely to include plant species other than P. pallida in their diet. The consistency of herbivory in both juveniles and adults makes the origin of herbivory in D. guttulatum very interesting. We discuss potential factors promoting the evolution of herbivory in this species and the importance of lizard herbivory in the dry ecosystems of northern Peru.

Relative effects of precipitation variability and warming on tallgrass prairie ecosystem function

Abstract. Precipitation and temperature drive many aspects of terrestrial ecosystem function. Climate change scenarios predict increasing precipitation variability and temperature, and long term experiments are required to evaluate the ecosystem consequences of interannual climate variation, increased growing season (intra-annual) rainfall variability, and warming. We present results from an experiment applying increased growing season rainfall variability and year round warming in native tallgrass prairie. During ten years of study, total growing season rainfall varied 2-fold, and we found ~50–200% interannual variability in plant growth and aboveground net primary productivity (ANPP), leaf carbon assimilation (ACO2), and soil CO2 efflux (JCO2) despite only ~40% variation in mean volumetric soil water content (0–15 cm, Θ15). Interannual variation in soil moisture was thus amplified in most measures of ecosystem response. Differences between years in Θ15 explained the greatest portion (14–52%) of the variation in these processes. Experimentally increased intra-annual season rainfall variability doubled the amplitude of intra-annual soil moisture variation and reduced Θ15 by 15%, causing most ecosystem processes to decrease 8–40% in some or all years with increased rainfall variability compared to ambient rainfall timing, suggesting reduced ecosystem rainfall use efficiency. Warming treatments increased soil temperature at 5 cm depth, particularly during spring, fall, and winter. Warming advanced canopy green up in spring, increased winter JCO2, and reduced summer JCO2 and forb ANPP, suggesting that the effects of warming differed in cooler versus warmer parts of the year. We conclude that (1) major ecosystem processes in this grassland may be substantially altered by predicted changes in interannual climate variability, intra-annual rainfall variability, and temperature, (2) interannual climate variation was a larger source of variation in ecosystem function than intra-annual rainfall variability and warming, and (3) effects of increased growing season rainfall variability and warming were small, but ecologically important. The relative effects of these climate drivers are likely to vary for different ecosystem processes and in wetter or drier ecosystems.

Soil-atmosphere greenhouse gases (CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O) exchange in evergreen oak woodland in southern Portugal

  A 10–20% decrease in annual precipitation is predicted in the Mediterranean basin, and in particular to the Iberian Peninsula, with foreseen effects on the exchange of soil-atmosphere greenhouse gases (GHGs; CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub>O). To simulate this scenario, we setup an experimental design in the particularly dry period of 2008–2009 using rainfall exclusion and irrigation, to obtain plots receiving 110% (538 mm), 100% (493 mm) and 74% (365 mm) of the natural precipitation. Soil CO<sub>2</sub> fluxes showed a strong increase from summer to autumn as a consequence of increasing soil heterotrophic respiration that resulted from rewetting. Fluxes of N<sub>2</sub>O were negligible. According to our data, soil was a permanent CH<sub>4</sub> sink independent of the soil water content (in the range between 6–26% WFPS – water-filled pore space) and of soil temperature (in the range of 7–28°C), supporting the concept that seasonally dry ecosystems (Mediterranean) may represent a significant sink of atmospheric CH<sub>4</sub>. The study provides evidence that the 26% decrease or 10% increase in the ambient rainfall from annual precipitation of ca 500 mm did not significantly affect soil functionality and had a limited impact on soil-atmosphere net GHGs exchange in evergreen oak woodlands in southern Portugal.

Impacts of climate change on fire regimes and carbon stocks of the U.S. Pacific Northwest

[1] The diverse vegetation types and carbon pools of the U.S. Pacific Northwest (PNW) are tightly coupled to fire regimes that depend on climate and fire suppression. To realistically assess the effects of twenty-first-century climate change on PNW fire and carbon dynamics, we developed a new fire suppression rule for the MC1 dynamic general vegetation model that we ran under three climate change scenarios. Climate projections from the CSIRO Mk3, MIROC 3.2 medres, and Hadley CM3 general circulation models, forced by the A2 CO2 emissions scenario, were downscaled to a 30 arc-second (∼0.6 km2) grid. Future climates amplify the already strong seasonality of temperature and precipitation across the domain. Simulations displayed large increases in area burned (76%–310%) and burn severities (29%–41%) by the end of the twenty-first century. The relatively dry ecosystems east of the Cascades gain carbon in the future despite projections of more intense wildfires, while the mesic maritime forests lose up to 1.2 Pg C from increased burning. Simulated fire suppression causes overall carbon gains yet leaves ecosystems vulnerable to large future fires. Overall, our simulations suggest the Pacific Northwest has the potential to sequester ∼1 Pg C over the next century unless summer droughts severely intensify fire regimes.

Influence of precipitation pulses on long-term Prosopis ferox dynamics in the Argentinean intermontane subtropics

Biological processes in arid communities are associated with episodic precipitation pulses. We postulate that annual to decadal-scale precipitation pulses modulate the dynamics of the intermontane Prepuna woodlands. To study this hypothesis, we have assessed the influence of precipitation pulses on the rates of growth and survival of Prosopis ferox in the Prepuna woodlands during the past century. Tree ages from several P. ferox stands were used to reconstruct the establishment patterns at each sampling site. Ring-width chronologies provided the basis to assess the influence of annual versus multiannual precipitation pulses on radial growth and establishment over time. Both the radial growth and the stand dynamics of P. ferox at the regional scale were found to be largely modulated by climate, with precipitation the dominant factor influencing interannual variations in P. ferox ring-widths. Our analysis of dendrochronological dating data on 885 individuals of P. ferox revealed a period of abundant establishment from the mid-1970s to beginning of 1990 s, which is coincident with an interval of remarkable above-average precipitation. However, tree-growth and establishment patterns at the local scale in the Prepuna also reflected land-use changes, particularly long-term variations in livestock intensity. The P. ferox dynamics documented here substantiates the hierarchical concept of "resource-pulse" in dry ecosystems, with precipitation pulses of different lengths modulating distinct dynamic processes in the P. ferox woodlands. Interannual variations in precipitation influence year-to-year patterns of P. ferox radial growth, whereas multiannual oscillations in rainfall influence episodic events of tree establishment. The long-term interval considered in this study enabled us to disentangle the roles of natural versus human controls on P. ferox dynamics in the region.