Changes In Moisture Availability Research Articles

Evolution of sexual systems, dispersal strategies and habitat selection in the liverwort genus Radula

• Shifts in sexual systems are among the most common and important transitions in plants and are correlated with a suite of life-history traits. The evolution of sexual systems and their relationships to gametophyte size, sexual and asexual reproduction, and epiphytism are examined here in the liverwort genus Radula. • The sequence of trait acquisition and the phylogenetic correlations between those traits was investigated using comparative methods. • Shifts in sexual systems recurrently occurred from dioecy to monoecy within facultative epiphyte lineages. Production of specialized asexual gemmae was correlated to neither dioecy nor strict epiphytism. • The significant correlations among life-history traits related to sexual systems and habitat conditions suggest the existence of evolutionary trade-offs. Obligate epiphytes do not produce gemmae more frequently than facultative epiphytes and disperse by whole gametophyte fragments, presumably to avoid the sensitive protonemal stage in a habitat prone to rapid changes in moisture availability. As dispersal ranges correlate with diaspore size, this reinforces the notion that epiphytes experience strong dispersal limitations. Our results thus provide the evolutionary complement to metapopulation, metacommunity and experimental studies demonstrating trade-offs between dispersal distance, establishment ability, and life-history strategy, which may be central to the evolution of reproductive strategies in bryophytes.

Browning in desert boundaries in Asia in recent decades

In this study, the changes in desert boundaries in Asia (Gobi, Karakum, Lut, Taklimakan, and Thar deserts) during the growing season (April October) in the years 1982 2008 were investigated by analyzing the normalized difference vegetation index (NDVI), precipitation, and temperature. In the desert boundary regions, the domain mean NDVI values increased by 7.2% per decade in 1982 1998 but decreased by 6.8% per decade thereafter. Accordingly, the bare soil areas (or nonvegetated areas) of the inside of the desert boundaries contracted by 9.8% per decade in the 1990s and expanded by 8.7% per decade in the 2000s. It is noted that the five deserts experience nearly simultaneous NDVI changes although they cover a very diverse area of Asia. In contrast, changes in temperature and precipitation in the deserts show rather diverse results. In desert boundaries located along 40 N (Gobi, Taklimakan, and Karakum), the decadal changes in vegetation greenness were mainly related to regional climate during the entire analysis period. Precipitation increased in the 1990s, providing favorable conditions for vegetation growth (i.e., greening), but precipitation reduced (19 mm per decade) and warming intensified (0.7 C per decade) in the 2000s, causing less moisture to be available for vegetation growth (i.e., browning). In desert boundaries below 40 N (Lut and Thar), although an increase in precipitation (8 mm per decade) led to greening in the 1990s, local changes in precipitation and temperature did not necessarily cause browning in the 2000s. Observed multidecadal changes in vegetation greenness in the present study suggest that under significant global and/or regional warming, changes in moisture availability for vegetation growth in desert boundaries are an important factor when understanding decadal changes in areas vulnerable to desertification over Asia.

Inferring lake depth using diatom assemblages in the shallow, seasonally variable lakes of the Nebraska Sand Hills (USA): calibration, validation, and application of a 69-lake training set

The Nebraska Sand Hills are a distinctive eco-region in the semi-arid Great Plains of the western United States. The water table underlying the Sand Hills is part of the High Plains/Ogallala aquifer, an important water resource for the central Great Plains. Lake levels are affected directly by fluctuations in the water table, which is recharged primarily by local precipitation and responds quickly to climatically induced changes in regional water balance. Instrumental records are available for only 50–100 years, and paleolimnological data provide important insights into the extremes and variability in moisture balance over longer time scales. A set of 69 lakes from across Nebraska was used to establish a statistical relationship between diatom community composition and water depth. This relationship was then used to develop a diatom-based inference model for water depth using weighted averaging regression and calibration techniques. Development of the inference model was complicated by strong intra-seasonal variability in water depth and the linkages between depth and other limnologic characteristics, including alkalinity, water clarity and nutrient concentrations. Analysis of historical diatom communities from eight lakes allowed for the reconstruction of lake-level fluctuations over the past several thousand years. Comparisons of the more recent portion of these reconstructions with the instrumental Palmer Drought Severity Index (PDSI) showed that sediment records may not faithfully reflect short-term fluctuations in water level, except where sedimentation rates are very high. However, large and persistent changes in moisture availability were discernible even in longer, low-resolution records. Thus, diatoms are a useful addition to the tools available for understanding past drought in the central Great Plains, especially when trajectories of change are constrained by data from multiple sites or other proxies.

Responses of boreal epiphytic bryophytes to different levels of partial canopy harvestThis paper is one of a selection of papers published as part of the special Schofield Gedenkschrift.

Epiphytic mosses and liverworts contribute substantially to the bryophyte diversity of circumpolar boreal forests but are susceptible to altered growing conditions after forest harvesting. Management practices that retain some trees after harvest may enhance epiphyte survival; however, the effectiveness of this emerging method needs to be assessed. We examined the survival, composition, and nearest neighbour relationships of epiphytic bryophytes on trembling aspen ( Populus tremuloides Michx.) across a range (10%–100%) of dispersed green-tree retention 5 years after harvest in boreal mixed-wood forest. Growth of the forest floor moss Hylocomium splendens (Hedw.) Schimp. in B.S.G. was used as an indicator of changes in moisture availability for epiphytes following harvesting. Epiphyte richness and abundance increased with canopy retention and were positively correlated with local abundance of coniferous trees. Positive associations among neighbouring species in intact forest demonstrated that interspecies relationships form naturally. However, there was a shift in species composition after harvesting and fewer interspecific associations with declining retention. These trends were accompanied by reduced Hylocomium splendens growth, which implies that moisture may be an important driver of epiphyte response. Although different levels of canopy retention were similarly capable of maintaining some epiphytes, the loss of species associated with intact forest will require consideration of alternative management practices for their conservation.

Ecology and conservation needs of nymphalid butterflies in disturbed tropical forest of eastern Himalayan biodiversity hotspot, Assam, India

We examine the hypothesis, whether the diversity of Nymphalid butterflies in primary forest is related to vegetation structure and canopy openness and that this relationship differs between butterfly taxa in relation to phylogenetic differences in light and shade preferences. The study also examines whether the increasing diversity of butterflies in degraded tropical forest is associated with the loss of species with restricted geographical distribution. Present study has considered eight habitat parameters for habitat data collections and the t-test using equal variance, spearman rank correlation and multiple regressions were used for statistical analyses. Species diversity was analyzed using Margalef’s D indices that indicate both the species richness and abundance. Bootstrap method was used to compare the diversity among samples. PCA was carried out to examine the relationship between vegetation structure and species diversity in primary and degraded forest. The relationship between vegetation factor scores and species diversity at each sampling station in primary and degraded forest was analyzed using stepwise multiple regression. Results indicates that the butterflies species sampled in closed canopy forest had more restricted geographical distribution than those being sampled in disturbed forest. The species with greater light preference had significantly wider geographical distribution, whereas, the species with greater shade preferences had significantly narrower geographical distributions. The stepwise analysis of multiple regressions between the diversity indices of shade groups of butterflies and vegetation density (PRIN1) of closed forest shows a significant positive relationship, but the relationship was negative when similar analysis was performed between species diversity indices of light preferred Nymphalid groups and vegetation density. Results indicate that the greater numbers of closed canopy forest butterflies are sensitive to changes in moisture availability and humidity. Thus, changes in canopy cover and light penetration, through microclimatic effects on adult and larval survival, does have an impact on butterfly distributions. While, the species richness and diversity are higher in forest gaps, the conservation value of close canopy forest lies more in the presence of species with restricted ranges. Owing to loss of heterogeneous vegetation in degraded forest, the dense canopy cover and transparent ground cover has been reduced and thus declination of forest butterflies species. Study has clearly indicated the strong and significant relationship between the species of narrow range of geographical distribution and species shade preference. The restricted ranges species are affected due to forest degradation. Thus, clearly bringing into light, that increasing diversity in degraded forest is associated with the loss of species with restricted geographical distribution. Out of seven gap preferred shade group of butterflies, two have wide geographical distribution and the other five have medium range distribution. Thus, there is a strong phylogenetic relationship between the genera of light preferred shade loving group of butterflies and the butterflies of light loving group and the genera of shade preferred light loving group of butterflies and the butterflies of shade loving group. Key words: Ecology, closed canopy forests, conservation, degraded forests, endemic species, geographic distribution range, light and shade groups, nymphalid butterflies, phylogeny, tropical forests.

Detecting invisible growth rings of trees in seasonally dry forests in Thailand: isotopic and wood anatomical approaches

We measured radial variation of carbon isotope composition and vessel traits in tree species in seasonally dry forests of Northeast Thailand to explore a more reliable and amenable method of tropical dendrochronology for trees that lack visually detectable and consistent growth rings. Six Dipterocarpaceae species (3 Shorea, 2 Dipterocarpus, and 1 Hopea species) with indistinct or irregular growth rings and teak (Tectona grandis), a species which forms distinct growth rings, were examined. The δ13C value variations in all species showed annual cyclicity. Dipterocarpaceae species usually marked the lowest values of δ13C in the middle of the growing season, whereas teak had the lowest values at nearly the end of the growing season. Since the growing season of the species examined almost corresponds to the rainy season in the study area, the δ13C variation was likely caused by the change in moisture availability. The different variation pattern of teak was attributable to its stronger dependence on 13C-enriched reserved material early in the growing season. Changes in tree vessel traits for all species examined also showed annual cyclicity. Dipterocarpaceae species showed significant correlation between δ13C values and vessel measurements. Vessel lumen (mean area, tangential and radial diameter, and proportion of total area) had a negative correlation, whereas vessel frequency showed a positive correlation. The correlations indicated that changes in vessel traits were caused by the seasonal variation of moisture available to the trees. Thus, we concluded that methods using wood anatomy, as well as δ13C, have great potential for use as tools in tropical dendrochronology within the context of seasonal climate.

Reduced early Holocene moisture availability in the Bayan Har Mountains, northeastern Tibetan Plateau, inferred from a multi-proxy lake record

A late glacial and Holocene lake sediment record from the northeastern Tibetan Plateau was investigated using ostracod and geochemical analysis. After Lake Koucha was established about 16 cal ka BP, oligohaline conditions gradually converted to mesohaline conditions about 10 cal ka BP clearly suggesting that the water body was a closed-basin lake. From about 10 cal ka BP, the salinity of the lake rose continuously until hyperhaline levels were reached about 7.5 cal ka BP. This increase in salinity was accompanied by a falling lake level. Extreme rainfall and flooding events in a generally dry climate hit the shallow saline lake around 8.5 cal ka BP causing a unique, thin gravel-containing layer within the continuous fine-grained lake sediments. The age control of our record does not allow us to correlate this event exactly to the widely recorded 8.2 cal ka BP event, however, the recovered sediments from Lake Koucha provide strong evidence that climate changes around 8.5 cal ka BP had significant environmental implications in northeastern Tibet. After about 7.3 cal ka BP, the available moisture significantly increased causing a continuous salinity decline until the present-day freshwater conditions of a through-flow lake were established about 6.5 cal ka BP in Lake Koucha. This major shift from a shallow saline to a deeper freshwater lake was probably accompanied by a fundamental change from a macrophyte-dominated to a phytoplankton-dominated lake. A slight reduction in available moisture in comparison to the periods before and afterward was recorded between 4.3 and 2.0 cal ka BP, in phase with numerous records from monsoonal Asia. The reconstructed overall change in moisture availability from dry conditions before about 7.3 cal ka BP to wetter conditions afterwards contradicts most palaeoclimate records from the Tibetan Plateau and its surroundings which show that wetter conditions in the early Holocene were replaced by drier and probably cooler conditions in the mid and late Holocene. However, in the semi-arid region of Lake Koucha with a mean annual precipitation of about 500 mm, the insolation-driven strengthened monsoon in the early Holocene may have resulted in a temperature rise and higher evaporation rates which outweighed the increase in precipitation and therefore led to significantly lower moisture availability. Our record provides further evidence for a regionally non-uniform response of the available moisture evolution to the overall monsoonal signal in the Holocene climate history of Central Asia.

Experiments on Lichen Growth, III. The Shape of the Age-Size Curve

ABSTRACTA field experiment was conducted in the Front Range of the Colorado Rocky Mountains to test the hypothesis that lichen age-size curves differ in shape because an inherently sigmoidal growth pattern is interrupted at different stages in its development by a linear growth phase. Large, circular thalli of three morphologically dissimilar species were studied on smooth rock surfaces. Thallus interiors were removed with a knife and wire brush, creating curved wedges of lichen tissue. Distances from reference marks to the unmodified outer margins of the thalli were measured at various wedge widths. Measurements were repeated after 2–16 years, depending upon species. As predicted by the hypothesis, radial growth of Xanthoparmelia coloradoensis and Lecanora novomexicana accelerated with increasing wedge width, becoming linear at average rates of 2.01 and 0.12 mm yr−1, respectively. Radial growth of Rhizocarpon superficiale accelerated to a maximum average rate of 0.016 mm yr−1, then slowed, defining a more complete sigmoidal curve. This species showed no evidence of a linear growth phase, either because none exists or because the wedges were too narrow to detect it. The margins of R. superficiale thalli alternately advance and retreat due to changes in moisture availability and differences in photosynthate production within outer rings of areolate tissue. Hypothalli and areolae grow independently of each other over the short term, though their long-term growth rates must necessarily be similar. The data suggest that areolate crustose lichens are fundamentally different from foliose and placodioid lichens, and that inferences based on one group should not necessarily be extrapolated to another.

Resident corticolous oribatid mites (Acari: Oribatida): Decay in community similarity with vertical distance from the ground

The decrease in community similarity was examined in corticolous oribatid mites (Acari: Oribatida) sampled along a 36-m vertical profile of 5 western redcedar trees in a temperate rainforest on Vancouver Island, Canada. Samples were collected every 2 m, and all adult oribatid mites were identified to species. When compared to species recorded from previous ground/canopy sampling efforts in the same trees, the 62 corticolous species unequivocally support the separation of these 2 communities at 4 m. All sampling heights contained canopy oribatid species, but only 0–4 m communities contained ground-dwelling oribatids. There was significant overall spatial autocorrelation and decay in community similarity with distance originating from species turnover at 4 m, suggesting limited range expansion of ground species into corticolous habitats. Community similarity, richness, and abundance of corticolous oribatid mite assemblages were not autocorrelated after 4 m above ground. Observed patterns at 4 m likely represent an environmental transition zone for ground-dwelling species, such as changes in moisture availability, rather than a physical dispersal barrier for individuals. We conclude that the trunk is not a dispersal corridor for ground species to colonize tree crowns and suggest that low similarity between nearest neighbouring sampling points, combined with the presence of immature and gravid oribatids, supports the assumption that corticolous oribatid mite assemblages are likely dispersal-limited residents.

Late Pleistocene glacial chronology of the Pietrele Valley, Retezat Mountains, Southern Carpathians constrained by 10Be exposure ages and pedological investigations

The Southern Carpathians are located in the transition zone between Mediterranean and continental climates and constituted the major areas of ice accumulation in the Carpathians during Pleistocene glaciations. An absolute glacial chronology had not yet been established. In this study we constrain the glacial history of the Pietrele Valley in the Retezat Mountains located in the Southern Carpathians and find that the timing of the late Würmian glacial advance is asynchronous to global climate records, likely reflecting changes in moisture availability in the area. The former ice extent of two major glacial advances (M1 or Lolaia glacial advance and M2 or Capra-Judele glacial advance) in the valley was reconstructed based on mapping and surveying of glacial features. Field relations and different pedological weathering indicators of till imply that the M1 glacial advance occurred well before the global Last Glacial Maximum (LGM). Its deposition during the penultimate glaciation is unlikely; no boulders suitable for exposure dating were found on M1-moraines. Seventeen exposure ages show that the moraines of the maximum late Würmian M2-glacial advance were abandoned around 16.1±1.6 ka. Another late glacial advance (M3 or Stevia advance) occurred during the Younger Dryas chron as constrained by two exposure ages. We suggest that the glacial advance that occurred during the time of the global LGM was less extensive than the M2 glacial advance and the deposits were overrun by the lateglacial M2 glacier, as we found no field evidence of glacial deposits between the M1 and the M2 moraines. We explain this obvious asynchronity of the local late Würmian ice extent with that of global records of ice accumulation with increased aridity in the Carpathians during the global LGM due to a lower sea-level. The reconstructed Late Pleistocene equilibrium line altitude (ELA) shows a distinct increase in the trend from the Alps and the Bavarian Forest to the Carpathians in comparison to the modern ELA. This finding supports the high aridity in the study area during the Late Pleistocene. Two distinct lateglacial moraines were deposited during times of reported colder and wetter climatic conditions around the North Atlantic (Heinrich-events H0 and H1).

Impact of climate variability on present and Holocene vegetation: A model-based study

A series of nine simulations has been made with the Lund–Potsdam–Jena Dynamic Global Vegetation Model (LPJ-DGVM) in order to explore the impacts of climate variability and Holocene changes in variability (as simulated by the Fast Ocean-Atmosphere Model, FOAM) on vegetation in three forest-dominated regions of China and in the semi-arid Sahelian region of northern Africa. The simulations illustrate that changes both in the magnitude of climate variability and in the persistence of above/below average conditions have the potential to modify the vegetation response to changes in mean climate. Simulated changes in moisture availability affect vegetation through drought stress or through changing the fuel availability in semi-arid regions where lack of fuel often limits the incidence of fire. Increasing moisture availability causes trees to replace grasses in China by reducing drought stress; increasing moisture availability in the Sahel increases the available fuel and hence reduces fire return times, favouring grasses. The modelling results imply that climate variability is important to vegetation dynamics; that not only the magnitude, but also the temporal structure of variability is important; and that correctly simulating vegetation changes in response to climate variability requires a realistic “baseline” simulation of plant community composition. They further indicate that the impacts of climate change on ecosystems can sometimes derive as much from changes in variability as from changes in mean climate.

Climate change in lowland Central America during the late deglacial and early Holocene

AbstractThe transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition (∼11 250 to 7500 cal. yr BP) inferred from sediment cores retrieved in Lake Petén Itzá, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by ∼11 250 cal. yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11 250 to 10 350 cal. yr BP, during the Preboreal period, lithologic changes in sediments from deep‐water cores (>50 m below modern water level) indicate several wet–dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1‐4) occurred centred at 11 200, 10 900, 10 700 and 10 400 cal. yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10 350 cal. yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Petén Itzá with other records from the circum‐Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high‐latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores–Bermuda high‐pressure system. This mechanism operated on millennial‐to‐submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC). Copyright © 2005 John Wiley & Sons, Ltd.

A new Quaternary record of regional tectonic, sedimentation and paleoclimate changes from drill core BDP-99 at Posolskaya Bank, Lake Baikal

This contribution presents the most recent sedimentary drill core section (BDP-99) from Lake Baikal. We discuss lithological composition and general stratigraphy, the BDP-99 age model, and draw implications for past sediment deposition changes at Posolskaya Bank in relation to tectonics and regional climate change. The BDP-99 drill core penetrated several sedimentary sequences identified in prior seismic surveys of the Selenga Delta area and helps to better constrain the age of these sequences. Lithological studies were used to identify erosional intervals apparently correlative with sequence boundaries at Posolskaya Bank. Intensified tectonic activity between ca. 1.15 and 0.8 Ma as observed at a number of locations in continental interior Asia, resulted in deposition of a ca. 90-m unit of remarkably uniform fine silty clay during the Jaramillo subchron with accumulation rates exceeding 100–160 cm/ka. A disconformity occurs at the top of this unit, and as a result, the sedimentary interval equivalent to ca. 1.0–0.8 Ma is not present in the BDP-99 section. At ca. 710–660 ka a transition to rather quiet hemipelagic sedimentation takes place as seen from an overall decrease in sedimentation rates and from higher diatom abundance in interglacial sediments. The new late Pleistocene palynological record from BDP-99 drill core shows repetitive landscape changes from steppe and forest-steppe environments during glacials and interstadials to coniferous taiga conditions during the present and last interglacial. Every glacial/interglacial transition of the past 130 ka is marked by an early peak of Siberian spruce ( Picea) pollen abundance. The MIS 4 interval is clearly divided into two zones due to changes in moisture availability. The late MIS 6 interval stands in stark contrast with subsequent glacial periods due to extremely low pollen abundance. Palynological records in the vicinity of the Selenga Delta contain overprinting signals from different landscape types in the extensive Selenga catchment basin.

Pollen‐based reconstructions of biome distributions for Australia, Southeast Asia and the Pacific (SEAPAC region) at 0, 6000 and 18,00014C yr BP

AbstractAim This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid‐Holocene and at the last glacial maximum (LGM).Methods Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 100014C yrbp.Results 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad‐scale patterns of vegetation distribution. The north–south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed‐canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad‐scale pattern emerges. 2. Differences between the modern and mid‐Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south‐eastern Australia some sites show a shift towards more moisture‐stressed vegetation in the mid‐Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm‐temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture‐demanding vegetation in the mid‐Holocene than today. South‐western Australia was slightly drier than today. The single site in north‐western Australia also shows conditions drier than today in the mid‐Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid‐Holocene, in sites occupied today by cool‐temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9 °C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity.Main conclusions This study provides the first continental‐scale reconstruction of mid‐Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project.

Using covariates to spatially interpolate moisture availability in the Murray–Darling Basin: A novel use of remotely sensed data

Moisture availability is estimated in the 1.1 million km 2 Murray–Darling Basin (MDB) in southeast Australia. Remotely sensed data from the Advanced Very High Resolution Radiometer (AVHRR) are combined with meteorological data to estimate the Normalised Difference Temperature Index (NDTI). The NDTI provides a measure of the moisture availability, the ratio of actual to potential evapotranspiration. Surface temperature minus air temperature, percent vegetation cover and net radiation explained 85% of variation in the modelled NDTI. Using these three covariates across the network of meteorological stations allows NDTI images, which maps changes in moisture availability across the MDB, to be calculated. This method uses a calculate then interpolate (CI) approach that uses the per-pixel variation present in the AVHRR data as the backbone for the spatial interpolation. Using the spatially dense AVHRR-based covariates in a CI approach avoids errors that occur between measurement points when interpolating variables for regional hydrologic modelling, most significantly the spatial pattern of rainfall. The NDTI provides a link into regional water balance modelling which does not require daily rainfall to be spatially interpolated. Assessing spatial and temporal interactions between the NDTI and the Normalised Difference Vegetation Index (NDVI) provides useful information about regional hydroecological processes, including agricultural management, within the context of Australia's highly variable climate and sparse network of meteorological stations.

Assessing the stability and uncertainty of predicted vegetation growth under climatic variability: northern mixed grass prairie

Ecosystem models which include both variability of driving variables as an input, and uncertainty and/or stability in their predictions are rare, especially outside of forest and cropland applications. Our objective is to investigate the stability of productivity levels and temporal patterns in a northern mixed grass prairie site using scenarios of varying levels of climate variability. Predictions of annual net primary productivity (NPP) are compared under a variety of global change and management scenarios. Specifically, we investigate the relative responses of C 3 and C 4 vegetation functional groups as a diagnostic of changes in resource availability. Scenarios of gradual temperature increase over 200 years demonstrate that warming will have different effects depending partially on the seasonal timing of that warming, but mostly on the concurrent changes in moisture availability. We propose that stability of vegetation communities may be more important than simply predicting levels of productivity for answering many questions related to the impacts of global change. This is demonstrated using frequencies of consecutive years with low productivity. Moderate increase in precipitation variability without increases to average rainfall can increase productivity and apparently increase stability. Further increase in precipitation variability decreases stability. The uncertainty in NPP predictions can be quantified by repeated simulations using stochastic variations in driving climate variables. Uncertainty in NPP predictions is found to be at the order of 20 g/m 2/year, or about 25% of long-term averages. This lets us qualify our conclusions and shows that further research can reduce this uncertainty by better predictions of moisture availability, which can be obtained using finer spatial and temporal resolution representations.

Land requirements for Pinus halepensis Mill. growth in a plantation in Huesca, Spain

Abstract. Land requirements for Pinus halepensis Mill. growth were studied in thirty plots of a 40 year‐old plantation in the semiarid Lower Ebro valley, northeast Spain, by comparing site index values to land characteristics. Site index at 40 years ranges from 4.1 m to 12.3 m. Moisture availability is the basic requirement for growth while nutrient availability has only a minor influence. Changes in moisture availability in the area are controlled by changes in soil rootable depth, with a minor effect of aspect. Soils developed on Tertiary gypsum rock are not suitable for afforestation with this species. Geomorphic and soil information may be combined, at various degrees of detail, to provide reliable estimates of Aleppo pine growth.

Photosynthesis of green algal soil crust lichens from arid lands in southern Utah, USA: role of water content on light and temperature responses of CO2 exchange

Summary Biotic soil crusts are a worldwide phenomenon in arid and semi-arid landscapes. Metabolic activity of the poikilohydric organisms found in these crusts is dominated by quick and drastic changes in moisture availability and long periods of drought. Under controlled conditions, we studied the role of water content on photosynthetic and respiratory CO 2 exchange of three green algal soil crust lichens from a desert site in southern Utah (USA): Diploschistes diacapsis (A ch .) L umbsch , Psora cerebriformis W. W eber , and Squamarina lentigera (W eber ) P oelt . Photosynthetic metabolism is activated by extremely small amounts of moisture; lower compensation values for net photosynthesis (NP) are reached between 0.05 and 0.27 mm of precipitation equivalent. Thus, the lichens can use very low degrees of hydration for carbon gain. Maximal NP occurs between 0.39 and 0.94 mm precipitation equivalent, and area-related rates equal 2.6–5.2 μmol CO 2 m −2 s −1 . All three tested species show ‘sun plant’ features, including high light requirements for CO 2 exchange compensation and for NP saturation. Diploschistes diacapsis maintains high rates of NP at full water saturation. In contrast, suprasaturated thalli of the other two species show a strong depression in NP which can be removed or reduced by increased external CO 2 concentration. Consequently, this depression is most probably caused by increased thallus diffusive resistances due to pathway blockage by water. This depression will greatly limit carbon gain of these species in the field after heavy rain. It occurs at all temperatures of ecological relevance and also under conditions of low light. However, maximum water holding capacity of P. cerebriformis and S. lentigera is higher than that of D. diacapsis . This could mean that periods of hydration favorable for metabolic activity for those two species last longer than those of D. diacapsis . This might compensate for their lower rates of NP during suprasaturation. Thus, two different strategies might have developed for lichen existence in the specific and extreme arid soil crust habitat. Data about habitat conditions for the different lichen species are needed in order to test this hypothesis and to allow interpretation and prediction of perfonnance of these soil crust lichens in nature.

Environmental Variability and Settlement Changes on the Pajarito Plateau, New Mexico

Recent studies have shown a relation between low- and high-frequency environmental variability and aspects of culture. This paper uses low-frequency alluvial and hydrological changes on the Colorado Plateaus and high-frequency changes in moisture availability for the northern Rio Grande between A.D. 1150 and A.D. 1600 to derive expectations for changes in settlement organization on the Pajarito Plateau. The expectations are evaluated using data on the distribution of population and field houses in elevation zones. Changes in population size and aggregation also are reviewed. Low-frequency processes especially appear to have played a role in settlement change until A.D. 1450. After this date, settlement does not conform to expectations. Reasons for this are suggested, including a poor understanding of low- frequency processes, conflict, and human-induced environmental degradation.

CONTINENTALITY INDEX: ITS USES AND LIMITATIONS APPLIED TO PERMAFROST IN THE CANADIAN CORDILLERA

The Continentality Index of Gorbunov (1978) should be based on the lower limit of continuous permafrost to be most effective in the Canadian Cordillera. A systematic increase in the Continentality Index northwards from southern Alberta into the Yukon Territory may be due to the greater influence of the continental Arctic air mass in the north. This correlates with changes in moisture availability and with vegetation. Superimposed on this trend is local variability probably due to edaphic moisture conditions. Edaphically dry areas have higher values of the Continentality Index than edaphically wet sites, but this variability is far less than the general gradient. [Key words: Continentality Index, soil moisture, geocryology mountains, alpine permafrost.]