The relative influences of climate and catchment processes on Holocene lake development in glaciated regions

Following deglaciation, the long-term pattern of change in diatom communities and the inferred history of the aquatic environment are affected by a hierarchy of environmental controls. These include direct climate impacts on a lake’s thermal and hydrologic budgets, as well as the indirect affects of climate on catchment processes, such as weathering, soil development, microbial activity, fire, and vegetation composition and productivity, which affect the transfer of solutes and particulates from the terrestrial ecosystem into the lake. Some of these catchment influences on lacustrine systems operate as time-dependent patterns of primary succession that are set in motion by glacier retreat. This paper provides a conceptual model of some dominant pathways of catchment influence on long-term lake development in glaciated regions and uses a series of paleolimnological examples from arctic, boreal, and temperate regions to evaluate the relative role of direct climate influences and of catchment processes in affecting the trajectory of aquatic ecosystems during the Holocene in different environmental contexts.     

An analysis of intra-event precipitation variability for the United States (1980–2010)

Hourly precipitation data were collected from 143 first-order US weather stations during the period from 1980 to 2009 to assess the internal distribution of precipitation events lasting at least three hours. A total of 46,595 individual precipitation events were identified and evaluated using the mean, standard deviation, skewness, kurtosis, and the number of peaks occurring within an event. Mean event duration is longest along the West and Northwest coasts, the Mid-South, the Mid-Atlantic, and the Northeast; while shorter-duration events are more frequent in the Rocky Mountains, the Southwest, and the Great Plains. Mean event precipitation and standard deviation are greatest along the Gulf Coast and decrease inland. Precipitation events are positively skewed, indicating that more precipitation tends to occur earlier in the event. The most positively-skewed events are also located in regions flanking the Gulf of Mexico, while less-skewed events are common in the Northwest and Rocky Mountain regions. Event kurtosis is negative throughout the entire USA, with the highest negative values generally west of the Front Range, where cyclonic development and transition produce more evenly distributed precipitation within storms. Intra-event precipitation maxima were also evaluated, with western Florida and the desert Southwest having the greatest number per event.     

Watermarking of digital geospatial datasets: a review of technical,legal and copyright issues

Gathering data accounts for more than 80% of the cost of any GIS project. Fast Internet connections and digital datasets threaten the investments of data producers through data piracy. Outside the GIS community this problem has been known for a long time, and possible solutions exist for digital imagery, formatted text, 3D meshes and so on, showing possible links to typical spatial data. This is largely achieved through embedding hidden information in a dataset without producing perceptible changes in the data, a process known as watermarking. The producer can recover the embedded information on request in order to produce evidence of ownership in a court, so the overall strategy relies on a legal basis rather than technical ones. This paper analyses the state-of-the-art for watermarking protection in digital geographical datasets. Digital imagery is demonstrably a more mature area than geographical information, even with multiple commercial vendors offering watermarking protection. 2D vector and point datasets have received less attention from the research community; however, 3D meshes have been considered by the CAD community and a handful of techniques are available for that case, and they are reviewed here.     

Spatio-temporal analysis of tree height in a young cork oak plantation

Cork oak is one of the most valuable natural forest genera in the Mediterranean basin. Modelling cork oak growth has been a challenge for foresters in recent years because of strong site and genetic influences, below-ground competition, management regimes and age effects. Because cork productivity is related to forest height, which is, in turn, related directly with site characteristics, an increase in the accuracy of height prediction implies improved productivity estimation. A Bayesian maximum entropy (BME) geostatistical model was applied to characterize the space–time pattern of height of young cork oak in a forest stand from central Sardinia in the years 2000, 2002, 2003, 2006 and 2008. Cork oak height maps were produced for each of the 5 years. The main goals were to analyse and interpret through time (i) the changes in spatial correlation and (ii) the changes in spatial distribution of cork oak height. The plantation was characterized by an increasing spatial dependence through time, whereas the temporal range was 2 years. Cork oak height was significantly correlated with wind speed (reduced by a neighbouring forest) in all the years implying a single trend. The correlations were larger for 2006 and 2008 than for previous years. Three other environmental variables (shade, elevation and slope) were less significant and their influence restricted to 2 years only. This research has several implications for the management of cork oak in the young phase.     

The inclusion of differentially assessed lands in urban growth model calibration: a comparison of two approaches using SLEUTH

This research sought to understand the role that differentially assessed lands (lands in the United States given tax breaks in return for their guarantee to remain in agriculture) play in influencing urban growth. Our method was to calibrate the SLEUTH urban growth model under two different conditions. The first used an excluded layer that ignored such lands, effectively rendering them available for development. The second treated those lands as totally excluded from development. Our hypothesis was that excluding those lands would yield better metrics of fit with past data. Our results validate our hypothesis since two different metrics that evaluate goodness of fit both yielded higher values when differentially assessed lands are treated as excluded. This suggests that, at least in our study area, differential assessment, which protects farm and ranch lands for tenuous periods of time, has indeed allowed farmland to resist urban development. Including differentially assessed lands also yielded very different calibrated coefficients of growth as the model tried to account for the same growth patterns over two very different excluded areas. Excluded layer design can greatly affect model behavior. Since differentially assessed lands are quite common through the United States and are often ignored in urban growth modeling, the findings of this research can assist other urban growth modelers in designing excluded layers that result in more accurate model calibration and thus forecasting.     

Seed germination of Southern Chihuahuan Desert plants in response to elevated temperatures

High temperature is one of the main factors that prevent germination, through premature aging of the embryo. The high temperatures reached in the soil of arid environments can affect seed survival and plant establishment. In this study we tested whether seed exposure to high temperature (40 °C and 70 °C) affected germination of eight species common to the Southern Chihuahuan Desert, and used for fodder, firewood and timber, fiber, edible flowers, fruits and stems. The responses to heat varied between species. Two of the tested species were not affected by heat exposure; for two other species germination was higher, and for the remaining four, germination was lower. There was also a delay of germination after heat exposure. Seeds of three species germinated >1 d slower after exposure to high temperatures. These results could help establish management programs for these Chihuahuan desert species under a climate change scenario.     

Dispersal of arbuscular mycorrhizal fungi and dark septate endophytes by Ctenomys cf. knighti (Rodentia) in the northern Monte Desert of Argentina

In arid and semi-arid environments, root-associated fungi may play a key role in plant communities (e.g., seedling establishment, nutrient acquisition, plant survival and heat tolerance). Several studies have shown the importance of small mammals as consumers and dispersal agents of mycorrhizal fungi spores in tropical and temperate ecosystems. However, little is known about the dispersal of infective propagules of endophytic fungi in arid and semi-arid ecosystems. This study analyzed the potential role of the subterranean rodent Ctenomys cf. knighti as a dispersal agent of root-associated fungi. In order to demonstrate this role, we analyzed: (1) the incidence of colonization of arbuscular mycorrhizae and dark septate endophytes on representative plant species of the Monte Desert; (2) the presence of fungal structures of arbuscular mycorrhizae and dark septate endophytes in C. cf. knighti fecal samples; and (3) the infectivity of the fungal propagules contained in the scat and their growth effects on nine native plant species. Data strongly suggest that this South American subterranean rodent may play a key role as a dispersal agent of arbuscular mycorrhizae and dark septate endophytes fungi in the arid environment of the northern Monte Desert of Argentina.     

Effects of increased summer precipitation and N deposition on Mojave Desert populations of the biological crust moss Syntrichia caninervis

Climate change in the Mojave Desert (USA) may result in a greater intensity of summer (monsoon) rain events and greater atmospheric N deposition. Patches of the dominant biological crust moss Syntrichia caninervis were exposed to field treatments of low and high nitrogen supplementation, added summer rain, and combinations thereof, for a period of five years. In the lab, shoots were subjected to a moderate (single rapid-dry treatment) and a severe (double rapid-dry treatment) desiccation stress. Shoots were then hydrated and allowed to regenerate for 6 weeks on sterile sand. Shoots exhibited lower aboveground biomass from the +monsoon treatment, indicating carbon balance deficits under conditions of recurring summer rainfall. The low N treatment and the severe desiccation stress promoted shoot burning (chlorosis) and negatively affected regeneration responses. High N treatment, however, only adversely affected the resumption of apical meristematic growth. Summer irrigation and N application interacted to mitigate the effects of later protonemal emergence time, lower protonemal cover, and lower shoot numbers. Increased monsoonal frequency and higher N deposition as forecast for the northern Mojave Desert may result in declines in shoot biomass and reduced regenerational vigor in S. caninervis.