<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Ludwig, J. A.</style></author><author><style face="normal" font="default" size="100%">Cunningham, G.L.</style></author><author><style face="normal" font="default" size="100%">Whitson, P. D.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Distribution of annual plants in North American deserts</style></title></titles><keywords><keyword><style  face="normal" font="default" size="100%">JRN</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1988</style></year></dates><volume><style face="normal" font="default" size="100%">15</style></volume><pages><style face="normal" font="default" size="100%">221-227</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Early researchers concluded that the winter-annual flora was richest in the California deserts and became relatively poorer towards the east, whereas summer-annuals were richest in the deserts of western Texas and their richness progressively declined in to eastern California.  US/IBP Desert Biome and subsequent studies support these trends and add much relevant information.  Winter-annuals have the C3 photosynthetic pathway, whereas most summer-annuals have the C4 pathway.  While the Sonoran and Chihuahuan deserts have a few C3 'summer' annuals (actually 'winter' annuals which can persist into the summer), the Mojave Desert lacks C3 summer-annuals.  The Great Basin Desert has only a few prevalent winter or summer-annuals (mostly introduced species).     Studies of the micro-distribution of desert-annuals have shown their close association with perennial shrubs.  Some shrubs produce substances that are reportedly toxic to some annuals; the role of such toxins in structuring annual plant communities is unclear.  The importance of nutrients associated with shrub canopies on the micro-distribution of many desert-annuals is becoming evident through LTER and other studies.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1988-91769</style></accession-num></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Ludwig, J. A.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Primary productivity in arid lands: myths and realities</style></title></titles><keywords><keyword><style  face="normal" font="default" size="100%">JRN</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1987</style></year></dates><volume><style face="normal" font="default" size="100%">13</style></volume><pages><style face="normal" font="default" size="100%">1-7</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">We tend to view arid environments as harsh and water-limited, due to low amounts of precipitation.  In fact, many sites within desert regions receive considerable amounts of water due to run-on; for example, washes (&lt;i&gt;arroyos, wadis&lt;/i&gt;).  The productivity of these can be high.  However, in reality, their extent is small.  We often assume productivity of deserts to be only water-limited.  Recent research in arid ecosystems indicates, however, that nutrients can be critical to production.  We also think of desert precipitation as being unpredictable, in addition to low in quantity.  Nevertheless, many of the major arid lands of the world are characterized by highly seasonal patterns of precipitation.  Native plant and animal populations have evolved numerous tactics which capitalized on the predictable timing of precipitation.  Humans have learned to exploit this predictability by growing crops and raising livestock that can gain from seasonal patters.  Humans also manipulate arid environments by removing the limits of productivity through irrigation and fertilization and, while some cases of agricultural production are noteworthy, the reality is that the cost/benefit ratio is not favorable.  Furthermore, extensive arid and semi-arid areas are undergoing rapid desertification.  Monitoring desertification is essential to our future understanding of arid and semi-arid land productivity.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1987-91843</style></accession-num></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>6</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Ludwig, J. A.</style></author><author><style face="normal" font="default" size="100%">Whitford, W. G.</style></author></authors><secondary-authors><author><style face="normal" font="default" size="100%">with the assistance of K. M. W. Howes (eds.),</style></author></secondary-authors></contributors><titles><title><style face="normal" font="default" size="100%">Short-term water and energy flow in arid ecosystems</style></title><secondary-title><style face="normal" font="default" size="100%">Arid Land Ecosystems: Structure, Function and Management</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">JRN</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1981</style></year></dates><publisher><style face="normal" font="default" size="100%">Cambridge University Press</style></publisher><pub-location><style face="normal" font="default" size="100%">Great Britain</style></pub-location><volume><style face="normal" font="default" size="100%">2</style></volume><pages><style face="normal" font="default" size="100%">271-299</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The objective of this chapter is to discuss the dynamic behavior of the biotic components of arid ecosystems in relation to water and energy flow between and within seasons.  The growth responses of the different plant species occupying adjacent ecosystems in a watershed will be related to water availability and to heat energy levels.  Growth and behavioral responses of groups of animals with contrasting adaptations to changing conditions of food and water availability will be discussed.  Plant and animal litter redistribution and decomposition patterns will be discussed with respect to patterns of energy flow and climatic variation.  Finally, general conclusions about desert ecosystem dynamics with respect to short-term water and energy flow will be stated.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1981-92116</style></accession-num></record></records></xml>