Shrub Invasion Decreases Diversity and Alters Community Stability in Northern Chihuahuan Desert Plant Communities

BACKGROUND:Global climate change is rapidly altering species range distributions and interactions within communities. As ranges expand, invading species change interactions in communities which may reduce stability, a mechanism known to affect biodiversity. In aridland ecosystems worldwide, the range of native shrubs is expanding as they invade and replace native grassland vegetation with significant consequences for biodiversity and ecosystem functioning. METHODOLOGY:We used two long-term data sets to determine the effects of shrub encroachment by Larrea tridentata on subdominant community composition and stability in formerly native perennial grassland dominated by Bouteloua eriopoda in New Mexico, USA. PRINCIPAL FINDINGS:Our results indicated that Larrea invasion decreased species richness during the last 100 years. We also found that over shorter temporal scales species-poor subdominant communities in areas invaded by Larrea were less stable (more variable in time) compared to species rich communities in grass-dominated vegetation. Compositional stability increased as cover of Bouteloua increased and decreased as cover of Larrea increased. SIGNIFICANCE:Changes in community stability due to altered interspecific interactions may be one mechanism by which biodiversity declines in grasslands following shrub invasion. As global warming increases, shrub encroachment into native grasslands worldwide will continue to alter species interactions and community stability both of which may lead to a decline in biodiversity

Root Processes Affecting the Soil Moisture Patterns in Ecohydrology

Soil moisture patterns arise from the combined processes induced by vegetation, soil properties, climate, topography, parent material, and time. In this chapter, we focus on how vegetation induces soil moisture patterns, particularly how plantroot processes affect the soil moisture distribution. Four different mechanisms were identified as potential drivers of soil moisture variability: root growth, root water uptake and transpiration, plant competitions, and rhizosphere properties. High transpiration, root growth, and root water uptake generally increase the soil moisture variability for drying conditions. On the other hand, other mechanisms reduce the soil moisture variation under drying condition including (1) compensation, which plants extract water in the wettest part of the soil; (2) hydrotropism, which roots tend to grow toward wetter zone of the soil; and (3) plant competition, which different plants try to segregate the depths at which they take up water. In addition, rhizosphere-specific properties tend to increase the variability when the soil is wetted from dry condition or to decrease it under wet conditions. We used a plant architecture model to illustrate how soil and root properties combine to generate or destroy soil moisture relations

Ecohydrological implications of aeolian processes in drylands

Aeolian processes, the erosion transport and deposition of soil particles by wind, are dominant geomorphological processes in many drylands, and important feedbacks are known to exist among aeolian, hydrological, and vegetation dynamics (Field et al. 2010; Ravi et al. 2011). The wind, a natural geomorphic agent, has been active as an erosive agent throughout geological times in many parts of the world. Outstanding examples are the extensive loess deposits along the Huanghe River (Yellow River) in China and along the Missouri and Mississippi rivers in the United States. Climatic changes and anthropogenic activities can greatly accelerate soil erosion by wind with implications for soil and vegetation degradation (Kok et al. 2012; Webb and Pierre 2018; Nauman et al. 2018). For instance, in the 1930s, a decreased precipitation coupled with intensive agricultural activities caused a dramatic increase in wind erosion in the Great Plains of the United States, resulting in the so-called Dust Bowl. Wind erosion can be activated also by land-use change. An example is provided by the Mu Us region in North China with an annual precipitation of 400 mm, which was once a grassland partially covered with forest, yet now is one of the major sources of dust in the world as a result of overgrazing and agricultural practices (Wang et al. 2005; Miao et al. 2016)