A comparison of conditions needed by cottonwood and salt cedar
Cottonwood (Populus spp.) is an indigenous plant to several boreal and temperate regions of North America where the absence of flood waters exposes salt to the surface of the soil. Cottonwoods can reproduce asexually. This occurs during crown breakage and when a tree falls during wind storms and flooding events. The branches sprout and develop strong shoots after being buried in the sediments of the soil. The Climatic condition, species as well as the drainage pattern of the area dictates whether the seedlings can develop from either asexual or sexual reproduction. Seedlings of cottonwood develop provided there is sufficient rainfall.
Cottonwood seedlings are shade intolerant and they develop due to large and relatively infrequent floods. Both water and light level availability are vital for the development of cottonwood seedlings in arid regions. Late summer establishment of seedlings relies on the amount soil moisture provided by flooding. Rapid decrease of the water table can hinder development of seedlings since the seedlings are prone to dry soils. Timing and nature of fluvial processes greatly determine seedling survival rates as well as life history characteristics of the riparian cottonwoods
The germination percentage of the salt cedar plant depends on seed collector and varies from 20% to 52%. When the seedlings develop they grow at a faster rate than other indigenous plants. Similar to the cottonwood plant, the plant can establish from broken branches and stems of plants which are buried in sediment by producing sprouts of growth. This salt cedar plant mostly grows in soils with a salinity of approximately 6000ppm and can thrive in areas with salinity from 19,000 to 37,000 ppm. Seedling establishment and seed germination of salt cedar is common in higher areas with weather conditions like high temperature and environmental conditions like saline regions. One major shortcoming of the Salt cedar is that once it thrives in a region, it spreads the salt on the surface of the soil and subsurface. Cottonwoods are susceptible to high invasion in riparian environmental conditions due to the large amount of hydrological interference in such areas. Upon development of salt cedar, indigenous riparian vegetation can be replaced due to extreme changes in channel structures and hydrologic setups which directly provides negative effects on biodiversity of aquatic and ecosystems of wildlife
A Response to the state of precipitation
Research shows that precipitation has increased by 5% over the last 50 years; this has been necessitated by increased rate of evaporation from the warmer ocean surfaces, increasing the humidity in warmer air resulting in bigger storms with heightened precipitation. A greater percentage of the precipitation gain has been in noted especially in the Northeastern part of the United States. New Mexico generally had a slight increase in November to March precipitation over the period 1950-1999. Numerous studies have so far indicated that precipitation patterns in the area presently cannot be pegged solely to anthropogenic causes, since the extent of the pattern so far is controlled by the magnitude of changes due to short-term and long term shifts in the Atlantic and Pacific sea surface temperatures.
Hydrological changes
The renewable supply of water for the Basin starts majorly from mountain snowmelt in northern New Mexico and Colorado. They average to about 2.5 million acre-feet (af) per annum. There is an extra 5% supply supplied by importation of San Juan water and the Closed Basin project in Colorado Early this century, when Rio Grande waters were being allocated, climate conditions were relatively wet and more water was available than normal. The ‘50s drought, in comparison, was severe exceeded only by the one in the 1100s that was so disastrous to Pueblo Indians from a hydrologic perspective; the reservoirs have had lots of effects, such as evaporation. Different parts of the sites exhibit varying degree of water depth.
Graph showing impression of Groundwater depth in one of the sites
Discharge, peak flows and flooding
With lower flood peaks, there has been an extreme narrowing of the channel just below
Albuquerque. The channel is only a third of its original width. Levees and other formations have contributed to this state, but the narrowing was conditional when the. Dams were constructed and the flood peaks minimized. Of great concern, a picture of the Rio Grande shows no change as far as the straightness of the channel is concerned. Some sections of the river experience large discharge while some parts do not.
SANTA FE RIVER ABOVE COCHITI DAM
RIO GRANDE BELOW ELEPHANT BUTTE RESERVOIR
Salinity
Before the twentieth century, there was a balance of salt levels in the Rio Grande Valley. Intermittent major floods led to reshaping the river morphology and resettlement of salt sinks. . The cumulative effects of reduced water supplies in the river and direction of the river to a permanent streamed have led to environmental conditions where soil salinity is no longer maintained by the flow of the river. The main source of salt into the river is the capillary rise, which comes from the upward water flow that originates from the ground water table. The quantity of capillary rise relies on the depth of the ground water table coupled with the physical characteristics of the soil profile. For instance, a ground water table depth of 1.9 m will cause a capillary flux of 0.2 mm/day for sand soil and 8 mm/day for loamy sand. Salt deposits by capillary rise will speedily reduce if the ground water table is lowered. However, in most cases, the ground water table remains relatively shallow due to ground water seepage.
Table 1
Texture Capillary flux cm/day
2.0 1.0 0.6 0.1 0.01
Sand 69 82 92 135 213
Loamy sand 151 185 213 334 572
Sand loamy 29 45 61 158 484
Loam 73 99 123 247 577
Salty loam 59 90 121 321 1025
Clay loamy 126 165 197 342 639
Salty clay loamy 7 12 18 65 219
Conclusion
The rate at which salt cedar is taking over the cottonwood seedlings is wanting owing to its vast establishment along the Rio Grande. It is important that management implications are incorporated into the systems to ensure indigenous species such as the cottonwood are protected to prevent their extinction within the ecosystem. At the same time, the environmental specialists have a great task in curbing further spread of the salt by carrying out research and giving relevant recommendation to the concerned authorities.
Bibliography
Glenn, E.P., and P.L.Nagler. 2005. Comparative ecophysiology of Tamarix ramosissima and native trees in western U.S. riparian zones. Journal of Arid Environments 61:419-446
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