A continuous 48,000-year-long paleoecological record from Neotropical lower montane forest reveals a consistent forest presence and an ice-age cooling of approximately 5 degrees to 9 degrees C. After 30,000 years of compositional stability, a steady turnover of species marks the 8000-year-long transition from ice-age to Holocene conditions. Although the changes were directional, the rates of community change were no different during this transitional period than in the preceding 30,000-year period of community stability. The warming rate of about 1 degrees C per millennium during the Pleistocene-Holocene transition was an order of magnitude less than the projected changes for the 21st century. 相似文献
Four greenhouse sand culture experiments were conducted with Kenhy tall fescue, a Lolium multiflorum X Festuca arundinacea hybrid derivative. These experiments were conducted to characterize mg accumulation and the chemical composition of Kenhy under various combinations of Mg, K, and N solution concentrations. Of primary interest was the shape and magnitude of response of tissue Mg concentration to solution K levels and potential for Mg accumulation that exists in Kenhy under low solution K levels. Analyses were made for Mg, K, Ca, Na, N, and nitrate.
Increased Kg concentrations were observed with increased solution Mg. Increased solution K was in all cases associated with lower concentrations of Mg. Under conditions of low solution K (0.125 mM) and adequate Mg (0.25 mM), Mg accumulation exceeded 1.0%. Increased solution N was associated with decreased Mg concentrations. Both the linear and quadratic components of Mg solution concentration contributed significantly to increased tissue Mg. Hawever, the linear component of K solution concentration was sufficient to account for decreased tissue Mg. The reduction of tissue Mg to solution K was greater at higher concentrations of K.
Potassium accumulation significantly increased with increased solution K. Increased solution Mg was associated with lower tissue K in which the greatest reduction in K accumulation occurred with the first Mg addition.
Calcium accumulation decreased with increased solution K. Higher solution Mg was associated with lower tissue Ca levels while higher levels of N were associated with increased tissue Ca. Sodium accumulation was significantly reduced by increased K concentrations but neither Mg nor N was effective in consistently altering tissue Na concentrations.
From these experiments it is evident that Kenhy tall fescue has the absorptive capability for high levels of Mg under conditions of low levels of solution K. However, even small increments of solution K were shown to be capable of substantially reducing the Mg content, Thus, the selection of forage grasses for Mg absorptive capability must be conducted under conditions of high solution K, if large improvements on present forage materials are to be obtained. In addition, the inverse relationship between Mg and K present in Kenhy seedlings confirms the need to consider K fertilization recommendations in attempting to increase forage Mg durirg the grass tetany period. 相似文献
This article provides a detailed empirical study of investment patterns in small-scale rural aquaculture and its relation to pond location based on a systematic fish pond survey in Lao PDR. Nominal investment categories of fish ponds were created based on stocking rate, feed and water and then spatially cross-referenced with a range of environmental factors, including distance to roads, land use, and distance to water resources. Contrary to current aquaculture development policies, the results show the dynamic nature of fish ponds as a source of water, native fish and exotic fish. It is concluded that policy makers and extension officers can make use of simple diagnostic models of fish pond use and investment to develop more contingent support to farmers that takes into consideration a wider portfolio of living aquatic resources in rural communities. 相似文献
The Vietnamese government's policies for an export-led economy have supported the rapid growth of Pangasius production but have had limited success in mitigating the environmental and social impacts stemming from unplanned and ad hoc expansion. Recognising the poor performance of state regulation the industry and government have turned to private or market-based environmental and social standards for Pangasius production. The success of these private governance arrangements is dependent on the capacity of producers to comply with standards within their wider environmental, social, cultural and economic context. This paper reviews current concerns over the sustainability of Pangasius production and draws attention to the challenges private governance initiatives face in steering towards sustainable production. 相似文献
An extreme cold exposure event occurred between March 14th and 19th 2011 in northern and central Lao PDR resulting in a major
mortality of cattle and buffalo. At least six northern and one central province reported losses, involving 46 districts and
1,384 smallholder farmers, with a total of 7,162 cattle and 3,744 buffalo reported to have died in association with cold weather.
Affected animals were observed to shiver, display slow and shallow respiration, lose consciousness and eventually die. Many
deaths occurred at night and were recorded in both sexes and all ages of large ruminants. However, mortalities occurred mostly
in animals that were free-grazing in the forest and natural grassland, and exposed to the cold weather. Some housed animals
that were provided with warmth from shelter and fires and supplementary feed did not die. Samples from dead animals collected
for laboratory analysis confirmed that bacterial or viral pathogens were not present. The cause of the mortality was attributed
to hypothermia, and the economic losses were estimated at USD 2,463,912.00. Xieng Khouang Province reported the most severe
losses with deaths of 4,600 cattle and 1,665 buffalo. At Thong Haihin meteorological station in this province on March 16th
and 17th 2011, minimum temperatures recorded were 6.7°C and 7.5°C and rainfall recorded was 36.6 mm and 61.7 mm, respectively.
This was the first reported extreme cold event in living memory occurring between the end of dry season and beginning of the
wet season in northern Laos. This event is reported in detail as it caused a major loss of wealth for poor smallholder farmers
and indicates that strategies to minimise the impact of extreme cold weather events need to be included in livestock development
extension programmes. 相似文献
Largemouth bass Micropterus salmoides (Lacepède) use of installed habitat structure was evaluated in a large Midwestern USA reservoir to determine whether or not these structures were used in similar proportion to natural habitats. Seventy largemouth bass (>380 mm total length) were surgically implanted with radio transmitters and a subset was relocated monthly during day and night for one year. The top habitat selection models (based on Akaike's information criterion) suggest largemouth bass select 2–4 m depths during night and 4–7 m during day, whereas littoral structure selection was similar across diel periods. Largemouth bass selected boat docks at twice the rate of other structures. Installed woody structure was selected at similar rates to naturally occurring complex woody structure, whereas both were selected at a higher rate than simple woody structure. The results suggest the addition of woody structure may concentrate largemouth bass and mitigate the loss of woody habitat in a large reservoir. 相似文献
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