在许多半干旱的地区中，同样存在树带界限的下限区域；在这片区域之内，由于缺乏水分，森林下沿区域的植被通常会逐渐变成干草原或沙漠。
In many semiarid areas there is also a lower timberline where the forest passes into steppe or desert at its lower edge, usually because of a lack of moisture.
流体间的接触面常常是渐变的而不是突变的，形成一个混合液体的过渡带。
The contact between fluids is usually gradual rather than sharp, forming a transition zone of mixed fluid.
这一渐变群是沿着萨克拉曼多谷地到西瓦内华达山脊的植被带存在的。
This cline exists along a transect from the Sacramento valley to near the crest of the sierra Nevada mountains.
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