The benefit of high survival to sand-trapping efficiency is most noticeable during the first 

 year of dune growth. After the first year, plantings with low density survival have filled in 

 sufficiently to trap sand at a maximum rate, as illustrated by the 1,200-foot dune-width 

 panicum planting on north Padre. The north half of this planting (Fig. 37) was made in 

 February 1972, on 2-foot centers; survival was 76 percent. The south half (Fig. 38) was 

 planted in April 1972, with 4-foot rows, and 2-foot centers within rows. Survival was 

 36 percent, but the density of surviving plants compared with a 2-foot-center planting was 

 only 18 percent. Thus, the surviving plant density of the north half was over 4 times that of 

 the south half. First-year sand accumulation was much greater for the north half when 

 comparing May 1973 profiles between Figures 37 and 38, but subsequent growth was nearly 

 equal. The south half is now a uniform dune, trapping all available sand, and is only slightly 

 smaller than the north half. 



Generally, a 2-foot center planting with 20 percent or greater survival is sufficient to 

 yield maximum dune growth after t le first year, although higher survival density results in 

 more rapid early dune growth. There also was good success on a sea oats planting with only 

 8 percent survival (south 400-foot sea oats, south Padre), although it normally would be 

 advisable to replant areas with survival this low. 



j. Width of Planting. To build a foredune quickly, all available blowing sand should be 

 trapped. Foredune construction costs are closely related to the number of culms planted; 

 therefore, it is important to determine the minimum planting width which will trap all 

 available sand. The 1,200-foot dune-width panicum plot, discussed previously, was planted 

 for this purpose. Four alternating blocks of two different widths (50 by 300 feet, and 

 100 by 300 feet) were planted with bitter panicum in February and April 1972. Dune 

 profiles up to 2 years after planting (Figs. 37 and 38) showed that only the shoreward 50 

 feet of either planting (high or low transplant survival) trapped sand for dune growth. No 

 sand reached the west half of the 100-foot-wide blocks, except for a small ridge at the 

 extreme west edge, which represented sand blown from behind the beach during "northers". 

 A photo sequence of the north half of this dune is shown in Figure 39. 



Conclusions from this experiment are: (a) initial plantings of greater than 50-foot width 

 did not result in improved dune growth, and culms planted in excess of 50 feet were not 

 used in trapping sand; and (b) the source of sand available for dune growth was almost 

 exclusively from the beach east of the planting, and only about 10 percent originated from 

 the west. 



k. Preparing the Field for Planting: Preplanting Irrigation. On elevated surfaces, such as 

 fence-built dunes, soil moisture was typically low (around 4 percent), and evaporation from 

 the surface layer was rapid. Leeward drifts up to several feet deep of wind-dried sand were 

 regular. Irrigation proved an essential preplanting procedure on all elevated surfaces except 

 during and soon after heavy rains. Also preplanting irrigation may be useful for winter beach 

 plantings during prolonged droughts, or any time in summer except the first week after a 



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