An experimental investigation into the response of New Zealand sand dune species to different depths of burial by sand

Thirty species found on New Zealand sand dunes were used in an experiment to investigate plant responses to burial. Plants were grown in four different treatments: surface (no burial), burial to two-thirds plant height, fully buried and full burial plus a further third of plant height, for 15 weeks. Over half the species were little affected in their biomass until fully buried. Shootiroot ratios usually decreased with burial depth, though six species showed increases. In Ammophila arenaria, the common dune builder, tillering occurred after partial burial but plant biomass was much lower than in surface plants. Full burial usually killed the plant, though some were still alive at the lowest depth. The ability to stay alive in mobile dunes is important. Of the other grasses examined, many perennial species survived partial burial, though full sand cover killed most. Many annual grasses, e.g. Bromus diandrus and Lagurus ovatus, were intolerant of even partial burial. The plastic nature of the morphological development of many species was emphasized. This was quantified to some extent for some species using leafistem ratios. Two species, A. arenaria and Desmoschoenus spiralis, had decreased ratios as the stem elongated in response to burial. The ratio increased, however, in Hydrocotyle novae-zelandia as the petiole lengthened. Morphological effects were varied; creeping herbs responded well to burial, with some, e.g. Centella uniflora growing up to the surface from fully plus a third buried. Burial often produced elongation of stems, e.g. in Lupinus arboreus and Euphorbia glauca. In Phormium tenax new leaves growing buried by the sand were a crinkled zig-zag shape. Correlations between burial response and field positions from four sand dune systems in southern New Zealand were mostly non-significant. However, at Cole Creek on the West Coast, positive partial burial responses were significantly negatively correlated to distance from the sea. Tolerance of sand deposition appears to be as necessary for rear dune species as it is for those of the front dunes.