inactive. Over hundreds or thousands of years, suites of foredunes may occur over
time, forming small to extensive foredune plains. Blowouts may form within the
foredunes and create a foredune–blowout complex. Blowouts may be quite small to
relatively large, and range in form from saucers through bowls to troughs. These too
may eventually stabilize and become part of the inactive dune system (Hesp 2011).
Parabolic dunes typically form from blowouts. They are characterized by
U- and V-shaped depositional lobes, trailing ridges and deflation basins or plains.
They may be long-walled types (linearly extensive downwind), oblate, short types,
or intermediate among these forms. They may be nested or overlapping, displaying
multiple episodes of formation. The depositional lobes may range from quite
simple forms to multiple-pronged digitate forms (Hesp 2004).
Transgressive dune sheets are flat to undulating sand plains. Transgressive
dunefields are small to extensive sand terrains featuring a variety of dune forms on
their surface. Transgressive dune sheets and dunefields are aeolian sand deposits
formed by the downwind movement (across or alongshore) or transgression of
sand over vegetated to semi-vegetated terrain. Such dunefields may range from
quite small sheets and nebkha fields (hundreds of meters in alongshore and
landward extent) to very large, unvegetated dunefields that can be similar in size to
some small to moderate-sized desert dunefields (or draa) (Hesp and Thom 1990;
Hesp 2011; Hesp et al. 2011).
Transgressive dunefields may be completely active (predominantly unvegetated),
partially vegetated, or completely vegetated post-formation. Transgressive dunefields may be dominated by active barchans, transverses, or barchanoid dunes. The
form may vary considerably depending on the age of the dunefield, dominant
migration direction relative to the coast, degree of vegetation cover, wind regime,
and sediment supply magnitude and variation over time. Star dunes, blowouts,
parabolic dunes, nebkha and nebkha fields, deflation basins and plains, slacks,
remnant knobs, bush pockets, shadow dunes, precipitation ridges, and trailing ridges,
etc., may be found within the dunefields (Hesp and Walker 2012).
1.1.2 Dune Vegetation
Because they are found in all latitudes and in all climate regimes, coastal dune
vegetation is very diverse and includes temperate to tropical forests, grasslands, and
shrublands (Hesp 2004; Hesp and Martínez 2008). Dune species differ between
dunes and among locations and have different biogeographic and phylogenetic
histories (van der Maarel 1993a, 1993b; Hesp et al. 2011; Gallego-Fernández and
Martínez 2011). However, in spite of these multiple differences, many plants typical
of coastal dunes share their physiological and morphological responses to the
environmental restrictions characteristic of coastal dunes (extreme temperatures,
drought, low availability of nutrients, disturbance (e.g., wave-driven beach and dune
erosion, aeolian erosion and deposition) and, most of all, salt spray and substrate
mobility) (Hesp 1991; Maun 2009; Hesp and Martínez 2008; Gallego-Fernández and
Martínez 2011) and are thus called psammophytes. The compendium of the
1 Coastal Dunes: Human Impact and Need for Restoration
3
time, forming small to extensive foredune plains. Blowouts may form within the
foredunes and create a foredune–blowout complex. Blowouts may be quite small to
relatively large, and range in form from saucers through bowls to troughs. These too
may eventually stabilize and become part of the inactive dune system (Hesp 2011).
Parabolic dunes typically form from blowouts. They are characterized by
U- and V-shaped depositional lobes, trailing ridges and deflation basins or plains.
They may be long-walled types (linearly extensive downwind), oblate, short types,
or intermediate among these forms. They may be nested or overlapping, displaying
multiple episodes of formation. The depositional lobes may range from quite
simple forms to multiple-pronged digitate forms (Hesp 2004).
Transgressive dune sheets are flat to undulating sand plains. Transgressive
dunefields are small to extensive sand terrains featuring a variety of dune forms on
their surface. Transgressive dune sheets and dunefields are aeolian sand deposits
formed by the downwind movement (across or alongshore) or transgression of
sand over vegetated to semi-vegetated terrain. Such dunefields may range from
quite small sheets and nebkha fields (hundreds of meters in alongshore and
landward extent) to very large, unvegetated dunefields that can be similar in size to
some small to moderate-sized desert dunefields (or draa) (Hesp and Thom 1990;
Hesp 2011; Hesp et al. 2011).
Transgressive dunefields may be completely active (predominantly unvegetated),
partially vegetated, or completely vegetated post-formation. Transgressive dunefields may be dominated by active barchans, transverses, or barchanoid dunes. The
form may vary considerably depending on the age of the dunefield, dominant
migration direction relative to the coast, degree of vegetation cover, wind regime,
and sediment supply magnitude and variation over time. Star dunes, blowouts,
parabolic dunes, nebkha and nebkha fields, deflation basins and plains, slacks,
remnant knobs, bush pockets, shadow dunes, precipitation ridges, and trailing ridges,
etc., may be found within the dunefields (Hesp and Walker 2012).
1.1.2 Dune Vegetation
Because they are found in all latitudes and in all climate regimes, coastal dune
vegetation is very diverse and includes temperate to tropical forests, grasslands, and
shrublands (Hesp 2004; Hesp and Martínez 2008). Dune species differ between
dunes and among locations and have different biogeographic and phylogenetic
histories (van der Maarel 1993a, 1993b; Hesp et al. 2011; Gallego-Fernández and
Martínez 2011). However, in spite of these multiple differences, many plants typical
of coastal dunes share their physiological and morphological responses to the
environmental restrictions characteristic of coastal dunes (extreme temperatures,
drought, low availability of nutrients, disturbance (e.g., wave-driven beach and dune
erosion, aeolian erosion and deposition) and, most of all, salt spray and substrate
mobility) (Hesp 1991; Maun 2009; Hesp and Martínez 2008; Gallego-Fernández and
Martínez 2011) and are thus called psammophytes. The compendium of the
1 Coastal Dunes: Human Impact and Need for Restoration
3