A primary succession on basaltic volcanic1644 Primary succession on coastal sand dunes

flows on Miyake-jima Island, Japan, was inferred from a known chrono- An extensive chronosequence of dune-

sequence (16, 37, 125 and >800 years old) capped beach ridges has been under-

(Figure 16.9a). In the 16-year-old flow, taken on the coast of Lake Michigan soil was very sparse and lacking in in the USA. Thirteen ridges of known importance of seed availability rather than facilitation in sand dune succession

125-year-old lava flow

16-year-old lava flow

125-year-old lava flow

16-year-old lava flow

Richness Primary Succession

37-year-old lava flow

37-year-old lava flow

2 km

year-old year-old year-old

125-year-old

800-year-old

year-old year-old year-old

125-year-old

800-year-old

Bare land

Alnus shrub

Machilus and Prunus forest

Castanopsis forest

Colonization of Alnus and Reynoutria

Facilitation by N fixation of Alnus Colonization of Prunus and Machilus Rapid above-ground biomass accumulation

Disappearance of Alnus and Prunus Colonization of Castanopsis

Colonization of Alnus and Reynoutria

Facilitation by N fixation of Alnus Colonization of Prunus and Machilus Rapid above-ground biomass accumulation

Disappearance of Alnus and Prunus Colonization of Castanopsis

Figure 16.9 (a) Vegetation was described on 16-, 37- and 125-year-old lava flows on Miyake-jima Island, Japan. Analysis of the 16-year-old flow was nonquantitative (no sample sites shown). Sample sites on the other flows are shown as solid circles. Sites outside the three flows are at least 800 years old. (b) The main features of the primary succession in relation to lava age. (After Kamijo et al., 2002.)

age (30-440 years old) show a clear pattern of primary succession to forest (Lichter, 2000). The dune grass Ammophila breviligulata dominates the youngest, still mobile dune ridge, but shrubby Prunus pumila and Salix spp. are also present. Within 100 years, these are replaced by evergreen shrubs such as Juniperus communis and by prairie bunch grass Schizachrium scoparium. Conifers such as Pinus spp., Larix laricina, Picea strobus and Thuja occidentalis begin colonizing the dune ridges after 150 years, and a mixed forest of Pinus strobus and P. resinosa develops between 225 and 400 years. Deciduous trees such as the oak Quercus rubra and the maple Acer rubrum do not become important components of the forest until 440 years.

It used to be thought that early successional dune species facilitated the later species by adding organic matter to the soil and increasing the availability of soil moisture and nitrogen (as in the volcanic primary succession). However, experimental seed addition and seedling transplant experiments have shown that later species are capable of germinating in young dunes (Figure 16.10a). While the more developed soil of older dunes may improve the performance of late successional species, their successful colonization of young dunes is mainly constrained by limited seed dispersal, together with seed predation by rodents (Figure 16.10b). Ammophila generally colonizes young, active dunes through horizontal vegetative growth. Schizachrium, one of the

H

Ammophila

Schizachrium

n

Pinus strobus

Pinus resinosa

60 150

Dune age (years)

Seed prédation No predation P < 0.0001

Species

Figure 16.10 (a) Seedling emergence (means + SE) from added seeds of species typical of different successional stages on dunes of four ages. (b) Seedling emergence of the four species (Ab, Ammophila breviligulata, Ss, Schizachrium scoparium, Ps, Pinus strobus, Pr, Pinus resinosa) in the presence and absence of rodent predators of seeds (After Lichter, 2000.)

dominants of open dunes before forest development, has rates of germination and seedling establishment that are no better than Pinus, but its seeds are not preyed upon. Also, Schizachrium has the advantage of quickly reaching maturity and can continue to provide seeds at a high rate. These early species are eventually competitively excluded as trees establish and grow. Lichter (2000) considers that dune succession is better described in terms of the transient dynamics of colonization and competitive displacement, rather than the result of facilitation by early species (improving soil conditions) followed by competitive displacement.

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