Primary succession

Early successional woody plants facilitate and ferns inhibit forest development on Puerto Rican landslides

Walker, L.R., Landau, F.H., Velázquez, E., Shiels,
A.B. and Sparrow, A.D. (2010). Early successional
woody plants facilitate and ferns inhibit forest
development on Puerto Rican landslides. Journal
of Ecology 98, 625-35.

1. The experimental removal of early successional species can explain how plant communities change over time. 2. During a 7.3-year period, early successional woody species, scrambling ferns and tree ferns were removed from a total of 10 landslides in the Luquillo Experimental Forest in north-eastern Puerto Rico. 3. Early successional woody plants in combination with tree ferns decreased species richness and cover of forbs and increased richness of late-successional woody plants compared to removals, facilitating long-term forest development. 4. Dense stands of scrambling ferns decreased both forb and woody plant richness compared to removals, inhibiting forest development. 5. Stands of monospecific tree ferns initially increased woody plant richness compared to removals, but overall decreased woody plant richness and cover, inhibiting forest development. 6. Synthesis. Early successional species both facilitate and inhibit succession on tropical landslides, but detailed predictions of successional trajectories remain elusive and are influenced by stochastic processes including arrival order, the life-form of colonizing species and their competitive interactions.

Ecosystem Development and Plant Succession on Landslides in the Caribbean

Ecosystem Development and Plant Succession on Landslides in the Caribbean
Lawrence R. Walker, Daniel J. Zarin, Ned Fetcher, Randall W. Myster and Arthur H. Johnson
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 566-576

Landslides are common in mountainous regions of the Caribbean and are triggered by heavy rains and earthquakes, and often occur in association with human disturbances (e.g., roads). Spatially heterogeneous removal of both substrate and vegetation is responsible for a variety of patterns of ecosystem development and plant successional trajectories within Caribbean landslides. Soil nutrient pools in exposed mineral soils reach levels comparable to mature forest soils within 55 yr but soil organic matter recovers more slowly. Plant colonization of landslides depends on the availability of propagules and suitable sites for germination, soil stability, and the presence of residual or newly deposited soil organic matter and associated nutrients. Once initial colonization occurs, the rate and trajectory of plant succession on landslides is strongly affected by plant/plant interactions. We present two conceptual models of landslide succession that summarize the major processes and pathways of ecosystem development and plant succession on landslides. Additional work is needed to characterize interactions between spatially heterogeneous zones, controls over soil development, impacts of key plant species, and the role of animals on Caribbean landslides.

Soil factors predict initial plant colonization on Puerto Rican landslides

Shiels, A.B., West, C.A., Weiss, L., Klawinski, P.D. &
Walker, L.R. 2008. Soil factors predict initial plant
colonization on Puerto Rican landslides. Plant
Ecology 195: 165–178.

Tropical storms are the principal cause of landslides in montane rainforests, such as the Luquillo Experimental Forest (LEF) of Puerto Rico. A storm in 2003 caused 30 new landslides in the LEF that we used to examine prior hypotheses that slope stability and organically enriched soils are prerequisites for plant colonization. We measured slope stability and litterfall 8–13 months following landslide formation. At 13 months we also measured microtopography, soil characteristics (organic matter, particle size, total nitrogen, and water-holding capacity), elevation, distance to forest edge, and canopy cover. When all landslides were analyzed together, plant biomass and cover at 13 months were not correlated with slope stability or organic matter, but instead with soil nitrogen, clay content, waterholding capacity, and elevation. When landslides were analyzed after separating by soil type, the distance from the forest edge and slope stability combined with soil factors (excluding organic matter) predicted initial plant colonization on volcaniclastic landslides, whereas on diorite landslides none of the measured characteristics affected initial plant colonization. The life forms of the colonizing plants reflected these differences in landslide soils, as trees, shrubs, and vines colonized high clay, high nitrogen, and low elevation volcaniclastic soils, whereas herbs were the dominant colonists on high sand, low nitrogen, and high elevation diorite soils. Therefore, the predictability of the initial stage of plant succession on LEF landslides is primarily determined by soil characteristics that are related to soil type.
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