Plant Succession on Coastal Sand Dunes

Plant Succession on Coastal Sand Dunes Joe Simonis IB 447 Succession: When (plant) communities change in terms of composition and structure in a directional manner through time Triggered by a disturbance of some kind, which leaves substrate available for plants to colonize Follows a general pattern, called a chronosequence, from early colonizers to the climax community Disturbance Colonizing spp Subsequent spp time www.countrysideinfo.co.uk Climax community Disturbances and Types of Succession: Primary Succession: Follows a disturbance which leaves only bare substrate Little or no actual soil exists, no propagules present Very harsh and variable environments Classic examples: post-glacier, post-volcanoes, emergent islands, sand dunes Secondary Succession: The opposite Classic examples: post-fire, abandoned agricultural field www.micro.utexas.edu Why/how does succession progress? Two general schools of thought: 1. Life history trade-offs: Dispersal, growth, survival, and reproduction 2. Direct species interactions: Facilitation Inhibition Tolerance *These aren’t mutually exclusive www.hawaii.edu Coastal sand dunes are great for studying primary succession for two main reasons: 1. A series of habitats in the successional sequence are typically present in order 2. The sequence often progresses relatively quickly www.cedarlodge.com Because of the geology and weather of the Midwest, Lake Michigan’s shores are prime for sand dune formation, especially on the eastern coast At Wilderness State Park: 72 shore-parallel dune ridges formed over the past 2375 years = 1 dune every 33 years Species turnover, community convergence, and successional changes in species diversity across the dunes aged 25-440 years Early species Characterize primary dunes (ages 0 - 50 years) Beach grass and sand reed grass are crucial early colonizers of coastal dunes They help stabilize the shifty sand and act as a wind-break, trapping more sand and building the dunes Important characteristics: High dispersal abilities (use rhizome fragments) Fast-growing, deep root and rhizome systems (stabilization, nutrient/water acquisition) Growth is stimulated by aeolian sand http://techalive.mtu.edu/meec/module09/ www.dnr.state.wi.us Middle species Characterize open secondary dunes (55 175 years old) www.savedunes.org The environment is still harsh as water and nutrient levels are not very high Evergreen shrubs (common bearberry and juniper) and bunchgrasses (little bluestem) become the dominant species Important characteristics: Good dispersal abilities Adaptations to water stress (evergreen leaves and/or deep roots) en.wikipedia.org botit.botany.wisc.edu Late species Mixed pine forests dominate dunes 200 years old and older Common species: white and red pine, white spruce, balsam fir, white cedar, and paper birch Species are characterized by lower dispersal abilities and higher nutrient requirements, but are longer-lived and can grow tall…shade Species are mostly still evergreen www.tarleton.edu Hardwood trees Red maple and red oak are present by 225 years, but aren’t important components until after 440 years Eastern hemlock, sugar maple, and beech are only really present and abundant on undisturbed old (1445+ years) dunes Photo by Lee Frelich. At this point, secondary succession is more important… www.whisperwood.net Not just about angiosperms… Lichens colonize young nonforested dune ridges but decline under shade after 225 years Mosses colonize in the shade of the juniper shrubs on secondary dunes and remain in the forest understory Moss, lichen, spikemoss GK, botit.botany.wisc.edu What is driving succession on dunes? Both trade-offs and interactions ? xana.webnami.com/clients/eupnta/assetpages www.kozmicdreams.com/ woods.htm Changes in abiotic environment Stabilization of sands New windward dunes (windbreaks) Water!!! Organic horizon development www.tarleton.edu Changes in abiotic environment Nutrients: Nitrogen, Phosphorous, Potassium Nitrogen fixers aren’t the main cause of this on dunes, it’s primarily from slow sequestration of atmospheric N into the soil Changes in biotic environment www.birderblog.com Presence of insects, birds, and mammals (pollinators, dispersers, fertilizers) Shade and litterfall from trees www.ent.iastate.edu www.airninja.com But does everything go so smoothly? www.tiscali.co.uk May Thielgaard Watts www.usc.edu Blowouts, floods, fires and other weather/natural disasters can halt/restart successional processes in certain locations Human impacts can also be quite large and exacerbate or lead to natural disasters Would everything have gone smoothly anyways? The idea of an A --> B --> C --> D sequence doesn’t always hold in plant succession, and in fact, is the exception, not the rule For coastal sand dunes, the deterministic nature of the sequence depends upon variability in topography and water table depth At Wilderness State Park, the geomorphology is very uniform and almost all dunes follow the classical path of succession However, at many other sites, such as Indiana State Dunes, the geomorphology is more variable, leading to diverse sites and alternative successional sequences Textual Sources Coastal Dunes. www.michigan.gov/dnr Gurevitch, J., S. M. Scheiner and G. A. Fox. 2006. The Ecology of Plants. Sinauer Associates. Lichter, J. 1998. Primary succession and forest development on coastal Lake Michigan sand dunes. Ecological Monographs 68: 487-510. Terrestrial Ecosystems: Coastal Dunes. www.techalive.mtu.edu