Wetland Biotopes: Hydrologic conditions, vegetation zonation and succession

1. Wetland Biotopes: Hydrologic conditions, vegetation zonation and succession Keith Edwards B259 kredwards59@yahoo.com

2. Wetland Hydrology • Wetlands – transitional between terrestrial and open water ecosystems • Are ecotonal systems • Wetland biotopes – determined mostly by hydrology - Source (precipitation, groundwater, surface water) - Water Depth - Flow rate and patterns - Flooding frequency and duration (pulses) • Hydrology – probably most important factor for wetland establishment and maintenance

3. HYDROLOGY Modifies and determines Climate Physicochemical Environment Basin Geomorphology Allows specific Biota Mitsch and Gosselink, 2000

4. Hydrology: Influences chemical and physical traits of wetlands - which influences plant species composition BUT: plants affect hydrology – ET, retarding flow rate Feedbacks

5. Slavošovice CW Water Velocity – Holcova, 2006 4 August 2005 (48 hours after) 1 December 2005 (30 hours after) 5 August 2005 (72 hours after) 2 December 2005 (46 hours after)

6. 7 August 2005 (120 hours after) 4 December (104 hours after) 9 August 2005 (168 hours after) 6 December (142 hours after)

7. Hydrologic Effects • Due to periodic flooding: - wetlands lower species diversity than uplands - waterlogged soils – low O2 levels – other chemical traits different from uplands - requires plant adaptations - only small % of all vascular plants have evolved such adaptations - wetlands have unique flora with low diversity

8. Hydrologic conditions affect biotope type - Longer flooding duration – lower species diversity - Greater fluctuation in flooding / water level – more heterogeneous habitat – more niches available – more species able to establish (lake/pond shores, riparian) - Flowing waters – increases erosion / sediment deposition rates – more heterogeneity - Coastal wetlands – low diversity – double stress of flooding and salinity

10. Wetland hydroperiod – seasonal water level pattern – rise and fall of water in a wetland: Examples: permanently flooded; seasonally flooded; saturated; temporarily flooded… • Degree of fluctuations – can help maintain particular biotopes – constancy of pattern year to year provides stability to wetland • Hydroperiod – integrates all inflows and outflows - influenced by physical terrain and distance to other water bodies

11. Production – affected by openness of wetland systems to hydrological fluxes: - systems with greater water flow through have higher NPP (but not always for marshes) - generally higher flow through means greater nutrient and energy inputs • Within-wetland variation in water level fluctuations: - produces environmental gradients that influence species distribution – plant zonation

16. Species change across space and time (succession) • Affected by: - internal factors (competition, facilitation, peat accumulation, etc.) – autochthonous - external factors (disturbance, hydrology, climate change, etc.) - allochthonous

17. Plant distribution / zonation • Originally thought due to successional processes – example: mangroves • Now – numerous models of plant change / zonation in wetlands

18. Hydrarch Model • Wetlands intermediate stage between purely aquatic to purely terrestrial climax community • Follows Clements’ ideas of succession and community development: - Vegetation occurs as recognizable groups of species - Autogenic processes most important - Linear sequence of stages ending in a very stable, mature climax stage

21. Many wetlands are ecotonal – accumulate OM from plant matter and trap sediments – autochthonous factors • BUT – wetlands also subject to allochthonous factors - Even if current upland stage on former wetlands does not mean change was due to autochthonous factors – must be tested

22. Now – hydrarch model considered to be only partly correct: - OM accumulation self-limiting process – rate decreases as wetland becomes drier – result in drier wetland biotope but not necessarily an upland community - External factors can affect hydrology - Northern peatlands likely exception – more direct control over hydrology – but may not change over time into uplands (paludification) - Lakes / ponds – some upland forests do occur on former wetlands – but again not clear if due to autochthonous factors – ex. INDU wetlands

23. INDU Ponds • Cowles (1899, 1901) and Shelford (1911) – first studied area • Ponds – formed by glacial action – of differing ages from inland to edge of Lake Michigan • Found young ponds deepest, dominated by aquatic plants • Older ponds – shallower with emergent vegetation • Oldest – little or no standing water – drier wetland systems or upland communities • Thought represented successional sequence

24. INDU Ponds • Later studies – 1980’s, 1990’s • Wilcox and Simonen (1987): - same plant species sequence found (youngest to oldest) - studied pollen and macrofossil record in sediment cores of one pond – whether similar sequence over time - older than 150 years BP – diverse grouping of aquatic, emergent and floating species - 150 years BP to now – rapid species change due to European settlement and industrialization

25. Singer (1996): - pollen and macrofossil record in pond - compared to regional terrestrial pollen record – record of long-term regional climate change - Pond vegetation mirrored changes in terrestrial pollen record - Concluded – changes in pond vegetation due more to regional climate changes than autochthonous factors

26. Plant species changes in wetlands: - interaction between autochthonous and allochthonous factors • Successional theory – lakes and wetlands considered to be “immature” ecosystems – higher production than respiration rates • However – wetlands are detrital-based systems – is trait of “mature” ecosystems • Wetlands have traits of both “immature” and “mature” systems

27. Trade-offs • Grime’s CSR model – plants grouped by life history traits, and response to stress and disturbance • Predict where species fall along stress and disturbance gradients: - Menges and Waller (1983) plant distribution in riparian wetlands related to flooding frequency and plant physiological traits

29. Basis – plants require same types of resources: - Light - Water - Nutrients - Space • Fundamental niches of species overlap at rich end of nutrient gradient Some species better competitors – others better able to tolerate stress A B C D E F Trade-off in allocation of fixed carbon Resources

30. Better competitors – found in nutrient-rich, less stressful areas • Actual distribution of plants along gradient – realized niche A B C D E F Poorer competitors – better stress tolerators – found in poorer quality habitats Resources Real wetlands – need to test that competition / stress tolerance main factors influencing plant distribution

31. Centrifugal Organization Model • Expanded CSR model • Wisheu and Keddy (1992): - Multiple gradients in wetlands - Benign ends of all gradients – core habitats – dominated by better competitors – lower species diversity - More adverse conditions – dominated by species with adaptations to particular stress / disturbance - Species diversity – hump-backed curve – highest in mid parts of gradients – but biomass greater in core habitat

32. Freshwater Wetlands, North America

33. Model predictions: - Rare species restricted to peripheral habitats - Moore et al (1989) - North American wetlands – found rare species were restricted to infertile, peripheral sites - Eutrophication – shift species composition towards that of core habitat – favor more competitive species – removal of peripheral habitats – decreased species diversity

34. Assembly Rules / Environmental Sieve Models • Assembly Rules (functional guilds): - Plant species placed into groups based on functional traits - Keddy (2000) – clustered 43 wetland species into 7 groups – fall along life history and growth forms in relation to light levels - Traits used to predict presence and response of plants to an important environmental factor (filter) - Filters – environmental conditions that restrict species pool - Can predict which plant traits prevent establishment / presence of particular species - Predict changes in species composition as environment changes

36. Environmental Sieve Model (van der Valk, 1981): - Gleasonian approach – continuum model - Developed to explain plant composition in prairie potholes under flooded and drained conditions - Prairie potholes – shallow depressional wetlands in mid- continental North America – typified by fluctuating water levels - Model – three life history traits; - life span (annual, short-lived or long-lived perennials) - propagule longevity – how long reproductive parts viable and available (persistent, forming a seed bank or short-lived but easily dispersed) - plant establishment requirements (require exposed soil – Type 1; can have standing water – type 2)

37. 12 possible life history types Example: Phragmites – is a VD-1 (long-lived perennial, V; easily dispersed, short-lived seeds, D; requires exposed soil to germinate -1)

38. - As environmental sieves change – other life history types favored: - long-term flooded wetlands – few or no annuals - S species favored – form seed banks - long-lived perennials persist - Sieve model: - qualitative model- predicts species presence but not amount - ignores autogenic factors

39. - Easily incorporate other environmental factors: - include fire frequency to predict change in species composition of depressional swamps in southeast US - swamps frequently drawn down – then more susceptible to fire - high fire frequency – results in grass / sedge meadows - intermediate fire frequency – hardwoods (maple) killed – end result is cypress (Taxodium ascendens) savannas - low fire frequency – mixed hardwood / cypress swamp