Hydrologic Influence

• Water “singular importance” to bottomland systems:– Ecological limiting factor

– Medium for biogeochemical processes

– Force that controls erosion & sedimentation events» (Hupp 2000)

• “Slight hydrological changes may result in only loosely predictable, yet often substantial responses” (Mitsch & Gosselink 1993)

• Floodplains are regularly inundated for months each year (during the wet period) – Prolonged saturation

– Physical damage

– Erosion of substrate

– Deposition of new sediments

• Disturbance highly variable on the landscape

• Species vary in susceptibility and tolerance to hydrologic disturbance

• Variations in floodplain forest composition are influenced by varying severity of flooding – Mortality

– Extreme stress

– Altering conditions for establishment

• Flood Tolerance

Geomorphic Influence

• Fluvial landforms (floodplains) are dynamic features– Constantly eroding

– Constantly aggrading

• Meandering streams and rivers migrate – Creates a heterogeneous landscape

• Floodplains tend to act as net storage basins for sediment during periods of high or rising sea level

• Floodplains aggrade in two ways

– Lateral accretion (point-bar extension)• Episodic process

• Occurs during high flows

• This results in ridge & swale topography

                                                                                                                                                                                                      

                                

• Vertical accretion – Also episodic

– Facilitated by reduction in flow velocity

(Hodges 1997)

Features of Modern Floodplains

River ChannelRiver Channel

Direction of Meander Direction of Meander MovementMovement

Point Bar DepositsPoint Bar Deposits

Back SwampsBack Swamps

Channel Fill DepositsChannel Fill Deposits

RidgeRidge

Swale DepositsSwale Deposits

Overflow ChannelOverflow Channel

Natural LeveeNatural Levee

Vegetative Patterns

• Likelihood of a particular spp. occupying a given landform is a function of:

– The suitability of the site for germination

– The environmental conditions that permit persistence until reproductive age

Vegetative Patterns cont…

• Spatial distribution (pattern) of a spp. is limited by:– Spp. ability to survive or tolerate local conditions (disturbance, stress

regimes)

– Competitive and facilitative influences

Stress GradientStress Gradient

CompetitionCompetition Geomorphic processesGeomorphic processes

Important: Species grow where they can compete successfully and tolerate local conditions, NOT where they grow best.

Bottomland Forests

• Bottomland forests are some of the most productive and diverse ecosystems in the United States

• Myriad of different species with different site requirements and growth habits makes management extremely complex and variable

Bottomland Hardwoods

• The silviculture is similar to upland forests except for:– Flooding that is largely, unpredictable and uncontrollable, and

– Site/Species relationships

Bottomland Hardwoods

• Water– Depth

– Frequency

– Duration

– Seasonal Timing

Bottomland HardwoodsBottomland Hardwoods

• Site/Species RelationshipsSite/Species Relationships

LandformLandform

Soil DrainageSoil Drainage

Soil TextureSoil Texture

DepositionDeposition

Patterns of DepositionPatterns of Deposition

Major Bottoms

• Bars and Fronts --- willow, elm, cottonwood, sycamore

• Flats --- Nuttall oak, green ash, sugarberry, elm, red maple

• Slough --- overcup oak, water hickory

• Swamp --- water tupelo, bald cypress

• Ridge --- sweetgum, green ash, hickory, water/willow oaks

Minor Bottoms

• Bar --- river birch

• Levee --- beech, sycamore, sweetgum, sycamore, yellow-poplar, oaks

• Flat --- sweetgum, oaks, hickories, blackgum

• Slough --- bald cypress, swamp tupelo

• Terrace --- white oaks, red oaks, hickory, yellow-poplar, sweetgum, loblolly pine

Bottomland Succession Patterns

Poorly drained, low elevation

Better drained, “high” elevation

Minor Bottoms

Bottomland Ecology Summary

• Know your sites

• Know the hydrology

• Know the ecological requirements of the species

•

• INTEGRATE ---- Match the species to the site conditions

Bottomland Systems are Dynamic!

Rapid change is part of the system. Sites and soils are in a constant state of change because of

deposition and erosion. This in turn is reflected in the vegetational composition

Questions, Comments or Opinions…..

Courtesy, National Geographic SocietyCourtesy, National Geographic Society

Even-aged stand ~60 yrs old in small creek bottom, red oak-gum

Silviculture of Bottomland Stands

• Cottonwood and Willow Type– Rotation Age or Size:

• Natural stands: < 50 years sawtimber, 30 to 35 years most common

• Plantations: 20 year sawtimber rotation

– Thinning greatly enhances growth

– Regeneration:• Seed-tree method

• Site prep may be necessary to control non merchantable shade tolerant species due to intolerant nature of target species

Silviculture of Bottomland Stands

• Cottonwood and Willow Type– Rotation Age or Size:

• Natural stands: < 50 years sawtimber, 30 to 35 years most common

• Plantations: 20 year sawtimber rotation

– Thinning greatly enhances growth

– Regeneration:• Seed-tree method

• Site prep may be necessary to control non merchantable shade tolerant species due to intolerant nature of target species

Silviculture of Bottomland Stands

• Baldcypress and Tupelo Type– Rotation Age or Size:

• 75 to 100 years

– Thinning• Pre-thin BA > 250 common in this type

• Residual BA 110 ft2 or less should be goal

– Heavy thinning can increase epicormic branching

– Regeneration:• Regeneration is difficult and highly variable

– Seedling establishment dependant on dry periods

• Advance regeneration and stump sprout dependent

– Clearcut when sufficient advance reproduction present

– Otherwise, shelterwood

Silviculture of Bottomland Stands

• Mixed Bottomland Hardwood Type– Growth rate:

• Yield > 250 board feet per acre per year

– Rotation age or size: • 60 to 80 years

– Thinning

Silviculture of Bottomland Stands

• Mixed Bottomland Hardwood Type– Regeneration:

• Light seeded species (e.g., sweetgum, yellow-poplar)

– Clearcut or seedtree

» Some research suggests that seedtree has minimal impact on species composition in this type

• Oaks

– Advance regeneration and stump sprout dependent

– Clearcut when sufficient advance reproduction present

– Shelterwood system in absence of advance reproduction

» Control shade tolerant midstory and understory competition