A Soil Bioengineering Guide - Chapter2 - The Riparian Ecosystem

7/22/2019 A Soil Bioengineering Guide - Chapter2 - The Riparian Ecosystem

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CHAPTER 2Th e Ripa ria n Ecos y s t em


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A SOIL BIOENGINEERING GUIDE

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This cha pter d i scusses the v a lue o f the r ipar i an

ecosys tem. It o f fe r s a d i f fe rent a pproach fo r us ing th e

r ip a r ia n e c os y s t e m a s a n i n d ic a t o r o f w h a t h a s g o n e

w r on g o r w h a t i s f un c t io n i n g w e ll , a s w e ll a s w h a t i s

impor t ant to pro tec t . I t a l so d i scusses the s t ruc tura l and

func t iona l charac ter i s t ic s o f the r ipar ian ecosys tem a nd

how these cha rac ter is t i cs are the key l inks to m aint a in ing

ecological integrity.

An y t h i n g a n d e v e ry t h i n g t h a t h a s a n i n fl u e n c e o n t h e

structu re and /or funct ion of the r ipar ian ecosy stem

af fec t s i t s in tegri t y. Ripar ian ecosys tems a re the m ost

sought-a f te r fo res ted areas by both hum an s and o th er

a n i m a l s. An y p l a n t c o m m u n i t ie s a s s o c ia t e d w it h w a t e r,

w h e t h e r t h ey a r e in d e s e r t s , f o ot h i ll s, o r m o u n t a i n s , a r e

considered r ipar i an . They o f fe r ma jor c rea ture com for t s

s u c h a s f o o d , w a t e r, a n d s h e lt e r. Ye t t h e y a r e t h e m o s t

m i s u s e d , m i s u n d e r s to o d , a n d a b u s e d p o rt io n s o f o u r

l andscape .

Ripar ian ecosys tems a re the cana r ies in the coa l mine .

They give wa rnings o f erosion an d pol lut ion problems

t h a t t h r ea t e n f o r es t s t r ea m s , r iv e rs , l a ke s , a n d o c ea n -

f ront s ac ross the Nat ion .They fur ther w arn tha t wh en

w ater qua l it y is impa c ted , the funda men ta l eco logy is

deeply disturbed.

Al l ac ross th e count ry , th i s Nat ion s r ipar ian areas fl our i sh

w i th bount i fu l popula t i ons o f w i ld l ife an d d iv erse p lan t

comm uni t i es . They serv e as a c lassroom fo r complex

eco logy and sh ow h ow in ter re la ted a nd in terdependent

ecosys tems a re . Ev en the m ost innocent o r inv is ible ac t s

im p a c t t h e r ip a r ia n e c os y s t e m a n d , u l ti m a t e ly , t h e w a t e r

w e dr ink . Ex am ples o f th ese d i srupt iv e ac t s inc lude

fer t il iz ing f arm l and s ; mow ing bes ide lakes , r iv ers , an d

s t ream s; remov ing shrubs a nd t rees ; cons t ruc t ing a ccess

roads an d t r a i ls fo r recrea t ion , logg ing , an d mining ;

fis hing f rom s t ream ban ks ; cam ping a t the w ater s edge ;

an d o th er recrea t ion a c t iv it i es .


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THE RIPARIAN ECOSYSTEM

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At the sam e t im e , w e t ru ly v a lue ripar ian ecosys tem s

m ore tha n a ny o ther t ype o f fores ted env ironmen t . They

o f fe r recrea t ion oppor tuni t ies th a t a re pa ra l le l t o n one .

They are impor t an t fo r fl ood m i t iga t i on ; wa ter qua l it y

cont ro l; an d regul a t ing the mov em ent o f wa t er, sed iment ,

m inera l s , an d woody debr is be tween te r res t r ia l and

aq uat i c ecosys tems. They o f fe r cr it i ca l ha b i t a t an d food

sources to a d iv erse popula t i on o f w i ld l ife , inc lud ing fi sh ,

f o w l , a n d p l a n t s p e ci es , a s w e ll a s t o h u m a n s .

Riparian Integrit yThe s t ruc tura l a nd func t iona l cha rac ter is t i cs o f the

r ipar i an ecosys tem are the key links to maint a in ing

ecological integri ty. Qui te o f ten r ipar ian forests a re

descr ibed as lan d and v ege ta ted areas a ssoc ia ted w i th

l a ke s , s t re a m s , r iv e rs , a n d w e t la n d s t h a t h a v e co m p l ex

ecosys tems a nd prov ide food , lodg ing , an d t r av e l co r ridors

fo r bo th a qua t i c and te r res t r ia l spec ies . The r ipar i an

concept sugges ted here i s b roadened to inc ludesurrounding infl uences .

The infl uences on th e r ipar i an ecosys tem should be

v iew ed topograph ica l l y f rom upst ream to dow nst ream ,

f rom upslope to downslope , f rom subsur face through the

v egeta ted canopy , an d ov er t ime . This i s be t te r ex pressed

a s lo n g it u d in a l , la t e r a l, v e rt ic a l , a n d t e m p o ra l i n fl u e n c e s.

The long i tud ina l infl uence ex tends th e l eng th o f the

s t r e a m .

The l a te ra l infl uence beg ins in the w ater body an d

ex tends through the r ipar i an v ege ta t i on , through the

t r ans i t i ona l eco tones , in to the uplan d fo res t or d ry lan d

v ege ta t i on , to the po in t w here ov er lan d fl ow (runo f f ) i s

ini t iated.

The v er t ica l infl u ence ex tends be low the dry-season

w a t e r t a b le a n d u p t h r o u gh t h e c a n o p y o f m a t u r e

v eg e t a t io n . In c e rt a i n e c o s y st e m s , g ra s s m a y b e t h e

na tura l ly ma ture vege ta t i on ; in o thers , i t may be cac t i

or scrubby trees.

Tempora l infl uences a re chan ges to th e ecology over t im e.


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Ripar ian areas a re no t t ied to a s e t num ber o f m eters (m )

from the s t ream but r a ther to changes in v ege ta t i on

types , so i l mo i s ture , an d o th er eco log ica l charac ter i s t ic s .

I f the s t ruc ture o r func t ion i s com promised , the conse-

q u e n c e s m a y b e c o m e a p p a r e n t i n h a b i t a t d e g ra d a t io n .

A Diff erent Planning ApproachA di f ferent p lan ning approach m an dates a c l ear

de l inea t ion o f r ipar i an charac ter i s t ic s through ac tua l

fi e ld assessm ents . In the ear ly s t ages o f pro jec t p lan ning ,

a fi e ld assessm ent conduc ted by a t eam o f speci a l is t s

can l ead to a c l ear i dent ifi ca t i on o f the r ipar i an ecosys tem

an d the out s ide infl uences tha t cont r ibute to it s hea l th

or infi rmi ty .The fi e ld as sessmen t c lear l y defines w hich

eco log ica l func t ions an d processes must rem ain

undi s turbed dur ing and a f t e r const ruc t ion pro jec t s , o r

during o th er groun d disturbing act iv it ies in th e forest ,

such as l ogg ing , graz ing , o r recrea t ing .

Po tent ia l im pac t s (l ong itud ina l , l a te ra l , v ert i ca l, an d

tempora l ) to w atershed a nd r ipar ian func t ions are

d i scov ered in t he ea r ly p l an ning ph ase . Al terna t i ves

to protect ecological funct ions ca n th en be developed.

Assessmen t a nd pro tect ion o f r ipar ian charac ter i s t ic s

autom at i ca l ly become a par t o f the p lan ning and d es ign

processes.

Structure and FunctionRipar ian ecosys tems a re the most im por t ant l ink betw een

t h e u p la n d f o re s t a n d t h e a q u a t ic h a b i t a t w i t h a u n i q u e

ar ray o f func t ions in the na tura l env ironmen t . Thest ruc ture and s era l ages o f the r ipar ian fo res t a re

complex an d d iverse.

Canopies o f l a rge t rees mesh to c rea te a m icroc limate

tha t func t ions to coo l the r ipar i an ecosys tem, ma int a in

t h e w a t e r t e m p e ra t u r e , a n d s h e l t er w e t a r e a s . In t h e

absence o f t rees , l ow -grow ing p lan t s an d grasses prov ide

sha de as do undercut banks . Canopies o f r ipar i an fo res t s

produce part iculate m at ter , pr ima ri ly leaf li t ter .This is an

impor t ant energy base fo r a qua t i c food w ebs . Pa l ik (1998)

found th a t one-th i rd o f lea f l i t t er in s t reams comes f rom

m o r e t h a n 3 0 m a w a y .

Li t t e r an d s t a nd ing b ioma ss a re a l so necessary fo r so il

regenerat ion. Without th e cycle o f li t ter an d biodegrad ing,

fl o o d i n g , a n d p l a n t g ro w t h , t h e s o il w o u ld n o t b e

replenished . Wi thout so il , p l ant s can no t g row ; w i thoutp l ant s , the so i l i s wa shed aw ay .When so i l i s impai red o r

the topso i l i s threa tened , p l ant s a re less p lent i fu l, hav e

s m a ll er b a s a l a r ea s , a n d h a v e m o r e s p a c e be t w e e n t h e m .

Such poor vegeta t ion cover leaves th e soi l even m ore

ex posed to shee t run o f f an d eros ion . As l it t l e o r no

mois ture is he ld in the ground , the w ater t ab le becomes

low er, w ater qua l it y su f fe rs , an d few er p l ant s surv iv e .

S t re a m s u r fa c e fl o w m a y c e a s e.

The p l ant s t ruc ture (s t an d ing and dow n), l ea f li t t e r, an d

unev en ground ca pture sed imen t an d s low runo f f by

add ing f r ic t ion to deenerg ize ov erl and fl ow s . For ex am ple,p l ant s w i th fl ex ib le s tems an d rh i zomatous roo t sys tems

li e fl a t a g a i n s t t h e g r ou n d a s fl o o d w a t e rs w a s h o ve r t h e m ,

shie ld ing the bank f rom eros ion . Such p lan t s an d upr ight

shrubs t r ap sed im ent . Tree spec ies s low w ater fl ow, an d

the i r roo t s ho ld the so i l t oge ther. Roo t sys tem s c rea te an

in terwov en s t ruc ture tha t h o lds so i ls toge ther , s t ab i l iz ing

s t re a m b a n k s . Th e y c a t c h a n d h o l d p o llu t a n t s , u s e

phospha tes adh er ing to the so i l and sed im ent pa r t ic les

deposited by runo f f o r fl oodw ater , an d ho ld harmful o r

tox ic subs t an ces in p l ace by m inim iz ing so i l mov ement .

(Natu ral Cha nn el System s 1994)


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Large w oody d ebris (LWD) af fect s th e confi gurat ion of a

s t ream by d iv er t ing w ater fl ow an d fo rming poo ls . The

debr is he lp regula te s to rage o f sed im ent , par t i cu la te , an d

organic m at te r , an d prov ide aq uat i c hab i t a t . (Murphy

1995) LWD also af fect s la keshores by providing a q ua t ic

ha b i t a t and by fo rming na tura l rev etm ents tha t she l ter

the shore , caus ing beaches to fo rm.

LWD is genera ted from several sources. Genera l ly , the

m ain source is f rom l arge t rees f a l ling in to a s t ream w hen

so i l ha s been eroded aw ay f rom th e roo t s by s t ream fl ow.

Murphy a nd Koski (1989) suggest tha t a s m uch a s 50

percent o f LWD orig ina tes f rom w i th in 1 m o f t he s t ream .

Ano ther source ind i ca tes tha t a 30-m uncut buf fe r zone

is needed to m aint ain long-term LWD inpu t . (Murphy

1995) In m at ure an d old-grow th forests in Oregon a nd

Wash ing ton , fo r exam ple, LWD is genera ted f rom w i th in

20 m of the strea m . (Dol lo ff 1994) In ar id c l im at es, w oody

debr is i s genera ted by shrubs ca t ching on a nd p i ling upaga ins t a rock or outc ropping a nd f rom sporad i c s t ands

o f t rees such as co t tonw ood o r green ash .

Ripar ian ecosys tems regula te n o t only the m ov ement

o f wa ter be tween te r res t ri a l an d aq uat i c ecosys tem s,

b u t a l s o t h e m o v e m e n t o f n u t rie n t s , s e d im e n t s , a n d

par t i cu la te o rgan ic ma t te r. Floodpl a ins , an o ther

impor t ant pa r t o f the r ipar i an fo res t , t r ap sed im ent an d

par t i cu la te o rganic ma t te r out s ide the a c t iv e chann e l

dur ing ov erbank fl ows . Wi thout th i s access r ipar ian

func t ion dec lines , as does s t ream ban k s t ab i li t y. (Swa nson

et a l . 1982; Harm on e t a l . 1986) Non-fl oodpla in fo res t st r ap sed iment in over lan d fl ow s , be fo re they enter the

aq uat i c sys tem . Tree bo les , coarse w oody debr is ,

herbaceous v ege ta t i on , an d l it t e r a l l t r ap sed iment in

overlan d fl ow. (Pal ik et a l . 1998)


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STRUCTURE AND FUNCTION

The riparian ecosystem is the most important link between the upland ecosystem and the aquatichabitat. The structures of the riparian ecosystem are complex and diverse and, as such, providean array of functions that are typical only of that ecosystem.


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Canopies of large trees mesh to create a microclimate that cools theriparian forest beneath. Canopies provide cover.

Root systems create an interwoven structure that holds soils together,stabilizing streambanks.

LWD affects the configuration of a stream by diverting flow and formingpools. It helps regulate storage of sediment and particulate and organicmatter and provides aquatic habitat. (Murphy 1995) It also promotes theprotection of lakeshores and the formation of beaches.

Leaf litter and standing biomass are necessary for soil regeneration.Without the cycle of litter and biodegrading, flooding, and plant growth, thesoil would not be replenished.

Riparian vegetation is an important food source for both animals andbenthic macroinvertebrates, and is used as travel corridors for certainspecies. (Forman 1995)

Floodplains trap sediments and particulate organic matter outside theactive channel during over bank flows. (Swanson et al. 1982; Harmon et al.1986)


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Roots Capture overland flow and nutrients .

Interwoven infrastructure

Remove nitrogen from soil.

Stabilize banks by holding the soil together.

Trap and retain pollutant s.

Use phosphates adhering to soil and

sediments.

Soil Holds moisture.

Offers a grow ing medium for plants.

Promotes good w ater quality by acting asa filter.

Canopy Provides food.

Trees, shrubs, grasses

Creates microclimates

Shade

provides cool forest.

provides cool w ater. shelters wet areas.

Creates migration corridors.

Provides shelter and protection.

Floodplain Traps sediment and part iculate matter

during floods.

Slows velocity of flood waters.

Holds nutrients and sediments deposited

during floods to enrich soil.

STRUCTURALCOM PONENTS FUNCTION EXAM PLES

Structure and Function Chart

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St anding and dow ned A ids w at er infi lt rat ion by slow ing flow .

vegetation, foliage,

branches, leaf litter,

uneven ground, and Prov ides bank prot ec tion plant s lay againststream substrate banks during high flow s.

Provides habitat.

Reduces near bank velocity and redirects

flow.

Traps sediment by slow ing down and

stopping runoff and floodwaters

(the sediment drops out).

La rge Woody Debr is (LWD) A ids i n floodp la in deve lopment .

large trees, tree branches,

s hr ub s cau gh t in s tr ea ms , an d A ff ec t s:

log jams formation of pools and riffles

formation of beaches and

seedbeds on lakes.

Provides habitat.

Provides resting and hiding cover for fish.

Stores sediment and organic matter.

Lit ter Provides food and habitat :

l eav es , tw i gs , n eed les , B en th ic an d m ac ro in ver teb rates f eed o n li tt er.

blossoms, seeds, snags,

rotting logs, and tree cavities

Provides food for fish and other aquatic

species.

Insects incubate on plants, then drop into

w ater as food.

Biodegrades into new topsoil.

St re am , ri ve r, lak e b as in , Car ri es aw a y or im po un ds ex ces s w a ter.

w etland, vernal pool, and

ground w ater level Provides food and w ater for anim als.

Water percolates into streams during low

flow periods.

Affects the microclimate.

STRUCTURALCOM PONENTS FUNCTION EXAM PLES

Structure and Function Chart

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Nonfunct ioning Riparian EcosystemsFai l ing r ipar ian ecosys tems ca nn o t buf fe r s t ream s aga ins t

mu d an d po llu t ant s f rom runo f f an d fl oods . These f a i led

areas d o no t h av e the res i li ency o f hea l thy p l ant s to ho ld

so i ls in p lace , enab l ing s t ream ban ks and l akeshores to

rebound a f t e r a fl ood .

Chan ges in th e na tura l d ischarge r a te o f lakes , r iv ers ,

an d s t ream s can cause th e wa ter t ab le to d rop . Li t t le o r

no fl ood ing is de t r imenta l t o ripar ian v egeta t i on . As the

w ater t ab le drops , r ipar i an p l ant spec ies d ie, a l l ow ing

upland p l an t spec ies to m ov e in . These upl and spec ies do

no t fi l t e r out tox ins o r absorb wat er as w e ll as the r ipar ian

pl ant spec ies do . The upl and p l ant s a re no t equipped w i th

t h e t e n a c i o us r o o t s y s t em s t h a t h o l d t h e s t r ea m b a n k s

toge ther and w i ths t an d the im pac t s o f fl ood ing .They do

no t h av e the h ab i t a t v a lue for w i ld l ife o r aq ua t i c l ife

found in hea l thy r ipar i an ecosys tem s. When the r ipar i an

s t ruc ture is comprom ised , the ba nks w i ll beg in to f a i l .

A m inima l ly func t ioning r ipar i an ecosys tem can no t do

i t s job o f ca t ching sed iment be fo re i t en ters a s t ream . I t

i s o f the u tmost im por t ance to ho ld so i l i n p lace , to t r ap

sed iment be fo re i t reaches the s t ream , an d to ho ld fl ood-

w aters on a fl oodpla in to a l l ow the sed iments to se t t l e out

be fo re the nut r i ent s an d po l lu t an t s they car ry enter the

s t r e a m .

These tw o photographs show upstream and dow nstream damage caused

w hen a road installation interrupted flow.

Upstream

Downstream

The fo llow ing pho tographs dem onst ra te w ha t can ha ppen

w hen t he in tegr it y o f r ipar i an ecosys tem s i s compromised .

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The area surrounding the

Oconee River, in Georgia, w as

cleared and planted in cotton up

to the edge of the river. A

succession of floods ended

agriculture and drove the

farmers out. In the 1930s, the

native hardw oods and riparian

plant species began to grow

again, and fish began to

repopulate the riv er. The banks

carry the scars of flooding.

The South Fork of the Flambeau

River was altered by logging

and log drives during the 19th

century. Just upstream from this

site w as a dam built specifically

to hold w ater and logs; a

sufficient burst of water was

necessary to transport massiveamounts of w ater and logs

dow nstream. (The rivers

gradient is 0.057 percent.) This

tore up the riverbanks.

Shorelines have been reforested

w ith nonnative pine plantations

that lack riparian root

characteristics.

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These three photographs show trail damage leading to and alongside the Situk River, AK. The area is a temperate rain forest .

Although soil on this trail is a sandy loam and gravel composition, it is so

compacted that w ater will not percolate.

Anglers have trampled and loosened the ground, exposing the roots of

riparian plants and causing soil to erode into the river.

Eventually, trees topple over into the river, releasing more soil and leaving a hole in the bank.

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Explori ng Riparian At tributesAl though r ipar i an fo res t s can be found in a lmost a ny

l andsca pe , a l l hav e the fo l lowing a t t r ibutes :

Water a bov e and be low th e ground sur face .

Water-dependent p l ant s , ev en i f they a ppear to be a l iv e

only par t o f the yea r.

Abili ty to support a grea ter biodiversi ty o f plan ts a nd

s t ruc tura l complex it y as com pared to ad jacent a reas .

This is a second growt h

hardwood forest; riparian

understory is hobblebush,

striped maple, mountain wood

sorrel, painted and red trillium,

ferns, and currant. A spruce/fir

forest is visible in the upland.

Zealand River, W hite M ountain

NF.

M ixed conifer, hardwood forest

on the t idal Neuse River.

Croatan NF.

Avai lable food sources.

Periodic flood ing.

The fo l lowing ph o tograph s f rom v ar ious wa tersheds

across the count ry i llus t ra te cha rac ter is t i c s comm on to

r ipar i an ecosys tem s.

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Pipestem is the small tree in the

left foreground. Background

trees include hophornbeam, red

maple, sw eetbay, redbay, red

mulberry, sw amp laurel oak, and

w ater oak. Leaning across the

creek is a cabbage palm (future

w oody debris). Stream at

Juniper Springs , Florida. Ocala

NF.


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Choctafaula Creek drainage

supports remnants of the

swamp chestnut oak

cherrybark oak ecosystem

w hose plants include w ater oak,

w illow oak, sugarberry,

American elm, river birch,

sycamore, red maple, yellow

poplar, green ash, swit ch cane,

needle palm (endangered

species) bluestem (spp

andropogon), dwarf palmetto

grasses, high bush and low

bush varieties of blueberry, wax

myrtle, dogw ood, blackberry,

and muscadine. Tuskegee NF.

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The upland to the right is mixed

deciduous/coniferous forest,

w ith w illow s near the w ater. On

the left is lowland mixed

hardwood and shrub. At w aters

edge is primarily reed canary

grass. South Fork of the

Flambeau River, Chequamegon

NF.

Aspen and alder can be seen on

the left and jack pine and alder

on the right of this shallow lake.

Sedges rim t he w ater and

yellow w ater lilies grow in it.

Dead flooded timber, aspen, and

red pine can be seen in the

background. Chippewa N F.

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Woody draw in grassland.

Typical t rees are green ash and

American elm with an

understory of western

snowberry, W oods rose, spiny

currant, Saskatoon serviceberry,

silver buffaloberry, common

chokecherry, Am erican plum,

haw thorn, and raspberry.

Badland s N P.

Sheep Creek runs through this

wet meadow ecosystem. The

meadow grasses are sedges

and reeds. Lodgepole pines are

in the foreground of this m ixed

conifer watershed. Wallowa-

W hitman NF.

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Grasses and sycamore

streamside at M adera Canyon

Recreation Area, Coronado NF.

This riparian community is

termed Interior and California

Riparian Deciduous Forests and

Woodlands. The deciduous tree

species are sycamore, ash,

cott onw ood, Arizona alder,

Arizona w alnut, and w illow. The

upland communities are Great

Basin Conifer Woodland,

jun ipe r-pi nyon; Relic t Conif er

Forest and Woodlands, Arizona

cypress; and Interior Chaparral,

shrub live oak, desert

ceanothus, and manzanita.

Sedona Creek, Coconino NF.

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The tops of sycam ore and

cottonw ood trees are visible in

this photograph. They grow

alongside the stream and up its

incised banks. Madera Canyon

Recreation Area, Coronado NF.

The east-facing slope to the left

is inland sage scrub and

chamise; the w est-facing slope,

to the right above the creek, is

scrub oak chaparral. Arroyo

willow scrub grows along the

creek. Pine Creek, Cleveland NF.

USDAF

orestService

USDAF

orestService


20/20


M endenhall Glacier is in the

background and is reflected in

this post-glacial successional

bog. Plants are w illow, alder,

spruce, and sedges. Tongass-

Chatham A rea, Juneau N F.

Temperate rain forest. Hemlock,

Sitka spruce, and alder line this

creek. Devils club (the large leaf

on the left near the w ater) and

berries are visible in the

understory. Tongass-Sitkine

Area, Tongass NF.

USDAF

orestService

USDAF

orestService

A Soil Bioengineering Guide - Chapter2 - The Riparian Ecosystem

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