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Changing Forest Habitats^ Succession - FOREST INSIGHTS^ Section 4
Glacier Bay Time MachineStages of SuccessionFire DesignsBoreal ForestCoastal Rainforest
PrimarySuccessionSecondarySuccessionBoreal ForestPrimarySuccession
SecondarySuccessionSecondarySuccession– no permafrost– permafrost
WildlifeFollow the HabitatCoastalRainforestBoreal Forest
One of the differences between living andthings grow and change in a predictable pattern. Communities of livingthings – ecosystems – also are dynamic and change. nonliving things is that living Succession environment is formed or after an existing environment is disturbed.Succession occurs in all types of ecosystems, from oceans and wetlands describes the patterns of change in ecosystems when a new to tundra, deserts, and forests. Bare Rock to Deep Forest. If we could look back in time, we would see some currently forested lands that once showed no sign of trees or anyother plantsa specific order of plants colonized the barren or disturbed site. (described in the following “Glacier Bay Time Machine). Over time, How Does It Happen? (1) competition,(2) differences in the needs of plants, and How a forest grows and which plants come first or second depends on (3) the effects of the nonliving environment on plants and other living things. Dynamic Wildlife Habitat. As the forest habitat changes, so does the list of wildlife that can call that stage of the forest their home. Where Some Animals Fit in Boreal Forest Succession
Bare Ground Shrubs YoungForest Mature Forest ClimaxForest
Black bear^ Boreal owl
Grasshopper Meadow voleSnowshoe hare PorcupineRed-backed vole Ruffed grouse Brown creeper
FOREST FACT - GLACIER BAY TIME MACHINE Alaska’s Very Own Time Machine As glaciers recede (melt) , they uncover a raw, new land – giving us a glimpse of how our continent looked thousandsof years ago. We can board the glacier “time machine” in Glacier Bay tosee in minutes what took hundreds of years of natural forestgrowth. GLACIER BAY: View 200 Years in a FLASH Historical records show that only 200 years ago in Glacier Bay there was no bay, no forest –just a huge glacier. Now the main glacier has receded many miles, leaving a time-machine record of how forestsdevelop. Year 0: and silt-laden runoff. No plants inhabit this area. Nearest the glacier’s toe, where the ice most recently melted, the land is barren rock Year 10: scattered patches of moss, fireweed, and dryas A short distance outward, where the ice has been gone about 10 years, we see (all pioneer plants ) among the gray rocks. Year 30: other herbs. We walk among alder, willows, and cottonwoods, stepping on grasses, dryas, and Year 50: we are. But we can step over small spruce that are just sprouting. Farther along the glacier’s former path, the alders and cottonwoods are taller than Year 200: encountered a wall of ice, we now see a dense spruce forest covering the land like a greenglacier. Little light reaches the forest floor under the spruce Near Bartlett Cove, where 200 years ago local Natives and explorer George Vancouver canopy so there are few understory shrubs, and thesaplings strain upward to find sunlight. ground cover is mainly moss. Scattered in the dark forest, small hemlock
Firedriving force, especially inAlaska’s is oftenboreal succession’s forest ecosystem. The dry climate,long days and hot summertemperatures create perfect conditions for fires to spread. Born of Fire. In Interior Alaska up to 2 million acres of forest burn every year due mainly tolightning strikes. Foresters at the University ofAlaska estimate that almost every part of the boreal forest burns at least once every 200 years. Patchwork Quilt Fires in Alaska’s boreal forests leap and danceacross the land, burning everything to charcoalin one spot, barely singeing tree branches in another. Succession begins whenever fire passes.• If fire kills trees and removes all the surface organic matter,soil building.forest are liverworts and mosses followed by Pioneer plantsprimary succession begins with in the boreal plants with windblown seeds such as fireweed,grasses, willows, and cottonwoods.
- In places where fire has burned less hotly andsoil remains intact,begins using remnant seeds or any blown in secondary succession from surrounding areas. Plants that grow thefastest and tallest shade out competitors tobecome dominant.
“Stump” the Scientists In Interior Alaska, the pattern ofsuccession is unclear to scientists, even now. There are few maturespruce forests with trees older than200 years even though white Evidence suggests that as the mossy carpet onspruce are long-lived trees. the forest floor grows thicker, it insulates theground and allowsthe surface. Ultimately, all boreal forests might permafrost to rise closer to become black spruce and tamarack, two speciesthat tolerate permafrost. In most boreal forest areas, succession neverreaches “climax” stage because a disturbancestops the clock and starts the process over again Fire Thrives in Mature Forests. As the boreal forest grows, so too, does its for wildfires. A patch of pioneering willows on asandbar is meager food for a lightning strike. But fuel a strike within a mature coniferous forest can starta fire that gets hotter and hotter as it consumestrees, shrubs, grasses, and all the natural litter left by slow decay in cold climates. Mosaic of Succession. The longer a forest has been without a fire, themore fuel it will have – and thehotter it will burn. Where fires are frequent, the forest isusuallysuccessional stages. a mosaic of
FOREST FACTS - BORN OF FIRE FIRE DESIGNS BOREAL FOREST
Primary Succession in the Coastal Rainforest
YOUNG FOREST: 70 to 100^ years after glacialretreat, cottonwoods, redalder, and some willows havereached tree height. A fewtall spruce are present andmany spruce saplings growbeneath the broadleaf canopy. Strawberry, lupine,club mosses, and othersform the^ ground cover
Because many of the treesare deciduous, the wintersnows reach the ground andaccumulate. TALL SHRUB STAGE: Within^ 5 to 20 years after the retreat of aglacier, a layer of organic soil
has developed on somesites. The^ pioneer willow, alder, andsoapberry continue togrow taller. Cotton-wood, Sitka spruce, andother plants begin toinvade the site. Most ofthe shrubs and saplingsare deciduous and donot trap much snow inwinter. The leaflessshrubs slow the winds,however, so several feetof snow may accumulateon the ground. PIONEER STAGE: Common^ pioneerplants^ include dryas,fireweed, willow, alder,and soapberry. Alderand dryas havesymbiotic bacteria intheir roots which takenitrogen from the air.This allows theseplants to grow on soilthat lacks an organicnitrogen-rich layer. Theleaves of these plants,once decayed, form animportant part of the organic soil
layer. Several feet of snowmay accumulate onthe ground inprotected sites inwinter. Strong windswill keep most otherareas snow-free.
CLIMAX FOREST (or Old-Growth): The length of time required varies, butsome scientists estimate
250 to 600 years. On well-drained sites the
canopy
trees are hemlock and Sitka spruce.Many large old conifers have died andfallen. Sunlight reaches the forest floor.Trees of all ages (seedlings, saplings,young trees, and old giants) are present.This forest will replace itself. Shrubs andherbs grow in the filtered sunlightincluding alder, salmonberry, devil’sclub, elderberry, huckleberry, skunkcabbage, false lily-of-the-valley, trailingbramble, ferns, and mosses. Treesbranches are covered with lichens andmosses.^ Snags
are riddled with woodpecker holes. Large branches of oldtrees catch much of the winter snow, sorelatively little snow accumulates on theground.
MATURE FOREST: 150 to 200 years
after glacial retreat, Sitka sprucetrees form the forest
canopy. Because cottonwood andalder trees only live 70 to 100years and their seedlings cannot survive in the shade ofconifers, few broadleafsremain. Hemlock seedlingsare tolerant of the shade andsome grow beneath thespruce. The needles ofspruce are slow to decay, somany litter the forest floor.Relatively few
ground cover plant species can grow amidthese needles and in theshade. Mosses, huckleberry,and wintergreen are oftenpresent. The dense tree canopy^ intercepts most ofthe snow that falls, so thatrelatively little snowaccumulates on the ground.
Areas where
glaciers^ have retreated provide a living laboratory for the study of primary succession. The chart below illustrates the pattern of change after glaciers retreat. Primary succession also occurs on new lands created by
rivers ,^ earthquakes
,^ landslides
, or^ volcanoes
. The patterns on these sites are similar, but pioneer plants may differ.
CLIMAX FOREST (or Old-Growth): Few forests in Interior Alaska survive to thisstage; fire or flood usually turns back theclock.^ After^ 200 years , white spruce trees form the
canopy^ and understory
, spanning all ages from seedling to old giant. At this stage theforest becomes self-renewing. A fewpoplars and birch grow here butseldom live more than 100 years.Their seedlings cannot survive in theshade of the spruce. Dead broadleafsor white spruce fall, creating openingsin the canopy and exposing bare soil.Sunlight reaches the forest floor andnew spruce seedlings start on theexposed soil. The forest floor iscovered by feather moss and somereindeer lichen. Shrubs and herbsthat grow in the filtered sunlightinclude alder, rose, a willow,wintergreen, low- bush cranberry,twinflower, and bunchberry. MATURE FOREST: In^ 100 to 200 years
, the canopy^ is a mixture ofbalsam poplar andsmaller white spruce.Rose, high- bushcranberry, and othershrubs form the understory
. Fireweed, horsetails, and grassesoccur in the
ground cover. When spruce treesdominate the canopy,shade-tolerant mossestake over the forest floor. YOUNG FOREST: In^ 30 to 100 years
poplars and birch havereached tree height,casting too muchshade for sun-lovingpioneer willows andalders. The better-developed soil layerand rarity of floodingallow white spruce tocolonize the site. Roseand high-bushcranberry shrubsbecome more common.
SHRUB STAGE: In^ 10 to 30 years
, willow and alder grow into tallshrubs. Newly createdsoil and frequentdeposits of silt raise theland level so it floodsless often. Now otherplants can invadeincluding poplar, birch,rose, high-bushcranberry, and a varietyof grasses and herbs.
PIONEER STAGE: Only hardy
pioneer plants (willow and alder) take root infloodplains. The rocky base isusually covered with mineralsalts. During high water, thesite may flood. Roots of thewillows and alders help to holdsand and trap more silt fromthe river. Silt combines withdecayed leaf litter to eventuallyform^ soil. Symbiotic bacteria inthe roots of the alder takenitrogen from the air and makeit available to the roots. Thisallows these plants to grow onsoil that lacks an organic,nitrogen-rich layer.
Primary Succession in the Boreal Forest
In Alaska’s boreal forest,
rivers^ often abandon old banks and sandbars to carve new channels. The chart below illustrates the pattern of change on abandoned river sites. Patterns of change would be somewhat similar on new lands created by
glaciers ,^ landslides
,^ earthquakes
,^ volcanoes
, and^ severe forest fires
that burn all organic soil.
Pioneer plants invading each site may differ.
Secondary Succession in the Boreal Forest: Non-Permafrost Sites Wild fire^ is succession’s driving force here. The chart below illustrates the pattern of change after fire on a
well-drained site
. Regrowth following
flooding ,^ insect outbreak
avalanche ,^ timber harvest
, or^ land clearing
would be somewhat similar.
Fire benefits the forest
in ways the other events do not. Fire (1) releases minerals stored in
wood, ensuring a nutrient-rich soil for the next stage, and (2) leaves many standing dead trees –
snags^ – so more animals can occupy the early regrowth stages.
CLIMAX FOREST(or Old-Growth): Some^ 150 to 300 years
after fire, if a site is not disturbedagain, this^
self-renewing
stage will be reached.
Organic soil
is about 5 inches thick. Whitespruce dominate the forest canopy , but some birch, aspen,and poplar may be present. Thecanopy is fairly open, so somesunlight reaches the forestfloor. High-bush cranberry androse are the main tall understory
, though some alder may be present. Low shrubsand^ ground cover
plants are mainly wintergreen, horsetails,and twinflower. Feather mosses,and sometimes lichens, areabundant. There are manyfallen logs and
snags , some with woodpecker holes. MATURE FOREST: From^ 45 to 150 years after fire,^ organic soil
is several inches thick. Amixture of broadleafs andwhite spruce form theforest^ canopy
. The abundance of whitespruce varies amongsites. The canopy is moreopen, so some birch andaspen seedlings andsaplings grow in the understory . High-bush cranberry and rose are themajor tall shrubs; thereare few willows. Lowshrubs and
ground cover plants thrive and includekinnikinnik, lingonberry,Labrador tea, twinflower,fireweed, horsetails, andtimberberry. There arefallen dead trees and afew large^ snags
REGROWTH YOUNGFOREST: From^ 25 to 45 years
after fire, the^ organic soil
layer is at least 2 inches deep. Birches, aspensand/or poplars form a denseforest^ canopy
. If present, the slow-growing spruce aresmaller than the broadleafs.Seedlings of birch, aspen, andpoplar cannot survive in theshade so they are absent. Fewtall shrubs are present exceptfor rose, alder, willows, andhigh-bush cranberry. Labradortea, lingonberry, bunchberry,twinflower, and wintergreen arecommon^ ground cover
plants. Feather mosses are abundant.Most fire-killed trees have fallenand are decaying into the soil.There are a few small
snags.
REGROWTH SHRUBTHICKET: Within^ 3 to 25 years
after a fire, most sites are covered bya variety of shrub and saplingtrees including willows, alder,raspberry, rose, birch, aspen,and poplar. A few whitespruce seedlings start theirslow growth. Fireweed,grasses, horsetails, chimingbells, and rock harlequin arethe most common herbs.There are fallen trees andlarge^ snags,
many with woodpecker holes.
REGROWTH HERBSTAGE: Fire returns the
minerals stored in trees to the soil,creating a nutrient-rich bedfor plant growth. At least aninch of^ organic soil
must remain for regrowth (ratherthan primary succession) tobegin. Seeds and sporesburied in the soil start tosprout. Other seeds blow infrom surrounding areas. Someplants start from roots andstumps not killed by the fire.Common plants includefireweed, wild geranium, rockharlequin, horsetail, chimingbells, raspberry, rose, aspen,birch, willow, alder, andspruce. Mosses, liverworts,and lichens also grow onrecent burn sites. Many
snags will be present if regrowthstarts from a mature or climaxforest site.
Wildlife Follow the Habitat All living things have adaptations or special traits that let them thrive in a particular environment.These adaptations may be structural shape) , physiological (diet, cold- or drought-tolerance) (body size and , or behavioralSome species (finding mates or defending territory) (such as brown bears) have broad habitat. requirements and wide ranges of tolerance forenvironmental conditions, so they occur in manydifferent environments. But species with narrow ranges of tolerance and very specific requirements occur only in specific environments. habitat The list of wildlife found in Alaska’s two forest typeschanges as certain habitats become available duringsuccession. Many animals, however, use more than one stage of succession as habitat, especially indifferent seasons. To determine if an animal could live in a habitatcreated by a stage of succession, ask: Does itcontain the food, shelter, water, and/or space needed by that animal? Nonliving Elements Restrict Users. In early successional stages, for example, the environmentis open and windy. Lots of sunlight reaches theground. The temperatures can change quickly, and rain and snow have a great effect on the plants andanimals. There are often daily and seasonal extremesof temperatures, wind, and moisture. Animals residents are restricted to those that can nest or hidenear the ground. Can I Reach My Food? shrubprovides the dietary needs thicket stage The of moose and snowshoehares. But as trees getolder and taller, both moose and hare are at adisadvantage. They can no longer reach the newbranches. Neither animal is adapted to use mature forests except for shelter.
Snag a Home. and boreal owls nest in cavities in the decaying softwood of snags Birds such as woodpeckers, chickadees, ( standing dead trees ). Their adaptation for cavity-nesting works well in old-growth climaxforests where snags are abundant. In turn, thisadaptation limits their use of earlier successional stages that contain few snags. Fish Need Forests Too. To hatch their eggs, salmon and other fish need (1) streams with a certaintemperature range and amount of oxygen and (2)streambeds of gravel of a certain size. Forests provide cool and clean stream habitat. Trees Protect Stream Habitat. Tree roots hold the soil, preventing erosion. Trees shade the streams, keepingthe water temperature stable. The roots of live anddead trees that protrude into streams provide places for fish to rest and hide. The leaves and twigs thatfall into streams feed the insects that fish eat. The following text highlights some wildlife facts notcovered in the preceding forest succession charts. Forcomplete species reference, check the forest-coded (“F”) Alaska Ecology Card for “Habitat” information. Wildlife in the Coastal Rainforest After pioneer plants start making the soil that allows other plants to follow, wildlife will be able to use thearea. The plants produce food foras insects and birds. Coyotes herbivores and ermine such (carnivores ) move in to feed on these herbivores. Detritivores Close the Cycle. detritivores microscopic organisms) The (^) spores(fungi and of are blown in by the wind,andprocess these of (^) decaybegin (^) andthe not yet a forest ecosystem, and forest animals couldmineral recycling. Thus anecosystem is formed. It is not survive in it, but it is a step toward theestablishment of a forest.
rainforest, spruce and hemlock trees^ In a true old-growth stand of coastalmay range in age from seedlings to 750 years old.
