Plant Ecology - Chapter 21

Plant Ecology - Chapter 21Global Change: Humans &

Plants

Acid Deposition

Automobiles as a SourceNO from cars

Widespread Secondary Air Pollution: Acid DepositionWet depositionDry deposition

Acid Deposition in the U.S.

Acid Deposition, Plants, and Soil


Lowers soil pHAffects mineral solubilityLeach out positively charged ions (K, Mg, Ca) from clay particlesEasily flushed away


Increases concentration of potentially toxic mineralsE.g., aluminumDamages xylem - reduces ability to take in water, nutrients - die from lack of moisture, nutrients


Direct damage to forest tree foliageErodes protective waxes from leaves, needlesLeaches nutrients from leaves


Has resulted in loss of large stands of trees in many different regions around worldCanada, New England, Smoky Mountains



Nearly 70% of forests in Czech Republic have been destroyedTrees in nearly half of Germany’s Black Forest have been impacted


Switzerland has lost 10% of its forestsIncreased chance of avalanches


Large portions of forests in Norway have been lost, especially in southern regions


Correlation between dying forests and thriving ground layer of mosses


Mosses are acid-lovingThick layer holds do much moisture that surface soils become saturatedFeeder roots, tree die from lack of oxygen (drown)


Mosses also may kill mycorrhizal fungiReduce uptake of nutrients


Dense layer of mosses may further acidify water passing through them into soilDissolve more toxic trace metals, leach more soil nutrients


Even if trees somehow manage to survive all these problems, their growth is reduced substantially



Varying effects on crop productivity, but wide distribution


Some evidence for direct damagePotatoes in Canada - damage to foliage, potential uptake of toxins


Coffee plants have shown damage to foliage in some areas


Although much evidence points toward harmful effects from acid rain, some studies show the opposite


Helpful to crops where soil nutrients may be very low - nitrogen-limitedAcidification may release nutrients, allow for greater uptake


Some evidence where crops show now effect of acid deposition, either negative or positiveBalance each other out

Acid Deposition and Aquatic Systems

Fish declines

Undesirable species

Aluminum toxicity

Acid shock

Global Carbon Cycle

Human effects: fossil fuel combustion,cutting and burning of trees

Global Carbon Cycle

Global Carbon CycleIncreasing atmospheric CO2 has brought about a rise in global temperature

Greenhouse EffectCO2 acts like glass in a global greenhouseSlows escape of infrared radiation from earth’s surface

Greenhouse EffectMany other gases are far more effective at trapping heatMethane, CFCs, nitrous oxide (N2O)20-270 X as effectiveCO2 responsible for 2/3 of increase in greenhouse effect

Greenhouse EffectCO2 concentrations increased 21.5% from 1870-1990Increasing consumption of fossil fuels, deforestationDoubling of CO2 concentrations may occur with continued fossil fuel use over 50-100 years

Greenhouse EffectCO2 doubling may increase average global temperature by 2-5°CGlobal temps have increased 0.8°C over last century, 0.6° of that in last 30 years

Major Climate ChangesWorldwide change in patterns of precipitation, storms, winds, ocean currentsEach 1°C increase pushes climatic zones 90 mi N in N. hemisphere

Major Climate ChangesVariable effects worldwide, but greatest changes between 40 and 70°N, in N. Amer. and EurasiaCaused by both warmer temps and increased CO2 (greater forest productivity)

Major Climate ChangesPolar ice sheets and glaciers have been melting, and changes would escalate

Major Climate ChangesSea levels would rise due to melting ice, expansion of warming water4°C increase would cause 0.5-1.5 m rise worldwideFlood coastal wetlands, low-lying cities, agricultural lands

Major Climate ChangesFrequency, intensity of weather extremes would increaseHeat waves, drought, hurricanes

Major Climate ChangesSpeed up decay of organic matterFurther increase CO2 concentrations in atmosphere

Major Climate ChangesWarmer climates spreading northward would bring insect-borne diseases, more pests into areas currently protected by cold temperatures

Major Climate ChangesGrowth rates of many tree species would be loweredRanges would have to shift northwardAt rate up to 10 X greater than they’ve ever done in the pastBirch, sugar maple

Major Climate ChangesStress from pests, disease microorganisms would increaseAdapt faster than tress to changing environments

Major Climate ChangesMore frequent firesForest and grasslandIncreased disturbance: decreased diversity?

Declining Global Biodiversity

300,000 plant species have been described and named1.5 million species of all kindsAt least 5-10 million living species not describedWhat’s out there?


Many large species may be at risk of extinctionBut so may many unknown or little known forms (like mycorrhizae)Also may lose genetic diversity as some populations disappear, losing unique genes


Many current threats to global diversityChanges in land use is greatestDestruction, degradation, fragmentation

Habitat LossOutright loss of habitatVarying degree of disturbance - elimination of important species, soil damage, overgrazing, altered disturbance regime

Biodiversity Hotspots


25 areas - 1.4% of earth’s land surfaceContain half of world’s known plant speciesRegions have lost 88% of original vegetation cover


20 are tropical forests or Mediterranean climates9 are oceanic islands/archipelagos

Long-term isolation - evolution of endemic species


800 species most at risk in 600 locationsMany are areas within biodiversity hotspotsLess than half have any legal protection


Example: Madagascar tropical forests10,000 plant species, 80% endemicRate of loss among highest in world - <10 of forests remain

Deforestation

Losses have been accelerating rapidly in the AmazonRate of loss increased >80% in 1990s

DeforestationBrazil: 17-year period

DeforestationSimilar rates of loss in tropical Africa, southeast AsiaWill disappear in 100 years at present rate

Forest FragmentationEven more dramatic increase in fragmentation - increased edgesPotential increase in herbivory, disease, invasives, decline/extinction of interior species

Threats to Other Communities

Biodiversity losses occur in communities with much lower diversities than tropical forestsNot always the rare species that are affected


American chestnut was once most common and heavily used timber species in eastern U.S.Disappeared because of invasive pathogen


Logging for teak, rosewoodFormerly some of most common species - now becoming rare (high value)


Brazil nuts are example of classic sustainable use of intact rain forestMost important food crop collected entirely from wild trees


Harvesting often done by native peoples“Save the rainforest. Eat Brazil nuts”


Brazil nut trees are dwindling, populations decliningSo much harvest that few or no young trees have developed - no seedsHarvest at present levels will lead to extinction


Even low-diversity ecosystems are not exempt from problemsMany cacti face extinction from amateur collectorsIllegal in many areas, but command high prices with risk of minimal fines


Many orchids are facing the same fate as cactiHigh prices on black market can lead to intense depredation from collectors


Overgrazing by livestock can destroy fragile grasslands, shrublandsMany Arizona grasslands destroyed by grazingDesertification


Overgrazing or overbrowsing has similar effects in other habitatsLow predator numbers, forest fragmentation, suburban protection have increased deer populations


Overbrowsing has had dramatic effects on forest regenerationKills tree saplings


Deer have been implicated in the decline of several species of spring wildflowersTrillium in PASo have non-native earthworms

The Human ImpactLand use changes related to changes in human population size, but also economic and political forcesConcerns in both developed, developing nations

The Human ImpactIn developing nations, habitat loss closely tied to growing populationsExpansion into new areas

The Human ImpactIn developing nations, populations not growingSuburbanization and vacation homes are fragmenting habitats

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Plant Ecology - Chapter 21