Plant Ecology

Major divisions of plants

• Bryophytes

• Pteridophytes

• Gymnosperms

• Angiosperms

Bryophytes

Seedless non-vascular plants

Liverworts, horworts and mosses

Pteridophytes

Seedless vascular plants

True ferns (pterophyta), Horsetails (sphenophyta), Lycophyta

Gymnosperms

Seeded plants

Conifers, cyads, ginko and gnyophyta

Angiosperms

Flowering plants

Dicotyledons and Monocotyledons

Plants and land in: Precambrian (>540mya)

Green algae

Supercontinent Rhodinia

When did green algae develop?

750mya

Plants in the Cambrian and Ordovician periods (540-440mya)

Primarily aquatic

Plantonic photosynthesising algae

Plants in Silurian period (440-410mya)

First land plant development (Cooksonia - oldest known vascular plant)

Plant adaptations to terrestriality

• Prevent dessication = cuticle

• Regilate gas exchange and water loss = stomata

• Vascular distribution of minerals (Xylem and Phloem)

• Support structure (vascular tissue and lignin)

• Anchoring system (roots)

• Fertilisation (wind and insect)

• Dvelopment of seed with a dormant embryo

Plants of the Devonian and Carboniferous periods (395- 286mya)

• First forests (Lycoscopic forests & Calamites)

• start of gymnosperm development

• Dominated by carboniferous swamp forests

• Continuous inundation of the sea in low laying areas (flooding and CO2 sequestion)

Calamites

extinct genus of aborescent trees

related to modern horsetails

Early Carboniferous to Upper Permian (360-260mya)

• Major plant development - evolution of gymnosperms

• >60% global flora = gymnosperms

Evolution of Angiosperms

• First fossil record = ~140mya (Cretaceous)

• Rapid diversification

• globally dominant by the Teriary period (65mya)

• originated at the paleotropics

Evolution of grasses

• Eocene Epoch (Tertiary) ~65-50mya

• presently 10000spp

What percentage of human carb intake consists of grasses?

52%

When did each major group of plants evolve?

Angiosperms - 145mya

Gymnosperms - 362mya

Land plants - 420mya

Quaternary period

2.6mya to present

• 50+ cold/temperate cycles

Most recent iceage

120,000 - 117,000 years ago

Holocene

• The current interglacial warm period

• Since 117,000 years ago

Factors of earth’s orbit that influence glaciation occurance

• Eccentricity - circular to eliplical orbit (96,000yr periodicity)

• Obliquity - tilt of earth’s axis (42,000yr periodicity)

• Precission of equinox - seasons (21,000yr periodicity)

When they all line up, an ice age occurs

What happened to tree genera in North Western Europe during each ice age?

Progressive loss of species

How can plants survive an ice age?

Plant refugia in Southern Europe

• Return north as ice retreats

Paleoecology and how is studied

Ecology of the past -analysis of subfossils preserved in anoxic environments

• Sedimental coring of ice or ocean sediment

• Tree rings dendrochronology

• Fossil pollen analysis

• Macrofossils

• Isotopes and carbon dating

Anoxic Environments

sediments of bogs, coastal lagoons, lakes and wetlands

British Woodland History - Early post-glacial (117,000yrs ago)

• treeless streppe - tundra flora

• Artic/Alpine flora

• Britain still attached to mainland Europe

• Plant migrations from European refugia

British Woodland History - 11,000 -10,000yrs ago

• increase in Juniper, Birch and the later end, Pine

• Cold climate becoming continental

British Woodland History - 10,000 - 8,000yrs ago

• rapid rise in Hazel

• appearance of oak and elm

• continental climate

• lime in the pollen record

Approximately how many years ago did Britain separate from mainland Europe?

8,000yrs ago

British Woodland History - 8,000 - 6,000yrs ago

• climate warm and wet (extremely oceanic)

• ‘wild wood’ forest dominated

What can be found from paleoecology?

• ecological relationships, processes and and environment of the past

• An understanding on how present-day ecosystems formed

• Help in conservation planning

Applications of paleoecology to conservation

• use of methods to directly address current conservation issues

• understand processes underlying the development of present-day ecosystems and biodiversity

• guide future management and conservation

• choose analysis sites to address specific questions

How can paleoecology reconstruct the plant species assemblages and environemnts of the past?

• fossil pollen

• macrofossils

• ‘ancient’ DNA

• charcoal

• fossil beetles (chironomids)

• stable isotopes

Caledonion pinewoods

Case study of major pine declines in scotland

• fossilised stumps in peat bogs date that they were wiped out around 4,400yrs ago

• Many hypotheses for cause of sudden decline

Hypotheses of pine decline in Scotland ~4,400yrs ago?

• Regional climate change

• anthropogenic impact (although not enough people for that large impact)

• volcanic eruption

• pathogenic attack

• change in fire frequency

What did coring and pollen analysis show about the Caledonion pinewoods (Scotland)?

• birch and juniper initially dominated

• then birch and hazel dominated

• pine peaks and then declines ~7,300yrs ago due to broadleaf competition

• 4,400yrs ago shows a blanket of peat and evidence of agriculture

How do the Galapagos have such high biodiversity and high extinction rates?

Human influence is only relatively recent (AD 1535), threatening the species with invasive species, habitat degradation and general human impact

The biome concept

organises large scale ecological variation

large scale framework to classify community in its environment

How are terrestrial biomes distinguished?

vegetation (which is mainly determined by temperature and rainfall)

Define: Biome

A large scale (regional/continental) distinct community of plants and animals, adapted to the region’s physical environment - typically the climax community

How is climate controlled?

how much solar energy is intercepted by Earth and its atmosphere

Global circulation concepts

Driven by Charles and Boyles laws, warm air is less dense than cold air and therefore is pushed up by the higher pressure cold air. The warm air rises, cools away from the earth and drops back down

Coriolis effect

• caused by earths rotation deflecting objects intended direction

• When heat rises it doesnt drop in the same place

• In the northern hemisphere, hot air deflects right

• In the southern hemisphere, hot air deflects left