Ecology BIO C 322 Soil Ecology Fire Ecology

Ecology – BIO C 322 Soil Ecology Fire Ecology

Soil Ecology • Pedosphere, Pedology, Pedogenesis. • Pulverized rock + Org matter (remains of life) • 45% minerals, 25% water, 25% air, 5% org. • Formed due to action of climate & organisms (vegetation & microbes).

• “Hotspots” of metabolic activity in soil: microbes in region surrounding roots (rhizosphere), wastes, other org material. • 90% of activity in “hotspots”, occupying 10% of soil volume.

Soil Texture: Sandy, Silty or Clay Soil

• Soil Water: Depends on soil texture. - Sandy soils: porous, good aeration; little water retention, nutrient deficient. - Clay soils: Poor drainage, water logging. • Characteristics of most fertile soils? • Soil Air: Less O 2, more CO 2 compared to atmospheric air.

Factors affecting Pedogenesis • Climate: Physical weathering Rain, ice, temp. - Chemical weathering Rain containing acid? ? • Organisms: - Blue-green algae Metabolic waste Chemical weathering. • Topography: Overall pedogenesis slow in cold, upland areas. Why? • Kind of parent material & time.

Snails Physical ingestion for lichen consumption.

Soil Profile / Horizons • A: Top soil: - A-0 (litter), A-1 (humus = Partial decayed org matter humification) - Small arthropods (shredders) & microbes (bacteria & fungi) • B: Mineral soil; - Org compounds Decomposition Inorg (Mineralization) - Leached from ‘A’ by water flow. • C: Unweathered / partially weathered parent rock

Humus • Detritus intermixed with soil. • Colloidal in nature (not homogenous). • Negatively charged (micelles of humic acids & clay) Prevent leaching of cations Determine cation exchange capacity (CEC) of soil.

Soil Calcification • Calcium bicarb dissolves in water, leaches down. • At 0. 5 -3 metres depth, precipitates. • A “hardpan” forms through which plant roots, animals & water can’t penetrate. • e. g. parts of North India

Pygmy forest on mineral “hardpan”

Grassland vs Forest soils • In grassland/prairie soils, rapid humification. - Thick humus layer (black). - e. g. 600 tons / acre • In forest soils, slow humification. - Narrow humus layer. - e. g. 50 tons / acre

The Role of Earthworms • Imp agents in soil mixing. • Ingest org material Through movement & egestion, cause mixing with mineral part. • Vermiculture & vermicomposting.

Fire Ecology • Imp in shaping history of vegetation in terrestrial ecosystems. • A valuable ecological tool. • Kinds of climate susceptible to fire: – Hot, dry summers; low humidity; equatorial regions. – e. g. some grasslands in US, African Savanna (grasslands with scattered trees), chaparrals (temperate shrublands), Yellowstone National Park (US)

Fire-type Ecosystems Grassland Savanna Chaparral

Cause(s) of Fire – Natural (such as Lightning)…

…or Human-caused. No Smok. . king !

Types of Fire • Crown fires/wildfires: - Intense; - Destroy entire plant & animal communities. - After fire, the biotic community must start from scratch. • Surface fires: - Not as destructive; - Burns only the litter layer on top. - Favour the development of fire-tolerant ecosystems (e. g. oak forests).

Crown Fire

Surface Fire

Fire – Beneficial Effects • Release of mineral nutrients for recycling / new plant growth. • Light surface fires reduce litter Chances of crown fires less. • Helpful in seed germination (some grasses/ legumes) & release of seeds from cones (jack pine, white pine). • Removal of competition for surviving species. – e. g. Longleaf pine seedlings protected by fire-resistant needles; – In absence of fire, scrub hardwood thrives, outcompeting pine, legumes & dependent animals.

Fire Helps to Release Seeds from Cones in Some Species Jack Pine White Pine

Long-leaf Pine: Protected by Fire-Resistant Needles

Loss by Fire • Destruction of communities. • Soil erosion. • Loss of aesthetic pleasure. • Loss of nutrients (nitrogen) by volatilization.

Adaptations in Fire-tolerant Plants • Resprout species: – More energy into underground storage parts, less into reproductive structures (inconspicuous flowers, little nectar, few seeds); – Quickly regenerate after fire. • Mature-die species: -- More energy into production of abundant fireresistant seeds; -- e. g. Fireweed

Fireweed (Epilobium augustifolium) – One of the First Plants to Grow after a Forest Fire Carpeted bombed areas of London in World War II

An Experience in Western Ghats, Karnataka

• In 1960 s & 70 s, forest Dept initiated chopping of tropical rain forests to plant monocultures of fast-growing eucalyptus. • Project estimates: yield of 14 -28 tonnes of wood per hectare every year. • Realized yields: 1. 5 -3 tonnes/ha/year. • Failure!! Why?

Reasons for Failure - Careful trials not conducted. - Tropical forest soil poor in nutrients. - Soil erosion due to forest destruction. - Rapid invasion by new weeds (Eupatorium) that fuelled major fires in summer. - Finally, after eucalyptus did grow, fungal attack (pink disease) wiped out the tree species.