Dynamic Earth 4-6

What is a slope>

• Slopes are the basic elements of landscapes – Up to 90% of land not under oceans or ice are hillslopes – Source of sediment and nutrients • Heavily managed • Source of hazards • A key focus of much theoretical and empirical research.

Factors affecting slope processes-

Tectonic activity— endogenic

nature of materials of slope

slope angle/ relief

weathering

vegetation — exogenic

When does mass movement occur and what is the equation

Mass movement occurs when stress > strength

when B is increased N=S and forces are balanced

Angle B increased further N<S- Risk of movement

What is sheer strength

Shear strength is related to cohesion and effective normal stress (σ) by the Coulomb-Terzaghi equation:

𝑆𝑆 = 𝐶 + 𝜎 tan𝜑

SS = shear strength of slope material

C = cohesion σ = effective normal stress tan

φ = coefficient of internal friction

Factor of safety equation

Shear strength / Shear stress

Where safety factor > 1.3, slope is stable

Where safety factor < 1, slope is actively unstable

Where safety factor 1 – 1.3, slope is conditionally unstable

What are the contributing factors of slope instability

Shear stress factors- Removal of lateral support, loading of slope, lateral pressure and transient stresses

Reduced shear strength factors- weathering, changes in pore-water pressure, changes of structure and organic effects

What is the classification fo mass movements

Mass movements are typically classified based on:

▪ the type of movement

▪ the type of materials involved

▪ the rate of movement

▪ the volume / size of materials

Speed of mass movements

This is called creep

Creep is the very slow downslope migration of soil and loose rock fragments. One cause of creep is frost wedging. Freezing lifts particles at right angles to the slope, and thawing allows the particles to fall back to a slightly lower level. Thus, each cycle moves the material a short distance downhill.

Rockfall (M/S)

Individual blocks drop in a free fall from a cliff or steep mountainside. Can be highly destructive. Limited transport distance. Facilitated / triggered by a range of factors (temperature, freeze-thaw, exfoliation, weathering, tectonics).

What happenned in Chamoli (2021)

A large rock and ice avalanche (27,000,000 tonnes; 76,455,495 m3 ) Sourced from a steep rock wall and hanging glacier

> 200 fatalities, dam collapse

“…rapidly transformed into an extraordinarily large and mobile debris flow that transported boulders greater than 20 meters in diameter and scoured the valley walls up to 220 meters above the valley floor. (Shugar et al. (2021)

Preparatory factors ▪ Steep slope (35°) and height difference (~3700 m) ▪ Rock (80%) and ice mixture (20%) → potential for liquefaction ▪ Fractures within the rockwall ▪ Climate change e.g., degrading permafrost or glacier shrinkage (uncovering/destabilising mountain flanks) ▪ Geological weaknesses (weathering) Triggering factors ▪ Pore-water pressures/freeze thaw ▪ Earthquake?

What does senecent mean

old/ aging

What are the key ingredients in trees

Leaves- Photosyntheisi, carbon fixation, contain: chloroplasts and stomata

Wood- Growth and water transport- Xylem- Cellulose and lignin

Roots- Anchorage and nutrient acquisition- (mycorrhizare)

Facts about forests

Dominant terrestrial ecosystem on Earth-

30% of the land area

75% of terrestrial primary production

80% of Earth’s biomass

80% of Earth’s Terrestrial biodiversity

Impacts forests have on the Earths system

Biological – ecosystems, biodiversity

Biophysical – land cover and climate feedbacks

Biogeochemical – carbon, nitrogen, nutrient cycles

What value to forests bring to us

Ecological services  Provisioning services  Regulating services  Cultural services

What is dieback?

“an episodic event characterised by premature, progressive loss of tree and stand vigour…”

 “…without obvious evidence of a single clearly identifiable causal factor” (Ciesla and Donaubauer, 1994)

 Synonyms: decline, forest dieback, stand level dieback, canopy dieback

What are the symtoms of die back>

 Reduced growth

 Chlorotic (yellowing) foliage

 Death of twigs and branches  Root necrosis  Tree death

Tree-to-Tree vs. Salt-and-Pepper

 Tree-to-tree dieback – many adjacent trees affected

 Salt-and-pepper dieback – dying trees in a matrix of healthy trees

Eucalyptus Marginata

 “Jarrah dieback” since 1940s in SW Australia

 Crown decline, foliar wilt, root death, tree mortality

 20,000 ha / yr affected in 70s and 80s

 Dieback also reported in >50 other species

What is Fraxinus Excelsior (Common ash)

Chalara ash dieback in Britain since 2012.

Olea Europaea (olive)

Xyella Fasatidiosa- Bacterial Pathogen of olives

Originating in the Americas, discovered in 2013 in Italy then Corsica in 2015 and spain in 2017

What are the drivers of Dieback

Climate stress- higher temps, trade off for less water and effective photosyntheisi, long term stress and acute injury

Pests and pathogens- Native and invasive

Soil degradation

fire regimes

Pollution- Acid rain

Human land use- Summer heat, disrupted seasonal cycles, storms and rain fall

hydrological changes

Competition and overgrowth

How to categories causes of forest dieback

Biotic or abiotic

Natrual or anthropogenic

Chronic or episodic

Internal or external

 Healthy trees shouldn’t die  Stress generally precedes dieback  Stressed trees more likely to die from secondary effects that aren’t fatal to healthy trees

Synergistic effects of forest dieback

Synergy: interaction of two or more agents to produce an effect greater than the sum of their separate effects

Consider: Drought stress + bark and beetle attack

acid rain _ soil nutrient leaching

Fertilisation + insect defoliation

What is the conceptual model for dieback?

 Predisposing, Inciting and Contributing Factors  Predisposing: long term factors that weaken trees  Inciting: short term physical or biological damage/injury  Contributing: ongoing factors that ultimately kill

Mountain pine beetle

 Dendroctonus ponderosae  Bark beetle (subfam. Scolytinae)  Native to western North America  Life cycle depends on pine trees  Inhabits multiple Pinus species, including P. ponderosa, P. contorta, P. flexilis…

What kills them>

Blue stain fungus

Symbiosis with MPB

Prevents healing of wood tissue damage

 MPB is a native species

 MPB prefers mature and old trees, and should help to remove weak individuals

 Cold temperatures in mountain areas should limit the size and activity of MPB populations

 Natural forest regeneration cycles should limit the number of suitable trees for MPB

 Largest epidemic of MPB in history

 Extending from Yukon Territory to New Mexico

 13 million ha (130,000 km2 ) of trees killed in British Columbia

 MPBs migrating upwards (elevation and latitude)

 Ongoing for over a decade

Synergistic factors in MPB Epidemic

 Wildfire reduction – higher proportion of old trees

 Drought stress – trees more vulnerable, internal defence mechanisms weakened

 Warming temperatures

 Warmer winters – greater overwintering survival of MPB

 Warmer summers – range extension into new areas (with lower genetic resistance to MPB)

 Longer summer season – larger window for flight and attack + changes to reproductive cycle

What are the impacts of forest die back the on the ESS

 Biodiversity  Vegetation composition  Ecosystem function

 Consider MPB forest dieback…  13 million hectares of MPB-killed trees in B.C. = 900 million tons of CO2 into the atmosphere = 5 x annual transportation emissions of Canada!-  Whole regions shift from carbon sinks to sources  Positive feedbacks for climate change

 Deeper snowpack in dieback areas  Faster spring melting  Changes to stream discharge, flooding risks and water resources

How to combat dieback?

 Monitoring programmes

 Phytosanitary inspections

 Containment of dieases – transport restrictions, e.g. DEFRA

 Treatment of diseased individuals / patches

 Destruction of diseased individuals

 Irrigation / nutrient regulation schemes

Different solutions at different spatial scales Prevention and management require scientific knowledge of the causes of dieback

What are wetlands

They are a presence of water with unique soil conditions and support unique biota

They have a deoth and duration of flooding, with a varying level of species, location and size

What are the different types of wetlands?

Marshes- frequently/ continually inundated, herbaceous plants, mineral substrate, freshwater saline, high in nutrients

Swamps- Permenantly saturated, trees and shrubs, more organic, freshwater, saline or brakish water, high in nutrients

Peatlands- permenantly saturated, highly organic, freshwater, rain fed, low/ high nutrients

There are two types of models for wetlands in the landscape

Transitional (Deepwater aquatic system) and isolated

Why are wetlands important

Providiing for all the ecosystem services

including- Cultural, regulating, supporting and provisioning services

Wetland degradation example

Mangrove destruction for shrimp farming in southern and SE Asia

Salt marsh dies in the UK and the USA

Drainage of tropical peat swamp forest for palm oil and wood pulp

Disconnecting rivers from floodplains

Clearing boreal peatlands for tar extraction in Canada

What are the wetlands protection on a global level?

Wetlands international, Sustainable development goals

Wetlands protection- regional/ national

ASEAN Programme for sustainable management of Peatland Ecosystems

IUCN- peatland programme

Wetland protection on a local scale

Moors for the future

Yorkshire peat Partnership

Pennine Peat life

What is wetland hydrology>

hydroperiod, water budgets, and biotic feedbacks

and they influence the functions of vegetation composition, primary productivity, the buildup of organic material, nutrient cycling, and availability.

What is a hydroperiod>

The duration and frequency of inundation or flooding in a wetland, essentially the amount of time a particular area of land is wet

What does the hydroperiod show

Balance between the inflows and outflows of water

Surface contour of the landscape

Subsurface soil, geology, and groundwater conditions

What is the correlation between hydroperiod and plant species richness

The increase in hydroperiod means an increase in plant richness

What is the function of wetland hydrology> w

Accumulation of organic material

Nutrient cycle and availability

What does deeper soils result in?

Increasing decomposition/ humification with depth

how do you knwo the minerals that are in soils

Oxidised minerals go orange-tinted

hydrophytic adaptation

Structural/ morphological - includes Adventurous, aerenchyma, stem hypertrophy, and phytotrophs.

physiological- pressurised gas flow, oxygenation, low water uptake, anaerobic respiration.

Whole plant strategies- timing of seed production, buoyant seeds, vivpary, large persistent seed bank

What does succession look like in wetland vegetation

Terrestrialisation and paludification

What chemicals does wetland biochemistry include?

Carbon, nitrogen and sulphur

Mangroves and swamps

Tropical/ subtropical wetlands, inpenetrable woody vegetation, unconsolidated peat deposits, adaptations to flooding, salinity, resilient deiverse ecosystems Mangroves are found in coastal regions in lots of asia and North East south America

Mangroves for coastal protection-

Protects against- tsunami waves, storm surges, storm winds and stems and leaves can attenuate larfe waves. Root structures and steep continental slopes, reefs may reduce of increase wave destructiveness depending on form

Peatlands

Accumulated layer of organic matter at the surface

Permanently waterlogged

Semi-decomposed plant material

Long-term carbon sequestration and storage

Diverse ecosystems

Found in the Northern hemisphere mostly- lots in Canada and Russia

Peatlands and flood control>

Erosion increases catchment flashiness

Increased drainage density and connectivity

Peatland restoration

Lag-time increases

Peak flows decrease

no change in rainfall: runoff

What are artificial wetlands

Nature-based Solutions

actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits

E>G> Laurel Run wetland, Maryland USA

Wetlands and folklore include-

Will-o-the-wisp

Monsters and bogeys

The curse of Tiddy Mun