L2 - Using technology to map habitat loss and fragmentation

Question 1

Previously why has reliable data on global deforestation rates not been reliable?

Answer 1

• Statistics were provided by national governments to UN
• Results inconsistent
• Often incentive to downplay deforestation

Question 2

How has quantifying deforestation rates changed drastically recently?

What are some limiting factors of this technique

Answer 2

Satellite-based optical remote sensing
- Measures flux of solar energy reflected off Earth to space

Must detect energy above background noise
- Increased pixel size (land area) helps
- But tradeoff between spatial and spectral resolution

Question 3

Describe the typical reflectance curve of a leaf

Sketch a graph of % reflectance against wavelength

Answer 3

Strong absorption of visible light (slightly more reflection of green)

High reflection in near infrared
-photons too low energy for plants
- reflectance here depends on leaf structure

Longer wavelengths contain absorbance features from specific molecules e.g. lignin + cellulose

Question 4

Describe the longest running Earth Observation programme and some of its results

Give a specific example of data collected that can be used to determine land use

Answer 4

NASA’s Landsat Programme
- 9 satellite missions with multispectral sensors
- Collect raw data of solar energy from Earth

Thematic Mapper (TM) on Landsat 4 + 5
- Measures reflectance of red and near-IR
- Creates Normalised Difference Vegetation Index (NDVI) = (NIR - R)/ (NIR + R)
- NDVI relates to LAI, detects deforestation + land use after correction (but saturates at LAI>3)

Question 5

Give an example of maps of land use change developed using optical remote sensing

Answer 5

Land use change maps in South Chile:
- 3 land maps from 1975 - 2000
- 67% reduction in natural forest cover seen
- Pinochet dictatorship incentivised conversion to pine + eucalyptus plantations

Question 6

Why is fragmentation of habitat an important factor

Answer 6

Fragmentation as well as total area has large impact, especially on “core species”
- Fragmentation indices calculated from connectedness, edge length, no. of patches

Question 7

What tool must also be used alongside remote sensing to calculate fragmentation and why?

Answer 7

Indices like NDVI saturate for LAI>3
- Many forests have LAI>3
- “Active” Airborne laser scanning used to produce 3D images of leaf position in canopy
- Used to document affect of forest structure by fragmentation

Question 8

Describe the 3 main consequences of fragmentation

Answer 8

1) Increased access by humans to residual areas via roads
- Increased hunting for commercial bush meat
- Access for illegal logging
- “Illegal” cattle sheltering in fragments
- Access for settlements
- Conduits for weed dispersal

2) Increased edges
- Increased tree mortality on edges (especially large trees)
- Carbon loss via deforestation due to fragmentation at 9 - 24% (Püitz et al. 2014) deforestation total = 10 - 25% global GHGs
- Reduces plant diversity as shade tolerant plants do worse

3) Reduced core area
- “Core species” that need old-growth forests unable to persist

Question 9

How is fragmentation being addressed in conservation?

Answer 9

• Aim to create fewer but larger protected areas
• Need to connect areas via strategically creating habitat corridors
• E.g. connecting Mexican + US wildernesses, wildlife bridges, hedgerows

Question 10

Why is it important to monitor the distribution of vegetation types and how is this does?

Give an example of where this is being actively used

Answer 10

Connecting similar vegetation types benefits wildlife

• Remote sensing unable to distinguish many vegetation types
• Imaging spectroscopy on aircraft + recently satellites as well can distinguish vegetation using many narrow wavebands
• Detection from broad vegetation type down to species sometimes possible
• E.g. used in Peruvian Amazon to identify under-protected habitat types (Asner et. al 2017)