A research team from an international conservation organisation has been studying the effects of land clearance in a region of tropical rainforest in the ce...

(a)(i) Two products obtained from tropical rainforests [1 each, max 2]:

• Timber/wood - used for construction, furniture, and paper production.
• Medicines/drugs - many pharmaceutical compounds are derived from rainforest plants.

Other valid answers include: rubber, fruits/nuts, spices, oils, fibres, charcoal/fuel, rattan.

(a)(ii) Deforestation is the permanent removal or clearance of forest or trees from an area of land [1]. The key word is "permanent" - temporary thinning or selective logging that allows regrowth is not usually classified as deforestation. In Borneo, clearing forest for oil palm plantations represents permanent conversion of forest to agricultural land.

(b) Using Table 3:

1. Forest cover decreased from 15,200 km² in 2000 to 7,800 km² in 2020, a loss of 7,400 km² or approximately 49% of the original area [1].
2. Oil palm plantation area increased from 1,200 km² to 5,900 km² over the same period, an increase of 4,700 km² [1].
3. As forest cover declined, plantation area expanded in an inverse pattern, strongly suggesting that forest was cleared specifically to make way for oil palm cultivation [1].

Note that the combined forest loss (7,400 km²) exceeds the plantation gain (4,700 km²), suggesting some land was also lost to cattle grazing (which increased from 300 to 620 km²) and other uses.

(c)(i) The removal of trees disrupts three key parts of the water cycle:

1. Interception reduced: Trees normally intercept rainfall on their leaves and branches, slowing its descent and reducing the volume of water striking the ground directly. Without trees, more rain reaches the soil surface with full force [1].
2. Transpiration reduced: Trees absorb water from the soil through their roots and release it back to the atmosphere through transpiration. Removing trees eliminates this major route of water return to the atmosphere, reducing moisture recycling [1].
3. Reduced local rainfall: Without the forest canopy, less water is recycled back to the atmosphere. Since transpiration from tropical rainforests generates much of the local rainfall, removing trees can reduce local rainfall totals and humidity levels [1].

(c)(ii) Changes to the water cycle affect rivers in two main ways:

1. Increased flood risk: Without trees to absorb and slow water movement, more rainwater runs off the surface directly into rivers. This increases the volume and speed of water entering river channels, raising flood risk [1].
2. Reduced water quality: Increased sediment load from eroding exposed soil makes rivers shallower, murkier and less suitable for aquatic organisms and human use [1].

(d) Deforestation leads to soil degradation through three linked processes:

1. Direct raindrop impact: Without tree cover, rainfall hits the exposed soil surface directly, dislodging soil particles through the kinetic energy of raindrop impact (known as splash erosion) [1].
2. Loss of root stability: Tree roots normally hold soil particles together and create a network that anchors the topsoil. Without roots, the soil is no longer bound together and becomes loose and vulnerable [1].
3. Surface runoff and erosion: Increased surface runoff carries loose soil particles downhill, removing the thin nutrient-rich topsoil (humus) layer. In tropical environments with heavy rainfall, this erosion can be extremely rapid [1].

(e) Nutrient cycling in a tropical rainforest operates as a closed loop:

1. Leaves and dead organisms fall from the trees to the forest floor, forming a litter layer [1].
2. Decomposers (bacteria and fungi) rapidly break down this litter in the warm, humid conditions (temperatures around 25-30 degrees C and high moisture). This rapid decomposition releases mineral nutrients back into the soil [1].
3. Tree roots absorb nutrients from the soil almost immediately and use them for growth, completing the cycle. Critically, most nutrients in a rainforest are stored in the living biomass of the trees rather than in the soil - unlike temperate ecosystems where nutrients accumulate in deep, fertile soils [1].

(f) Tropical rainforest soil becomes infertile within a few years of clearing for three reasons:

1. Main nutrient store removed: Most nutrients in a rainforest ecosystem are stored in the living trees, not in the soil. When trees are removed (felled and burned), the main nutrient reservoir is permanently lost [1].
2. No nutrient replenishment: The thin humus layer provides nutrients temporarily, but without continuous leaf fall and decomposition from the standing forest, no new nutrients are added to replace those removed by crops [1].
3. Leaching: Heavy tropical rainfall (the region receives high annual totals) causes rapid leaching, washing remaining soluble nutrients deep into the soil profile - beyond the reach of crop roots [1].

(g)(i) Deforestation contributes to rising atmospheric CO₂ through three mechanisms:

1. Carbon release from burning: When trees are felled and burned, the carbon stored in their biomass (trunks, branches, roots) is oxidised and released as carbon dioxide into the atmosphere [1].
2. Reduced carbon absorption: Living trees absorb carbon dioxide through photosynthesis. Removing trees reduces the number of plants actively removing CO₂ from the air - the forest acts as a carbon sink, and deforestation destroys this sink [1].
3. Decomposition of organic matter: Remaining roots and organic matter in the soil also decompose, releasing their stored carbon as CO₂ over the following months and years [1].

(g)(ii) Increased atmospheric CO₂ affects global climate through:

1. Enhanced greenhouse effect: Carbon dioxide in the atmosphere absorbs and re-emits infrared radiation, trapping heat that would otherwise escape to space. More CO₂ means more heat is retained, leading to a rise in average global temperatures [1].
2. Cascading climate impacts: Higher global temperatures lead to more extreme weather events, melting of polar ice caps, rising sea levels, changes to rainfall patterns, and disruption to ecosystems worldwide [1].

(h) Five strategies to reduce deforestation while allowing economic development:

1. Legally protected areas: Establish zones where no further clearing is allowed, preserving remaining biodiversity and the carbon storage function of the forest [1].
2. Sustainable forestry: Promote selective logging, where only certain mature trees are harvested and the forest structure is maintained. This allows timber extraction without destroying the ecosystem [1].
3. Certification schemes: Develop and enforce certification schemes (such as RSPO for palm oil) that require producers to avoid clearing primary forest. Consumers can then choose certified products [1].
4. Alternative livelihoods: Support local communities with income sources that do not require forest clearance - such as ecotourism, sustainable harvest of non-timber forest products (rubber, nuts, medicines), or payments for ecosystem services (PES) [1].
5. Rehabilitation of degraded land: Invest in replanting programmes on land that has already been degraded, rather than clearing new forest for plantations. This makes better use of existing agricultural land [1].