Download Forest mensuration, management, and more Lecture notes Environmental science in PDF only on Docsity!
Forest Mensuration, Silviculture, Forest Seeds, and Forest Resources in Ethiopia
- Introduction Forest mensuration is the science of measuring the characteristics of trees and forests. Silviculture is the practice of managing the establishment, growth, composition, health, and quality of forests. Forest seeds are essential for regeneration and plantation establishment. Forest inventory systematically collects data about forest resources, including tree measurements, stand attributes, volume, biomass, and forest health. Key Objectives: Estimate tree volume, basal area, and growing stock. Calculate yield and allowable annual cut (AAC). Assess forest density, biodiversity, and forest condition. Apply silvicultural practices to improve forest productivity and sustainability. Collect, store, and use forest seeds for regeneration and reforestation. 2. Forest Seeds Definition: Forest seeds are reproductive units of trees and shrubs used for natural regeneration or artificial propagation of forests. Importance: Ensure forest regeneration. Provide genetic diversity.
Support plantation and reforestation programs. Maintain ecological balance. 2.1 Types of Forest Seeds
- Based on origin: o Native seeds: Collected from indigenous forests. o Exotic seeds: Introduced species for plantations or research.
- Based on dispersal method: o Wind-dispersed seeds (Anemochory): Light and small seeds carried by wind, e.g., Eucalyptus. o Animal-dispersed seeds (Zoochory): Often fleshy or with hooks, dispersed by birds, mammals, or insects, e.g., Ficus, Acacia. o Gravity-dispersed seeds (Barochory): Heavy seeds that fall near the parent tree, e.g., Podocarpus.
- Based on seed structure: o Naked seeds (Gymnosperms): Seeds not enclosed in a fruit, e.g., Podocarpus, Juniperus. o Covered seeds (Angiosperms): Seeds enclosed within a fruit, e.g., Acacia, Cordia.
- Based on storage behavior: o Orthodox seeds: Can be dried and stored for long periods at low temperatures without losing viability. Examples: Pinus, Acacia. o Recalcitrant seeds: Cannot tolerate drying or freezing; short-lived and must be sown soon after collection. Examples: Avocado, Ficus, some tropical hardwoods.
Seed Processing, Storage, and Nursery Practices: Remove pulp, shells, or husks. Clean and sort by size and quality. Dry seeds carefully to reduce moisture content (for orthodox seeds). Store in cool, dry, and pest-free conditions (orthodox seeds). Sow recalcitrant seeds immediately after collection. Sow in raised beds, polybags, or trays. Apply proper soil mix, irrigation, and pest protection. Forest Pests Definition: Forest pests are insects or animals that cause damage to trees, forest products, or forest ecosystems, reducing timber quality, growth, or survival. Types of Forest Pests:
- Insect Pests: o Bark beetles (e.g., Dendroctonus species) – bore into tree bark, causing tree death. o Defoliators (e.g., gypsy moth, Lymantria dispar ) – feed on leaves, reducing photosynthesis. o Wood borers – damage wood, reducing timber value.
- Vertebrate Pests: o Deer, monkeys, porcupines – feed on seedlings, bark, or fruits. Effects:
Reduces timber quantity and quality. Alters forest composition and structure. Can trigger secondary problems like disease or fire. Control Measures: Silvicultural: proper spacing, pruning, and removal of infested trees. Biological: natural predators, parasitoids, or pathogens of pests. Chemical: pesticides (used carefully to avoid environmental damage). Integrated Pest Management (IPM): combines ecological, biological, and chemical methods.
2. Forest Diseases Definition: Forest diseases are caused by pathogens such as fungi, bacteria, viruses, or nematodes that adversely affect tree health. Types of Forest Diseases: 1. Fungal Diseases: o Root rot ( Armillaria spp.) – decays roots, killing trees. o Rusts ( Cronartium spp.) – affect leaves, stems, and cones. o Leaf spots – reduce photosynthesis and weaken trees. 2. Bacterial Diseases: o Bacterial blight ( Pseudomonas spp.) – causes leaf, twig, or stem dieback.
Pathogens: Chestnut blight fungus ( Cryphonectria parasitica ). Effects: Outcompete native species for light, nutrients, and space. Reduce biodiversity and alter habitat. Cause economic losses in timber, agriculture, and ecosystem services. Can act as new hosts for pests or diseases. Control Measures: Mechanical removal or containment. Biological control using natural enemies. Chemical control where appropriate. Early detection and rapid response (prevention is more effective than eradication). Summary Table: Category Causes/Agents Effects Control Measures Pests Insects, vertebrates Tree damage, reduced growth Silviculture, biological, chemical, IPM Diseases Fungi, bacteria, viruses Mortality, defoliation, timber loss Resistant species, hygiene, chemical treatment Invasive Species Non-native plants, animals, microbes Biodiversity loss, ecosystem disruption Mechanical, biological, chemical, prevention
3. Silviculture Definition: Silviculture is the art and science of controlling the establishment, growth, composition, health, and quality of forests to meet objectives such as timber, fuelwood, biodiversity conservation, and ecosystem services. Key Components:
- Regeneration: Natural or artificial.
- Tending and Thinning: Thinning and pruning to improve growth.
- Weeding and Cleaning: Remove competing vegetation.
- Protection: Guard against pests, diseases, fires, and grazing.
- Rotation and Harvesting: Determine optimal rotation period. Silvicultural Systems in Ethiopia: Selection System Clear-cutting Shelterwood System Coppice System Selection System
2. Clear-Cutting System Definition: Clear-cutting involves the removal of all trees in a designated area at once, followed by regeneration of the area through natural seeding or artificial planting. Key Features: Results in even-aged stands. Simplifies harvesting operations. Often combined with planting fast-growing species. Advantages: Economically efficient and simple to implement. Encourages regeneration of shade-intolerant species. Reduces risk of disease and pest infestation. Disadvantages: Causes soil erosion , nutrient loss, and microclimate changes. Negative visual impact and reduced biodiversity temporarily. Potential adverse effects on watershed and aquatic ecosystems. Suitable for: Coniferous plantations and fast-growing commercial forests.
3. Shelterwood System Definition: The shelterwood system is a method of even-aged management where trees are removed in a series of cuts over time, leaving some mature trees to provide shade and protection for natural regeneration. Key Features: Usually involves three stages : preparatory cut, seed cut, and removal cut. Encourages natural regeneration under partial shade. Ensures gradual exposure of seedlings to full sunlight. Advantages: Protects soil and seedlings during establishment. Maintains forest aesthetic and ecological functions temporarily. Reduces sudden habitat loss compared to clear-cutting. Disadvantages: Requires careful planning and skilled management. More expensive than clear-cutting due to multiple operations. Some residual trees may be damaged during final harvest. Suitable for:
Unsuitable for species with poor sprouting ability. Suitable for: Fast-growing species for firewood, fodder, and poles. Areas requiring frequent harvests without long-term stand establishment. Objectives of Silviculture: Improve timber quality and yield. Restore degraded forests. Maintain biodiversity. Provide non-timber forest products. Protect watersheds and soil
4. Forest Inventory and Mensuration Tree measurements: DBH, height, crown diameter, species identification. Stand attributes: Tree density, basal area, age structure. Volume and biomass: Timber volume, fuelwood, carbon stock. Forest health: Pests, diseases, degradation. 5. Forest Types in Ethiopia By Ownership: Government, Community, Private, and Forest Owners Association By Forest Origin: Natural, Plantation / Artificial By Biome / Ecological Type: Afro-montane, Dry Afromontane, Riverine, Lowland Woodlands, and Bushlands
By Generation (Age / Succession): Primary / Old-Growth, Secondary / Regenerated, Plantation / Artificial By Biodiversity: High, Moderate, and Low
6. Forest Mensuration Calculations Basal Area (BA) = (π × DBH²)/ Tree Volume (V) = BA × H × F Stand Volume / Growing Stock V_s = V × N Allowable Annual Cut AAC = Total Growing Stock / Rotation Age Basal Area per Hectare BA_ha = BA × N Volume Equations: Smalian, Huber, Newton 7. Practice Problems & Solved Examples Tree DBH 40 cm, H 25 m, F 0.5 → BA ≈ 0.126 m², V ≈ 1.57 m³ Stand 600 trees/ha, V = 1.2 m³ → V_s = 720 m³/ha Growing stock 500,000 m³, rotation 25 years → AAC = 20,000 m³/year Smalian's formula: base 0.5 m², top 0.3 m², L 12 m → V = 4.8 m³ 8. Summary Table: Forest Types in Ethiopia Classification Types / Examples Key Features Ownership Government, Community, Private, Forest Owners Association Access and management differ; association forests collectively managed Origin Natural, Plantation / Artificial Natural forests develop without human intervention; plantations are human-
9.1 Carbon (C) Definition: Carbon is a chemical element that forms the structural basis of all organic matter. In forests, carbon is stored in living biomass, dead organic matter, and soil. Role of Forests: Forests act as carbon sinks , absorbing atmospheric CO ₂through photosynthesis. Carbon is stored in plant tissues and released through respiration, decomposition, or burning. 9.2 Carbon Stock Definition: Carbon stock is the quantity of carbon stored in a forest ecosystem at a specific time , expressed per unit area. Major Forest Carbon Pools:
- Above-ground biomass (AGB)
- Below-ground biomass (BGB / roots)
- Dead wood
- Litter
- Soil organic carbon (SOC) Units:
t C/ha (tonnes of carbon per hectare) t CO e/ha (tonnes of carbon dioxide equivalent per hectare)₂ 9.3 Carbon Equivalent (CO e)₂ Definition: Carbon equivalent expresses stored or emitted carbon in terms of carbon dioxide (CO )₂. Scientific Basis: Atomic weight of Carbon (C) = 12 Molecular weight of CO ₂= 44 Conversion of Carbon (C) to Carbon Dioxide Equivalent (CO e)₂ Formula: CO e = C × (44/12)₂ Where: C = Carbon stock (t C/ha) 44 = Molecular weight of CO₂ 12 = Atomic weight of Carbon So, CO e = C × 3.67₂
10.5 Carbon Measurement in Forests 10.5.1 Biomass Estimation Carbon is estimated indirectly through biomass measurement. Allometric Equation (general form): Biomass Estimation from DBH Biomass = a × (DBH)^b Where: DBH = Diameter at Breast Height of the tree (cm) a, b = species- or region-specific constants Biomass is usually expressed in t/ha This allometric equation is commonly used in forest mensuration to estimate tree biomass from DBH measurements. 10.5.2 Biomass to Carbon Conversion On average, 50% of dry biomass is carbon. Carbon (C) = Biomass × 0. Where: Biomass = total dry mass of trees (t/ha) 0.5 = conversion factor from biomass to carbon
10.5.3 Carbon to CO ₂Equivalent CO e = Carbon × (44/12)₂ CO e = Carbon × 3.67₂ 10.6 Worked Carbon Stock Calculation (Exam Standard) Given:
- Above-ground biomass = 120 t/ha Step 1: Carbon Stock C = 120 × 0.5 = 60 t C/ha Step 2: CO ₂Equivalent CO e = 60 × (44/12)₂ CO e = 60 × 3.67 = 220 t CO e/ha₂ ₂ Final Answer: ✅ 220 t CO e per hectare₂ 10.7 Total Forest Carbon Stock Formula Total Carbon Stock = C_{AGB} + C_{BGB} + C_{DW} + C_{L} + C_{SOC} Where: C_{AGB} = Carbon in Above-Ground Biomass
