Forest Ecology Notes PDF

**What is ecology?** The scientific study of processes influencing the distribution and abundance of organisms, the interactions among organisms and the interactions between... Different types of ecology, marine, forest,... **Population** = an interbreeding collection of individuals of the same s...

**What is ecology?** The scientific study of processes influencing the distribution and abundance of organisms, the interactions among organisms and the interactions between... Different types of ecology, marine, forest,... **Population** = an interbreeding collection of individuals of the same species living in the same local area **Metapopulation** = a spatially structured group of individuals interacting via dispersal **Community** = An assemblage of different individual species (populations) occupying the same local area, and usually interacting with each other **Ecosystem** = A community and all aspects of the physical environment make up the habitat **Attributes of Ecosystems:** - - - -3D Spatial arrangement of compositional and structural elements - Composition of Biodiversity:\ Species present -and genetic variety Relative **Structure of Ecosystems** -Physical "pieces" that make up the forest -Trees(many varieties, sizes, conditions) -shrubs -dead wood, snags -underbrush Structure all the way at individual trees and within trees DEAD WOOD IS SUPER IMPORTANT, ESSENTIAL PART OF STRUCTURE Spatial pattern of Ecosystems -Spatial arrangements of the "pieces" or structural elements -homogenous: uniform distribution -Random: no spatial relationship -Heterogenous: spatially patterned, clumped "FORESTS ARE 3-DIMENSIONAL SYSTEMS" **Functions of Ecosystems:**\ -Primary production, carbon fixation -Hydrologic regulation -Nutrient cycling and retention -Soil formation and conservation -Provision of habitat **Attributes of Ecosystems** **Dynamics: Change over time** **Drivers:** Disturbances Biotic interactions Physical template Species attributes *Leads to:* Composition} Structure} Ecosystem Function Pattern} **Disturbances dominate ecosystem structure, composition, and function** -Wildfire -Floods -Bank Erosion -Debris flow (Description of Ecosystem attributes is not the end goal but rather the understanding of the processes and the complexity) **How do plants grow (gain C?)** Photosynthesis: how plants use energy(light) to create sugars (food) 1. 2. 3. Electrons -\> high energy compounds ATP NADPH Typically Autotrophs that fix sunlight to create carbon Most plants use C3 photosynthesis Only 1-2% of sun\'s energy is used in photosynthesis Respiration: how plants use sugars(food) to produce energy (to do work) Some C energy used in respiration by leaves in the process (10-20%) With the excess the plant can either repair existing biomass or create new biomass More photosynthesis than respiration = growth More respiration than photosynthesis = unsustainable Carbon+Water+Energy = Glucose+Oxygen (takes place in green tissues, little organelles called chloroplast) Respiration is the opposite equation \^\^ Three main elements of a tree = Carbon, Hydrogen, Oxygen What impacts photosynthesis? Temperature, Light, Gas Exchange(CO2 & H2O) Temperature regulates rates of photosynthesis and respiration Photosynthesis increases with increasing light levels, slope of this line is called photosynthesis efficiency Light compensation point is the light level at which photosynthesis equals respiration (net 0) Light Saturation point = the light level where photosynthesis rate hits a maximum and increasing levels of light do not result in any increasing rate of photosynthesis. Light rxns are to high of a level to be used by dark reactions How would you expect the shape of a light response curve to change in response to changing CO2 concentration? CO2 \^\^ then the saturation point gets higher **Leaf Gas Exchange (CO2 & H2O vapor)** - - - There is an inherent trade off! - - - Water molecules are brought in through the roots then up through the the xylem system up to the branches and the leaves them respiration happens Soil water potential (SWP) Matric potential:(main factor of SWP) Measure of how tightly held water is in the soil Ponderosa pine has exceptional drought resilience through the ability to well regulate its stomata, on the contrary, Western Larch has terrible stomata regulation **Forest Light Variation** Tremendous amount of light variation, especially in disturbance areas Latitude, season, cloud cover, stem density, vertical leaf area distribution, crown density, species composition,\... Plants are not mobile, must react to the light environment in which they find themselves in Forests create their own light environment because they produce woody biomass and create canopies **Morphological Plasticity:**\ General changes in leaf inclination and leaf morphology along light gradient with increasing height within trees. (leaf inclination, stomatal density, Palisade layer) The plant will grow differently depending on the light conditions those particular leafs are in, more sun thicker fatter, multiple layers of palisades. Less sun, thinner, longer, one layer of palisades. Metrics\^\^ **Specific Leaf Area(SLA):** Ration of leaf area (one side) to leaf dry mass. m\^2/g **Leaf Mass per Area(LMA)**: Inverse of SLA. g/m\^2 Lots of variation between/within species Sensitive to drought/water stress as well as light environment **Morphological Acclimation within tree crowns** Different branches from the same whorl: growing into openings (sun foliage) and into clumps (shade foliage) LIGHT RESPONSE CURVES WILL BE ON EXAM Increasing light intensity across X-axis and Y-axis has net photosynthesis(at the leaf scale) Sun leaves can do more photosynthesis at high light levels but the tradeoff is there is more living tissue and therefore a higher respiratory cost The shade tolerance of plant species is very predictive for how well a plant is able to survive other things Shade tolerant does not equal shade obligate (NOT THE SAME THING) Shade obligates require darkness, THERE ARE NOT MANY OF THESE, MAYBE DENSE TROPICS Shade tolerant can do just fine in bright sunlight, there competitive advantage is they can also do well in shade Canopy structure - light profile relationships **LAI: Leaf Area Index** Total one-sided surface area of leaves per unit ground area (m\^2/m\^2 so unitless index) Measured most reliably with destructive sampling or litterfall traps. LAI is important for understanding and modeling rates of energy and material exchange between the forest canopy and the atmosphere, and is a key parameter for ecosystem models. - - - - **Beer-Lambert Law**: Describes attenuation of light passing through a material. Applied to forest canopy **Weather and Climate** Weather = short term condition and changes in the atmosphere Climate = Long term average for weather at a given location **Climate Normals** = Standardized climate summaries based on a 30 year period of observations. The current climate normals are based on weather observations during 1991-2020. Climate normals are updated every ten years. Climate is strongly influenced by the amount of solar radiation  Also note global atmospheric circulation; Hadley cells, Trade winds, polar fronts...ect El Nino - - - - - La Nina - - - - - **Potential Impacts on climate variability:** - - - - - - - - **Regional to Local Spatial Climate Variation** **Physiography**: Surface features of a region (10-100s km)\ **Topography:** Configuration of landforms (100s m to 10s km)\ **Orographic lift:** Movement of an air mass from low to high elevations as it moves across rising or mountainous terrain **Adiabatic heating/cooling:** An increase/decrease in temperature of a substance (such as a parcel of air) caused by corresponding increase/decrease of pressure Topography is an important driver of local variation of microclimate and vegetation: topography decouples local (site) climate from regional climate. **Three main influences of topography on local climate:** 1. 2. 3. **Man Influences of topography on microclimates:** 1. 2. 3. **Slope and Aspect effects:** Aspect influences radiation load, temperature, relative humidity, and evapotranspiration Most pronounced in arid environments In general, for the northern hemisphere, south-facing slopes receive more sunlight and become more xeric and warmer, supporting drought-resistant vegetation and less conducive for tree growth, while north-facing slopes retain moisture and are cold and humid, supporting moisture-loving plants.  Latitudinal variation of solar radiation drives global and regional climate Physiography influences regional patterns of precipitation and vegetation through orographic effects Topography drives local variation in climate (especially temp) via cold air drainage, slope/aspect effects **Plants require water to use energy for photosynthesis:** - - PNW snow forest is ENERGY LIMITED Colorado Plateau desert is WATER LIMITED Climatic water balance parameters are a way to compare climate as sensed by plants **(PETₘ) = Monthly potential evapotranspiration** **(AET) = Actual evapotranspiration (Not true measured, just the real in the model)** AET is a measure of the energy and water simultaneously available to be used for photosynthesis AET is a proxy for potential productivity **PET = AET + D(deficit)** Deficit (D) is a measure of drought stress--unmet evaporative demand Deficit is the amount of water the ideal patch of grass would like to have, the amount it could use if it had all it could want. PET = (Days in a month)(Mean day length)(Heat load index to account for latitude, slope and aspect)(Saturation vapor pressure at mean temp) **(Wₘ) = Monthly water input** **W = AET + S(surplus)** Available Water (W) is the total amount of liquid water reaching the soil, minus the **(SOILₘ) = Monthly soil water balance** **Natural Stand Development** - - - - - - - - **Cohort Establishment:** An aggregation of trees in a stand that starts as a result of a single disturbance. Typically takes 30-40-50 years or more, but can be variable The period of time getting the new generation of trees established, comes to a stop when canopy closure occurs **Canopy Closure:** the amount of the sky obscured by the canopy from a certain point on the ground. - - - - - **Biomass Accumulation and Competitive Exclusion:** Rapid growth and biomass accumulation, intense competition. - **Competition-Based Mortality:** The size growth of the trees in a stand and their increasing individual demand for resources causes competition and, as a result, mortality and growth in size occur simultaneously - - - - **Maturation:** Individual height and crown spread occurs in dominant individuals, canopy thins, coarse wood low, understory beings to re-establish - - - - **Agent-Cause Mortality:** - - - - **Young Old-Growth Forest Stage:** tree size, accumulations of large dead woody material, number of canopy layers, species composition and ecosystem function. - \- Development of "decadence" \- Increased recruitment of CWD \- Increased woody debris **Old-Growth Forest Stage:** later stages of stand development that typically differ from earlier stages - - - **Ancient Old Growth:** contain large, old trees of long-lived species that are beyond traditional rotation (harvest) age. High-quality old growth forests also have relatively complex stand structure (such as snags and woody debris), high stand mortality, and few invasive species. - - - **KEY CAVEATS:** - - - - - **Canopy closure and competitive exclusion:**\ Factors influencing tree growth and survival: - - **COMPETITION:** Interactions for limited resources that affect the performance of individual plants: - - - - Competition is a spatial process-interactions and access to resources are distance dependent **Types of Competition:** - - - - - - - - - - **How do we study Competition?** Experiment: - - - Observations: - - Mechanisms driving change in spatial distribution of living trees Initial aggregated distribution in young forests Density dependent, dying trees have more crowded neighborhoods Increasing uniformity \[ Competition and self thinning clearly are important agents of change - for stand competition, structure and pattern - but we have to consider other processes simultaneously to fully understand the mechanisms of change. \] **Relative Density:** ranges from 0 to 1 **Canopy Closure** = RD of about 0.15, Large trees but site not fully occupied. Density can increase w/o decreasing mean tree groth. RD of 0.15 to 0.4, yield per unit area increasing with density, but mean tree growth declines RD of 0.4 to 0.55, stand yield not sensitive to density-this is the zone of max growth **Zone of imminent competition mortality** RD = 0.55 to 1.0 ---\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- **Tree Mortality, Gaps and Canopy Turnover** **Major Questions:** - - - - Much of forest ecology theory argues or assumes a fundamental division of tree mortality according to competitive or non-competitive casual agents But We usually can\'t make the distinction between competitive mortality and biological mortality in field studies, but you can between biological and mechanical mortality. Tree Death as an ecological process: a chain of events Need to think in terms of factors associated with tree death, and detailed pathologies to explain tree mortality dynamics, i.e lighting, drought, bark beetles, fungus... Tree death itself can cause other mechanical damage **Forest Gap Dynamics:**\ - What are the gap characteristics of forest canopies?\ - How do trees reach the canopy of mature and old growth?\ - How are gaps made?\ - Who fills the gaps?\ - What are the consequences for forest composition? Stability? Change? **Structural def/ Developmental** : A region of the main canopy unoccupied by a tree crown. **Functional def.** : A portion of the forest where one or more resources are more plentiful than the immediate surroundings Gap formation becomes important the later you are in forest development. Edaphic Gap = Open canopy on south facing slope Developmental Gap = Open canopy on north facing slope. Supports trees. What Causes Gaps?? **Roots/butt rots, spruce beetle**, stem rots, armillaria, wind throw/snap, chronic wind stress, other. Competitive mortality DOES NOT usually cause gaps as it only kills smaller trees not apart of the canopy A large part of the transition you see over the scale of tree stand development **TAKE HOME POINTS:**\ 1) Mechanical mortality provides a baseline for understanding mortality processes among forests. 2\) Canopy gaps (disturbances) usually have a greater effect on growth of establishing seedlings and saplings than on establishment of new seedlings. 3\) Biological and mechanical mortality agents cause nearly all developmental canopy gaps - not competition. 4\) Mortality at seedling/sapling stage regulates the pool of potential recruits available to fill canopy gaps **Tree Regeneration and Seedling Dynamics:** Life History Stage Based Model\ 1) Reproductive adult density and distribution (Limiting processes: Seed production per adult(or time)) 2\) Seed density and dist 3\) Germinant density and dist 4\) Seedling density and dist The LOGIC: 1. 2. 3. **Principles of Experimental Design:** 1. 2. 3. 4. **Ecological facilitation** or probiosis describes species interactions that benefit at least one of the participants and cause harm to neither. Facilitations can be categorized as mutualisms, in which both species benefit, or commensalisms, in which one species benefits and the other is unaffected. Trees love snowdrifts Substrate effects: Nurse Logs Ex. Spruce, Southern Beech, Hemlock Happens in older forests, in moist sites **Plant functional Traits:** Any measurable characteristic that directly or indirectly plant performance and function especially through its effects establishment growth, survival rate, thickness, seed size, seed number, leaf number, and max photosynthesis Evergreen leaves interrupt and disrupt the energy balance of snow sites more than deciduous larch trees. Water balance, snowpack accumulation... **Fire adaptations: (or floods, wind, icestorm, ect. disturbances)** Functional traits that: - - - Serotinous cones: canopy seed bank (i.e. lodgepole pine or knobcone) - - Germination response: fire scarifies seed coat - Fruit and flower production: - Thick fire resistant bark: i.e. sequoiadendron - Self trimming limbs Sprouting from adventitious buds (Adventitious roots are plant roots that form from any non root tissue and are produced both during normal development) Fire in the rainforests: Thin bark and organic soils = dead trees **Plant Fire Response Strats** - - - - - **Fire Behavior:** the magnitude, direction and intensity of fire spread Fire intensity: The rate of energy released along a unit length of fire line Fire Severity: The effect of fire on plant communities. Expressed in terms of the proportion of vegetation killed. And how severely altered the soil was. Fuels, Weather, Topography } **Fire Behavior** **Fire Regime:** Description of the long-term characteristic attributes (temporal(frequency), magnitude) of fires occurring at a given place. (more like climate, where behavior is more like weather) **Methods of Studying Fire:**\ Fire history reconstructions (tree rings, fire scars) can be used to obtain fire intervals, mean, median Frequency: fire rotation, the length of time necessary for an area equal to the size of the study area to burn Long Term Experiments **Ponderosa Pine Forest Fires:** - - - - **Western Fire Management:** - - - - - - - - **Effects of Fire Exclusion: Bitterroot** - - - Frequent surface fires are a stabilizing feedback, and fire suppression has changed this by breaking up this pattern.