NRES 493

What is ecology

simple terms-the study of how nature works. Ecology is the study of how energy and matter flux within an ecosystem and why.

In forests, how can age structure be used to infer historical population processes, and to project future stand development? Be able to relate age (or size) structure to disturbance history.

When a forest's recruitment is high and there is a disturbance that wipes out older trees, the stand has a chance to be replaced by a more homogenous cohort. Basal area is a good indicator of resource availability and competition within an area.

What are the different modes of plant recruitment?

Seed rain: wind/plant driven plants use this, distance dependent, negative exponential function

Seed bank: dormancy like manzanita

Bud bank: important for resprouting and asexual reproduction

Seedling bank: refers to seedlings, typically of shade-tolerant species, that are capable of remaining in the understory for long time periods.

Describe the life cycle of a woody plant, and the necessary requirements of successful recruitment.

Successful recruitment must meet the requirements of a series of ecological filters: Seed dispersal to suitable microsite> Successful germination> survive first growing season>Survive to reproductive maturity

how can plant community structure be measured?

This can be measured in different ways:
Density (#/unit area)
Frequency (% occurrence)
Coverage (% of ground covered)
Basal Area of dbh (diameter at breast height)(e.g. ft2/acre; m2/hectare)
Height
Biomass (dry weight/unit ground area)
Structure is the vertical arrangement and spatial organization of the plants. It can also refer to the relative abundances of each of the species present (often referred to as community composition). Components of community structure include: Physical arrangement , life forms present, spatial pattern, species composition, successional stage, biomass, functional processes (energy; nutrient cycling).

What is an ecosystem? Describe some key attributes of ecosystems.

An ecosystem is the biotic community interacting with the physical (abiotic) environment. Some key attributes are:
Composition: the array of plants and animals present in an ecosystem
Structure: the spatial arrangement of various components of the ecosystem, such as heights of various canopy levels and spacing of trees
Function: how various ecological processes are accomplished and the rates at which they occur
Interaction: How all the components interact and influence each other
Change: How an ecosystem structures & functions change over time

How can forest structure be described?

Forest structure is a fluid, always changing composition of trees and other species that occur in an area together that vary in age, height, and distribution.

What does ecosystem stability refer to? What are the distinctions among species stability, structural stability and functional stability?

the ability of an ecosystem to maintain a steady state, even after a stress or disturbance has occurredThe concept of ecological stability can refer to:

Species Stability, or the maintenance of viable populations or metapopulations

Structural Stability, referring to the network of interactions among ecosystem components (e.g. food webs), or to patterns of biodiversity, or landscape structure (e.g. the spatial arrangement of different forest types or forest structural stages)

Functional Stability, or the maintenance of critical ecosystem processes such as primary productivity, nutrient cycling, hydrologic processes, etc.

How can ecosystem stability be understood in light of ecological resistance and resilience concepts?

Ecosystem stability can be understood as the ability of an ecosystem to.

Resist: ability of a community to absorb perturbation without changing it

Be resilient: ability of a community to absorb a perturbation and recover.

What are some fundamental, general ways in which mismanagement of forests can lead to loss of ecosystem stability, or ecosystem degradation?

One is soil fertility loss, that commonly arises from (a) loss of organic matter, (b) soil compaction, or (c) harvesting at too frequent a rotation. This can lead to a loss of bioregulation, due to the breakdown of plant-soil linkages, leading to (a) surface soil erosion and resulting increased inputs of sediment to streams, (b) leaching of nutrients, (c) degraded soil structure, and (d) degradation of mycorrhizae and the soil microbial community.
Removing forest cover increases surface erosion because: (1) rainfall impacts soils with more force (less canopy, less litter), and the extra energy is transferred into moving soil; and (2) the mechanical holding power of plant roots is lost or diminished.

(Loss of Bioregulation - breaking plant-soil linkages. Surface soil erosion, sediment inputs to streams. Leaching of nutrients. Soil structure. Mycorrhizae and soil microbial community)

Why might certain types of natural disturbances be stabilizing for an ecosystem, and others stabilizing?

Some ecosystems can be stabilized from a natural disturbance because it is part of their natural disturbance regime. Destabilizing disturbances are those that lie outside the historic disturbance regime. The initial destabilizing disturbance triggers secondary stresses and disturbances (insect, pathogen outbreaks)

What is meant by the term "no-analog forest community" in the context of paleoecological reconstruction of past conditions? What are the implications of the existence of such communities in the paleoecological record?

No-analog forest communities refer to communities found that have no close reference point; these are novel communities that exist or have existed as unique configurations of different biota, temperatures, and abiotic factors than have been previously described
The implications of these in the paleoecological record and in reconstructions are that it's important to remember that communities now are largely configured by chance over the years

What are some of the different mechanisms that can cause tree species distributions to shift dramatically over millennial time scales?

Evolution and adaptation of species, glacial movement, plate tectonics, long-term interactions among climate, fire, biota, consequences of climate change

What are the limiting factors of the environment? List these factors and how they influence forest dynamics.

Irradiance: limited ability for plants to photosynthesize

Water + nutrients: influence amount for foliar biomass

Temperature: length of growing season, rates of photosynthesis, rates of respiration

The distribution of vegetation types, including forests, is mediated by a suite of environmental influences. Describe these different influences from local to global scales. What ultimately limits the distribution of forests?

Vegetation types are distributed by precipitation and temperature. Local vegetation types are determined by topography, soils, historical factors, and anthropogenic influences. Forests occur where "there is enough water for trees to cope with evaporative demands driven by temperature and atmospheric humidity

How does elevation influence the distribution of tree species and forest types?

Elevation largely influences tree distribution through its correlations with temperature (and cold resiliency of species that are able to grow in such environments)

How does slope aspect influence the distribution of tree species and forest types?

The slope aspect influences the distribution of trees and forest types because N and S facing slopes have temperature differences. South facing slopes have more sun exposure which leads to more evaporation which leads to less soil moisture. North facing slopes have less sunlight exposure and higher soil moisture. In forests with snow packs, the north facing slopes are better at keeping the snow pack which insulates the soil and keeps the temperature warmer than south facing slopes that do not have snow insulation.

What portions of the electromagnetic spectrum do plants use, and how does shading by the canopy influence the quality of light?

Plants can use PAR = photosynthetically active radiation (400-77nm). Shading can act as a limiting factor in the environment because it limits the PAR available.

How does forest management influence the forest energy balance, and the distribution of temperatures across space and over time?

Forest management for any objective requires maintenance of net primary production (NPP). When trees are removed from a forest, it increases the soil temperature which can cause a greater overall increase in temperature. Forests also experience less fluctuation in temperature changes through the day and night, so the removal of forests can change temperature in that way.

What is photosynthesis? Why is it best thought of as a two-step process?

Photosynthesis is the process by which plants take sunlight, water, and carbon dioxide and convert it into chemical energy. It is best thought of as a two step process because it is thought of as two steps: capturing sunlight into a chemical form, and then using that energy to add the H+ and CO2 to make sugar for the plant. This is to better understand photosynthesis

standing crop

Standing crop (plant biomass within a forest stand or plant community)

net primary productivity (NPP)

NPP = GPP - Ra, where NPP = net primary productivity, GPP = gross primary productivity, Ra = autotrophic respiration (approximately 50% of GPP)

net ecosystem productivity

NEP = GPP - Re, where NEP = net ecosystem productivity, GPP = gross primary productivity, Re = ecosystem respiration = Ra + Rh, where Rh = respiration of heterotrophs

What does it mean to describe certain tree species as having masting behavior, and why might such behavior be adaptive?

Certain tree species are masting species that produce large seed crops episodically, often at regular intervals of several years, or corresponding with favorable years. This can be adaptive because stronger masting patterns are seen in tree species that are adapted to drier climates.

For most tree species, how does survivorship change with increasing age of a cohort of individuals?

For most tree species, there are less individuals with each age cohort. (Type III survivorship curve)

How, or under what conditions, does insect herbivory lead to tree mortality?

Bark beetles kill trees by introducing fungi (often blue stain fungus) that interrupt sap flow. This often lethal effect is independent of the amount of biomass consumed.

What are the factors that regulate forest herbivore populations?

Regulations include nutritional quality of plants, toxic chemicals, predators and pathogens, climate, and the change in abundance of food.

How is bark beetle herbivory influenced by forest density and tree size?

More initial stocking and higher tree size lead to higher mortality rate.

direct effects of forest herbivores on forest ecosystem structure and function

Direct Effects of Herbivory: Effects on forest tree regeneration, rates of succession, and subsequent forest dynamics, Effects on forest herbaceous communities

The author of your textbook (Dr. Dan Binkley) states that "History has no need to repeat itself." What is the basis for this statement? What are its implications?

Environmental conditions are always changing (glaciation, disturbances, etc) which causes species to adapt to make new novel communities. There is no need to try to return to historic communities because conditions no longer support historical conditions.

what are the key components of an ecosystem?

There are many key components to an ecosystem, but the ones forest ecology focuses on are An energy source, Raw materials, Mechanisms for storing and recycling, andMechanisms for persistence (resilience to disturbance).

How do the photosynthetic response curves of shade-tolerant tree species differ from those of shade-intolerant tree species?

Willows and birches, which are shade intolerant, have a higher light-saturated zone of net carbon uptake in photosynthesis than shade tolerant species such as pine and spruce.

compensatory growth

change in growth rate (usually positive) following a period of reduced biomass or slowed growth due to some perturbation

Describe the fundamental trade-off between drought tolerance and drought avoidance in plants.

Drought tolerant plant are able to survive and respirate in drought conditions, and
Drought avoidant plants close or regulate stomata depending on atmospheric humidity and soil moisture, and may experience lower productivity in dry periods

What is meant by the phrase: "Trees are not prisoners of their environment?"

Trees have the ability to influence their environments through the moisture of the soil, and through the regulation of temperature through shade
Trees species have changed their ranges over time, in very slow but eventual migrations across continents

Your textbook observes that "Growth happens after photosynthesis." What does this mean, and why might it be an important observation?

Photosynthesis is the means for a plant to obtain energy, after which the process of growth begins
It's an easy assumption that growth and photosynthesis are the same step of the same process

How do trees (plants) defend themselves against herbivores?

Nutritional quality of plant tissues (foliage can be nutrient poor which makes herbivores need a lot), they can grow fast to get out of the reach of herbivores, they can produce toxic chemicals

What conditions lead to epidemic levels of forest herbivory (e.g. massive outbreaks of phytophagous insects)?

Epidemic levels: can lead to total defoliation of large expanses of forest, Associated with climate conditions (e.g. drought), but also an outcome of intrinsic insect population cycles. More severe fluctuations in forests of high latitudes and high elevations (boreal and subalpine forests)

What is the role of endemic herbivory in forest ecosystem dynamics? Of epidemic herbivory?

Herbivory at both endemic and epidemic levels is a natural disturbance process, Creates canopy gaps for new regeneration, Creates structural diversity, Can accelerate nutrient cycling, Critically important for food webs

Discuss the life-history trade-offs associated with producing numerous small seeds vs. fewer large seeds.

Numerous small seeds tend do be more nutrient poor than larger seeds and individually have a lower chance of success
Fewer large seeds tend to be more nutrient-rich and are sometimes released only in good conditions, leading to a higher chance of them being successful

What role do different types of roots play for tree function, life history, and development? What is the importance of symbiotic associations formed with tree roots?

Coarse Roots play a critical role for structure, support, conduction of water and nutrients through the belowground system, and to allow trees to access novel areas that are rich in water or nutrients. They "turn over" slowly (like large branches, aboveground). Fine Roots, interacting with mycorrhizal fungi, play a critical role for taking up water and nutrients from the soil. They "turn over" quite rapidly (even much more rapidly than leaves do, aboveground).