Plant Succession
The Investigation of Succession
Clements (1916) emphasizes the importance of understanding plant succession. The complete method involves inference, sequence, and experiment to trace the course of succession, even within a few years. Intensive investigation requires synchronous study of development between stages.
Methods of Investigation
Experiment
Experimentation is a valuable adjunct to the sequence method, allowing reproduction and intensive observation of developmental stages. It's crucial in climax areas with few seral communities and expedites conclusive results in areas with predominant developmental stages. It is especially dependent upon the quadrat method.
Special Methods
Special methods for successional investigation include:
Quadrat method
Mapping
Instrumentation
Recording
These methods are intensive, used with sequence and experiment. The quadrat method is fundamental for studying development. Instruments are essential for analyzing habitat and plant reactions. Adequate record-keeping is crucial, detailing observations and experiments separately from their interpretation.
The Quadrat Method
The quadrat method encompasses exact methods for determining plant community composition and structure, regardless of shape or size. It includes the transect, bisect, and migration circle, all based on enumeration or charting individuals within a defined area, revealing changes in population and structure. Squares have been used for enumeration for over a century, but Pound and Clements (1898, 1900) organized it into a system for studying vegetation structure and development.
Kinds of Quadrats
Quadrats are categorized by purpose, location, or size:
Purpose/Use: list, chart, permanent, and denuded quadrats.
Location: layer, soil, water, lichen, moss quadrats, etc.
Size: unit quadrat (1 meter square), subquadrats (decimeter or centimeter square), or perquadrats (up to 100 or 1,000 meters square).
The meter quadrat is standard for herbland, the 10-meter for scrub, and the 100-meter for forest.
List quadrats are useful for census-taking and floristic comparisons.
Chart quadrats record composition and structure.
Permanent and denuded quadrats are designed for succession studies using sequence and experiment methods.
List Quadrat
The list quadrat has limited value for succession studies due to its lack of year-to-year study of a specific area. It's useful for reconnaissance but not for intensive investigation. Jaccard and Raunkiaer developed applications based on list quadrats:
Jaccard's method establishes a statistical method for floristics, focusing on the origin of a region's flora. It uses:
Coefficient of community
Degree of frequence of each species
Generic coefficient (percentage relation of genera to species)
Jaccard's principles have limited applicability for present-day succession, being better suited for tracing flora differentiation into climaxes and migrations during a clisere.
Raunkiaer's system classifies life-forms based on bud protection during unfavorable seasons, allowing definite comparisons and correlation of life-forms and climate. Analyzing a region's flora into life-forms yields a biologic or phyto-climatic spectrum, compared with a normal spectrum. Raunkiaer also uses a list quadrat (later a circle) but it fails to account for succession and has only floristic value.
Chart Quadrat
Chart quadrats, unlike permanent and denuded ones, are not fixed and revisited annually but use the same charting methods. An area (usually 1 or 10 meters) is staked out with quadrat tapes divided into centimeters, with eyelets at decimeter or meter intervals. Charting is done decimeter by decimeter, using special sheets, with each plant indicated by initials (generic name if unique, otherwise abbreviated), exponents for stem numbers (e.g., ), and lines for seedlings (horizontal) or flowering/fruiting plants (vertical). Forest quadrat uses small letters for seedlings and capital for matures.
Chart quadrats are used for comparing different examples of the same community or adjacent zones/stages of a sere and are essential for inferring sere sequences from scattered stages. Permanent quadrats provide all values of simple chart quadrats.
Permanent Quadrat
In successional research, it's crucial to follow development in detail from year to year, especially across sun-spot cycles, using permanent quadrats. These quadrats enable a complete record of successional changes and are recorded as charts. They fall into two groups:
Permanent quadrats proper: reveal changes in different stages/associes of a sere.
Denuded quadrats: reestablish earlier conditions by removing reactions.
The combination of permanent and denuded quadrats in pairs, across seral communities and zones, is most effective.
Denuded Quadrat
A denuded quadrat is a permanent quadrat with the plant covering removed after charting/photographing. It's useful for studying ecesis and competition relative to reaction. Denuding helps analyze succession and reveals otherwise unavailable stages. Mapping, photographing, and labeling occurs before vegetation removal via removal, burning, or flooding. The type/degree of denudation depends on the sought evidence.
Quadrat Series and Sequences
Paired quadrats (permanent + denuded) are located side by side in each associes or consocies and charted annually. Recording light, humidity, temperature, and soil factors gives a complete succession picture. Permanent quadrats connect stages, while denuded quadrats analyze migration, ecesis, competition, and reaction, aided by instrument data.
A time sequence involves denuding one quadrat each year, with space between areas for invasion, reproducing a series of stages for comparative study. A sequence in space analyzes reaction by denuding areas in the same community in different ways/depths.
Various Quadrats
The quadrat method, with modifications, applies to all plant communities, including pioneer communities in water and on rock. Chart quadrats of aquatic consocies are readily created. Lichen and moss quadrats are easily made permanent/denuded. Soil quadrats may facilitate analysis of root relations.
The Transect
The transect, an elongated quadrat, reveals population changes and helps delimit ecotones. The line transect indicates species encountered along a line, while the belt transect (varying width) corresponds to the chart quadrat and can be permanent/denuded.
A line transect involves pacing and noting species. Belt transects use tapes to mark a strip, with width varying by area. For diversified areas, topography is determined with a transit. Charting follows quadrat methods, recording transect segments on the same sheet. Belt transects becomes more valuable if it is made permanent, by using a transit or compass. The transect has a stake at each end with direction, length, and ecotone positions. The quadrat provides information about the composition/structure of a typical portion of a community, but the transect traces change through ecotones. The combination of quadrat and transect works best for grassland and forest undergrowth.
Denuded Transect
The denuded transect adds value to a permanent one, providing new stages for analysis of each zone/ecotone. A permanent transect of double width can be charted, then one-half denuded.
The Bisect
The layer transect records vertical species relations in a layered community, recording the disappearance of layers as the climax is reached and root relations are considered. A bisect is a cross-section showing shoots and roots in their normal position and used to show relations of aquatic and swamp plants, along with the exact relations of layers.
The Migration Circle
The migration circle (migrarc) analyzes migration, particularly without ecesis. Studies of migration have focused on establishment, but local and mass migration drives succession. A migration circle is located relative to an individual, community, or ecotone, concentric circles marked out to measure dispersal. The determination of migration alone demands the most minute study. Study of actual movement can best be made upon snow surfaces or upon the bare ground.
Methods of Mapping
Schröter discusses ecological cartography. Intensive succession studies focus on micrographic methods dealing with individual plants/communities. These methods include:
Extensions of the quadrat method.
Ecotone and community mapping.
Combined quadrat and map method.
The gridiron method indicates contours and community outlines rather than individuals. The method of squares employs areas square, continuously covering area to be mapped.
Community Charts and Ecotone Maps
Community charts resemble gridiron maps of Oliver and Tansley. Ecotone maps relate to zones and alternes and are constructed by tracing ecotones between zones.
Survey Maps
Vegetation surveys combine topographic/ecotone maps with quadrats and transects. The mapping unit is the "forty." Topographic and artificial features and ecotones of communities are mapped in detail. Cultural and natural communities are indicated, taking instrument readings and photographs. This provides a complete structure/development along with contributing physical factors. It leads to a complete overall vegetation picture providing insight to the forestry, grazing and agriculture.
Climax Maps
Vegetation maps often fail to distinguish between climax and developmental communities. Climax formations provide the basic area structure, however transition areas need to be settled by intensive studies.
Instrumental Methods
Instrumental studies of vegetation are not yet a rule. Instruments are used to analyze habitat and critical processes in succession, such as reaction, ecesis, and competition. The primary reactions control the movement of successive populations and the effect of reaction is felt during germination and during any of the mixed populations.
Measurement of Reactions
Instrumental investigation is critical for understanding succession. General measurements, such as meteorological observations, are of little value. The instrumental study should concentrate on factors in primary control, such as water and light reactions. It should be recognized that the reaction affects the quality and quantity, and humidity along with water-content. While instruments provide measurements, using Standard plants is also essential.
Measurement of Water Reactions
Community reaction on water affects the amount of holard and echard, or humidity degree. It can change water-content by altering nutrient content. Accurate field study of reaction requires:
Determining holard in soil's reaction-level.
Determining chresard/echard at root depths in reaction-level.
Measuring humidity/evaporation in air's reaction-level.
Determining soil-water acidity/alkalinity at different depths.
Measuring evaporation is standardized by the porous-cup method. It is Inevitable that transpiration be largely substituted to compensate for its effects to control reactions. Methods determine the degree of acidity, lack of oxygen, and that the oxygen leads to a real factor of effect. The determination of the alkalinity to the soil solution is already thoroughly worked out.
Measurement of Light Reactions
Various methods measure light values. Light measuring instruments are based on the use of photographic paper. The writer has designed photometers such as: simple photometer, stop-watch photometer, water photometer, selagraph (recording photometer), spectro-photometer. A method is being made to develop photosynthesis amounts with standardized plants in each seral stage.
Growth Methods
Ring-Counts
Annual rings are important in determining successional relations and woody dominants. Exact methods of ring-counts and quadrats help support exact counts to any conclusions. Ring counts are used in ecotone recognition and dominants in mictis. In reproduction, ages determine success and invasion. Lumbering and clearing leads to intensive succession, stump counts, and constant use of any required tools.
Burn-Scars
Ring counts and scars from fire help determine fire dates and successional changes. Scars and root suckers on trees show fire action at various locations. Scars consist of position, depth, heal/hidden, and white/cinder scars. Fire severity is indicated by depth of scars, differentiating bark/wood scars, and the observation of soil layers also help.
Evidence from fire scars and annual rings determines the possibility of fire error to the exact dates. If the growing season is not over, scars and root suckers will show one more ring. Simple rules exist for these issues and can show the trunks that got cut to lead any required measurements.