North American boreal and western temperate forest vegetation

Salvador Rivas-Martínez, Daniel Sánchez-Mata & Manuel Costa

Itinera Geobotanica 12:5-316 (1999)

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Association. Fundamental and basic unit of the Phytosociology. It is a plant community-type with particular floristic, biogeographic, ecological, successional, historic and antropogenic features. It owns a particular ecological and geographic territory, some characteristic and differential species or a precise characteristic statistically reliable combination of species and diagnostic bioindicators. It may be determined from the comparative study of relevés, in which the floristic composition is annotated and quantified, like the rest of the ecological and geographic information of a particular homogeneous plant community. Making association relevés is the most important part of the phytosociological research. Associations with similar floristic composition, dynamic stage, structure, habitat or vicariant distribution may be taken together in types or units of higher rank (alliances, orders, classes).

Biogeocoenosis. The biostructure and environment of the terrestrial ecosystems, meaning the expression of the geobiosphere biocoenosis. They are constituted by the plant and animal communities, their biotope and their habitat. It is usual practise among the terrestrial plant ecologists to systematize the biogeocoenosis by their plant communities as well as by their particular mesologic factors and by their geographic distribution. So, the vegetation and its environment become the main support of its typology in the context of the Earth Sciences. The validity of this way of working, in the attempt of a biome modelization by means of its plant communities biodiversity, is justified by the success in its prediction power and the accurate ecogeographic jurisdiction of such units (if they are, of course, well structured, defined and verified).

Catena. Ensemble of contiguous plant communities ordered by any changing ecological factor (temperature, moisture, topography, etc.). It is the landscape representation of the zonation phenomena.

Climatic dominion. Area in which a climactical plant association has really or virtually the climax function. Taking in to account its usual pluri-teselar diversity, more homogeneous lower ranked units could be recognized.

Climax. Final equilibrium stage in geobotanic succesion. Plant community or phytocoenosis territorially representing the stage of biologically stable maximum. It can be also employed as the expression of a mature phytocoenosis, as well as the last stage or stable association of a vegetation series.

Geosigmetum. Also denominated geosigmassociation or geoseries, is one of the basic units of the Integrated Phytosociology (Geosymphytosociology). It seeks to be the catenal and successional expression of landscape science. It is built up with the contiguous sigmeta or vegetation series.

Microgeosigmetum. Vegetation transects or microcatenas constituted by microsigmassociations with a reduced surface. They are delimited by exceptional microtopographic and edaphic features which, in a small piece of ground, cause numerous ecological niches and teselas, covered by non-stratified permanent plant communities whose dynamic balance seems to have been reached. Under these conditions, the reference to a mature plant community of the theoric regional sigmetums is not possible or should be ambiguous. In general, the microgeosigmetums are monostratum vegetation-types ordered in microcatenas according to their determinant mesologic features. The most auspicious biotopes for the microsigmetum development are the cliffs and rock crevices, bogs, snowdrifts, mobile dunes, shores of lakes and ponds, springs, etc. The study of these neighboring plant community complexes must be made within their geomorphologic and ecological limits, following the increasing degree of their causing ecological factor. 
For their hierarchic ordination (-etum, -ion, -etalia, -etea) must be noted their biogeographic location, their bioclimatic peculiarities, as well as its statistical fidelity to the rest of communities also present in the microcatena, not to mention the possible vicariances with similar microcatenas in other territories.

Phytosociology. Science dealing with biocoenosis from a botanical perspective (phytocoenosis or phytosyntaxa). In others words, it is concerned with plant communities, their relationships with the environment and the temporary processes modifying them. With all this information, by means of inductive and statistic method, based on the reality of the vegetation phytosociological relevé, it attempts to create an universal hierarchic typology with the association as the basic unit of the syntaxonomical system. Nowadays we distinguish, besides classic or Braun-Blanquet"s Phytosociology (association level), Dynamic-Catenal or Landscape Phytosociology, whose units are the series or sigmetum (Dynamic or Successional Phytosociology) and the geoseries or geosigmetum (Catenal Phytosociology).

Potential natural vegetation (plant communities). Steady plant community which should be present in an area, as a consequence of the progressive succession, if there were not human influences. In practise, potential vegetation is considered synonymous to climax and to primitive vegetation (not altered yet by man). We must distinguish between the climatophilous (natural potential vegetation) and the edaphophilous series (permanent plant communities).

Sigmetum. Typological unit in Dynamic Phytosociology (Symphytosociology), it is also called Synassociation or Vegetation Series. It is the most important notion and unit in the Phytosocological Landscape Science, the one which has been used in our bioclimatic and biogeographic new approaches. It is a geobotanic notion that tries to express all the plant communities, or collection of stages, that can be found in similar teselar places as a result of the succession processes: and so, a Geosigmetum includes not only the representative vegetation type of the mature stage, or head series, but also the initial or subserial communities replacing it. If we integrate to a series their contiguos ones, that is, if we take into account, besides the succession, the catenal phenomenon, -for instance, the climatophilous and edaphophilous series that can be in contact- we have another more complex and integrated unit known as geoseries or geosigmetum (see above).

Succession. Natural process by which certain plant communities or vegetation stages replace each other in a particular order, within the same place unit or Tesela (see below). We may speak of progressive succession, which tends upwards to the stable optimum or climax (progression, preseral stages), and of regressive succession, the opposite (regression; subseral stages). The progressive and regressive processes do not follow necessarily the same stages.

Tesela. Elemental unit in the Biogeography. It is a territory or geographic area, greater or smaller in size, but ecologically homogeneous because only one vegetation series, that is, only one potential vegetation-type and only one sequence of successional plant communities, can settle within it.

Types of forests. In the following table we summarize both forest types and tree life-forms (biotypes), according to the heigth at their canopy top.

Types Meters Feet Life form
Microforest 3-12 9-37 Microphanerophyte
Mesoforest 12-24 37-73 Mesophanerophyte
Macroforest 24-50 73-152 Macrophanerophyte
Megaforest > 50 > 152 Megaphanerophyte

Vegetation series. Geobotanic unit expressing all the various stages of plant communities that can be found in similar teselar places as a result of the succession processes. It includes, together with the representative vegetation-type of the mature stage of series head (climax), the initial preseral and subseral communities replacing it. Thus considered, the vegetation series is a synonym of synassociation or sigmetum (see above), the basic unit of the Dynamic Phytosociology (Symphytosociology). If we integrate a series with those contiguous with it, that is, if we take in to account, besides the succession, the catenal phenomenon -for instance, the climatophilous and edaphophilous series that may be in contact- we have anothers complexer unit known as geoseries (geosigmetum), the basic unit of Catenal Phytosociology.

Zones and latitudinal belts in the Earth. The Earth has three distinguishable broad latitudinal zones: 1. Warm or torrid (0º to 35ºN & S), 2. Cool or temperate(35º to 66ºN & S), 3. Cold or frigid (66ºN to 90º), as well as eleven latitudinal belts in total (North and South). The latitudinal figures are in correspondence with major bioclimatic boundaries. Macrobioclimate acronyms, Tr: Tropical, Me: Mediterranean, Te: Temperate, Bo: Boreal, Po: Polar.

Zones Belts Bioclimate
1. Warm (Torrid)
 (0º to 35º N & S)
7ºN to 7ºS Equatorial 0º to 23º N & S World Tr territory
7º to 23ºN & S Eutropical 23º N & S Me and Te edge
23º to 35ºN & S Subtropical 35º N & S Tr edge
2. Cool (Temperate)
 (35º to 66º N & S)
35º to 52ºN & S Eutemperate 52º N & S Me edge
52º to 66ºN & S Subtemperate 52º N & S Po edge [51º45'N]
3. Cold (Frigid)
 (66º to 90º N & S)
66º to 90ºN Arctic 66º N Te edge
66º to 90ºS Antarctic 66º S Athermic edge


Figure 4. Distribution of Macroclimates in North America (between parenthesis those North American bioclimates, Aleutian Islands included): 1. Polar (Hyperoceanic Po., Oceanic Po., Continental Po., Xeric Po., Pergelic Po.), 2. Boreal (Hyperoceanic Bo. , Oceanic Bo., Subcontinental Bo., Continental Bo., Xeric Bo.), 3. Temperate (Hyperoceanic Te., Oceanic Te., Continental Te., Xeric Te. ), 4. Mediterranean (Pluviseasonal Oceanic Me., Pluviseasonal Continental Me., Xeric Oceanic Me., Xeric Continental Me., Desertic Oceanic Me., Desertic Continental Me. ), 5. Tropical (Pluvial Tr., Pluviseasonal Tr., Xeric Tr., Desertic Tr. ). [Synthesis by S. Rivas-Martínez with the collaboration of M. Costa, J. Giménez de Azcárate, A. Penas and D. Sánchez-Mata].