Climatic control of zonal vegetation in northern Asia
Pavel V. Krestov
Botanical Garden-Institute FEB RAS, Vladivostok, 690024, Russia
This study focuses at the problem of indication of climatic gradients by vegetation complexes at local and regional scales and aims to quantify the local and regional scale relations of vegetation units, their complexes and climatic parameters within boreal vegetation zone in Northeast Asia.
We used phytosociological (over 5000 releves), climatic (2200 climatic stations) and floristic (distribution records for 22 000 species) databases. Identification of bioclimates was made in accordance with Rivas-Martínez et al. (1999) approach using different climatic parameters that include Kira's warmth (WK) and coldness (CK) indices, continentality index (CI), ombro-evapotranspirational (OEI) index and winter precipitation (WP).
Analysis of indices calculated with an aid of developed models showed the significant differences of vegetation units of the order rank in bioclimatic ranges. WK decreases from values over 75 in the middle temperate zone (Saso-Fagetalia, Aceri-Quercetalia) to 20 in subarctic zone. Among boreal vegetation units the orders of Betulo-Ranunculetea have the lowest warmth index in the circumboreal zone that can be explained by cool summer in conditions of oceanic climate. CK varies between values of -25 and -150 within boreal and temperate zones with prevalence of deciduous broadleaved, mixed and evergreen broadleaved forests. The boreal orders Lathyro-Laricetalia and Ledo-Laricetalia representing boreal deciduous coniferous forests are characterized by very low values of coldness index that, in this case, is comparable to that of subarctic orders.
The ranges of orders along the continentality gradient are reflected by changes of vegetation types within a zone with proximity to the ocean. In boreal zone the lowest values of CI are characteristic to the forestless and not yet described class of Aleutian meadows, followed by Alnus fruticosa scrub and Betula ermanii forests of the class Betuletea ermanii. Highest values belong to deciduous coniferous orders Lathyro-Laricetalia and Ledo-Laricetalia.
The snow affects vegetation strongly in the conditions of continental climate within northern subzone of temperate zone, where lack of snow in winter causes a shortage of moisture in spring and early summer, and in oceanic regions of boreal zone, where the strong accumulation of snow causes 2-3 week delay of its melting and a considerable shortening of growing season. The communities of Betula ermanii, Alnus fruticosa and tall-forb meadows are characteristic to the regions with slower-melting heavy snow deposits.
Zonal subarctic vegetation is represented by communities of provisional class Betuletea glanduloso-divaricatae composed of species complexes of Pacific coastal mountainous regions. In boreal zone, vegetation of Asian ultracontinental to maritime sectors is represented by communities of Vaccinio-Piceetea, Asian suboceanic to hyperoceanic sectors – by communities of Betulo-Ranunculetea. The boreal classes were likely differentiated in Pre-Pleistocene time due to the well developed floristic centers under the different climatic situations.