No abstract

Forest succesion was studied in a species—rich cove forest of the Great Smoky Mountains, Tennessee. Long—term compositional and structural changes in secondary stands, 15—63 yr after agricultural abandonment circa 1920, were compared to an adjacent old—growth stand. Later successional trends were projected by computer simulation. The colonizing stand (15 yr) was dominated by Liriodendron tulipifera and Robinia pseudoacacia. Common old—growth species absent at this early stage included Aesculus octandra, Fagus grandifolia, and Tsuga Canadensis. By year 40, Liriodendron dominated the overstory and all old—growth dominants were represented in the understory. After 60 yr, Acer saccharum was clearly the most abundant understory species; gap model projections indicated that after 200 yr it will dominate the forest. The actual old—growth stand was dominated by Acer saccharum. Species richness peaked at mid—succession (°50 yr), while diversity (H') and evenness (J') of species biomass were highest at the old—growth stage. Richness peaked with the coexistence of shade—intolerant colonizers in the overstory and shade—tolerants in the understory. Canopy—gap processes of the secondary and old—growth stands differed sharply. The old—growth canopy was composed of large, spreading, and overlapping crowns, while the second—growth stand was composed of narrow, nonoverlapping crowns. Gaps in the secondary stand tended to be small (<100 m2) but numerous. The regeneration of intolerants was low and individual gap microsites were not markedly different from the understory as a whole. Old—growth gaps were often larger, higher light microsites which contrasted sharply with the shaded forest floor. The wider range of gap sizes in old forests accommodates a variety of species, including intolerants, contributing to the high canopy species diversity of old—growth cove forests.

Alpine plants of Oxyria digyna have higher apparent photosynthesis rates at various carbon dioxide concentrations than arctic, sea-level plants of the same species. The ability to utilize carbon dioxide effectively at low concentrations may be involved in the survival of plants at high elevations.

Aboveground biomass and aboveground net primary production (ANPP) were determined for leaf, branch, and bole compartments of cove forests in the Great Smoky Mountains, Tennessee. The sample plots included young stands (42-63 years following agricultural abandonment) and old stands with no history of logging or catastrophic fire. Tree species, diameter at breast height (DBH), and 10-year radial growth increment data were collected on plots of 0.4–1.0 ha. Biomass was estimated with species-specific allometric equations for the Great Smoky Mountains and eastern Tennessee. ANPP was estimated using diameter growth measurements to determine biomass accumulation over the preceding 10-year interval. Biomass estimates for the predominantly deciduous old-growth stands ranged from 326 to 394 Mg•ha−1 on plots ≥ 0.4 ha. These were consistently greater than the corresponding estimates of 216–277 Mg•ha−1 for young stands. The old Tsuga-dominated stands had the highest biomass estimates of 415–471 Mg•ha−1 for 1.0-ha plots. Annual ANPP estimates were high (11.7–13.1 Mg•ha−1) among the young stands. These stands had particularly high bolewood production. ANPP of the old-growth plots ≥ 0.4 ha ranged from 6.3 to 8.6 Mg•ha−1•year−1 for the deciduous stands and 8.0–10.1 Mg•ha−1•year−1 for the coniferous–deciduous stands. Previous biomass estimates for primeval cove forests were well above temperate forest means of 300–350 Mg•ha−1. Our estimates based on larger plots were lower than previous estimates of 500–610 Mg•ha−1, but they still exceeded temperate forest means. Our deciduous values were 26–94 Mg•ha−1 above the temperate deciduous forest mean of 300 Mg•ha−1, and our Tsuga–deciduous values were 65–121 Mg•ha−1 above the temperate coniferous forest mean of 350 Mg•ha−1.

A general amelioration of climate inland from the northernmost tip of Alaska is accompanied by distinctive changes in vegetation within a few miles, including an increase in the shrubby component of the vegetation, and a decrease in the prominence of the graminoid element. Simple instruments provided periodic values for rainfall, evaporation and evapotranspiration. Sod block evapotranspirometers, weighed at intervals, gave reasonable and consistent estimates of evapotranspiration rates, which increased by more than a third between the Ocean and 28 miles inland. RÉSUMÉ. Gradients du climat et de la végétation en été, près de Barrow, Alaska. À l'extrême pointe du nord de l'Alaska, on constate une amélioration générale du climat vers l'intérieur des terres, qui s'accompagne de changements visibles de la végétation en quelques milles seulement, dont une augmentation de l'élément broussailleux et une diminution d'importance de l'Clément graminacé. Des instruments très simples ont permis de recueillir des données périodiques sur la pluie, I'évaporation et l'évapotranspiration. Le pesage à intervalles réguliers d'évapotranspiromètres à motte de gazon a donné des estimations raisonnables des taux d'évapotranspiration, qui augmentent de plus du tiers entre l'océan et des lieux situés à 28 milles (45 km) à l'intérieur. PEBIOME. JIemnue xwuxamuuemue zpaauenmN u pacmumewbnbdi noxpos e paüone Eappoy (Awncxa). O6rqee y n y w u e H H e K n H M a T a no M e p e ynanemsr OT ~am6onee CeBepHOfi OKOHeYHOCTH AJIRCKH arny6b CTpaHbI COnpOBOECAWTCR OTqeTJIHBbIM HBMeHeHHeM B PaCTHTenbHOM nOKPOB€!, BaMeTHbIM yXe H a PaCCTOsrHEiH B HeCKOJIbKO MMJlb. B TaCTHOCTEI, POnb KyCTaPHHROB B03p&CTaeT, a POJIb SJIaIEOBbIX YeCKH E13MePSIJlEICb C IIOMOII(bI0 IIpOCTbIX np~160po~. &pHOAH4eCKOe BSBeIIIHBaHHe n o H H x a e T c R. I C o a m e c T B o O c a A K o B , ssanopaq~sr H ssano~pa~cn~paq~sr nepmoan-B e c o B x x H c n a p m e n e f i Aasano A o c T a T o s H o T o m N e H n o c n e A o B a T e n b H b I e oqemm C X O~O C T H 3 s a r r o~p a~c n~p a q~~, K o T o p a s r ysemsxxsanacb 60nee 9 e M H a T p e m H a paCCTORHHH B 28 MHJIb OT nobepexbsr O K e a H a .