No abstract

No abstract

This paper considers the productivity and nutrient cycling in examples of the major forest types in interior Alaska. These ecosystem properties are examined from the standpoint of the control exerted over them by soil temperature and forest-floor chemistry. We conclude that black spruce Piceamariana (Mill.) B.S.P. occupies the coldest, wettest sites which support tree growth in interior Alaska. Average seasonal heat sums (1132 ± 32 degree days (DD)) for all other forest types were significantly higher than those encountered for black spruce (640 ± 40 DD). In addition, black spruce ecosystems display the highest average seasonal forest-floor and mineral-soil moisture contents. Forest-floor chemistry interacts with soil temperature in black spruce to produce the most decay-resistant organic matter. In black spruce the material is characterized by the highest lignin content and widest C/N (44) and C/P (404) ratios. Across the range of forest types examined in this study, soil temperature is strongly related to net annual aboveground tree production and the annual tree requirement for N, P, K, Ca, and Mg. Forest floor C/N and C/P ratios are strongly related to annual tree N and P requirement and the C/N ratio to annual tree production. In all cases these controls act to produce, in black spruce, the smallest accumulation of tree biomass, standing crop of elements, annual production, and element requirement in aboveground tree components.

Vegetative changes were documented for 7 years on permanent milacre plots located in three clearcut logged units in the western Cascade Mountains of Oregon. Plant cover and composition were observed the year prior to logging the old—growth Pseudotsuga menziesii forest, after logging but before burning, and during each of five growing seasons following broadcast slash burning. Total plant cover was 15.2 49.3, and 75.5% in the first, second and fifth years after slash burning, respectively. Invading herbaceous species dominated from the second through fourth growing seasons after burning but by the fifth year residual herbaceous species regained dominance. Differences in disturbance from logging and burning strongly influenced successional trends. In undisturbed soil areas, residual species, such as Acer circinatum, Oxalis oregana, and Gaultheira shallon, dominated. Areas disturbed by logging but unburned supported a wide variety of both residual and invader species. Light to severely burned sites were largely occupied by invaders such as Ceanothus velutinus, Epilobium angustifolium, and E. paniculatum. Although often obscured by varying degrees of disturbance, relationships between early stages of succession and prelogging plant community were discernible. For example, of the species considered characteristic of five undisturbed plant communities, only 13 percent were absent from the plots 5 years after burning. The invaders Ceanothus velutinus, Agoseris grandiflora, and Gnaphalium microcephalum var. thermale were restricted to sites previously supporting rather xeric communities; while Rubus leucodermis and Anaphalis margaritacea were found on plots characteristic of the more mesic communities.

Vegetation, forest productivity, and soils of 23 forest stands in the taiga of interior Alaska are described. The stands are arranged on an environmental gradient from an aspen (Populustremuloides Michx.) stand on a dry, steep south-facing bluff, to open black spruce (Piceamariana (Mill.) B.S.P.) stands underlain by permafrost on north-facing slopes. The coldest site is a mixed white spruce (Piceaglauca (Moench) Voss) and black spruce woodland at the treeline. Mesic upland sites are represented by successional stands of paper birch (Betulapapyrifera Marsh.) and aspen, and highly productive stands of white spruce. Several floodplain stands represent the successional sequence from productive balsam poplar (Populusbalsamifera L.) and white spruce to black spruce stands underlain by permafrost on the older terraces. The environmental gradient is described by using two soil factors: soil moisture and annual accumulated soil degree days (SDD), which range from 2217 SDD for the warmest aspen stand to 480 SDD for the coldest permafrost-dominated black spruce site. Soils vary from Alfie Cryochrepts on most of the mesic sites to Histic Pergelic Cryochrepts on the colder sites underlain by permafrost. A typical soil profile is described for each major forest type. A black spruce stand on permafrost has the lowest tree standing crop (15806 g•m−2) and annual productivity (56 g•m−2•year−1) whereas a mature white spruce stand has the largest tree standing crop (24 577 g•m−2) and an annual productivity of 540 g•m−2•year−1, but the successional balsam poplar stand on flood plain alluvium has the highest annual tree increment (952 g•m−2•year−1). The study supports the hypothesis that black spruce is a nutrient poor, unproductive forest type and that its low productivity is primarily the result of low soil temperature and high soil moisture.