Aboveground biomass and nitrogen nutrition in a chronosequence of pristine Dahurian Larix stands in eastern Siberia

Abstract

Measurements of aboveground biomass and nitrogen (N) nutrition were made during July 1993 in 50-, 130-, and 380-year-old stands of Larixgmelinii (Rupr.) Rupr. in eastern Siberia. Constituting six forest types based on understorey plants, the stands were representative of vegetation throughout the Yakutsk region. Average tree height, diameter, and density ranged from 2 m, 23 mm, and 50 800 stems/ha in the 50-year-old stand to 11 m, 160 mm, and 600 stems/ha in the oldest stand. Aboveground biomass in the 50-year-old stand was 4.4 kg•m−2, and the aboveground N pool was 1.1 mol•m−2. This was slightly higher than the N pool in a 125-year-old stand with a Ledum understorey (1.0 mol•m−2), despite its higher biomass (7.2 kg•m−2). The highest observed aboveground biomass in a 125-year-old stand (characterized by the N2-fixing understorey plant Alnasterfruticosa) reached 12.0 kg•m−2, but the corresponding N pool was only 1.6 mol•m−2. In the oldest stand, aboveground biomass was 8.9 kg•m−2 and the N pool was 1.1 mol•m−2. There was thus a relatively constant quantity of N in the aboveground biomass of stands differing in age by almost 400 years. We postulate that N sets a limit on carbon accumulation in this boreal forest type. Trees were extremely slow growing, and there was essentially no aboveground biomass accumulation between the ages of 130 and 380 years because of a lack of available N. This conclusion was supported by graphical analysis indicating that the self-thinning process in our stands was not governed by the availability of radiation according to allometric theory. Much of the available N was used in the production of tree stems where 86% of the aboveground N (and 96% of aboveground biomass) was immobilized in the oldest stand. N in wood of the old stand exceeded the N pool in the litter layer and was 20% of the N pool in the Ah horizon. The processes of carbon and N partitioning were further explored by the estimation of carbon and N fluxes during three periods of forest development. We calculated a loss of ecosystem N during the period of self-thinning, while in the mature stands the N cycle appeared to be very tight. The immobilized N is returned from the wood into a plant-available form only by a recurrent fire cycle, which regenerates the N cycle. Thus fire is an essential component for the persistence of the L. gmelinii forest.

Nitrogen availability in the taiga forest ecosystem of northeastern Siberia

“…To evaluate the amount of recycled nutrients, we estimated N demand for our 150-year-old larch stand. In previous reports (Schulze et al 1995;Shibuya et al 2004), in northeastern Siberia, forest aboveground biomass becomes saturated at the age of 120-130 yr and does not change much after that. Therefore, we assume that the biomass production reported for 120 and 125-yearold stands (Schulze et al 1995;Shibuya et al 2004) was similar to that of our 150-year-old study site.…”

“…The majority of these works have been reported in Russian; therefore, up to now, these studies have not been available to most scientists outside Russia. Based on accessible information, the available inorganic N was likely to be a limiting factor for plant growth in central (Tokuchi et al 2010) and northeastern parts of Siberia (Schulze et al 1995). In addition, the amount of N in the soil pools, the plant N , the soil inorganic N, and the decomposition rate (Shugalei and Vedrova 2004) in central Siberia, have been observed.…”

Forest–atmosphere carbon dioxide exchange in eastern Siberia

“…Schulze et al (1995) found $47 t C ha À1 in the forest aboveground biomass, 5 t C ha À1 in the litter and $37 t C ha À1 in the top soil (Ah) horizon. To this we could add an estimated 5 t C ha À1 in coarse roots.…”

Parallel Seasonal Patterns of Photosynthesis, Fluorescence, and Reflectance Indices in Boreal Trees

“…Deciduous species have thinner leaves with a greater surface area than evergreens, allowing them to be more productive during favorable conditions, whereas evergreens have thick leaves that avoid damage brought on by frost or drought during unfavorable seasons [41]. The conifer L. laricina, though deciduous, showed very similar photosynthetic rates to evergreen species, and typically has low summer rates of photosynthetic activity and growth [42].…”