Primary succession of the warm-temperate broad-leaved forest on a volcanic island, Miyake-jima, Japan

The primary successional sere of a warm-temperate forest was inferred from an age sequence of four basaltic volcanic substrates (16-, 37- and 125-yr-old lava flows, and volcanic ejecta older than 800 years) at several altitudes (ranging from 30 to 550 m) on Miyake-jima Island. The DCA analysis of species composition indicated that the vegetation is patterned by substrate age and altitude. The vegetation successionally changed fromAlnus sieboldiana shrub, toMachilus thunbergii andPrunus speciosa forest, toCastanopsis sieboldii forest at all altitudes. The rate of succession seems to be slower at higher altitudes. The above-ground biomass was 20 kg/m² (160 m a.s.l.) and 12 kg/m² (300 m a.s.l.) on the 125-yr-old lava flow, and 54 kg/m² (100 m a.s.l.) and 16 kg/m² (350 m a.s.l.) on the old ejecta. However, the large difference of above-ground biomass between low versus high altitudes on the old ejecta might not only reflect climatic differences but also past human disturbances at the higher altitude. In spite of the colder climate of Miyake-jima the rate of above-ground biomass accumulation here was considerably faster than that of a Hawaiian montane tropical evergreen forest on the same basaltic lava substrate. We suggest that the faster above-ground biomass development is due to the facilitation effects of N-fixation byAlnus. The inorganic N soil concentration was extremely high on the 37- and 125-yr-old lava flows whereAlnus was dominant. The foliar N concentration inAlnus was 2% irrespective of substrate age. The deposition of N fromAlnus via litterfall would decrease the soil C/N ratio, which in turn facilitates net soil N mineralization and consequently provides an ample supply of inorganic N to plants. N limitation on vegetation development, which is prevalent during the early stage of succession on volcanic lava flows or similar substrates elsewhere, is thus alleviated.     

Primary plant successions of forest belt vegetation on the Tolbachinskii Dol volcanic plateau (Kamchatka)

Primary plant successions on volcanic deposits of the Tolbachinskii Dol Plateau (Central Kamchatka) were studied. The main factors determining the succession rate were revealed. The peculiarities of plant successions on lava flows and ash–scoria deposits differed significantly. Some common mechanisms for all volcanic regions of the world were revealed. The leading factors of plant succession on lava flows were the type of lava surface, the texture of lava, and the fine tephra accumulation rate. The main factors determining plant succession on ash–scoria deposits were wind and water erosion and the distance to the seed sources. The time of formation of a secondary permanent larch (Larix cajanderi Mayr.) forest should take about 1500–2000 years on lava flows and up to 1000 years (but not less than 300–500 years) on ash–scoria plains.     

Stabilization of recent soil carbon in the humid tropics following land use changes: evidence from aggregate fractionation and stable isotope analyses

Quantitative knowledge of stabilization- and decomposition processes is necessary to understand, assess and predict effects of land use changes on storage and stability of soil organic carbon (soil C) in the tropics. Although it is well documented that different soil types have different soil C stocks, it is presently unknown how different soil types affect the stability of recently formed soil C. Here, we analyze the main controls of soil C storage in the top 0.1 m of soils developed on Tertiary sediments and soils developed on volcanic ashes. Using a combination of fractionation techniques with ¹³C isotopes analyses we had the opportunity to trace origin and stability of soil carbon in different aggregate fractions under pasture and secondary forest. Soil C contents were higher in volcanic ash soils (47–130 g kg⁻¹) than in sedimentary soils (19–50 g kg⁻¹). Mean residence time (MRT) of forest-derived carbon in pastures increased from 37 to 57 years with increasing silt + clay content in sedimentary soils, but was independent from soil properties in volcanic ash soils. MRTs of pasture-derived carbon in secondary forests were considerably shorter, especially in volcanic ash soils, where no pasture-derived carbon could be detected in any of the four studied secondary forests. The implications of these results are that the MRT of recently incorporated organic carbon depends on clay mineralogy and is longer in soils dominated by smectite than non-crystalline minerals. Our results show that the presence of soil C stabilization processes, does not necessarily mean that recent incorporated soil C will also be effectively stabilized.     

Soil-nutrient availability and the nutrient-use efficiencies of forests along an altitudinal gradient on Yakushima Island,Japan

The vegetation on Yakushima Island, Japan, grows on soils derived from Akahoya volcanic ash, released from the Kikai Caldera about 7300 years ago. The eruption was devastating and it is believed that primary succession and soil formation reinitiated across all altitudes at this point. We hypothesize that the concentrations of soil total phosphorus (P) and labile P fractions increase with increasing altitude because the soil formation has progressed less in upslope areas as a result of the cooler temperature and because of the ample P source of the volcanic ash. Conversely, we hypothesize that the concentration of soil inorganic nitrogen (N) decreases with increasing altitude. Available soil P and N would result in increasing P limitation downslope and increasing N limitation upslope, respectively. We studied soil P fractions and soil inorganic N, and P- and N-use efficiencies of the seven forests on Yakushima along an elevation gradient (170–1550 m a.s.l.). Contrary to our hypotheses, soil total P, labile soil P fractions, and inorganic N decreased with increasing altitude. The P- and N-use efficiencies of the forests were negatively correlated with the concentration of soil total active P (total P minus occluded P) and inorganic N, respectively. We suggest that progressive soil acidity and slower decomposition under cooler and wetter environments upslope must have dissolved the P contained in volcanic ash and accelerated P leaching. Forest ecosystems on Yakushima that show a distinct altitudinal zonation are, therefore, characterized by increasing P and N shortage with increasing altitude.     

Soil carbon and nitrogen stocks in forests along an altitudinal gradient in the eastern Himalayas and a meta‐analysis of global data

High‐altitude soils potentially store a large pool of carbon (C) and nitrogen (N). The assessment of total C and N stocks in soils is vital to understanding the C and N dynamics in terrestrial ecosystems. In this study, we examined effects of altitude and forest composition on soil C and N along a transect from 317 to 3300 m a.s.l. in the eastern Himalayas. We used meta‐analysis to establish the context for our results on the effects of altitude on soil C, including variation with depth. Total C and N contents of soils significantly increased with altitude, but decreased with soil depth. Carbon and N were similarly correlated with altitude and temperature, and temperature was seemingly the main driver of soil C along the altitudinal gradient. Altitude accounted for 73% of the variation in C and 47% of the variation in N stocks. Soil pH and cation exchange capacity were correlated with both soil C and N stocks. Increases in soil C and N stocks were related to forest composition, forest basal area as well as quantity of leaf litter that were in turn influenced by altitude and temperature. Concentrations of C in foliage increased by 2.1% for every 1000 m rise in altitude, while that in leaf litter increased by 2.3%.     

Carbon, nitrogen and phosphorus in volcanic soils following afforestation with native birch (Betula pubescens) and introduced larch (Larix sibirica) in Iceland

Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth) and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed to a slow accumulation of organic matter. Soil N concentrations and soil P_tot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material (400 Mg soil ha⁻¹ in 0–10 cm depth and 600 Mg soil ha⁻¹ in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average 23.6 Mg ha⁻¹ in the upper soil layer and 16.9 Mg ha⁻¹ in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha⁻¹ year⁻¹ in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha⁻¹ in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass of the growing trees. Soil P_tot pools were in average 220 and 320 kg P ha⁻¹ in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence on the availability of N and P to the trees. Responsible Editor: Hans Lambers.     

Fire effects on ecosystem nitrogen cycling in a Californian bishop pine forest

Fire can cause severe nitrogen (N) losses from grassland, chaparral, and temperate and boreal forest ecosystems. Paradoxically, soil ammonium levels are markedly increased by fire, resulting in high rates of primary production in re-establishing plant communities. In a manipulative experiment, we examined the influence of wild-fire ash residues on soil, microbial and plant N pools in a recently burned Californian bishop pine (Pinus muricata D. Don) forest. Ash stimulated post-fire primary production and ecosystem N retention through direct N inputs from ash to soils, as well as indirect ash effects on soil N availability to plants. These results suggest that redistribution of surface ash after fire by wind or water may cause substantial heterogeneity in soil N availability to plants, and could be an important mechanism contributing to vegetation patchiness in fire-prone ecosystems. In addition, we investigated the impact of fire on ecosystem N cycling by comparing ¹⁵N natural abundance values from recently burned and nearby unburned P. muricata forest communities. At the burned site, ¹⁵N natural abundance in recolonising species was similar to that in bulk soil organic matter. By contrast, there was a marked ¹⁵N depletion in the same species relative to the total soil N pool at the unburned site. These results suggest that plant uptake of nitrate (which tends to be strongly depleted in ¹⁵N because of fractionation during nitrification) is low in recently burned forest communities but could be an important component of eco- system N cycling in mature conifer stands. Received: 29 June 1999 / Accepted: 24 October 1999     

The effect of fire on nutrients in a pine forest soil

The effect of a hot summer fire on soil nutrient contents in the upper 2 cm of Aleppo pine forest with a dense woody understory was studied from September 1985 to May 1986. In comparison with the adjacent unburned forest, total nitrogen decreased by 25% but available forms of nitrogen were much higher. In burned and unburned soils there was a similar trend to increase and decrease in NH ₄ ⁺ −N, However, while (NO ₂ ⁻ +NO ₃ ⁻ −N decreased in the unburned soil it rose rapidly in the burned ash soil. Total phosphorus increased by 300% after the fire but decreased again 2 months later. Also water-soluble P increased up to November and then decreased to the levels of the unburned soils. The same was true for electrical conductivity and pH, increasing immediately after the fire and then leveling off again. This increase in nutrient levels in the “ash soil” was reflected in the striking increase in shoot and root biomass and in the content of N, P, Mg, K, Ca, Zn and Fe in wheat and clover plants grown in pots in these soils. These nutrient levels were much higher in the wheat plants, which also produced 12 times more seeds in the “ash soil.” It seems that fire in these pine forests causes a short-term flush of the mineral elements in the upper “ash soil” layer which is reverted gradually via the herbaceous post-fire to the ecosystem.     

Microbial Responses to Long-Term N Deposition in a Semiarid Grassland

Nitrogen (N) enrichment of the biosphere is an expanding problem to which arid ecosystems may be particularly sensitive. In semiarid grasslands, scarce precipitation uncouples plant and microbial activities, and creates within the soil a spatial mosaic of rhizosphere and cyanobacterial crust communities. We investigated the impact of elevated N deposition on these soil microbial communities at a grama-dominated study site located incentral New Mexico (USA). The study plots were established in 1995 and receive 10 kg ha⁻¹ year⁻¹ of supplemental N in the form of NH₄NO₃. Soil samples were collected in July 2004, following 2 years of severe drought, and again in March 2005 following a winter of record high precipitation. Soils were assayed for potential activities of 20 extracellular enzymes and N₂O production. The rhizosphere and crust-associated soils had peptidase and peroxidase potentials that were extreme in relation to those of temperate soils. N addition enhanced glycosidase and phosphatase activities and depressed peptidase. In contrast to temperate forest soils, oxidative enzyme activity did not respond to N treatment. Across sampling dates, extracellular enzyme activity responses correlated with inorganic N concentrations. N₂O generation did not vary significantly with soil cover or N treatment. Microbial responses to N deposition in this semiarid grassland were distinct from those of forest ecosystems and appear to be modulated by inorganic N accumulation, which is linked to precipitation patterns.     

Carbon cycling and sequestration in a Japanese red pine (Pinus densiflora) forest on lava flow of Mt. Fuji

Biometric-based carbon flux measurements were conducted in a pine forest on lava flow of Mt. Fuji, Japan, in order to estimate carbon cycling and sequestration. The forest consists mainly of Japanese red pine (Pinus densiflora) in a canopy layer and Japanese holly (Ilex pedunculosa) in a subtree layer. The lava remains exposed on the ground surface, and the soil on the lava flow is still immature with no mineral soil layer. The results showed that the net primary production (NPP) of the forest was 7.3 ± 0.7 t C ha^?1 year^?1, of which 1.4 ± 0.4 t C ha^?1 year^?1 was partitioned to biomass increment, 3.2 ± 0.5 t C ha^?1 year^?1 to above-ground fine litter production, 1.9 t C ha^?1 year^?1 to fine root production, and 0.8 ± 0.2 t C ha^?1 year^?1 to coarse woody debris. The total amount of annual soil surface CO₂ efflux was estimated as 6.1 ± 2.9 t C ha^?1 year^?1, using a closed chamber method. The estimated decomposition rate of soil organic matter, which subtracted annual root respiration from soil respiration, was 4.2 ± 3.1 t C ha^?1 year^?1. Biometric-based net ecosystem production (NEP) in the pine forest was estimated at 2.9 ± 3.2 t C ha^?1 year^?1, with high uncertainty due mainly to the model estimation error of annual soil respiration and root respiration. The sequestered carbon being allocated in roughly equal amounts to living biomass (1.4 t C ha^?1 year^?1) and the non-living C pool (1.5 t C ha^?1 year^?1). Our estimate of biometric-based NEP was 25 % lower than the eddy covariance-based NEP in this pine forest, due partly to the underestimation of NPP and difficulty of estimation of soil and root respiration in the pine forest on lava flows that have large heterogeneity of soil depth. However, our results indicate that the mature pine forest acted as a significant carbon sink even when established on lava flow with low nutrient content in immature soils, and that sequestration strength, both in biomass and in soil organic matter, is large.