The size and composition of soil seed-banks in remnant patches of three structural rainforest types in North Queensland

The size and species composition of the soil seed-bank in a remnant patch of each of three structurally and floristically distinct rainforests (Complex Mesophyll Vine Forest, Complex Notophyll Vine Forest and Semi-Evergreen Vine Thicket) were assessed. Seeds of 94 species germinated from 12 surface soil samples collected from each site. All three seed-banks were composed mostly of herbs characteristic of roadsides and agricultural land, and pioneer rainforest trees and shrubs. Agglomerative classifications indicated that the seed-bank samples from each rainforest remnant had a characteristic species composition and could be distinguished reliably from seed-bank samples drawn from other sites. Seeds of species present in the standing forest were poorly represented in the seed-banks except for one long-lived pioneer tree, Dendrocnide photinophylla, at one site. The seed-bank from the seasonally dry vine thicket was significantly larger (4000 seeds m^-2) than those from the two moister sites (400–600 seeds m^-2, contained more seeds of roadside and agricultural herbs, and fewer seeds of rainforest pioneer and secondary shrubs and trees. We suggest three explanations for the different seed-bank structure observed in the seasonally dry forest site. First, with increased deciduousness in rainforests, seed-banks are increasingly subject to invasion and domination by seeds of rapidly maturing herbs. Second, long-lived seeds that germinate in canopy gaps would be less likely to accumulate under deciduous forests because they would he exposed annually to conditions suitable for germination. Third, chronic disturbance by cattle and pigs produces sites suitable for the establishment of rapidly maturing herbs, and possibly disperses their seeds into the forest.     

Ecological aspects of soil seed-banks in relation to bauxite mining. II. Twelve year old rehabilitated mines

Abstract Germinable seed stores were estimated for 12–13 year old rehabilitation sites in the jarrah forest over two seasons (autumn and spring). Collected soils were subjected to combinations of smoking and heating treatments before the germination procedure was commenced. The mean topsoil seed reserve to a depth of 10 cm was 1938 seeds m^?2. Of this total reserve, more than 80% was found in the upper 5 cm of soil. The topsoil seed reserve of these rehabilitation areas was almost seven times that of the adjacent native jarrah forest (292 seeds m^?2; Ward et al. 1997). There was a seasonal effect with autumn-collected soils having significantly more germinable seeds (2723 seeds m^?2) than soils collected in spring (1153 seeds m^?2). More than half (53%) of the topsoil seed reserve in rehabilitated areas was composed of annual weed species, dominated by Aira caryophyllea, Centaurium erythraea and the native Levenhookia pusilla. Of the total of 70 species identified, 13 species showed significantly higher germination in smoked trays while 11 species exhibited significantly higher germination in heated trays. Species responding to the smoking treatment tended to be annuals while those responding to the heating treatment were typically legume shrub species. Examination of the topsoil seed reserve and the vegetation present in these areas showed that while the species composition was similar between the seed store and the vegetation, there was a large difference in densities, with species occurring at much higher densities in the topsoil than in the vegetation. However, the rankings of species were significantly correlated between the topsoil seed reserve and the vegetation present at the site. The implications of these results to prescribed burning of these rehabilitated areas is discussed.     

Ecological aspects of soil seed-banks in relation to bauxite mining. I. Unmined jarrah forest

Abstract Germinable seed stores were measured in jarrah forest soils at six sites during one year. The overall mean seed content to a depth of 5 cm was 292 seeds m^?2. There was a significant seasonal difference, with a maximum of 435 seeds m^?2 in summer, after the majority of species in this Mediterranean ecosystem had flowered and set seed, and a minimum of 207 seeds m^?2 in winter. There were also large site differences in both the densities of seed present and the species represented in the soil seed store. More than 85 species were represented in the germinable seed store from a total sampling area of 17.28 m². The germination of Acacia drummondii, Acacia pulchella, Bossiaea aquifolium, Kennedia coccinea, Lasiopeialum floribundum and Trymalium ledifolium were significantly increased by heating the soil. Smoke produced a significant positive germination response in one species (Trymalium ledifolium). To maximize the contribution of the soil seed store to mine rehabilitation, the ideal revegetation sequence is to collect the topsoil immediately after clearing the vegetation in summer, immediately return the soil to an area to be revegetated, and carry out all earthmoving, landscaping and seedbed preparations prior to the onset of the autumn rains.     

Biomass and nutrient distribution in a 15.5 year old forest growing on a rehabilitated bauxite mine

Abstract Above-ground biomass and its nutrient content were measured in a 15.5 year old rehabilitated bauxite mine in the jarrah forest of southwest Australia. The litterfall and its nutrient content was also measured on the same site, 4–6 years and 8–10 years after rehabilitation. The total mass of the vegetation and litter was 103t ha^?1, 25% of that in a nearby jarrah forest. The mass of the trees was 58t ha^?1, approximately 22% of that in the jarrah forest. The amount of nitrogen in the soil, in the litter and in the understorey, and in the total system, exceeded that in the nearby jarrah forest. Annual litterfall in the rehabilitated area was comparable to that measured in the jarrah forest and other dry sclerophyll forests. The nitrogen content of the litterfall in the rehabilitated area was around three to four times that in other dry sclerophyll forests.     

Aspects of the dynamics of the seed-banks and seedling populations of Acacia victoriae and Cassia spp. in arid western New South Wales

Acacia victoriae, Cassia nemophila and C. phyllodinea are shrubs which occur throughout large areas of arid and semi-arid Australia. This paper examines aspects of the dynamics of the seed-banks and seedling populations of these plants to determine their influence upon recruitment frequency. Seed-banks in the soil are large, ranging from 50 to 3900 seeds m^-2for A. victoriae and from 5 to 400 seeds m^-2for Cassia spp. A large proportion (ca. 80%) of these seeds are viable. Seedling densities soon after emergence range up to 25.7 m^-2for A. victoriae and up to 21.7 m^-2for Cassia spp. Any individual cohort of seedlings represents only a small proportion (< 6%) of the total seed-bank. Most viable seeds fail to germinate even when adequate moisture is available. Seedling mortality rates are high (ca. 100%) during the first 12 months after germination. If recruitment of these shrubs is intermittent, it is most likely a result of low seedling survival rather than infrequent germination.     

The dynamics of the soil seed bank after a fire event in a woody savanna in central Brazil

The seed-bank dynamics of cerrado, a savanna-like vegetation type in central Brazil, was monitored for a year after a fire event in the mid-dry season. Fifty paired soil and litter samples were collected 1 day before and 1 day after the fire to record the immediate effects on the seed bank, and thereafter at monthly intervals to investigate the post-fire seed bank dynamics. The samples were hand-sorted and the intact seeds were classified as monocot or dicot and counted. All seeds underwent germination trials in a germination chamber for 1 month. Seeds that did not germinate were checked for the presence and viability of the embryo. The sorted soil samples were placed in a greenhouse for 6 months, and the count of emerging seedlings was added to the number of germinated and dormant seeds from the germination trials to estimate the total number of viable seeds per sample. The fire did not affect the total seed-bank density: 63 ± 8 seeds m^?2 before the fire, and 83 ± 20 seeds m^?2 (mean ± se) immediately after it. Although monocots represented 65 % of the pre-fire seed bank, 1 year after the fire, the monocot seed density did not reach the pre-fire value, whereas the density of dicot seeds increased threefold. After the fire, the viable seed density and species richness, decreased with the onset of the rainy season coinciding with germination in the field. Therefore, post-fire recruitment increases genetic variability and contributes to the persistence of plant populations in cerrado communities.     

Seeds of the annual grasses Schizachyrium spp. as a food resource for tropical granivorous birds

Seed dynamics of the annual tropical grasses Schizachyrium fragile (R. Br.) A. Camus, S. pachyarthron C. Gardner and S. pseudeulalia (Hosok.) S.T. Blake were studied with the aim of documenting fluxes in granivore food resources. In S. fragile, seed production began in the early dry season, and seed output was primarily influenced by seedling survival. Following seed-fall, there were 651 S. fragile seeds/m² (393 kernels/m²⁾ and 1014 S. pachyarthron seeds/m² (593 kernels/m²) across the study area, with a combined kernel biomass of 14.1 × 10³ g/ha. Seed densities remained stable through the dry season, then declined rapidly after wet season rain. Initial wet season rains of up to 25 mm, 40 mm and 50 mm resulted in seed-bank germination of < 5%, 57%, and 93%, respectively. Some seeds were buried by rain and resurfaced or germinated later, but about 30% was lost. Widespread and abrupt depletion of the seed-bank is likely to occur at the start of about 8% of wet seasons on central Cape York Peninsula, leaving little seed, either for subsequent germination or as food for granivores. Burning early in the dry season, when most seeds were still on the plants, reduced seed densities by 85%. The proportion of seeds with sound kernels was reduced in areas burnt by dry season fires, both directly after the fires and, subsequently, as a result of preferential granivore activity. Areas burnt in the dry season were thus depleted of seed earlier than were unburnt areas. Food availability for granivores should therefore be optimized by fire regimes that include a range of burning histories, including fires in both early dry and early wet seasons as well as keeping other areas unburnt.     

The soil seed bank and understorey regeneration in Eucalyptus regnans forest,Victoria

Abstract The soil seed bank and its relation to the extant vegetation in a Eucalyptus regnans F. Muell. forest in the Central Highlands of Victoria were examined. The average seed density was 430 germinable seeds m^?2 to a depth of 2 cm. There was a polynomial regression relationship between the density and species richness of seeds in soil and forest age (0. 6–54 years). Species richness was not significantly different among soil depths (0- 2 , 2- 5 , 5–10 and 10–20 cm) in the forest stand of 54 years old. More seeds germinated from the 5–10 cm depth than from the other depths. Forbs accounted for 73% of the total germinable seeds and there was no germination of E. regnans. The number of species, particularly woody plant species, germinating from the soil seed bank were significantly lower than in the extant vegetation. However, almost all species present in the soil seed bank were present in the vegetation. The soil seed bank provides an important source for the rapid regeneration of understorey vegetation following clear-cutting and slash-burning in the E. regnans forest. The rapid understorey establishment may play an important role in protecting soil from erosion, in nutrient conservation, replacement and redistribution. The soil seed bank may also be a necessary source of maintaining genetic diversity in the forest over the long term.     

Dynamics of carbon stocks in soils and detritus across chronosequences of different forest types in the Pacific Northwest, USA

We investigated variation in carbon stock in soils and detritus (forest floor and woody debris) in chronosequences that represent the range of forest types in the US Pacific Northwest. Stands range in age from <13 to >600 years. Soil carbon, to a depth of 100 cm, was highest in coastal Sitka spruce/western hemlock forests (36±10 kg C m^?2) and lowest in semiarid ponderosa pine forests (7±10 kg C m^?2). Forests distributed across the Cascade Mountains had intermediate values between 10 and 25 kg C m^?2. Soil carbon stocks were best described as a linear function of net primary productivity (r²=0.52), annual precipitation (r²=0.51), and a power function of forest floor mean residence time (r²=0.67). The highest rates of soil and detritus carbon turnover were recorded on mesic sites of Douglas‐fir/western hemlock forests in the Cascade Mountains with lower rates in wetter and drier habitats, similar to the pattern of site productivity. The relative contribution of soil and detritus carbon to total ecosystem carbon decreased as a negative exponential function of stand age to a value of ～35% between 150 and 200 years across the forest types. These age‐dependent trends in the portioning of carbon between biomass and necromass were not different among forest types. Model estimates of soil carbon storage based on decomposition of legacy carbon and carbon accumulation following stand‐replacing disturbance showed that soil carbon storage reached an asymptote between 150 and 200 years, which has significant implications to modeling carbon dynamics of the temperate coniferous forests following a stand‐replacing disturbance.     

Estimates of soil respiration and net primary production of three forests at different succession stages in South China

Soil respiration (heterotropic and autotropic respiration, R_g) and aboveground litter fall carbon were measured at three forests at different succession (early, middle and advanced) stages in Dinghushan Biosphere Reserve, Southern China. It was found that the soil respiration increases exponentially with soil temperature at 5 cm depth (T_s) according to the relation R_g=a exp(bT_s), and the more advanced forest community during succession has a higher value of a because of higher litter carbon input than the forests at early or middle succession stages. It was also found that the monthly soil respiration is linearly correlated with the aboveground litter carbon input of the previous month. Using measurements of aboveground litter and soil respiration, the net primary productions (NPPs) of three forests were estimated using nonlinear inversion. They are 475, 678 and 1148 g C m^?2 yr^?1 for the Masson pine forest (MPF), coniferous and broad‐leaf mixed forest (MF) and subtropical monsoon evergreen broad‐leaf forest (MEBF), respectively, in year 2003/2004, of which 54%, 37% and 62% are belowground NPP for those three respective forests if no change in live plant biomass is assumed. After taking account of the decrease in live plant biomass, we estimated the NPP of the subtropical MEBF is 970 g C m^?2 yr^?1 in year 2003/2004. Total amount of carbon allocated below ground for plant roots is 388 g C m^?2 yr^?1 for the MPF, 504 g C m^?2 yr^?1 for the coniferous and broad‐leaf MF and 1254 g C m^?2 yr^?1 for the subtropical MEBF in 2003/2004. Our results support the hypothesis that the amount of carbon allocation belowground increases during forest succession.     

Comparative seed germination ecology of Austrostipa compressa and Ehrharta calycina (Poaceae) in a Western Australian Banksia woodland

Austrostipa compressa, a native ephemeral of southwest Western Australia was stimulated to germinate under a range of temperatures, in the presence of light, and exposure to smoke-water. This combination of environmental cues results in winter-maximum germination in immediate postfire and disturbed-soil environments of this Mediterranean-type climate. In contrast, Ehrharta calycina, an introduced perennial grass from southern Africa that has invaded Banksia woodlands, germinated under a wide range of temperature and light conditions, but showed no promotive response to smoke-water. Although A. compressa seeds tolerated heat shock better than E. calycina, the self-burial mechanism of A. compressa seeds ensures protection from fire. High-intensity fire could have a greater impact on E. calycina, as the seeds of this species tend to accumulate in the top of the soil profile where they are more susceptible to high temperatures. Although seeds of E. calycina are more susceptible to high temperatures, survival of mature individuals by postfire resprouting ensures continued survival in native woodlands. Estimates of soil seed bank densities showed extreme variability, but some recently burnt areas of the Yule Brook Botany Reserve contained up to 8000 seed m^?2 of A. compressa and nearly 75 000 seeds m^?2 of E. calycina. Viable soil seed bank densities of A. compressa are reduced with time-since-last fire, but areas of greater than 45 years since the last fire, still contained up to 119 seeds m^?2. In both species, only about half their soil seed bank germinates following fire, thus ensuring the potential for later recruitment. Massive soil seed populations of E. calycina in native Banksia woodlands pose a major problem to management of this plant community type.     

Germinable soil seed-bank of former grassland converted to coniferous plantation

The influence of afforestation with cedars on field layer vegetation and on the germinable soil seed-bank were investigated along a 60-m transect merging from open grassland to sparse and dense canopy cover. A total of 132 species were found, 76 in the seed-bank and 109 in the vegetation, with 53 species in common. Conifer cover was not found to be associated with a decrease in total number of species in the vegetation or seed-bank, but the mean number of species in the vegetation, total cover in field layer vegetation and mean number of individuals in the seed-bank decreased significantly from grassland to forest stands. The grassland seed-bank was dominated by Saxifraga tridactylites and Veronica agrestis; the seed-bank of plots of scattered cedars was dominated by Trifolium incarnatum ssp. molinerii; and that of dense cedar plantations was dominated by Campanula rapunculus. The number and cover of grassland species of field layer vegetation decreased in the forest, with respect to open grassland, and the same trend was found for density of individuals in the seed-bank. It is concluded that grassland restoration by cutting cedars cannot rely on the presence of grassland species in the soil seed-bank.     

Community dynamics of evergreen broadleaf forests in southwestern Japan. II. Species composition and density of seeds buried in the soil of a climax evergreen oak forest

The species composition and density of seeds in the soil of a climax evergeen oak forest in the Kasugayama Forest Reserve, Nara, Japan were studied by directly extracting seeds from soil samples and using soil samples in planting boxes as the basis of germination tests. A total of 33 species were identified from all seeds collected in 6 stands: 11 evergreen broadleaf, 15 deciduous broadleaf, 2 coniferous, 2 liana, 1 herb, and 2 grass species. Species producing sap fruits and dry fruits accounted for 60% and 40% of the total number of species, respectively. The species composition of all the seeds was independent of the species composition of the forest vegetation. The mean density of the seeds was 22,134 seeds/m²·5 cm.Eurya japonica, of which seeds were found in all soil samples, was the most abundant species, followed byCryptomeria japonica, Ilex micrococca, andBoehmeria longispica. Pioneer species such asMallotus japonicus, Zanthoxylum ailanthoides, andAralia elata were found in all soil samples in spite of the paucity of adult trees in the forest. Seeds of evergreen oaks were relatively aboundant but no viable seeds were found. ViableE. japonica, I. micrococca, Symplocos prunifolia, andB. longispica seeds were abundant.     

Soil seed banks in different environments: initial forest,mature forest,Pinus and Eucalyptus abandoned stands

Abstract

Different environments (initial forest, mature forest, Pinus and Eucalyptus stands) found in Seasonal Semideciduous Forest fragments affect the density of viable seeds, as well as the floristic similarity, diversity, and richness of tree species in soil seed banks. This hypothesis was tested in the current study. Soil seed bank samples were collected in the aforementioned environments during rainy and dry seasons, and taken to a shade house, where they remained under favorable seed germination conditions. Tree seedling emergence was measured, and sample species were identified every 15?days, for six months, in each sampling period. In total, 97 individuals m^?2 and 23 species emerged in all environments and periods. The highest density of viable seeds of tree species in the soil seed bank was found in the initial forest stretch, mature forest stretch and abandoned Eucalyptus stand. Only the Pinus stand seed bank in the dry season had different floristic and lower viable seed density than the mature forest seed bank. Thus, all environments, except the abandoned Pinus stand, can preserved Seasonal Semideciduous Forest fragments.     

Natural regeneration of Spanish black pine [Pinus nigra Arn. ssp. salzmannii (Dunal) Franco] at contrasting altitudes in a Mediterranean mountain area

Information on plant seed dispersal, natural loss dynamics of seeds and germination are critical for understanding natural regeneration mechanisms. The aim of this study was to assess the effect of different forest stand densities on seedfall, seed predation, and seedling germination of two populations of the endangered Spanish black Pine forests located at lower (Central population) and higher elevation near the limit of the species?? range (peripheral population) in the Cuenca Mountains of Central Spain. The seed predation and germination experiment also included a nested site preparation treatment. Seed fall varied significantly between 2006 and 2005 or 2007 in both populations. During the only mast year of 2006, higher seedfall was observed at lower elevation and in higher density stands. Predation rates were influenced by the seed crop since predators consumed more than 75?% of seeds in years with lower production and less than 15?% in a mast year. Seed germination is influenced by forest habitat, stand density and soil scalping. For common habitat types, and in a high seed production year, better seed germination rates were observed in medium and dense stands (25?C30 and 35?C40?m²?ha^?1, respectively, in terms of basal area). No statistical difference in seed germination rate was found for Spanish black pine forest at its ecological distribution limit between lower and higher densities (15?C20 and 35?C40?m²?ha^?1, in terms of basal area). In both sites, closed stands with soil scalping exhibited higher germination rates.     

灵山湾国家森林公园垂序商陆土壤种子库时空动态及其对防除措施的响应

土壤种子库是植物潜在的种群,对生态系统稳定和未来植被的结构、功能有着举足轻重的影响。垂序商陆(Phytolacca americana)的入侵已对山东省胶南市灵山湾国家森林公园的森林生态系统构成严重危害。为调查该物种在公园内的潜在扩散能力,于2009—2014年调查了刺槐(Robinia pseudoacacia)林、黑松(Pinus thunbergii)林、刺槐黑松混交林和紫穗槐(Amorpha fruticosa)林(灌丛)4种林分类型,以及2009年采用物理和化学控制入侵危害严重的刺槐林内的土壤种子库。结果表明:垂序商陆种子在4种林分中均有发现,在刺槐、黑松林内表现为由林缘至林内逐步降低的趋势。垂序商陆种子只存在于枯落物层和5 cm以上的土壤中,随土层深度的增加而减少,枯落物层土壤种子库由林缘到林内呈递减趋势。与2009年相比,2014年黑松林和灌丛中平均种子库密度分别降低46%和44%,刺槐林和混交林分别增加299%和355%。垂序商陆种子发芽率在10%以下,随土层深度的增加而依次降低。采用物理、化学控制措施的刺槐林内垂序商陆的更新量、结实量、种子库含量均明显高于紫穗槐林的。调查结果表明垂序商陆土壤种子库具有明显的空间异质性,并且保持了较强的繁殖潜力,营造紫穗槐灌丛可以有效控制垂序商陆的扩散,可为经营沿海防护林提供理论指导。     

Enhancement of seed germination in high salinity by engineering mannitol expression in Arabidopsis thaliana

The bacterial gene mtlD, which encodes mannitol 1-phosphate dehydrogenase (E. C. 1. 1. 1. 17), was transformed into Arabidopsis thaliana and expressed under control of the CaMV 35S promoter. MtlD-transformants accumulated mannitol, a sugar alcohol that is not normally found in Arabidopsis. Amounts of soluble carbohydrates, sucrose, glucose, fructose, myo-inositol and mannitol were determined in different tissues of wild-type and transgenic plants. We estimated that less than 1& of the carbon assimilated was converted into mannitol by the transgenic plants. The establishment of individual transformed lines (after self-crossing three times) resulted in high and low mannitol-producing lines which were stably maintained. The presence of mannitol did not alter plant appearance or growth habit. When MtlD-expressing seeds and control seeds (T3 generation) were imbibed with solutions containing NaCl (range 0 to 400 mol m^?3), transgenic seeds containing mannitol germinated in medium supplemented with up to 400 mol m^?3 NaCl, while control seeds ceased germination at 100 mol m^?3 NaCl. It is doubtful whether the ability to germinate in high salt was a result of an osmotic effect exerted by elevated levels of mannitol, considering that mannitol concentrations were in the mol m^?3 range in seeds. A specific effect of polyols, for example on the integrity of subcellular membranes or enzymes, cannot be excluded.     

Viable soil seed banks in disturbed lowland tropical rainforest sites in North Queensland

Four 0.125 m² soil samples, 50 mm deep, from each of eight tropical lowland rainforest sites ranging from primary and secondary forests to degraded Imperata grasslands were exposed to shade-house conditions. Germinations of soil seeds were monitored over 28 weeks in April-October. The viable seed banks in the primary forest (592 m^-2) and the secondary forest sites resulting from one cycle of clearing and abandonment (1300–1400 m^-2) were composed predominantly of secondary species. The viable seed banks were small in Imperata grassland sites that had been burnt regularly (200–400 m^-2) and very large (2000–3000 m^-2) in sites that had not been burnt for five years or more. The seed banks of the burnt and unburnt Imperata grassland sites were composed mostly of agricultural weeds whilst seeds of secondary rainforest trees were rare or absent. Similarities between the species composition of soil seed banks and regrowth vegetation types suggest that soil seed composition is important in determining the initial floristic composition following disturbance and that lack of seed of secondary rainforest trees is one factor which restricts re-growth and secondary succession on degraded Imperata grasslands. Species such as Eucalyptus intermedia R. T. Bak., E. pellita F. Muell. and Imperata cylindrica (L.)Beauv. which can establish and deflect the normal rainforest secondary succession were not present in the soil seed bank, and these species appear to rely on fresh seed inputs, lignotubers or rhizomes to colonize and regenerate after disturbance.     

Paired-tower measurements of carbon and energy fluxes following disturbance in the boreal forest

Disturbances by fire and harvesting are thought to regulate the carbon balance of the Canadian boreal forest over scales of several decades. However, there are few direct measurements of carbon fluxes following disturbances to provide data needed to refine mathematical models. The eddy covariance technique was used with paired towers to measure fluxes simultaneously at disturbed and undisturbed sites over periods of about one week during the growing season in 1998 and 1999. Comparisons were conducted at three sites: a 1‐y‐old burned jackpine stand subjected to an intense crown fire at the International Crown Fire Modelling Experiment site near Fort Providence, North‐west Territories; a 1‐y‐old clearcut aspen area at the EMEND project near Peace River, Alberta; and a 10‐y‐old burned, mixed forest near Prince Albert National Park, Saskatchewan. Nearby mature forest stands of the same types were also measured as controls. The harvested site had lower net radiation (R_n), sensible (H) and latent (LE) heat fluxes, and greater ground heat fluxes (G) than the mature forest. Daytime CO₂ fluxes were much reduced, but night‐time CO₂ fluxes were identical to that of the mature aspen forest. It is hypothesized that the aspen roots remained alive following harvesting, and dominated soil respiration. The overall effect was that the harvested site was a carbon source of about 1.6 gC m^?2 day^?1, while the mature site was a sink of about ?3.8 gC m^?2 day^?1. The one‐year‐old burn had lower R_n, H and LE than the mature jackpine forest, and had a continuous CO₂ efflux of about 0.8 gC m^–2 day^?1 compared to the mature forest sink of ? 0.5 g C m^?2 day^?1. The carbon source was likely caused by decomposition of fire‐killed vegetation. The 10‐y‐old burned site had similar H, LE, and G to the mature mixed forest site. Although the diurnal amplitude of the CO₂ fluxes were slightly lower at the 10‐y‐old site, there was no significant difference between the daily integrals (? 1.3 gC m^?2 day^?1 at both sites). It appears that most of the change in carbon flux occurs within the first 10 years following disturbance, but more data are needed on other forest and disturbance types for the first 20 years following the disturbance event.