Abundance and Production of Riparian Trees in the Lowland Floodplain of the Queets River, Washington

Riparian zones associated with alluvial rivers are spatially dynamic, forming distinct vegetative mosaics that exhibit sharp contrasts in structure and processes related to the underlying biophysical template. The productivity of riparian plants, especially trees, influences streamside community characteristics as well as the forms and fluxes of organic matter to adjacent streams – thereby strongly impacting patterns of channel morphology, water flow, sedimentation, and habitat in rivers. As part of a comprehensive investigation of riparian dynamics in coastal rain forest rivers of the Pacific Northwest (USA), we examined riparian tree abundance (density, basal area, and biomass) and rates of production (basal area growth [BAI] and bole wood biomass increase [P]) of seven common species – red alder (Alnus rubra), Sitka spruce (Picea sitchensis), bigleaf maple (Acer macrophyllum), western hemlock (Tsuga heterophylla), black cottonwood (Populus trichocarpa), vine maple (Acer circinatum) and willow (Salix spp.) – in the lowland floodplain of the Queets River (Olympic National Park), Washington. Measurements were made annually for three years (1999 – 2001) in 16 permanent plots on three biophysical templates that formed a toposequence – active floodplain, young terrace and mature terrace. Stem density was highest in the active floodplain (∼27,000 stems/ ha), decreasing in the young terrace (∼2,700 stems /ha) and the mature terrace (∼500 stems/ha). Basal area and total stem biomass were lowest in the active floodplain (∼16 m2/ha and ∼18 Mg dry weight/ha, respectively) and higher on the young terrace (∼32 m2/ha and ∼134 Mg dry weight/ha) and on the mature terrace (∼69 m2/ha and ∼540 Mg dry weight /ha). Total plot-scale BAI was not significantly different among the physical templates with mean values ranging from approximately 1.4 (low terrace) to approximately 2.8 m2/ha/y (active floodplain). In contrast, P was significantly higher on the mature terrace (10.3 Mg/ha) than the active floodplain (3.2 Mg/ha) but there was no significant difference between young terrace (6.5 Mg/ha) and mature terrace. For the entire Queets River floodplain (57 km² over 77 km of river length), the mature terrace contributed 81% of the total annual production (28,764 Mg) whereas the active floodplain and young terrace accounted only for 5 and 14%, respectively. Overall, we show that riparian trees grow quickly in this coastal Pacific Northwest system and that the older riparian forests on mature terraces are the main contributors to stem production at the plot and floodplain scales for at least 350 years after stand initiation. This suggests that, in combination with the rapid lateral migrations of many alluvial rivers, the older riparian forests on those terraces are important and sustained sources of organic matter (especially large woody debris, LWD) that, over decades to centuries, shape the character of coastal rivers in the Pacific Northwest.     

Growth and protection against oxidative stress in young clones and mature spruce trees (Picea abies L.) at high altitudes

Clones of Norway spruce (Picea abies L.) were grown for several years on an altitudinal gradient (1750 m, 1150 m and 800 m above sea level) to study the effects of environmental × genetic interactions on growth and foliar metabolites (protein, pigments, antioxidants). Clones at the tree line showed 4.3-fold lower growth rates and contained 60% less chlorophyll (per gram of dry matter) than those at valley level. The extent of growth reduction was clone-dependent. The mortality of the clones was low and not altitude-dependent. At valley level, but not at high altitude, needles of mature spruce trees showed lower pigment and protein concentrations than clones. In general, antioxidative systems in needles of the mature trees and young clones did not increase with increasing altitude. Needles of all trees at high altitude showed higher concentrations of dehydroascorbate than at lower altitudes, indicating higher oxidative stress. In one clone, previously identified as sensitive to acute ozone doses, this increase was significantly higher and the growth reduction was stronger than in the other genotypes. This clone also displayed a significant reduction in glutathione reductase activity at high altitude. These results suggest that induction of antioxidative systems is apparently not a general prerequisite to cope with altitude in clones whose mother plants originated from higher altitudes (about 650–1100 m above sea level, Hercycnic-Carpathian distribution area), but that the genetic constitution for maintenance of high antioxidative protection is important for stress compensation at the tree line. Received: 13 October 1998 / Accepted: 22 June 1999     

Transpiration and whole-tree conductance in ponderosa pine trees of different heights

Changes in leaf physiology with tree age and size could alter forest growth, water yield, and carbon fluxes. We measured tree water flux (Q) for 14 ponderosa pine trees in two size classes (12 m tall and ∼40 years old, and 36 m tall and ∼ 290 years old) to determine if transpiration (E) and whole-tree conductance (g _t) differed between the two sizes of trees. For both size classes, E was approximately equal to Q measured 2 m above the ground: Q was most highly correlated with current, not lagged, water vapor pressure deficit, and night Q was <12% of total daily flux. E for days 165–195 and 240–260 averaged 0.97 mmol m^–2 (leaf area, projected) s^–1 for the 12-m trees and 0.57 mmol m^–2 (leaf area) s^–1 for the 36-m trees. When photosynthetically active radiation (I _P) exceeded the light saturation for photosynthesis in ponderosa pine (900 μmol m^–2 (ground) s^–1), differences in E were more pronounced: 2.4 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 1.2 mmol m^–2 s^–1 for the 36-m trees, yielding g _t of 140 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 72 mmol m^–2 s^–1 for the 36-m trees. Extrapolated to forests with leaf area index =1, the 36-m trees would transpire 117 mm between 1 June and 31 August compared to 170 mm for the 12-m trees, a difference of 15% of average annual precipitation. Lower g _t in the taller trees also likely lowers photosynthesis during the growing season. Received: 19 April 1999 / Accepted: 23 March 2000     

Tree height and age-related decline in growth in Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.)

Growth and seasonal water use was measured amongst trees growing in an old growth Scots pine forest in the Scottish Highlands. Three sites which differed in their recent management history and contained old and naturally regenerated young trees growing together were monitored in the field. Our results showed a clear decrease in growth efficiency with age, from values of around 0.25 kg m⁻² leaves year⁻¹ in approximately 25-year-old trees to less than 0.1 kg m⁻² leaves year⁻¹ in trees over 200 years old. When the old trees in one of the field sites were released from competition by thinning, their growth efficiency reverted to that of coexisting young trees, indicating that the decline in growth was reversible. This is consistent with the results of a parallel study showing that cambial age had no effect on the physiology or growth of grafted seedlings originating from the same population studied here (Mencuccini et al. 2005). Our detailed study of tree water use in the field showed an overall decrease in whole-tree hydraulic conductance and stomatal canopy conductance with tree height in the unthinned stands, in agreement with the hydraulic limitation hypothesis. However, the effect of this reduction in hydraulic efficiency on growth was comparatively small, and old trees also showed consistently lower nitrogen concentrations in needles, suggesting that hydraulic and nutritional factors combined to produce the decline in growth efficiency with age observed in the studied populations.     

Age-dependent responses of tree-ring growth and intra-annual density fluctuations of Pinus pinaster to Mediterranean climate

Dendrochronology generally assumes that climate–growth relationships are age independent once the biological growth trend has been removed. However, tree physiology, namely, photosynthetic capacity and hydraulic conductivity changes with age. We tested whether the radial-growth response to climate and the intra-annual density fluctuations (IADFs) of Pinus pinaster Ait. varied with age. Trees were sampled in Pinhal de Leiria (Portugal), and were divided in two age classes: young (<65 years old) and old (>115 years old). Earlywood and tree-ring width of young P. pinaster trees were more sensitive to climate influence while the response of latewood width to climate was stronger in old trees. Young trees start the growing season earlier, thus a time window delay occurs between young and old trees during which wood cells of young trees integrate environmental signals. Young trees usually have a longer growing season and respond faster to climate conditions, thus young P. pinaster trees presented a higher frequency of IADFs compared with old trees. Most of the IADFs were located in latewood and were positively correlated to autumn precipitation. The radial-growth response of P. pinaster to climate and the IADFs frequency were age dependent. The use of trees with different age to create a tree-ring chronology for climate studies can increase the resolution of climatic signals. Age-dependent responses to climate can also give important clues to predict how young and old trees react to climate change.     

Energy requirement for foliage construction depends on tree size inyoung Picea abies trees

 The relationship between stand biomass production, and tree age and size is generally a curve with a maximum. To understand why wood production decreases in the final stages of stand development, the influence of increasing tree size on foliage chemical composition and substrate requirement for foliage construction in terms of glucose [CC, g glucose (g dry mass)^{–  1}] was investigated in the evergreen conifer Picea abies (L.) Karst. Because it was already known that irradiance affects both foliage morphology and chemistry in this species, and it was expected that the foliage in large overstory trees would intercept on average more light than that in saplings in understory, irradiance was measured in the sampling locations and included in the statistical models. CC of needles increased with increasing total tree height (TH) and was independent of relative irradiance. A major reason for increasing CC with increasing TH was a greater proportion of carbon-rich lignin in the needles in large trees. However, lignin did not fully account for the observed changes in CC, and it was necessary to assume that certain other carbon-rich secondary metabolites such as terpenes also accumulate in the foliage of large trees. Enhanced requirements for needle mechanical strength as evidenced by greater lignin concentrations in large trees were attributed to increased water limitations with increasing tree height. Because water relations may also control the sink capacities for assimilate usage, apart from the mechanical requirements, they may provide an explanation for the accumulation of other energetically expensive compounds in the needles as well. Biomass partitioning within the shoot was another foliar parameter modified in response to increasing tree size. The proportion of shoot axes, which serve to provide needles with mechanical support and to supply them with water, decreased with increasing TH. This may limit water availability in the needles, and/or manifest a lower water requirement of the needles containing proportionally more supporting and storage substances, and consequently, less physiologically active compounds such as proteins. Probably the same factors which caused CC of the needles to depend on TH, were also responsible for greater CC of the shoot axes in larger trees. These results collectively suggest that increasingly more adverse water relations with increasing tree size may provide a mechanistic explanation for the decline in foliar biomass and its functional activity during stand ageing. Received: 9 April 1996 / Accepted: 14 January 1997     

Growth and Nutrient Retranslocation in Needles of Radiata Pine in Relation to Nitrogen Supply

The effects of N application on tree growth and the retranslocationof N, P, and K from young needles to new growth were examinedin young radiata pine (Pinus radiata D. Don) trees. Nitrogen fertilization increased the number and size of needles,rates of shoot production, stem volume growth and tree biomass.Foliar N and P contents (µg per needle) fluctuated ina cyclic fashion with prominent phases of accumulation, retranslocationand replenishment. The patterns of these fluctuations in controland N-fertilized trees were similar, although the fluxes ofN, P and K in and out of needles were increased by N fertilization.Greater translocation (g per tree) of N and K from needles ofN fertilized trees occurred because fertilization increasedthe needle weight and the proportion of N and K retranslocatedfrom individual needles. Nitrogen fertilization increased theretranslocation of P largely as a result of higher needle mass.Trees supplied with more than adequate amounts of P in the soilretranslocated up to 58 per cent of the initial pool of P fromyoung needles. The periods of high retranslocation coincidedwith periods of high concentrations of soil mineral N and withshoot production. Conversely, the periods of rapid replenishmentof N and P into the needles coincided with the time of slowshoot growth and low concentration of soil mineral N. The growthrate of trees, rather than the availability of nutrients inthe soil was the main factor controlling retranslocation. For radiata pine, retranslocation from needles is not a mechanismspecific for coping with low soil fertility. It seems to bea mechanism which enhances the nutrient supply to apical growingpoints, especially during periods of flushing. Pinus radiata, nitrogen supply, shoot growth, nutrient fluctuations and retranslocation, nutrient use and adaptation     

Idaho forest growth response to post‐thinning energy biomass removal and complementary soil amendments

Utilization of woody biomass for biofuel can help meet the need for renewable energy production. However, there is a concern biomass removal will deplete soil nutrients, having short‐ and long‐term effects on tree growth. This study aimed to develop short‐term indicators to assess the impacts of the first three years after small‐diameter woody biomass removal on forest productivity to establish optimal biomass retention levels for mixed‐conifer forests in the Inland Northwest region, and to evaluate the ability of soil amendments to compensate for potential adverse effects from biomass removal. We examined impacts of four biomass retention‐level treatments at two study locations: full biomass removal (0x), full biomass retention (1x), double biomass retention (2x), and unthinned control. We combined biomass retention with four soil amendment treatments: biochar (B), fertilizer (F), fertilizer and biochar combined (FB), and an untreated control (C). We considered treatment effects on basal area and total stem volume growth for all trees per plot (plot trees) and for the six largest trees per plot (crop trees). Biomass removal had no effect on plot (P > 0.40) or crop tree growth (P > 0.65) compared to normal biomass retention. High biomass retention (2x) decreased plot tree growth as compared to normal biomass retention (1x) levels (P < 0.05) after three years. This growth difference was not explained by soil moisture, temperature, or nutrient uptake. While there were strong tree growth differences between study locations, patterns of biomass and amendment treatment responses did not differ. Fertilizer increased basal area growth and total volume growth (P < 0.10) as expected, because nitrogen is limiting in the region. Biochar had no effect on tree growth (P > 0.47). Initial findings after three years suggest removing small‐diameter biomass for biofuel feedstocks is feasible in the Inland Northwest without negative impacts on tree growth.     

Nitrogen dynamics of a boreal black spruce wildfire chronosequence

This study examined the nitrogen (N) dynamics of a black spruce (Picea mariana (Mill.) BSP)-dominated chronosequence in Manitoba, Canada. The seven sites studied each contained separate well- and poorly drained stands, originated from stand-killing wildfires, and were between 3 and 151 years old. Our goals were to (i) measure total N concentration ([N]) of all biomass components and major soil horizons; (ii) compare N content and select vegetation N cycle processes among the stands; and (iii) examine relationships between ecosystem C and N cycling for these stands. Vegetation [N] varied significantly by tissue type, species, soil drainage, and stand age; woody debris [N] increased with decay state and decreased with debris size. Soil [N] declined with horizon depth but did not vary with stand age. Total (live + dead) biomass N content ranged from 18.4 to 99.7 g N m⁻² in the well-drained stands and 37.8–154.6 g N m⁻² in the poorly drained stands. Mean soil N content (380.6 g N m⁻²) was unaffected by stand age. Annual vegetation N requirement (5.9 and 8.4 g N m⁻² yr⁻¹ in the middle-aged well- and poorly drained stands, respectively) was dominated by trees and fine roots in the well-drained stands, and bryophytes in the poorly drained stands. Fraction N retranslocated was significantly higher in deciduous than evergreen tree species, and in older than younger stands. Nitrogen use efficiency (NUE) was significantly lower in bryophytes than in trees, and in deciduous than in evergreen trees. Tree NUE increased with stand age, but overall stand NUE was roughly constant (∼ ∼150 g g⁻¹ N) across the entire chronosequence.     

Gap size and succession in cutover southern Appalachian forests: an 18 year study of vegetation dynamics

We used clearcut logging in establishing four replicated sizes of canopy openings (0.016, 0.08, 0.4, and 2.0 ha) in a southern Appalachian hardwood forest in 1981 to examine the long-term effects of disturbance size on plant community structure, biomass accumulation, aboveground net primary productivity (NPP), and mode of recovery. The reestablishment of NPP and biomass following logging was 6–7-fold greater in large than small openings by 17 years. Total biomass in the 2.0 ha openings (127.3 Mg ha⁻¹) recovered 59.5% as NPP (19.7 Mg ha⁻¹ yr⁻¹) reached 225% of precut forest levels. Biomass accumulation was 2.6–3.6-fold greater in interior than edge locations of all but the 0.016 ha gaps. The absence of significant patch size or edge vs. interior differences in tree densities suggests that growth rates of individual trees were enhanced in more insolated microenvironments. Sprouting (86–95% of tree NPP) was much more important than advance regeneration (4–10%) or seedling germination (<2%) during early recovery in all opening sizes. Canopy dominant Quercus and Carya trees exhibited limited sprouting following disturbance. Instead, shade-intolerant Robinia pseudoacacia and Liriodendron tulipifera were major sprouters that used N-fixation (Robinia) and rapid growth (Liriodendron) in attaining 7.4 and 5.9 fold greater biomass accumulation, respectively in 2.0 ha than 0.016 ha opening sizes. Seedling germination and understory production were extensive in all openings following logging, but declined rapidly as the young tree canopy began closing by 4–6 years. The relative importance of shade-intolerant tree biomass approximately doubled over 17 years as shade-tolerant tree seedlings, herbs, and shrubs gradually regained importance under the emerging canopy. Sprouting caused the persistence of a tree species composition in all openings that remained relatively similar to the precut forest. Large disturbances on mountain slopes of the southern Appalachians generally promote sprouting and rapid recovery, whereas small disturbances in low-elevation cove forests lead to a gradual recovery through seedling germination and/or advance regeneration. Continued logging in the southern Appalachians will increase the relative size and frequency of large disturbances, further the importance of sprouting of shade-intolerant species, and lead to more even-aged forest stands throughout the region.     

马尾松三代选择群体生长性状变异及选择研究

以浙江省淳安县姥山林场的6×6半双列遗传交配设计的三代测定幼林为对象,分析幼林期（2、3和5 a）的生长性状的遗传参数和育种值,及2 a生时生物量的累积与分配。结果表明,马尾松幼林期不同杂交组合间的树高、地径、冠幅和活枝数均存在显著的遗传差异,且生物量在2 a生亦存在显著的遗传差异。杂交组合2 a生的地上生物量占植株总生物量的87.17%。幼林期生长性状以树高的增长量最大,5 a生较2 a生增长了4.23倍。采用综合育种值法,依据预测的树高（H）育种值为主,结合地径（D₀）和2 a生茎干生物量（B_s）指标的配合选择方式,以入选率20%优选出杂交组合分别为22×44、33×22、40×44。以5 a生时树高、地径的单株育种值为依据,2%的入选率优选出16个单株,其树高、地径、冠幅及活枝数平均增益分别为1.07 m、1.58 cm、0.32 m和4.67个。     

Development processes and growth pattern of Pinus densiflora stands in central eastern Korea

Stand growth and developmental processes were investigated in Pinus densiflora Siebold et Zucc. stands of different ages in the central eastern region of Korea. Stands were inventoried and five trees per stand were sampled for stem analysis, age estimation, and growth analysis. More than 80% of sampled trees in a stand were established within 3–5 years, and most stands had a single cohort structure. The initial growth of pine seedlings was slow, but the height growth accelerated beyond 2–3 m height, 5–10 years after establishment. Linear growth was maintained until 10–12 m height, at which suppressed trees fell behind and might die out. The young stand was composed of pure pines, while few pine seedlings and saplings were found in the understory of older stands. The peak of diameter growth rate occurred around 5–15 years after tree establishment, implying that competition begins during that period. The pine stand development follows four stages: (1) the young stage when the growth rate increases and peaks; (2) the height competition stage when trees focus on height growth for light while maintaining a narrow DBH and height distribution; (3) the differentiation stage when suppressed trees die out, and the DBH distribution becomes wider; and (4) the mature stage when stands have a multi-canopy structure with a wide DBH and height distribution, while the understory is dominated by other tree species. The changes in growth rates and stand structure through forest development would be implemented to predict alterations of above-ground carbon sequestration rates.     

Impacts of Selective Logging and Agricultural Clearing on Forest Structure, Floristic Composition and Diversity, and Timber Tree Regeneration in the Ituri Forest, Democratic Republic of Congo

Mature tropical forests at agricultural frontiers are of global conservation concern as the leading edge of global deforestation. In the Ituri Forest of DRC, as in other tropical forest areas, road creation associated with selective logging results in spontaneous human colonization, leading to the clearing of mature forest for agricultural purposes. Following 1-3 years of cultivation, farmlands are left fallow for periods that may exceed 20 years, resulting in extensive secondary forest areas impacted by both selective logging and swidden agriculture. In this study, we assessed forest structure, tree species composition and diversity and the regeneration of timber trees in secondary forest stands (5-10 and ~40 years old), selectively logged forest stands, and undisturbed forests at two sites in the Ituri region. Stem density was lower in old secondary forests (~40 years old) than in either young secondary or mature forests. Overall tree diversity did not significantly differ between forest types, but the diversity of trees ≥10 cm dbh was substantially lower in young secondary forest stands than in old secondary or mature forests. The species composition of secondary forests differed from that of mature forests, with the dominant Caesalpinoid legume species of mature forests poorly represented in secondary forests. However, in spite of prior logging, the regeneration of high value timber trees such as African mahoganies (Khaya anthotheca and Entandrophragma spp.) was at least 10 times greater in young secondary forests than in mature forests. We argue that, if properly managed and protected, secondary forests, even those impacted by both selective logging and small-scale shifting agriculture, may have high potential conservation and economic value.     

Seasonal variation in leaf-litter input and leaf dispersal distances to streams: the effect of converting broadleaf riparian zones to conifer plantations in central Japan

Sugi (Cryptomeria japonica D. Don) is one of the most important evergreen coniferous plantation species in Japan. Much of the riparian forest that was originally dominated by deciduous broadleaf trees has been converted into sugi plantations. The present study investigated the seasonality of leaf-litter input and leaf dispersal to streams to assess the effects of converting riparian forest to sugi plantations. The seasonality of leaf-litter input was assessed at three streams in Nagoya University Forest. At one stream dominated by deciduous broadleaf trees, input was limited to autumn. At two streams in a sugi plantation, input was prolonged from autumn to early spring, and was dominated by sugi needles from winter to early spring. These results suggest that sugi plantations alter the seasonality of leaf-litter input from riparian forests and affect stream ecosystems. Leaf dispersal was assessed by considering the relationship between leaf dispersal distance from three forest layers to the stream and leaf-litter input into two streams. The maximum leaf dispersal distance was 26–28 m for deciduous broadleaf trees from mid-October to November and 10–12 m for sugi needles from December to April. Leaf dispersal distance depended on the tree species. Four species of deciduous broadleaf tree showed greater leaf dispersal than that of sugi. The mean weight of individual sugi needles was higher than that of the broadleaf trees’ leaves, and dispersal depended on strong winds in winter and early spring. Although the leaf dispersal distance from the understory was within 2–4 m, it could be a significant source of leaf-litter input to streams.     

Variation with Tree Age of Needle Cuticle Topography and Stomatal Structure in Pinus radiate D. Don

Scanning electron microscopy reveals differences in the surfacetopography and stomatal structure of 1-year-old needles of Pinusradiata sampled from trees of different ages. The cuticularridges on young-tree needles show an even pitch, whereas theridges on mature-tree needles appear slightly puckered, withsmall discontinuities. The stomata on mature-tree needles havea smaller pore (10–15 µm) than young-tree needles(15–20 µm). In young trees a fine rodlet, or tubularwax covers the walls of the guard and subsidiary cells. Thestomatal antechamber predominating in mature-tree needles containsan amorphous wax, which frequently closes the pore between theoverarching stomatal lips. The yield of crude wax from chloroformextracts of needles of trees of all ages is approximately 0.2per cent, and there is more of the acidic component in the waxof mature-tree needles. It is suggested that wax occlusionswithin the stomatal antechamber of P. radiata may contributeto mature-tree resistance to the needle pathogen, Dothistromapini Hulbary.     

Spatial and age-dependent tree-ring growth responses of Larix gmelinii to climate in northeastern China

Tree-ring width chronologies from 276 Larix gmelinii cores taken in northeastern China were used to analyze spatial and age-dependent growth–climate response relationships. Tree radial growth from five localities showed similar patterns, while exhibiting different tree-ring growth responses to local climate. The rotated principal component analysis (RPCA) indicated that tree age, growing season moisture conditions, and ambient air temperature variations resulted from location differences (e.g., longitude, latitude, and altitude), which could explain the non-stationary spatial climate–growth relations observed. The study tested the fundamental assumption that the climate–growth of L. gmelinii was age independent after the removal of size trends and disturbance signals. The age-related climate–growth relationship might potentially improve the veracity of past climate reconstructions. Bootstrapped correlation function analyses suggested that the response of L. gmelinii radial growth to climate differed between trees ≥150 years old and <150 years old. Mean sensitivity and standard deviation for trees increased with age in the <150 years old tree class; whereas trees ≥150 years old had no significant relationship with age. These results showed that the assumption of age-independent climate–growth relationship is invalid at these sites. Physiological processes and/or hydraulic constraints dependent on tree age, together with detrending techniques could be the possible causal factors of clear age-dependent responses. These results suggested the importance of incorporating trees of all ages into the chronology to recover a detailed climatic signal in a reconstruction of L. gmelinii for this region.     

Recovery of Aboveground Plant Biomass and Productivity After Fire in Mesic and Dry Black Spruce Forests of Interior Alaska

Plant biomass accumulation and productivity are important determinants of ecosystem carbon (C) balance during post-fire succession. In boreal black spruce (Picea mariana) forests near Delta Junction, Alaska, we quantified aboveground plant biomass and net primary productivity (ANPP) for 4 years after a 1999 wildfire in a well-drained (dry) site, and also across a dry and a moderately well-drained (mesic) chronosequence of sites that varied in time since fire (2 to ∼116 years). Four years after fire, total biomass at the 1999 burn site had increased exponentially to 160 ± 21 g m⁻² (mean ± 1SE) and vascular ANPP had recovered to 138 ± 32 g m⁻² y⁻¹, which was not different than that of a nearby unburned stand (160 ± 48 g m⁻² y⁻¹) that had similar pre-fire stand structure and understory composition. Production in the young site was dominated by re-sprouting graminoids, whereas production in the unburned site was dominated by black spruce. On the dry and mesic chronosequences, total biomass pools, including overstory and understory vascular and non-vascular plants, and lichens, increased logarithmically (dry) or linearly (mesic) with increasing site age, reaching a maximum of 2469 ± 180 (dry) and 4008 ± 233 g m⁻² (mesic) in mature stands. Biomass differences were primarily due to higher tree density in the mesic sites because mass per tree was similar between sites. ANPP of vascular and non-vascular plants increased linearly over time in the mesic chronosequence to 335 ± 68 g m⁻² y⁻¹ in the mature site, but in the dry chronosequence it peaked at 410 ± 43 g m⁻² y⁻¹ in a 15-year-old stand dominated by deciduous trees and shrubs. Key factors regulating biomass accumulation and production in these ecosystems appear to be the abundance and composition of re-sprouting species early in succession, the abundance of deciduous trees and shrubs in intermediate aged stands, and the density of black spruce across all stand ages. A better understanding of the controls over these factors will help predict how changes in climate and fire regime will affect the carbon balance of Interior Alaska. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Response over two growing seasons of a Sitka spruce stand to 15N-urea fertilizer

Urea fertilizer labelled with ¹⁵N (2.5 atom %) was applied to a 20 year old Sitka spruce stand on a peaty gley at a rate equivalent to 160 kg N ha⁻¹. The application of urea resulted in increased biomass and N concentration of needles and enhanced development of the crown. Differences in N concentrations of the amended trees were also observed for new wood and bark. Analysis of ¹⁵N in tree biomass showed a continued influence of fertilizer N in the second growing season following urea application. The overall recovery of fertilizer N in the trees was estimated to be about 10%.     

Changes of carbon and nitrogen metabolites in white spruce (Picea glauca [Moench] Voss) of contrasted growth phenotypes

The present study documents the changes occurring at the biochemical level in white spruce trees (Picea glauca [Moench] Voss) with contrasted growth phenotypes during the summer period. Full-siblings of tall versus small spruces were grown under controlled conditions at constant day/night temperatures (24/15°C) and exposed to a decreasing photoperiod (15.7–12.2 h) simulating natural photoperiod reduction during the summer in eastern Canada. Growth parameters (stem height and tree biomass) were determined and non structural carbohydrates, soluble proteins and amino acids were quantified in current-year needles and stem, oldest stem and roots from mid-July until the end of September 2006. Sucrose was the main soluble sugar found in all organs, but its concentrations did not significantly change during the summer. In contrast, starch concentrations rapidly declined by the end of the experiment, especially in needles and stems. Both sucrose and starch did not generally differ between growth phenotypes. Total soluble protein significantly accumulated by mid-August (14.4 h of photoperiod) in small trees. Arginine and glutamine were the most abundant amino acids found in spruce organs, and their concentrations strongly increased at 14.4 h of photoperiod, especially in small trees. Our results highlight marked differences in nitrogen metabolism in late summer between contrasted growth phenotypes, especially for arginine, an amino acid typically associated with growth arrest and nitrogen reserve in perennial species. They also reveal that old stems and roots are important storage organs of organic reserves.     

Nutrient status in needles of Norway spruce and Scots pine following harvesting of logging residues

Nutrient concentrations in current and 1-year old needles from two Picea abies (L.) Karst and two Pinus sylvestris L. stands in Sweden were determined 8–10, 16–18 and 22–24 years after clear-felling and experimental manipulation of harvesting intensity. On all sites, three levels of harvest intensity had been applied in a randomized block design (n=4); (i) conventional stem-only harvesting, where all logging residues (i.e. tops, branches and needles) were evenly distributed on the ground, (ii) harvesting all above-ground tree parts except needles and (iii) above-ground whole-tree harvesting (no residues left on site). At stand age 8–10 years, nitrogen concentrations in the current year needles in plots where all residues or needles only were retained were higher than in whole-tree harvested plots, whereas concentrations of K, Ca and Mg were lower. The latter response was interpreted as a dilution effect. P:N, K:N, Ca:N, Mg:N, Mn:N and Zn:N were in general higher after whole-tree harvesting treatments than after the treatments where all residues or only needles had been left on site. At stand age 16–18 years, no significant differences in nitrogen concentrations were observed between treatments, but the levels of Ca, Mg and Mn in both current and 1-year-old needles were lower after whole-tree harvesting than after the treatments where logging residues remained on site. By contrast, potassium levels in the foliage were highest in treatments where only the needles were left on site, whereas the lowest levels were observed for treatments where all residues was left. At stand age 22–24 years, the treatment effects had diminished, except for the effects on Ca and K on the southern Norway spruce stand. It is concluded that the nutrient release from logging residues enhances nutrient uptake in trees of the succeeding forest generation, but this effect does not occur simultaneously for all elements. This revised version was published online in June 2006 with corrections to the Cover Date.