Flavonoids with DNA strand-scission activity from Rhus javanica var. roxburghiana

The flavonoids isolated from the stems of Rhus javanica var. roxburghiana, taxifolin (1), fisetin (2), fustin (3), 3,7,4'-trihydroxyflavanone (4) and 3,7,4'-trihydroxyflavone (5) caused breakage of supercoiled plasmid pBR322 DNA in the presence of Cu(II). Cu(I) was shown to be an essential intermediate by using the Cu(I)-specific sequestering reagent neocuproine. The Cu(II)-mediated DNA scissions induced by 1, 2, 3 and 5 were inhibited by the addition of catalase and exhibited DNA strand break by the addition of KI and superoxide dimutase (SOD), while in the Cu(II)-mediated DNA scissions induced by 4 was inhibited by the addition of KI, SOD, and catalase. It is concluded that 1, 2, 3, and 5 can induce H(2)O(2) and superoxide anion, while 4 can induce OH() and H(2)O(2) and subsequent oxidative damage of DNA in the presence of Cu(II).     

Water stress decreases the transfer conductance of Douglas-fir (Pseudotsuga menziesii) seedlings

We tested the hypothesis that transfer conductance (gi) of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings is reduced by water stress. Seedlings were irrigated with a solution of 25% polyethylene glycol so as to impose water stress rapidly, thereby limiting acclimatory responses. Transfer conductance was measured pre-treatment and post-treatment by two methods. Water stress reduced net photosynthesis by 20-50%. The initial slope of the rate of photosynthesis (A) over the intercellular carbon dioxide (CO2) concentration (Ci) response was reduced by water stress, indicating that reduced photosynthesis was not wholly accounted for by reduced stomatal conductance. The carbon isotope and chlorophyll fluorescence methods both indicated that water stress decreased gi. From isotopic measurements with 1% O2, gi was 0.076 +/- 0.009 (mean +/- SE) mol m(-2) s(-1) in well-watered seedlings and 0.044 +/- 0.004 mol m(-2) s(-1) in water-stressed seedlings. Fluorescence estimates of gi were 0.08 +/- 0.01 mol m(-2) s(-1) in well-watered seedlings and 0.044 +/- 0.004 mol m(-2) s(-1) in water-stressed seedlings. The drought-induced reduction in gi was responsible for the reduction in slope of the A/Ci response, and thus there was no difference in the slope of the A over the chloroplastic CO2 concentration (Cc) response between treatments and no indication of impaired mesophyll metabolism. These data illustrate that impairments of mesophyll metabolism can be revealed only from analysis of the A/Cc response.     

Seasonal and interannual variability of photosynthetic capacity in relation to leaf nitrogen in a deciduous forest plantation in northern Italy

Gas exchange was measured in a forest plantation dominated by Fraxinus angustifolia Vahl. and Quercus robur L. in northern Italy, over three growing seasons that differed in water availability (2001, 2002 and 2003). The objectives were to: (1) determine variability in the photosynthetic parameters V(cmax) (maximum carboxylation capacity) and J(max) (maximum rate of electron transport) in relation to species, leaf ontogeny and drought; and (2) assess the potential of the photosynthesis-nitrogen relationship for estimating leaf photosynthetic capacity. Marked seasonal and interannual variability in photosynthetic capacity was observed, primarily caused by changes in leaf ontogeny and water stress. Relatively small differences were apparent between species. In the absence of water stress (year 2002), the seasonal patterns of V(cmax) and J(max) were characterized by a rapid increase during spring, a relatively steady state during summer and a rapid decline during autumn. In years with a moderate (year 2001) or a severe (year 2003) water stress, photosynthetic capacity decreased during the summer in proportion to drought intensity, without a parallel decline in leaf nitrogen content. The V(cmax)-nitrogen relationship was significantly affected by both leaf ontogeny and drought. As a consequence, the use of a single annual regression to predict V(cmax) from leaf nitrogen yielded good estimates only during the summer and in the absence of water stress. Irrespective of the mechanisms by which photosynthetic capacity is affected by water stress, its large seasonal and interannual variability is of great relevance for modeling the forest carbon cycle.     

太行山低山丘陵区苹果生姜间作系统综合效应研究

本文对太行山低山丘陵区苹果生姜间作系统的生态效应，生理效应，产量效应及土地利用率进行研究，结果表明，对比单作姜园平均可使生姜冠层叶温降低２．５℃，空气相对湿度提高１６％，对比清耕果园，可使０－５０cm土层土壤含水量提高８．５％，可使生姜叶片叶绿素含量提高１６．６％，苹果光合速率提高１０．０％，生姜和苹果单位产量分别提高３．１％和２．０％，间作系统土地当量值可达１．６４，总体土地利用率可提高６４％。     

12个山茶属植物花的挥发性物质研究

应用顶空固相微萃取和气相色谱—质谱联用方法,对贵州、云南两省12种山茶属植物物种及类型花的挥发性物质及其相对含量进行分析.共分离鉴定出237种挥发性化合物,占总挥发性化合物种类的99.58％.主要包括醛类、酮类、醇类、酯类、萜烯类、烷烃类、酸类及其他类等8类化合物.以怒江山茶花的挥发物种类最多(88种),离蕊金花茶最少(41种).有51种化合物为12个物种及类型中的多数植物所共有.其中,100％共有的5种;90％共有的8种;80％共有的10种;70％共有的10种;50％共有的18种;50％以下共有的100种.有86种化合物为各物种所独有.归类分析表明,醇类比例最高,达29.87％;萜烯类次之,为27.79％;再次为酯类,为22.48％.化合物中相对含量第1为L-芳樟醇,相对含量达75.94％;第2为(Z)-3-己烯酯,为42.48％;第3为庚烷-2-酮,为31.67％;第4为(Z)-3-己烯-1-醇和(S)-2-庚醇,分别达23.79％和20.95％.     

Kinetics of nitrogen uptake by Populus tremuloides in relation to atmospheric CO(2) and soil nitrogen availability

Sustained increases in plant production in response to elevated atmospheric carbon dioxide (CO(2)) concentration may be constrained by the availability of soil nitrogen (N). However, it is possible that plants will respond to N limitation at elevated CO(2) concentration by increasing the specific N uptake capacity of their roots. To explore this possibility, we examined the kinetics of (15)NH(4) (+) and (15)NO(3) (-) uptake by excised roots of Populus tremuloides Michx. grown in ambient and twice-ambient CO(2) concentrations, and in soils of low- and high-N availability. Elevated CO(2) concentration had no effect on either NH(4) (+) or NO(3) (-) uptake, whereas high-N availability decreased the capacity of roots to take up both NH(4) (+) and NO(3) (-). The maximal rate of NH(4) (+) uptake decreased from 12 to 8 &mgr;mol g(-1) h(-1), and K(m) increased from 49 to 162 &mgr;mol l(-1), from low to high soil N availability.Because NO(3) (-) uptake exhibited mixedkinetics over the concentration range we used (10-500 &mgr;mol l( -1)), it was not possible to calculate V(max) and K(m). Instead, we used an uptake rate of 100 &mgr;mol g(-1) h(-1) as our metric of NO(3) (-) uptake capacity, which averaged 0.45 and 0.23 &mgr;mol g(-1) h(-1) at low- and high-N availability, respectively. The proximal mechanisms for decreased N uptake capacity at high-N availability appeared to be an increase in fine-root carbohydrate status and a decrease in fine-root N concentration. Both NH(4) (+) and NO(3) (-) uptake were inversely related to fine-root N concentration, and positively related to fine-root total nonstructural carbohydrate concentration. We conclude that soil N availability, through its effects on fine-root N and carbohydrate status, has a much greater influence on the specific uptake capacity of P. tremuloides fine roots than elevated atmospheric CO(2). In elevated atmospheric CO(2), changes in N acquisition by P. tremuloides appeared to be driven by changes in root architecture and biomass, rather than by changes in the amount or activity of N-uptake enzymes.     

Seasonal acclimation of photosystem II in Pinus sylvestris. I. Estimating the rate constants of sustained thermal energy dissipation and photochemistry

Acclimation of the partitioning of absorbed light energy in Photosystem II (PSII) between photochemical and non-photochemical processes includes short-term adjustments that are rapidly reversed in the dark and seasonal acclimation processes that are unaffected by dark acclimation. Thus, by using dark-acclimated leaves to study the seasonal acclimation of PSII, the confounding effect of short-term adjustments is eliminated. The maximum quantum yield of photochemistry, estimated by chlorophyll fluorescence analysis as F(v)/F(m), where F(v) = (F(m) - F(o)), and F(m) and F(o) are maximum and minimum chlorophyll fluorescence, respectively, has been widely used to follow the seasonal acclimation of PSII, because it is measured in dark-acclimated leaves. Seasonal changes in F(v)/F(m) can be caused by adjustments in either the photochemical capacity in PSII, or the capacity of thermal dissipation in PSII, or both. However, there is a lack of chlorophyll fluorescence parameters that can distinguish between these processes. In this study, we introduce two new parameters: the rate constants of sustained thermal energy dissipation (k(NPQ)) and of photochemistry (k(P)). We estimated k(NPQ) and k(P) from dark-acclimated F(o) and F(m) measured during spring recovery of photosynthesis in Scots pine (Pinus sylvestris L.) trees. We suggest that k(NPQ) and k(P) be used to study the mechanisms underlying the observed seasonal acclimation in PSII, because these parameters provide quantitative data that complement and extend F(v)/F(m) measurements.     

A simple model of light and water use evaluated for Pinus radiata

An existing model of light and water use by crops (RESCAP) was adapted and evaluated for trees. In the model, growth on any given day is determined either by the amount of intercepted radiation (by means of the light utilization coefficient, epsilon) or by the maximum rate of water extraction by roots (a function of root biomass and soil water content). In either case, transpiration and growth are related by the water-use efficiency (q), which is inversely proportional to the daily mean saturation vapor pressure deficit (D). The model was applied to two Pinus radiata (D. Don) stands (control (C) and fertilized (F)) growing near Canberra, Australia, using data collected during the Biology of Forest Growth experiment (1983-1988). For both stands, predicted and measured soil water contents were in close agreement (r(2) > 0.9) over a 4-year period involving several wet-dry cycles. The parameter combination epsilon/qD was estimated to be 0.28 and 0.26 kg H(2)O (MJ total)(-1) kPa(-1) for the C and F stands, respectively. Because of the close physiological link between water use and CO(2) uptake, the results suggest that tree growth may be realistically simulated by simple models based on conservative values for epsilon and qD.     

Assessing nitrogen fixation in mixed- and single-species plantations of Eucalyptus globulus and Acacia mearnsii

Mixtures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman are twice as productive as E. globulus monocultures growing on the same site in East Gippsland, Victoria, Australia, possibly because of increased nitrogen (N) availability owing to N(2) fixation by A. mearnsii. To investigate whether N(2) fixation by A. mearnsii could account for the mixed-species growth responses, we assessed N(2) fixation by the accretion method and the (15)N natural abundance method. Nitrogen gained by E. globulus and A. mearnsii mixtures and monocultures was calculated by the accretion method with plant and soil samples collected 10 years after plantation establishment. Nitrogen in biomass and soil confirmed that A. mearnsii influenced N dynamics. Assuming that the differences in soil, forest floor litter and biomass N of plots containing A. mearnsii compared with E. globulus monocultures were due to N(2) fixation, the 10-year annual mean rates of N(2) fixation were 38 and 86 kg ha(-1) year(-1) in 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation by A. mearnsii could not be quantified on the basis of the natural abundance of (15)N because such factors as mycorrhization type and fractionation of N isotopes during N cycling within the plant confounded the effect of the N source on the N isotopic signature of plants. This study shows that A. mearnsii fixed significant quantities of N(2) when mixed with E. globulus. A decline in delta(15)N values of E. globulus and A. mearnsii with time, from 2 to 10 years, is further evidence that N(2) was fixed and cycled through the stands. The increased aboveground biomass production of E. globulus trees in mixtures when compared with monocultures can be attributed to increases in N availability.     

Photosynthetic responses of field-grown Pinus radiata trees to artificial and aphid-induced defoliation

The phloem-feeding aphid Essigella californica represents a potential threat to the productivity of Pinus radiata plantations in south-eastern Australia. Five- and nine-year-old field trials were used to characterize the effects of artificial and natural aphid-induced (E. californica) defoliation, respectively, on shoot photosynthesis and growth. Photosynthetic capacity (A(max)) was significantly greater following a 25% (D25) (13.8 μmol m(-2) s(-1)) and a 50% (D50) (15.9 μmol m(-2) s(-1)) single-event upper-crown artificial defoliation, 3 weeks after defoliation than in undefoliated control trees (12.9 μmol m(-2) s(-1)). This response was consistently observed for up to 11 weeks after the defoliation event; by Week 16, there was no difference in A(max) between control and defoliated trees. In the D50 treatment, this increased A(max) was not sufficient to fully compensate for the foliage loss as evidenced by the reduced diameter increment (by 15%) in defoliated trees 36 weeks after defoliation. In contrast, diameter increment of trees in the D25 treatment was unaffected by defoliation. The A(max) of trees experiencing upper-crown defoliation by natural and repeated E. californica infestations varied, depending on host genotype. Despite clear differences in defoliation levels between resistant and susceptible genotypes (17 vs. 35% of tree crown defoliated, respectively), growth of susceptible genotypes was not significantly different from that of resistant genotypes. The observed increases in A(max) in the lower crown of the canopy following attack suggested that susceptible genotypes were able to partly compensate for the loss of foliage by compensatory photosynthesis. The capacity of P. radiata to regulate photosynthesis in response to natural aphid-induced defoliation provides evidence that the impact of E. californica attack on stem growth will be less than expected, at least for up to 35% defoliation.     

Celastrus paniculatus seed water soluble extracts protect cultured rat forebrain neuronal cells from hydrogen peroxide-induced oxidative injury

The effects of aqueous extracts of Celastrus paniculatus (CP) seeds were shown to have antioxidant properties in rats. In the study reported here, we have investigated the free radical scavenging capacity of three aqueous extracts (WSEs) obtained from CP seeds: a room temperature extract (WF); a hot water extract (HF); an acid extract (AF). All the WSEs exhibited a dose-dependent free radical scavenging capacity for 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) and also for superoxide-generated assays (in vitro assays). In addition, we used enriched forebrain primary neuronal cell (FBNC) cultures to evaluate the neuroprotective effects of the three CP-WSE extracts on H(2)O(2)-induced toxicity. FBNC were pre-treated with the CP-WSE and then with H(2)O(2) to evaluate the protection afforded against H(2)O(2)-induced toxicity. The criteria for neuroprotection by the WSEs were based on a mitochondrial function test following the H(2)O(2)-induced neurotoxicity. All the WSEs significantly attenuated H(2)O(2)-induced neuronal death, and AF was the most effective in protecting the neuronal cells against oxidative injury caused by H(2)O(2). In 10 day FBNC, cellular superoxide dismutase activity was not affected by the WSEs or H(2)O(2), but catalase activity was decreased and levels of malondialdehyde were increased by H(2)O(2) treatment. When the neuronal cells were treated with WSEs prior to H(2)O(2) exposure, catalase activity was increased and levels of malondialdehyde were decreased significantly. The data presented here suggest that CP seed WSEs protected neuronal cells in part by their free radical scavenging properties, by reducing lipid peroxidation, and also by their ability to induce the antioxidant enzyme catalase. Our results indicate that WSEs might exert neuroprotective effects against increased oxidative stress resulting from free radical damage that is associated with a number of neurodegenerative diseases.     

Effect of knife wear on finger-joint strength of silver fir (Abies alba) wood

Abstract

This study was carried out to determine the effect of knife wear, as measured in hours of use, on the finger-joint strength of silver fir wood (Abies alba), bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives. Wood samples were collected after 1, 32 and 64 h of knife wear. Results showed that as knife wear increased, bending strength or modulus of rupture (MOR) of the finger-jointed samples was reduced by 11.1% (PVAc) to 21.2% (PU) after 32 h of knife wear, and by 19.6% (PVAc) to 27.6% (PU) after 64 h of knife wear, whereas modulus of elasticity (MOE) of the finger-jointed samples was reduced by 10.5% (PVAc) to 12.5% (PU) after 32 h of knife wear, and by 11.7% (PVAc) to 10.0% (PU) after 64 h of knife wear. Tension strength of the finger-jointed samples was reduced by 2.1% (PVAc) to 1.5% (PU) after 32 h of knife wear, and by 5.4% (PVAc) to 16.0% (PU) after 64 h of knife wear.     

Optimal tree fallow rotations: some principles revealed by modelling

A model (ROTATE) of the nitrogen (N) cycle during the tree and crop phases of fallow systems [Robertson, 1994] was used to determine the primary factors influencing longterm crop yields. The model simulated the expected patterns of increase in old (recalcitrant) soil organic N during tree rotations and their decrease under continuous cropping. After 3–4 fallow cycles an equilibrium soil organic N content is reached, where N losses by crop removal are balanced by N gains by the trees (either by fixation or pumping from depth) plus small inputs in rain. The rotation period has two variable components; the cycle length (tree plus crop period) and the fraction of years in each cycle occupied by trees (1 = sole trees, 0 = sole crops). Both components have optima determined by the time taken for the trees to increase the old soil organic N pool to an optimal (but not maximal) size. This optimum exists because the rate of increase in old organic N slows as the tree fallow progresses and a time is reached (often soon after the trees reach full size) when the benefits of further improvements in soil fertility are outweighed by crop yield foregone. In the example chosen of Acacia/sorghum in the Sahel, the optimum cycle seemed to be about 50 years with half of the time in trees. The optimum fallow period is shortened by growing fast-growing trees, and the benefit of fallow periods are greatest when (i) a large proportion of the N in litter (above and belowground) is transferred to the recalcitrant soil pool, and (ii) the trees attain a large size with correspondingly large annual additions of N to the soil.     

Effects of short-term ozone exposure and soil water availability on the carbon economy of juvenile Douglas-fir

Effects of ozone and soil water availability on partitioning and translocation of assimilates were studied in three-year-old Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings exposed, in separate experiments, to 0 and 106 or 0 and 514 micro g m(-3) ozone for 8 h day(-1) for 9 days. The dynamics of carbon from assimilated (14)CO(2) were followed. No interactions between ozone and soil water content were observed. Total net uptake of carbon was reduced by low soil water content, but was unaffected by ozone. Both ozone and low soil water content increased the amount of (14)C-photosynthates retained in the current-year needles. Total starch content in old and current-year needles was unaffected by ozone, but was reduced by low water availability. Translocation of carbon to the root-soil compartment was additively affected by ozone and low soil water content. The results suggest that dry periods in summer combined with high ozone concentrations cause the greatest reduction in the supply of carbon compounds to the root-soil compartment.     

Changes in net ecosystem productivity with forest age following clearcutting of a coastal Douglas-fir forest: testing a mathematical model with eddy covariance measurements along a forest chronosequence

We hypothesized that changes in net ecosystem productivity (NEP) during aging of coastal Douglas-fir (Pseudotsuga menziesii Mirb. Franco) stands could be explained by (1) changing nutrient uptake caused by different time scales for decomposition of fine, non-woody and coarse woody litter left after harvesting, (2) declines in canopy water status with lengthening of the water uptake pathway during bole and branch growth, and (3) increases in the ratio of autotrophic respiration (R (a)) to gross primary productivity (GPP) with phytomass accumulation. These hypotheses were implemented and tested in the mathematical model ecosys against eddy covariance (EC) measurements of forest CO(2) and energy exchange in a post-clearcut Douglas-fir chronosequence. Hypothesis 1 explained how (a) an initial rise in GPP observed during the first 3 years after clearcutting could be caused by nutrient mineralization from rapid decomposition of fine, non-woody litter with lower C:N ratios (assart effect), (b) a slower rise in GPP during the next 20 years could be caused by immobilization during later decomposition of coarse woody litter, and (c) a rapid rise in GPP between 20 and 40 years after clearcutting could be caused by nutrient mineralization with further decomposition of coarse woody litter and of its decomposition products. During periods (a) and (b), heterotrophic respiration (R (h)) from decomposition of fine and coarse litter greatly exceeded net primary productivity (NPP = GPP - R (a)) so that Douglas-fir stands were large sources of CO(2). During period (c), NPP exceeded R (h) so that these stands became large sinks for CO(2). Hypothesis 2 explained how declines in NPP during later growth in period (c) could be caused by lower hydraulic conductances in taller trees that would force lower canopy water potentials and hence greater sensitivity of stomatal conductances and CO(2) uptake to vapor pressure deficits. Enhanced sensitivity to vapor pressure deficits was also apparent in the EC measurements over the post-clearcut chronosequence. Hypothesis 3 did not contribute to the explanation of forest age effects on NEP.     

Chemical characterization of Pinus halepensis sapwood and heartwood

ABSTRACT

This paper describes the chemical composition of sapwood (SW) and heartwood (HW) of Pinus halepensis Mill stem. Extractives were first isolated by accelerated solvent extraction and then analysed by gas chromatography-mass spectrometry (GC-MS). The cellulosic polysaccharide content present in the pre-extracted wood samples was determined with acid hydrolysis and GC. The hemicelluloses content was determined with acid methanolysis and GC. Free monomers were additionally analysed by GC. The amount of lignin was determined gravimetrically by the Klason lignin method and the acid-soluble lignin was determined by a UV method. Formic and acetic acids in wood were determined after alkaline hydrolysis and analysed by HP-SEC. It was found that lipophilic and hydrophilic extractives were more abundant in heartwood (1.6% and 2.5%) than in sapwood (1.1% and 1.8%). Celluloses content was higher in sapwood (42.5%) than in heartwood (39.7%), whereas lignin, hemicelluloses and sugar monomer contents were more abundant in heartwood (28.9%, 26.8% and 0.3%) than in sapwood (28.0%, 24.5% and 0.2%). The variation in acetic and formic acids and ash contents between sapwood (0.7%, 0.2% and 0.5%) and heartwood (0.6%, 0.1% and 0.4%) was small. The acetylation degrees were found to be slightly similar in sapwood (0.4) and heartwood (0.3).     

Size, shape and surface morphology of starch granules from Norway spruce needles revealed by transmission electron microscopy and atomic force microscopy: effects of elevated CO(2) concentration

We compared the effects of ambient (350 ppm) and elevated CO(2) concentration (700 ppm) on the size and shape of starch granules in Norway spruce (Picea abies (L.) Karst.) needles during one growing season. Starch granules were isolated from needles by alkaline digestion and analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Measurements made with a particle size analyzer indicated that starch granules ranged between 0.5 and 10 microm. Granule size and shape varied according to needle developmental stage and CO(2) concentration. Generally, elevated CO(2) concentration increased the size of the starch granules. Fine surface structures (< 10 nm in size) studied by AFM were characterized by the presence of protrusions, furrows and pores.     

Use of goats as biological agents for the renovation of pastures in the Appalachian region of the United States

Much of hill-land pasture in the Appalachian region of the United States is dominated by herbaceous weeds and brush. Low cost, low input and environmentally acceptable reclamation procedures are needed to maintain the productivity of these pastures. This experiment evaluated the effectiveness of using goats (Capra hircus hircus) alone (30 mature, brush does/ha) or cattle (Bos taurus) with goats (17 mature, brush does/ha + two to three steers/ha -- 225 kg average live weight) to reclaim a pasture from an abandoned, overgrown 5.9 ha orchard left untouched for 15 years. Over four grazing seasons, managed defoliation resulted in a substantial increase in herbaceous vegetative cover in plots grazed by goats alone (65 to 86%) and by goats with cattle (65 to 80%) while vegetative cover decreased from 70 to 22% in the control plot. Similarly, the cover by grass species increased in the grazed plots (goats: 16 to 63%; goats + cattle: 13 to 54%) while averaging 10% in the control plot. Multiflora rose (Rosa multiflora Thumb.) bushes were practically eliminated after four grazing seasons as quantified by an average reduction in height from 2.1 m to 0.6 m, and by the number of dead canes (stems) in both the goat (100%) or goat + cattle (92%) treatments. Results indicated that the foraging habits of goats resulted in the elimination of multiflora rose bushes and in a significant increase in desirable forage species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Precommercial thinning as a silvicultural option for treating very dense conifer stands

Lack of available workforce in motor-manual operations has led to increased interest in mechanized precommercial thinning (PCT) treatments. We evaluated 15 years of growth and yield development of a very dense (27,000 stems ha^–1) balsam fir (Abies balsamea (L.) Mill) and black spruce (Picea mariana (Mill.) B.S.P.) stand after six PCT treatments: (1) motor-manual (MAN), (2) motor-manual with crop tree release (MAN-C), (3) mechanized (MEC), (4) mechanized with residual patches (MEC-P), (5) semi-mechanized (mechanized followed by motor-manual, MEC-S), and (6) unthinned control (CON). Compared to CON, both MAN and MEC-S increased height of balsam fir study trees by 53–56% and diameter at breast height (DBH) by 57–58%. MAN-C and MEC-S increased DBH of black spruce study trees by 15–31% over all other treatments. The proportion of merchantable basal area (BA) was higher in MAN (62%) and MEC-S (56%) than in CON (22%) and MEC (25%), without a reduction in total BA. PCT treatments that provided a uniform distribution of potential crop trees (MAN, MEC-S) performed better than MAN-C and MEC-P, while MEC yielded the poorest responses. Our findings highlight the need to develop new tailored mechanized systems for high wood production and low operational cost.     

Interannual consistency in canopy stomatal conductance control of leaf water potential across seven tree species

We investigated interannual variability of canopy transpiration per unit ground area (E (C)) and per unit leaf area (E (L)) across seven tree species in northern Wisconsin over two years. These species have previously been shown to be sufficient to upscale stand-level transpiration to the landscape level during one growing season. Our objective was to test whether a simple plant hydraulic model could capture interannual variation in transpiration. Three species, wetland balsam fir (Abies balsamea (L.) Mill), basswood (Tilia Americana L.) and speckled alder (Alnus rugosa (DuRoi) Spreng), had no change in E (C) or E (L) between 2000 and 2001. Red pine (Pinus resinosa Ait) had a 57 and 19% increase in E (C) and E (L), respectively, and sugar maple (Acer saccharum Marsh) had an 83 and 41% increase in E (C) and E (L), respectively, from 2000 to 2001. Quaking aspen (Populus tremuloides Michx) had a 50 and 21% decrease in E (C) and E (L), respectively, from 2000 to 2001 in response to complete defoliation by forest tent caterpillar (Malascoma distria Hüber) and subsequent lower total leaf area index of the reflushed foliage. White cedar (Thuja occidentalis L.) had a 20% decrease in both E (C) and E (L) caused by lowered surface water in wetlands in 2001 because of lower precipitation and wetland flow management. Upland A. balsamea increased E (L) and E (C) by 55 and 53%, respectively, as a result of release from light competition of the defoliated, overstory P. tremuloides. We hypothesized that regardless of different drivers of interannual variability in E (C) and E (L), minimum leaf water potential would be regulated at the same value. Minimum midday water potentials were consistent over the two years within each of the seven species despite large changes in transpiration between years. This regulation was independently verified by the exponential saturation between daily E (C) and vapor pressure deficit (D) and the tradeoff between a reference canopy stomatal conductance (G (S)) and the sensitivity of G (S) to D, indicating that trees with high G (S) must decrease G (S) in response to atmospheric drought faster than trees with low G (S). Our results show that models of forest canopy transpiration can be simplified by incorporating G (S) regulation of minimum leaf water potential for isohydric species.