Timber investment returns for selected plantations and native forests in South America and the Southern United States

Timber investment returns were estimated for the principal exotic and selected native species in the Southern Cone of Latin America and in the Southern United States. Exotic eucalyptus plantations in South America were most profitable, with internal rates of returns (IRRs) ranging from 13% to 23%, followed by exotic loblolly pine, with IRRs from 9% to 17%. Average loblolly pine plantation returns in the US South were less profitable, with an IRR of about 9.5%, and natural forest management in the South had IRRs of 4% to 8%. Subtropical native species plantations of the best araucaria and nothofagus species had reasonable financial returns, with IRRs ranging from 5% to 13%. Subtropical or tropical native forests had fewer commercial timber species, and had much lower growth rates and returns. Their IRRs were less than 4%, or even negative for unmanaged stands. State subsidy payments for forest plantations or for timber stand improvements increased IRRs somewhat and reserving areas for environmental protection reduced their IRRs slightly. Including land costs in the cash flows decreased these internal rates of return substantially. Natural stand returns in Latin America were much less than those of plantations, but management of those stands offered better rates of return than only holding the land.     

转型中的亚洲林业(续二)

在过去的20年里,亚洲林业经历了引人注目的转型,包括从计划经济到市场经济的转变,从天然林供给木材到人工林供给木材的转变,木材替代品与非木质林产品的增加,地方分权与当地群众的参与,生态时代的发展与生态系统管理。在促进亚洲可持续森林资源管理中,市场工具、社区参与和环境服务都得到了应用。亚洲林业的转型表现出多样化,其森林、社会与环境之间的联系是丰富多彩的。     

Abiotic factors limiting photosynthesis in Abies lasiocarpa and Picea engelmannii seedlings below and above the alpine timberline

Most research on the occurrence and stability of alpine timberlines has focused on correlations between adult tree growth and mean temperatures rather than on specific mechanisms. Timberline migration to higher altitude is dependent on new seedling establishment in the tree-line ecotone; however, reductions in photosynthetic carbon gain in establishing seedlings have previously been interpreted solely in terms of decreased seedling survival. Our objective was to evaluate the impact of abiotic factors (temperature, light and water) on photosynthetic carbon gain in young seedlings of the two dominant conifer tree species occurring naturally above (tree-line ecotone site, TS) and below (forest site, FS) a Rocky Mountain timberline in southeastern Wyoming, USA. Coincidentally, measurements were made during an unusually dry summer. Mean daily photosynthesis in seedlings of both Abies lasiocarpa (Hook.) Nutt. (subalpine fir) and Picea engelmannii Parry ex Engelm. (Engelmann spruce) was less at TS than at FS (19 and 29%, respectively). Minimum nighttime temperatures below 2 degrees C were more frequent at TS than at FS and were associated with reduced maximum photosynthesis the following day. Low midday water potentials were associated with a reduction in carbon gain at both sites early in the season, prior to snowmelt, as well as late in the season when soils began to dry. However, the lower photosynthetic rates at TS than at FS appeared to be unrelated to seedling water status because seedlings at both sites had similar xylem pressure potentials. Solar irradiance was highly variable at both sites as a result of uneven shading by neighboring trees, although this variation was substantially reduced on cloudy days (44% of all days observed). Compared with sunny days, cloudy days resulted in greater integrated daily carbon gain at both sites (41% increase at TS and 69% increase at FS), based on a simulated photosynthesis model. Photosynthetic responses to temperature, sunlight and water suggest that variable solar irradiance and nighttime temperatures were major abiotic factors limiting photosynthetic carbon acquisition in these young seedlings, especially for seedlings growing in the tree-line ecotone.     

Effects of mass inoculation on induced oleoresin response in intensively managed loblolly pine

Oleoresin flow is an important factor in the resistance of pines to attack by southern pine beetle, Dendroctonus frontalis Zimm., and its associated fungi. Abiotic factors, such as nutrient supply and water relations, have the potential to modify this plant-insect-fungus interaction; however, little is known of the effects of inoculation with beetle-associated fungi on oleoresin flow. We observed that constitutive and induced resin yield in loblolly pine, Pinus taeda L., were affected by either fungal inoculation (with the southern pine beetle-associated fungus Ophiostoma minus (Hedgcock) H. & P. Sydow) or silvicultural treatment. The effects of mass wounding (400 wounds m(-2)) and mass wounding and inoculation with O. minus were assessed by comparison with untreated (control) trees. The treatments were applied to trees in a 2 x 2 factorial combination of fertilizer and irrigation treatments. Fertilization did not significantly affect constitutive resin yield. Even as long as 105 days post-treatment, however, mass-inoculated trees produced higher induced resin yields than control or wounded-only trees, indicating a localized induced response to fungal inoculation. We noted no systemic induction of host defenses against fungal colonization. Although beetles attacking previously attacked trees face a greater resinous response from their host than beetles attacking trees that had not been previously attacked, the effect of an earlier attack may not last more than one flight season. Despite mass inoculations, O. minus did not kill the host trees, suggesting that this fungus is not a virulent plant pathogen.     

Effects of drought preconditioning on thermotolerance of photosystem II and susceptibility of photosynthesis to heat stress in cedar seedlings

Changes in photosystem II (PSII) thermotolerance during drought and recovery were studied under controlled conditions in three Mediterranean cedar species (Cedrus brevifolia Henry, C. libani Loudon and C. atlantica Manetti). The temperature at which the quantum yield of PSII photochemistry was reduced by 15% of its value at 25 degrees C was 3 to 4 degrees C higher in drought-treated plants than in well-watered plants. The drought-induced increase in PSII thermotolerance was already evident 8 days after water had been withheld from the seedlings, when net CO(2) assimilation was still at 80% of its initial value, and was visible for up to 12 days after re-watering. When seedlings of the three species were exposed to temperatures above 45 degrees C for 5 h, both maximal quantum yield of PSII photochemistry and net CO(2) assimilation rate were significantly reduced in unconditioned seedlings, whereas drought-preconditioned seedlings were almost unaffected by the heat treatment. Drought-preconditioned seedlings still exhibited a higher tolerance to heat stress than unconditioned seedlings 60 days after re-watering, although the transient, drought-induced osmotic adjustment had fully disappeared. Among species, C. atlantica was the most heat sensitive, whereas the heat treatment had no significant effect on the parameters measured in C. brevifolia.     

Determination of Young’s and shear moduli of common yew and Norway spruce by means of ultrasonic waves

Despite the exceptional position of yew among the gymnosperms concerning its elastomechanical properties, no reference values for its elastic constants apart from the longitudinal Young’s modulus have been available from literature so far. Hence, this study’s objective was to determine the Young’s moduli E _L, E _R and E _T and the shear moduli G _LR, G _LT and G _RT of yew wood. For that purpose, we measured the ultrasound velocities of longitudinal and transversal waves applied to small cubic specimens and derived the elastic constants from the results. The tests were carried out at varying wood moisture contents and were applied to spruce specimens as well in order to put the results into perspective. Results indicate that E _L is in the same order of magnitude for both species, which means that a high-density wood species like yew does not inevitably have to have a high longitudinal Young’s modulus. For the transverse Young’s moduli of yew, however, we obtained 1.5–2 times, for the shear moduli even 3–6 times higher values compared to spruce. The variation of moisture content primarily revealed differences between both species concerning the shear modulus of the RT plane. We concluded that anatomical features such as the microfibril angle, the high ray percentage and presumably the large amount of extractives must fulfil important functions for the extraordinary elastomechanical behaviour of yew wood which still has to be investigated in subsequent micromechanical studies.     

Patterns of regeneration and ground vegetation associated with canopy gaps in a managed beechwood in southern England

In autumn 2001, 15 canopy gaps were selected for study in RumerhedgeWood, a semi-natural, mesotrophic beechwood in southern England.The gaps were located in mature, beech-dominated stands, andhad originated from openings created during a thinning in theearly 1980s and wind damage in 1987/1990 and/or the consequentsalvage operations. The extent of each gap and surrounding treeswere mapped. Tree/shrub regeneration, ground vegetation, bareearth, leaf litter and canopy openness (using a canopy-scope)were measured within and around the gaps using a 5 x 5-m gridand placing a 1 x 1-m quadrat at each grid intersection (totalnumber of quadrats = 400). Most of the gaps were <75 m² inarea. The largest was 241 m². They were generally irregularin shape and there was little or no understorey present. Mostsurrounding trees were beech Fagus sylvatica L. Bramble Rubusfruticosus L. formed a moderate to dense ground vegetation belowmost gaps and declined around the edges only once the gap openingwas substantially obscured. Apart from a few larger saplings,most regeneration was small and of beech. Most of the latterappeared to be in their fifth or sixth growing season, were10–35 cm tall, had an erect base and flat top, had increasedby <5 cm in height during 2001 and were not browsed by deer.Their height and growth form was related to (1) their positionwithin gaps, (2) the degree of canopy openness and (3) the coverof ground vegetation. This was translated into the followingzonation—(1) around the centre of larger gaps: canopyopenness increased to >15 per cent; bramble cover was nearcomplete; litter depth was low; many places had no beech seedlings,but some of the few present were among the tallest, most uprightand fastest growing; (2) towards the edges of the large gapsor directly below smaller gaps: canopy openness was about 4–10per cent; bramble cover was slightly less; beech seedlings weremoderately abundant but patchy, generally shorter, more flattopped and slow growing than in the gap centre, albeit somewere still among the tallest, most upright and fastest growing;(3) beyond the edge of the large/medium gaps (with the gap onlypartially visible) or directly below very small gaps: canopyopenness was only about 2–3 per cent; bramble was muchreduced; beech seedlings were at their most abundant but stillpatchy in distribution and even shorter, more flat topped andslower growing than in the above zone; (4) in an outer zonebeyond or almost beyond the sight of the gaps: canopy opennesswas <2 per cent; bramble was weak and sparse; beech seedlingswere mostly at low densities and predominately short, slow growingand flat topped. This ring pattern of beech regeneration appearedto relate mainly to (1) differences in light availability affectingthe survival, growth rate and form of seedlings; (2) competitionfrom bramble and possibly (3) limited dispersal of beech seedinto gaps. Recommendations are given for managers who wish touse natural regeneration to restock beech woodland.     

Effects of logging, liana tangles and pasture on seed fate of dry forest tree species in Central Brazil

We assessed seed fate of six tree species in a seasonally deciduous forest of Central Brazil. Seed germination, predation, removal and death caused by pathogens or dessication were followed in an undisturbed forest site, a logged forest site, and an active pasture. In both forest types we sowed seeds under patches of liana tangles (Low Forest habitat) and under patches of mature forest (High Forest habitat). Seeds were monitored weekly for up to 8 months. Overall, small-seeded species (Astronium fraxinifolium and Tabebuia impetiginosa) had high germination, although germination was lower in the pasture due to insect predation. The hard-coated seeds of Erythrina sp. had higher germination rates in the pasture. The large-seeded Cavanillesia arborea and Swartzia multijuga had high seed removal (ca. 90%) in the pasture and under High Forest, but only 23–34% under Low Forest in the logged site. Lower removal of large seeds in Low Forest suggests that this habitat conceals the seeds and constrains the movement of large mammals. Both species were favored in Low Forest, suggesting that caution should be used when managing lianas. When protected from predation, seeds with a soft coat and high water content, such as the seeds of Eugenia dysenterica and S. multijuga, died from desiccation in the pasture. Restoration efforts must take into consideration high mortality caused by desiccation or insect predation in abandoned pastures of dry forests.     

Effects of regulated deficit irrigation during the pre-harvest period on gas exchange, leaf development and crop yield of mature almond trees

We investigated the effects of regulated deficit irrigation (RDI) during the pre-harvest period (kernel-filling stage) on water relations, leaf development and crop yield in mature almond (Prunus dulcis (Mill.) D.A. Webb cv. Cartagenera) trees during a 2-year field experiment. Trees were either irrigated at full-crop evapotranspiration (ETc=100%) (well-irrigated control treatment) or subjected to an RDI treatment that consisted of full irrigation for the full season, except from early June to early August (kernel-filling stage), when 20% ETc was applied. The severity of water stress was characterized by measurements of soil water content, predawn leaf water potential (Psipd) and relative water content (RWC). Stomatal conductance (gs), net CO2 assimilation rate (A), transpiration rate (E), leaf abscission, leaf expansion rate and crop yield were also measured. In both years, Psipd and RWC of well-irrigated trees were maintained above -1.0 MPa and 92%, respectively, whereas the corresponding values for trees in the RDI treatment were -2.37 MPa and 82%. Long-term water stress led to a progressive decline in gs, A and E, with significant reductions after 21 days in the RDI treatment. At the time of maximum stress (48 days after commencement of RDI), A, gs and E were 64, 67 and 56% lower than control values, respectively. High correlations between A, E and gs were observed. Plant water status recovered within 15 days after the resumption of irrigation and was associated with recovery of soil water content. A relatively rapid and complete recovery of A and gs was also observed, although the recovery was slower than for Psipd and RWC. Severe water stress during the kernel-filling stage resulted in premature defoliation (caused by increased leaf abscission) and a reduction in leaf growth rate, which decreased tree leaf area. Although kernel yield was correlated with leaf water potential, RDI caused a nonsignificant 7% reduction in kernel yield and had no effect on kernel size. The RDI treatment also improved water-use efficiency because about 30% less irrigation water was applied in the RDI treatment than in the control treatment. We conclude that high-cropping almonds can be successfully grown in semiarid regions in an RDI regime provided that Psipd is maintained above a threshold value of -2 MPa.     

Biomass production by two-year-old poplar clones on floodplain sites in the Lower Midwest, USA

Four Populus clones were grown for two years at 1×1 m spacing for study of total biomass production and carbon sequestration capacity on floodplain sites previously in forage grasses under climatic conditions of the lower Midwest, U.S.A. Total biomass (above-and below-ground) in the first year ranged from 3.9 Mg ha^–1 in a Populus deltoides x P. nigra clone (I45/51) to 1.9 Mg ha^–1 for a local-source Populus deltoides clone (2059). Second year total biomass production was substantially higher, ranging from 13.9 Mg ha^–1 in I45/51 to 7.4 Mg ha^–1 in P. deltoides clone 26C6R51. Second-year leaf area index (LAI) values for I45/51 plants reached 4 during mid-season, indicating essentially complete canopy closure in this clone by the second year after planting. In contrast, maximum mid-season, second-year LAI was significantly lower in P. deltoides clones ( 2.4). There was some evidence for differential allocation to roots and shoots among Populus clones, with 26C6R51 showing relatively more allocation to root biomass than other clones. Second-year growth in Populus deltoides clone 2059 accelerated substantially, and this genotype exhibited two-year biomass accumulation nearly equal to that of I45/51 despite having less leaf area. This result suggested a higher photosynthetic capacity or assimilation efficiency in the former. This revised version was published online in August 2006 with corrections to the Cover Date.