林芝云杉不同地理种源苗期性状变异

正林芝云杉(Picea likiangensis var.linzhiensis Cheng et L.K.Fu)是松科(Pinaceae)云杉属(Picea Dietr.)常绿高大乔木,为西藏高原亚高山暗针叶林主要、特有的建群树种之一[1-2]。主要分布在西藏东南的林芝、米林、波密等地,并向西分布至朗县、错那、洛扎、隆子、工布江达。林芝云杉是云杉属中木材品质系数最高的树种[3],生长迅速,寿命持久,在水热条件优越的地区能长成罕见的巨树,胸径可达2.5 m,最大树高可达73 m,单株立木材积达到50     

乐东拟单性木兰地理种源变异与选择研究

对乐东拟单性木兰14个种源种子、苗期以及幼林期生长性状进行了调查分析.结果表明:种子千粒质量、苗高、地径、叶长和叶宽等5个性状在种源间差异极显著;造林保存率种源间差异显著,来自北部的种源,如浙江龙泉种源保存率较高,而来自南部的海南尖峰岭种源保存率较低;幼林期4年生树高、5年生树高和胸径、6年生树高和胸径等5个主要生长性状种源间差异均达到极显著水平,其生长性状广义遗传力为0.855～0.930,说明乐东拟单性木兰幼林期主要生长性状的表型差异主要受遗传因素的控制;乐东拟单性木兰苗高和地径与纬度负相关,表明随种源纬度的升高,乐东拟单性木兰种源苗期生长有减小趋势;乐东拟单性木兰幼林期树高和胸径与经度正相关,与纬度极显著正相关.根据乐东拟单性木兰种源幼林期试验结果,选择出浙江龙泉、福建顺昌和湖南新宁3个优良种源.通过聚类分析,把乐东拟单性木兰种源初步划分为3个区:西部种源区、东部种源区和南部种源区.     

7年生木荷生长和木材基本密度地理遗传变异及种源选择

针对福建建瓯的7年生33个产地的木荷种源试验林,研究揭示其生长和木材基本密度的种源差异及地理变异模式,并依据聚类分析结果进行速生优质种源选择。结果表明,木荷胸径、树高、枝下高、材积指数和木材基本密度等存在显著或极显著的种源变异,其中以材积指数的种源变异最大。木荷生长和木材基本密度的种源变异主要受产地温度影响,呈典型的纬向变异模式,来自纬度较低、温度较高产地的木荷种源,其树高、胸径和材积指数等生长量较大,木材基本密度较小。木荷各性状间也存在相关性,其木材基本密度与生长性状呈显著负相关。除存在显著的种源效应外,不同重复间的微立地效应也非常显著,在较差立地条件下,木荷种源的生长量较小,但木材基本密度呈现增大趋势。基于生长和木材基本密度进行种源聚类,可大致将木荷划分为中心种源区、中部种源区和北部种源区3个种源区。同时,以高于材积指数和木材基本密度种源总体均值为选择标准,分别初选出17个速生型和11个速生优质型木荷优良种源,其中多数优良种源来源于南岭山脉—武夷山脉的中心种源区。     

青藏高原特有种砂生槐不同种源地种子萌发特征研究

对采自6个种源地砂生槐的种子进行了萌发研究,分析了种子大小、萌发特性与海拔之间的关系。结果表明:1)每荚种子数变幅为2.96 4.50粒;种子千粒质量变幅为30.639 47.415 g;种子纵径变幅为4.3144.962 mm;种子横径变幅为3.244 3.693 mm;种子纵横径比变幅为1.306 1.383,差异较小。方差分析结果显示,种源间每荚种子数(F=8.52**)、千粒质量(F=19.73**)、种子纵径(F=6.17**)和种子横径(F=5.79**)差异均达到极显著水平,而种子纵径与横径的比值差异不显著(F=1.47)。2)6个种源砂生槐种子发芽率变幅为43.16%90.03%。其中萨迦种源发芽率90.03%为最高,最低是米瑞种源为43.16%。3)6个砂生槐种源的种子在发芽起始时间上仅差异1 d;萌发持续时间在14 23 d之间,种源间持续发芽时间差异最多达到9 d;萌发高峰期在17 27 d之间,种源间差异较大,其中萨迦种源最短,朗县种源最长。4)每荚种子数随着海拔的升高而显著降低(R=-0.844 3,P0.05),而种子千粒质量则随着海拔的升高而显著升高(R=0.614 3,P0.05)。5)种子发芽起始时间与海拔之间呈现出负相关的关系,但不显著(R=-0.505 6,P0.05);种子萌发持续时间与海拔具有显著的负相关关系(R=-0.883 6,P0.05),而种子发芽率则与海拔具有显著的正相关关系(R=0.804 7,P0.05)。     

Driving factors for natural tree rejuvenation in anthropogenic pine (Pinus sylvestris L.) forests of NE Germany

The rejuvenation ecology of three main tree species in anthropogenic pine (Pinus sylvestris L.) forests is explored in our study. We focus on the scale of micro-plots, which provide the safe sites for tree rejuvenation. We thrive on the multi-factorial relationship of tree establishment and driving ecological factors using a large dataset from pine stands in NE Germany and applying multivariate analyses. The success of the establishment of the investigated focal tree species Fagus sylvatica L., Quercus petraea Liebl. and Pinus sylvestris L. is, on general, mostly affected by three factors, i.e. water balance of the upper soil layers, browsing pressure, and diaspore sources. Our investigations on the micro-plot scale revealed species-specific differences. For beech saplings <50 cm growth height, primarily the availability of water, indicated by available water capacity (AWC), thickness, quality, and structure of the organic layer, silt and humus content in the topsoil, and the lack of a dense competitive herb layer, were identified as most important factors. On the contrary, oak seems hardly be restricted by hydrologic and/or trophic deficits in the topsoil or humus layer. In conclusion and comparison to Fagus sylvatica L., we assume for Quercus petraea Liebl. advantages in natural regeneration processes under sub-continental climate conditions and thus under the scenarios of climate change. Pinus sylvestris L. regeneration in our investigation area occurs only in a narrow niche. We conclude with regard to future forest development and the objective of stand conversion with low management intensity that oak should be favoured within natural stand regeneration.     

Weeds in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> subsp. <Emphasis Type="Italic">maidenii</Emphasis> (F. Muell) establishment: effects of competition on sapling growth and survivorship

The effect of herbaceous vegetation on growth and survival was assessed in planted eucalyptus saplings grown under four levels of weed cover. Seedlings of Eucalyptus globulus subsp. maidenii were planted with 0 (W0), 25 (W25), 50 (W50) and 100% (W100) weed cover. Weed species composition and aboveground biomass was determined. Soil water content was evaluated by the gravimetric method. Seedling leaf area, diameter and height were evaluated at planting and during the 3 months following establishment. Tree height, diameter and stem volume was estimated at 12, 24 and 36 months. First year tree survival was recorded. The ratio of cumulative stem growth under W100: cumulative stem growth under W0 was used to measure competitive performance. Regression analysis was used to determine competition thresholds. Weeds seriously threaten the growth of E. globulus subsp. maidenii. Early negative effects of competition on growth were evident as from the second month after establishment, and both seedlings and 1-year-old saplings were more affected than 2- and 3-year-old ones. A “minimum-response threshold” was determined near 500 kg/ha (corresponding to W25 cover). No clear effect was found between sapling survival and weed biomass.     

不同除草剂对长柄扁桃苗圃杂草的防治效果

对1年生长柄扁桃苗圃杂草进行了10种除草剂茎叶处理,结果表明：苗圃中的杂草以藜科和禾本科为主,所有除草剂处理对藜科杂草均有防除作用,14%草除灵、10.8%盖草能、12.5%拿扑净、48%排草丹、10.8%高盖+48%排草丹、12.5%拿扑净+48%灭草松、50%异丙隆对禾本科杂草的防效率较高,其中,50%异丙隆的杀草谱最广。48%灭草松和12.5%拿扑净+48%灭草松处理的杂草防效率高,但其对苗木的为害严重。高剂量10.8%盖草能和12.5%拿扑净处理下,杂草防效率达到了68%和56%,长柄扁桃苗未表现出药害症状,二者适用于长柄扁桃苗圃杂草的防治。     

Photosynthetic characteristics of Fagus sylvatica and Quercus robur established for stand conversion from Picea abies

Efforts in Europe to convert Norway spruce (Picea abies) plantations to broadleaf or mixed broadleaf-conifer forests could be bolstered by an increased understanding of how artificial regeneration acclimates and functions under a range of Norway spruce stand conditions. We studied foliage characteristics and leaf-level photosynthesis on 7-year-old European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) regeneration established in open patches and shelterwoods of a partially harvested Norway spruce plantation in southwestern Sweden. Both species exhibited morphological plasticity at the leaf level by developing leaf blades in patches with an average mass per unit area (LMA) 54% greater than of those in shelterwoods, and at the plant level by maintaining a leaf area ratio (LAR) in shelterwoods that was 78% greater than in patches. However, we observed interspecific differences in photosynthetic capacity relative to spruce canopy openness. Photosynthetic capacity (A₁₆₀₀, net photosynthesis at a photosynthetic photon flux density of 1600 μmol photons m⁻² s⁻¹) of beech in respect to the canopy gradient was best related to leaf mass, and declined substantially with increasing canopy openness primarily because leaf nitrogen (N) in this species decreased about 0.9 mg g⁻¹ with each 10% rise in canopy openness. In contrast, A₁₆₀₀ of oak showed a weak response to mass-based N, and furthermore the percentage of N remained constant in oak leaf tissues across the canopy gradient. Therefore, oak photosynthetic capacity along the canopy gradient was best related to leaf area, and increased as the spruce canopy thinned primarily because LMA rose 8.6 g m⁻² for each 10% increase in canopy openness. These findings support the premise that spruce stand structure regulates photosynthetic capacity of beech through processes that determine N status of this species; leaf N (mass basis) was greatest under relatively closed spruce canopies where leaves apparently acclimate by enhancing light harvesting mechanisms. Spruce stand structure regulates photosynthetic capacity of oak through processes that control LMA; LMA was greatest under open spruce canopies of high light availability where leaves apparently acclimate by enhancing CO₂ fixation mechanisms.     

Understory vegetation in old-growth and second-growth Tsuga canadensis forests in western Massachusetts

We compared the understory communities (herbs, shrubs, and tree seedlings and saplings) of old-growth and second-growth eastern hemlock forests (Tsuga canadensis) in western Massachusetts, USA. Second-growth hemlock forests originated following clear-cut logging in the late 1800s and were 108–136 years old at the time of sampling. Old-growth hemlock forests contained total ground cover of herbaceous and shrub species that was approximately 4 times greater than in second-growth forests (4.02 ± 0.41%/m² versus 1.06 ± 0.47%/m²) and supported greater overall species richness and diversity. In addition, seedling and sapling densities were greater in old-growth stands compared to second-growth stands and the composition of these layers was positively correlated with overstory species composition (Mantel tests, r > 0.26, P < 0.05) highlighting the strong positive neighborhood effects in these systems. Ordination of study site understory species composition identified a strong gradient in community composition from second-growth to old-growth stands. Vector overlays of environmental and forest structural variables indicated that these gradients were related to differences in overstory tree density, nitrogen availability, and coarse woody debris characteristics among hemlock stands. These relationships suggest that differences in resource availability (e.g., light, moisture, and nutrients) and microhabitat heterogeneity between old-growth and second-growth stands were likely driving these compositional patterns. Interestingly, several common forest understory plants, including Aralia nudicaulis, Dryopteris intermedia, and Viburnum alnifolium, were significant indicator species for old-growth hemlock stands, highlighting the lasting legacy of past land use on the reestablishment and growth of these common species within second-growth areas. The return of old-growth understory conditions to these second-growth areas will largely be dependent on disturbance and self-thinning mediated changes in overstory structure, resource availability, and microhabitat heterogeneity.     

Why do large,nitrogen rich seedlings better resist stressful transplanting conditions? A physiological analysis in two functionally contrasting Mediterranean forest species

We analysed the physiological bases that explain why large and high nitrogen (N) concentration seedlings frequently have improved survival and growth relative to small seedlings in Mediterranean woodland plantations. Large seedlings of Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.) with high N concentration (L+), and small seedlings with either high (S+) or low (S−) N concentration, were planted on two sites of different weed competition intensity that created contrasting stress conditions. Seedling survival, growth, gas exchange, N remobilization (N_R) and uptake (N_U), and water potential were assessed through the first growing season. Weeds reduced survival and growth, but seedling response to weed competition varied among phenotypes and between species. At the end of the first growing season, L+ Aleppo pine seedlings had higher survival than both small seedling types in presence of weeds but no differences were observed in absence of weeds. Mortality differences among phenotypes occurred in spring but not in summer. L+ Aleppo pines grew more than small Aleppo pines independently of weed competition. No holm oak seedling type survived in presence of weeds and no mortality differences among phenotypes where observed in absence of weeds, although L+ holm oak seedlings grew more than small seedlings. Mortality and growth differences in Aleppo pine were linked to marked physiological differences among phenotypes while physiological differences were small among holm oak phenotypes. L+ Aleppo pines had greater root growth, gas exchange, N_R, and N_U than small seedlings, irrespective of their N concentration. Seedling size in Aleppo pine had a greater role in the performance of transplanted seedlings than N concentration. The functional differences among oak phenotypes were small whereas they were large in pine seedlings, which led to smaller differences in transplanting performance in holm oak than in pine. This suggests that the nursery seedling quality improvement for planting in dry sites could depend on the species-specific phenotypic plasticity and functional strategy. Improved transplanting performance in large Aleppo pine seedlings relative to small seedlings was linked to greater gas exchange, root growth and N cycling.     

长白落叶松高固碳种源选择研究

以东北林业大学帽儿山试验林场31年生长白落叶松种源试验林为研究对象。首先对林木碳储量研究中非破坏性取样方法进行探究,通过对比树干1.3 m处木芯样品含碳率与树干平均含碳率数据,发现二者存在较强的线性关系,利用回归分析计算出直线方程y=0.908 2x+4.379 4,R2=0.842 5,方程拟合程度达到理想水平,利用1.3 m处木芯样品含碳率推算树干平均含碳率方法可行。对不同种源长白落叶松的生长、材性、含碳率、干材生物量、碳储量等性状进行测定,结合方差分析、多重比较、相关分析等数理统计方法,最终筛选出生长优良,固碳能力强的种源。结果显示:干材生物量与碳储量存在较丰富的变异,平均变异系数分别为21.33%和21.30%。相关分析结果显示,碳储量与生长性状、干材生物量呈极显著正相关,与综纤维素含量和木质素含量相关不显著。通过方差分析与Duncan法多重比较,最终选择出小北湖与白刀山两个种源为高固碳能力种源。小北湖与白刀山种源单株干材碳储量分别为74.38 kg和69.27 kg,二者平均值高出总平均值27.83%,比对照CK高出54.45%。以现有试验林为标准,若选择小北湖种源,则每公顷固碳27 297.46 kg,比利用碳储量最小的露水河种源造林每公顷固碳量高47.85%。     

不同种源南方红豆杉幼林生长和紫杉醇含量的研究

利用在福建明溪和浙江龙泉农田庇荫设施栽培的24个种源的2年生南方红豆杉种源试验林,研究幼林收获期生长、分枝、生物收获量和枝叶紫杉醇含量的种源差异和地理变异模式,并综合选育出一批药用优良种源。结果表明:南方红豆杉幼树树高、当年抽梢长、地径、冠幅、最长侧枝长、当年侧枝数、侧枝总数和鲜枝叶紫杉醇含量等在种源间差异显著,不存在明显的地理变异模式。来自气候温暖但年降水量较少地区的种源生长快、分枝多、树冠浓密。与生长和分枝性状不同,产地年均温低、≥10 ℃积温小的种源其鲜枝叶紫杉醇含量较高,产地年降水量对种源鲜枝叶紫杉醇含量影响较小。南方红豆杉生长和分枝性状不仅存在显著的种源效应,而且存在明显的地点效应和种源×地点互作,栽植地水热资源丰富及适宜栽植密度可显著促进植株的树高和分枝生长及生物收获量的提高。种源生长和分枝性状间呈显著的正相关,而种源鲜枝叶紫杉醇含量与生长、分枝性状和生物收获量则不显著负相关或不显著正相关,有利于生物收获量大、紫杉醇含量高的优良种源选择。依据鲜枝叶紫杉醇含量和产量筛选出安徽黄山、福建柘荣、湖南桑植、贵州黎平、云南石屏5个药用优良种源,其单株鲜枝叶紫杉醇产量大于种源总体平均值的17.65%-25.77%,鲜枝叶紫杉醇含量皆在97 mg·kg^-1以上。     

水分胁迫对毛红椿幼苗生长和生物量分配的影响

以我国亚热带落叶阔叶优势树种毛红椿的1年生幼苗为试验材料,设置4个水分胁迫处理,模拟研究不同水分胁迫强度下毛红椿幼苗生长和生物量分配规律。结果表明:水分胁迫对毛红椿幼苗根系生长的限制作用明显大于对苗高生长的限制作用,对地径生长限制作用不明显;随着水分胁迫程度增加,根质量比表现出先增大后减小的趋势;叶质量比在处理初期和中期增大,在处理后期和末期降低;在整个处理阶段,茎质量比始终保持增加趋势;根系平均直径在处理中期和后期逐渐减小,处理末期则有所上升;细根/总根长比值则在处理中期和后期逐渐增大,处理末期则有所降低;不同水分胁迫程度导致根尖数量差异显著。在整个处理阶段,水分首先保证苗高和叶片生长,根系生长受到限制;随着水分胁迫程度增加,通过落叶和根系二次生长来保障根系的水分需求和提高水分吸收效率,以此来缓解水分胁迫对生存的胁迫。     

Tree age and soil phosphorus conditions influence N2-fixation rates and soil N dynamics in natural populations of Acacia senegal

Acacia senegal, an important leguminous tree in arid and semi-arid environments, has shown promise as a multipurpose species, including gum production and soil fertility improvement, linked with N₂-fixation capabilities. Of particular interest are ontogenetic and edaphic effects on A. senegal performance in natural populations. Our research objectives were to investigate the effect of tree age and site phosphorus conditions on (1) tree N₂-fixation and (2) soil N and C dynamics in natural stands of A. senegal var. senegal, Baringo District, in the Rift Valley, Kenya. Sites consisted of A. senegal saplings (9 months) and mature A. senegal trees (7 years) along an edaphic gradient of soil P availability. A single-tree neighborhood approach was employed using a two by two factorial design: site conditions [high and low soil P contents] and tree age class [juvenile and mature]. Soil (N and C pools and fluxes) and plant metrics were quantified. A soil transfer experiment was also employed to confirm age and site effects on soil N mineralization. On the high soil P site, A. senegal had significantly lower foliar (¹⁵N levels than neighboring non-leguminous species (Balanites aegyptiaca), while foliar δ¹⁵N values in A. senegal on the low P site exhibited no significant difference with our reference plant, B. aegyptiaca. Across P sites, B. aegyptiaca had similar foliar δ¹⁵N values. These results indicate that the rate of N₂-fixation of A. senegal trees, as determined with foliar ¹⁵N natural abundance methodology, increased with increasing soil P availability in these natural populations. However, N₂-fixation rates declined with age. Although soil texture and soil CO₂ efflux did not differ between sites or across ages, soils under mature A. senegal at the high P site exhibited significantly greater total N content and total C content in comparison to soils at the low P site and under juvenile plants. Furthermore, under mature A. senegal trees, soil N mineralization rates were significantly greater as compared to under saplings. Soil transplants confirmed that soil microbial activity may be stimulated under mature trees as N mineralization rates were 2-3 fold greater compared to under A. senegal saplings. Our findings suggest that tree age and soil P availability are important factors in the nitrogen budget of natural populations of A. senegal, determining N₂-fixation rates, and potentially influencing soil total N and C pools and soil mineral N. This study provides information regarding the adaptation of A. senegal under differing edaphic conditions thus increasing accuracy of management support for A. senegal populations as productive agroforests.     

Seasonal evolution of water status after outplanting of two provenances of Holm oak nursery seedlings

Forest restoration programs using Holm oak (Quercus ilex ssp. ballota [Desf.] Samp.) have had limited success. The effect of plant provenance on plantation success is uncertain, although some previous studies suggest that some provenances may be better able to tolerate stress. We studied the tolerance to drought in seedlings from two Spanish provenances of Holm oak before and after outplanting. One provenance was from a continental climate with cold winters (GR) and the other was from a xeric climate (HU). Seedlings were subjected to a water stress test in the nursery during the summer and survival was visually assessed after 2?weeks. In addition, 35 healthy seedlings of each provenance that were not subjected to the water stress tests were used for outplanting experiment. In these plants the seasonal changes in water potential at dawn (Ψ), specific leaf area (SLA), cuticular transpiration (E_c), and loss of xylem hydraulic conductance of twigs (PLC) were measured over 18?months. After the water stress test in summer, mortality was 44.3?% for GR seedlings and 12.6?% for HU seedlings. In addition there were differences between the two provenances in plant water status after planting. The HU provenance had a better water status and was more water conservative in the summer (higher Ψ, lower E_c, lower PLC), but not in the winter. The different drought tolerance and water relations parameters of these two provenances indicate that provenance should be considered in forest restoration and conservation programs involving Holm oak.     

柚木种源生长和与材质有关特性的遗传变异及综合评价

对海南岛乐东尖峰岭27年生柚木6个种源的生长及与材质有关特性进行测定与分析,结果表明:种源间树皮厚度、心材宽度、基本密度差异极显著,树高、材积、枝下高、边材宽度差异显著,而胸径、边材年轮数及心材率差异不显著,说明在种源水平上对柚木进行生长和与材质有关特性的改良具有较大的潜力,尤其进行木材生长性状、基本密度和心材宽度的种...     

Genetic variation and division of Pinus sylvestris provenances by ISSR markers

Inter Simple Sequence Repeat (ISSR) was used to detect genetic variation among nine provenances, including 135 individuals. A total of 108 loci were amplified using 10 random primers. The differentiation of the percentage of polymorphic bands (PPB) among different provenances was evident, ranging from 27% to 54%, of which Honghuaerji provenance had the highest PPB and Kalunshan provenance had the lowest PPB. Shannon's Information index (I) at species level was 0.1581 and Nei's gene diversity (h) was 0.2393. Coefficient of gene differentiation (G_ST) calculated by Popgene was 0.3965, these results indicated that majority of genetic variation (60.35%) was found within provenances. According to dendrogram amongpinus sylvestriv provenances, nine provenances were divided into two provenance areas, namely Daxing's and Xiaoxing'an Mountains provenance area and Hulunbeier provenance area. Foundation item: This study was supported by National Scientific and Technological Brainstorm Project. Biography: LI Hui-yu (1978-), female, Ph.D. candidate, Northeast Forestry University, Harbin 150040, P. R. China. Responsible editor: Song Funan     

Potential for Cleopus japonicus to control the weed Buddleja davidii in plantation forests in New Zealand

Buddleja davidii (buddleia) is an invasive weed in commercial Pinus radiata D. Don plantation forests in New Zealand. For the first time, forestry managers are assessing the potential of a newly established biological control agent to manage B. davidii. Initial releases of the leaf feeding weevil Cleopus japonicus Wingelmüller (Coleoptera: Curculionidae) were made in 2006 at three P. radiata plantations located in cool temperate areas within the North Island in New Zealand. At each site, 1000 adults were released at a central point and their movement monitored along four 150 m transects, radiating outwards from the point of release, for three years. Measurements included the establishment and rates of spread of C. japonicus and damage to B. davidii by the weevils.C. japonicus established at all sites. Feeding damage to B. davidii was strongly seasonal, with damage peaking each autumn, and achieving up to 95% defoliation within three years. A model of adult dispersal probability from the central release point predicted the population front was moving on average 65 m, 42 m and 27 m per annum at each of the three sites. There was an initial time lag of approximately one year between the arrival of the weevil dispersal front, and the agent causing damage of greater than 30% defoliation to B. davidii.Effective B. davidii control needs to occur in the first few years after planting. Our results suggest that C. japonicus could be quite effective at controlling B. davidii during this time if integrated with a complementary weed management technique, such as the spot application of herbicides around plantation seedlings, rather than broadcast application. This would maximize C. japonicus establishment throughout stands.     

Cambial activity, wood formation and sapling survival of Pinus halepensis exposed to different irrigation regimes

Wood formation and the anatomical characteristics of tree-rings play a decisive role in plant performance and survival due to the importance of water transport. Saplings may be especially vulnerable to water stress; however, the level of water stress that they can endure still remains largely unexamined. Thus, the general objective of our research is to determine the plasticity of wood formation in Pinus halepensis saplings. We evaluated cambial activity, xylem growth ring formation and its anatomical characteristics in different experimental irrigation conditions and tested for its influence on the success rate of sapling establishment. Our results demonstrate a high phenological plasticity in wood formation with juvenile P. halepensis saplings in relation to water availability. Dry conditions during spring and summer strongly limit their cambial activity, which is suggested to be linked to sapling survival during summer. Width and anatomical characteristics of tree-rings differ in saplings exposed to different irrigation conditions. Our results suggest that increasing water stress during spring and summer periods, as predicted by future climate change scenarios, may seriously affect the success of both natural regeneration and reforestation of P. halepensis, and this could severely modify potential distribution of the species.     

Afforestation method affects the isotopic composition of planted Pinus halepensis in a semiarid region of Spain

We used an isotopic approach to evaluate the effects of three afforestation methods on the ecophysiology of an Aleppo pine plantation in semiarid Spain. The site preparation methods tested were excavation of planting holes (H), subsoiling (S), and subsoiling with addition of urban solid refuse to soil (S + USR). Five years after plantation establishment, trees in the S + USR treatment were over three times larger than those in the S treatment, and nearly five-fold larger than those planted in holes. Differences in tree biomass per hectare were even greater due to disparities in initial planting density and pine tree mortality among treatments. Pine trees in the S + USR treatment showed higher foliar P concentration, δ¹³C and δ¹⁵N than those in the S or H treatments. Foliar δ¹⁵N data proved that trees in the S + USR treatment utilized USR as a source of nitrogen. Foliar δ¹³C and δ¹⁸O data suggest that improved nutrient status differentially stimulated photosynthesis over stomatal conductance in the pine trees of the S + USR treatment, thus enhancing water use efficiency and growth. In the spring of 2002, trees in the S + USR treatment exhibited the most negative predawn water potentials of all the treatments, indicating that the rapid early growth induced by USR accelerated the onset of intense intra-specific competition for water. The results of this study have implications for the establishment and management of Aleppo pine plantations on semiarid soils. Planting seedlings at low density and/or early thinning of pine stands are strongly recommended if fast tree growth is to be maintained beyond the first few years after USR addition to soil. Foliar C, O and N isotope measurements can provide much insight into how resource acquisition by trees is affected by afforestation techniques in pine plantations under dry climatic conditions.