Tree allometry, leaf size and adult tree size in old-growth forests of western Oregon

Relationships between tree height and crown dimensions and trunk diameter were determined for shade-tolerant species of old-growth forests of western Oregon. The study included both understory and overstory species, deciduous and evergreen angiosperms and evergreen conifers. A comparison of adult understory species with sapling overstory species of similar height showed greater crown width and trunk diameter in the former, whether the comparison is made among conifers or deciduous trees. Conifer saplings had wider crowns than deciduous saplings, but the crown widths of the two groups converged with increase in tree height. Conifer saplings had thicker trunks than deciduous saplings of similar crown width, possibly because of selection for resistance to stem bending under snow loads. The results suggest that understory species have morphologies that increase light interception and persistence in the understory, whereas overstory species allocate their biomass for efficient height growth, thereby attaining the high-light environment of the canopy. The greater crown widths and the additional strength requirements imposed by snow loads on conifer saplings result in less height growth per biomass increment in conifer saplings than in deciduous saplings. However, the convergence in crown width of the two groups at heights greater than 20 m, and the proportionately smaller effect of snow loads on large trees, may result in older conifers equalling or surpassing deciduous trees in biomass allocation to height growth.     

Spatial pattern and regeneration dynamics in a temperate Abies–Tsuga forest in southwestern Japan

This article reports the regeneration dynamics of a temperate Abies–Tsuga forest in Kirishima Yaku National Park, southwestern Japan, and examines the influence of species coexistence mediated by gap disturbances on biomass production. All trees taller than 2 m in a 1-ha plot were monitored over four growing seasons. Three growth-form groups occupied different vertical layers. Evergreen conifers and deciduous broad-leaved trees tended to be spatially segregated from evergreen broad-leaved trees, which formed thickets in the understorey. The regeneration of understorey evergreen broad-leaved trees was affected by canopy gaps. The recruitment of conifers and deciduous broad-leaved species was not observed during the four growing seasons. This suggests that regeneration is sporadic and the present environmental conditions are not favorable for these canopy species. The mortality and unsuccessful recruitment of conifers and deciduous trees appeared to cause fluctuations in the productivity of the stand. However, an abundance of canopy gaps accelerates the regrowth of shorter species, and the fluctuation of productivity resulting from the population dynamics of canopy species would be partly mitigated by the regeneration of evergreen understorey species. The horizontal and vertical heterogeneity of the temperate mixed forest was a result of the patch structures of the three growth-form groups. The different regeneration patterns among the three groups, which were driven by interactions of species-specific regeneration niches and disturbance regimes, might be an important factor in maintaining the aboveground productivity in a transitional mixed forest between warm-temperate and cool-temperate zones.     

Radiation use efficiency in adjacent hardwood and pine forests in the southern Appalachians

The efficiency with which trees convert photosynthetically active radiation (PAR) to biomass has been shown to be consistent within stands of an individual species, which is useful for estimating biomass production and carbon accumulation. However, radiation use efficiency (?) has rarely been measured in mixed-species forests, and it is unclear how species diversity may affect the consistency of ?, particularly across environmental gradients. We compared aboveground net primary productivity (ANPP), intercepted photosynthetically active solar radiation (IPAR), and radiation use efficiency (? = ANPP/IPAR) between a mixed deciduous forest and a 50-year-old white pine (Pinus strobus L.) plantation in the southern Appalachian Mountains. Average ANPP was similar in the deciduous forest (11.5 Mg ha⁻¹ y⁻¹) and pine plantation (10.2 Mg ha⁻¹ y⁻¹), while ? was significantly greater in the deciduous forest (1.25 g MJ⁻¹) than in the white pine plantation (0.63 g MJ⁻¹). Our results demonstrate that late-secondary hardwood forests can attain similar ANPP as mature P. strobus plantations in the southern Appalachians, despite substantially less annual IPAR and mineral-nitrogen availability, suggesting greater resource-use efficiency and potential for long-term carbon accumulation in biomass. Along a 260 m elevation gradient within each forest there was not significant variation in ?. Radiation use efficiency may be stable for specific forest types across a range of environmental conditions in the southern Appalachian Mountains, and thus useful for generating estimates of ANPP at the scale of individual watersheds.     

Contrasting seasonal leaf habits of canopy trees between tropical dry-deciduous and evergreen forests in Thailand

We compared differences in leaf properties, leaf gas exchange and photochemical properties between drought-deciduous and evergreen trees in tropical dry forests, where soil nutrients differed but rainfall was similar. Three canopy trees (Shorea siamensis Miq., Xylia xylocarpa (Roxb.) W. Theob. and Vitex peduncularis Wall. ex Schauer) in a drought-deciduous forest and a canopy tree (Hopea ferrea Lanessan) in an evergreen forest were selected. Soil nutrient availability is lower in the evergreen forest than in the deciduous forest. Compared with the evergreen tree, the deciduous trees had shorter leaf life spans, lower leaf masses per area, higher leaf mass-based nitrogen (N) contents, higher leaf mass-based photosynthetic rates (mass-based P(n)), higher leaf N-based P(n), higher daily maximum stomatal conductance (g(s)) and wider conduits in wood xylem. Mass-based P(n) decreased from the wet to the dry season for all species. Following onset of the dry season, daily maximum g(s) and sensitivity of g(s) to leaf-to-air vapor pressure deficit remained relatively unchanged in the deciduous trees, whereas both properties decreased in the evergreen tree during the dry season. Photochemical capacity and non-photochemical quenching (NPQ) of photosystem II (PSII) also remained relatively unchanged in the deciduous trees even after the onset of the dry season. In contrast, photochemical capacity decreased and NPQ increased in the evergreen tree during the dry season, indicating that the leaves coped with prolonged drought by down-regulating PSII. Thus, the drought-avoidant deciduous species were characterized by high N allocation for leaf carbon assimilation, high water use and photoinhibition avoidance, whereas the drought-tolerant evergreen was characterized by low N allocation for leaf carbon assimilation, conservative water use and photoinhibition tolerance.     

Enhanced forage production under Samanea saman in a subhumid tropical grassland

The effects of isolated, mature Samanea saman trees on herbaceous production and species composition were investigated over the 1993/1994 growing season in a subhumid tropical grassland in north-east Queensland, Australia. Under the crown, the cumulative aboveground biomass over the season was almost 90% above that of the open grassland. This increase was associated with a difference in species composition. The principal grass under the crown was Panicum maximum, while in the open grassland, the dominant species was Urochloa mosambicensis. Near the crown, cumulative biomass was intermediate and this was reflected in a mixed species composition. This study confirms earlier, largely anecdotal reports of the potential beneficial effects of S. saman on forage production, but by itself was unable to explain the mechanism by which this increase occurred. This revised version was published online in June 2006 with corrections to the Cover Date.     

Forage production in natural and afforested grasslands of the Pampas: ecological complementarity and management opportunities

In managed rangelands periods of low primary productivity determine troughs of forage availability, constraining animal production year-round. Although alternative tools to increase forage availability during critical seasons exists, most of them are unaffordable and short-lived in marginal areas. We explore the potential benefits of deciduous tree plantations favoring winter forage productivity by comparing aboveground net primary productivity (ANPP) patterns in herbaceous understory to tree plantations and natural grasslands in the Pampas (Argentina). These temperate subhumid grasslands are characterized by the coexistence of winter species, mainly C3 grasses of the native genera Stipa, Piptochaetium, and Bromus and the exotic genera Lolium and Festuca) and summer species (mainly C4 grasses of the native genera Paspalum, Bothriochloa, and Stenotaphrum) that replace each other throughout the seasons, with domination of the latter. We hypothesize that the natural decoupling of growing seasons between winter deciduous trees and winter grasses could provide the basis for the sustainable promotion of winter forage. We measured ANPP on two 23-year-old Populus deltoides plantations and their understory and compared them with adjacent open grasslands. Afforested stands had 55–75% higher annual ANPP than their non-afforested neighbors, with trees contributing ~70% to total ANPP. Herbaceous canopies beneath plantations achieved about half of the ANPP observed in non-afforested situations with a contrasting seasonal distribution associated with shifts from C4 to C3 grass dominance. Winter ANPP, the most critical source of forage in these grazing systems, was similar or higher in the herbaceous understory of tree plantations to that on their non-afforested counterparts, suggesting that mixed systems involving deciduous trees and understory pastures are a valid and viable option in the region.     

Assessment of crown woody biomass in <Emphasis Type="Italic">Eucalyptus grandis</Emphasis> and <Emphasis Type="Italic">E. globulus</Emphasis> plantations

Young trees were harvested to explore non-destructive methodologies to estimate live branch dry weights in young fast-growing Eucalyptus species under different spacing and fertilizer treatments. Branch growth can vary with silvicultural management such as spacing, fertilizing and thinning, and over relatively short periods in response to environmental conditions. Many published regressions based on standard measurements of height and diameter are site, age and treatment specific. The aim of this study was to improve our capacity to predict woody crown dry weight, based on stem measurements, and to minimize (or eliminate) treatment effects on the resulting model. In young trees, branches are temporary support structures for foliage and are often discarded as the base of the green crown rises. As temporary structures they represent an investment of biomass and nutrient elements, and are subject to selection pressures to maximize the return on investment by the tree. Trees were harvested from existing plantation experiments located in south-eastern Queensland for E. grandis W. Hill ex Maiden (ranging from 0.28 to 15.85 m in height, to 5 years old) and south-western Australia for E. globulus Labill. (0.10–34.4 m in height, to 10.2 years) in order to examine the impact of spacing, nitrogen and phosphorus fertilization on early growth. Relationships to estimate crown woody biomass from non-destructive measurements were developed, and these relationships tended to have different slopes and intercepts for trees with predominantly juvenile foliage and those with intermediate or adult foliage. Dry weight of whole-crown live branch wood (W_branch) was related to heights and/or diameter at breast height (D_BH), but the regressions parameters were different, depending on treatment. The relationships became more generic (i.e. less dependent on treatment effects) between W_branch and stem sectional area at the height of the base of the green crown (SA_CB), consistent with the pipe model theory (R² > 0.91 for the two species for trees with intermediate/adult leaves). However, W_branch was more closely related again to the stem volume above the base of the green crown and treatment effects were not significant (V_Con,gc, R² > 0.93). Branches exit the stem below the green crown, and for E. grandis the best relationship was on stem volume above the lowest live branch (V_Con,llb, R² 0.94). Limited sampling from four other species with similar or contrasting crown characteristics indicated that the relationship could be applied quite generally. Individual E. grandis branch woody dry weight was closely related to the conical volume of the main (first order) branch (V_con,br, R² 0.98₎. The whole crown equivalent, branch woody dry weight plus stem dry weight above the lowest live branch, was also closely related to the stem volume within the woody crown (V_Con,llb, R² 0.97–0.99). While the slope of this relationship was still significantly different between trees with juvenile and intermediate/adult foliage, it had a similar form, suggesting that trees with juvenile foliage allocated a different proportion of their woody biomass within the crown to branches than older trees.     

Differences in transpiration between a forest and an agroforestry tree species in the Sudanian belt

Average population growth in the African Sudanian belt is 3 % per year. This leads to a significant increase in cultivated areas at the expense of fallows and forests. For centuries, rural populations have been practicing agroforestry dominated by Vitellaria paradoxa parklands. We wanted to know whether agroforestry can improve local rainfall recycling as well as forest. We compared transpiration and its seasonal variations between Vitellaria paradoxa, the dominant species in fallows, and Isoberlinia doka, the dominant species in dry forests in the Sudanian belt. The fallow and dry forest we studied are located in northwestern Benin, where average annual rainfall is 1200 mm. Sap flow density (SFD) was measured by transient thermal dissipation, from which tree transpiration was deduced. Transpiration of five trees per species was estimated by taking into account the radial profile of SFD. The effect of the species and of the season on transpiration was tested with a generalized linear mixed model. Over the three-year study period, daily transpiration of the agroforestry trees, V. paradoxa (diameters 8–38 cm) ranged between 4.4 and 26.8 L day^?1 while that of the forest trees, I. doka, (diameters 20–38 cm) ranged from 9.8 to 92.6 L day^?1. Daily transpiration of V. paradoxa was significantly lower (15 %) in the dry season than in the rainy season, whereas daily transpiration by I. doka was significantly higher (13 %) in the dry season than in the rainy season. Our results indicate that the woody cover of agroforestry systems is less efficient in recycling local rainfall than forest cover, not only due to lower tree density but also to species composition.     

Productivity of temperate broad-leaved forest stands differing in tree species diversity

? Understanding the effects of tree species diversity on biomass and production of forests is fundamental for carbon sequestration strategies, particularly in the perspective of the current climate change. However, the diversity-productivity relationship in old-growth forests is not well understood.

? We quantified biomass and above-ground production in nine forest stands with increasing tree species diversity from monocultures of beech to stands consisting of up to five deciduous tree species (Fagus sylvatica, Fraxinus excelsior, Tilia spp., Carpinus betulus, Acer spp.) to examine (a) if mixed stands are more productive than monospecific stands, (b) how tree species differ in the productivity of stem wood, leaves and fruits, and (c) if beech productivity increases with tree diversity due to lower intraspecific competition and complementary resource use.

? Total above-ground biomass and wood production decreased with increasing tree species diversity. In Fagus and Fraxinus, the basal area-related wood productivity exceeded those of the co-occurring tree species, while Tilia had the highest leaf productivity. Fagus trees showed no elevated production per basal area in the mixed stands.

? We found no evidence of complementary resource use associated with biomass production. We conclude that above-ground productivity of old-growth temperate deciduous forests depend more on tree species-specific traits than on tree diversity itself.

     

Tree morphology responds to neighbourhood competition and slope in species-rich forests of subtropical China

Trees are able to respond to their local biotic and abiotic environment with morphological adjustments which improve resource acquisition and, thus, growth. In forests, light is broadly recognised as one of the major factors determining growth, and morphological responses comprise changes in crown architecture and stem stature. On sloping terrain, the interplay of phototropism and gravitropism may further affect morphological growth characteristics. However, different tree species are expected to show species-specific responses. In this study, we analysed three growth characteristics of tree individuals belonging to four species of two functional groups (evergreen: Schima superba, Castanopsis eyrei, deciduous: Quercus serrata var. brevipetiolata, Castanea henryi) in a species-rich Chinese subtropical forest. Crown projection area, relative crown displacement and stem inclination were related to biotic (local species richness, functional richness, competition, stand age) and abiotic (slope aspect and inclination, soil depth) variables in the local neighbourhood of the tree individuals. We hypothesised that (i) there are species-specific differences in the morphological response of crown architecture and stem stature and (ii) that crown size and asymmetry as well as stem inclination are influenced by both, biotic and abiotic factors. In contrast to our expectations we were unable to reveal any species-specific differences in any of the three growth characteristics. The results of mixed effects models showed that crown area was mainly affected by the target tree's dbh and biotic variables related to neighbours (competition, functional diversity), whereas stem inclination was mainly influenced by slope. Relative crown displacement was influenced by both, biotic and abiotic variables. We conclude that growth responses resulting in crown displacement and stem inclination seem to be an important mechanism to ameliorate foraging for light in our study area, but that these responses appear to be species-independent. The interplay of stem inclination and crown displacement allows for a plastic response of tree individuals in biotically and abiotically heterogeneous environments. Our results indicate that forest management in this region should focus on functionally diverse stands which are promoting crown area positively resulting in increased growth rates of individual trees.     

Evaluation of leaf display of evergreen broadleaved tree species and deciduous tree species in warm temperate conifer plantations

We investigated the sapling leaf display in the shade among trees of various leaf lifespans co-occurring under the canopy of a warm-temperate conifer plantation. We measured leaf-area ratio (aLAR) and morphological traits of saplings of evergreen broadleaved tree species and a deciduous tree species. Although we found large interspecific and intraspecific differences in aLAR even among saplings of similar size in the homogeneous light environment, we did not find a consistent trend in aLAR with leaf lifespan among the species. While deciduous trees annually produced a large leaf area, some evergreen broadleaved trees retained their leaves across years and had aLAR values as high as those of deciduous trees. Among leaf-level, shoot-level, and individual-level morphological traits, aLAR was positively correlated with current-year shoots mass per aboveground biomass in deciduous trees, and with the area of old leaves per aboveground mass in evergreen broadleaved trees. Thus, tree-to-tree variation in the degrees of annual shoot production and the accumulation of old leaves were responsible for the interspecific and intraspecific variations in aLAR.     

Transport,storage and mobilization of nitrogen by trees and shrubs in the wet/dry tropics of northern Australia

Xylem sap from woody species in the wet/dry tropics of northern Australia was analyzed for N compounds. At the peak of the dry season, arginine was the main N compound in sap of most species of woodlands and deciduous monsoon forest. In the wet season, a marked change occurred with amides becoming the main sap N constituents of most species. Species from an evergreen monsoon forest, with a permanent water source, transported amides in the dry season. In the dry season, nitrate accounted for 7 and 12% of total xylem sap N in species of deciduous and evergreen monsoon forests, respectively. In the wet season, the proportion of N present as nitrate increased to 22% in deciduous monsoon forest species. These results suggest that N is taken up and assimilated mainly in the wet season and that this newly assimilated N is mostly transported as amide-N (woodland species, monsoon forest species) and nitrate (monsoon forest species). Arginine is the form in which stored N is remobilized and transported by woodland and deciduous monsoon forest species in the dry season. Several proteins, which may represent bark storage proteins, were detected in inner bark tissue from a range of trees in the dry season, indicating that, although N uptake appears to be limited in the dry season, the many tree and shrub species that produce flowers, fruit or leaves in the dry season use stored N to support growth. Nitrogen characteristics of the studied species are discussed in relation to the tropical environment.     

缙云山常绿阔叶林凋落动态及组成

[目的]从组成群落的主要树种角度研究森林凋落物生产与物候的关系,分析群落尺度上的凋落物产量、组成、季节动态、分布及主要树种的叶凋落节律,探讨缙云山常绿阔叶林凋落物的基本特征和凋落高峰的形成原因,为其保护、恢复及管理经营提供科学参考,同时也为亚热带常绿阔叶林生态系统的物质循环和功能及维持生物多样性机制等研究提供基础资料。[方法]以研究地1 hm²常绿阔叶林群落固定监测样地为平台,通过均匀交叉布设173个凋落物收集器,每月对收集到的凋落物进行分类、鉴定、称量。[结果]表明:1)2013—2014年的年凋落量为5 310.52 kg·hm^-2,其中叶凋落量(3 814.01 kg·hm^-2)最多,占年总凋落量的71.82%(常绿树叶90.95%,落叶树叶9.05%),枝条占12.51%,花果等繁殖器官占8.74%,树皮碎屑占1.00%,杂物占6.04%。2)1 a内,凋落物收集器内共收集到36种树木的凋落叶,占样地内树种总数(43种)的83.72%。3)不同收集器之间凋落量存在较大差异,55个收集器中的凋落量在250~300 g,4个收集器的凋落量超过400 g;单个收集器全年最多可收集到24种树种的凋落叶,收到14种凋落叶种数的收集器最多(29个)。[结论]1)全年凋落量月动态呈明显双峰型,叶凋落量月动态与凋落总量变化相同。栲(Castanopsis fargesii Franch)、润楠(Machilus pingii (Oliv.) Hemsl)、薯豆(Elaeocarpus japonicus Sieb. et Zucc)三者落叶量之和为落叶总量的55.89%,是凋落叶的主要来源。2)主要树种均具有明显的叶凋落节律,根据其节律特点可分为2类:单峰型和双峰型。根据其出现时间可分为4类:在春末夏初和秋季均出现落叶高峰的常绿树;仅在春末夏初出现高峰的常绿树;仅在夏末秋初出现高峰的常绿树;以及在秋冬季出现高峰的落叶树。叶凋落高峰主要受物候的影响。     

Biomass and nitrogen dynamics in an irrigated hybrid poplar plantation

A 3-year study measured the effects of ground cover treatments and N fertilization on biomass and nitrogen dynamics in an irridiated hybrid poplar (Populus deltoides Bartr. X P. trichocarpa Torr. and Gray, clone NC-9922) plantation in northern Wisconsin, U.S.A. Annually fertilized (112 kg N ha⁻¹ year⁻¹) and unfertilized plots were maintained weed free (bare soil), allowed to revegetate with native weeds, or seeded to birdsfoot trefoil (Lotus corniculatus L.). Biomass and N in trees and ground-cover vegetation were sampled before and after each growing season.Trees in bare-soil plots responded to fertilization primarily in the third growing season, but total biomass of 3-year-old trees was not increased by annual fertilization. In plots with a ground cover,fertilization increased tree growth but cover crop treatment had no effect. Ground cover biomass peaked during the second growing season, but declined thereafter, primarily due to reductions in below-ground biomass. Estimated recovery of fertilizer N was low in bare soil plots after 3 years, with 2% in the ‘perennial’ portion of the trees and 13% in the leaf litter. In contrast, recovery in the cover crop plots was 44%–51% in years 2–4. During that period, both biomass and N pool dominance shifted from primarily cover crop to primarily trees. The ground cover appeared to reduce tree growth in years 1–3, but total tree biomass after 4 years was greater in fertilized plots with ground cover (22.7 Mg/ha) than in fertilized bare soil plots (16.7 Mg/ha). Biomass production in fertilized trefoil plots in the fourth year (15.1 Mg ha⁻¹ year⁻¹, excluding leaves) exceeds that of local forests by 50%, and may be comparable to corn productivity in the area.     

Do vegetative and reproductive phenophases of deciduous tropical spe-cies respond similarly to rainfall pulses?

Deciduous trees with high-density wood that occur in dry seasonal tropical regions respond to rainfall seasonality with synchrony in phenophases. However, they may exhibit interannual differences in sy...     

Mixed-species plantations of Acacia mangium and Eucalyptus grandis in Brazil: 1. Growth dynamics and aboveground net primary production

Nitrogen fertilizer inputs increased sharply over the last decade in Brazilian eucalypt plantations. Due to the economic and potential environmental cost of fertilizers, mixed plantations with N-fixing species might be an attractive option to improve the long-term soil N status. A randomized block design was set up in southern Brazil, including a replacement series and an additive series design, as well as a nitrogen fertilization treatment. The development of mono-specific stands of Eucalyptus grandis (0A:100E) and Acacia mangium (100A:0E) was compared with mixed plantations in proportions of 1:1 (50A:50E), and other stands with different densities of acacia for the same density of eucalypts. The objective was to assess the effect of inter-specific interactions on the early development of the two species. Aboveground biomass was measured 6, 12, 18 and 30 months after planting, sampling 6–10 trees of each species per treatment at each age, and allometric equations were established in 0A:100E, 100A:0E, 50A:50E and 50A:100E. The height and basal area of E. grandis seedlings were enhanced by 12% and 30%, respectively by N fertilization at age 1 year. Inter-specific competition led to a stratified canopy, with suppression in acacia growth earlier for basal area than for height. The mean number of stems per acacia tree at 36 months after planting was significantly higher in pure stands (3.7), than in 50A:50E (2.7) and in the additive series (between 1.6 and 1.8). H/D ratios were highly sensitive to inter-tree competition for the two species. The suppressed acacia understorey in mixed-species stands did not influence biomass production and partitioning within eucalypts. This pattern led to biomass accumulation combining the two species in 50A:100E that was about 10% higher than in 0A:100E, from age 12 months onwards. Aboveground net primary production (ANPP) amounted to 25 Mg ha⁻¹ and 37 Mg ha⁻¹ from age 18 to 30 months in 100A:0E and 0A:100E, respectively. Acacia ANPP in 50A:100E amounted to 2 Mg ha⁻¹ over the same period, as a result of substantial inter-specific competition. An increment in biomass production in these very fast-growing eucalypt plantations was achieved introducing acacia as an understorey and not in the 50A:50E design, as observed in other studies.     

Interspecific variation in vessel size, growth and drought tolerance of broad-leaved trees in semi-arid regions of Kenya

In semi-arid regions, trees often wither during the dry season. Withering is sometimes manifest as die-back, whereby whithering results in shoot death, which progresses downward from the uppermost part of the crown. In this study, we measured the relationships between height growth and diameter at breast height, die-back frequency and severity, vessel size and specific hydraulic conductivity of four evergreen (Senna siamea (Lamk) H.S. Irwin & Barneby, Jacaranda mimosifolia D. Don, Azadirachta indica A.H.L. Juss and Acacia gerrardii Benth.) and one deciduous (Melia volkensii Gürke) plantation tree species in Kenya, which has a conspicuous dry season. Die-back occurred readily in some species, but not in others. Senna siamea showed the highest specific hydraulic conductivity and the highest growth rate among the five species and was quite susceptible to die-back. Among species, height growth and specific hydraulic conductivity were positively correlated with vessel size and negatively correlated with die-back frequency, suggesting a trade-off between growth rate and drought tolerance. This implies that an adaptation to rapid growth under humid conditions leads to low drought tolerance. However, the deciduous tree Melia volkensii showed high specific hydraulic conductivity and growth, with no symptoms of die-back, implying that a mechanism associated with the deciduous habit results in drought avoidance by reducing the requirement for water during the dry season.     

科尔沁沙质草地生物量对水、氮、磷添加的响应(英文)

为探寻科尔沁沙地东南部草地生产力自然恢复的主要限制因素,该文采用3因素2水平析因设计研究了水、氮、磷添加对沙质草地的影响。8种处理分别为添加水(W)、加氮肥(N)、加磷肥(P)、加水+氮肥(WN)、加水+磷肥(WP)、加氮肥+磷肥(NP)、加水+氮肥+磷肥(WNP)和对照(CK),每种处理6次重复,随机分配在48个4m×4m的样方中,样方之间留2m缓冲带。研究结果表明:科尔沁沙质草地生产力的恢复受氮素的限制,与水和磷无关;2005年生长季所有添加氮肥的样方,生物量和地上净初级生产力均较对照明显增加(P<0.05);禾本科根量在地下生物量中占优势。受限于地下生物量测定,目前的研究可能低估了我国北方草地的净初级生产力。     

Quercus calliprinos regrowth advantage under grazing in Mediterranean maquis and its management implications

The post disturbance natural succession of the Mediterranean maquis, which turns open and species-rich landscapes into dense, closed stands of sclerophyllous woody vegetation is a principal threat to plant and animal diversity. Therefore, in the absence of traditional agricultural disturbance, active management regimes that include cutting and grazing are proposed to preserve biodiversity. The Mediterranean woody vegetation in Israel is strongly dominated by one species - the evergreen sclerophyllous Quercus calliprinos (Kermes oak). We hypothesized that under cutting and grazing, the evergreen Q. calliprinos has a relative regrowth advantage over other competing tree species. Here we examined the effect of grazing and the effect of tree structural traits on the regrowth after clear cutting of all trees in our study plots at Mt. Meron LTER site, Israel. All trees were removed from five blocks of 2000 m² and each block was divided into two plots, five of which were exposed to grazing livestock while five were wire-fenced and ungrazed. The regrowth rate of Q. calliprinos under grazing was higher than that of all other tree species suggesting that in the long-term, under such a conservation management regime, the dominance of the evergreen sclerophyllous Q. calliprinos over the deciduous tree species will increase and consequently will decrease plant and animal diversity. Therefore, we conclude that to protect landscape and species diversity in Mediterranean ecosystems dominated by evergreen oaks, when cutting and grazing are applied, special care must be paid to trees that are more negatively affected by such treatment.     

Which factors most influence heartwood distribution and radial growth in plantation teak?

? To investigate the effect of climate on radial growth in young plantation grown teak (Tectona grandis L.), growth ring width was measured in 105 trees and correlated to precipitation and temperature data.

? The social status of trees within the stand was also determined and cross-sectional area (CSA) for the trunk correlated to the proportion of heartwood (HW) within the tree. HW develops asymmetrically in leaning stems of some conifer species, but it is not known if this phenomenon also occurs in broadleaf species. Therefore, we measured HW proportion in leaning and straight stems, along with the number of growth rings in the HW.

? Annual ring width depended strongly on mean monthly temperature during the rainy season and the most significant relationships were found corresponding to the months of June and July. With regard to the weaker relationship between precipitation and radial growth, correlations were highest during the period of bud-break at the beginning of the rainy season.

? The very high stand density affected radial growth, particularly in suppressed trees, which responded little to thinning operations. HW formation was greatest in dominant trees, and was highly regressed with stem CSA.

? Therefore, rapid growth of young stands should be encouraged by reducing stand density. Asymmetric HW formation occurred in both leaning and straight trees, and was significantly greater along the upper sides of leaning stems. It is probable that this eccentric HW formation is linked to mechanical loading on the tree.