Root biomass and rooting profile of naturally regenerated beech in mid-elevation Scots pine woodlands

The natural establishment of shade-tolerant forest species such as beech (Fagus sylvatica L.) occurs in naturally regenerated Scots pine (Pinus sylvestris L.) woodlands that develop on former pastures and cultivated lands. To examine possible effects of underground competition in beech establishment, we studied the root biomass and the rooting profile of 53 mixed Scots pine-natural beech woodlands in French mid-elevation volcanic areas. Stands were arranged along a maturation gradient. Roots were sampled using the root-auger technique (0 to 75 cm depth every 15 cm). In addition, 23 young beeches were uprooted to study the entire root system. Total beech fine-root biomass was closely correlated with most beech aerial characteristics, (e.g., height, diameter and girth), and correlated moderately with tree age. However, it correlated poorly with basic competition indices such as stand density and basal area. Conversely, competition indices including vertical dimensions of competing trees were correlated with the underground biomass, probably as a result of redundancy with beech height. The rooting profile (fine roots, < 5 mm) of beech and pine were quite similar, and did not change significantly along the stand maturation gradient. Beech has a heart-shaped root system while pine is more plate-like and dimorphic. Beech fine-root biomass progressively surpassed pine biomass throughout the soil layers, thus confirming that it is dynamic and competitive in mature mixed stands. The coexistence of the root systems of beech and pine in the same soil layers presumably results in strong underground competition.     

Rooting strategy of naturally regenerated beech in Silver birch and Scots pine woodlands

This study investigated the belowground development and strategy of late-successional European beech (Fagus sylvatica L.) in ageing natural Scots pine (Pinus sylvestris L.) and Silver birch (Betula pendula Roth.) woodlands in a French volcanic mid-elevation area. For this purpose root biomass, root profile and fine-root architecture of competitor trees were examined in 53 mixed pine–beech and 42 birch–beech woodlands along a stand maturation gradient, using the root auger technique (0–75-cm). The total beech fine-root biomass highly correlated with aerial dimensions such as stem height and girth, whereas it moderately correlated with its age, thus indicating the effects of competition. Basic stand biometric data such as stand density and basal area had no significant effect on beech root biomass. Conversely, competition indices taking into account the vertical dimensions of competitor trees were efficient, probably due to redundancy with beech height. At similar age and height, beeches under birch had a greater belowground development than beeches under pine. Each species exhibited specific rooting pattern and plasticity of fine-root architecture along the gradients of stand maturation and competition. Beech had a heart-shaped rooting habit in both mixings, which strongly increased along stand maturation. Its fine-root system adopted a foraging strategy to respond to increasing stand competition. The Scots pine fine-root system was plate-like and showed a low morphological plasticity, thus presumably a conservative strategy. Silver birch exhibited a high biomass and a foraging capacity in the topsoil but a loose root system in the subsoil. The coexistence of pine and beech roots in the upper soil presumably leads to a high belowground competition. Beech root system becomes predominant throughout the soil profile and it adopts an efficient foraging strategy, but at the expense of its belowground development. Conversely, the niche partitioning strategy between beech and birch may explain why beech develops strongly belowground in spite of the fact that birch has a dense rooting and a competitive fine-root architecture. As a consequence, beech mid-term regeneration and development may be facilitated under birch as compared with pine.     

Biomass and production of a naturally regenerated oak forest in southern Korea

Biomass and production of two stands with Quercus variabilis Bl. as the dominant species (stands 1 and 3) and one with Q. mongolica Fisch. as the dominant species (stand 2) were investigated in southern Korea. Stands 1 and 3 naturally occurred on sites with southerly aspects while stand 2 naturally occurred on northerly aspects; stand ages were similar for the three stands (36–38 years old). Total above- and belowground biomass including understory vegetation (Mg ha^–1) was 108.4 for stand 1, 115.6 for stand 2, and 132.0 for stand 3, respectively. Understory vegetation constituted 17.4% of the total biomass in stand 1 but only 3.7–4.5% in stand 2 and stand 3. Roots constituted 20.1–24.6% of the biomass of the overstory vegetation. Although stand 3 showed the highest total biomass, net production was highest in stand 2 at 12.6 (Mg ha^–1 year^–1); net production levels for stands 1 and 3 were 11.7 and 11.1 (Mg ha^–1 year^–1), respectively. It appeared that the differences in site conditions related to aspect influenced the distribution of naturally regenerated oak species within a relatively small area and resulted in differences in biomass and production among the stands.     

Carbon exchange of a mature,naturally regenerated pine forest in north Florida

We used eddy covariance and biomass measurements to quantify the carbon (C) dynamics of a naturally regenerated longleaf pine/slash pine flatwoods ecosystem in north Florida for 4 years, July 2000 to June 2002 and 2004 to 2005, to quantify how forest type, silvicultural intensity and environment influence stand‐level C balance. Precipitation over the study periods ranged from extreme drought (July 2000–June 2002) to above‐average precipitation (2004 and 2005). After photosynthetic photon flux density (PPFD), vapor pressure deficit (VPD) >1.5 kPa and air temperature <10 °C were important constraints on daytime half‐hourly net CO₂ exchange (NEE_day) and reduced the magnitude of midday CO₂ exchange by >5 μmol CO₂ m^?2 s^?1. Analysis of water use efficiency indicated that stomatal closure at VPD>1.5 kPa moderated transpiration similarly in both drought and wet years. Night‐time exchange (NEE_night) was an exponential function of air temperature, with rates further modulated by soil moisture. Estimated annual net ecosystem production (NEP) was remarkably consistent among the four measurement years (range: 158–192 g C m^?2 yr^?1). In comparison, annual ecosystem C assimilation estimates from biomass measurements between 2000 and 2002 ranged from 77 to 136 g C m^?2 yr^?1. Understory fluxes accounted for approximately 25–35% of above‐canopy NEE over 24‐h periods, and 85% and 27% of whole‐ecosystem fluxes during night and midday (11:00–15:00 hours) periods, respectively. Concurrent measurements of a nearby intensively managed slash pine plantation showed that annual NEP was three to four times greater than that of the Austin Cary Memorial Forest, highlighting the importance of silviculture and management in regulating stand‐level C budgets.     

Plant and arthropod communities in young oak stands: are they determined by site history?

Effect of site history on forest plant and insect communities was studied by comparing afforestations on former agricultural land with reafforestations on ancient woodland sites. Vascular plants, mosses, true bugs, lacewings and saproxylic beetles were surveyed at 18 young broadleaved forest sites dominated by oak (Quercus robur), established between 1986 and 1994 in three different growth regions in Bavaria, Germany. Two strata, near ground level and the canopy, were sampled. Compared to woodland reafforestations greater species density and abundance of plants and true bugs were observed in field layer of afforestation sites. Proportion of forest species among plants and true bugs was however significantly lower in afforestations than on ancient woodland sites. In the canopy, zoo-phytophagous true bugs were significantly better represented in afforestations and zoophagous true bugs in reafforestations. Saproxylic beetles, especially inhabitants of old dead wood, were species-poor in afforestations. Results indicate that site history affects both producer and consumer communities in multiple ways, even 20 years after afforestation of former agricultural land. However, afforestations adjacent to existing forest stands can be regarded as valuable to nature conservation in effectively extending forest habitats. Investment in such afforestation therefore represents more than just an agricultural subsidy. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Belowground drought response of European beech: fine root biomass and carbon partitioning in 14 mature stands across a precipitation gradient

How tree root systems will respond to increased drought stress, as predicted for parts of Central Europe, is not well understood. According to the optimal partitioning theory, plants should enhance root growth relative to aboveground growth in order to reduce water limitations. We tested this prediction in a transect study with 14 mature forest stands of European beech (Fagus sylvatica L.) by analysing the response of the fine root system to a large decrease in annual precipitation (970–520 mm yr⁻¹). In 3 years with contrasting precipitation regimes, we investigated leaf area and leaf biomass, fine root biomass and necromass (organic layer and mineral soil to 40 cm) and fine root productivity (ingrowth core approach), and analysed the dependence on precipitation, temperature, soil nutrient availability and stand structure. In contrast to the optimal partitioning theory, fine root biomass decreased by about a third from stands with >950 mm yr⁻¹ to those with <550 mm yr⁻¹, while leaf biomass remained constant, resulting in a significant decrease, and not an increase, in the fine root/leaf biomass ratio towards drier sites. Average fine root diameter decreased towards the drier stands, thereby partly compensating for the loss in root biomass and surface area. Both δ¹³C‐signature of fine root mass and the ingrowth core data indicated a higher fine root turnover in the drier stands. Principal components analyses (PCA) and regression analyses revealed a positive influence of precipitation on the profile total of fine root biomass in the 14 stands and a negative one of temperature and plant‐available soil phosphorus. We hypothesize that summer droughts lead to increased fine root mortality, thereby reducing root biomass, but they also stimulate compensatory fine root production in the drier stands. We conclude that the optimal partitioning theory fails to explain the observed decrease in the fine root/leaf biomass ratio, but is supported by the data if carbon allocation to roots is considered, which would account for enhanced root turnover in drier environments.     

Evidence of hydraulic lift in a young beech and oak mixed forest using 18O soil water labelling

Hydraulic lift (HL) by tree roots in a young, broad-leaved, mixed temperate European forest was investigated during the 2008 growing season by injecting ¹⁸O-enriched soil water at a depth of 75–90 cm under drought conditions experimentally imposed in a rain-exclusion system. Based on sap flow, leaf water potential, 2-D root distribution measurements, soil isotope profiles, and xylem water isotope composition, water acquisition and use by two tree species, beech (Fagus sylvatica) and oak (Quercus petraea) was compared. We showed that, unlike oak, beech experienced a marked decrease in sap flow and predawn leaf water potential with increasing soil drought. This behaviour was logical considering the shallower root system in beech than in oak. Six days after ¹⁸O-labelling, we observed isotopic enrichment in the shallower soil layers. Since the intermediate soil layers did not display any enrichment, our results clearly pointed to hydraulic lift by tree roots. The superficial enrichment that was observed in the vicinity of oak trunks and the increase in the isotopic signature of xylem sap in the oak trees but not in the beech trees confirmed the predominant role of oak in the hydraulic lift at our site. Even though facilitation for water acquisition among species was not observed here, our results suggest a potential positive contribution of species like oak toward maintaining species diversity in mixed forest ecosystems submitted to severe drought events.     

Psychosocial factors in blood pressure variation: A comparative study of young Samoans

Abstract

Traditional peoples contacting modern cultures frequently experience increased levels of blood pressure. The aim of this investigation was to identify some acculturation‐related psychosocial factors which might contribute to those elevations. Young Samoans living in a traditional village, in modernizing American Samoa, and as migrants in Hawaii were studied. Casual blood pressure, anthropometric measurements, and extensive interview data were collected. The most important factor predicting variation in blood pressure was body mass (BMI). This finding was particularly evident among the acculturated and migrant Samoans. In those locations women's abandonment of breast feeding may contribute to their higher BMI. Among acculturated and migrant women, measures of social support favored lower blood pressures. Among men in all locations a greater number of close social ties was linked to higher blood pressures with the exception of ties with parents. Parental ties were linked to substantially lower blood pressures. A knowledge of Samoan traditions favored lower blood pressure among migrant men, while knowledge of American culture favored higher pressures. Coping strategies and complaint behavior were also significant contributors in all locations.     

Earthworm numbers,biomass and respiratory metabolism in a beech woodland-Wytham Woods,Oxford

Summary The mean annual population density of earthworms was found to be 164.6 m^-2 during a period of detailed study between October 1971 and September 1972. In a year of less detailed study between November 1972 and October 1973 the population density was 117.5 m^-2 (139.8 m^-2 when the type of extraction method was allowed for). Mean biomass densities in the two years of investigation were 41.0 g preserved wet wt m^-2 (1971–1972) and 38.6 (possibly 39.2) g preserved wet wt m^-2 (1972–1973).Comparison of the Brogden's Belt population and biomass densities with those reported from other woodlands indicates that soil type is more important than leaf litter type in determining the numerical abundance of earthworms. Population densities are lower in beechwoods on mor soils, mor soils also support significantly fewer species. As with numbers, mean biomass density in beechwoods on mor soils was significantly lower than that occurring in beechwoods on mull soils; the latter, in turn, being lower than those found in mixed deciduous woods on mull soils. Unlike population density biomass density is influenced by both soil and litter type, this is discussed by reference to mean body weights and food quality as reflected by tannin, nitrogen and carbohydrate content.The annual respiratory metabolism of the Brogden's Belt earthworms was calculated to be between 10.7 and 13.41 O₂ m^-2 a^-1, which is equivalent to between 4.1 and 5.1% of the total soil metabolism. A production/biomass ratio of 0.49–0.58 was estimated, as was a net population efficiency of 22%.     

马尾松-阔叶树混交异龄林生物量与生产力分配格局

在25年生的马尾松林下分别套种1年生火力楠、闽粤栲、苦槠、格氏栲、青栲和拉氏栲幼苗,经过16a的培育后形成了郁闭的针阔混交异龄林。应用分层平均标准木收获法,建立相对生长方程,对上述6种混交林及马尾松纯林的生物量与生产力分配格局进行了研究。6个混交林的林木总生物量分别为216·41、260·06、221·92、221·65、246·13t/hm2及201·04t/hm2,而马尾松纯林的生物量为204·37t/hm2;其中地上部分占81·4%~83·7%,林分之间差异较小。在混交林中,处于主林层的马尾松生物量占林分总生物量的比例为73·5%~85·4%。在各林分生物量组成中,干材生物量最大,占总生物量的56·4%~64·8%,其它组分所占的比例依次为根(16·3%~18·6%)>枝(9·0%~16·9%)>皮(4·9%~7·3%)>叶(1·1%~4·3%)。生物量的空间结构在马尾松纯林和混交林之间存在明显差异,混交林中0~9m高度的生物量分配比例(67·1%)明显大于马尾松纯林(53·7%);混交林中,在2~3m高度就出现了枝、叶的分布,而马尾松纯林中则出现在13~14m。混交林中,阔叶树根系的生物量主要集中于0~40cm土层,占根系总生物量的74%~99%,60cm以下土层则根系分布很少,而马尾松的根系则主要分布于土壤表层(0~20cm)和60cm以下土层,分别占总生物量的26%和49%。各混交林分的净初级生产力为10·60~15·25t/(hm2·a),而马尾松纯林的生产力仅7·34t/(hm2·a)。林分净初级生产力(NPP)与光合器官/地上部分生物量比(X1)、细根生物量/地下部分生物量比(X2)存在显著的非线形关系:NPP=5·5745+1·1985X1+2·6479X22。在所研究的林分中,细根(d<2mm)生物量占林分总生物量的平均比例为0·2%,但细根生产力占林分净生产力的平均比达2·9%。     

皖东松树纯林与复层混交林比较研究

通过对皖东地区松树纯林和零星分布的复层林的调查,比较了单纯林和复层林的材积生长以及林地土壤理化性质的改善情况,研究了林内的光环境和庇荫下的林木的生理生态特性,认为建立充分发挥森林多种效益的人工复层林施业体系是该地区林业经营的方向．     

Spatial distribution and biomass of root nodules in a naturally regenerated stand of Alnus hirsuta (Turcz.) var. sibirica

To estimate nodule biomass of Alnus hirsuta var. sibirica, an N₂-fixing tree species, we examined the distribution pattern and size structure of nodules in a 17 to 18 year old stand naturally regenerated after disturbance by road construction in Japan. Nodules were harvested within 1 m from the outer edge of stems of plants with different sizes on four occasions from June to October. The diameter of the subtending root at the base of each nodule and nodule dry weight were measured in 20 cm increments outwards from the base of each stem. Horizontal distribution of nodules around each tree varied greatly among tree diameters at 1.3 m (dbh) within the even-aged stand. In particular, smaller individuals had a concentrated distribution of nodules close to the stem. Nodule abundance occurred further from the stems with increasing tree size. Nodule biomass within 1 m from the outer edge of individual stems increased with tree size ([nodule biomass] = 0.442 [dbh]^2.01, R ²?=?0.747, P?<?0.05). By using the relationship, nodule biomasses were estimated to be 84.1 kg ha^?1. These results suggest that it is necessary to take into account tree size and patterns of tree distribution in nodule biomass estimates.     

Driving factors of a vegetation shift from Scots pine to pubescent oak in dry Alpine forests

An increasing number of studies have reported on forest declines and vegetation shifts triggered by drought. In the Swiss Rhone valley (Valais), one of the driest inner‐Alpine regions, the species composition in low elevation forests is changing: The sub‐boreal Scots pine (Pinus sylvestris L.) dominating the dry forests is showing high mortality rates. Concurrently the sub‐Mediterranean pubescent oak (Quercus pubescens Willd.) has locally increased in abundance. However, it remains unclear whether this local change in species composition is part of a larger‐scale vegetation shift. To study variability in mortality and regeneration in these dry forests we analysed data from the Swiss national forest inventory (NFI) on a regular grid between 1983 and 2003, and combined it with annual mortality data from a monitoring site. Pine mortality was found to be highest at low elevation (below 1000 m a.s.l.). Annual variation in pine mortality was correlated with a drought index computed for the summer months prior to observed tree death. A generalized linear mixed‐effects model indicated for the NFI data increased pine mortality on dryer sites with high stand competition, particularly for small‐diameter trees. Pine regeneration was low in comparison to its occurrence in the overstorey, whereas oak regeneration was comparably abundant. Although both species regenerated well at dry sites, pine regeneration was favoured at cooler sites at higher altitude and oak regeneration was more frequent at warmer sites, indicating a higher adaptation potential of oaks under future warming. Our results thus suggest that an extended shift in species composition is actually occurring in the pine forests in the Valais. The main driving factors are found to be climatic variability, particularly drought, and variability in stand structure and topography. Thus, pine forests at low elevations are developing into oak forests with unknown consequences for these ecosystems and their goods and services.     

Enchytraeid numbers,biomass and respiratory metabolism in a beech woodland - Wytham Woods,Oxford

Summary The mean annual population density of enchytraeids in the litter and upper 6 cm of soil was found to be 14,590 m^-2. Mean individual weights approximated 116, 158 and 151 g wet wt. in the litter, 0–3 cm and 3–6 cm strata respectively. The mean biomass was estimated to be 1.908 g wet wt m^-2. Vertical migration was shown to occur, the upward migration in late Autumn was a response to temperatures in the litter being temporarily higher than those of the 0–3 cm stratum. As a result of upward vertical migration and possibly recruitment, numbers reached a maximum in the litter during Winter. On an annual basis the litter, 0–3 and 3–6 cm strata contained 41.43, 46.44 and 12.12% respectively of the extracted enchytraeids. The equivalent biomass values were 33.18, 52.46 and 14.36%. Total numbers and biomass revealed a general picture of high values in late Autumn to Winter which gradually decreased through Spring and Summer except for a minor peak in May–June. The annual oxygen consumption of the enchytraeids approximated 4.285 l O₂ m^-2 yr^-1 (20.461 kcal85.610 kJ) and accounted for 1.63% of the total soil metabolism. A production/biomass (P/B) ratio of 4.93 was estimated as was a net population efficiency of 32%. For this site the contribution by enchytraeids to total soil respiration is about one-third that of the earthworms and an order of magnitude greater than that of the nematodes.     

Distribution of roots and root nodules and biomass allocation in young intensively managed grey alder stands on a peat bog

Development of below-ground biomass and biomass allocation were studied in two different stands of young grey alder stands growing on a peat bog. Both stands were given the same fertilization and irrigation treatment. The roots were investigated from 1) open plastic tubes enclosing the complete root systems in 1982, and 2) root cores 1984–86. Coarse roots (diameter>1 mm) were mainly found close to the trunk of the trees while fine roots (≤1 mm) were more evenly distributed in the stands. Root nodules were intermediate in distribution. The root systems were shallow, with more than 90% of the biomass in the uppermost 9–10 cm of the soil, probably because of low oxygen availability in the peat soil. The biomass allocation to the above-ground parts increased during the study period.