Fine-root dynamics in a young hinoki cypress (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) stand for 3 years following thinning

Fine roots play a key role in carbon and nutrient dynamics in forested ecosystems. Fine-root dynamics can be significantly affected by forest management practices such as thinning, but research on this topic is limited. This study examined dynamics of fine roots <1 mm in diameter in a 10-year-old stand of hinoki cypress (Chamaecyparis obtusa) for 3 years following thinning (65% in basal area). Fine-root production and mortality rates were estimated using a minirhizotron technique in combination with soil coring. In both thinned and un-thinned control plots, fine-root elongation occurred from early spring to winter (March to December) and fluctuated seasonally. In the thinned and the control plots, the annual fine-root production rates were estimated to be 101 and 120 g m⁻² year⁻¹, respectively, whereas the estimated annual fine-root mortality rates were 77 and 69 g m⁻² year⁻¹, respectively. At 3 years after thinning, live fine-root biomass was significantly smaller in the thinned plot (143 g m⁻²) than in the control plot (218 g m⁻²), whereas dead fine-root biomass was not (147 and 103 g m⁻², respectively). Morphological and physiological indices of fine roots such as diameter, specific root length, and root tissue density of the live fine roots was similar in both plots. These results suggested that thinning tended to decrease biomass and production of fine roots, but the effects on characteristics of fine roots would be less evident.     

Effects of simulated drought stress on the fine roots of Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) in a plantation forest on the Kanto Plain,eastern Japan

Drought stress was simulated in a 28-year-old Japanese cedar plantation (Kanto Plain, Japan) between April and October 2004 by removing throughfall using rain shelters. Changes in fine-root parameters caused by this drought treatment were examined by sequential soil coring. Drought effects on fine roots were analyzed separately for particular soil depths (0–5, 5–15, and 15–25 cm) and root diameters (<1 and 1–2 mm). Generally, fine-root biomass and root tip numbers decreased by the drought treatment. Drought stress was most intense for fine roots in the topsoil and weakest for fine roots in the deepest soil layer. Fine roots less than 1 mm in diameter were affected more severely than 1- to 2-mm roots. The effect of drought treatment was most remarkable for the number of white root tips, which decreased to 17% of the control at the soil depth of 0–5 cm. These results suggest that white root tip is the most suitable indicator of drought stress. Simulated drought reduced production of fine roots less than 1 mm and 1–2 mm in diameter. Fine-root mortality was stimulated for roots less than 1 mm, but not for 1- to 2-mm roots. These results suggest that fine roots with larger diameters can survive drought stress at a level simulated in this study, but processes of fine-root production were inhibited regardless of the diameter classes. The duration of drought stress and phenology of fine roots should also be considered in diagnosing the effects of drought on fine-root parameters.     

Fine root dynamics in a developing Populus deltoides plantation

A closely spaced (1 x 1 m) cottonwood (Populus deltoides Bartr.) plantation was established to evaluate the effects of nutrient availability on fine root dynamics. Slow-release fertilizer (17:6:12 N,P,K plus micronutrients) was applied to 225-m(2) plots at 0, 50, 100 and 200 kg N ha(-1), and plots were monitored for two growing seasons. Fine root production, mortality, live root standing crop and life span were analyzed based on monthly minirhizotron observations. Fine root biomass was measured in soil cores. Fine root dynamics were controlled more by temporal, depth and root diameter factors than by fertilization. Cumulative fine root production and mortality showed strong seasonal patterns; production was greatest in the middle of the growing season and mortality was greatest after the growing season. Small diameter roots at shallow soil depths cycled more rapidly than larger or deeper roots. The strongest treatment effects were found in the most rapidly cycling roots. The standing crop of live roots increased with fertilizer treatment according to both minirhizotron and soil coring methods. However, production and mortality had unique treatment response patterns. Although cumulative mortality decreased in response to increased fertilization, cumulative production was intermediate at 0 kg N ha(-1), lowest with 50 kg N ha (-1), and highest with 200 kg N ha(-1). Aboveground growth responded positively to fertilization up to an application rate of 50 kg N ha(-1), but no further increases in growth were observed despite a threefold increase in application rate. Median fine root life span varied from 307 to over 700 days and increased with depth, diameter and nutrient availability.     

Root development across a chronosequence in a Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantation

We investigated the biomass, vertical distribution, and specific root length (SRL) of fine and small roots in a chronosequence of Japanese cedar (Cryptomeria japonica D. Don) plantations in Nara Prefecture, central Japan. Roots were collected from soil blocks up to 50 cm in depth in five plantations of differing age: 4, 15, 30, 41, and 88 years old. Fine-root biomass reached a maximum (639 g m₋₂) in the 15-year-old stand before canopy closure, decreased in the 30-year-old stand (422 g m₋₂), and thereafter was stable. Except in the 30-year-old stand, fine-root biomass increased in deeper soil layers as stand age increased, and the depth at which the cumulative biomass of fine roots reached 90% exhibited a good allometric relationship with mean stem diameter. Both root-length density (root length per unit soil volume) and SRL decreased with soil depth in all stands, indicating that plants mainly acquire water and nutrients from shallow soils. The highest SRL was observed in the 4-year-old stand, but the relationship between SRL and stand age was unclear in older stands. The SRL in surface soils seemed to decrease with increases in root-length density, suggesting that branching of the fine-root system during development is related to density-dependent processes rather than age.     

Estimation of the fine root biomass in a Japanese cedar (Cryptomeria japonica) plantation using minirhizotrons

We estimated fine root biomass in a Japanese cedar (Cryptomeria japonica) plantation using a min-irhizotron technique. Since data obtained from minirhizo-trons are limited to the length and diameter of fine roots observed on minirhizotron tubes, data conversion is necessary to determine the fine root biomass per unit soil volume or unit stand area. We first examined the regression between diameter squared and weight per unit length of fine roots in soil core samples, and calculated the fine root biomass on minirhizotron tubes from their length and diameter. Then we determined conversion factors based on the ratio of the fine root biomass in soil core samples to that on minirhizotron tubes. We examined calculation methods, using a single conversion factor for total fine root biomass in the soil for depths of 0–40cm (Cal1), or using four conversion factors for fine roots in the soil at 10-cm intervals (Cal2). Cal1 overestimated fine root biomass in the lower soil or underestimated that in the upper soil, while fine root biomass calculated using Cal2 better matched that in soil core samples. These results suggest that minirhizotron data should be converted separately for different soil depths to better estimate fine root biomass.     

Biomass of fine and small roots in two Japanese black pine stands of different ages

The biomass and the spatial distribution of fine and small roots were studied in two Japanese black pine (Pinus thunbergii Parl.) stands growing on a sandy soil. More biomass of fine and small roots was found in the 17-year-old than in the 40-year-old stand. There were 62 g m⁻² of fine roots and 56 g m⁻² of small roots in the older stand, which represented mean values of 608 g for fine and 552 g for small roots per tree, respectively. In the younger stand, a total of 85 g m⁻² of fine roots and 66 g m⁻² of small roots were determined, representing a mean of 238 g for fine and 186 g for small roots per tree, respectively. Fine and small root biomasses decreased linearly with a soil depth of 0–50 cm in the older stand. In the younger stand, the fine and small roots developed only up to a depth of 30 cm. Horizontal distributions (with regard to distance from a tree) of both root groups were homogeneous. A positive correlation in the amount of biomass of fine and small roots per m² relative to tree size was found. Fine and small root biomasses increased consistently from April to July in both stands. The results also indicated earlier growth activity of the fine roots than small roots at the beginning of the growing season. The seasonal increases in fine and small root biomasses were slightly higher in the younger stand than the older stand.     

Effects of experimental drought on the fine root system of mature Norway spruce

Norway spruce (Picea abies (L.) Karst.) is an economically important, but relatively drought-sensitive tree species that might suffer from increasing drought intensities and frequencies, which are predicted to occur in parts of central Europe under future climatic change. In a throughfall exclusion experiment using sub-canopy roofs, we tested the hypothesis that enhanced drought leads to an increase in fine root mortality, and also to a higher, subsequent fine root growth. Fine root production and mortality were assessed using two independent approaches, sequential soil coring (organic layer) and direct observations in minirhizotrons (organic layer plus upper mineral soil). Six weeks of throughfall exclusion resulted in mild drought stress, i.e. a reduction in average soil moisture from 20 to 12 vol.% during the treatment. Based on the sequential coring data, experimental drought did not result in significant changes in fine root biomass during the 6-week treatment period, but caused an increase in fine root mortality by 61% in the 6 weeks following the drought treatment. Remarkably, fine root production showed a synchronous increase in this period, which more than compensated for the loss due to increased mortality. The minirhizotron data confirmed that the drought treatment increased fine root loss in the organic layer. Based on this method, however, root loss occurred during the drought period and was not compensated by increased root production. The mild drought stress was mainly restricted to the organic layer and did not significantly influence fine root dynamics in the mineral soil. We calculated that the drought event resulted in an extra input of about 28 g C m⁻² and 1.1 g N m⁻² to the soil due to increased fine root mortality. We conclude that even periods of mild drought significantly increase fine root mortality and the associated input of root-derived C to the soil organic matter pool in temperate Norway spruce forests.     

Fine root dynamics in three central Himalayan high elevation forests ranging from closed canopied to open-canopied treeline vegetation

Fine root biomass, rates of dry matter production and nutrients dynamics were estimated for 1 year in three high elevation forests of the Indian central Himalaya. Fine root biomass and productivity were higher in closed canopied cappadocian maple forest (9.92 Mg ha⁻¹ and 6.34 Mg ha⁻¹ year⁻¹, respectively), followed by Himalayan birch forest (6.35 Mg ha⁻¹ and 4.44 Mg ha⁻¹ year⁻¹) and Bell rhododendron forest (6.23 Mg ha⁻¹ and 2.94 Mg ha⁻¹ year⁻¹). Both fine root biomass and productivity declined with an increase in elevation. Across the sites, fine root biomass was maximal in fall and minimal in summer. In all sites, maximum nutrient concentration in fine roots was in the rainy season and minimum in winter. Fine root biomass per unit basal area was positively related with elevation, Bell rhododendron forest having the largest fine root biomass per unit of basal area (0.53 Mg m⁻²) and cappadocian maple the least (0.18 Mg m⁻²). The production efficiency of fine roots per unit of leaf biomass also increased with elevation and ranged from 1.13 g g⁻¹ leaf mass year⁻¹ in cappadocian maple forest to 1.28 g g⁻¹ leaf mass year⁻¹ in Bell rhododendron forest. Present fine root turnover estimates showed a decline towards higher elevations (0.72 year⁻¹ in cappadocian maple and 0.58 year⁻¹ in Bell rhododendron forest) and are higher than global estimates (0.52).     

Effects of slash retention and wood ash addition on fine root biomass and production and fungal mycelium in a Norway spruce stand in SW Sweden

In the study reported here we examined the short-term effects (1–3 years) of slash retention (SR) and the long-term effects (13–15 years) of wood-ash application (A) on fine roots and mycorrhizae in a 40-year-old Norway spruce forest in southwest Sweden. Soil cores were used to obtain estimates of the biomass (g m⁻²) of roots in three diameter classes (<0.5, 0.5–1 and 1–2 mm), root length density (RLD), specific root length (SRL) and mycorrhizal root tip density (RTD). Fine root (<1 mm) length production and mortality, and mycelium production, were estimated using minirhizotron and mesh bag techniques, respectively. Compared with the control plots (C), the biomass of fine roots in diameter classes <0.5 mm and 0.5–1 mm was significantly higher in A plots, but lower in SR plots. In addition, RLD was significantly lower in the humus layer of SR plots than in the humus layers of C and A plots, but not in the other layers. None of the treatments affected the SRL. In all soil layers, the SR treatment resulted in significant reductions in the number of ectomycorrhizal root tips, and the mycelia production of fungi in mesh bags, relative to the C treatment, but the C and A treatments induced no significant changes in these variables. Fine root length production in the C, A and SR plots amounted to 94, 87 and 70 mm tube⁻¹ during the 2003 growing season, respectively. Fine root mortality in treated plots did not change over the course of the study. We suggest that leaving logging residues on fertile sites may result in nitrogen mineralisation, which may in turn induce reductions in root biomass, and both root and mycelium production, and consequently affect nutrient uptake and the accumulation of organic carbon in soil derived from roots and mycorrhizae.     

Effects of chronic nitrogen application on the growth and nutrient status of a Japanese cedar (Cryptomeria japonica) stand

To investigate the potential effects of nitrogen (N) deposition on Japanese forests, a chronic N-addition experiment that included three treatments (HNO₃, NH₄NO₃, and control) was carried out in a 20-year-old Japanese cedar (Cryptomeria japonica D. Don) stand in eastern Japan over 7 years. The amount of N applied was 168 kg N ha⁻¹ year⁻¹ on the HNO₃ plots and 336 kg N ha⁻¹ year⁻¹ on the NH₄NO₃ plots. Tree growth, current needle N concentration, and soil solution chemistry were measured. Nitrogen application decreased the pH and increased NO₃ ⁻, Ca²⁺, Mg²⁺, and Al concentrations in the soil solution. The needle N concentration increased in both of the N plots during the first 3 years. Nevertheless, the annual increments in height and in the diameter at breast height of the Japanese cedars were not affected by N application, and no visible signs of stress were detected in the crowns. Our results suggest that young Japanese cedar trees are not deleteriously affected by an excess N load.     

Fine root dynamics in 60-year-old stands of <Emphasis Type="Italic">Fagus sylvatica</Emphasis> and <Emphasis Type="Italic">Picea abies</Emphasis> growing on haplic luvisol soil

Fine root dynamics in mono-specific stands of mature Fagus sylvatica L. and Picea abies Karst. was studied from December 2003 to December 2004 in a stand in Southern Germany. Minirhizotrons were used to draw between species comparisons concerning fine root (≤1 mm) longevity and temporal patterns of fine root dynamics (growth and mortality) as related to seasonal changes in soil water content and soil temperature. In F. sylvatica, median fine root longevity from early seasonal to late-seasonal cohorts was low (77 days). Fine root dynamics scaled positively with seasonal changes in soil water and temperature indicating accelerated fine root turnover during favourable soil conditions. In contrast, fine root longevity in P. abies (273 days) was significantly higher when compared to F. sylvatica and increased from early seasonal to late-seasonal cohorts. Fine root dynamics in P. abies did not correlate with soil environmental conditions. Rather a large proportion of new fine roots occurred during the dry season in superficial soil layers. The data suggest species inherent patterns of fine root longevity and temporal patterns of fine root dynamics.     

Responses of fine root mass,length, production and turnover to soil nitrogen fertilization in <Emphasis Type="Italic">Larix gmelinii</Emphasis> and <Emphasis Type="Italic">Fraxinus mandshurica</Emphasis> forests in Northeastern China

The responses of fine root mass, length, production and turnover to the increase in soil N availability are not well understood in forest ecosystems. In this study, sequential soil core and ingrowth core methods were employed to examine the responses of fine root (≤1 mm) standing biomass, root length density (RLD), specific root length (SRL), biomass production and turnover rate to soil N fertilization (10 g N m⁻² year⁻¹) in Larix gmelinii (larch) and Fraxinus mandshurica (ash) plantations. N fertilization significantly reduced fine root standing biomass from 130.7 to 103.4 g m⁻² in ash, but had no significant influence in larch (81.5 g m⁻² in the control and 81.9 g m⁻² in the fertilized plots). Similarly, N fertilization reduced mean RLD from 6,857 to 5,822 m m⁻² in ash, but did not influence RLD in larch (1,875 m m⁻² in the control and 1,858 m m⁻² in the fertilized plots). In both species, N fertilization did not alter SRL. Additionally, N fertilization did not significantly alter root production and turnover rate estimated from sequential soil cores, but did reduce root production and turnover rate estimated from the ingrowth core method. These results suggested that N fertilization had a substantial influence on fine root standing biomass, RLD, biomass production and turnover rate, but the direction and magnitude of the influence depended on species and methods.     

A Review of Fine Root Dynamics in Populus Plantations

Production of native and hybridized varieties of Populus has received considerable interest in temperate regions as an alternative to agricultural crops and an additional wood source, while acting as a potential carbon (C) sink to offset emissions of fossil fuel-based greenhouse gases. Research of root system dynamics in Populus species is expanding, however, our understanding of the nature and role of fine roots (FR) is incomplete. The study objective, therefore, was to review the literature regarding FR production, mortality and longevity in Populus, and evaluate the magnitude and significance of the FR fraction to C sequestration. FRs, conventionally defined as less than 2 mm in diameter and responsible for water and nutrient uptake, are an essential component of the tree. Populus FRs are relatively short-lived, with reported lifespans ranging from 30 to 300 days, depending on root diameter, tree species and age, and soil environmental factors. Standing FR biomass fluctuates throughout the growing season. Fine root production generally peaks in mid-summer, and ranges between 1.0 and 5.0 mg ha⁻¹ yr⁻¹, while FR mortality has less seasonal amplitude. Production and mortality dynamics in Populus are highly plastic in response to soil environmental conditions, and although opposing conclusions have been proposed, research suggests soil moisture and nitrogen to be most important. Results from the literature indicate annual FR turnover to the soil C pool may be small (0.2–1.6 mg C ha⁻¹ yr⁻¹), but substantial in maintaining or enhancing C levels in natural and managed stands of Populus.     

Impact factors on fine root seasonal dynamics in Fraxinus mandshurica plantations

Fine root turnover plays important roles in carbon allocation and nutrient cycling in forest ecosystems. Seasonal dynamics of fine roots is critical for understanding the processes of fine root turnover. From May to October 2002, soil core method was used for estimating the seasonal pattern of fine root (diameter < 1 mm) parameters (biomass, specific root length (SRL) and root length density (RLD)) in a Manchurian ash (Fraxinus mandshurica) plantation located at the Maoershan Experiment Station, Heilongjiang Province, northeast of China. The relationships of fine root biomass, SRL and RLD with available nitrogen in soil, average soil temperature per month in 10 cm depth and soil moisture content were analyzed. Seasonal variation of fine root biomass was significant (P < 0.05). The peak values of fine root biomass were observed both in spring and in autumn, but SRL and RLD were the highest in spring and lowest in autumn. Specific root length and root length density were higher in spring and summer, which means that fine root diameter was thinner. In autumn, both parameters decreased significantly due to secondary incrassation of fine root diameter or the increase of tissue density. Seasonal dynamics of fine roots was associated with available nitrogen in soil, soil temperature in 10 cm depth and moisture content. Fine root biomass has a significant relationship with available NH₄ ⁺-N in soil. Available NO₃ ⁻-N in soil, soil temperature in 10-cm depth and moisture content have a positive correlation with fine root biomass, SRL and RLD, although these correlations are not significant (P > 0.05). But the compound effects of soil available N, soil temperature and soil moisture content are significant to every root parameter. The variations of these three root parameters in different seasons show different physiological and ecological functions in different growing periods. Translated from Scientia Silvae Sinicae, 2006, 42(9): 7–12 [译自: 林业科学]     

Tree roots in a changing world

Globally, forests cover 4 billion hectares or 30% of the Earth's land surface, and 20%–40% of the forest biomass is made up of roots. Roots play a key role for trees: they take up water and nutrients from the soil, store carbon (C) compounds, and provide physical stabilization. Estimations from temperate forests of Central Europe reveal that C storage in trees accounts for about 110 t C ha₋₁, of which 26 t C ha₋₁ is in coarse roots and 1.2 t C ha₋₁ is in fine roots. Compared with soil C, which is about 65 t C ha₋₁ (without roots), the contribution of the root C to the total belowground C pool is about 42%. Flux of C into soils by plant litter (stemwood excluded) compared with the total soil C pool, however, is relatively small (4.4 t C ha₋₁ year₋₁) with the coarse and fine roots each contributing about 20%. Elevated CO₂ concentrations and N depositions lead to increased plant biomass, including that of roots. Recent analysis in experiments with elevated CO₂ concentrations have shown increases of the forest net primary productivity by about 23%, and, in the case of poplars, an increase of the standing root biomass by about 62%. The turnover of fine roots is also positively influenced by elevated CO₂ concentrations and can be increased in poplars by 25%–45%. A recently established international platform for scientists working on woody root processes, COST action E38, allows the exchange of information, ideas, and personnel, and it has the aim to identify knowledge gaps and initiate future collaborations and research activities.     

Changes in fine root production and longevity in relation to water and nutrient availability in a Norway spruce stand in northern Sweden

Effects of irrigation and liquid fertilization on fine root (< 1 mm) production and longevity, and fine root (< 0.5-2 mm) biomass were studied in a Norway spruce (Picea abies (L.) Karst.) stand in northern Sweden. Fine root length production and longevity were measured by the minirhizotron technique at 0-10 cm depth in the following treatments: irrigation (I), liquid fertilization (IL) and control (C). Standing root biomass and root length density (RLD) were studied in the litter-fermented humus (LFH) layer and at depths of 0-10, 10-20 and 20-30 cm using soil cores in solid fertilized (F) and C plots. Minirhizotrons were installed in October 1994 and measurements recorded monthly from July to September 1995 and during the growing season in 1996. Soil cores were sampled in 1996. Fine root production increased significantly in IL plots compared with C plots, but the I treatment did not increase root production. Root mortality increased significantly in IL plots compared with C plots. Fine root longevity in IL plots was significantly lower compared with C and I plots. No significant difference was found between longevity of fine roots in I and C plots. Compared with C, F treatment increased fine root biomass in the LFH and mineral soil layers, and increased the amount of fine roots in mineral soil layers relative to the LFH layer. Furthermore, F increased RLD and the number of mycorrhizal root tips significantly.     

Spatiotemporal distribution of aboveground litter in a Cryptomeria japonica plantation

We assessed the vertical distribution of litter and its seasonal patterns in the canopy and on the forest floor (soil), as well as litterfall (the flux of litter from the canopy to the soil) in a 33-year-old plantation of Japanese cedar (Cryptomeria japonica D. Don). The masses of total litter, dead leaves, and dead branches in the canopy of C. japonica trees averaged 34.09, 19.53, and 14.56 t dry wt ha⁻¹, respectively, and were almost constant during the study period. The total masses of the annual litterfall were 4.17 and 5.88 t dry wt ha⁻¹ year⁻¹ in the two consecutive years of the study. The mass of the soil litter averaged 7.95 t dry wt ha⁻¹ during the same period. All relationships between the mass of canopy litter and tree-size parameters (diameters at breast height and at the lowest living branch) were linear in a log-linear regression. Compared with the results for this plantation at a younger stage (16 years old), our results suggest that the total mass of dead leaves attached to each tree increases markedly with increasing age, but that the trajectory of this increase as a function of tree size may change from an exponential to a saturation curve with increasing stand age.     

Fine root dynamics along an elevational gradient in the southern Appalachian Mountains,USA

Attributes of fine roots (<2.0 mm diameter) were quantified in five southern Appalachian plant communities along an elevational gradient. These attributes include the seasonal dynamics of fine root mass and length, the depth distribution of fine roots, fine root width and, most importantly, the annual appearance and disappearance of fine roots. The principal objectives of this study were two-fold: (1) to compare these attributes of fine roots between plant communities and (2) to compare the results of the two methods used to quantify the attributes: (1) harvesting roots from forest soil with soil cores and (2) photographing roots growing against the windows of minirhizotron boxes. The plant communities that were sampled are characteristic of the region and are designated as follows from lowest elevation (782 m) to highest elevation (1347 m): (1) xeric ridge, (2) cove hardwoods, (3) low elevation mixed oak, (4) high elevation mixed oak, and (5) northern hardwoods. Fine root mass varies seasonally in this temperate region with lowest and highest mass in the spring and autumn, respectively. Fine root mass and fine root mass appearance were lowest in the cove hardwood community and highest in the low elevation mixed oak community. The total length of fine roots was highest in the xeric ridge community and lowest in the low elevation mixed oak community. The high total root length in the xeric ridge community was due to the presence of an exceptionally dense mat of very fine roots found there. The width of these roots was significantly less than that of roots on all other plots. Subsequent regression illustrates two strong patterns in the data. First, fine root mass, fine root mass appearance and leaf production were positively correlated. Second, fine root length and soil moisture were negatively correlated. The accumulation of root mass in these communities was linked to overall site productivity and the development of root length in response to moisture stress. Only the timing of root growth initiation was related to elevation and the associated parameter of soil temperature. The best estimates of fine root appearance and disappearance were generated by harvesting roots rather than photographing them. Some methodological problems with root photography implemented in this study are addressed.     

Thinning effects on carbon allocation to fine roots in a Quercus ilex forest

The dynamics of the fine root system are relevant to calculations of the carbon balance of the ecosystem, and there is also a need to quantify changes in this component caused by disturbances. Mediterranean forest systems have historically been coppiced to obtain charcoal. As a result of the resprouting capacity of holm oaks (Quercus ilex L.), these forests present more than 50% of their biomass below ground (stump + roots > 1 cm in diameter), but the effects of thinning on the fine root system are unknown. Fine root biomass, production, mortality and longevity were studied in a control and a thinned Mediterranean holm oak forest by minirhizotron methodology. Observations of fine roots started 2 years after thinning and continued for almost 3 years. Extraction of 80% of the former basal area of the forest greatly affected carbon allocation patterns. Biomass increased by more than 100%, production increased by 76%, mortality increased by 32% and longevity decreased by around 2 weeks. The greatest differences between treatments were associated with differences in growth during autumn months in the top 40 cm of soil, particularly between 10 and 20 cm depth.     

Root distribution of Fagus sylvatica in a chronosequence in western France

The distribution of fine (<2 mm diameter) and small roots (2–20 mm diameter) was investigated in a chronosequence consisting of 9-year-old, 26-year-old, 82-year-old and 146-year-old European beech (Fagus sylvatica) stands. A combination of trench wall observations and destructive root sampling was used to establish whether root distribution and total biomass of fine and small roots varied with stand age. Root density decreased with soil depth in all stands, and variability appeared to be highest in subsoil horizons, especially where compacted soil layers occurred. Roots clustered in patches in the top 0–50 cm of the soil or were present as root channels at greater depths. Cluster number, cluster size and number of root channels were comparable in all stands, and high values of soil exploitation occurred throughout the entire chronosequence. Overall fine root biomass at depths of 0–120 cm ranged from 7.4 Mg ha⁻¹ to 9.8 Mg ha⁻¹, being highest in the two youngest stands. Small root biomass ranged from 3.6 Mg ha⁻¹ to 13.3 Mg ha⁻¹. Use of trench wall observations combined with destructive root samples reduced the variability of these estimates. These records showed that variability in fine root distribution depended more on soil depth and edaphic conditions than on stand age, and suggest that trench wall studies provide a useful tool to improve estimates of fine root biomass.