Evaluation of fine root length and diameter measurements obtained using RHIZO image analysis

Image analysis systems facilitate rapid measurement of root length and diameter, but their accuracy is not easily determined. The objective of this study was to develop a set of simple experiments for evaluating the accuracy of fine root measurements obtained using image analysis. Using the system RHIZO (trademark of Regent Instruments, Quebec), we tested the accuracy of (i) length measurements made over a range of root lengths per unit area, (ii) average diameter measurements and length per diameter distributions in string, wire, and fine root samples of varying diameter, and (iii) diameter measurements on short segments of diagonally oriented objects. Our results suggest that preliminary testing of image analysis systems is absolutely necessary for producing reliable root measurements. Total length was accurately determined for typically encountered length per unit areas of <1.5cm cm-2. For samples with higher values, however, the method underestimated total length by >5%. It is therefore recommended that users of image analysis systems determine this maximum length per unit area for accurate determinations of total root length. In samples that contained different string diameters, the total sample length and average string diameter could accurately be measured. However, the length per diameter class was underestimated by >20% when the string diameter was less than one pixel smaller than the upper limit of the diameter class. Adjustment of diameter intervals and increasing the scanner resolution are required to reduce this underestimation. Both the length and the angle of the short segments analyzed were found to influence diameter measurements. Similar sets of experiments are proposed for a rigorous evaluation of the performance of other image analysis systems on root measurements

Soil exploitation strategies of fine roots in different tree species of the southern boreal forest of eastern Canada

This study compared the ability of conifers (Abies balsamea (L.) Mill., Picea glauca (Moench) Voss) and deciduous trees (Populus tremuloides Michx., Betula papyrifera Marsh.) and shrubs and herbs to exploit soils in a southern boreal forest. Root samples were collected from undisturbed soil and ingrowth cores (disturbed soil) of aspenand conifer-dominated plots. Total fine-root biomass was similar in aspen and conifer plots but length density was higher under aspen. The low root length density (0.7 cm·cm-3) of conifers suggests a dependency on mycorrhizal associations for effective nutrient uptake. Coniferous fine roots were thicker than in the other species. Root tip and internode lengths in deciduous trees showed little differences between undisturbed and disturbed soil, whereas these parameters increased substantially in conifers in disturbed soil. Root growth and architecture in disturbed soil indicated that conifers follow a conservative strategy of optimizing soil exploitation efficiency through the relatively slow development of coarse fine-root systems. In contrast, deciduous trees and understorey shrubs and herbs colonized favourable soil environments to a larger extent maintaining highly ramified thin fine roots to optimize the exploited soil volume. The different soil exploitation strategies may be as important as those differences reported for aboveground growth to explain the coexistence of these species

Does soil heterogeneity and compaction in ingrowth-cores affect the growth and morphology of Picea mariana fine-roots?

Ingrowth-cores are commonly used in studies of fine-root production in forest stands. However, some concerns have been expressed regarding changes in root growth in the artificial soil environment created in ingrowth-cores, In this study, the effects that homogenization and compaction of soil might have on fine-root growth and morphology of black spruce (Picea mariana Mill.) were examined. Fine-root (<2mm) morphology was characterized by diameter and internode length. There was no difference in fine-root biomass and morphology between conventional ingrowth-cores (soil sieved and homogenized) and compacted cores (soil density increased by one third). However, fine-root biomass was substantially higher in ingrowth-cores in which the soil was distributed in layers of different fertility (patchy treatment) and both diameter and internode length values were closer to that found in the undisturbed soil cores. In the heterogenous treatment, the root internode length and biomass was significantly higher in rich patches than in poor patches, Our results indicate that fine-root production assessment using conventional ingrowth-cores where the soil is sieved and homogenized may underestimate the true production found in undisturbed soil, Fine-root architectural parameters in the patchy treatment were more similar to those found in the undisturbed soil cores. This study suggests that stratification or increased patchiness of the ingrowth-core growing medium should better mimic the conditions associated in undisturbed soils

Composition, structure, light attenuation and nutrient content of the understory vegetation in Eucalyptus sieberi regrowth stand 6 years after thinning and fertilisation

In this study, we investigated the effects of commercial thinning and fertiliser application 6 years after treatment on the structure, composition, and nutrient concentrations of understorey vegetation in a Eucalyptus sieberi regrowth forest in East Gippsland. The stand was thinned at age 26 years, reducing the basal area by ca. 50% and lowering the stocking from ca. 1350 to ca. 250 stems ha-1. Whereas the species diversity and richness of the understorey were not significantly affected by the treatments, thinning promoted the abundance of herbaceous species, and fertilisation increased the proportion of ground ferns such as Pteridium esculentum. Fertilisation with 100 kg N ha-1 and 100 kg P ha-1 decreased the foliage N concentration in Tetrarrhena juncea and Gonocarpus teucrioides, and increased the foliage P concentrations in four of the five most frequent species. This suggested that the understorey was more limited by P than by N. The photosynthetically active radiation above the understorey was 41% of that in the open in thinned stands and 32-34% in unthinned stands, showing that 6 years after thinning the canopy density had not yet returned to pre-treatment levels. However, light attenuation within the understorey did not differ among treatments, confirming that the understorey cover had not increased in response to increased light and nutrient availability. The small changes in the understorey may be attributed to the fact that light and nutrients are not the major factors limiting its development, and that most species are well adapted to disturbance

A simplified inventory approach for estimating carbon in coarse woody debris in high-biomass forests

Forests carrying large quantities of live and dead wood are important carbon (C) stores. Here, we investigate how the inventory of coarse woody debris (CWD) and its embedded C (CWD-C) may be designed efficiently at the scale of logs, plots, and the landscape in Tasmanian tall Eucalyptus obliqua forests, which have very high levels of CWD (here 375–1085 m³ ha–1). From a set of 12 sites representing different times since disturbance, a thorough census of dead wood >10 cm in diameter was carried out at five sites using a fixed-plot (50 × 50 m) approach. This showed that 90% of the volume can be captured by recording only CWD logs >40 cm in diameter. Based on this approach and on the known density and C content of five different decay-classes, volume, mass, and CWD-C was determined for all 12 sites. To obtain an accurate estimate of CWD-C at the landscape scale, it was found to be sufficient to allocate entire individual logs to single decay-classes and to use one global value for C content instead of decay-class-specific values. The most decayed logs, which are difficult to measure, could be ignored. However, at the plot level, no relationships were found between CWD mass and either standing or downed CWD or standing-tree biomass, limiting the utility of these proxies for assessing CWD volume

Post-logging stand dynamics of a tropical rain forest in the Brazilian Amazon.

Edição dos abstracts do 24º IUFRO World Congress, 2014, Salt Lake City. Sustaining forests, sustaining people: the role of research

Neighbourhood species richness and drought-tolerance traits modulate tree growth and delta¹³C responses to drought

International audienceMixed-species forests are promoted as a forest management strategy for climate change adaptation, but whether they are more resistant to drought than monospecific forests remains contested. In particular, the trait-based mechanisms driving the role of tree diversity under drought remain elusive. Using tree cores from a large-scale biodiversity experiment, we investigated tree growth and physiological stress responses (i.e. increase in wood carbon isotopic ratio; delta C-13) to changes in climate-induced water availability (wet to dry years) along gradients in neighbourhood tree species richness and drought-tolerance traits. We hypothesized that neighbourhood species richness increases growth and decreases delta C-13 and that these relationships are modulated by the abiotic (i.e. climatic conditions) and the biotic context. We characterised the biotic context using drought-tolerance traits of focal trees and their neighbours. These traits are related to cavitation resistance versus resource acquisition and stomatal control.Tree growth increased with neighbourhood species richness. However, we did not observe a universal relief of water stress in species-rich neighbourhoods. The effects of neighbourhood species richness and climate on growth and delta C-13 were modulated by the traits of focal trees and the traits of their neighbours. At either end of each drought-tolerance gradient, species responded in opposing directions during dry and wet years.We show that species' drought-tolerance traits can explain the strength and nature of biodiversity-ecosystem functioning relationships in experimental tree communities experiencing drought. Mixing tree species can increase growth but may not universally relieve drought stress

Tree Diversity Drives Forest Stand Resistance to Natural Disturbances

Purpose of review Forests are frequently exposed to natural disturbances, which are likely to increase with global change, and may jeopardize the delivery of ecosystem services. Mixed-species forests have often been shown to be more productive than monocultures, but it is unclear whether this results from mixed stands being in part more resistant to various biotic and abiotic disturbance factors. This review investigates the relationships between tree diversity and stand resistance to natural disturbances and explores the ecological mechanisms behind the observed relationships.Recent findings Mixed forests appear to be more resistant than monocultures to small mammalian herbivores, soil-borne fungal diseases and specialized insect herbivores. Admixing broadleaves to conifers also increases the resistance to fire and windstorms when compared to pure conifer stands. However, mixed forests may be more affected by drought depending on the species in the mixture.Summary Overall, our findings suggest that mixed forests are more resistant to natural disturbances that are relatively small-scale and selective in their effect. However, benefits provided by mixtures are less evident for larger-scale disturbances. Higher tree diversity translates into increased resistance to disturbances as a result of ecological trait complementarity among species, reduction of fuel and food resources for herbivores, enhancement of diversion or disruption processes, and multi-trophic interactions such as predation or symbiosis.To promote resistance, the selection of tree species with different functional characteristics appears more important than increasing only the number of species in the stand. Trees with different levels of susceptibility to different hazards should be intermixed in order to reduce the amount of exposed resources and to generate barriers against contagion.However, more research is needed to further improve associational resistance in mixed forests, through a better understanding of the most relevant spatial and temporal scales of species interactions and to optimize the overall provision of ecosystem services

Fine-root production in small experimental gaps in successional mixed boreal forests

The effects of small 10 m x 10 m experimental above-ground gaps on fine-root production for the first two years were studied in three fire-initiated stands of the northwestern mixed broad-leaf-conifer boreal forest of Quebec. The 48-yr-old forest is dominated by Populus tremuloides (Trembling aspen), the 122-yr-old forest by a mixture of P. tremuloides, Abies balsamea (balsam fir) and Picea glauca (white spruce), and the 232-yr-old forest by Thuja occidentalis (eastern white cedar) and A. balsamea, with some P. tremuloides. 40 root-ingrowth bags were installed in different locations in and around each gap (at gap center, 1 to 2 m either side of gap edge and in adjacent control plots). Half of the ingrowth bags were harvested after one year following gap creation, the other half after two years. Roots were sorted into different species grouping. Fine-root production was statistically (P < 0.05) larger in the youngest forest compared to the two older ones after one year, but not after two years. The individual species or groups of species increased, decreased or showed no change in fine-root production in gaps, but overall we did not observe a major shift in species proportion between gap and control plots after two years. Some herbs and also Taxus canadensis seemed to benefit in terms of fine-root growth from such small openings after two years. No statistical differences (P > 0.10) in total fine-root production were found among locations within and outside gaps in either year. However, there was a clear tendency for fine-root production to be smaller in gap center than in the other locations for the two younger successional forests the first year after gap creation. We conclude that small above-ground gaps (i.e. < 100 m2) do not produce a significant and long-lasting below-ground gap in terms of total fine-root production in the successional forests investigated