196,530 research outputs found
Monitoring spruce web-spinning sawflies Cephalcia spp.: the correlation between trap catches and soil sampling
No full textThe web-spinning sawflies of the genus Cephalcia Panzer (Hymenoptera, Pamphiliidae) are usually monitored by sampling prepupae in soil and by catching adults with visual traps, including yellow sticky traps. However, adult catches have never been compared with the actual density of prepupae. In this paper, a relationship is presented between the catches of Cephalcia arvensis Panzer adults (mostly males) and the number of prepupae ready to emerge (pronymphs) in ail outbreak area of spruce forest (Picea abies Karsten) in the Southern Alps (Asiago, Italy). A significant linear relationship between the logarithmic estimates of the two variables was found. The model includes a spatial autoregressive parameter because adult catches were spatially correlated. The relationship allows to know whether or not the defoliation threshold of 20 pronymphs/m(2) in spring samples is being exceeded, based on the number of adults caught on yellow sticky traps (defoliation threshold of 14.26 adults/trap). The variance not explained by the model is probably due to the flight behaviour of adult males, to the low precision of the estimated pronymph density at low population levels, and to the attraction of males by few females that are trapped and remain alive. The model was validated in a large monitoring programme of undamaged alpine spruce forests and allowed detection of two newly infested stands out of six that were considered at risk of defoliation, because of adult catch exceeded the threshold. Low adult catches were always associated with absence of defoliation. Our conclusion is that trapping of adult sawflies is a cheaper and easier monitoring method than prepupae sampling in the soil. This makes earlier detection of outbreaks possible, and consequently more efficient control
Forest soil respiration under climate changing
No full textSoil respiration is a process of prime relevance for understanding the carbon cycle in forest
ecosystems and for properly comprehending the role of forests in climate change mitigation. The
process is divided into two components: (i) autotrophic soil respiration, i.e. the efflux of CO2 from
the respiration of tree roots, and (ii) heterotrophic soil respiration, i.e. the efflux of CO2 due to
respiration of soil microorganisms. A third component, the respiration of mycorrhizae, is still
debated and it is not yet clear whether it should be accounted for in autotrophic or heterotrophic soil
respiration, respectively, or whether it should be treated as a third component.
The rate of soil respiration is controlled by environmental factors. Expectedly, the strongest
driver is soil temperature, followed by soil moisture. The relevance of either factor depends on site
properties. Two papers are reinforcing this view. An asset of the paper compilation is the collection of
case studies where other factors besides temperature and soil moisture are evidently greatly affecting
the rate of soil respiration. The characteristics of the forest stand such as tree density, stand age, and
tree species and additional soil properties such as aggregate stability are influencing soil respiration.
The book gives guidance on the current state of knowledge and helps identifying knowledge gaps
for future research endeavour
Inter-tree distribution of the spruce web-spinning sawfly, Cephalcia abietis, at endemic density
No full textIndirect partitioning of soil respiration in a series of evergreen forest ecosystems
No full textA simple estimation of heterotrophic respiration can be obtained analytically as the y-intercept of the linear regression between soil-surface CO2 efflux and root biomass. In the present study, a development of this indirect methodology is presented by taking into consideration both the temporal variation and the spatial heterogeneity of heterotrophic respiration. For this purpose, soil CO2 efflux, soil carbon content and main
stand characteristics were estimated in seven evergreen forest ecosystems along an elevation gradient ranging from 250 to 1740 m. For each site and for each sampling date the measured soil CO2 efflux (RS) was predicted with the model RS = a x SC + b x RD±e, where SC is soil carbon content per unit area to a depth of 30 cm and RD is the root density of the 2–5 mm root class. Regressions with statistically significant
a and b coefficients allowed the indirect separation of the two components of soil CO2 efflux. Considering that the different sampling dates were characterized by different soil temperature, it was possible to investigate the temporal and thermal dependency of autotrophic and heterotrophic respiration. It was estimated that annual autotrophic respiration accounts for 16–58% of total soil CO2 efflux in the seven
different evergreen ecosystems. In addition, our observations show a decrease of annual autotrophic respiration at increasing availability of soil nitrogen
Main determinants of forest soil respiration along an elevation/temperature gradient in the Italian Alps
No full textThe main determinants of soil respiration were investigated in 11 forest types distributed along an altitudinal and thermal gradient in the southern Italian Alps
(altitudinal range 1520 m, range in mean annual temperature 7.8 1C). Soil respiration, soil carbon content and principal stand characteristics were measured with standardized methods. Soil CO2 fluxes were measured at each site every 15–20 days with a closed dynamic system (LI-COR 6400) using soil collars from spring 2000 to spring 2002. At the same time, soil temperature at a depth of 10 cm and soil water content (m3m-3) were measured at each collar. Soil samples were collected to a depth of 30 cm and stones, root content and bulk density were determined in order to obtain reliable estimates of carbon content per unit area (kgCm-2). Soil respiration and temperature data were fitted with a simple logistic model separately for each site, so that base respiration rates and mean annual soil respiration were estimated. Then the same regression model was applied to all sites simultaneously, with each model parameter being expressed as a linear function of site variables. The general model explained about 86% of the intersite variability of soil respiration. In particular, soil mean annual temperature explained the most of the variance of the model (0.41), followed by soil temperature interquartlile range (0.24), soil carbon content (0.16) and soil water content (0.05)
Current status, uncertainty and future needs in soil carbon monitoring
No full textThe need for cataloguing global soil carbon was recently highlighted by Gianelle et
al., (2010) in a letter to Science, where the importance of considering soils and
SOM sensitivity to temperature were underscored. Moreover the need to understand
the global distribution of soil carbon is a real concern for climate change
international policy issues. In order to establish the status of our knowledge regarding global soil carbon stocks in relation to climate change problems, an International workshop named G-SCAN (Global Soil Carbon Network) was organized in Florence (20-21, April) by the Edmund Mach Foundation (San Michele All'Adige, Italy). Some of the top scientists working on soil carbon dynamics from Europe and the US discussed the topic according to three working groups: a) Methodological standardization of soil C stocks; b) Detecting changes in Soil C; and c) Long-term experiments. Starting from real situations of soil carbon inventories and databases, the main problems and needs related to monitoring were highlighted and discussed. The results of the workshop will be published soon as an opinion paper in a peer reviewed journal. The unresolved problems still concerning soil carbon monitoring were discussed and could serve as a basis to homogenize current databases,
compare soil inventories and improve global soil mappin
Spatial Variability and Optimal Sampling Strategy of Soil Respiration
No full textSoil respiration is the second largest flux of carbon between terrestrial ecosystems and the atmosphere and is affecting climate sensitivity and vulnerability of the terrestrial carbon stock. Monitoring soil carbon dioxide efflux is a complex task, due to the high spatial and temporal variability of the fluxes. For this reason, more than 30 sampling points are required to attain reliable estimates of ecosystem soil respiration. However, the number of sampled points is often limited by labour, time and budget constraints. Stratified sampling is an alternative to random sampling as a method to reduce the number of sampling points when an effective proxy variable is available for the definition of the strata.
In order to evaluate different sampling strategies we tested, with a Monte Carlo simulation, the effectiveness of random and stratified samplings, using experimental data collected in three alpine ecosystems (two forests and one grassland). We evaluated an innovative method for defining the strata to be sampled. The method is based on an initial sampling of soil respiration from a large number of candidate points in order to account for the spatial variability. The minimum number of sampling points required to adequately represent soil respiration for the entire area were then selected using stratified statistical sampling.We show that this method is unbiased and that it reduces considerably the uncertainty in the sampling process compared to random sampling. The method was highly effective in the two forest ecosystems, characterized by a high spatial variability in soil respiration and by a high temporal correlation of the fluxes. On the contrary the method was not so effective in the grassland site, where fluxes have lower spatial variability and temporal correlation. However, the stratified sampling offered a consistent reduction of the error (%) of the estimated annual soil CO2 efflux in all the ecosystems. At the grassland ecosystem the average reduction of the error (%) of the annual CO2 efflux was about 12%, while at the forest ecosystems the average reductions were 55% and 57%, respectively.
# 2007 Elsevier B.V. All rights reserved.JRC.H.2 - Climate chang
On the Sawfly Pristiphora subarctica (Forsslund, 1936) (Hymenoptera: Tenthredinidae) in Spruce Plantations of the Southern Alps
No full textPristiphora subarctica is commonly considered a rare sawfly species feeding on Norway spruce (Picea abies (L.) Karsten) with central and northern European distribution. In this paper the occurrence of a large population of this sawfly species in spruce plantations of the Southern Alps (Asiago Plateau, Venetian Prealps, Italy) is documented. Three plantations were attacked for two subsequent years starting from spring 1998. Although no trees died as a consequence of the defoliation, the crown architecture was compromised by the growth of multiple shoots derived from proventitious
buds. Th e population density of verwintering stages of the sawfly was estimated by searching for cocoons in soil
samples and density of adults was monitored with yellow sticky traps. The damage to the plantations was evaluated by counting the number of trees bearing red defoliated
leaders
- …
