http://http://dspace.unitus.it:80 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Thu, 23 May 2013 18:17:51 GMT 2013-05-23T18:17:51Z http://hdl.handle.net/2067/2150 Title: Assessing the attributes of scattered trees outside the forest by a multi-phase sampling strategy Authors: Baffetta, Federica; Corona, Piermaria; Fattorini, Lorenzo Abstract: A sampling strategy to be used with multi - phase forest inventories is proposed for assessing scattered trees outside the forest on large territories. The fi rst phase is carried out by means of a systematic search over the area to be inventoried. The area is partitioned into regular polygons of the same size and points are randomly located, one per polygon. Subsequently, in the second phase, the land cover class of the fi rst-phase points is determined by very high - resolution remotely sensed imagery and a sample of points are selected from each land cover stratum. Then, the number of trees outside the forest lying within plots at the sampled points is recorded on the imagery. Finally, in the third phase, a subsample is selected from the second-phase samples of each stratum and the biophysical attributes of trees within plots are measured in the fi eld. Approximately unbiased estimators of abundance and of totals and averages of biophysical attributes are achieved in the second and third phase , respectively, together with the estimators of the corresponding variances. A simulation study is performed in order to assess the accuracy of the strategy under random and aggregated distributions of trees. The sampling errors achieved in the second phase using sampling fractions of ~ 0.3 per cent of trees vary from 6 to 13 per cent , whereas the errors achieved in the third phase using sampling fractions of ~ 0.15 per cent vary from 15 to 31 per cent . The results obtained from three case studies carried out in Italy confi rm the accuracy levels achieved in the simulation. Description: L'articolo è disponibile sul sito dell'editore http://forestry.oxfordjournals.org/ Fri, 31 Dec 2010 23:00:00 GMT http://hdl.handle.net/2067/2150 2010-12-31T23:00:00Z http://hdl.handle.net/2067/2081 Title: Design-based approach to k-nearest neighbours technique for coupling field and remotely sensed data in forest surveys Authors: Baffetta, Federica; Fattorini, Lorenzo; Franceschi, Sara; Corona, Piermaria Abstract: The statistical properties of the k-NN estimators are investigated in a design-based framework, avoiding any assumption about the population under study. The issue of coupling remotely sensed digital imagery with data arising from forest inventories conducted using probabilistic sampling schemes is considered. General results are obtained for the k-NN estimator at the pixel level. When averages (or totals) of forest attributes for the whole study area or sub-areas are of interest, the use of the empirical difference estimator is proposed. The estimator is shown to be approximately unbiased with a variance admitting unbiased or conservative estimators. The performance of the empirical difference estimator is evaluated by an extensive simulation study performed on several populations whose dimensions and covariate values are taken from a real case study. Samples are selected from the populations by means of simple random sampling without replacement. Comparisons with the generalized regression estimator and Horvitz–Thompson estimators are also performed. An application to a local forest inventory on a test area of central Italy is considered. Description: L'articolo è disponibile sul sito dell'editore www.sciencedirect.com Wed, 31 Dec 2008 23:00:00 GMT http://hdl.handle.net/2067/2081 2008-12-31T23:00:00Z http://hdl.handle.net/2067/2099 Title: Area-based lidar-assisted estimation of forest standing volume Authors: Corona, Piermaria; Fattorini, Lorenzo Abstract: Airborne laser scanning (lidar) technology is increasingly being applied in forest ecosystem surveys. This research note proposes a design-based approach for the lidar-assisted estimation of forest standing volume when ground surveys are performed by means of fixed-area plots. The lidar measurement of the height of the upper canopy (digital crown model) is performed for the whole study area, and the resulting pixel heights are adopted as auxiliary information to couple with the standing volume acquired on the ground by means of sample plots. The ratio estimator for the total volume of the forest is derived in a complete design-based framework together with an unbiased estimator of its sampling variance and the corresponding confidence interval. The proposed procedure has been tested in Bosco della Fontana, a lowland forest in Northern Italy, obtaining a 95% confidence interval for the total volume, which is approximately 2/3 smaller than that obtained by solely using information arising from field plots. Description: L'articolo è disponibile sul sito dell'editore www.nrcresearchpress.com Mon, 31 Dec 2007 23:00:00 GMT http://hdl.handle.net/2067/2099 2007-12-31T23:00:00Z http://hdl.handle.net/2067/2094 Title: Design-based diagnostics for k-NN estimators of forest resources Authors: Baffetta, Federica; Corona, Piermaria; Fattorini, Lorenzo Abstract: The k-nearest neighbours (k-NN) method constitutes a possible approach to improve the precision of the Horvitz– Thompson estimator of a single interest variable using auxiliary information at the estimation stage. Improvements are likely to occur when the neighbouring structure in the space of auxiliary variables is similar to the neighbouring structure in the space of the survey variables. Populations suitable for k-NN can be identified via the scores of the first principal component computed on the variance–covariance matrix of auxiliary variables. If the first principal component explains a large portion of the whole variability, distances among scores provide good approximations of distances in the space of auxiliary variables in such a way that the effectiveness of k-NN can be assessed by plotting the first principal component scores versus the sampled values of each of the interest variables. Monotone relationships with high values of Spearman’s correlation coefficients should denote effectiveness. Otherwise, when the first principal component explains small fractions of the total variation, an index that directly quantifies the similarity between the neighbouring structure in the space of interest and auxiliary variables is proposed. The validity of the proposed diagnostics is theoretically argued and empirically proven by a simulation study performed on a wide range of artificial and real populations. Description: L'articolo è disponibile sul sito dell'editore www.nrcresearchpress.com Fri, 31 Dec 2010 23:00:00 GMT http://hdl.handle.net/2067/2094 2010-12-31T23:00:00Z http://hdl.handle.net/2067/2214 Title: Two-stage sector sampling for estimating small woodlot attributes Authors: Corona, Piermaria; Fattorini, Lorenzo; Franceschi, Sara Abstract: A two-stage sampling strategy is proposed to assess small woodlots outside the forests scattered on extensive ter- ritories. The first stage is performed to select a sample of small woodlots using fixed-size sampling schemes, and the second stage is performed to sample trees within woodlots selected at first stage. Usually, fixed- or variable-area plots are adopted to sample trees. However, the use of plot sampling in small patches such as woodlots is likely to induce a relevant amount of bias owing to edge effects. In this framework, sector sampling proves to be particularly effective. The present paper in- vestigates the statistical properties of two-stage sampling strategies for estimating forest attributes of woodlot populations when sector sampling is adopted at the second stage. A two-stage estimator of population totals is derived together with a conservative estimator of its sampling variance. By means of a simulation study, the performance of the proposed estimator is checked and compared with that achieved using traditional plot sampling with edge corrections. Simulation results prove the adequacy of sector sampling and provide some guidelines for the effective planning of the strategy. In some countries, the proposed strategy can be performed with few modifications within the framework of large-scale forest inventories. Description: L'articolo è disponibile sul sito dell'editore www.nrcresearchpress.com Fri, 31 Dec 2010 23:00:00 GMT http://hdl.handle.net/2067/2214 2010-12-31T23:00:00Z http://hdl.handle.net/2067/2136 Title: Estimating forest area at the year 1990 by two-phase sampling on historical remotely sensed imagery in Italy Authors: Corona, Piermaria; Fattorini, Lorenzo; Chirici, Gherardo; Valentini, Riccardo; Marchetti, Marco Abstract: Forest area in the year 1990 is a fi gure of great interest under the Kyoto Protocol. This note is devoted to a scientifi c exercise for the probabilistic ex post assessment of such a fi gure in Italy. Estimation was performed by twophase point sampling, which made use of historical remotely sensed imagery. In the fi rst phase, a sample of 12 089 points was selected according to an unaligned systematic sampling and the selected points were classifi ed in land-use categories by Landsat 5 TM imagery. In the second phase, a sample of 3000 points was selected by stratifi ed sampling in which the strata were determined by the satellite classifi cation and the selected points were classifi ed by aerial photos, assumed as ground truth. A two-phase estimate of land-use coverage partitioning the Italian territory was obtained together with a conservative estimate of the sampling variance-covariance. The procedure has proved to be of relatively easy implementation and objective repeatability Description: L'articolo è disponibile sul sito dell'editore http://www.springerlink.com/ Sun, 31 Dec 2006 23:00:00 GMT http://hdl.handle.net/2067/2136 2006-12-31T23:00:00Z http://hdl.handle.net/2067/2125 Title: Estimation of small woodlot and tree row attributes in large-scale forest inventories Authors: Baffetta, Federica; Fattorini, Lorenzo; Corona, Piermaria Abstract: Forest surveys performed over a large scale (e.g. national inventories) involve several phases of sampling. The first phase is usually performed by means of a systematic search of the study region, in which the region is partitioned into regular polygons of the same size and points are randomly or systematically selected, one per polygon. In most cases, first-phase points are selected and recognized in orthophotos or very high resolution satellite images available for the whole study area. Disregarding the subsequent phases, the first phase of sampling can be effectively adopted to select small woodlots and tree rows, in the sense that a unit is selected when at least one firstphase point falls within it. On the basis of such a scheme of sampling, approximately unbiased estimators of abundance, coverage and other physical attributes readily measurable from orthophotos (e.g. tree-row length) are proposed, together with estimators of the corresponding variances. A simulation study is performed in order to check the performance of the estimators under several distributions of units over the study area (random, clustered, spatially trended). Description: L'articolo è disponibile sul sito dell'editore www.springerlink.com Fri, 31 Dec 2010 23:00:00 GMT http://hdl.handle.net/2067/2125 2010-12-31T23:00:00Z http://hdl.handle.net/2067/2065 Title: Estimating the volume of forest growing stock using auxiliary information derived from relascope or ocular assessments Authors: Corona, Piermaria; Fattorini, Lorenzo; Franceschi, Sara Abstract: The aim of this study is to demonstrate the potential of integrating probabilistic sampling and estimation with the conventional technique referred to as forest inventory by compartments. The objective of this paper is to propose two strategies for the assessment of growing stock volume using two-phase sampling, namely: (i) relascope basal area estimation performed on first-phase sampling points followed by volume estimation performed on a sub-sample of points selected in the second phase; (ii) ocular evaluation of growing stock volume performed on first-phase sampling plots of fixed size followed by volume estimation performed on a sub-sample of plots selected in the second phase. The effectiveness of using the auxiliary information gathered in the first phase is assessed by comparing the double-expansion estimator of total volume which depends solely on the second-phase sample with the two-phase ratio estimator which instead calibrates the double-expansion estimator on the basis of first-phase information. Conservative estimators of sampling variances and confidence intervals are derived for both the estimators. As is usual in forest inventories, first-phase sampling is assumed to be performed on a systematic random grid while three different schemes are considered for drawing the second-phase sample: simple random sampling without replacement, stratified sampling and 3-P sampling. The performance of double-expansion and ratio estimators under the three schemes adopted in the second phase is empirically checked by means of a simulation study performed on a real compartment in a beech forest of Central Italy. Simulation results show that the use of auxiliary information generated in the first phase constitutes a very effective way of increasing the accuracy of volume estimation at the compartment level, with a moderate increase of fieldwork. Wed, 31 Dec 2008 23:00:00 GMT http://hdl.handle.net/2067/2065 2008-12-31T23:00:00Z http://hdl.handle.net/2067/2119 Title: The assessment of tree row attributes by stratified two-stage sampling Authors: Corona, Piermaria; Fattorini, Lorenzo Abstract: Tree row inventories are of increasing interest because tree rows mitigate wind erosion and desertification, protect agricultural crops, enhance rural landscape quality, act as bio-corridors, carbon sinks, and a source for bio-energy. The main objective of tree row inventories is to estimate population parameters such as total tree numbers, total tree numbers by species, the mean stem diameter at breast height, the mean tree height and total wood volume. The estimation of these quantities may be straightforwardly carried out whenever aerial images are available in such a way that tree rows can be counted: in these cases, a two-stage cluster sampling may be performed in which the primary units sampled in the first stage are the tree rows in the study area while the secondary units sampled in the second stage are the trees within the selected rows. This paper proposes two sets of two-stage estimators for the interest parameters, based on the Horvitz–Thompson and ratio criteria, together with the corresponding estimators for their sampling variances. The use of stratification is also considered. The proposed procedure was applied to perform a tree row inventory in the Pontina plain (Central Italy): in this case, the tree rows were enumerated by means of ortho-corrected airborne images and stratification was carried out on the basis of the prevailing species and age classes. The inventory results are interesting from a forestry perspective as well as for checking the effectiveness of the procedure. Description: L'articolo è disponibile sul sito dell'editore www.springerlink.com Sat, 31 Dec 2005 23:00:00 GMT http://hdl.handle.net/2067/2119 2005-12-31T23:00:00Z http://hdl.handle.net/2067/2111 Title: Monitoring and assessing old-growth forest stands by plot sampling Authors: Corona, Piermaria; Blasi, Carlo; Chirici, Gherardo; Facioni, Laura; Fattorini, Lorenzo; Ferrari, Barbara Abstract: Forest inventories are evolving towards multipurpose resource surveys, broadening their scope by including additional topics such as biodiversity issues. Surprisingly, few quantitative surveys have been devoted to old-growth forests, even if they constitute the most acknowledged forest biodiversity icons. In this framework, the use of probabilistic sampling may provide an effective as well as rigorous support for monitoring and assessing old-growth forests. To this purpose, the present paper proposes a two-phase sampling scheme. In the first phase, a coarse survey of few floristic and stand structural attributes is carried out by means of small plots systematically placed on the study area. Subsequently, in the second phase, a fine assessment of a large number of ecological attributes is performed on a subset of enlarged plots selected among the first-phase ones by means of simple random sampling without replacement. The proposed sampling scheme is implemented for monitoring and assessing the old forests of Cilento National Park (southern Italy). Results and comments are provided as an exemplicative case study. Description: L'articolo è disponibile sul sito dell'editore www.tandf.co.uk/journals/ Thu, 31 Dec 2009 23:00:00 GMT http://hdl.handle.net/2067/2111 2009-12-31T23:00:00Z http://hdl.handle.net/2067/2120 Title: Aerial assessment of landscape net change by means of two-phase network sampling: an application to central Italy Authors: Corona, Piermaria; Fattorini, Lorenzo; Pompei, Enrico Abstract: A design-based procedure for estimating the land cover net change between two dates in time is considered by means of aerial information. The aerial information in the first date consists of analogical photos while the aerial information in the second date consists of digital photos or satellite imagery. In the first phase of sampling a set of points is selected on the study area by means of unaligned systematic sampling. The digital imagery available for the second date may be readily adopted for spotting and classifying the first-phase points, thus obtaining a firstphase estimator of the areal extents in the second date. On the other hand, owing to the operational difficulties of spotting all the first-phase points on the analogical photos, a second-phase sample selected from these points is necessary to estimate the areal extents of the land categories in the first date. Finally, the land cover net changes may be estimated by means of the difference between the resulting estimates in the two dates. The use of stratified network sampling is considered in the second phase in order to handle the presence of analogical photos overlapping each other at their boundaries. An application of the procedure is considered for assessing the land cover net change in the Abruzzo Region (Central Italy) between the years 1954 and 2002. Description: L'articolo è disponibile sul sito dell'editore www.interscience.wiley.com Sun, 31 Dec 2006 23:00:00 GMT http://hdl.handle.net/2067/2120 2006-12-31T23:00:00Z http://hdl.handle.net/2067/2313 Title: A matching procedure to improve k-NN estimation of forest attribute maps Authors: Baffetta, Federica; Corona, Piermaria; Fattorini, Lorenzo Abstract: The integration of forest inventory and mapping has emerged as a major issue for assessing forest attributes and multiple environmental functions. Associations between remotely sensed data and the biophysical attributes of forest vegetation (standing wood volume, biomass increment, etc.) can be exploited to estimate the attribute values for sampled and non-sampled pixels, thus producing maps for the entire region of interest. Among the available procedures, the k-nearest neighbours (k-NN) technique is becoming popular, even for practical applications. However, the k-NN estimates at the pixel level tend to average towards the population mean and to have suppressed variance, since large values are usually underestimated and small values overestimated. This tendency may be detrimental for k-NN applications in forest resource management planning and scenario analysis where the representation of the spatial variability of each attribute of interest across the surveyed territory is fundamental. The present paper proposes a procedure to tackle such an issue by modifying k-NN estimates via a post-processing procedure of distribution matching. The empirical distribution function of the population values is estimated from the sample of ground data by using the 0-inflated beta distribution as the assisting model and the k-NN estimates are subsequently modified in such a way as to match the estimated distribution. The statistical properties of the distribution matching estimators for totals and averages are theoretically derived, while the performance of the distribution matching estimator at the pixel level are empirically evaluated by a simulation study. Description: L'articolo è disponibile sul sito dell'editore www.Journals.elsevier.com Sat, 31 Dec 2011 23:00:00 GMT http://hdl.handle.net/2067/2313 2011-12-31T23:00:00Z http://hdl.handle.net/2067/2316 Title: Extending large-scale forest inventories to assess urban forests Authors: Corona, Piermaria; Agrimi, Mariagrazia; Baffetta, Federica; Barbati, Anna; Chiriacò, Maria Vincenza; Fattorini, Lorenzo; Pompei, Enrico; Valentini, Riccardo; Mattioli, Walter Abstract: Urban areas are continuously expanding today, extending their influence on an increasingly large proportion of woods and trees located in or nearby urban and urbanizing areas, the socalled urban forests. Although these forests have the potential for significantly improving the quality the urban environment and the well-being of the urban population, data to quantify the extent and characteristics of urban forests are still lacking or fragmentary on a large scale. In this regard, an expansion of the domain of multipurpose forest inventories like National Forest Inventories (NFIs) towards urban forests would be required. To this end, it would be convenient to exploit the same sampling scheme applied in NFIs to assess the basic features of urban forests. This paper considers approximately unbiased estimators of abundance and coverage of urban forests, together with estimators of the corresponding variances, which can be achieved from the first phase of most largescale forest inventories. A simulation study is carried out in order to check the performance of the considered estimators under various situations involving the spatial distribution of the urban forests over the study area. An application is worked out on the data from the Italian NFI. Description: L'articolo è disponibile sul sito dell'editore www.springer.com Sat, 31 Dec 2011 23:00:00 GMT http://hdl.handle.net/2067/2316 2011-12-31T23:00:00Z http://hdl.handle.net/2067/2346 Title: Land use inventory as framework for environmental accounting: an application in Italy Authors: Corona, Piermaria; Barbati, Anna; Tomao, Antonio; Bertani, Remo; Valentini, Riccardo; Marchetti, Marco; Fattorini, Lorenzo; Perugini, Lucia Abstract: Land use inventories are sound measures to provide information on the area occupied by different land use or land cover types and their changes, although less widespread than traditional mapping; as such, they are distinctively wellestablished tools for generating statistics on the state and the dynamics of land use in the European Union. Italy has recently set up a land use inventory system (IUTI) as a key instrument for accounting removals and emissions of greenhouse gases (GHG) associated to land use, land use change and forestry (LULUCF) activities elected by Italy under the Kyoto Protocol. IUTI adopts a statistical sampling procedure to estimate the area covered by LULUCF land use categories in Italy, and associated uncertainty estimates. Estimates of land use have been so far processed for the period 1990-2008 and highlight three interlinked land use change patterns in Italy: (i) increase in forest land for a total uptake of 1.7% of the Italian territory; forest cover estimates, with a standard error of 0.1%, indicate an annual increase of forestland higher over the period 1990-2000 (32 901 ha year-1) than in 2000-2008 (22 857 ha year-1); surprisingly, also a significant deforestation rate is observed (-7000 ha year-1), due to forest land conversion mainly into artificial areas; (ii) consumption of arable land (-4.2% of the Italian territory) primarily due to land uptake by urban areas and to conversions to permanent crops (mainly orchards and vineyards); (iii) urban sprawl uptakes 1.6% of the Italian territory in this period, with a total coverage of settlements reaching 7.1% of total land surface in Italy in 2008. Overall, land use dynamic results in land uptake by forest land is of the same magnitude of land uptake by urban areas, but the effects of these processes on GHG removals (by forest sinks) and emissions (by urban areas) is expected to be significantly different. In a broader perspective, IUTI methodology, by providing reliable estimates and well-defined levels of statistical uncertainty for assessing stocks and flows of land use at national level, can be further implemented to frame other key questions for sustainable development policies, like the set up of environmental-economic accounting systems. Description: L'articolo è disponibile sul sito dell'editore www.sisef.it Sat, 31 Dec 2011 23:00:00 GMT http://hdl.handle.net/2067/2346 2011-12-31T23:00:00Z