Site Index Estimates Research Articles

SITE INDEX FOR PROSOPIS ALBA PLANTATIONS IN THE SEMI-ARID CHACO THROUGH MIXED MODELS

ABSTRACT The classification of sites through curves of Site Index allows to predict the yield of the planted forests at a certain age of the stand and to plan cultural treatments. The goal of this research was to compare linear and non-linear models of fixed effects vs. mixed non-linear models to estimate the site index in plantations of Prosopis alba var Griseb in the irrigated area of the province of Santiago del Estero, Argentina using the guide curve method. The data used comes from temporary plots, permanent plots and growth data from the stem analysis of selected individuals based on their greater growth in height within the sampled areas. The registered variable for the evaluation of the site was the dominant Height (HD), defined as the average height of the 100 thickest trees per hectare. Considering that the source of data from repeated measurements on the same subject implies the presence of correlation and/or heteroscedasticity, it was proposed to evaluate statistical models that allow to properly representing the structure of the variance-covariance matrix, improving the accuracy in the adjustment. From the analysis of the results, it appears that the models non-linear mixed models have had better performance in the adjustment of the Site Index than linear and non-linear models of fixed effects. The most accurate model (smallest AIC and BIC) in the site index estimation was the mixed non-linear regression model of “Gompertz”, with structure of composite symmetry correlation and exponential heteroscedasticity.

Age-independent site index mapping with repeated single-tree airborne laser scanning

ABSTRACTA novel method for age-independent site index estimation is demonstrated using repeated single-tree airborne laser scanning (ALS) data. A spruce-dominated study area of 114 km2 in southern Norway was covered by single-tree ALS twice, i.e. in 2008 and 2014. We identified top height trees wall-to-wall, and for each of them we derived based on the two heights and the 6-year period length. We reconstructed past, annual height growth in a field campaign on 31 sample trees, and this showed good correspondence with ALS based heights. We found a considerable increase in site index, i.e. about 5 m in the H40 system, from the old site index values. This increase corresponded to a productivity increase of 62%. This increase appeared to mainly represent a real temporal trend caused by changing growing conditions. In addition, the increase could partly result from underestimation in old site index values. The method has the advantages of not requiring tree-age data, of representing current growing conditions, and as well that it is a cost-effective method with wall-to-wall coverage. In slow-growing forests and short time periods, the method is least reliable due to possible systematic differences in canopy penetration between repeated ALS scans.

Artificial neural networks, quantile regression, and linear regression for site index prediction in the presence of outliers

Abstract: The objective of this work was to compare methods of obtaining the site index for eucalyptus (Eucalyptus spp.) stands, as well as to evaluate their impact on the stability of this index in databases with and without outliers. Three methods were tested, using linear regression, quantile regression, and artificial neural network. Twenty-two permanent plots from a continuous forest inventory were used, measured in trees with ages from 23 to 83 months. The outliers were identified using a boxplot graphic. The artificial neural network showed better results than the linear and quantile regressions, both for dominant height and site index estimates. The stability obtained for the site index classification by the artificial neural network was also better than the one obtained by the other methods, regardless of the presence or the absence of outliers in the database. This shows that the artificial neural network is a solid modelling technique in the presence of outliers. When the cause of the presence of outliers in the database is not known, they can be kept in it if techniques as artificial neural networks or quantile regression are used.

Modelos dinámicos de índice de sitio para cuatro especies de pino en Oaxaca

Los modelos de índice de sitio representan una herramienta silvícola muy importante para clasificar la productividad de los bosques. El objetivo de este trabajo fue desarrollar ecuaciones dinámicas de índice de sitio derivadas, mediante el método de Diferencias Algebraicas Generalizadas (GADA), para cuatro especies de pino en la Sierra Norte del estado de Oaxaca, México. Para el ajuste de las ecuaciones se utilizaron datos de análisis de tronco de árboles de Pinus oaxacana, P. douglasiana, P. patula y P. pseudostrobus. Los árboles se seleccionaron en rodales mixtos e irregulares, intentando cubrir las diferentes calidades de estación presentes en las áreas sujetas a manejo forestal en los bosques de la Unidad de Manejo Forestal Regional 2001. Los ajustes se realizaron con el método iterativo y una estructura de error autoregresiva de tiempo continuo de segundo orden (CAR2), para corregir la autocorrelación del término del error. Los resultados indicaron que la formulación GADA del modelo de Bertalanffy-Richards puede ser utilizada para describir con precisión el índice de sitio de las cuatro especies estudiadas. La función desarrollada es polimórfica, dinámica, invariable con la edad de referencia y tiene múltiples asíntotas. El modelo genera, para las cuatro especies, estimaciones compatibles de índice de sitio y de altura dominante.

Development of Site Index Curves and Height-DBH Growth Model of Larix kaempferi for Deogyu Mountain in South Korea

In this study, we aimed to develop site index curves and a height growth model using forest data with the measured height, diameter at breast height (DBH), and age targeting a Larix kaempferi stand located on Mt. Deogyu in Muju, Jeollabuk-do. The site index estimation was calculated using Chapman-Richards equation. The coefficients were found to be α = 20.7837, β = 0.0566, γ = 1.6607, and MSE = 1.2034. The height growth model of the dominant trees depending on the DBH was determined to be α = 0.4872, β = 0.3687, and MSE = 1.8212 using the Petterson growth model. The Mean residual values for above two models were analyzed as 0.00004 and −0.00007, respectively. When comparing the skewness and kurtosis of the residual, the skewness values were 0.1659 and −0.1272, and the kurtosis values were −0.2310 and −0.5543. Therefore, the fitness was considered to be good because they were close to the normal distribution. The results of Shapiro-Wilk test showed P-values (0.77 for the height growth model and 0.62 for the height-DBH model) significantly higher than the alpha level of 0.05, and the residual form of the estimated values for the measured values showed uniform distribution indicating that the fitness of the two models was excellent.

Índice de sitio para bosques naturales de Pinus teocote Schlecht. & Cham. en el oriente del estado de Hidalgo


 
 
 La estimación de la productividad de los sitios forestales es indispensable para el manejo sostenible de los bosques y el índice de sitio constituye la metodología más utilizada en el mundo para este fin. Sin embargo, uno de los problemas más graves en el manejo forestal es la falta de ordenamiento de los rodales en función a su productividad, lo que propicia sobreexplotación de los recursos en algunos casos y la subexplotación en otros. Por ello, el objetivo del presente estudio fue estimar el índice de sitio y comparar la factibilidad de emplear las curvas anamórficas y polimórficas para bosques naturales de Pinus teocote en la región oriente del estado de Hidalgo. Se manejaron 345 pares de valores edad-altura de árboles dominantes y codominantes evaluados en rodales puros de este taxon; se ajustó el modelo de crecimiento de Schumacher que de acuerdo al bajo valor del Cuadrado Medio del Error, el alto valor de Pseudo R2 ajustada y la correcta distribución de residuales mostró un ajuste adecuado a los datos, para determinar la curva guía y la construcción de las familias de curvas anamórficas y polimórficas de índice de sitio. Se establecieron calidades de estación de I, II, III, IV y V, en los valores de 27, 23, 19,15 y 1 m, respectivamente, a una edad base de 50 años.
 
 

The effect of leader damage on white spruce (Picea glauca) site tree height growth and site index

Site trees used to estimate site index are selected based on characteristics that ensure that the tree reflects the potential productivity of the site. Hidden leader damage can make it difficult to identify site trees. Using these trees as site trees could lead to erroneous estimates of site index and height growth trajectories. One hundred and fifteen white spruce (Picea glauca (Moench) Voss) trees were selected, harvested, and split open to identify hidden damage and to quantify the effect of the damage on height growth and site index. A mixed-effects height growth model based on the Chapman–Richards function was formulated. A height growth modifier was included in the model to estimate the effect of leader damage on height growth. It was found that height growth was reduced by 28% in the year that the damage occurred and by 6% and 3% in the following two years. This results in a reduction of about 0.16 m in site index per incidence of damage on average, although this will depend on the age when the damage occurred and the timing between damage events. Since the damage is not outwardly visible, this creates problems when developing and applying site index models.

The effect of leader damage on lodgepole pine site tree height growth

Site index is an important parameter in forest management. Selecting good site trees is critical for both developing and applying models to estimate site index. Along with other characteristics, site trees must be free of damage so that the growth of the tree reflects the potential productivity of the site. Detecting and avoiding leader damage in site trees is very difficult because radial stem growth eventually hides the damage, even in young trees. This project quantifies the loss in height growth due to hidden leader damage. Thirty-seven lodgepole pine (Pinus contorta var. latifolia) site trees were destructively sampled. Annual height growth was measured and incidents of leader damage noted. Height growth was modelled in a mixed-effects framework and allowed for growth reductions due to leader damage. Height growth was reduced on average by 35% in the year the damage occurred and by 15% in the year after the damage event. Height growth returned to normal in subsequent years. The effect of leader damage on the estimated site index depends on when and how many damage events occur, and when the site index estimate is made. For a tree with a site index of 20 m at base age 50 years at breast height that has leader damage at age 8, a reduction in the estimated site index of 0.59 m and 0.31 m can be expected when site index is estimated at ages 10 and 25, respectively.

Rootable depth controls height growth of Pinus halepensis Mill. in gypsiferous and non-gypsiferous soils

Pinus halepensis is generally considered a species adapted to soils with gypsum but there is hardly any data available to support such statement nor to assess the degree to which soil gypsum may constrain tree development. We studied fifty five 200m2-plots in a P. halepensis plantation in NE Spain, 23 on soils with gypsum and 32 on soils without gypsum. Trees were measured to estimate site index at age 40years (SI40). A soil pit was described in each plot to a depth of 1m or to a root-limiting layer, and samples of the various horizons analysed for pH, organic carbon (C), total nitrogen, Olsen phosphorus (P), exchangeable potassium (extracted with NH4OAc), calcium carbonate (calcimeter method), and gypsum concentration (Artieda method), and texture. We studied root development in the soil horizons of 15 of these plots by counting root numbers at depths of 0–30cm, 30–55cm, and 55–80cm in three 100cm2-squares per depth. Penetration resistance and bulk density were also measured in these horizons. Soils with gypsum were frequently less than 25cm deep, and had negligible concentrations of Olsen phosphorus. Values of SI40, with a maximum of 15.5m, were primarily determined, in all types of soils, by a positive effect of soil rootable depth, indicating the dominant influence of water availability, and to a lesser extent by the negative effect of the C/P ratio and rock fragment content in the upper 30cm of soil. Density of fine and very fine roots decreased in deeper soil horizons from a maximum value of 97 roots·dm−2 in the surface horizons. Mechanical impedance by increased penetration resistance was the main limitation for root development. Soil gypsum does not have a direct influence on growth but constrains the volume of soil that may be explored by roots.

Regional rates of young US forest growth estimated from annual Landsat disturbance history and IKONOS stereo imagery

Forests of the Contiguous United States (CONUS) have been found to be a large contributor to the global atmospheric carbon sink. The magnitude and nature of this sink is still uncertain and recent studies have sought to define the dynamics that control its strength and longevity. The Landsat series of satellites has been a vital resource to understand the long-term changes in land cover that can impact ecosystem function and terrestrial carbonstock. We combine annual Landsat forest disturbance history from 1985 to 2011 with single date IKONOS stereoimagery to estimate the change in young forest canopy height and above ground live dry biomass accumulation for selected sites in the CONUS. Our approach follows an approximately linear growth rate following clearing over short intervals and does not estimate the distinct non-linear growth rate over longer intervals.We produced canopy height models by differencing digital surface models estimated from IKONOS stereo pairs with national elevation data (NED). Correlations between height and biomass were established independently using airborne LiDAR, and then applied to the IKONOS-estimated canopy height models. Graphing current biomass against time since disturbance provided biomass accumulation rates. For 20 study sites distributed across five regions of the CONUS, 19 showed statistically significant recovery trends (p is less than 0.001) with canopy growth from 0.26 m yr-1to 0.73 m yr-1. Above ground live dry biomass (AGB) density accumulation ranged from 1.31 t/ha yr-1 to 12.47 t/ha yr-1. Mean forest AGB accumulationwas 6.31 t/ha yr-1 among all sites with significant growth trends. We evaluated the accuracy of our estimates by comparing to field estimated site index curves of growth, airborne LiDAR data, and independent model predictions of C accumulation. Growth estimates found with this approach are consistent with site index curves and total biomass estimates fall within the range of field estimates. This is aviable approach to estimate forest biomass accumulation in regions with clear-cut harvest disturbances.

English

Coal is an important source of energy for electricity and is used in making steel and various other products. West Virginia is the largest coal producing state within the Appalachian region. Surface mining of coal drastically disturbs ecologically diverse forests and the reforestation of these areas after mining is an important first step to helping restore their ecosystem functions. After mining, operators are often left with brown and gray sandstone to use as topsoil substitutes. Brown sandstone has been more weathered and has physical and chemical properties that are better for tree growth (lower pH, higher percent fines, and higher available nutrients) than gray sandstone. Two study sites were established on former mine sites in West Virginia to assess the effects of brown and gray sandstone, with and without mulch treatments, on tree establishment. Tree growth data for tulip poplar (Liriodendron tulipifera L.), white oak (Quercus alba L.) and northern red oak (Q. rubra L.), and for soil samples (analyzed for pH, EC, percent fines, and extractable nutrients) have been collected annually for the last 10 years. The pH of brown sandstone was 5.2 to 5.4, gray sandstone was 6.5 to 6.8, and mulch treatments were 7.0. Percent fines ranged from 42 to 60% on all treatments. The mulch treatment had high levels of Ca (197 cmolc/kg). The height growth of each tree species on both mine sites was compared to the growth of trees growing on clear-cut areas at the Fernow Forest, WV. In addition, an estimated site index prior to disturbance was calculated and used to predict tree growth rates based on NRCS soil survey data. Tree heights (25 to 175 cm) on gray sandstone were significantly lower than height on brown sandstone (197 to 544 cm) for all three species. Trees on mulched plots were up to 229 cm taller than trees on un-mulched plots. Tulip poplar height on the brown treatment (544 cm) was greater than on a clear-cut area with a site index 62 at 10 years (503 cm). Tree heights on average were 50% lower on mined sites compared to heights calculated from pre-mining site indices.

Spatial Variation in Dominant Height and Basal Area Development in a Coast Redwood Forest: Implications for Inventory and Modeling

We studied spatial autocorrelation in productivity across 110 ha of coast redwood (Sequoia sempervirens) forest in north coastal California. Height growth of dominant redwood trees, basal area (BA) growth, and volume growth were assessed in a grid of 234 permanent sample plots. Semi-variance analysis indicated that productivity was spatially autocorrelated yet variable at smaller spatial scales (i.e., between nearby sample plots). Dominant redwood height growth lacked spatial continuity beyond 200 m, indicating that estimates of site index from plots closer than 200 m would be spatially autocorrelated. BA development was spatially autocorrelated in plots up to 300 m apart within the study area characterized by heterogeneous topography and variable species composition. These findings suggest that estimates of redwood site index demand greater sampling intensity than sampling to index BA or volume productivity. Our analysis provides a framework for refining estimates of forest growth, yield, and carbon stocks in natural forests in accordance with divergent gradients of productivity.

Evaluation of age-independent methods of estimating site index and predicting height growth: a case study for maritime pine in Asturias (NW Spain)

Site index is the most common measure of forest site productivity used worldwide, serving as an important baseline for forest-level planning and helping to formulate silviculture strategies. Site index is usually obtained through measurement of dominant height and stand age. However, age is not available in many cases, such as in most national forest inventories or when it is not a main determinant of growth. Age-independent methods have been developed to overcome this problem, allowing modelling of the dominant height growth and estimation of site index in the absence of age data. The purpose of this study was to compare the most widely used age-dependent method and several age-independent alternatives, namely the growth intercept method, the age-independent difference equation method and an iterative method proposed in this study. We used stem analysis and permanent sample plot data from Pinus pinaster Ait. stands in Asturias, Spain, to test the alternative methods. It was found that for site index estimation, a 7-year growth intercept was the most accurate method. However, for prediction of dominant height growth, an age-independent equation that depends on climatic factors performed best, even better than the traditional age-dependent site quality curves. The iterative method proposed in this study proved to be the least accurate alternative, although it performed well in predicting height growth for long intervals starting from low heights. Finally, we provide recommendations regarding when the different methods should be used.

기후변화에 따른 생태권역별·임상별 산림 바이오매스 변화량 예측

본 연구는 수치산림입지도, 수치기후도, 제5차 국가 산림자원조사 등의 누적된 자료와 다양한 통계모형을 이용하여 기후변화에 따른 생태권역별 임상별 산림 바이오매스 변화를 예측하였다. 그 결과 시간 경과에 따른 산림 바이오매스 변화량은 생태권역별 임상별로 서로 다른 패턴을 보였다. 산악권역, 남동산야권역, 남서산야권역에서는 시간이 경과함에 따라 모든 임상에서 산림 바이오매스가 감소하는 것으로 예측되었다. 반면에 중부산야권역의 침엽수림과 혼효림은 기후변화의 영향으로 바이오매스가 증가하는 것으로 분석되었다. 또한 해안도서권역에서는 침엽수림을 제외한 임상에서 산림 바이오매스가 증가하는 것으로 추정되었다. 본 연구는 기후변화 시나리오에 따른 지위지수 추정치 변화에 근거하여 산림 바이오매스 변화량을 산출함으로써 기후변화에 따른 산림재해 변화 패턴을 예측할 수 있는 정보를 마련하였다. 본 연구의 결과는 산림재해 대응전략 수립에 필요한 정보로 활용될 수 있을 것으로 기대된다. This study was conducted to predict the changes in forest biomass in different ecoprovinces and forest types under climate change scenario based on cumulative data (i.e., digital forest site and climate maps, National Forest Inventory data) and various prediction models. The results from this study showed that predicted changes over time in biomass varied according to ecoprovince and forest type in Korea. A reduction in biomass was predicted for all forest types associated with the mountain, southeastern hilly, and southwestern hilly ecoprovinces. On the other hand, the biomass was predicted to increase for the coniferous forest and mixed-forest types in the central hilly ecoprovince. Furthermore, increases in biomass are predicted for all forest types, except coniferous forests, in the coastal ecoprovince. The results from this study provide a basis for developing technology to predict forest impacts due to climate change by predicting changes in forest biomass based on the estimation of site index.

Management and productivity of cedar-hemlock-salal scrub forests on the north coast of British Columbia

The outer north coast of British Columbia has extensive areas (approx. 235,000ha) of old-growth forests characterized by western redcedar (Thuja plicata), yellow-cedar (Chamaecyparis nootkatensis) and salal (Gaultheria shallon) on gentle to moderate slopes with imperfectly-drained soils and deep forest floor accumulations. Uncertainty surrounding the long-term sustained yield of these low productivity forests led to the establishment of an operational trial in 2001 on Porcher Island, British Columbia, to address management issues, including the risk of paludification with tree removal, the uncertainty in site potential estimates, and the possible extent of nutrient deficiency amelioration with soil raking, mounding or phosphorus fertilization. Each site treatment was randomly replicated four times in an 18ha cutblock. In the second year following logging, the aerobic depth of the soil (as determined by the extent of rust on steel pins) averaged 16.9cm and did not differ between unharvested and harvested plots, suggesting losses in canopy interception and evapotranspiration did not alter the site hydrological balance. Western redcedar survival was 95% with planting and browse protection, and site index estimates of the plantation by age 12 averaged 19.5m at 50years (range 7.6–25.9), in stark contrast to measurements of 3.9m obtained from old-growth stands. Cedar foliar N concentrations increased significantly (range 0.9–1.3%) with the mineral content of soil mounds, demonstrating the benefit of mixing subsoils into the rooting zone, but the wide range in forest floor depths resulted in mounds being overall no more effective than light raking of the forest floor in improving productivity. Phosphorus fertilization (75kgha−1) also provided no gains in soil fertility or cedar nutrition, and initial increases in inorganic P were not detected in soils after 10years. Both site treatments stimulated the natural establishment of red alder (Alnus rubra), averaging 3950 stems per ha, which may both facilitate and compete with the cedar plantation over time. Overall we found few obstacles to sustainable yields from cedar-hemlock-salal scrub forests, albeit with the recognition of longer rotation lengths and smaller volume increments than current operational sites on the north coast of British Columbia.

Improving site index estimates for pine and spruce plantations: a case study in the sub-boreal spruce zone in British Columbia

Site index (SI) expresses the growth potential for a species on a given site. Three SI determination methods were used for each managed stand sampled in the southern portion of the Prince George Timber Supply Area (TSA): forest inventory, calculated growth intercept or height over age, and site index biogeoclimatic ecosystem classification (SIBEC). Interior spruce and lodgepole pine leading stands were sampled in the Bowron Valley and only pine stands were sampled in the rest of the TSA. In the Bowron Valley for both species, calculated SI was greater than SIBEC SI, which was greater than inventory SI. Increases were greater for spruce. In the remaining pine areas sampled, the same relationship was observed. Pine yield model projections indicate mean annual increment (MAI) culmination occurred 5.7 and 16.4 years sooner for calculated SI compared with SIBEC and inventory SI, respectively, with yields increasing by 8% and 13%. The increases could be due to improved silviculture, tree response to climate change or a combination of the two. Differences could result in a mid-term timber supply available sooner or a greater yield at planned harvest age. This is particularly important in areas attacked by mountain pine beetle.

A Height Growth Model and Associated Growth Intercept Models for Estimating Site Index in Black Spruce (Picea mariana Mill. B.S.P.) Plantations in Northern Ontario, Canada

Abstract Site quality is a key component of growth and yield models because height growth rates are known to be influenced by available site resources. Accurate prediction of future growth and yield requires site quality information for both plantations and natural stands. The forest industry in northern Ontario relies on high-quality wood and fiber from black spruce (Picea mariana Mill. B.S.P.); therefore, these tools are essential to ensure sustainable forest management. Although there are site index (SI) models for natural-origin black spruce stands in northern Ontario, models for estimating site quality of young black spruce plantations have not been developed. We used stem analysis data collected from 62 plantations (>40 years of age) of pure black spruce across northern Ontario to develop height growth, SI, and variable growth intercept models. The distinct height growth patterns we observed may be attributed to early silvicultural treatments (site preparation and herbicide) in plantations allowing black spruce trees to attain breast height (1.3 m) faster than in fire-origin stands in northern Ontario. Our models can be used to estimate site quality of black spruce plantations, a key consideration for silviculture and forest management planning. We also compare our managed stand SI model to one we developed from a comparable subset of data from black spruce growing in unmanaged stands and propose a method to assign an SI with a common base age to pure upland black spruce stands regardless of origin.

ALS-based estimation of plot volume and site index in a eucalyptus plantation with a nonlinear mixed-effect model that accounts for the clone effect

Most airborne laser scanning (ALS) studies have been carried out in semi-natural forests, but some research has also been carried out in plantations. Results indicate that methods similar to those which are used in semi-natural forest are also usable in plantation forestry. The study was conducted in a pulpwood plantation growing Eucalyptus urograndis in Bahia State, Brazil. The aims of this study are to investigate (1) how accurately the plot volume may be estimated by ALS data in eucalyptus plantations and (2) how to estimate the site index directly by combining ALS data and stand age. The plot volume and site index were estimated by means of nonlinear mixed-effect modeling in order to take into account the stand-within-clone hierarchy of the data. The obtained accuracies are quite good if compared to those obtained in semi-natural forests. The root-mean-square error was 8.2% for plot volume and 2.7% for site index when the clone effect was used in prediction. Precision forestry applied in plantations differs in many ways from the forestry practiced in a semi-natural environment. ALS-based forest inventory methods have a great deal of potential in pulpwood plantations when the unique features of plantation forestry are taken into account.

Assessing the effect of measurement error in age on dominant height and site index estimates

Stand age is often hard to measure accurately. Measurement error in age affects height estimates when height is projected from one age to another age. In this study, our objective was to derive an estimator for the variance of the component of projection error associated with the error in age. To evaluate the estimator, a simulation approach was employed and the results showed that the estimator worked well in most cases. When the variance of the error in age increases and the projection is forward, however, the estimator might not work as well as in other cases. Another objective was to examine how the error in age behaved under different height–age models and to what extent it affected height and site index estimates. The effect of the error in age depended on its magnitude, the height–age model, initial value of dominant height and age, and projection length. It was also shown that the effect was sometimes negligible, but it could be considerable in other cases. Data from 80 ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) trees in British Columbia, Canada, were used in an illustrative example.

Environmental variability and its relationship to site index in Mediterranean maritime pine

Environmental variability and site productivity relationships, estimated by means of soil-site equations, are considered a milestone in decision making of forest management. The adequacy of silvicultural systems is related to tree response to environmental conditions. The objectives of this paper are to study climatic and edaphic variability in Mediterranean Maritime pine (Pinus pinaster) forests in Spain, and the practical use of such variability in determining forest productivity by means of site index estimation. Principal component analysis was used to describe environmental conditions and patterns. Site index predictive models were fitted using partial least squares and parsimoniously by ordinary least square. Climatic variables along with parent material defined an ecological regionalization from warm and humid to cold and dry sites. Results showed that temperature and precipitation in autumn and winter, along with longitudinal gradient define extreme site qualities. The best qualities are located in warm and humid sites whereas the poorest ones are found in cold and dry regions. Site index values are poorly explained by soil properties. However, clay content in the first mineral horizon improved the soil-site model considerably. Climate is the main driver of productivity of Mediterranean Maritime pine in a broad scale. Site index differences within a homogenous climatic region are associated to soil properties.