Genetic control of growth and form in early-age tests of Casuarina equisetifolia in Andhra Pradesh, India

Early results from three test plantings of Casuarina equisetifolia spp. equisetifolia are reported: a clonal test of 40 locally selected clones, a progeny test of 16 wind-pollinated families of local origin, and a family-in-provenance test of 100 wind-pollinated families which is part of an international provenance trial. All tests were planted in 1996 at the Regional Forest Research Centre, Rajahmundry, Andhra Pradesh, India. Height, stem straightness and axis persistence were measured in the family tests at 6 and 12 months of age. The height of the clonal test was measured at 12 months of age. Heritability estimates obtained were ca. 0.3, 0.2 and 0.1 for height, stem straightness and axis persistence, respectively. Heritability estimates for height were reasonably consistent across the three tests; however, estimates for stem straightness and axis persistence were generally higher in the small test of locally selected families. Height and the other two traits are most probably either weakly correlated or uncorrelated, while stem straightness and axis persistence are positively correlated. Provenances spread across the range of natural- and land-race populations tested demonstrated good growth potential at Rajahmundry. However, natural provenances from Malaysia and Thailand generally showed superior growth, while the land-race populations often demonstrated superior stem straightness. Based on these results some aspects of a breeding strategy are outlined: (a) the establishment of three unrelated sublines; (b) an initial clonal test of all parents; and (c) wind-pollinated mating within clonal breeding orchards.     

Physiological and growth responses of three sizes of containerized Picea mariana seedlings outplanted with and without vegetation control

Three different stock sizes of containerized black spruce (Picea mariana [Mill.] B.S.P.) seedlings were planted in an abandoned agricultural field. The small planting stock was of a conventional type produced in 110 cm³ containers. The experimental medium and large stock types were produced in 340 and 700 cm³ containers, respectively. Gas exchange, xylem water potential and dry masses were measured six times during each of the first two growing seasons in field plots with and without vegetation control. During the first growing season, the effect of planting shock masked most physiological and growth differences among seedling types. During the second growing season, in plots with vegetation control, small and medium seedlings had similar values of physiological variables and of growth as measured by relative growth rates (RGR), but the large seedlings showed lower values of both net photosynthesis and of RGR, a difference attributed to low initial quality of the root system in the larger seedlings. In plots without vegetation control, the trend was identical, but differences were not significant; the greater height of the larger seedlings, and the resulting greater access to light, compensated for their lower initial quality. The similarity in response between the medium and the small seedlings shows that a fourfold increase in shoot size (1.68–6.82 g) in the initial size and a doubling of the shoot : root ratio (2.17–4.54) of the planting stock did not result in increased planting shock or reduced growth in these containerized conifer stock types. The results also show the importance of the interaction between stock height and the vertical light profile created by the competing vegetation in the final assessment of stock performance.     

Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae) oviposition on seven naturally co-occurring Eucalyptus species

Gonipterus scutellatus is a significant insect pest of eucalypts in most countries where that genus has been introduced, but is usually only of minor significance in its native Australia. Because of this, much of the research on its biology and host preferences has been done outside Australia. This fact has the potential to produce misleading results as the insect may be forced to choose less preferred hosts, if normally preferred species are unavailable. In part of its native range, in Tasmania, oviposition of G. scutellatus was recorded on seven naturally co-occurring Eucalyptus species that were planted in even aged, replicated plots. Among the seven species were the economically important species, E. globulus and E. viminalis, which have been previously reported as highly preferred hosts. Within plots, oviposition occurred most commonly on three peppermint species (E. pulchella, E. tenuiramis and E. amygdalina) and was rare or absent on the other species (E. globulus, E. viminalis, E. ovata and E. obliqua). Of the peppermints, E. pulchella was the most preferred species for oviposition at this site. A low percentage of peppermints in mixed forest (containing these seven species) immediately adjacent to plots was always matched by low numbers of G. scutellatus eggs within plots; but high percentages of peppermints outside plots could either be matched by high or low numbers of eggs within plots. In the discussion, we suggest that previous studies of G. scutellatus host range may have been limited because the insect was not exposed to hosts it naturally encounters.     

Testing site index–site-factor relationships for predicting Pinus contorta and Picea engelmannii×P. glauca productivity in central British Columbia, Canada

Measures of forest productivity for various site conditions are necessary for forest management planning, where timber production is the objective. This study was undertaken to test whether autecological productivity relationships developed for lodgepole pine (Pinus contorta) and interior spruce (Picea engelmannii×P. glauca) using the biogeoclimatic ecosystem classification system of British Columbia are useful as practical field-based procedures to predict site index. Independent data sets consisting of 111 plots for pine and 114 plots for spruce were collected for use in testing the bias and precision of the models. A regression on residuals (predicted minus test values) indicated that the lodgepole pine model was unbiased in estimating site index (p=0.08). However, there was a lack of precision, with a square root of the mean squared prediction error (root-MSPR) of 2.8 m. Only 56% of the test plots had differences from the predicted values of 2.0 m or less. Residual analysis showed that the interior spruce model was biased in estimating site index (p<0.01), generally predicting greater site index than the test values. The model also lacked precision, with a root-MSPR of 3.2 m. Only 44% of the test plots had differences from the predicted values of 2.0 m or less. Forest managers requiring a site-index prediction tool need to decide whether the degree of accuracy precision provided by these models is acceptable.     

The impact of aspect on forest structure and floristics in some Eastern Australian sites

Aspect exerts a major influence on the structure and floristics of forests at upslope positions on steep ridges near the escarpment of north-eastern New South Wales. The vegetation of northwest facing sites differed from that of the southeast aspect in species richness and diversity, canopy cover, and canopy height, whilst differences between northeast and southwest aspects were significant for fewer attributes. The gross effect of aspect was in segregating eucalypt and rainforest communities. Aspect-induced differences in light, heat, moisture and edaphic conditions produced a sort of potential canopy species during recruitment. In the absence of substantial disturbance, the divergence of the structural character of developing forest canopies between aspects tends to enhance the floristic divergence in the subcanopy space. Although the study area is representative of a large region of forested steeplands in the hinterland of north-eastern New South Wales, the upper slope segments and four aspects studied can be expected to represent the extreme manipulation. In any event, it is unlikely that the extent of site divergence represented in these old-growth forests would be maintained under managed re-growth strategies.     

Patterns of forest use and endemism in resident bird communities of north-central Michoacán, Mexico

We compared breeding avian communities among 11 habitat types in north-central Michoacán, Mexico, to determine patterns of forest use by endemic and nonendemic resident species. Point counts of birds and vegetation measurements were conducted at 124 sampling localities from May through July, in 1994 and 1995. Six native forest types sampled were pine, pine–oak, oak–pine, oak, fir, and cloud forests; three habitat types were plantations of Eucalyptus, pine, and mixed species; and the remaining two habitats were shrublands and pastures. Pastures had lower bird-species richness and abundance than pine, oak–pine, and mixed-species plantations. Pine forests had greater bird abundance and species richness than oak forests and shrublands. Species richness and abundance of endemics were greatest in fir forests, followed by cloud forests. Bird abundance and richness significantly increased with greater tree-layer complexity, although sites with intermediate tree complexity also supported high abundances. When detrended correspondence-analysis scores were plotted for each site, bird species composition did not differ substantially among the four native oak-and-pine forest types, but cloud and fir forests, Eucalyptus plantations, and mixed-species plantations formed relatively distinct groups. Plantations supported a mixture of species found in native forests, shrublands, and pastures. Pastures and shrublands shared many species in common, varied greatly among sites in bird-species composition, and contained more species specific to these habitats than did forest types.     

Height–diameter models for tropical forests on Hainan Island in southern China

Measurements on 8352 felled trees from 31 plots in tropical forests on Hainan Island provided information to investigate the relationship between total tree height and diameter at 1.3 m (DBH). Out of 33 model forms either published or derivable from published forms, a modification of the exponential model published by Meyer (Meyer, H.A. A mathematical expression for height curves. J. For. 38 (1940) 415–420) was selected based on low bias and relatively good precision of its predictions on individual plots. Variations from plot-to-plot were significant. Therefore, a parameter prediction method based on predictor variables derived from all DBH values on a plot was developed in order to provide a method to localize the model. In a test with independent data from an additional 36 plots, the localized height-prediction model produced predictions with a pooled mean-squared error of 3.8 m², a pooled R² of 0.72, and an average bias of −0.2 m. Even though tremendous variability exists in tropical forests and modeling height–DBH relationships never provides high levels of precision, this model will provide a useful and economical alternative to attempting height measurements during inventories of these forests.     

Mitigating fire risk to late-successional forest reserves on the east slope of the Washington Cascade Range, USA

A fire-risk model was developed using a stand-structure approach for the forests of the eastern slopes of the Washington Cascade Range, USA. The model was used to evaluate effects of seven landscape-scale silvicultural regimes on fire risk at two spatial scales: (1) the risk to the entire landscape; and (2) the risk to three reserve stands with stand structures associated with high conservation priorities (layered canopy, large trees, multiple species). A 1000 ha landscape was projected five decades for each management regime using an individual tree, distance-independent growth model. Results suggest that a variety of silvicultural approaches will reduce landscape fire risk; however, reserve stand fire risk is minimally decreased by thinning treatments to neighboring stands. Intensive fuel reduction through prescribed burning and selection of reserve stands in favorable topographic positions provide substantial fire risk reductions.     

Tropical forest fragmentation and greenhouse gas emissions

Rainforest fragments in central Amazonia have been found to experience a marked loss of above-ground biomass caused by sharply increased rates of tree mortality and damage near fragment margins. These findings suggest that fragmentation of tropical forests is likely to increase emissions of CO₂ and other greenhouse gases above and beyond that caused by deforestation per se. We estimated committed carbon emissions from deforestation and fragmentation in Amazonia, using three simulated models of landscape change: a ‘Rondônia scenario,' which mimicked settlement schemes of small farmers in the southern Amazon; a ‘Pará scenario,' which imitated large cattle ranches in the eastern Amazon; and a ‘random scenario,' in which forest tracts were cleared randomly. Estimates of carbon emissions for specific landscapes were from 0.3 to 42% too low, depending on the amount and spatial pattern of clearing, when based solely on deforestation. Because they created irregular habitat edges or many forest perforations which increased tree mortality, the Rondônia and random-clearing scenarios produced 2–5 times more fragmentation-induced carbon emissions than did the Pará scenario, for any given level of clearing. Using current estimates of forest conversion, our simulations suggest that committed carbon emissions from forest fragmentation alone will range from 3.0 to 15.6 million t/year in the Brazilian Amazon, and from 22 to 149 million t/year for tropical forests globally.     

Impacts of mechanical site preparation on foliar nutrients of planted white spruce seedlings on mixed-wood boreal forest sites in Alberta

The impacts of different methods of mechanical site preparation (MSP) on performance and foliar nutrition of planted white spruce (Picea glauca (Moench) Voss) seedlings were examined at two mixed-wood boreal forest sites (Judy Creek, Fox Creek) in Alberta, Canada. The treatments included three types of MSP: disc trench, ripper plough, and bladed, the latter including thin and thick microsites (based on depth of remaining organic matter); as well as a harvested-control (no MSP). Seedlings were planted in June 1991, four months after MSP, and foliar N, P, K, Ca, Mg, S, Mn, Fe, and Al were assessed in the second and third growing seasons (13, 25, and 28 months later). Nutrient concentration and relative (among treatments) foliar nutrient content scaled up to the level of the whole seedling were examined. Following analysis of variance, significant responses were interpreted using vector analysis. MSP did not significantly affect seedling survival, height or unit needle weight. There was a non-significant trend of higher foliar biomass for seedlings in MSP areas than for control seedlings. Overall, the impact of MSP on foliar nutrient status on these sites was minimal. The only consistent positive effect of MSP on seedling nutrition was increased foliar Mg concentrations in blade-thin sites at Fox Creek. Indications of possible negative impacts of MSP include: increased Fe and Al concentrations in MSP areas at both sites; reduced P and K concentrations at both sites; and reduced Mn concentration and content at one site. The ripper treatment had the greatest positive effect on foliar nutrient status (P, K, Mn concentration). Blading (particularly blade-thin) resulted in the lowest concentrations of foliar P, K and Mn and the greatest increases in foliar Fe and Al.     

Fine litterfall and nutrient dynamics during forest regrowth in the humid subtropics of north-eastern India

Fine litterfall and nutrient return patterns were studied in three subtropical humid forest stands (7-, 13- and 16-year old), regrowing after selective tree cutting in north-eastern India. The seasonality of fine litterfall was unimodal, with a peak during spring and a trough during rainy season in the forest regrowths of three different ages. The rate of fine litterfall increased with increasing basal area of the woody vegetation during forest regrowth. Leaf litter accounted for 83% of the total litterfall. N concentration was maximum during autumn and minimum during rainy season; nutrient concentrations were highest in the leaf litter. Seasonal variation in P concentration was small. Maximum and minimum input of N and P to the forest floor through fine litter coincided with the respective periods of litter production.     

Structure of silver fir (Abies alba Mill.) natural regeneration in the ‘Jata'' reserve in Poland

Over the last 20 years, investigations have been carried out to determine the influence of various ecological factors on silver fir natural regeneration in highlands and mountains. However, there has been little research on the structure and development of fir regeneration in lowlands. Results of this study indicate that three main stand characteristics play a very important part in the structure of fir regeneration in the lowland. The results revealed that the quantity, frequency and growth rate of fir regeneration were affected by site conditions. One of the most important ecological factors differentiating quantity and quality of fir regeneration was the proportion of fir in a stand. It was found that, with an increase in the percentage of fir in a stand, the quantity and the sum of heights and the sum of height increments of fir regeneration tends to increase. Results of this study showed that the number and development of fir regeneration were influenced by species composition of a stand; fir regenerated not only in pure fir stands but also in mixed forests. A positive influence of pine and birch canopy on initiation and development of fir regeneration was confirmed. Optimal conditions for the growth and development of fir with respect to species composition were found in mixed fir stands with an admixture of hornbeam. In contrast, results of the study suggest that the worst conditions for fir regeneration were found in the stands composed of species, such as ash, alder, oak, aspen, lime and spruce.     

Modifying the microclimate around young oaks through vegetation manipulation: Effects on seedling growth and branching

The objective of this research was to evaluate the influence of vegetation control on the microclimate (light, air temperature, vapor-pressure deficit (VPD)) and on the growth of young planted, sessile oak seedlings. Three types of vegetation control, creating a range of above-ground interaction intensity, were compared. In the open treatment, vegetation was chemically controlled and was maintained at a low height; in the closed treatment, vegetation was manually controlled and a few dominant individuals that overtopped the oak seedlings were cut; and in the sheath treatment, the vegetation in a 0.5-m diameter circle around each seedling was manually cut to a height equal to three quarters of the total seedling height. In all treatments, a strong reduction of incoming radiation was observed, as well as an increase in air temperature and VPD during the day, and a decrease in daily PET, compared to the reference located 4 m above the vegetation. However, the neighboring vegetation did not modify the microclimate around the seedling to a level that could have induced a significant reduction in seedling photosynthesis and, thus, in seedling growth. Seven years after planting, seedlings were shortest in the open treatment and tallest in the closed treatment (334, 372, 378 cm in the open, sheath and closed treatments, respectively). Seedlings in the open treatment allocated proportionally more biomass to diameter increment than to height growth, compared to seedlings in the sheath and closed treatments. The seedlings averaged 1.77, 1.10 and 1.00 forks in the open, sheath and closed treatments, respectively, and the average height of the lowest fork was 171, 206 and 226 cm in the same treatments. The reduction of the number of forks per seedling was not related to a reduction of the appearance of new forks, but rather to a reduction in the persistence of the existing forks. These changes in stem allometry and in fork development seemed to be related to the lateral shade afforded by the vegetation.     

Small-mammal abundance at three elevations on a mountain in central Vermont, USA: a sixteen-year record

As part of a study of forest resilience to gypsy moth (Lymantria dispar) defoliation, small mammals were sampled with live (box) and pitfall traps for 16 years at three elevations on a mountain in west-central Vermont, USA. The more mesic, lower-slope location had the most diverse small-mammal community. White-footed mice (Peromyscus leucopus) were the most commonly captured small mammal at all locations, but less so at the lowest elevation. Southern red-backed voles (Clethrionomys gapperi), eastern chipmunks (Tamias striatus), and northern short-tailed shrews (Blarina brevicauda) were also regularly captured over the 16 years. Captures of all species showed considerable year-to-year variation. During the study, white-footed mouse density ranged from 3.7/ha (lower-slope June 1984) to 93.4/ha (mid-slope, July 1985). Over the 16 years, median density estimates across locations ranged from 12 to 19/ha in June and from 25 to 32/ha in July. Annual fluctuations in mouse abundance were synchronous across elevations, probably in response to regional-scale fluctuations in acorn production. In addition to those for white-footed mice, standardized capture rates are presented for the three other common species, and time to first capture is presented for 11 infrequently encountered species. The study demonstrates the importance of long-term surveys to properly characterize a small mammal community.     

Some nutrient dynamics associated with litterfall and litter decomposition in hoop pine plantations of southeast Queensland, Australia

Litterfall was collected over a 12-month period with littertraps in hoop pine (Araucaria cunninghamii) plantations aged 10, 14 and 62 years in southeast Queensland, Australia. The bulk of litterfall occurred during spring, mainly as hoop pine foliage with the annual litterfall ranging between 6.0 and 10.9 t ha⁻¹, respectively, for the younger stands (10 and 14 years) and the mature 62-year old stand. The amount of nitrogen (N) and phosphorous (P) recycled annually through litterfall was lower in the younger stands (28–37 kg N ha⁻¹ and 4.4–5.3 kg P ha⁻¹) compared with that of the mature stand (85 N ha⁻¹ and 6.2 kg P ha⁻¹). The N and P retranslocated during senescence varied across the three stands studied with a trend for N and P retranslocation to increase as availability of soil mineral-N decreased.

Decomposition of the hoop pine foliage component of litter was also studied in the same stands using a litterbag technique and mass-balance analysis. The estimated half-life of hoop pine foliage mass ranged between 1.5 and 1.8 years. Litter-mass loss was strongly correlated with litter substrate quality indicators of N, C, P, C/N ratio, lignin, lignin/N ratio and polyphenols. During the course of the study, there was no difference in litter-mass loss between the stands of different ages. During the 15-month period, the order of element release from the hoop pine litter was K>Na>C>Mg>P, with N, Ca and Mn generally demonstrating varying degrees of net accumulation. During the course of the study, the lignin/C ratio of the hoop pine litter increased from 0.61 to 0.96. This suggested that the litter-C was predominantly in a recalcitrant form and, therefore, the associated N was unlikely to be rapidly released in the hoop pine litter layer.     

Change in soil macrofauna and vegetation when fast-growing trees are planted on savanna soils

Many forest species can be found in understory vegetation of old plantation plots, despite the fact that the native vegetation was a poor savanna growing on highly nonfertile sandy soils. The aim of the present paper is to describe the changes that occur in the environmental conditions when savanna is planted with fast-growing trees, and is particularly concerned with vegetation and soil macrofauna. The study was carried out in industrial eucalyptus plantations, and in experimental Acacia and pine plantations. Most plots were located on sandy soil, but some measurements were also carried out on clay soil planted with the same species in order to assess the influence of soil type.

A strong correlation was shown between the age of the eucalyptus trees and the percentage of forest species in undergrowth, emphasizing the progressive change from savanna vegetation towards forest vegetation.

Biomass and density of macrofauna were very low in both sandy and clayey savanna soils, total biomass being 3.3 and 5.8 g/m² respectively. Soil macrofauna became more important as the age of plantations increased, and biomass reached 29 g/m² in the 20-year-old eucalyptus plot on sandy soil, and 74 g/m² in 26-year-old eucalyptus plantation on clay soil, compared to 33 g/m² in the natural forest plot on sandy soil; however, frequency of occurrence and number of taxa were lower in old eucalyptus plot as compared to forest. Large differences in the abundance of macrofauna were observed in relation to planted species. Acacia was most favourable to soil macrofauna, with a total biomass of 60 g/m² on sandy soil and many taxa present. Pine plantations had a poor macrofauna and several taxa were lacking, particularly in the sandy soil.

Total macrofauna frequency was significantly correlated with the percentage of forest species in understory vegetation. Both were correlated with soil pH and soil organic-matter content. The results suggest that soil organic matter and litter quality are of main importance in changing the above- and below-ground habitat in plantations.     

Effects of age and frequency of cutting on productivity of Mediterranean deciduous fodder tree and shrub plantations

Deciduous fodder trees and shrubs are important feed resources for the critical summer period in semi-arid and sub-humid Mediterranean environments. Eleven such species were established in central Macedonia, Greece as 1-year old seedlings in 1987 and studied through 1994. Height and biomass were statistically different among species and tended to increase with the age of plants. Common Robinia pseudoacacia was the tallest and the most productive species, reaching more than 3 m height and 4 kg DM/plant 8 years since planting; it was followed by Ostrya carpinifolia, the variety monophylla of Robinia, Colutea arborescens and Amorpha fruticosa. Grazeable proportion of total biomass was about 50% and decreased as the age of plants increased. Repeated annual cutting resulted in significant reduction of both height and total biomass by 51% and 88%, respectively as compared with uncut plants at the end of the eighth year while frequent cutting tended to increase the grazeable proportion of biomass after the fourth year. To attain an optimum combination of quantity and quality of biomass in deciduous fodder tree and shrub plantations cutting or grazing should not start earlier than the third year since establishment.     

A comparison of plant and carabid beetle communities in an Irish oak woodland with a nearby conifer plantation and clearfelled site

In 1996, plant and carabid beetle communities were examined in a semi-natural oak woodland (Derryclare Wood) and compared with communities of a nearby mature conifer plantation and a plantation clearfelled in 1994. At each site, 10 quadrats (2 m×2 m) and 10 pitfall traps were used to sample the ground vegetation and carabid beetle communities, respectively. Forty-one plant species were recorded in the oak woodland while 38 species were found in the clearfelled site and 19 species in the conifer plantation. The median plant-species richness per quadrat was significantly greater (p<0.01) in the oak woodland (16.5) than in the other two sites and the clearfelled site (11) was significantly more species-rich (p<0.02) than the conifer plantation (6.5). A total of 21 carabid species (895 individuals) were captured, with 74.5, 13.9 and 11.6% of individuals being caught at the oak woodland, clearfelled site and conifer plantation, respectively. The median number of carabid species per pitfall trap was significantly greater (p<0.01) in the oak woodland (6) than in the clearfelled site (3.5) and conifer plantation (2). In addition, median species richness per pitfall trap was significantly higher in the clearfelled site than in the conifer plantation at p<0.02. Median diversity per pitfall trap was also significantly less in the conifer plantation (1.19) than in the oak woodland (2.43, p<0.01) and clearfelled site (1.55, p<0.05). While the Sorenson similarity index for both vegetation and carabids shows that the conifer plantation and the clearfelled site were most similar in species composition; nevertheless, the clearfelled site has demonstrated signs of increasing species richness only 2 years after clearfelling. It is concluded that while semi-natural woodlands support a greater range of species than conifer plantations, clearfelled areas which are not replanted can enhance species richness within commercial conifer plantations.     

Phosphorus cycling and soil P fractions in Douglas-fir and red alder stands

Nitrogen-fixing species can dramatically increase soil acidity and organic matter content, and potentially alter biogeochemical P dynamics. We compared ecosystem P cycling in adjacent stands of N₂-fixing red alder (Alnus rubra Bong.) and non-fixing Douglas-fir (Pseudotsuga menziesii Franco) in order to determine whether P-cycling rates within stands were related to soil P forms as measured by sequential P fractionation. Above-ground annual P uptake was 61% greater in the red alder stand, although soil available P, as measured by Bray (NH₄F–HCl) extraction, was only 10% of that found in the Douglas-fir stand. Total ecosystem P in the alder stand was only 69% of that found in the Douglas-fir stand, and could indicate a pre-establishment difference between stands. However, the percentage of total soil P released by Bray or NaOH extraction was also lower in the alder stand, which suggests that differences in total P alone did not control the patterns observed in P fractions. Concentrations of inorganic P sorbed to Fe and Al minerals and contained in Fe minerals and apatite were greater under Douglas-fir, while organic P was slightly greater under red alder. While fluxes of P in litterfall, uptake and resorption were 94, 60 and 292% higher in the alder stand, soil extractable fractions meant to represent available P were lower under alder. Static measures of available P do not appear to adequately reflect P supply, and the development of techniques to assess P turnover is needed to better understand cycling and plant availability of P.     

Relationship between environmental factors and site index in Douglas-fir plantations in central Italy

Accurate and reliable evaluation of site suitability for the cultivation of selected species and availability of potential timber yield information is vital for the assessment of afforestation projects. This study examined the relationship between site index and environmental factors in Douglas-fir (Pseudotsuga menziesii var. menziesii) plantations in the province of Firenze (central Italy). The aim was to predict site index by readily measurable factors. The influence of climatic (temperature and rainfall), topographic (elevation, aspect, topographical exposure, etc.) and soil (pH, texture, etc.) on Douglas-fir site index was evaluated by multiple regression analysis exploiting data from 71 plots distributed across the study area. Approximately 58% of the observed site index variation is explained by annual rainfall, water surplus, clay content, calcium-carbonate content and east–west component of aspect. Climatic factors directly related to water balance have a greater influence on the productivity of examined Douglas-fir plantations than examined topographic and soil factors. Results of the study are ecologically sound and of practical value for field foresters, with reference to the study area. The precision of the model may be only indicative for assessing site index for single sites. At a landscape mapping level, estimate reliability is quite appropriate.