Mean Spring Temperature Research Articles

Climatic sensitivity of streamflow timing in the extratropical western Andes Cordillera

Summary This paper presents an analysis on the hydrological regimes from several rivers flowing from the western slope of the Andes Cordillera. We compiled a database of 40 unimpaired average monthly streamflow records located in central and southern Chile, spanning the region between latitudes 30°S and 40°S and the period between years 1961 and 2006. River categories encompass snowmelt, mixed and rainfall dominated watersheds. The water year hydrograph center of timing (CT) is used as an indicator of flow regime and as a proxy for streamflow distribution throughout the year. The CT for each river is correlated to local climatic variables such as seasonal temperature and precipitation, and to large-scale circulation indexes. We assess CT trends using the Mann–Kendall test for varying time windows within the study period. Overall results for the 1961–2006 period show a significant (95% confidence level) negative trend (CT date shifting towards earlier in the year) for 23 out of the 40 analyzed series. However, when studying time windows within the entire period there seems to be a break in the trend during the late 1970s, with positive or null changes for the latter half of the study period for most of the stations analyzed. We found that even though the CT is significantly correlated (r > 0.5) to temperature indexes in the snowfed watersheds, there has been no significant change in CT timing for most of these watersheds despite documented warming on the region. CT for all types of watersheds present clear correlation to precipitation indexes (r > 0.8), and we observed high and significant correlation between CT and ONI, SOI and MEI indexes for all the study region: higher (lower) precipitation amounts during El Nino (La Nina), rather than temperature variations, seem to be the most important factor controlling CT timing during these episodes. In order of importance, the CT showed higher correlation with annual precipitation amounts and timing, MEI, ONI and SOI, mean winter and spring temperature, and finally PDO. The detected trends are consistent only with trends in precipitation, as rivers that showed high correlation to temperature do not show any trend. These conclusions suggest that rivers on the region show a different response to temperature changes when compared to rivers of similar regime in the northern hemisphere, and that precipitation amount and timing are the source of most of the variability in streamflow timing for both snowmelt and rainfall dominated watersheds. Temperature induced variability in streamflow timing should be studied with more precise hydrological models, as the CT has a complex behavior due to multiple climatical dependencies. Studying such behavior using only historical data might be insufficient for drawing more precise conclusions.

Is the alpine divide becoming more permeable to biological invasions? – Insights on the invasion and establishment of the Walnut Husk Fly, Rhagoletis completa (Diptera: Tephritidae) in Switzerland

The Walnut Husk Fly, Rhagoletis completa Cresson (Diptera: Tephritidae), is native to North America (Midwestern US and north-eastern Mexico) and has invaded several European countries in the past decades by likely crossing the alpine divide separating most parts of Switzerland from Italy. Here, we determined its current distribution in Switzerland by sampling walnuts (Juglans regia L.) in ecologically and climatically distinct regions along potential invasion corridors. R. completa was found to be firmly established in most low altitude areas of Switzerland where walnuts thrive, but notably not a single parasitoid was recovered from any of the samples. Infested fruit was recovered in 42 of the 71 localities that were surveyed, with mean fruit infestation rate varying greatly among sites. The incidence of R. completa in Switzerland is closely related to meteorological mean spring temperature patterns influencing growing season length, but not to winter temperatures, reflecting survival potential during hibernation. Importantly, areas in which the fly is absent correspond with localities where the mean spring temperatures fall below 7°C. Historical data records show that the natural cold barrier around the Alpine divide in the central Swiss Alps corresponding to such minimal temperatures has shrunk significantly from a width of more than 40 km before 1990 to around 20 km after 2000. We hypothesize on possible invasion/expansion routes along alpine valleys, dwell on distribution patterns in relation to climate, and outline future research needs as the incursion of R. completa into Switzerland; and, more recently, other European countries, such as Germany, Austria, France and Slovenia, represent an example of alien species that settle first in the Mediterranean Basin and from there become invasive by crossing the Alps.

Spatial distribution of wildfire risk in the Monte biome (Patagonia, Argentina)

Please click here to download the map associated with this article. In many rangeland ecosystems, the role of wildfires has been the object of detailed studies. However, in Argentina and especially in the Monte biome this knowledge is limited. This region is prone to wildfires during late spring and summer, when high winds and temperatures are coupled with low relative humidity. In addition, this region also presents cases of extreme wildfire behaviour. The aim of this study is to develop a probability-based model for estimating wildfire risk at a regional scale based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Hot Spot data. The map presented here covers an area of approximately 246,000 km at a 1:100,000 scale. It is the result of fitting the 2001–2010 hot spot time series with a logistic regression model to 15 potentially explanatory environmental and anthropogenic variables. At a regional scale, mean net primary production, spring temperature, spring and summer precipitation, elevation, slope, distance to nearest road are the most important factors explaining wildfire risk.

Validation of biological collections as a source of phenological data for use in climate change studies: a case study with the orchid Ophrys sphegodes

Summary 1. The scarcity of reliable long‐term phenological data has severely hindered the study of the responses of species to climate change. Biological collections in herbaria and museums are potential sources of long‐term data for such study, but their use for this purpose needs independent validation. Here we report a rigorous test of the validity of using herbarium specimens for phenological studies, by comparing relationships between climate and time of peak flowering derived from herbarium records and from direct field‐based observations, for the terrestrial orchid Ophrys sphegodes. 2. We examined herbarium specimens of O. sphegodes collected between 1848 and 1958, and recorded peak flowering time directly in one population of O. sphegodes between 1975 and 2006. The response of flowering time to variation in mean spring temperature (March–May) was virtually identical in both sets of data, even though they covered different periods of time which differ in extent of anthropogenic temperature change. In both cases flowering was advanced by c. 6 days per °C rise in average spring temperature. 3. The proportion of variation in flowering time explained by spring temperature was lower in the herbarium record than in direct field observations. It is likely that some of the additional variation was due to geographical variation in collection site, as flowering was significantly earlier at more westerly sites, which have had warmer springs, over their range of 3.44° of longitude. 4. Predictions of peak flowering time based on the herbarium data corresponded closely with observed peak flowering times in the field, indicating that flowering response to temperature had not altered between the two separate periods over which the herbarium and field data were collected. 5. Synthesis. These results provide the first direct validation of the use of herbarium collections to examine the relationships between phenology and climate when field‐based observational data are not available.

Remote sensing of larch phenological cycle and analysis of relationships with climate in the Alpine region

AbstractThis research aims at developing a remote sensing technique for monitoring the interannual variability of the European larch phenological cycle in the Alpine region of Aosta Valley (Northern Italy) and to evaluate its relationships with climatic factors. Phenological field observations were conducted in eight test sites from 2005 to 2007 to determine the dates of completion of different phenological phases. MODerate Resolution Imaging Spectrometer (MODIS) 250 m 16‐days normalized difference vegetation index (NDVI) time series were fitted with double logistic curves and the dates corresponding to different features of the curves were determined. Comparison with field data showed that the features of the fitted NDVI curve that allowed the best estimate of the start and end of the growing season were the zeroes of its third derivative (MAE of 6 and 4 days, respectively). The start and end of season were also estimated with the spring warming (SW) and growing season index (GSI) phenological models. MODIS start and end of season dates generally agreed with those obtained by the SW and GSI climate‐driven phenological models. However, phenological models provided erroneous results when applied in years with anomalous meteorological conditions. The relationships between interannual variability of the larch phenological cycle and climate were investigated by comparing the mean start and end of season yearly anomalies with air temperature anomalies. A strong linear relationship (R2=0.91) was found between mean spring temperatures and mean start of season dates, with an increase of 1 °C in mean spring temperature leading to a 7‐day anticipation of mean larch bud‐burst date. Leaf coloring dates were found to be best related with mean September temperature (R2=0.77), but with higher spring temperatures appearing to lead to earlier leaf coloring.

Population trends of European common birds are predicted by characteristics of their climatic niche

AbstractTemperate species are projected to experience the greatest temperature increases across a range of modelled climate change scenarios, and climate warming has been linked to geographical range and population changes of individual species at such latitudes. However, beyond the multiple modelling approaches, we lack empirical evidence of contemporary climate change impacts on populations in broad taxonomic groups and at continental scales. Identifying reliable predictors of species resilience or susceptibility to climate warming is of critical importance in assessing potential risks to species, ecosystems and ecosystem services. Here we analysed long‐term trends of 110 common breeding birds across Europe (20 countries), to identify climate niche characteristics, adjusted to other environmental and life history traits, that predict large‐scale population changes accounting for phylogenetic relatedness among species. Beyond the now well‐documented decline of farmland specialists, we found that species with the lowest thermal maxima (as the mean spring and summer temperature of the hottest part of the breeding distribution in Europe) showed the sharpest declines between 1980 and 2005. Thermal maximum predicted the recent trends independently of other potential predictors. This study emphasizes the need to account for both land‐use and climate changes to assess the fate of species. Moreover, we highlight that thermal maximum appears as a reliable and simple predictor of the long‐term trends of such endothermic species facing climate change.

Multiple Climate Signals Characterize Cassiope Mertensiana Chronologies for a Site on Mount Rainier, Washington, USA

This study investigates the nature and strength of the climate signals that characterize an alpine dwarf-shrub, Cassiope mertensiana (mountain bell heather). For the first time, we present six new C. mertensiana chronologies (two growth, two reproduction, 1963-2004; δ13C, δ18O, 1975-2005) based on 14 plants from a subalpine meadow site on Mount Rainier, Washington, USA. Correlation, factor, and multivariate regression analyses revealed that multiple and different climate factors control the chronologies. Annual growth and leaf production are controlled by previous- and current- year growing season and previous-year February temperature. Warm growing season temperatures positively influence soil nutrient uptake rates, while winter temperatures may temporally alter moisture distribution resulting in reduced plant growth. Annual flower bud production is controlled by previous and current-year mean summer, growing season, and annual dewpoint temperature. Annual flower production is controlled by current-year mean spring, summer, growing-season, and annual dewpoint temperature. Increased atmospheric moisture facilitates open stomata, higher photosynthetic activity, and increased reproduction. Previous-year growing season and annual dew-point temperature, fall relative humidity, and temperature control δ18O values, indicating the influence of stomatal conductance on evaporative enrichment. Previous-year spring dewpoint and annual maximum temperature control δ13C values, suggesting the values are a product of photosynthetic rate controlled by temperature or photon flux.

Strengthening recruitment of exploited scallops Pecten maximus with ocean warming

There is evidence that ocean warming has effects on the ecology, including recruitment dynamics, of marine organisms. In association with rising mean spring temperatures in the Irish Sea, a time-series of juvenile scallop Pecten maximus density around the Isle of Man showed a significant increasing trend since 1991. Favorable conditions (warmer water and correspondingly greater food availability) during gonad development can increase scallop gamete production. We examined the possibility that ocean warming has directly increased recruitment of exploited P. maximus around the Isle of Man by enhancing gonad development. From 1991–2007, there was a significant positive correlation between scallop recruitment and mean spring (the main period of gonad development) temperature in the year of larval settlement. Detrended (i.e., accounting for a time effect) recruitment data showed a marginally non-significant correlation to temperature. Gonadal somatic index of adult scallops and temperature were positively correlated. These relationships support the hypothesis that greater gamete production associated with ocean warming may be primarily responsible for observed increases in recruitment success and CPUE in a commercially important shellfish stock.

Note: Effects of spring temperatures on the first egg-laying dates of the nuthatch(Sitta europaea)

I examined long-term changes in the egg-laying dates of the nuthatch (Sitta auropaea) from 1982 to 2007 in the Hrvatsko Zagorje area (northwestern Croatia) in relation to mean spring temperature and to potential climate change effects. Negative correlations between egg-laying date and year, and egg-laying date and local mean spring temperatures (mean of March-April values) were statistically significant. Based on the linear regression slopes, the models indicate that in 2007, nuthatches laid 6.5 days earlier than in 1982. These results suggest that nuthatch breeding in the Hrvatsko Zagorje area responds to climate fluctuations by shifting the date of clutch initiation.

The time series of flowering and leaf bud burst of boreal trees (1846–2005) support the direct temperature observations of climatic warming

The timing of spring phenological events of boreal trees, such as flowering and leaf bud burst, is controlled to a great extent by the ambient air temperature, and these events are already showing an advancement that can be attributed to climatic warming. In this paper we utilised this phenomenon to verify direct observations of climatic warming. We constructed eight phenological time series using observations covering 160 years of the leaf bud burst of two species and of the flowering of six species of native deciduous trees growing in Finland. To eliminate the effect of urbanization on local temperature, we rejected the observations made in densely populated areas. When analyzing the trends in the timing of leaf bud burst and flowering we found an advancement of these phenological events ranging from 3.3 to 11.0 days per century. We then converted the observed phenological trends into temperature trends by using thermal time-type models that link the timing of bud burst and flowering to the temperature conditions during bud development. Warming estimates derived from the phenological trends suggested that the mean spring temperature increase in Finland has been 1.8 °C per century, which is very close to the value of 1.5 °C per century indicated by long-term temperature records.

Disentangling the roles of climate, propagule pressure and land use on the current and potential elevational distribution of the invasive weed Oxalis pes-caprae L. on Crete

Abstract Climatic warming and land use change are likely to facilitate range expansions in invasive plant species, although the ability to predict such changes requires a better mechanistic understanding of the biological limits of populations. The introduced weed Oxalis pes-caprae, a significant pest of cultivation in many Mediterranean-type ecosystems, presents a suitable case study. The species distribution in the Mediterranean Basin closely follows that of olive cultivation, limited to below 600 m; yet its potential to colonise vulnerable areas at higher elevations has yet to be adequately assessed. To investigate the possibility, plant performance was assessed by experimentally sowing O. pes-caprae bulbils along an altitudinal gradient in the Lefka Ori mountains, Crete. The survivorship and bulbil biomass of the resulting plants all declined significantly with elevation, irrespective of soil type, initial bulbil size or seasonal variation. Whilst plants survived vegetatively up to 1400 m, seasonal bulbil productivity, likely to be critical to population viability, exceeded that of the sown bulbil biomass only below 750 m. These data indicate that the current elevation of O. pes-caprae is close to, but not at, its current climatic limit, and that low propagule pressure and scarcity of suitable habitat probably also act to limit the altitudinal distribution. Plant performance was correlated strongly with the duration of spring snow cover. Despite a 2 °C difference in mean spring temperatures in the 2 years of study, the predicted elevational change was only 37 m higher in the milder conditions. Overall, our results suggest that while O. pes-caprae performance is strongly linked to climate and is currently close to its climatic limit on Crete, there is limited scope for further spread unless land use and/or propagule pressure change at higher elevations. For this species, these elements are likely to be more significant drivers of invasion risk than the predicted changes of future climates.

Trends and temperature response in the phenology of crops in Germany

AbstractThe phenology of 78 agricultural and horticultural events from a national survey in Germany spanning the years 1951–2004 is examined. The majority of events are significantly earlier now than 53 years ago, with a mean advance of 1.1–1.3 days per decade. The mean trends for ‘true phases’, such as emergence and flowering, of annual and perennial crops are not significantly different, although more trends (78% vs. 46%) are significant for annual crops. We attempt to remove the influence of technological advance or altered farming practices on phenology by detrending the respective time series by linear regression of date (day number) on year. Subsequently, we estimate responses to mean monthly and seasonal temperature by correlation and regression in two ways; with and without removing the year trend first. Nearly all (97%) correlation coefficients are negative, suggesting earlier events in warmer years. Between 82% and 94% of the coefficients with seasonal spring and summer temperatures are significant. The conservative estimate (detrended) of mean temperature response against mean March–May temperature (−3.73 days °C−1) is significantly less than the full estimate (−4.31 days °C−1), the ‘true’ size of phenological temperature response may lie in between. Perennial crops exhibited a significantly higher temperature response to mean spring temperature than the annual crops.

Laying date of marsh tits Parus palustris in relation to climate change

Increasing evidence suggests that climate change affects bird breeding phenology and other life-history traits of wildlife. This study is based on the mean spring temperatures (February, March, April) and laying dates of first eggs of the marsh tit Parus palustris. We collected data from 1984 to 2004 for the Mokrice area in NW Croatia. Correlation between laying date and mean spring temperatures was significant. The relationship between mean laying date (y) and air temperature (x) can be expressed as y = 44.69 − 2.08x. Results indicate that spring temperatures are a good predictor of timing of laying eggs. Such long-term data could than be used in order to assess the effects on biological systems if human activities influence climate.

Effects of food abundance, density and climate change on reproduction in the sparrowhawk Accipiter nisus

The reproductive success of predators depends on abiotic environmental conditions, food abundance and population density, and food abundance, density and their interactions may respond to changes in climatic conditions. Timing of reproduction by five of the eight numerically most common prey of the sparrowhawk Accipiter nisus advanced significantly since 1971, during a period of temperature increase. There was no evidence that mean laying date or any other reproductive parameter of sparrowhawks changed consistently during the study period 1977-1997. Laying date advanced and percentage of unsuccessful female sparrowhawks decreased with beech mast in the current year, an index of food abundance for avian prey. Mean laying date of sparrowhawks was advanced in warmer springs, and although mean clutch size was not larger in warm than in cold springs, mean brood size of successful pairs and breeding success increased in such springs, showing that sparrowhawks enjoyed a fitness gain when reproducing early. The timing of sparrowhawk reproduction with respect to the peak in abundance of fledgling prey increased, from a good match between mean timing of fledging by prey and maximum demand for food by the predator in 1977, to reproduction occurring later than the peak in fledging prey availability in 1997. The size of the breeding population of sparrowhawks was not predicted by mean spring temperature, the size of the breeding population the previous year or beech mast crop. The size of the post-breeding population was predicted by size of the breeding and post-breeding population the previous year and by the proportion of unsuccessful females the current year. These findings imply that sparrowhawks did not respond to change in climate, although climate changed the timing of reproduction by the main prey species.

Tree-ring growth of silver fir ( Abies alba Mill.) in two stands under different silvicultural systems in central Italy

A preliminary analysis was made of growth trends in two silver fir forests in the Apennines in central Italy. The forests are closely located but were managed differently in the past. The aim was to verify the climatic variation over time, the influence of extreme events on radial growth and the role of silvicultural systems in defining growth response. The two forests have distinct structures due to differing past silvicultural management. The Camaldoli Forest, containing one-storeyed, evenaged, pure silver fir stands, was essentially managed in the past for wood production and featured high plantation density, low to moderate thinning, and clear cutting every 80–100 years. The La Verna Forest includes multi-layered, unevenaged stands that are mixed in with beech and other broadleaves. Increment cores were collected from aged dominant and healthy trees in the two forests. Climatic data were taken from the Camaldoli station and covers the period 1885–1994. All the analysed dendroecological parameters displayed similar patterns and indicated suitable site conditions for the silver fir. Silvicultural systems played an important role in defining growth pattern and rate. In the evenaged system there were higher growth rates and a greater number of pointer years, whereas there were lower growth rates and long, homogeneous development stages in the semi-natural conditions of La Verna. A rising growth trend recorded in the last three decades in both series could be explained by the consistent extension of the growing season due to a significant increase of mean spring and autumn temperatures. No correlation was found with precipitation while significant correlations were found between tree ring growth and February, April and August temperatures. Preliminary results indicated that the silvicultural system does not bias, but just enhances the ability of the species to record the effects of disturbing factors.

Evidence that climate change has caused 'emergence' of tick-borne diseases in Europe?

Even though tick-borne disease systems are highly susceptible to climatic influences, climate change to date is not necessarily the cause of the marked increased incidence of a variety of tick-borne diseases in many parts of Europe over the past two decades. To test for causality, rather than coincidence, we need to examine whether the right sorts of climate change have occurred at the right time and in the right places to account for the observed heterogeneous temporal and spatial patterns of tick-borne disease 'emergence'. Tick-borne encephalitis (TBE) incidence, for example, showed a 3-fold step increase from 1983 to 1986 in Sweden, doubled in 1993 in the Czech Republic, increased even more dramatically in the same year in Lithuania and Poland, but declined markedly in 1997 in Hungary, Croatia and Slovenia. Within each country, TBE incidence has changed to different degrees in different regions. Because other tick-borne diseases, notably Lyme borreliosis, has commonly 'emerged' in parallel with TBE, we should first examine climate variables predicted to have a general effect on tick abundance, which has indeed increased in the past decade. These include temperature and moisture stress, which have seasonally differential impacts. Monthly mean records for 1960-2000 from the UK Climate Research Unit's interpolated global climate surface reveal that mean spring, spring-autumn and winter temperatures have all increased gradually over the past 40 years, but apparently most sharply in the late 1980s, when moisture stress also increased. These climate data do not reveal any obvious differences between sites where TBE did or did not 'emerge', and in Sweden increases in TBE pre-dated the onset of warmer springs and winters. If recorded climate changes cannot yet satisfactorily explain the temporal and spatial patterns of tick-borne disease change in Europe, the impact of biotic factors, such as increases in deer abundance and changing habitat structure, and of socio-political changes following the end of communist rule, demand more detailed quantitative analyses.

Potential Impact of Global Climate Change on Species Richness of Long‐Distance Migrants

Abstract: Little evidence exists demonstrating that global climate change leads to systematic changes in the structure of ecological communities. For avian communities, one would expect warmer winters to lead to declines in numbers of long‐distance migrants if resident birds benefit from warmer winters and impose increasing competitive pressure on migrants. To study the potential influence of global climate change on long‐distance migrants, we correlated the number of all species of land birds and the number and proportion of long‐distance migrants, short‐distance migrants, and residents in 595 grid cells across Europe. We used mean temperature of the coldest month, mean spring temperature, and spring precipitation as measures of climatic conditions in winter and during the breeding period. The number and proportion of long‐distance migrants decreased with increasing winter temperature, decreasing spring temperature, and increasing spring precipitation. We used this spatial relationship between bird community structure and climate in Europe to make predictions about changes in bird communities of the Lake Constance region, Central Europe, between two census periods ( 1980–1981 and 1990–1992 ). Winter temperature in this region increased significantly between the two censuses, whereas spring temperature and precipitation did not change. As predicted from the models, the proportion of long‐distance migrants decreased and the number and proportion of short‐distance migrants and residents increased between the two censuses. The significant declines of the long‐distance migrants in the Lake Constance region are of a magnitude that can be explained by the observed climate change. Our results suggest that increasingly warmer winters may pose a more severe threat to long‐distance migrants than to the other bird groups.

Tree-Ring-Based Spring Temperature Patterns over the Past Four Centuries in Western Himalaya

A network of 12 tree-ring width chronologies of Himalayan cedar (Cedrus deodara) from the western Himalayan region, India, has been used to reconstruct mean spring (March–May) temperature variations back to A.D. 1600. The most conspicuous feature of the temperature reconstruction is the long-term cooling trend since the late 17th century that ended early in the 20th century. The warmest 30-yr mean for the 20th century was recorded during 1945–1974. However, this warming, in the context of the past four centuries is well within the range of natural variability, since warmer springs of greater magnitude occurred in the later part of the 17th century (1662–1691).

ESTIMATING DORMANCY AND SURVIVAL OF A RARE HERBACEOUS PERENNIAL USING MARK–RECAPTURE MODELS

Mark-recapture statistics have rarely been applied to plants, yet they can be useful for estimating plant demographic traits where individuals may be missed or unob- servable. We applied mark-recapture statistics based on an information theory approach to estimate annual probabilities of dormancy in a five-year study of a threatened, perennial plant, the small yellow lady's slipper orchid ( Cypripedium calceolusssp. parviflorum (Sal- isb.) Fernald). The aboveground states of 548 genets in eight patches were monitored over five years. Apparent survival probabilities (f), corrected for dormancy, were calculated. The best-fit model suggested that apparent survival was constant throughout the study for all patches, while dormancy varied additively with time among patches. The mean prob- ability of dormancy was 0.320 6 0.024, with a mean maximum overestimation of 0.067 as calculated using an estimate of the probability of detection. Dormancy typically lasted for no longer than two consecutive years, although dormancy as long as four years was observed. Dormancy displayed a strong covariate relationship with spring frost days, al- though effects of precipitation and mean spring temperature were almost equally strong. Mean apparent survival probabilities were high in each patch ( f5 0.878), but dormancy probabilities varied considerably among patches (d 5 0.188-0.672). Conventional re- sprouting probabilities underestimated apparent survival by a mean difference of 0.288 (range: 0.150-0.589). This novel application of mark-recapture statistics to plant demog- raphy allowed robust survival estimates that accounted for uncertainty due to an unob- servable, dormant life stage.

Models to predict the general yield class of Douglas fir, Japanese larch and Scots pine on better quality land in Scotland

Summary Recent changes in forestry incentives mean that there is potential for an increase in afforestation on better quality agricultural land in Scotland. As a result improved information is required about timber yields from a range of species on better quality sites for production forecasting, financial appraisal, and planning at the local, regional and strategic levels. This paper describes the development of models that enable General Yield Class (GYC) to be predicted from site factors for Douglas fir, Japanese larch and Scots pine. Temporary sample plots were established in stands below 350 m on Land Capability for Forestry class I to V sites. At each location GYC was assessed, as well as the soil, climate and topographic factors which had been demonstrated to influence forest productivity in earlier studies in Scotland. The models, based on a step-wise multiple regression procedure, indicate that mean spring temperature, geomorphic shelter (topex), and crop age are most important in determining the productivity of Douglas fir and Japanese larch. For Scots pine, mean spring temperature, mean winter temperature, and crop age are the most important factors. The models accounted for between 34 and 45 per cent of variation in General Yield Class and are sufficiently precise for estimating mean productivity at regional and national levels.