Aim The objectives of this study were to determine the relationships between climatic factors and litterfall in coniferous and broadleaf forests in Eurasia and to explore the difference in litterfall between coniferous and broadleaf forests as related to climate at a continental scale.Location We have used data from across Eurasia. MethodsThe relationships between litterfall and climatic factors were examined using linear regression analysis of a compilation of published data from coniferous and broadleaf forests in Eurasia. ResultsThe relationships between litterfall and climatic factors show that in the temperate, subtropical, and tropical areas, broadleaf forests had higher litterfall than coniferous ones, whilst the opposite was found for boreal forests. Combining all climatic zones, a multiple regression analysis using annual mean temperature (T) and annual precipitation (P) as independent variables gave an adjusted R 2 ( R 2 adj ) of 0.272 for total litterfall in coniferous forests ( n = 199, P < 0.001), 0.498 for broadleaf litterfall ( n = 240, P < 0.001), and 0.535 for combined coniferous and broadleaf litterfall ( n = 439, P < 0.001). The linear models for broadleaf stands have significantly higher coefficients for T and P than those for coniferous ones but the intercepts were similar. Thus, litterfall in broadleaf forests increased faster with T and P than that in coniferous forests. Further, a transformation of temperature and precipitation to relative units showed that a relative-unit change in T had a larger impact than P on total litterfall in broadleaf forests. The results indicate that at a continental scale, climatic controls over litterfall differ between coniferous and broadleaf forests.Conclusions A relative unit change in annual mean temperature has a greater effect on litterfall compared to the same change in annual precipitation across the Eurasian forests. Further, the higher response to T for broadleaf forests indicates a difference in climate control between coniferous and broadleaf forests at a continental scale, and consequently different litterfall responses to climate change. BIOSKETCHChunjiang Liu is a research scientist in the Ecology Centre, Christian-Albrechts University of Kiel. His research interests are focused on the environmental control of ecological processes in forest ecosystems at different geographical scales in the context of global change. The approaches used in his work include field studies, meta-analysis and theoretical simulation.
e f f e r s~In boreal mixedwood forests, aspen (Populus tremuloides) and Des les forets melangees boreales, le tremble (Populus tremuwhite spruce (Picea glauca) commonly grow in mixture. These loides) et l'epinette blanche (Picea glauca) poussent souvent en species may avoid competition through differential shade tolerassociation. Ces especes peuvent probablement eviter d'etre en ance, physical separation of canopies, phenological differences, competition par une tolerance differentielle a l'ombre, par une sep successional separation, and differences in soil resource utilizaaration de l'etage des cimes, par des differences phenologiques, tion. Aspen may also be able to positively affect the growth of white par une separation successionne11e, et par des differences dans l'utilspruce by improving litter decomposition and nutrient cycling rates, isation des ressources pedologiques. Le tremble peut egalement controlling grass and shrub competition, ameliorating environaffecter positivement la croissance de l'epinette en ameliorant mental extremes, and reducing pest attack. These positive relala decomposition de la litiere et les cycles des elements, en contionships likely make mixedespecies stands more productive trolant la competition herbacee et arbustive, en uniformisant les than pure stands of the same species. The evidence regarding the extremes en~ir~Ilnementaux, et en reduisant les attaques d'agents productivity of pure versus mixed aspen/white spruce stands in ravageurs. Cette relation positive semble rendre les peuplements natural unmanaged forests is examined in this paper.d'especes melanges plus productifs que les peuplements purs composes d'une seule espece. L'evidence de la productivite des K~~ T~ mixm; productivity; boreal mixedW&; peuplements purs par rapport aux peuplements melanges tremwhite spruce blelepinette dans les forets naturelles non-amenagees est etudiee dans cet expose.
Photosynthetic light and temperature response curves were measured seasonally in seedlings of white spruce (Picea glauca (Moench.) Voss) grown for two years in the understory of aspen (Populus tremuloides Michx.) or in the open in central Alberta. Light-saturated rate of net photosynthesis, the optimum temperature for net photosynthesis, transpiration rate, photochemical efficiency, and stomatal and mesophyll conductances increased from spring to summer and declined thereafter, whereas dark respiration rate and compensation and saturation points were highest in spring. Depression of photosynthetic parameters was greater in open-grown seedlings than in understory seedlings during the periods in spring and autumn when night frosts were common. Net photosynthetic rates were similar in understory and open-grown seedlings in summer, but they were significantly lower in open-grown seedlings in spring and autumn. Significantly lower transpiration rates and stomatal conductances in open-grown seedlings than in understory seedlings were also observed at 15 and 25 degrees C in the autumn. Shoot and needle growth were less in open-grown seedlings than in understory seedlings. In summer, when irradiances were low in the aspen understory, understory white spruce seedlings maintained a positive carbon balance by decreasing their compensation and saturation points and increasing their photochemical efficiency compared to spring and autumn.
Microclimate and seedling response of planted white spruce Les modifications du microclimat et les rkactions des semis were investigated under four canopy densities (control -a 120-d'Cpinette blanche en plantation ont Ct C CtudiCes sous quatre year old uncut aspenlwhite spruce stand, low and high residual densitCs de couvert forestier (un tCmoin -un peuplement non perdensities of shelterwood canopy, and cl-ut) and three site preps- diameter growth. This study danonstrates how diamktre sous les coupes progressives que dans les coupes h blanc shelterwoods and site preparation can improve the establishet pour le tkmoin. La preparation du sol a fait augment6 la ternment of white spruce. The findings of this study can be applied *ramre d~ sol, diminuC la m o d t C des semis et amtliod la croisto the situations where white spruce establishes in the understory. sance, surtout la croissance en diambtre. Cette Cmde dkmontre comment les coupes progressives et la preparation du sol peuvent Key words: shelterwood, site preparation, white spruce, seedling am6liorer l'ttablissement de l'tpinette blanche. Les rksultats de response, microclimatic conditions. cette Ctude peuvent stre appliquCs 2 des situations 02 1'Cpinette blanche s'Ctablit sous couvert.
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