Sophan Chhin

Growth–climate relationships vary with height along the stem in lodgepole pine

This study tests the hypothesis that ring growth in the upper stem portion of trees is affected by climatic conditions differently than rings formed at breast height (1.3 m). A total of 389 trees from a network of 65 lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta were examined using detailed stem analysis in order to examine interannual patterns of basal area increment and volume increment at different positions along the stem. Growth at lower sections of the bole was mainly driven by temperature and moisture conditions in the seasons prior to the growing season in the year of ring formation, while upper stem growth was more related to conditions during the year of growth, i.e., temperature in the early summer, or moisture in late winter to early spring. This translates into increased allocation of wood to the lower stem when prior late summer conditions are cool and wet, prior winters are mild (warm with little snow) and early summer conditions in the year of ring formation are hot and dry.

Influences of climate on the radial growth of lodgepole pine in Alberta

We examined a network of 17 lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta in the cordilleran forests along the eastern slopes of the Rocky Mountains and in western Cypress Hills, using a dendrochronological approach to identify the principal climatic factors that have influenced the historical, regional-scale pattern of radial growth of lodgepole pine. Correlation and regression analysis of the regional growth-climate relationships showed that radial growth was negatively associated with late-summer temperatures, and positively related to the late- summer precipitation totals from the previous growth season. Radial growth also responded positively to winter and spring temperatures, and was negatively related to late winter-early spring precipitation. The results suggested that the lag in re- sponse to heat and moisture stress, cold and snowy winters, and the length of the current growing season are important de- terminants of the radial growth of lodgepole pine in Alberta.

Climatic response of Picea glauca seedlings in a forest-prairie ecotone of western Canada

We examined radial and height growth-climate relationships of juvenile white spruce in three contrasting microenvironments within a prairie-forest ecotone of western Canada. The three microenvironments were (1) the understory of mature trembling aspen (Populus tremuloides Michx.) groves, (2) the understory of mature white spruce (Picea glauca (Moench) Voss) tree islands, and (3) the open prairie outside the influence of mature trees. Interannual patterns in radial and height growth from each of the three environments were related to the regional climate (temperature and precipitation). The growth-climate relationships identified indicated that growth of juvenile white spruce was conditioned primarily by direct moisture stress during the wettest month of the year, namely June precipitation in the current growing season (t). The growth of juvenile white spruce also responded secondarily to moisture stress indirectly induced by high temperatures in June (t). The results support the general understanding that the southern limit of conifer species in western Canada is controlled mainly by moisture stress either directly by low precipitation or indirectly due to temperature-induced drought stress.RésuméNous avons examiné les relations climat-croissance radiale et croissance en hauteur de jeunes Picea glauca dans trois microenvironnements contrastés de l’écotone prairie—forêt de l’ouest du Canada. Les trois microenvironnements étaient : (1) un sous-bois de bosquets de trembles matures (Populus tremuloïdes Michx.), (2) un sous-bois d’îlots de Picea glauca (Moench) Voss) matures et (3) la prairie ouverte en dehors de l’influence des arbres. Les patrons interannuels de croissance radiale et de croissance en hauteur de chacun des trois environnements ont été reliés au climat régional (température et précipitations). Les relations croissance—climat qui ont été identifiées indiquent que la croissance des jeunes Picea glauca était essentiellement conditionnée directement par un stress de sécheresse pendant le mois le plus humide de l’année, c’est-à-dire les précipitations du mois de juin de l’année de croissance en cours (t). La croissance des jeunes Picea glauca a aussi secondairement répondu au stress hydrique indirectement induit par les fortes températures de juin (t). Les résultats confortent l’interprétation générale de la limite sud des conifères dans l’ouest du Canada, qui est principalement contrôlée par la sécheresse induite directement par les faibles précipitations ou indirectement par les températures élevées.

Dendrochronological Potential and Productivity of Tropical Tree Species in Western Kenya

Abstract This study focuses on tropical tree growth rates in Western Kenya. The dendrochronological potential of each study species was determined by visual examination of rings, and then cumulative growth trajectories for diameter were synthesized for species of sufficient sample size (n ≥ 3), based on ring-width chronologies. The 14 tree species considered were: Acacia mearnsii, Bridelia micrantha, Combretum molle, Croton macrostachyus, Cupressus lustianica, Eucalyptus camaldulensis, Eucalyptus grandis, Eucalyptus saligna, Grevillea robusta, Mangifera indica, Markhamia lutea, Persia Americana, Syzygium cumini, and Trilepisium madagascariensis. The species with the highest dendrochronological potential included Acacia mearnsii, Cupressus lusitanica, the Eucalyptus spp. and Mangifera indica, which are all non-native species that successfully crossdated. The results also indicated that the species with highest dendrochronological potential had strong radial growth synchrony, which was reflected in high inter-tree correlation and (or) high growth variance explained by the first principal component axis. Furthermore, A. mearnsii and E. camaldulensis were sensitive to annual precipitation and moisture index. The species with the lowest dendrochronological potential were Grevillea robusta and Markhamia lutea. In terms of productivity, the three fastest growing species in the study, based on annual diameter increment, were Eucalyptus camaldulensis, Eucalyptus grandis, and Acacia mearnsii. This study also has great potential to extrapolate historical patterns of diameter growth to understanding annual aboveground biomass and carbon dynamics in Western Kenya.

Growth-Climate Relationships of Pinus strobus In the Floodway Versus Terrace Forest Along the Banks of the Red Cedar River, Michigan

Abstract We examined the effects of climate (i.e. temperature, precipitation, moisture index, river discharge) on the radial growth of eastern white pine (Pinus strobus) in two contrasting microhabitats (floodway versus terrace) in relation to an elevational and moisture gradient along the banks of the Red Cedar River, Michigan. We hypothesized that trees growing on the terrace sites would have a greater sensitivity to climatic factors than trees growing in the floodway. Increment cores were sampled and crossdated from dominant and co-dominant trees in the floodway and terrace sites and standardized growth chronologies were developed. Mean sensitivity, standard deviation, percentage of absent rings, and intertree correlation were generally greater for eastern white pine on the terrace compared to the floodway forests. Dendroclimatic relationships were examined with bootstrapped correlation analysis, which indicated that radial growth of eastern white pine in both floodway and terrace sites was negatively associated with summer temperature (i.e. June and July) of the current growing season. Radial growth in both floodway and terrace sites were positively related to current May precipitation, moisture index, and river discharge. Dendroclimatic response of eastern white pine in floodway and terrace sites differed in that the effect of summer moisture stress was more persistent in the terrace sites into later summer (i.e. current July ) whereas floodway sites showed a negative response to prior-year May precipitation and moisture index. Although precipitation and hydrological conditions of the river were generally favorable during the summer months, which appeared to have promoted soil moisture recharge, flooding in early winter (i.e. prior November) had a negative impact on growth in both microhabitats. The effect of winter river discharge was significantly negative in January (t) in the floodway sites compared to the terrace sites.