Simulation of tree species composition and organic matter accumulation in Finnish boreal forests under changing climatic conditions

A model simulating the regeneration, growth and death of trees and the consequent carbon and nitrogen dynamics of the forest ecosystem was applied to determine the effect of expected temperature rise on tree species composition and the accumulation of organic matter in the boreal forest ecosystem in Finland (between latitudes 60°–70° N). In the southern and middle boreal zones a temperature rise of 2–3° C (temperature for 2 x CO₂) over a period of one hundred years increased the competitive capacity of Scots pine (Pinus sylvestris) and birch species (Betula pendula and B. pubescens), and slowed down the invasion by Norway spruce (Picea abies). In the northern boreal zone a corresponding rise in temperature promoted the invasion of sites by Norway spruce. The accumulation of organic matter was promoted only slightly compared to that taking place in the current climatic conditions.A further doubling of temperature (temperature for 4 x CO₂) over an additional period of two hundred years led to the replacement of coniferous stands with deciduous onesin the southern and middle boreal zones. In the northern boreal zone an admixture of coniferous and deciduous species replaced pure coniferous stands with the latter taking over sites formerly classified as tundra woodland. In the southern and middle boreal zones the replacement of coniferous species induced a substantial decrease in the amount of organic matter; this returned to its former level following the establishment of deciduous species. In the northern boreal zone there was no major change in the amount of organic matter such as occurred in the case of the tundra woodland where the amount of organic matter accumulated was nearly as high as in the northern boreal zone.     

Inter-species variation of photosynthetic and xylem hydraulic traits in the deciduous and evergreen Euphorbiaceae tree species from a seasonally tropical forest in south-western China

The objective of the present study was to examine the functional coordination among hydraulic traits, xylem characteristics and gas exchange rates across three deciduous Euphorbiaceae tree species (Hevea brasiliensis, Macaranga denticulata and Bischofia javanica) and three evergreen Euphorbiaceae tree species (Drypetes indica, Aleurites moluccana and Codiaeum variegatum) from a seasonally tropical forest in south-western China. The deciduous tree species were more vulnerable to water stress-induced embolism than the evergreen tree species. However, the deciduous tree species generally had higher maximal rates of sapwood and leaf-specific hydraulic conductivity (K _S and K _L), respectively. Compared with the evergreen tree species, the deciduous tree species, however, possessed a lower density of sapwood and a wider diameter of xylem vessels. Regardless of leaf phenology, the hydraulic vulnerability and conductivity were significantly correlated with sapwood density and mean vessel diameter. Furthermore, the hydraulic vulnerability was positively correlated with water transport efficiency. In addition, the deciduous tree species exhibited higher maximal photosynthetic rates (A _max) and stomatal conductance (g _max), but lower water use efficiency (WUE). Interestingly, the A _max, g _max and WUE were strongly correlated with K _S and K _L across the deciduous and evergreen tree species. These results suggest that xylem structure, rather than leaf phenology, accounts for the difference in hydraulic traits between the deciduous tree species and the evergreen tree species. Meanwhile, our results show that there is a significant trade-off between hydraulic efficiency and safety, and a strong functional correlation between the hydraulic capacity and gas exchange rates across the deciduous and evergreen tree species.     

Phenology and water relations of tree sprouts and seedlings in a tropical deciduous forest of South India

The phenology of sprouts (>1 year old, up to 1.5 m in height) and seedlings (<1 year old) of six woody species (four deciduous, one brevi-deciduous, and one evergreen) was examined during the dry season in a tropical deciduous forest of South India. Xylem water potential (_x), leaf relative water content (RWC; % turgid weight), and xylem specific conductivity (K _S; kg s^–1 m^–1 MPa^–1) of sprouts were measured on two occasions during the dry season. In addition, K _S of seedlings (<1 year old) of one deciduous and one evergreen species was determined to allow comparison with sprouts. _x of deciduous species was significantly higher at the second sampling date and was accompanied by a significant increase in K _S and RWC, while the brevi-deciduous and evergreen species did not show any difference in _x. Seedlings of Terminalia crenulata (deciduous) and Ixora parviflora (evergreen) had significantly lower K _S compared to sprouts, while seedlings of all four deciduous species shed their leaves much earlier in the dry season than did conspecific sprouts. More favorable water relations of sprouts compared to seedlings during the peak of the dry season may explain the lower rates of die-back and mortality of sprouts observed in dry deciduous forests of India.

---

This revised version was published online in May 2005 with corrections to Received-/Accepted-dates.     

Pattern of changes in species diversity,structure and dynamics of forest ecosystems along latitudinal gradients in East Asia

We examined effects of seasonality of climate and dominant life form (evergreen/deciduous, broad-leaf/coniferous) together with energy condition on species diversity, forest structure, forest dynamics, and productivity of forest ecosystems by comparing the patterns of changes in these ecosystem attributes along altitudinal gradients in tropical regions without seasonality and along a latitudinal gradient from tropical to temperate regions in humid East Asia. We used warmth index (temperature sum during growing season, WI) as an index of energy condition common to both altitudinal and latitudinal gradients. There were apparent differences in patterns of changes in the ecosystem attributes in relation to WI among four forest formations that were classified according to dominant life form and climatic zone (tropical/temperate). Many of the ecosystem attributes—Fishers alpha of species-diversity indices, maximum tree height and stem density, productivity [increment rate of aboveground biomass (AGB)], and population and biomass turnover rates—changed sharply with WI in tropical and temperate evergreen broad-leaved forests, but did not change linearly or changed only loosely with WI in temperate deciduous broad-leaved and evergreen coniferous forests. Values of these ecosystem attributes in temperate deciduous broad-leaved and evergreen coniferous forests were higher (stem density was lower) than those in tropical and temperate evergreen broad-leaved forests under colder conditions (WI below 100°C). Present results indicate that seasonality of climate and resultant change in dominant life form work to buffer the effects of energy reduction on ecosystem attributes along latitudinal gradients.     

Intraspecific variation in spring leaf phenology and duration of leaf expansion in relation to leaf habit and leaf size of temperate tree species

Plant Ecology - Spring leaf phenology has been intensively studied in temperate deciduous broad-leaved tree species, but the phenology of evergreen broad-leaved tree species has seldom been focused...     

Photosynthetic capacity and leaf nitrogen decline along a controlled climate gradient in provenances of two widely distributed Eucalyptus species

Climate is an important factor limiting tree distributions and adaptation to different thermal environments may influence how tree populations respond to climate warming. Given the current rate of warming, it has been hypothesized that tree populations in warmer, more thermally stable climates may have limited capacity to respond physiologically to warming compared to populations from cooler, more seasonal climates. We determined in a controlled environment how several provenances of widely distributed Eucalyptus tereticornis and E. grandis adjusted their photosynthetic capacity to +3.5°C warming along their native distribution range (~16–38°S) and whether climate of seed origin of the provenances influenced their response to different growth temperatures. We also tested how temperature optima (T_opt) of photosynthesis and J_max responded to higher growth temperatures. Our results showed increased photosynthesis rates at a standardized temperature with warming in temperate provenances, while rates in tropical provenances were reduced by about 40% compared to their temperate counterparts. Temperature optima of photosynthesis increased as provenances were exposed to warmer growth temperatures. Both species had ~30% reduced photosynthetic capacity in tropical and subtropical provenances related to reduced leaf nitrogen and leaf Rubisco content compared to temperate provenances. Tropical provenances operated closer to their thermal optimum and came within 3% of the T_opt of J_max during the daily temperature maxima. Hence, further warming may negatively affect C uptake and tree growth in warmer climates, whereas eucalypts in cooler climates may benefit from moderate warming.     

Differences in leaf phenology between juvenile and adult individuals of two tree species in a seasonally dry tropical woodland

In temperate forests, juvenile trees anticipate leaf phenology compared to adults, thus avoiding shading and herbivory. This is also expected to occur in seasonal tropical forests due to intense herbivory and shading during the rainy season; however, the anticipation of leaf phenology by juveniles in seasonal tropical forests has yet to be demonstrated. Stem‐succulent species are expected to be prone to juvenile phenological anticipation because these species are able to use water stored in their stems for leaf flushing in the dry season. We investigated this hypothesis by comparing leaf phenology (bud break, leaf expansion) of juveniles and adults of two species with contrasting wood densities in the transition between dry and rainy seasons in a tropical dry woodland. We also investigated the level of light limitation that juveniles experience in the rainy season. Both species exhibited bud break during the dry season, but only expanded their leaves with the occurrence of the first rains. In general, the stem‐succulent species had a more precocious bud break; however, anticipation by juveniles occurred only in the species with more dense wood. Canopy openness was lower than in temperate deciduous forests, but the fact that the full expansion of leaves occurred only with rainfall indicates that bud break in anticipation of canopy closure contributes only to keeping leaf photosynthetic balance from going negative, and not to higher carbon gain. The importance of anticipated budding for escaping herbivory remains an alternative explanation in need of investigation.     

Leaf phenology in relation to canopy closure in southern Appalachian trees

Leaf phenology varies markedly across tree species of temperate deciduous forests. Early leafing in spring may increase light capture and carbon gain prior to canopy closure, allowing saplings to survive in understory sites deeply shaded in midsummer. We quantified sapling leaf phenology for 18 tree species and seasonal variation in understory light availability at three sites along a ridge-slope-cove landform gradient in the Great Smoky Mountains National Park. Early leafing species (e.g., Aesculus flava, Carpinus caroliniana) broke bud an average of 24 d before late leafers (e.g., Magnolia fraseri, Nyssa sylvatica). Canopy closure occurred 14-18 d earlier and summer understory light was on average 63-74% lower on intermediate and mesic sites than on the xeric site. Early leafing species intercepted 45-80% of their growing season photon flux before canopy closure vs. 8-15% for late leafers. However, earlier leafing increased exposure to freezing temperatures by 5.5% per week near the mean time of bud break. Early leafing is strongly correlated with midsummer shade, risk of freezing temperatures, and distribution on mesic sites across a "main spectrum" of 15 deciduous species. Differences in leaf phenology and resultant impacts on spring carbon gain may help determine tree shade tolerance and distribution in southern Appalachian forests.     

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Summary The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P_o) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P₀ values at physiological temperatures (200–300 kN·m^–2) were similar for Antarctic, temperate, and tropical species. A temperature induced tension hysteresis was observed in muscle fibres from some species. Exposure to <0°C in Antarctic and <2°C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the half-times for activation and relaxation of twitch and tetanic tension increased in the order Antarctic>temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q₁₀ values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P₀ iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V_max) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s^–;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s^–1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.Abbreviations ET environmental temperature - m. add. p major adductor profundis - m. add. s. major adductor superficialis - NBT normal body temperature - P ₀ maximum isometric tension - P-V force velocity - SR sarcoplasmic reticulum - T 1/2 a half activation time - T 1/2 r half relaxation time - V _max unloaded contraction     

Growth and photosynthetic responses of <Emphasis Type="Italic">Fagus crenata</Emphasis> seedlings to O<Subscript>3 </Subscript>under different nitrogen loads

To obtain the basic data for evaluating the critical level of ozone (O₃) to protect Japanese deciduous broad-leaved forest tree species, the growth and photosynthetic responses of Fagus crenata seedlings to O₃ under different nitrogen (N) loads were investigated. The seedlings were grown in potted andisol supplied with N as NH₄NO₃ solution at 0, 20 or 50 kg ha⁻¹ year⁻¹ and were exposed to charcoal-filtered air or O₃ at 1.0, 1.5 and 2.0 times the ambient concentration for two growing seasons. The interactive effect of O₃ and N load on the whole-plant dry mass of the seedlings at the end of the second growing season was significant. The O₃-induced reduction in the whole-plant dry mass of the seedlings was greater in the relatively high N treatment than that in the low N treatment. This interactive effect was mainly due to the difference in the degree of O₃-induced reduction in net photosynthesis among the N treatments. The degree of O₃-induced reduction in N availability to photosynthesis was greater in the relatively high N treatment than that in the low N treatment. In conclusion, the sensitivity of growth and photosynthetic parameters of F. crenata seedlings to O₃ become high with increasing amounts of N added to the soil. Therefore, N deposition from the atmosphere should be taken into account to evaluate the critical level of O₃ to protect Japanese deciduous broad-leaved forest tree species.