Facilitative and competitive effects of a N-fixing shrub on white fir saplings

In Sierra Nevada forests, shrubs are considered strong soil moisture competitors with regenerating trees, reducing seedling establishment, and slowing growth. Recent studies, however, suggest that in some circumstances shrubs can facilitate tree establishment and growth by modifying harsh microclimate conditions; increasing acquisition of water, carbon, and/or nutrients via shared mycorrhizal connections; or enhancing soil fertility, particularly under nitrogen-fixing shrubs such as Ceanothus spp. We examined the establishment dates and growth rates and patterns of white fir saplings growing in greenleaf manzanita, whitethorn ceanothus, and bare patches to examine whether establishment was correlated with past wet years, whether saplings growing in ceanothus had nitrogen-enriched foliage or faster growth rates than in the other two patches, and whether saplings in shrub patches experienced competition for light.Sapling establishment was not correlated with high precipitation or heavy snowpack years, suggesting shade-tolerant saplings do not need wet years to become established. Soils under ceanothus were nitrogen enriched, but white fir sapling foliage did not have higher nitrogen concentrations and saplings did not grow faster in ceanothus than in the other two patches. Because growth rates of saplings were comparable in all patch types examined despite significantly different edaphic and abiotic conditions, we inferred that the various competitive and facilitative interactions affecting tree growth are in net balance across the patch types examined. However, competition for light is important—a significant percentage of growth release events occurred after saplings emerged above their host shrubs. Where shrubs are present, shade-tolerant species (i.e., white fir) are favored over drought-tolerant (pine) species. Our results may help interpret changes in understory conditions that are contributing to mixed conifer's compositional shift toward more shade-tolerant species after a century of fire-suppression.     

Susceptibility of red fir and white fir to fir dwarf mistletoe (Arceuthobium abietinum) in California

Fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) is a damaging parasite of true firs (Abies spp.) in California. In the Sierra Nevada Mountains, fir dwarf mistletoe consists of two special forms (formae speciales, f. sp.) which are morphologically similar, but exhibit a high degree of host specificity: A. abietinum f. sp. concoloris whose principal host is Sierra white fir (Abies lowiana) and A. abietinum f. sp. magnificae which only parasitizes red fir (Abies magnifica). Although field observations and cross‐inoculation studies have consistently supported the extreme host specialization demonstrated by these special forms of fir dwarf mistletoe, little quantitative data from mixed red fir/white fir stands infested with fir dwarf mistletoe have been available. Therefore, I sampled 20 mixed conifer stands dominated by red and white fir and infested with f. sp. concoloris (8 stands) or f. sp. magnificae (12 stands) from near Mount Shasta to the southern Sierra Nevada Mountains near Sherman Pass. Infection of red and white fir was evaluated using temporary circular plots (0.012 ha) established around large, severely infected trees and with rectangular transects placed within fir dwarf mistletoe‐infested stands. In each plot and transect, live trees >5 cm in diameter at breast height were assigned a dwarf mistletoe rating (6‐class system). A total of 55 plots and 51 transects were established in the 20 stands, and over 1,900 red firs and 1,700 white firs were sampled. Ninety‐nine per cent of the red firs and 98% of the white firs were infected in stands infested with f. sp. magnificae or f. sp. concoloris, respectively. In contrast, no infection of red fir was observed in stands infested with f. sp. concoloris and no infected white firs were observed in stands infested with f. sp. magnificae. These data provide further support that the special forms of fir dwarf mistletoe are extremely host specific in California.     

Use of modeled photosynthesis and decomposition to describe tree growth at the northern tree line

Growth of subarctic Scots pine (Pinus sylvestris L.) trees was investigated by a combination of process-based models and dendroecological approaches. Tree ring width indices were strongly autocorrelated and correlated with simulated photosynthetic production of the previous year and with organic matter N mineralization of the current year. An autoregressive model, with photosynthesis and N mineralization as external inputs, explained growth of the trees well. However, relationships for the period 1950-1992 differed significantly from relationships for the period 1876-1949; the slope of the regression of tree ring width index and photosynthesis was lower for the 1950-1992 period. Also, the autocorrelation structure of the data changed. First-order autocorrelation decreased and second-order autocorrelation increased from the earlier to the later period. This means that growth is becoming less sensitive to variations in photosynthetic production, whereas the relationships between growth and N mineralization are remaining fairly constant. We postulate that, although photosynthesis has increased in response to increasing CO2 concentrations, tree growth rate cannot parallel the increase in photosynthesis because potential growth rate is limited directly by temperature.     

Adapting a growth equation to model tree regeneration in mountain forests

Management and risk analysis of protection forests depend on a reliable estimation of regeneration processes and tree growth under different site conditions. While the growth of forest stands and thus the average growth of larger trees is well studied and published in yield tables as well as embodied in numerous simulation models, there is still a lack of information about the crucial initial stages of tree growth. Thus, we evaluated juvenile tree growth for different site conditions in the Swiss Alps and developed an approach to model both the early and later stages of growth based on the Bertalanffy equation. This equation is physiologically well founded and requires only two parameter estimates: a maximum tree height and a growth parameter. Data for the parameter estimation were available from studies of tree regeneration at a range of sites in Switzerland: growth patterns of larch (Larix decidua) were available from a high-elevation afforestation experiment. For spruce (Picea abies), data were obtained from a blowdown area in the Alps. The growth equation was fitted to the observed data and we found a good correlation of the fitted curves with the observed data. The parameter estimates were validated with independent data sets. The extrapolated growth curves, calculated with the estimated growth rates, correspond well to the validation data. Thus, it is possible to use the Bertalanffy equation to model both the early and later stages of growth. With this approach, we provide a basis for modelling the growth of juvenile and mature trees of different tree species in mountain forests of the European Alps.     

Synergistic effects of past historical logging and drought on the decline of Pyrenean silver fir forests

The causal factors and effects of forest declines are not well understood in temperate conifer forests. Most studies have focused on climatic and environmental stressors and have obviated the potential role of historical forest management as a predisposing factor of decline. Here, we assess if the recent silver fir (Abies alba) decline observed in the Spanish Pyrenees was predisposed by historical logging and incited by warming-induced drought stress. We analysed a dataset of environmental, structural, and historical variables at the tree and stand level including 32 sites with contrasting degrees of defoliation distributed over 5600 km². We followed a dendroecological approach to reconstruct historical logging and to infer the effects of warming-induced drought stress on growth. The silver fir decline was more severe and widespread in western low-elevation mixed forests dominated by trees of small size and slow growth. These sites were subject to higher water deficits than eastern sites, where late-summer rainfall as the key climatic variable controlling silver fir growth was higher. Declining sites showed more frequent growth releases induced by historical logging than non-declining sites. Historical logging and warming-induced drought acted as long-term predisposing and short-term inciting factors of silver fir decline in the Pyrenees, respectively. We suggest that biomass increases caused by past intense logging affected the vulnerability of silver fir against late-summer water deficit. Future research in declining temperate conifer forests should consider the interacting role of predisposing historical management and inducing climatic stressors such as droughts.     

First-year growth of planted Douglas-fir and white fir seedling under different shelterwood regimes in California

A 17-ha area in the central California Sierra was harvested in 1979 to provide three shelterwoods with residual basal areas of 10, 15 and 20 m²/ha. An adjacent uncut stand of 75 m²/ha was used as a control. During the summer of 1980, seedling performance was assessed along with five microenvironmental characteristics. Maximum air temperature was similar among shelterwoods; minimum air temperature varied by about 3°C. Daily potential evaporation in all shelterwoods was similar and doubledfrom June to July and remained constant through September. Evaporation in the control was half of the shelterwoods. Subsurface soil temperature reached a maximum in August of 24°C in the least-dense shelterwood and 16°C in the control. Subsurface soil moisture was 35% for all treatments in May, but in September was 18% in the least-dense shelterwood and 12% in the control. Daily incident light in June ranged from 76% to 54% of maximum in the least-dense and most-dense shelterwood respectively, and 12% of maximum in the control.Survival of Douglas-fir was greater than 93% in all treatments. However, survival of white fir ranged from 63% to 85% as the overstory density increased; these differences were not significant. The period of rapid white fir mortality occurred later in the summer with increasing canopy cover. Height growth of both species was about 2.3 cm in the control to 3.1 cm under the least-dense shelterwood; however, treatment differences were significant only for white fir, Stem diameter growth of about 1.3 mm in treatments 10 and 15 was significantly greater than the growth of 0.3 mm in treatments 20 and the control. In Douglas-fir shoot: root ratios and biomass tended to increase with decreasing shelterwood. In white fir, the reverse trend was observed for shoot:root ratio but biomass production was similar in each shelterwood. Seedling sshowed the least overall growth in the uncut stand where plant moisture stress reached -19 bar (-1.9 MPa) in Douglas-fir and -22 bar (-2.2 MPa) in white fir.Results indicate that a 10 m²/ha shelterwood provides conditions for successful 1st-year survival and growth of container-grown Douglas-fir, but a 15 m²/ha density is preferable for bare-root white fir. Shoot growth initiation does not seem to be delayed under shelterwoods of up to 20 m²/ha.     

Testing a process-based model of tree seedling growth by manipulating

A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The model was parameterized with data from experiments on seedlings of sycamore (Acer pseudoplatanus L.), Sitka spruce (Picea sitchensis (Bong) Carr.) and young birch trees (Betula pendula Roth.). In these experiments, CO2 concentration ([CO2]) and nutrient addition rate were varied. Parameters quantifying nutrient uptake, translocation and starch synthesis were fitted, based on data from control treatments. Elevated [CO2] and low-nutrient treatments were then used to test the predicted response of growth and allocation against observations. The model accurately predicted total seedling growth in the elevated [CO2] treatments. A response of growth to elevated [CO2] was seen in the birch and sycamore experiments, but not in the Sitka spruce, because of photosynthetic down-regulation. Predictions of allocation were reasonably accurate in the birch and Sitka spruce experiments, but were notably poorer in the sycamore experiments, possibly because of differences in sink strength between root and shoot. In the birch and sycamore experiments, little change in allocation with elevated [CO2] was observed or predicted. This was ascribed to the relative values of K(Tc) and K(Tn), the translocation coefficients that determine the sensitivity of allocation to carbon and nitrogen uptake rates, respectively. Growth and allocation in the low-nutrient treatments were poorly predicted by the model. In Sitka spruce, it was suspected that the photosynthetic parameters measured in August 1994 had been higher earlier in the season, before nutrients became depleted. In sycamore, the discrepancies were thought to relate to differences in sink strength between root and shoot that could not be described by the model.     

Individual-scale responses of five dominant tree species to single-tree selection harvesting in a mixed forest in Hokkaido, northern Japan

We investigated the individual-scale responses of five dominant species (Abies sachalinensis, Acer mono, Tilia japonica, Quercus crispula, and Betula ermanii) to single-tree selection harvesting in a conifer–broadleaved mixed forest in Hokkaido, northern Japan. Using data from stems with a diameter at breast height of ≥12.5 cm, collected during 20 years of monitoring a 6.7-ha stand, we analyzed the effects of harvesting in the neighborhood on tree recruitment and the growth (diameter class transition) and mortality of the residual trees. The effects of harvesting varied considerably among tree sizes and species. Harvesting improved the recruitment of A. mono and B. ermanii, and moderated the negative effect of the initial basal area of the surrounding canopy trees on the recruitment of Q. crispula. Conversely, harvesting limited the recruitment of A. sachalinensis by offsetting the positive effect of the initial basal area of the surrounding canopy trees. The growth of A. sachalinensis and Q. crispula decreased with the initial basal area of the surrounding canopy trees. Harvesting in the neighborhood resulted in an improvement in the growth of the trees of these species only in the smaller size classes. With increasing local harvesting intensity, the mortality of smaller A. sachalinensis trees decreased, whereas the mortality of larger trees increased. These results suggest that differences in the local harvesting intensity, spatial patterns of harvesting, and initial stand structures influence the stand-scale dynamics in response to partial harvesting in the mixed forests of this region.     

Tracing drought effects from the tree to the stand growth in temperate and Mediterranean forests: insights and consequences for forest ecology and management

European Journal of Forest Research - How drought affects tree and stand growth is an old question, but is getting unprecedented relevance in view of climate change. Stress effects related to...     

不同树种幼林生长差异及对土壤营养的影响

通过调查不同树种新造林树高生长量及其林地土壤有机质和速效氮、磷、钾含量,研究其生长及对土壤营养的影响.结果为：光皮桦、四川桤木、楸树、栾树、湿地松6年生树高分别为8.2、7.7、7.4、7.0、5.3 m;不同树种造林后对土壤营养物质含量的提高有明显差异,5个树种造林后效果排序的先后次序为光皮桦、四川桤木、栾木、楸树、湿地松;新造林均表现为造林当年土壤营养含量明显下降,第2年起逐年增加,第3～5年超过造林前水平.     

Variation in surface conductance to water vapor diffusion in peach fruit and its effects on fruit growth assessed by a simulation model

Surface conductance to water vapor diffusion was measured in individual peach fruits (Prunus persica (L.) Batsch) and plotted as a function of fresh fruit mass for four cultivars. Surface conductance increased with fresh fruit mass, but the pattern differed with cultivar, and fruit-to-fruit variation occurred. Relationships between fruit mass and surface conductance were modeled by fitting mathematical equations to the data. The simulation model of Fishman and Génard (1998) was used to study dry mass and water components of fruit growth (1) when surface conductance varied with fruit size or was constant, and (2) when surface conductance values were high, moderate or low with respect to fruit mass. Increased surface conductance with fresh fruit mass resulted in fruit growth cessation. Fruits differing in surface conductance had similar dry mass. However, under well-watered conditions (stem water potential between -1 and -0.2 MPa), the water balance components of growth (osmotic and hydrostatic pressure, water potential and water balance) differed greatly and, as a result, the lower the surface conductance the greater the fresh fruit mass. These differences were buffered under drought conditions (stem water potential between -2.4 and -0.6 MPa).     

坡位对杉木纯林生长的影响

通过对不同坡位7年生杉木纯林生长的调查与研究,结果显示:坡位对杉木纯林各生长指标均有显著影响;林分的平均胸径、树高、冠幅、枝下高、平均单株材积、单位面积木材蓄积量等生长指标一致表现为下坡位>中坡位>上坡位。坡位间以胸径和树高差异最为显著,下坡位林分平均胸径达到10.59 cm,高出中坡位的11.6%,高出上坡位的20.0%;下坡位林分平均树高为7.25 m,高出中坡位的16.7%,高出上坡位的25.4%。下坡位林分的单位面积木材蓄积量要远远高于中坡位和上坡位的,下坡位林分的单位面积木材蓄积量分别高出上坡位的75.1%,中坡位的44.8%。     

An application of Neurogenetic Algorithm System to individual tree growth model

A neural network system with genetic algorithms (Neurogenetic Algorithm System, or NGAS) was employed to develop individual coniferous tree growth models. A multivariable regression model was applied to compare the performance of NGAS. An IBM personal computer with the BioComp System’s software program of NGO was used to execute this comparison. The results indicate that NGAS is more accurate and effective than the conventional regression method in modeling individual tree growth based on the criteria of Sum of Squared Error (SSE), Average Absolute Error (AAE), Mean Squared Error (MSE) and Final Predicted Error (FPE). This study also suggests that individual tree growth may indeed be a non-linear process. Using this flexible neural network system to model individual tree growth can yield satisfactory prediction results.     

DESPOT, a process-based tree growth model that allocates carbon to maximize carbon gain

We present a new model of tree growth, DESPOT (Deducing Emergent Structure and Physiology Of Trees), in which carbon (C) allocation is adjusted in each time step to maximize whole-tree net C gain in the next time step. Carbon gain, respiration and the acquisition and transport of substitutable photosynthetic resources (nitrogen, water and light) are modeled on a process basis. The current form of DESPOT simulates a uniform, monospecific, self-thinning stand. This paper describes DESPOT and its general behavior in comparison to published data, and presents an evaluation of the sensitivity of its qualitative predictions by Monte Carlo parameter sensitivity analysis. DESPOT predicts determinate height growth and steady stand-level net primary productivity (NPP), but slow declines in aboveground NPP and leaf area index. Monte Carlo analysis, wherein the model was run repeatedly with randomly different parameter sets, revealed that many parameter sets do not lead to sustainable NPP. Of those that do lead to sustainable growth, the ratios at maturity of net to gross primary productivity and of leaf area to sapwood area are highly conserved.     

Development and assessment of a gap-type model to predict the effects of climate change on forests based on spatial forest data

A gap-model was modified in order to utilise ground-true forest data to predict the effect of climate change on forests in Finland. The model's resonse to climate change was evaluated by using test scenarios of changing temperature and precipitation in Finland. Model computations indicated that in Southern Finland conifers, Norway spruce in particular, suffered from rapidly increasing temperature (0.5°C in a decade), but Scots pine derived a small benefit from a temperature increase of 0.1°C in a decade. Pendula birch profited by increasing temperature. In Northern Finland all tree species (Scots pine, Norway spruce, Pendula birch and Pubescent birch) used in simulations increased their stand volume and total production due to increased temperature. Precipitation changes had only little effect on stand volume and total production of trees on sites with coarse moraine as soil texture. The effect of soil texture on model performance was examined at a southern site under current climate using moraine, sand and silt as soil textures. Stand volume and total production of coniferous trees remained at a lower level on sand than on moraine soils or on silt. Response of birches to soil texture was similar to that of the conifers, but differences in total production between soil textures remained smaller.     

The effect of different atmospheric ozone partial pressures on photosynthesis and growth of nine fruit and nut tree species

Nursery stock of peach (Prunus persica L. Batsch, cv. O'Henry), nectarine (P. persica L. Batsch, cv. Fantasia), plum (P. salicina Lindel., cv. Casselman), apricot (P. armeniaca L., cv. Tilton), almond (P. dulcis Mill., cv. Nonpareil), prune (P. domestica L., cv. Improved French), cherry (P. avium L., cv. Bing), oriental pear (Pyrus pyrifolia Rehd., cv. 20th Century), and apple (Malus pumula Mill., cv. Granny Smith) were planted in open-top chambers on April 1, 1988 at the University of California's Kearney Agricultural Center located in the San Joaquin Valley (30 degrees 40' N 119 degrees 40' W). Trees were exposed to three atmospheric ozone partial pressures (charcoal-filtered air (C), ambient air (A), or ambient air + ozone (T)) from August 1 to November 17, 1988. The mean 12-h (0800 to 2000 h) ozone partial pressures measured in open-top chambers during the experimental period were 0.030, 0.051, and 0.117 microPa Pa(-1) in the C, A and T treatments, respectively. Leaf net CO(2) assimilation rate decreased linearly with increasing 12-h mean ozone partial pressure for the almond, plum, apricot, prune, pear, and apple cultivars. Stomatal conductances of apricot, apple, almond, and plum decreased linearly with increasing ozone partial pressure. Cross-sectional area relative growth rates of almond, plum, apricot, and pear decreased linearly with increasing ozone partial pressure. Net CO(2) assimilation rate, stomatal conductance, and trunk growth of cherry, peach and nectarine were unaffected by the ozone treatments. Reduced leaf gas exchange probably contributed to ozone-induced growth reduction of the susceptible species and cultivars. Several of the commercial fruit tree species and cultivars studied were relatively tolerant to the ozone treatments.     

杉茶复合经营效应的研究

在对杉茶复合种植模式进行调查的基础上,分析了不同杉木密度对茶树体生长、茶叶产量、品质的影响,并对其经济效益进行测算,提出了合理的杉茶复合种植模式;杉茶复合种植,杉木采用单行南北向种植,株距２ｍ左右,行距１２－１６ｍ;如散生种植,杉木密度控制在３１３－４１７株／ｈｍ＾２时,茶叶产量不受影响。每年每公顷木材生长可增加产值９５０元。     

Use of a simulation model and ecosystem flux data to examine carbon-water interactions in ponderosa pine

Drought stress plays an important role in determining both the structure and function of forest ecosystems, because of the close association between the carbon (C) and hydrological cycles. We used a detailed model of the soil-plant-atmosphere continuum to investigate the links between carbon uptake and the hydrological cycle in a mature, open stand of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at the Metolius river in eastern Oregon over a 2-year period (1996-1997). The model was parameterized from local measurements of vegetation structure, soil properties and meteorology, and tested against independent measurements of ecosystem latent energy (LE) and carbon fluxes and soil water content. Although the 2 years had very different precipitation regimes, annual uptake of C and total transpiration were similar in both years, according to both direct observation and simulations. There were important differences in ratios of evaporation to transpiration, and in the patterns of water abstraction from the soil profile, depending on the frequency of summer storms. Simulations showed that, during periods of maximum water limitation in late summer, plants maintained a remarkably constant evapotranspirative flux because of deep rooting, whereas changes in rates of C accumulation were determined by interactions between atmospheric vapor pressure deficit and stomatal conductance. Sensitivity analyses with the model suggest a highly conservative allocation strategy in the vegetation, focused belowground on accessing a soil volume large enough to buffer summer droughts, and optimized to account for interannual variability in precipitation. The model suggests that increased allocation to leaf area would greatly increase productivity, but with the associated risk of greater soil water depletion and drought stress in some years. By constructing sparse canopies and deep rooting systems, these stands balance reduced productivity in the short term with risk avoidance over the long term.     

Carry-over effects of ozone on root growth and carbohydrate concentrations of ponderosa pine seedlings

Ozone exposure decreases belowground carbon allocation and root growth of plants; however, the extent to which these effects persist and the cumulative impact of ozone stress on plant growth are poorly understood. To evaluate the potential for plant compensation, we followed the progression of ozone effects, with particular emphasis on the development of new roots. Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings were exposed to ozone for 2 years. Following removal of the seedlings from ozone, root growth was assessed to characterize the carry-over effects on new root production, and carbohydrate concentrations were measured to determine if allocation strategies differed among ozone treatments. Four months after removal from ozone, dormant seedlings had significantly lower starch concentrations in stems, coarse roots and fine roots than control seedlings. Following root flushing, starch concentrations in all seedlings decreased, with ozone-treated seedlings containing significantly less starch, sucrose, fructose, glucose and total monosaccharides than control seedlings. There was some evidence that stem starch was mobilized to compensate partially for the lower concentrations of root starch in ozone-treated seedlings; however, there was significantly less new root production in seedlings previously exposed to ozone for 2 years than in control seedlings. Early senescence of older needle age classes, perhaps resulting in inadequate available photosynthate, may be responsible for the reduction in new root production during the year following exposure to ozone. Stored carbohydrate reserves, which were depleted in seedlings previously exposed to ozone, were insufficient to compensate for the ozone-induced reduction in canopy photosynthate. We conclude that there are carry-over effects of ozone exposure on ponderosa pine seedlings, including an enhanced potential for seedling susceptibility to other stresses even in respite years when ozone concentrations are low.