Zhu Jiao-jun

Comparison of stand structure and growth between artificial and natural forests ofPinus sylvestiris var.mongolica on sandy land

Mongolian pine (Pinus sylvestiris Linnaeus var.mongolica Litvinov) as a valuable conifer tree species has been broadly introduced to the sandy land areas in “Three North” regions (North, northwest and northeast of China), but many problems occurred in the earliest Mongolian pine plantations in Zhanggutai, Zhangwu County, Liaoning Province (ZZL). In order to clarify the reason, comprehensive investigations were carried out on differences in structure characteristics, growth processes and ecological factors between artificial stands (the first plantation established in ZZL in 1950s) and natural stands (the origin forests of the tree species in Honghuaerji, Inner Mongolia) on sandy land. The results showed that variation of diameter-class distributions in artificial stands and natural stands could be described by Weibull and Normal distribution models, respectively. Chapman-Richards growth model was employed to reconstruct the growth process of Mongolian pine based on the data from field investigation and stem analysis. The ages of maximum of relative growth rate and average growth rate of DBH, height, and volume of planted trees were 11, 22 years, 8, 15 years and 35, 59 years earlier than those of natural stand trees, respectively. In respects of the incremental acceleration of volume, the artificial and natural stands reached their maximum values at 14 years and 33 years respectively. The quantitative maturity ages of artificial stands and natural stands were 43 years and 102 years respectively. It was concluded that the life span of the Mongolian pine trees in natural stands was about 60 years longer than those in artificial stands. The differences mentioned above between artificial and natural Mongolian pine forests on sandy land were partially attributed to the drastic variations of ecological conditions such as latitude, temperature, precipitation, evaporation and height above sea level. Human beings’ disturbances and higher density in plantation forest may be ascribed as additional reasons. Those results may be potentially useful for the management and afforestation of Mongolian pine plantations on sandy land in arid and semi-arid areas.

Microclimate regimes following gap formation in a montane secondary forest of eastern Liaoning Province, China

In order to improve the understanding of the role of a canopy opening/gap on the physical environments in a secondary forest in Northeastern China, a case study was conducted in and around a small irregular gap in a montane secondary forest. The secondary forest, which was severely disturbed by human beings about 50 years ago, was dominated by Quercus mongolica and Fraxinus rhynchophyllaan. Temporal variation in photosynthetic photon flux density (PPFD), air temperature (TA) at 10 cm above the ground, soil temperature (TS) and soil water content (SWC) at top-layer (0–15 cm) and sub-layer (15–30 cm) were measured from May to September after the second year since the formation of the small gap (the ratios of gap diameter to stand height were less than 0.5) in 2006 respectively. Results indicated that the highest value of PPFD occurred at the northern edge of the gap, particularly at the beginning of the growing season in May. On sunny days, the highest value of PPFD appeared earlier than that on overcast days. Maximum and mean values of TA were higher in the northern part of the gap, and the minimum values of TA were at the southern edge of the gap. Soil temperature varied obviously in the gap with the range from 1 to 8 °C. Maximum values of TS occurred at the northern part of the gap, which was significantly correlated with the maximum values of TA (R = 0.735, P<0.05). SWC was higher in the top-layer (0–15 cm) than that in sub-layer (15–30 cm), but the difference of them was not significant (p>0.05), which might be attributed to the small gap size and the effects of aboveground vegetations. From these results, the maximum of PPFD in the study area occurred at the northern part of the gap, which was consistent with the results observed in north hemisphere, but the occurrence time varied with the differences of the latitudes. The highest values of air and soil temperatures also occurred in the northern part of the gap because they were affected by the radiation. However, the variation of temperature in July was different from other months due to the influence of gap size. And the values of soil water content were neither higher in the gap in the wet season nor lower in the dry season, which might be affected by the gap size and topography the gap located. The variations of light, soil and air temperatures, and soil moisture in this small irregular gap might be related to the effects of the micro-site, which affects the regeneration of plant species.

Review: effects of wind on trees

Wind not only causes extensive damages to trees in many parts of the world, it also has more subtle effects on the growth and morphology of trees and forest ecology as well. Wind damage to trees has historically been the field of silviculture, but increasing recognition of the importance and complexity of the subject has recently got people involved from many other disciplines. Due to the global climate changes, it is believed that the risk of further and stronger storms is increasing. In order to better understand the effects of wind on individual trees, forest stand and forest ecosystem, and further to practice the management of forests, it is necessary to summarize the research results related to this subject. This review was mostly based on the references from recent researches in the field, especially from the symposium volumes of some international conferences on this subject. The results indicated that there have been significant progresses in the following aspects: 1) the aerodynamic interaction between wind and trees, 2) the mechanics of trees under wind loading and adaptive growth, 3) the trees physiological responses to wind, and 4) the risk assessment of wind damage to forest. However, there are some aspects which may need further studies: 1) wind damage to natural forests, 2) wind-driven gap formation and forest dynamics, 3) the effects of changes resulted from wind disturbances on ecological processes of forest ecosystem, and 4) management for the wind-damaged forests.

Effects of thinning on microsites and natural regeneration in aLarix olgensis plantation in mountainous regions of eastern Liaoning Province, China

In order to understand the effects of thinning on microsite conditions and natural regeneration in the larch plantation, thinning experiment was conducted in a 40-year-oldLarix olgensis plantation in Qingyuan County in eastern Liaoning Province, China in 2003–2004. Five thinning treatments (0%, 10.2%, 19.8%, 29.7% and 40.3% thinned) were designed on the same site. After thinning, canopy openness and the microsite conditions such as photosynthetic photon flux density (PPFD), soil moisture content, and soil temperature were measured in one growing season. Meanwhile, the investigation of natural regeneration was conducted at the end of the growing season. The results showed that the canopy openness increased with the increase of thinning intensities. PPFD and soil temperature and soil moisture content in different soil layers were positively relative with canopy openness after thinning. The richness of regenerating tree species did not significantly increase (p=0.30) after one growing season since thinning, but the regeneration density and frequency of tree species increased significantly (p<0.05). In addition, the number of regenerating tree species increased, and the increment was correlated with the characteristics of individual tree species. The increasing percentage of regenerating seedlings of the shade-intolerant tree species was more than that of shade-tolerant tree species. Among the investigated regeneration species, the biggest response of seedling emergency to the canopy openness wasPhellodendron amurense. This paper confirmed the following conclusions: after thinning, the variety of regenerating tree species was correlative with the characteristics of regenerating tree species, and the distribution of unthinned trees and the site conditions in the investigated larch plantation were the additional factors influencing the regeneration.

Wind profiles in and over trees

One of the most important and frequently studied variable in forests and the most basic element in governing transport processes of airflow is wind speed. The study of wind profile, defined as the change of wind velocity with height, and wind velocity are important because of tree physiological and developmental responses. Generally, wind profiles above the ground or at a canopy surface follow classical logarithm law, but wind profiles in a single tree and in a forest stand are not logarithmic. This paper summarizes the results of wind profile studies within a single tree, in a forest stand, above the forest canopy and in a forest area from recent research in a coastal pine forest. The results demonstrate that: 1) wind profiles with in a single conifer tree crown showed an exponential function with height, 2) wind profiles in forest stands were able to be expressed by attenuation coefficient of wind, 3) wind profiles over a forest canopy could be determined using profile parameters (friction velocity, roughness length and displacement), and 4) for a forest area, the extreme wind speed could be predicted reasonably using the methods developed for the design of buildings. More research will be required to demonstrate: 1) relationships between wind profiles and tree or stand characteristics, 2) the simple methods for predicting wind profile parameters, and 3) the applications of wind profile in studies of tree physiology, forest ecology and management, and the detail ecological effects of wind on tree growth.

Spacing interval between principal tree windbreaks——Based on the relationship between windbreak structure and wind reduction

Relative windspeed reduction was measured behind nine relatively narrow, homogenous tree windbreaks with porosities between 0.13–0.33, and behind 28 combinations of model stubble barriers representing 25 different optical porosities (0.00–0.80). The optimum porosities observed were 0.25 and 0.13 for tree windbreaks and stubble barriers respectively. Based on the relationship between windbreak structure (optical porosity) and wind reduction, the chief indices for determining spacing interval, i.e., the windbreak structure index (δ) and the parameter of microclimate, represented by the problem wind (Lrp), were determined. Additionally, investigations on shelterbelt trees were carried out, and stem-analysis techniques were used, to develop a method for determining the mature height of tree windbreaks (H0). Optimal spacing intervals between windbreaks could be predicted from the indices of a given windbreak structure, percentage of reduction of windspeed desired and tree growth model. A hypothetical example for determining the spacing interval of principal poplar windbreaks is given at the end of this paper. The results can be applied not only to tree windbreak design but also to other plant materials and artificial barriers for wind protection.

Natural regeneration characteristics of Pinus sylvestris var. mongolica forests on sandy land in Honghuaerji, China

Natural regeneration in Mongolian pine,Pinus sylvestris var.mongolica, forest at honghuaerji of China (the original of the natural Mongolian pine, forest on sandy land) was studied in 2004. The total mean values of regeneration indexes were higher in mature stands (more than 80% individual stems were older than 50 years), the maximum of regeneration index reached 29 seedlings·m−2, with lowest values in the younger stand, e.g., in 32-year old and 43-year old stands. The stand age was an important factor determining the natural regeneration, which was the best in the older stands in this investigation (e.g. about 80-year old). The regeneration index seemed not to be closely in relation to canopy openness although Mongolian pine is a photophilic tree species. In each type of gaps, natural regeneration was very well. Regeneration indexes were satisfactory at the south and east edges in the circle gaps; and at the east edge of the narrow-square gaps. Results indicated that Mongolian pine, seedlings could endure shading understory, but it would not enter the canopy layer without gap or large disturbance, e.g., fire, wind/snow damage or clear cutting etc. These results may provide potentially references to the management and afforestation of Mongolian pine, plantations on sandy land in arid and semi-arid areas. Researches such as the comprehensive comparisons on regeneration, structure and ecological conditions and so on between natural Mongolian pine, forests and plantations should be conducted in the future.

Effects of thinning on wind damage inPinus thunbergii plantation

Based on paper of “Theoretical derivation of risk-ratios for assessing wind damage in coastal forest”, wind damage in the pine coastal forest, which was thinned at four levels in December of 1997, was investigated for four successive growing seasons. Besides wind damage, the wind profiles outside and inside the coastal forest stand and the distributions of optical stratification porosity (OSP) were also observed. Based on these data, risk-ratios of wind damage for both individual trees and stands were estimated according to the methods developed in “Theoretical derivation of risk-ratios for assessing wind damage in a coastal forest”. The results showed that risk-ratios of wind damage, which were calculated from the mean height and diameter only and from the combination of wind and stand structure profiles, accurately predicted wind damage in the plantation. Relationships between different thinning ratios and incidence of wind damage showed that stand stability decreased soon after the thinning. This was due to the immediate effects of thinning on increasing the canopy roughness and wind load, and on decreasing the sheltering effects from surrounding trees. However, thinning strategies could improve the stability by long-term effects on growth and development of trees against extreme wind. Only canopy damage was recorded during the experimental period, no stem damage was found, even though the maximum 10-min wind speed outside the coastal forest attained 30.2 m s−1. The results obtained in this study indicate that thinning is the most effective silvicultural strategy available for managing coastal forest despite the increased probability of wind damage soon after thinning.

Theoretical derivation of risk-ratios for assessing wind damage in a coastal forest

Based on the discussion of relationships between thinning and wind damage, and published information, a method for estimating risk ratios of wind damage was developed. Estimations of risk-ratio forPinus thunbergii trees and stands were deduced from stem bending theory and coefficients characterizing wind profile, distribution of branches and optical stratification porosity. The results showed that if the value of constant β in the branch distribution-model equals the attenuation coefficient αs in the wind profile model for a single tree crown, then the parameter H/D1.33 (height over stem diameter cubed) can be used to compare and evaluate the risk-ratio of wind damage for individual trees. The same method can be applied to stands using the coefficient of wind profile in a stand, i.e. attenuation coefficient α, the coefficient from distributions of optical stratification porosity, i.e. extinction coefficient ν, and the parameter D1.33. The application of parameter H/D1.33 and the process of determining risk ratios of wind damage for stands were also given in the paper.

Method of evaluation of response extent of forests to disturbances and its application - a case study of Qingyuan Experimental Station of Forest Ecology, Institute of Applied Ecology, Chinese Academy of Sciences.

Based on the phenomena that disturbances for different forest types are different, an index system for evaluating the response extent of forests to disturbances (REFD) was constructed for Qingyuan Experimental Station of Forest Ecology, Institute of Applied Ecology, Chinese Academy of Sciences. Furthermore, REFD was also quantitatively evaluated for different forest types using the optimal distance method. Using the indices about diversity, productivity, stand structure, ecological function, stand health level, etc, of forest, with the broadleaf-Pinus koraiensis forest as target forest, REFD for eight existing forest types at Qingyuan Experimental Station of Forest Ecology were evaluated via the optimal distance method. The results show that REFD of the old growth forest and the broadleaf mixed forest is 0.317 8 and 0.398 9 respectively, which is the minimum among the eight forest types and with the nearest distance to the target forest. REFD for Mongolian oak forest, Fraxinus mandshurica forest, F. rhynchophylla forest and Juglans mandshuria forest is 0.426 2, 0.487, 0.498 3 and 0.501 6 respectively. However, REFD for Korean pine plantation and larch plantation is 0.635 8 and 0.686 4 respectively, which is the maximum among the eight forest types. These findings imply that the distance between the plantations and the target forest in the mountain regions of eastern Liaoning Province is the farthest.