A rainfall interception model for inhomogeneous forest canopy

The process of rainfall interception by an inhomogeneous forest canopy composed of tree crowns with some gaps among them were considered, and the previous theoretical models of rainfall interception were modified to model an inhomogeneous canopy instead of a statistically homogeneous canopy. The paper deals with the following. First, the process of rainfall interception in tree crowns and that of rainfall in the gaps among them are studied respectively to acquire the average rainfall interception of a forest canopy. Based on the model derived by Liu (1987) and setting the canopy density value, both the relevant partial equations and a formula to estimate rainfall interception were derived. Moreover, the new model was solved through a numerical method and was illustrated with typical values of some ecological factors; three groups of curves were acquired by calculation with the VisualBasic program. A model of rainfall interception by an inhomogeneous forest canopy is classified as a multi-layer model, which is different from previous models (models where all the parameters represent the whole canopy). The results from the model in this paper could be used to determine the relationship between interception and each ecological factor in detail. __________ Translated from Scientia Silvae Sinicae, 2007, 43(3): 8–14 [译自: 林业科学]     

Importance of transitional leaf states in canopy rainfall partitioning dynamics

The temporal dynamics of forest canopy rainfall partitioning are important to forest ecology and management as it influences all subsequent hydrological processes along the rainfall-to-discharge flow path. Despite a growing body of literature on the importance of coupled hydrological–ecological interactions during periodic forest life cycle events, little work has examined how canopy rainfall partitioning varies across transitional leaf states (between the leafed vs. leafless states). This study analyzed a 3 year field monitoring campaign for two tree species in semiarid Iran (Robinia pseudoacacia and Platanus orientalis) to describe rainfall partitioning dynamics across the full-leaf, senescence, leafless, and leafing states. Crown saturation point, canopy storage capacity, free throughfall coefficient and the ratio of wet canopy evaporation rate to mean rainfall intensity were related to decreases/increases in plant area index and canopy closure. The high variability of rainfall partitioning observed in this study highlights the importance of transitional leaf states in the temporal characterization of water inputs to forest surfaces and boundary layer.     

Predicted models for potential canopy rainfall interception capacity of landscape trees in Shanghai,China

This study aimed to build urban green space with environmental functions (e.g., canopy interception of rainfall) and adjust hydrographic balance to some extent for forecasting the potential canopy rainfall interception capacity of landscape trees and the effects on rainfall distribution. The effects of urban green space on interception and runoff reduction have been conceptualized, but not quantified. Therefore, the leaf area index and the water storage abilities of 17 kinds of landscape trees in common use were measured, at Shanghai, and canopy rainfall interception capacity was calculated using the interception formula. The predicted rainfall interception capacity models were established choosing tree morphological characteristics (diameter at the breast height, height, and crown width) as variables. The model test showed that the errors of 12 models were less than 5% between the predicted and the measured data and the errors of four models were within 5 and 10%, with the error for only one model being between 10 and 11%. Also, the study indicated that conifer trees were able to hold more rainfall compared with broad-leaved trees per unit area (k). The results showed that these models could effectively predict the potential capacity of canopy rainfall interception for landscape trees in Shanghai area and were beneficial for species selection in constructing plant communities, aiming to improve the rainfall interception capacity of urban green space.     

Relationship between annual rainfall and interception ratio for forests across Japan

Several previous studies in Japan have examined differences in rainfall interception amounts induced by differences in forest properties by comparing the annual rainfall interception ratios (annual rainfall interception divided by annual rainfall) from various sites without considering variations in meteorological conditions between sites. Rainfall interception actually depends on meteorological conditions as well as forest properties. This study examined variations in the annual interception ratio relating to the variation in annual rainfall, which would be the primary factor relating to the interception ratio, across Japan with the use of a rainfall interception model assuming the same forest properties (i.e., the canopy storage capacity, canopy closure, leaf area index (LAI), and the bulk coefficient for sensible heat transfer). The ratio ranged between 0.12 and 0.24 across Japan and was highly correlated to annual rainfall. This indicates that considering the variation in annual rainfall is critical for assessing the difference in rainfall interception amounts induced by forest properties. We reconsidered the results of previous studies in Japan that compared annual interception ratios between sites with different forest properties: (i) there is no clear difference in interception amounts between broadleaf and coniferous forests and (ii) there is a positive correlation in stem density and interception amounts for coniferous forests. These results still held when considering differences in annual rainfall between sites.     

Shoot structure,light interception,and distribution of nitrogen in an Abies amabilis canopy

We studied the effects of variation in shoot structure and needle morphology on the distributions of light and nitrogen within a Pacific silver fir (Abies amabilis (Dougl.) Forbes) canopy. Specifically, we investigated the role of morphological shade acclimation in the determination of resource use efficiency, which is claimed to be optimal when the distribution of nitrogen within the canopy is directly proportional to the distribution of intercepted photosynthetically active radiation (PAR). Shoots were collected from different heights in the crowns of trees representing four different size classes. A new method was developed to estimate seasonal light interceptance (SLI, intercepted PAR per unit needle area) of the shoots using a model for the directional distribution of above-canopy PAR, measurements of shoot silhouette area and canopy gap fraction in different directions. The ratio SLI/SLI(o), where the reference value SLI(o) represents the seasonal light interceptance of a spherical surface at the shoot location, was used to quantify the efficiency of light capture by a shoot. The ratio SLI/SLI(o) doubled from the top to the bottom of the canopy, mainly as a result of smaller internal shading in shade shoots than in sun shoots. Increased light-capturing efficiency of shade shoots implies that the difference in intercepted light by sun shoots versus shade shoots is much less than the decrease in available light from the upper to the lower canopy. For example, SLI of the five most sunlit shoots was only about 20 times greater than the SLI of the five most shaded shoots, whereas SLI(o) was 40 times greater for sun shoots than for shade shoots. Nitrogen content per unit needle area was about three times higher in sun needles than in shade needles. This variation, however, was not enough to produce proportionality between the amounts of nitrogen and intercepted PAR throughout the canopy.     

Light interception and partitioning between shoots in apple cultivars influenced by training

The effect of two training systems (Central Leader with branch pruning versus Centrifugal Training with minimal pruning, i.e., removal of fruiting laterals only) on canopy structure and light interception was analyzed in three architecturally contrasting apple (Malus domestica Borkh.) cultivars: 'Scarletspur Delicious' (Type II); 'Golden Delicious' (Type III); and 'Granny Smith' (Type IV). Trees were 3D-digitized at the shoot scale at the 2004 and 2005 harvests. Shoots were separated according to length (short versus long) and type (fruiting versus vegetative). Leaf area density (LAD) and its relative variance (xi), total leaf area (TLA) and crown volume (V) varied consistently with cultivar. 'Scarletspur Delicious' had higher LAD and xi and lower TLA and V compared with the other cultivars with more open canopies. At the whole-tree scale, training had no effect on structure and light interception parameters (silhouette to total area ratio, STAR; projected leaf area, PLA). At the shoot scale, Centrifugal Training increased STAR values compared with Central Leader. In both training systems, vegetative shoots had higher STAR values than fruiting shoots. However, vegetative and fruiting shoots had similar TLA and PLA in Centrifugal Trained trees, whereas vegetative shoots had higher TLA and PLA than fruiting shoots in Central Leader trees. This unbalanced distribution of leaf area and light interception between shoot types in Central Leader trees partly resulted from the high proportion of long vegetative shoots that developed from latent buds. These shoots developed in the interior shaded zone of the canopy and therefore had low STAR and PLA. In conclusion, training may greatly affect the development and spatial positioning of shoots, which in turn significantly affects light interception by fruiting shoots.     

侧柏栎类混交林林冠截留模拟研究

林冠截留能力是反映森林与水关系的一个重要指标,该研究充分考虑林冠结构特征与降雨特性,采用机械布样的方法,对侧柏栎类混交林林分内的3种主要水源保护林树种生长季的降雨再分配特点进行了研究。结果表明:3种树种生长季场降雨的林冠截留量都表现出随降雨量的增大而增大,截留率随降雨量的增大而减少,在降雨初期下降幅度最大,以后趋于平稳。干流量在低雨量级时随降雨量的增加而增大,但其增加幅度有限,干流率起初也均随林外降雨量的增加而呈增加的趋势。透雨量随林外降雨量的增大而增大,透雨率逐渐增大,但当林外降雨量增大到一定时透雨率基本不变。3个树种的截留量、干流量、穿透降雨量林外降雨量均呈线性相关。该文采用谢春华等的林冠截留模型对3种水源林树种进行模拟,模拟误差为11%左右,基本上可以满足林冠截留模拟需要。     

Role of canopy interception on water and nutrient cycling in Chinese fir plantation ecosystem

The role of canopy interception on nutrient cycling in Chinese fir plantation ecosystem was studied on the basis of the position data during four years. Results indicate that the average canopy interception amount was 267.0 mm/year. Canopy interception play a significant role in water cycle and nutrient cycle processes in ecosystem, and was an important part of evaporation from the Chinese fir plantation ecosystem, being up to 27.2%. The evaporation from the canopy interception was an important way of water output from ecosystem, up to 19.9%. The flush-eluviation of branches and leaves caused by canopy interception brought nutrient input of 143.629 kg/(hm² · year), which was 117.2% of the input 63.924 kg/(hm² · year) from the atmospheric precipitation. The decreased amount of 80.1 mm precipitation input caused by canopy interception reduced the amount of rainfall into the stand surface and infiltration into the soil, reduced the output with runoff and drainage, and decreased nutrient loss through output water. Therefore, the additional preserve of nutrient by canopy interception was 8.664 kg/(hm² · year). __________ Translated from Scientia Silvae Sinicae, 2006, 42(12): 1–5 [译自: 林业科学]     

Drought-dependent responses of photosynthesis,transpiration and water use efficiency of Japanese cypress and Japanese red pine seedlings

This study was conducted to investigate the potential for modifying drought tolerance of Japanese cypress (Chamaecyparis obtusa Endl.) and Japanese red pine (Pinus densiflora Sieb. et Zucc.). Three-year-old seedlings were controlled for five-months at three different soil water potentials ({ie73-1}). Japanese cypress exposed to high {ie73-2} was able to maintain higher photosynthesis (Ph_n), transpiration (Tr) and stomatal conductance to H₂O (gH₂O) in comparison to low {ie73-3} pretreatments, however, there was no significant difference in Ph_n for Japanese red pine. Soil water potential at the threshold from the maximum to limited Ph_n was higher in high {ie73-4} pretreatments than in low {ie73-5} pretreatments. Net photosynthesis, Tr and gH₂O decreased more rapidly in high {ie73-6} pretreatments than in low {ie73-7} pretreatments. Transpiration decreased more significantly than Ph_n, thus, resulted in increased water use efficiency. All these factors are likely to result in significant improvements in the drought tolerance. Japanese red pine seems more drought-tolerant than Japanese cypress. Japanese cypress is suitable to soil of −0.05 MPa water potential, and Japanese red pine is suitable to −0.16 MPa and even dryer soils.     

不同密度对福建柏林下植物和土壤肥力变化研究

根据对10年生不同造林密度福建柏人工林林下植被生长状况调查和土壤理化性质的测定,结果表明,随福建柏人工林造林密度增大,林下植被高度、覆盖度和生物量减少,土壤物理性质不良,土壤养分含量降低。福建柏人工林生长过程中要经常调整密度以促进林下植被生长,从而改善土壤理化状况,提高土壤肥力。     

林冠截留对杉木人工林生态系统物质循环的影响

根据1999-2002年连续4年的观测数据,对林冠截留在杉木林生态系统物质循环中的作用进行研究.结果表明:每年林冠截留降雨量267.0 mm; 林冠截留蒸发散量占杉木人工林总蒸发散量的27.2%,林冠截留水分的物理蒸发量占杉木林集水区水分输出的18.97%;林内净降水的营养物质为143.329 kg·hm-2a-1,比冠上大气降水输入的63.924 kg·hm-2a-1多74.905 kg·hm-2a-1,增加了117.2%; 林冠截留减少了到达林地表面和入渗土壤的水分,减少了集水区地表水和土壤漏水的输出,从而减少了营养物质的输出,可见,林冠截留是系统保存营养物质的重要机制之一.     

人工同龄纯林理论郁闭度测定计算的研究

通过人工同龄纯林树冠面积与林地面积的相关比例关系，推导，计算出人工同龄纯林林木品字形排列和矩形排列，且株行距不同的林分理论郁闭度。使用者在使用时，只要根据林木的不同排列方式，株行距，树冠半径长，即可计算出相应的理论郁闭度值，解决了人工同龄纯林在一定范围内理论郁闭度的测定计算问题。     

Tree water use and rainfall partitioning in a mature poplar-pasture system

Traditionally, poplars (Populus) have been planted to control erosion on New Zealand's hill-slopes, because of their capacity to dry out and bind together the soil, by reducing effective rainfall and increasing evapotranspiration and soil strength. However, the effect of widely spaced poplars on the partitioning of soil water and rainfall has not been reported. This study determined rainfall partitioning for 18 mid-spring days in a mature P. deltoides (Bart. ex Marsh, Clone I78)-pasture association (37 stems per hectare, unevenly spaced at 16.4 +/- 0.4 m) and compared it with a traditional open pasture system in grazed areas of a hill environment. Tree transpiration was measured by the heat pulse technique. A time-driven mathematical model was used to set a zero offset, adjust anomalous values and describe simultaneous sap velocity time courses of trees. The model showed that daylight sap flow velocities can be represented with a nonlinear Beta function (R(2) > 0.98), and differences in the parameters representing the initiation, duration and conformation of the sap velocity can be tested statistically to discern tree transpiration differences during the day. Evapotranspiration was greater for the poplar-pasture association than for the open pasture (2.7-3.0 versus 2.2 mm day(-1)). The tree canopy alone contributed 0.92 mm day(-1) as transpiration and 1.37 mm day(-1) as interception, whereas evapotranspiration of the pasture understory was only 0.4-0.6 mm day(-1). Despite the higher water use of the poplar-pasture association, soil water in the 0-300 mm soil stratum was higher than, or similar to, that of the open pasture. Tree shading decreased evapotranspiration and pasture accumulation under the trees.     

Distribution of lignin and lignin precursors in differentiating xylem of Japanese cypress and poplar

Lignin is an integral component of the cell wall of vascular plants. The mechanism of supply of lignin precursors from the cytosol into the cell wall of differentiating xylem has not yet been elucidated. The present study showed that a certain amount of coniferyl alcohol glucoside (coniferin) occurred in the differentiating xylem of Japanese cypress (Chamaecyparis obtusa), as previously reported in gymnosperms. Coniferin content peaked in the early stages of secondary wall formation and decreased during lignification. In contrast to gymnosperms, coniferin content was limited in the differentiating xylem of poplar (Populus sieboldii × Populus grandidentata). Moreover, coniferyl alcohol was not detected in all specimens. In the differentiating xylem of poplar, a higher amount of sinapyl alcohol occurred than glucoside (syringin). However, the phloem contained syringin and not sinapyl alcohol. The sinapyl alcohol content in the xylem peaked in the cells with ceasing cell wall formation, and decreased gradually towards the boundary of the annual ring, where the lignin content kept increasing. Sinapyl alcohol in the differentiating xylem of poplar may be used for the lignification of the xylem.     

Evapotranspiration and deep percolation of a small catchment with a mature Japanese cypress plantation

Quantification of hydrological components was conducted in order to clarify the water budget, especially deep percolation (D) into underlying rock, of a small headwater catchment covered by an old Japanese cypress plantation. Precipitation (P), canopy interception (E _i), soil evaporation (E _s) transpiration (E _t), and runoff (R) were observed for 1 year in a 0.41-ha catchment in southern Kyushu, Japan. E _i was calculated from P, throughfall and stemflow measurements, and E _s and E _t were measured using evaporimeters and heat pulse sensors, respectively. From these observations, deep percolation (D) under steady state condition into underlying sedimentary rock was estimated. As for the annual water budget, almost half of P was R and one-third was evapotranspiration (E), which was the sum of the E _i, E _s and E _t. E _i was almost the same magnitude as predicted for an old conifer plantation modeled by Komatsu et al. (J Hydrol 336:361–375, 2007b), but E _t was lower compared to the model. E was not comparable to water loss in the catchment (P minus R). Therefore, D was estimated as a quarter of P and was slightly higher compared to previously reported values for sedimentary rock catchments.     

Influence of ground flora on Fraxinus mandshurica seedling growth on abandoned land and beneath forest canopy

A better understanding of root/shoot interactions influencing seedling growth on abandoned land could yield insight into seedling regeneration and restoration of the abandoned lands. Field work had been conducted for 2 years (2008–2009) to investigate the impacts of neighbouring plants on Manchurian Ash (Fraxinus mandshurica) seedling growth under the canopy of an old secondary forest and on the abandoned land exposed to full solar radiation in North-eastern China. Four different interaction treatments were designed for the study: neither shoot nor root interaction, shoot interaction only, root interaction only, and both shoot and root interaction. The presence of either the shoots or roots of neighbours had a competitive effect, reducing the growth of the target seedlings at each site. The total competitive effect of roots and shoots of neighbouring plants was significantly less than the sum of root and shoot competition separately on the abandoned land, but this difference was not significant beneath the forest canopy. Root competition was more restraining than shoot competition on the abandoned land. Target seedlings adjusted their root morphology and growth rates in response to the competitive effects from different parts of the neighbouring plants. Our results indicated that the root:shoot ratios of the target seedlings at the end of the experiment were affected by neither initial tree size nor the competition from either above- or belowground at either site. The results also highlight the importance of reducing root competition in boosting seedling regeneration and forest rehabilitation on the abandoned land.     

Effects of root zone trenching on soil nitrogen dynamics in Japanese cedar and cypress plantations

The effects of root exclusion and planted tree species on soil nitrogen (N) dynamics were examined at two plantations, one planted with Japanese cedar and the other with Japanese cypress. We set up ten 1 × 1 × 0.2-m-deep trenched sites and ten untrenched control sites at each plantation. We measured the pool size and leaching of inorganic N at each site for 2 years and the net N mineralization 1 and 2 years after trenching. Despite similar soil conditions, the cedar plantation showed higher net N mineralization than the cypress plantation. Stopped tree uptake of N was expected to cause an increased pool size and leaching of inorganic N at the trenched sites. Nevertheless, we found no significant increase in those variables at both plantations. The trenched cypress sites showed no decrease in the net N mineralization during the 2 years after trenching. However, the net nitrification at the trenched cypress sites increased remarkably at the deeper horizons in comparison with that at the control sites. Enhanced nitrification might result from improved ammonium availability through root exclusion. Net N mineralization at the trenched cedar sites decreased more than 60% compared with that at the control sites 2 years after trenching. Higher nitrification potential at the cedar plantation and enhanced nitrification potential at the trenched cypress sites never resulted in increased leaching of N, due to added fine root litter which acted as an immobilization agent for excess N, thus preventing N loss.     

洞庭湖区防浪林林分林冠结构的研究

对洞庭湖区河洲、滩地上的不同林龄的旱柳、杨树防浪林、芦苇林进行了标准地调查,选取标准株(地),对其茎杆、枝条、叶片的空间分布进行了测定,通过对其差异进行比较分析,旨在间接测定不同防浪林的防浪效益的差异。