Forest canopy cover and canopy closure: comparison of assessment techniques

The article, in relation to the importance of canopy cover as stand density and biodiversity indicator, describes the main related field measurement techniques. In particular the authors emphasize the distinction between canopy cover and canopy closure when forest cover is usually measured through the current techniques. After a conceptual clarification the study focuses on the comparison of three ground-based canopy cover estimation techniques and two ground-based canopy closure estimation techniques, analyzing the data collected in a test carried out on Alpine stands. As expected, the results indicate that some techniques [GRS densiometer, visual estimation and hemispherical photographs (HP) assessed with a narrow angle of view] are more suitable to measure canopy cover, while others (spherical densiometer and HP with a wide angle of view) are more adapted to estimate canopy closure. In general, the techniques that use a wide angle of view tend to overestimate the canopy cover.

基于树冠投影判别分析的林分郁闭度测定

采用任意二值图面积测定为方法,以Word产生不同复杂程度的二值图为数据源,对非监督分类、监督分类、像素统计法测定林分郁闭度的方法进行对比分析.结果表明:非监督分类、监督分类、像素统计法对林分郁闭度的测定结果均偏大,监督分类、像素统计法对林分郁闭度测定的精度较非监督分类法测定的要高.像素统计法操作简单、测算速度快、准确程度高,是一种通过树冠投影法测定林分郁闭度的有效方法.     

Role of topography, canopy structure, and floristics in nest-site selection and nesting success of canopy songbirds

Although oaks (Quercus spp.) have historically dominated many forests in eastern North America, forest composition is changing due to anthropogenic impacts on disturbance regimes. Silvicultural practices, such as partial harvesting, are one component of management to promote oak regeneration. From 2007 to 2009 our research examined nest-site selection and nesting success for a guild of five canopy songbirds in upland mixed-oak forests in southeastern Ohio, USA. We monitored >700 nests across three state forests in both open canopy shelterwood stands harvested to approximately 50% stocking, and closed-canopy mature second-growth. Habitat attributes, including topography, canopy structure, and floristics, were measured at nest sites and random plots ?100 m from nests representing microhabitat available within the territory. Canopy songbirds selected specific topographic microclimates: Eastern Wood-pewees (Contopus virens) nested on xeric ridgetops, Blue-gray Gnatcachers (Polioptila caerulea) favored valleys, and Cerulean Warblers (Dendroica cerulea) preferred productive northeast-facing slopes. Nest sites differed among species in terms of concealment, nest support, topographic position on the slope, and basal area of trees >38 cm dbh. Four of the five focal species selected Quercus alba as the nest substrate more than twice as much as available, and three species avoided Quercus rubra. Daily survival rates of nests were negatively associated with basal area of red oak species (both Quercus velutina and Q. rubra) for several species individually and across the canopy-nesting guild. Additional factors related to success included time of season for Eastern Wood-pewees, nest age for Cerulean Warblers, and concealment and size of the support branch for Scarlet Tanagers (Piranga olivacea). In the long-term management for oak regeneration could benefit canopy songbirds, but our results indicate that white oaks, especially Q. alba, may be preferable to red oak species.     

Optimality and nitrogen allocation in a tree canopy

Physical and functional properties of foliage were measured at a variety of microsites in a broad-leaved Nothofagus fusca (Hook. f.) ?rst. canopy. The light climate of the foliage at these sites was monitored for 39 days in the late spring and early summer with in situ sensors. Foliage nitrogen content (N), mean leaf angle, and gas exchange characteristics were all correlated with the amount of light reaching the microsites during foliage development. Foliage N content on a leaf area basis ranged between ~1 and 2.5 g N m(-2) and was highest at the brightest sites. Light-saturated photosynthetic rates ranged between ~4 and 9 micro mol m(-2) s(-1), increasing from the darkest to brightest sites. A biochemical model of photosynthesis was fitted to foliage characteristics at the different microsites and used to integrate foliage assimilation among the sites over 39 days. The actual arrangement of foliage physiological characteristics in the observed microsites led to higher total canopy rates of net assimilation than > 99% of the combinations of observed foliage characteristics randomly assigned to the observed microsites. Additional simulations first related the maximum rates of electron transport (J(max)), ribulose bisphosphate turnover (V(c,max)), and dark respiration (R(d)) of Nothofagus fusca foliage to nitrogen content and then allowed foliage N (and consequently leaf gas exchange characteristics) to vary across the canopy. The observed N allocation pattern results in greater total canopy assimilation than uniform or > 99% of the simulations with random distributions of N among the microsites (constrained so that the total N allocated was equivalent to that observed in the microsites). However, the observed pattern of N allocation places less N in the brightest microsites and results in substantially less total assimilation than a simulated canopy in which N was allocated in an optimal manner where the N distribution is such that the partial derivative of leaf assimilation (A) with respect to leaf nitrogen content, partial differential A/ partial differential N, is constant among microsites. These results suggest that other factors such as wind or herbivory reduce the integrated assimilation of high-N foliage relatively more than lower-N foliage and that a partial differential A/ partial differential N optimality criteria based only on formulations of leaf gas exchange overestimate canopy assimilation.     

New sampler for dry deposition in forest canopy

A new type of sampler for dry deposition in a forest canopy was designed and tested to confirm its usefulness. The new sampler is made of Teflon chips packed in a nylon net, and tied on a rod like a branch in the canopy. The validity and characteristics of the new sampler were checked by comparing it with the conventional bucket sampler and the foliar extraction method using hinoki (Chamaecyparis obtusa) trees. The comparison between the deposited amounts on the dummy branch and those on the bucket indicates that the dummy could trap gaseous matter more effective than the bucket. From a comparison with the foliar extracting method, it is concluded that the trapping of particulate matter by the new dummy branch is comparable to that of natural needle leaves. However, its efficiency for gaseous matter is relatively small. This disadvantage should be improved by applying other materials to the dummy. Moreover, it is found that the uptake of gas especially SO₂ through the stomata is an important point in the discussion about dry deposition. To evaluate the amounts of dry deposition in the forest canopy more precisely, combination with the additional method should be useful. This study was supported in part by a grant-in-aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan.     

郁闭后杨树林下养鸡效益分析

研究了郁闭后杨树林下养鸡对林木生长、土壤肥力的影响及其经济效益。结果表明：在郁闭后的杨树林下套养本地鸡种2年后,杨树胸径、树高和蓄积分别比对照提高6.8%、7.1%和20.6%,6年生杨树蓄积增加14.2 m3/hm2。不同土层土壤的各主要养分含量均有所提高,其中以速效N的含量提高最大,上土层提高186.3%,中土层提高296.5%;其次是上土层的速效P含量提高了50.5%;不同土层土壤有机质、全N、速效K含量均提高11.5%～26.3%不等。在不计林木增产收入、不支付地租的前提下,年均利润达22 237.5元/hm2,纯养殖投资回报率为25.8%;支付1 500元/（hm2.年）的地租成本后,还有20 737.5元/hm2的年均利润,套养2年的总利润为41 475元/hm2。因此,在郁闭的杨树林下养鸡是一种很好的＂林禽＂模式,适合在洞庭湖区郁闭后杨树林下大面积推广。     

Planting mahogany in canopy gaps created by commercial harvesting

Attempts at natural forest management of mahogany (Swietenia macrophylla King) have so far met with limited success, whilst many plantations are beset by the shoot borer Hypsipyla spp. In this paper we present preliminary results of an approach to enrichment planting that aims to balance economic returns (rapid growth and good silvicultural form) with intervention costs and changes to forest structure. Mahogany seedlings were planted in gaps created by selective timber harvesting and that ranged in vertical projected area from 91 to 542 m² (mean = 257 m²). Seedlings grew within the matrix of gap regrowth, with limited control of competing vegetation. Sixty-one percent of seedlings had survived by 4.4 years (equivalent to an annual mortality rate of 10.5% year⁻¹), and had reached a mean height of 4.5 m. Stocking levels of mahogany were similar to that of naturally regenerated commercial species in unplanted gaps of the same age, but mahogany seedlings were significantly taller. The incidence of shoot borer attack on mahogany stems was relatively low (54.7%), but, more importantly, most damaged stems (58%) responded by producing a single replacement leader. The cost of the proposed methodology (US$ 94 per gap over 4.4 years) was low compared to the high value of mahogany timber relative to other species in the forest. The implications of planting mahogany in gaps for forest management and the potential benefits to conservation of the species are considered.     

Effects of slope and canopy trees on light conditions and biomass of dwarf bamboo under a coppice canopy

Dwarf bamboo, Pleioblastus chino, grows extensively in abandoned coppice woodlands on the Kanto Plain in central Japan and suppresses other understory plants. In order to clarify the factors determining the growth of P. chino, we considered the effect of light conditions under a coppice canopy and examined its relationship with slope aspect, slope angle, and basal area of the trees. The relative photon flux density under the canopy was highly correlated with canopy coverage (R ² = 0.97). The light conditions under the canopy were almost the same at all sites in the summer leafy season regardless of the stand type, while they were remarkably different among the sites and depended on the basal area of evergreen trees in the winter leafless season. The biomass of P. chino on the forest floor was described by the equation: y = 3.18 x ₁ – 0.05 x ₂ + 3.11 (R ² = 0.77, P < 0.01), where y is the log-transformed value of P. chino biomass (gdrymassm^–2), x ₁ is cos at solar noon at the winter solstice, and x ₂ is the canopy coverage during the winter leafless season. is the angle between the suns rays and the normal to the surface and changes with slope aspect and angle. We concluded that light conditions under the canopy in the leafless season had a great effect on P. chino biomass, and that the basal area of evergreen trees and slope characteristics can provide useful guidelines in the control and management of P. chino.     

森林冠层节肢动物取样研究进展

冠层节肢动物的研究是近来生物多样性研究的国际前沿，文章主要介绍了森林冠层节肢动物的取样方法，如烟雾杀虫剂击倒法、取样树叶和小枝、非引诱式捕获器、诱捕器及其它取样法，并指出了各类取样法的优缺点。     

择伐林分冠下造林技术

1造林地选择冠下造林适宜择伐后林分保留木少(一般不足200株 hm2),林内天然更新差,幼苗、幼树少(不足500株 hm2),郁闭度小,立地条件好,土壤湿润易更新等地段。选择造林时,必须做到适地适树的原则。2造林树种选择由于林内光照强度小,通风不良,地表温度低,林内土壤疏松,腐殖质含量高,肥力大,水分充足,因此需要选择幼龄时期有较强的耐阴性、耐湿性,同时又具有很强的可塑性与适应性的树种。在我省东部林区,适宜冠下造林的树种主要有红松、云杉(红皮臭)、水曲柳。现将这些树种的主要的生物学特性和生态学特性简介如下:2 1红松是中性树种,喜深厚肥…     

Bird predation effects on bush canopy arthropods in suburban forests

Urban and suburban forests provide important recreational values to the public and can also contain high levels of biodiversity even though management regimes of such forests often include the clearing of bushes, shrubs and small trees to make them more attractive to people. In a field experiment, we studied the importance of bush canopies as foraging sites for insectivorous birds. In suburban forests, the canopies of rowan (Sorbus aucuparia) and alder buckthorn (Frangula alnus) were net-enclosed for two months at three study sites in SW Sweden. We compared abundance, biomass and body size distributions of arthropods between experimental and control canopies of rowan and alder buckthorn and found the effects to be strong. Biomass of arthropods was generally an order of magnitude higher on canopies protected from bird predation than on controls. Dermaptera contributed most to the biomass estimated in net-enclosed bushes. In certain taxa, however, the biomass was not significantly affected by the experimental treatment, possibly in part due to on-going reproduction during the experimental period. Furthermore, median body size in net-enclosed bushes was 1.3–3.0 times the control, excluding Araneae. The relative difference in arthropod biomass due to the experimental treatment was related to the density of breeding insectivorous birds at each site. We concluded that bush canopies are important foraging sites for birds in suburban forests, although we cannot rule out trait-mediated effects. Management regimes that include clearing of the ground may affect the bird community negatively.     

Regeneration of Norway spruce in canopy gaps in Sphagnum-Myrtillus old-growth forests

Gap-associated spruce (Picea abies (L.) Karst.) regeneration in Sphagnum-Myrtillus stands of south taiga forests (Central Forest Biosphere reserve, Tver region, Russia) was studied to evaluate the role of different disturbances in spruce dynamics. Sampled gaps (n=70) ranged from 40 m² to 1.7 ha in size, and from 1 to 70 years since disturbance moment. Formation of gaps lead to increase in the number of stems per ha in all gap size classes (small: 40–200 m², medium: 200–3000 m², and large: >3000 m² gaps). Spruce was the most important species in gap refilling, although its role was not the same in different gap classes. The highest values of relative abundance (compared to other species) were recorded in small gaps, and much lower values – in middle and large gaps. However, as refilling of gaps proceeded, spruce showed rather active regeneration in middle and large gaps and partly regained its abundance in middle-age disturbances. In general, all types of gaps studied supported spruce regeneration into the forest canopy. Almost perfect correlation between predicted outcome of spruce dynamics in gaps and its current role in the canopy of Sphagnum-Myrtillus stands suggests a good adaptation of this species to the current disturbance regime and a steady state of the these forests.     

Development of canopy stratification during early succession in northern hardwoods

Canopy development on a 6-year-old strip cut was analyzed by measuring the heights to terminal buds and bud scale scars of the tallest individuals of each species present on 50 plots of radius 6 m. Phenology of height growth was monitored during the following growing season. Pin cherry (Prunus pensylvania L.), an intolerant short-lived tree, had the fastest growth rate and was on the average the tallest species from the second to the sixth year of regrowth. Although advance regeneration of sugar maple (Acer saccharum Marsh.) and beech (Fagus grandifoloa Ehrh.) were the tallest trees during the first growing season, their slower growth rate insured that they would not keep up with the pin cherry. Trembling aspen (Populus tremuloides Michx.), striped maple (Acer pensylvanicum L.) and yellow birch (Betula alleghaniensis Britt.) occupied an intermediate position in the canopy by the end of the sixth growing season, and showed relatively greater annual height increment than beech or sugar maple. Height growth phenology differed slightly for each species. Beech, ash (Fraxinus americana L.) and sugar maple commenced growth early, grew rapidly and set buds all by 1 August (beech by 15 June). Yellow birch, pin cherry and trembling aspen started growing as early as the others, grew more slowly at first but then grew for a longer period of time. Striped maple seemed to be somewhat intermediate. Growth phenology and growth rate are related to the tolerance and growth form type (e.g. determinate or indeterminate) of the species. The most tolerant species tend to be determinate in growth form, have slower growth rates and complete height growth earlier. The intolerant species tend to be indeterminate, have a faster growth rate and continue to grow for a longer period. These may be mechanisms by which many species can grow together and avoid adverse effects such as suppression.     

郁闭后杨树林下不同间作模式效益分析

研究了郁闭后杨树林下间作麦冬、百合和生姜对林木生长、土壤肥力的影响及经济效益。结果表明：郁闭后杨树林下间作麦冬和百合对林木生长均有一定的促进作用。间作麦冬、百合第1年,杨树胸径连年生长量均比对照提高15.8％,树高连年生长量分别比对照提高31.6％和26.3％;间作麦冬第3年,杨树胸径和树高连年生长量分别比对照提高33.3％、13.3％。间作麦冬0～40em土层土壤有机质及N、P、K主要养分含量均比间作前有所下降。研究出郁闭后的杨树林下最适宜间作麦冬,年均利润高达12776元／hm^2,并且一个轮伐期至少增加木材收益5800元／hm^2。     

Estimating foliar biochemistry from hyperspectral data in mixed forest canopy

Estimating canopy biochemical composition in mixed forests at the level of tree species represents a critical tool for a better understanding and modeling of ecosystem functioning since many species exhibit differences in functional attributes or decomposition rates. We used airborne hyperspectral data to estimate the foliar concentration of nitrogen, carbon and water in three mixed forest canopies in Switzerland. With multiple linear regression models, continuum-removed and normalized HyMap spectra were related to foliar biochemistry on an individual tree level. The six spectral wavebands used in the regression models were selected using both an enumerative branch-and-bound (B&B) and a forward search algorithm. The models estimated foliar concentrations with adjusted R² values between 0.47 and 0.63, based on the best-sampled study site. Regression models composed of wavebands selected by the B&B algorithm always performed better than those developed with forward search. When extrapolating nitrogen concentrations from one to another study site, regression models solely based on causal wavebands (known from literature) mostly outperformed models based on all wavebands. The study demonstrates the potential of both the use of causal wavebands and of the B&B algorithm.     

Light-use properties in two sun-adapted shrubs with contrasting canopy structures

We investigated the impact of high solar irradiance and elevated temperature on carbon gain by two, co-occurring, sun-adapted, dwarf shrub species, Planchonella obovata var. dubia (Koidz.) Hatusima and Hibiscus glaber Matsumura, growing on sun-exposed ridges in the Bonin Islands, in the subtropical Pacific Ocean. Planchonella had steeply inclined, longer lived, sclerophyllous leaves, whereas Hibiscus has thinner, more horizontally oriented, and shorter lived leaves. We tested the hypothesis that leaf physiological tolerance to high light is lower in Planchonella than in Hibiscus. Under relatively high irradiances (photosynthetic photon flux density, PPFD, > 500 micromol m(-2) s(-1)), net photosynthetic rate (P(n)) was about 8.0 and 0.4 micromol m(-2) s(-1) in mature and young leaves of Planchonella, and about 12.4 and 10.3 micromol m(-2) s(-1) in mature and young leaves of Hibiscus, respectively. Both P(n) and photosystem II (PSII) quantum yield at a given PPFD were lower in Planchonella than in Hibiscus, whereas non-photochemical quenching (NPQ) at a given PPFD was higher in Planchonella. When leaf discs were exposed to high light (1900 micromol m(-2) s(-1) PPFD) at 37, 40 or 43 degrees C for 3 h, the recovery of PSII quantum yield (F(v)/F(m)) in the following 60-min dark period was slower in Planchonella than in Hibiscus, indicating that the ability of PSII to tolerate high light and high temperature was less in Planchonella than in Hibiscus. We postulate that there is a linkage between leaf display and leaf photochemical ability in sun-adapted shrub species.     

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.     

刺五加林冠下栽培技术

本文从林地选择、硬枝扦插育苗、移栽和田间管理、采收四个方面介绍了刺五加林冠下栽培技术.