Effects of thinning on the understory light environment of different stands and the photosynthetic performance and growth of the reforestation species Phoebe bournei

Light levels determine regeneration in stands and a key concern is how to regulate the light environment of different stand types to the requirements of the understory.In this study,we selected three stands typical in south China(a Cryptomeria japonica plantation,a Quercus acutissima plantation,and a mixed stand of both)and three thinning intensities to determine the best understory light environ-ment for 3-year-old Phoebe bournei seedlings.The canopy structure,understory light environment,and photosynthe-sis and growth indicators were assessed following thin-ning.Thinning improved canopy structure and understory light availability of each stand;species composition was the reason for differences in the understory light environ-ment.Under the same thinning intensity,the mixed stand had the greatest light radiation and most balanced spectral composition.P.bournei photosynthesis and growth were closely related to the light environment;all three stands required heavy thinning to create an effective and sustained understory light environment.In a suitable understory light environment,the efficiency of light interception,absorption,and use by seedlings was enhanced,resulting in a higher carbon assimilation the main limiting factor was stomatal conductance.As a shade-avoidance signal,red/far-red radia-tion is a critical factor driving changes in photosynthesis and growth of P.bournei seedlings,and a reduction increased light absorption and use capacity and height:diameter ratios.The growth advantage transformed from diameter to height,enabling seedlings to access more light.Our findings suggest that the regeneration of shade-tolerant species such as P.bournei could be enhanced if a targeted approach to thinning based on stand type was adopted.

Effects of thinning and understory removal on water use efficiency of Pinus massoniana:evidence from photosynthetic capacity and stable carbon isotope analyses

Understanding the relationship between forest management and water use efficiency(WUE)is important for evaluating forest adaptability to climate change.However,the effects of thinning and understory removal on WUE and its key controlling processes are not well understood,which limits our comprehension of the physiological mechanisms of various management practices.In this study,four forest management measures(no thinning:NT;understory removal:UR;light thinning:LT;and heavy thinning:HT)were carried out in Pinus massoniana plantations in a subtropical region of China.Photosynthetic capacity and needle stable carbon isotope composition(δ^(13)C)were measured to assess instantaneous water use efficiency(WUE_(inst))and long-term water use efficiency(WUE_(i)).Multiple regression models and structural equation modelling(SEM)identified the effects of soil properties and physiological performances on WUE_(inst)and WUE_(i).The results show that WUE_(inst)values among the four treatments were insignificant.However,compared with the NT stand(35.8μmol·mol^(-1)),WUE_(i)values significantly increased to 41.7μmol·mol^(-1)in the UR,50.1μmol·mol^(-1)in the LT and 46.6μmol·mol^(-1)in HT treatments,largely explained by photosynthetic capacity and soil water content.Understory removal did not change physiological performance(needle water potential and photosynthetic capacity).Thinning increased the net photosynthetic rate(A_n)but not stomatal conductance(g_s)or predawn needle water potential(ψ_(pd)),implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability.In general,thinning may be an appropriate management measure to promote P.massoniana WUE to cope with seasonal droughts under future extreme climates.

Early response of understory vegetation to the mass dieback of Norway spruce in the European lowland temperate forest

Spruce-dominated forests are commonly exposed to disturbances associated with mass occurrences of bark beetles.The dieback of trees triggers many physical and chemical processes in the ecosystem resulting in rapid changes in the vegetation of the lower forest layers.We aimed to determine the response of non-tree understory vegetation to the mass dieback of Norway spruce(Picea abies)in the first years after the disturbance caused by the European spruce bark beetle(Ips typographus)outbreak.Our study area was the Białowieża Biosphere Reserve covering the Polish part of the emblematic Białowieża Forest,in total 597km^(2).The main data source comprised 3,900 phytosociological relevés(combined spring and summer campaigns)collected from 1,300 systematically distributed forest sites in 2016–2018–the peak years of the bark beetle outbreak.We found that the understory responded immediately to mass spruce dieback,with the most pronounced changes observed in the year of the disturbance and the subsequent year.Shade-tolerant forest species declined in the initial years following the mass spruce dieback,while hemicryptophytes,therophytes,light-demanding species associated with non-forest seminatural communities,as well as water-demanding forest species,expanded.Oxalis acetosella,the most common understory species in the Białowieża Forest,showed a distinct fluctuation pattern,with strong short-term expansion right after spruce dieback,followed by a gradual decline over the next 3–4 years to a cover level 5 percentage points lower than before the disturbance.Thus,our study revealed that mass spruce dieback selectively affects individual herb species,and their responses can be directional and non-directional(fluctuation).Furthermore,we demonstrated that the mass dieback of spruce temporarily increases plant species diversity(α-diversity).

Different Understory Cultivation Techniques of Paris polyphylla Smith

This study was conducted for the purposes of reducing consumption of wild resources of Paris polyphylla Smith, satisfying the market demand, saving the production cost, improving utilization rate of forest land, increasing income of foresters and protecting ecological environment. Three types of fores{ land, i.e., the evergreen forest land （China fir forest）, deciduous forest land （walnut forest） and shrub land （honey suckle forest.） were selected, and seeds and cut rhizomes of Paris polyphylla Smith produced in Bamian Mountain, Hunan, were used in the study on understory seedling raising and cultivation techniques. The results showed that： when using different propagation materials, seed propagation could be adopted to reduce the consumption of wild resources and provide a large number of seedlings, and was beneficial to large-scale planting; and when conducing seedling and plantlet raising followed by transplanting and direct seeding and planting using different propagation materials in large-scale understory cultivation, direct seeding/ planting was appropriate for saving save production cost with the advantage of early production. Among the 3 different types of forest land, the best choice was broad- leaved forest land, which could achieve better economic benefit because of con- forming with the ecological habit and growth and development law of Paris poly- phylla Smith.

Soil CH_4 fluxes response to understory removal and N-fixing species addition in four forest plantations in Southern China

CH4 is one of the most important greenhouse gases, and mainly comes from soils in forest ecosystems. The objective of this study was to determine the effects of forest management practices such as understory removal and N-fixing species （Cassia alata） addition, on soil CH4 fluxes in four forest plantations in southern China. Fluxes of CH4 were measured in Eucalyptus urophylla plantation （B1）, Acacia crassi-carpa plantation （B2）, 10-native-species-mixed plantation （B3）, and 30-native-species-mixed plantation （B4） stands using the static chamber method in Southern China. Four forest management treatments, includ-ing （1） understory removal and replacement with C. alata （UR＋CA）; （2） understory removal only （UR）; （3） C. alata addition only （CA）; and （4） control without any disturbances （CK）, were applied in the four forest plantations. The results showed that plantation types had a significant effect on soil CH4 fluxes. B1 and B2 tended to be CH4 consumers, while B3 and B4 inclined to be CH4 producers. UR decreased CH4 fluxes by providing a more optimal soil temperature and moisture regime for mi-croorganism community and increasing substrate mineralization. How-ever, CA enhanced CH4 fluxes in B1 and B2 for N-fixing function of C. alata while lowered CH4 fluxes in B3 and B4. Soil CH4 flux rate was significantly related to soil temperature and moisture conditions in the top 10-cm soil layer. Furthermore, the quality of substrates, such as Soil Organic Carbon （SOC） and mineral N might also be important driving factors for CH4 fluxes. This study improved our understanding on CH4 fluxes in plantations under different management practices such as UR and CA.

Abiotic and biotic drivers of species diversity in understory layers of cold temperate coniferous forests in North China

Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures,function realization,and community succession.However,little is known about how abiotic and biotic drivers affect the diversity of understory species in cold temperate coniferous forests in the semiarid climate region of North China.We hypothesized that(1)topographic factors are important environmental factors affecting the distribution and variation of understory strata,and(2)different understory strata respond differently to environmental factors;shrubs may be significantly affected by the overstory stratum,and herbs may be more affected by surface soil conditions.To test these hypotheses,we used the boosted regression tree method to analyze abiotic and biotic environmental factors that influence understory species diversity,using data from 280 subplots across 56 sites in cold temperate coniferous forests of North China.Elevation and slope aspect were the dominant and indirect abiotic drivers affecting understory species diversity,and individual tree size inequality(DBH variation)was the dominant biotic driver of understory species diversity;soil water content was the main edaphic factors affecting herb layers.Elevation,slope aspect,and DBH variation accounted for 36.4,14.5,and 12.1%,respectively,of shrub stratum diversity.Shrub diversity decreased with elevation within the range of altitude of this study,but increased with DBH variation;shrub diversity was highest on north-oriented slopes.The strongest factor affecting herb stratum species diversity was slope aspect,accounting for 25.9%of the diversity,followed by elevation(15.7%),slope(12.2%),and soil water content(10.3%).The highest herb diversity was found on southeast-oriented slopes and the lowest on northeast-oriented slopes;herb diversity decreased with elevation and soil water content,but increased with slope.The results of the study provide a reference for scientific management and biodiversity protection in cold temperate coniferous forests of North China.

The effects of understory vegetation on P availability in Pinus radiata forest stands: A review

In many second-rotation Pinus radiata forest planta-tions, there has been a steady trend towards wider tree spacing and an increased rate of application of P fertiliser. Under these regimes, the potential for understory growth is expected to in-crease through increased light and greater nutrient resources. Therefore, understory vegetation could become a more signifi-cant component of P cycling in P. radiata forests than under closely-spaced stands. Studies have shown that growth rates and survival of trees is reduced in the presence of understory vegeta-tion due to the competition of understory vegetation with trees. Other studies have suggested that understory vegetation might have beneficial effects on nutrient cycling and conservation within forest stands. This review discusses the significance of understory vegetation in radiata pine forest stands, especially their role in enhancing or reducing P availability to forest trees.

Effect of abiotic factors on understory community structures in moist deciduous forests of northern India

Understory vegetation controls, in a significant way, the regeneration of overstory trees, carbon sequestration and nutrient retention in tropical forests. Development and organization of understory vegetation depend on climate, edaphic and biotic factors which are not well correlated with plant community structures. This study aimed to explore the relationships between understory vegetation and abiotic factors in natural and planted forest ecosystems. A non-metric multidimensional scaling(NMS) ordination technique was applied to represent forest understory vegetation among five forest communities, i.e., a dry miscellaneous forest(DMF), a sal mixed forest(SMF), a teak plantation(TP), a low-land miscellaneous forest(LMF) and a savanna area(SAV) of the Katerniaghat Wildlife Sanctuary, located in northern India. Microclimatic variables, such as photosynthetically active radiation(PAR), air temperature(AT), soil temperature(ST), ambient atmospheric CO 2 concentration, absolute air humidity(AH), physical and chemical soil properties as well as biological properties were measured. Understory species were assessed via 100 random quadrats(5 m × 5 m) in each of the five forests in which a total of 75 species were recorded encompassing 67 genera from 37 families, consisting of 32 shrubs and 43 plant saplings. DMF was the most dense forest with 34,068 understory individuals per ha of different species, whereas the lowest understory population(13,900 per ha) was observed in the savanna. Ordination and correlation revealed that microclimate factors are most important in their effect compared to edaphic factors, on the development of understory vegetation in the various forest communities in the north of India.

Species composition and influencing factors of understory woody species in Robinia pseudoacacia plantations on the Loess Plateau

Black locust(Robinia pseudoacacia L.)plantations have contributed significantly to soil and water conservation and ecological reconstruction on China’s Loess Plateau.Understanding the impact of stand and environment on species composition of understory woody plants will improve the stability of existing black locust plantations.Ten stands were selected in second-generation black locust plantations in tableland and gully areas of the Loess Plateau.The number of understory tree species in the tablelands was significantly lower than in the gully stands.Regenerated black locust(19.76%)and Rubus corchorifolius L.f.(64.85%)were the most abundant understory tree and shrub species,respectively,in the tableland stands;Broussonetia papyrifera(L.)L’Hér.ex Vent.(6.77%)and Acanthopanax senticosus(Rupr.Maxim.)Harms.(37.22%)were most abundant in the gully stands.Species richness(S),Shannon diversity(H),and evenness index(J)of the understory plants were significantly lower in the tableland stands than in the gully stands.More diverse understory species and community structures occurred in the gully stands.Differences in species diversity among landform positions may be attributed to differences in soil moisture.In addition,77.57%of the variation in understory species composition was explained,among which shrub and herb coverage,stand age,leaf area index,slope and total soil phosphorus in the 10-20 cm layer were the main factors.Soil organic carbon and total potassium significantly impacted S,H and J.Considering the environmental conditions and the biological characteristics of the plants investigated,R.corchorifolius should be given priority in the development of tableland stands,while B.papyrifera and Celtis sinensis Pers.should form mixed forests with black locust in gully stands.This management could promote biodiversity and stability of the existing black locust plantations but also optimize regional landscape patterns.

The influence of canopy-layer composition on understory plant diversity in southern temperate forests

Background： Understory plants represents the largest component of biodiversity in most forest ecosystems and plays a key role in forest functioning.Despite their importance, the influence of overstory-layer composition on understory plant diversity is relatively poorly understood within deciduous-evergreen broadleaved mixed forests.The aim of this work was to evaluate how tree overstory-layer composition influences on understory-layer diversity in three forest types（monospecific deciduous Nothofagus pumilio（Np）, monospecific evergreen Nothofagus betuloides（Nb）, and mixed N.pumilio-N.betuloides（M） forests）, comparing also between two geographical locations（coast and mountain） to estimate differences at landscape level.Results： We recorded 46 plant species： 4 ferns, 12 monocots, and 30 dicots.Canopy-layer composition influences the herb-layer structure and diversity in two different ways： while mixed forests have greater similarity to evergreen forests in the understory structural features, deciduous and mixed were similar in terms of the specific composition of plant assemblage.Deciduous pure stands were the most diverse, meanwhile evergreen stands were least diverse.Lack of exclusive species of mixed forest could represent a transition where evergreen and deciduous communities meet and integrate.Moreover, landscape has a major influence on the structure, diversity and richness of understory vegetation of pure and mixed forests likely associated to the magnitude and frequency of natural disturbances, where mountain forest not only had highest herb-layer diversity but also more exclusive species.Conclusions： Our study suggests that mixed Nothofagus forest supports coexistence of both pure deciduous and pure evergreen understory plant species and different assemblages in coastal and mountain sites.Maintaining the mixture of canopy patch types within mixed stands will be important for conserving the natural patterns of understory plant composition in southern beech mixed forests.

Phosphorus fertilizer induced changes in the soil available P,the P nutrition and the growth of Pinus radiata seedlings grown in association with understory

A study was carried out to investigate changes in the soil plant-available P,the P nutrition and the growth of Pinus radiata seedlings grown in association with understory,broom（Cytisus scoparius L.） or ryegrass（Lolium multiflorum） on Orthic Allophanic Soil,following the application of three rates of triple superphosphate（TSP）（0,50,and 100 mg·kg^-1P） under a glasshouse condition.The application of P fertilizer enhanced P availability in the rhizospheric of radiata seedlings and the bulk soils in a P-deficient site.P availability in the rhizospheric soils of ryegrass and broom,grown in association with radiata,were also increased by the presence of radiata roots.P concentrations in new shoot needles,old shoot needles,stem and roots of radiata pine increased with increase rates of TSP application,but the effects of ryegrass and broom on P nutrition of radiata seedlings depended on the soil P status.In the absence of P fertilizer addition（control treatment）,P concentrations in new shoot needles,old shoot needles,stem,and roots of radiata grown in association with broom were higher than those with ryegrass,whereas,when P fertilizer was added（50 and 100 mg·kg^-1） the P concentration was lower.This is probably related to the growth of broom that may have removed much of the plant-available P in the soil as indicated by the consistently lower Bray-2 P concentration in the rhizosphere soil of radiata in association with broom than that in the rhizosphere soil of radiata in association with grass at the two high P rates.Furthermore,in the high P fertile soil（application rate of 100 mg·kg^-1）,the dry matter yield of radiata was lower when it was grown with broom than with ryegrass.This result suggests that in moderate to high P fertile soils,P.radiata seedlings grow better with ryegrass than with broom,because broom grows vigorously in high P fertile soil and competes with P.radiata for P and perhaps for other nutrients as well.

Decomposition of Mongolian pine litter in the presence of understory species in semi-arid northeast China

The effects of understory plant litter on domi- nant tree litter decomposition are not well documented especially in semi-arid forests. In this study, we used a microcosm experiment to examine the effects of two understory species （Artemisia scoparia and Setaria viridis） litter on the mass loss and N release of Mongolian pine （Pinus sylvestris var. mongolica） litter in Keerqin Sandy Lands, northeast China, and identified the influencing mechanism from the chemical quality of decomposing litter. Four litter combinations were set up： one monocul- ture of Mongolian pine and three mixtures of Mongolian pine and one or two understory species in equal mass proportions of each species. Total C, total N, lignin, cel- lulose and polyphenol concentrations, and mass loss of pine litter were analyzed at days 84 and 182 of incubation.The chemistry of pine litter not only changed with the stages of decomposition, but was also strongly influenced by the presence of understory species during decomposition. Both understory species promoted mass loss of pine litter at 84 days, while only the simultaneous presence of two understory species promoted mass loss of pine litter at 182 days. Mass loss of pine litter was negatively correlated with initial ratios of C/N, lignin/N and polyphenol/N of litter combinations during the entire incubation period; at 182 days it was negatively correlated with polyphenol concentration and ratios of C/N and polyphenol/N of litter combinations at 84 days of incubation. Nitrogen release of pine litter was promoted in the presence of understory species. Nitrogen release at 84 days was negatively correlated with initial N concentration; at 182 days it was negatively correlated with initial polyphenol concentration of litter combinations and positively correlated with lignin concentration of litter com- binations at 84 days of incubation. Our results suggest that the presence ofunderstory species causes substantial changes in chemical components of pine litter that can exert strong influences on subsequent decomposition of pine litter.

Relationship of species diversity between overstory trees and understory herbs along the environmental gradients in the Tianshan Wild Fruit Forests, Northwest China

In forest ecosystems, interactions between overstory trees and understory herbs play an important role in driving plant species diversity. However, reported links between overstory tree and understory herb species diversity have been inconsistent, due to variations in forest types and environmental conditions. Here, we measured species richness(SR) and diversity(Shannon-Wiener(H') and Simpson's(D) indices) of overstory trees and understory herbs in the protected Tianshan Wild Fruit Forest(TWFF), Northwest China, to explore their relationships along the latitudinal, longitudinal, elevational, and climatic(current climate and paleoclimate) gradients in 2018. We found that SR, and H' and D diversity indices of overstory trees and understory herbs exhibited a unimodal pattern with increasing latitude and elevation(P<0.05) and negative associations with longitude(P<0.01). Along the climatic gradients, there were U-shaped patterns in SR, and H' and D diversity indices between trees and herbs(P<0.05). SR, and H' and D diversity indices for overstory tree species were positively associated with those for understory herbs(P<0.01). These findings indicate that overstory trees and understory herbs should be protected concurrently in the TWFF to increase effectiveness of species diversity conservation programs.

Response of understory plant species richness and tree regeneration to thinning in Pinus tabuliformis plantations in northern China

Background:Chinese pine(Pinus tabuliformis Carr.)is one of the major afforestation species in northern China and plays a key role in restoring forest ecosystems and preserving soil and water.However,most Chinese pine plantations are experiencing ecological problems such as the low diversity of understory plants and difficulty in natural regeneration.Thinning has been widely used to maintain and improve a variety of forest ecosystem services from plantations.To date,however,few studies have been conducted to systematically determine the effects of thinning on understory plant diversity and the regeneration of Chinese pine in plantations.Methods:We conducted a literature search,and selected 22 publications covering a total of 83 treatments related to thinning effects on the species richness of understory plants and 15 publications covering a total of 43 treatments related to thinning effects on the regeneration of Chinese pine,in tree plantations of northern China.The data from the literature were synthesized and evaluated with meta-analysis approach to determine the treatment effects.Results:Compared with the control stands,thinning increased the species richness of shrubs and herbs by an average of 25.3%and 26.5%,respectively.While the varying thinning intensities all had significantly positive effects on the species richness of understory plants,only moderate thinning(30%–50%)had a positive effect on the density of regenerating seedlings and saplings of Chinese pine(60.2%).The species richness of understory plants was greatest after 14 years of thinning with an increase of 36.3%,whereas the density of regenerating Chinese pine seedlings and saplings reached a maximum after≥11 years of thinning with an increase of 76.5%,compared to that of the unthinned stands.Thinning in the half-mature plantations had the greatest effects on the understory shrub richness(44.1%)and the density of regenerating Chinese pine seedlings and saplings(86.5%).Both single and multiple thinning were found to significantly promote the species richness of understory plants and the density of regenerating Chinese pine seedlings and saplings,and the positive effects of thinning were greater in areas with a humidity index(HI)<30 than in areas with an HI≥30.In general,age group,planting density and recovery time were prominent factors affecting the species richness of understory plants,whereas the slope,HI and recovery time were the dominant controls of the density of regenerating Chinese pine seedlings and saplings,indicating differential effects of thinning on the species richness of understory plants and the regeneration capacity of Chinese pine in plantations.Conclusion:Thinning appears to be a feasible management measure to improve the understory plant diversity and regeneration capacity of Chinese pine in plantations.We postulate that moderate thinning in half-mature forest stands with an HI<30 can help effectively promote the species diversity of understory plants and the natural regeneration of Chinese pine,thereby maintaining a more resilient stand structure and the development of Chinese pine plantations.

Understory vascular plant community assembly in relation to time-since-fire and environmental variables in a Chinese boreal forest

Understanding the response of understory vegetation to fire disturbance is vital to biodiversity conservation and management of boreal forests. We surveyed understory vascular plant richness and composition, and measured related environmental variables along a toposequence within three successional stages, initial （3 years post-fire）, early （13 years post-fire） and late （〉1oo years post-fire） successional stages. Using permutation multivariate ANOVA and nonmetric multidimensional scaling, we analyzed how understory species richness and composition change as time-since-fire proceeds, and their correlative relationships with environmental variables. Species richness and composition showed significant differences among the three successional stages. Understory species richness and abundance were significantly associated with time-since-fire, topographic position, elevation and organic layer depth. Among these variables, time-since-fire had the strongest effect and topographic position was the second major factor on affecting understorycommunity assembly. In overwhelmed the effects addition, time-since-fire of soil pH in the initial successional stage and gravimetric soil moisture in early and late successional stages on understory species composition

The effect of dead wood and understory coverage on small rodent abundance in Korean forest

This study was conducted to investigate the population characteristics of small rodents in different habitats with the artificial presence and absence of dead wood, and understory vegetation after forest cutting at natural deciduous forest in north-eastern South Korea from April to December in 1997 and 1998. Two forests, one hectare each (100 100 m), were se-lected and designated as the control and the treatment area. Forest structure of mid and high canopy layers in both study areas was similar. But number and volume of fallen trees, and coverage of understory vegetation were higher in the control area than in the treatment area. Total captures of small rodents in two areas combined comprised Eothenomys regulus (55.5%, n = 211) and Apodemus peninsulae (44.5%, n = 169). Total abundance of E. regulus and A. peninsulae, and population stability were sig-nificantly greater in the control area than in the treatment area. The difference in the captured number of two small rodents be-tween the two sites was caused by the difference in reproduction and residency. The structure of forest floor appears to be im-portant to small rodents. The presence of dead wood and understory vegetation after the forest cutting would be necessary for the maintenance of small rodent population in the forest cutting areas.

Assessing forest understory biomass in northwest Florida (USA) and its potential to meet the state energy needs

A stratified random sampling approach was employed to quantify total biomass across prevalent non-commercial forest understory species found in six counties of northwest Florida, USA. The moisture content （wet basis） and calorific values of these species were also measured. Total green biomass from forest understory species was estimated to be around 12 million metric tons, mostly comprised of Cliftonia monophylla （titi, buckwheat tree） and Cyrilla racemiflora （white titi, swamp titi）. This understory forest biomass would be sufficient to generate about 28.8 million GJ of electricity or 1589.25 million liters of ethanol. A need was identified to determine the inventory of forest understory biomass at the state level and assess the overall sustainability of utilizing forest understory biomass for bioenergy.

Investigation and Analysis of Understory Vegetation in Casuarina equisetifolia Forests in Northern Hainan Province

Understory vegetation in the Casuarina equisetifolia forests at different ages was sampled and analyzed fi rstly, and then the structural features, biomass, and distribution characteristics of carbon stock of the understory vegetation, as well as the quantity and thickness of the understory litter were studied. The results show that the understory vegetation in the C. equisetifolia forests is mainly composed of herbaceous plants, and there are nearly no shrubs in the study area. Moreover, the quantity of herbaceous plants rises obviously with the increase of forest age. There is a big difference between the woodlands at different ages in total biomass of herbaceous plants, and the maximum of total biomass can be found in 15-year-old woodland, reaching 1.68 t/hm^2; the biomass of overground parts of herbaceous plants is higher than that of underground parts. There is a big difference between the woodlands at different ages in thickness of the understory litter, and the thickness of understory litter in 10-yearold woodland is the highest, reaching 6.67 cm. The maximum quantity of the understory litter has reached 14.69 t/hm^2, and the thickness of the half decomposed litter is larger than that of the undercomposed litter in most woodlands.

Characteristics of Light Availability Under Forest Canopies and Its Influences on Photosynthesis of Understory Plants

Available light under forest canopies includes two components, diffuse light and direct light (sunflecks), and is characterized as low and highly dynamic. Understory habitats under different forest types experience different light conditions. Sunflecks as a critical resource for understory plants have great importance on carbon gain of understory plants. Under the light-limiting habitat, understory plants exhibit a high light utilization efficiency attributed by a post-illumination CO2 uptake. Although different species have different photosynthetic responses, shade plants appear to be acclimated to respond more quickly and efficiently to sunflecks. This acclimation includes a faster induction, relatively lower rate of induction loss, lower photosynthetic compensation point, and higher water use efficiency. The process that shade plants harvest light energy is not well known. Studies of photosynthetic responses to sunflecks in natural conditions are rare. Little is known about constraints on sunfleck utilization, which may change seasonally. Extensive field studies in conjunction with laboratory investigations will be needed to further understand potential and actual constraints on sunfleck utilization. Most studies on photosynthetic responses to fluctuating light condition were done in the level of leaves. Fluctuating light utilization on the basis of whole plants and populations presents future challenges to ecologists.

Construction of Understory Landscapes for Mountain Amenity Forest in Guangdong Province,China

Based on the investigation of understory landscapes in mountain amenity forest in Guangdong, plant selection and spatial structure of understory landscapes were explored from the perspective of influencing factors such as terrain, stand structure, canopy density. It was proposed that plant selection for the construction of understory landscapes should use more indigenous plants, follow ecological attributes of plants and pay attention for ornamental value of plants. Three modes of constructing understory landscapes were proposed: ornamental, recreational and ecological.