Differences In Shade Tolerance Research Articles

Spatial association of bamboos with trees in a commercial tree plantation forest in Myanmar

Abstract Bamboos are mainly distributed in subtropical to tropical areas. Bamboos provide numerous ecosystem services, while the expansion of bamboo gives negative impacts on forest ecosystems. Despite big impacts of bamboos on a forest ecosystem, ecological characteristics of bamboo remain poorly understood. The spatial distributional patterns of three bamboo species, Cephalostachyum pergracile, Bambusa polymorpha, and Dinochloa maclellandii, were studied in a commercial tree plantation of native deciduous tree species in the Bago Mountains, Myanmar. A point process analysis revealed a clumped distribution for each bamboo species. The distributional overlapping of the species was analysed for every pair of two species. The distribution of C. pergracile was little overlapped with those of D. maclellandii and B. polymorpha. Cephalostachyum pergracile was significantly more abundant on gently sloping ridges, whereas D. maclellandii was more abundant on a steeply sloping site. Bambusa polymorpha did not show these patterns with topography. The exclusive distribution of C. pergracile and D. maclellandii may be, at least partly, explained by the opposite topographic preferences of the species. Cephalostachyum pergracile tended to be found far from large trees that cast shade, although B. polymorpha tended to be found with large trees, suggesting that B. polymorpha may be more shade tolerant than C. pergracile. The difference in shade tolerance may contribute to the exclusive distribution of the species. The habitat preference information obtained in this study will contribute to sound bamboo management practices in Myanmar and enable bamboo population sizes to be increased through creation of favourable habitats in forests.

The effects of stump size and within-gap position on sprout non-structural carbohydrates concentrations and regeneration in forest gaps vary among species with different shade tolerances

BackgroundTo restore secondary forests (major forest resources worldwide), it is essential to accelerate the natural regeneration of dominant trees by altering micro-environments. Forest gaps are products of various disturbances, ranging from natural storms or wildfires to anthropogenic events like logging and slashing-and-burning, and sprouts of most tree species with non-structural carbohydrates (NSCs) storage can regenerate from stumps after gap formation. However, how the stump sprouts with diverse NSCs storages and stump sizes (i.e., diameters) adapt to various micro-environments of within-gap positions remains unclear. Therefore in this study, we monitored the stump sprout regeneration (density, survival, and growth) and NSCs concentrations of three dominant tree species with different shade tolerances and varying stump diameters at five within-gap positions for the first two consecutive years after gap formation.ResultsStump diameter was positively correlated with sprout density, growth, and survival of all three tree species, but insignificantly related with sprout NSCs concentrations at the early stage after gap formation. The effect of within-gap position on sprout NSCs concentrations was different among species. After an environmental adaptation of two growing seasons, the north of gap (higher light availability and lower soil moisture habitat) was the least conducive for shade-intolerant Quercus mongolica to accumulate leaf NSCs, and the east of gap (shadier and drier habitat) was conducive to increasing the leaf NSCs concentrations of shade-tolerant Tilia mandshurica.ConclusionsWithin-gap position significantly affected leaf NSCs concentrations of all three tree species, but most of the sprout growth, survival, and stem NSCs concentrations were independent of the various within-gap positions. Besides stump diameter, the NSCs stored in stump and root systems and the interspecific differences in shade tolerance also contributed more in sprout regeneration at the early stage (2 years) of gap formation. A prolonged monitoring (> 10 years) is needed to further examine the long-term effects of stump diameter and within-gap position on sprout regeneration. All of these findings could be applied to gap-based silviculture by promoting sprout regeneration of dominant tree species with different shade tolerances, which would help accelerate the restoration of temperate secondary forests.

Interpretation of the difference in shade tolerance of two subtropical forest tree species of different successional stages at the transcriptome and physiological levels.

Differences in plant shade tolerance constitute a major mechanism driving the succession of forest communities in subtropical forests. However, the indirect effects of differences in light requirements on the growth of mid- and late-successional tree species are unclear, and this potential growth effect has not been explained at the transcriptome level. Here, a typical mid-successional dominant tree species, Schima superba Gardn. et Champ, and a typical late-successional dominant tree species, Cryptocarya concinna Hance were used as materials and planted under 100% full light (FL) and 30% FL (low light, LL) to explore the responses of tree species in different successional stages of subtropical forests to different light environments. Transcriptome sequencing was used to analyze the expression changes in genes related to growth and photoprotection under different light environments. The young leaves of S. superba accumulated more malondialdehyde (MDA) and superoxide radicals (${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$) under LL. A lower hormone content (auxin, cytokinin, gibberellin) in the young leaves, a weaker photosynthetic capacity in the mature leaves and significant downregulation of related gene expression were also found under LL, which resulted in the total biomass of S. superba under LL being lower than that under FL. The young leaves of C. concinna had less MDA and ${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$, and a higher hormone contents under LL than those under FL. There was no significant difference in photosynthetic capacity between mature leaves in contrasting light environments. Although the biomass of C. concinna under LL was less than that under FL, the height of C. concinna under LL was higher than that under FL, indicating that C. concinna could grow well under the two light environments. Our results describing the acclimatization of light at the physiological, molecular and transcriptome levels are important for a complete understanding of successional mechanisms.

Intercropping of climbing bean (Phaseolus vulgaris, L.) and East African highland banana (Musa spp.) in the Ugandan highlands

AbstractEast African highland bananas and climbing beans are important crops for food and income in the highlands of Uganda. Intercropping of banana with legume crops is a common practice, yet climbing bean intercropping with perennials has rarely been studied in Uganda. To understand how best to improve the production system, we assessed the effects of pruning of banana leaves on light availability for climbing beans, resulting effects on bean yields and potential differences in shade tolerance between two climbing bean varieties in the eastern and southwestern highlands of Uganda. Measurements of the transmission of photosynthetically active radiation (PAR) through the banana canopy were combined with yield measurements of a local and improved climbing bean variety and with banana pseudostem girth in two seasons (2016A and 2016B). We also compared yields of intercropped with sole-cropped climbing beans. The mean fractions of PAR transmitted through the banana canopy – hence available for beans – were 0.43 on pruned and 0.38 on non-pruned subplots, a significant 15% difference. The improved light availability did not increase climbing bean yield. Although no direct relationship between light interception and bean yields was found, bean yields on the most and least shaded parts of the intercropped fields differed significantly, suggesting that beans do benefit from improved light availability in intercropping. Generally, yields of sole-cropped beans were significantly larger than of intercropped beans, but we could not single out the effects of competition for light, water, and/or nutrients. The bean varieties responded similarly to the pruning treatments. The local variety tended to perform relatively better in intercropping, the improved variety in sole cropping, though differences were not significant overall. Pruning and retention of eight banana leaves over the course of a season did not affect banana pseudostem girths in the mature banana plantations. Although light availability improved, farmers may not expect a major effect on bean yield. Future research may focus on the effects of a lower number of leaves retained, comparing a number of bean varieties for suitability in sole or intercropping, or on other factors influencing the relation between the two crops such as relative plant densities of beans and bananas.

Disentangling the effects of atmospheric CO2 and climate on intrinsic water-use efficiency in South Asian tropical moist forest trees.

Due to the increase in atmospheric CO2 concentrations, the ratio of carbon fixed by assimilation to water lost by transpiration through stomatal conductance (intrinsic water-use efficiency, iWUE) shows a long-term increasing trend globally. However, the drivers of short-term (inter-annual) variability in iWUE of tropical trees are poorly understood. We studied the inter-annual variability in iWUE of three South Asian tropical moist forest tree species (Chukrasia tabularis A.Juss., Toona ciliata M. Roem. and Lagerstroemia speciosa L.) derived from tree-ring stable carbon isotope ratio (δ13C) in response to variations of environmental conditions. We found a significantly decreasing trend in carbon discrimination (Δ13C) and an increasing trend in iWUE in all the three species, with a species-specific long-term trend in intercellular CO2 concentration (Ci). Growing season temperatures were the main driver of inter-annual variability of iWUE in C. tabularis and L. speciosa, whereas previous year temperatures determined the iWUE variability in T. ciliata. Vapor pressure deficit was linked with iWUE only in C. tabularis. Differences in shade tolerance, tree stature and canopy position might have caused this species-specific variation in iWUE response to climate. Linear mixed effect modeling successfully simulated iWUE variability, explaining 41-51% of the total variance varying with species. Commonality analysis revealed that temperatures had a dominant influence on the inter-annual iWUE variability (64-77%) over precipitation (7-22%) and atmospheric CO2 concentration (3-6%). However, the long-term variations in iWUE were explicitly determined by the atmospheric CO2 increase (83-94%). Our results suggest that the elevated CO2 and concomitant global warming might have detrimental effects on gas exchange and other physiological processes in South Asian tropical moist forest trees.

Quantitative division of succession and spatial patterns among different stand developmental stages in Changbai Mountains

Broadleaf-Korean pine forests exhibit high species richness and distinctive species composition, which are currently becoming more dominant among natural forests in Changbai Mountains of north-eastern China. Understanding the ecological process of restored vegetation is quite important for ecosystem reconstruction. Distinguishing stand development stages and analyzing the dynamic spatial patterns could provide insights into significant community coexistence mechanisms. In the present study, eight permanent study areas were established according to the substituting space for time method in Changbai Mountains of north-eastern China. The optimal division method was used to quantify the successional series into different stand development stages, and the point pattern analysis method (L(r) function) was used to analyse the dynamic changes in spatial patterns and interspecific associations. Our results suggested that: (1) The stand development process was divided into five stages: the first three stages were poplar-birch secondary forests in different stages of recovery, the fourth stage was the spruce-fir mixed forest, and the last stage was the primary broadleaf-Korean pine forest; (2) The spatial pattern showed an aggregated distribution at a small scale and changed to a random distribution as the scale increased in poplar-birch secondary forests, but the spatial pattern appeared to be randomly distributed in spruce-fir mixed forest and broadleaf-Korean pine forest; (3) The interspecific associations between pioneer species and climax species changed from negative to positive among the different stand stages, and environmental resources were shared among these species. Interspecific differences in shade tolerance among the tree species were key determinants of forest dynamics and structure. Our study is vital to the understanding of the forest development; thus, the spatial change features should receive greater attention when forest management is being planned and restoration strategies are being developed for the Changbai Mountains.

Shading constrains the growth of invasive submerged macrophytes in streams

Submerged macrophytes are an important component of stream ecosystems but invasion by non-native species can threaten the natural structure and function of these systems. Restoration of riparian shading may help to regulate the growth of macrophytes, particularly invasive species, which often proliferate in open streams. In a large, flowing outdoor mesocosm we studied the establishment and colonization success of three non-native macrophyte species (Egeria densa, Elodea canadensis and Ceratophyllum demersum) and one native charophyte (Nitella spp. aff. cristata) that commonly occur in stream systems. Plant shoots were grown at five shade levels (35%, 63%, 79%, 90% and 95%) for eight weeks with regular monitoring of growth, morphology and biomass accrual. All species were able to establish at all shading levels. At high shade (≥ 90%) we found a reduction in lateral spread and branching and an increase in main stem length for the non-native species, while Nitella did not show any response for these traits. Biomass accumulation was delayed at high shade for all species. At the end of the experiment, the highest biomass accrual was observed at the lowest shade level (35%) for E. densa and E. canadensis, at 63% shade for C. demersum and at 79% shade for Nitella. Our results confirm, and provide additional examples, that both native and non-native submerged macrophytes can establish and colonize streams that are highly shaded but that the growth of non-native species, in particular, can be limited. Our study also highlights that there are differences in shade tolerance among non-native species.

Transgressive overyielding in mixed compared with monospecific Scots pine (Pinus sylvestris L.) and oak (Quercus robur L., Quercus petraea (Matt.) Liebl.) stands – Productivity gains increase with annual water supply

Tree species mixing has become a crucial tool in European forest management as positive interactions between species have been found to promote the provision of multiple ecosystem services, while at the same time reducing the risks associated with climate change. However, mixing effects have proven to be strongly context-dependant and some species combinations have still not been studied in detail. Here we focus on mixed forests of Scots pine and oak, which are likely to become increasingly popular for balancing wood production and other ecosystem services under climate change. Using 20-year growth data from newly established triplets in Germany and Denmark, this study investigates how mean tree and stand characteristics as well as productivity in mixed Scots pine-oak stands compare with adjacent monocultures and how stable the observed productivity relation is, considering inter-annual variations in local climate. Species mixing on average resulted in 15% higher standing volume and 14% higher volume productivity compared with the weighted mean of the adjacent monocultures. Oak profited most in mixture, showing overyielding of 19%. Overyielding on the stand and species level increased in years with higher water supply. In mixture, standing volume of Scots pine was 25% higher than in monocultures. Both species were found to modify their morphology in mixture. Oak in mixture showed a significantly higher inequality in stem volume compared with monocultures. We hypothesise that the observed overyielding of Scots pine-oak mixtures mainly results from complementary light use, where differences in shade tolerance, crown architecture and leaf phenology may be contributing factors.

Tree allometry variation in response to intra- and inter-specific competitions

Crown, height and stem allometry vary with stand density and species composition, the plasticity in response to inter- and intra-specific competitions being related to species shade tolerances. Determining the way in which variability in tree allometry is modulated by intra- and inter-specific competitions in different species and stand compositions is of particular interest for forest modelling and practice. In this study, we explore this variability by developing models for tree crown diameter, total height and diameter at a height of 4 m, which include intra- and inter-specific competition terms. More than 19,000 Scots pine, silver fir, sessile oak and European beech trees from 4711 sample plots belonging to the Spanish National Forest Inventory were included in the study, covering both monospecific and two species mixed stands in Northern Spain. Trees growing under conditions of high competition displayed narrower crowns, greater heights and less taper for a given tree diameter, the plasticity in crown and height in response to intra-specific competition being related to species shade tolerance. The inter-specific competition effect on crown diameter and height was related to the difference in shade tolerance between the two species of the mixture, while stem taper did not exhibit this pattern. These results suggest that trees in mixed stands indeed show a modified allometry, which might be related to complementary resource acquisition strategies. The large variability observed in tree allometry indicates the need to consider both intra- and inter-specific competitions in allometric models.

Difference in shade tolerance drives the mixture effect on oak productivity

Abstract Assessing how species productivity in mixtures is influenced by species shade tolerance (ST) and phylogeny would be helpful to improve our general understanding of the relationship between tree species diversity and productivity in forests. We investigated the effects of differences in ST and phylogenetic distances (PDs) between pairs of species on the productivity of Quercus petraea growing in 18 mixtures in lowland temperate forests. We calculated the mixture effect as the difference in productivity of Q. petraea in mixed vs. pure stands. Our analyses were based on data from seven annual campaigns of the French National Forest Inventory covering 1,573 plots. The mixture effect on Q. petraea productivity increased when the ST of the companion species decreased. Compared to its productivity in pure stands, Q. petraea productivity in mixed coniferous stands varied from −14.6% up to +39.6% as the ST of the companion species inversely varied from highest to lowest. With broadleaved companion species, the mixture effect varied from −10% up to +13.9% with decreasing ST. We found no effect of PD between Q. petraea and the companion species on the mixture effect. Synthesis. Our results confirm that shade tolerance is an important driver of the diversity effect on productivity at species level in temperate forests and that phylogenetic distance is not a relevant proxy for species functional dissimilarity.

Phenotypic Plasticity and Turf Performance of Zoysiagrass in Response to Reduced Light Intensities

Understanding phenotypic plasticity and patterns of biomass allocation of turfgrass under shade is needed for better turfgrass management and the development of cultivars that persist under shade. The objectives of this study were to (i) compare turf performance and determine the relationship between the phenotypic plasticity in growth, biomass allocation and turfgrass quality (TQ) under different light intensities under greenhouse condition; and (ii) assess the turf establishment and performance in response to moderate shade under field conditions in zoysiagrass (Zoysia spp.). A greenhouse experiment evaluated 11 cultivars under four shade levels. Plasticity in leaf extension rate (LER) had a positive relationship with the plasticity in clipping dry weight (CDW, R2 = 0.31), total dry weight (TDW, R2 = 0.16), and TQ (R2 = 0.32), indicating less decline in TQ was associated with more biomass allocated to shoot growth and/or more biomass storage during the study period. Under 90% shade, cultivars JaMur (plasticity in TQ = −0.12), Empire (−0.13), El Toro (−0.16), Palisades (−0.17), and BA‐305 (−0.21) were identified as the top performers with less decline in TQ and higher turf performance index (TPI). Cultivar Emerald demonstrated a low reduction in TDW and no plasticity in LER, indicating a different shade response mechanism compared to BA‐305. A separate field experiment evaluated eight cultivars under full sun and 63% shade. The moderate shade resulted in limited variation and results on cultivar difference in shade tolerance were inconclusive. Nonetheless, cultivars BA‐189, Shadow Turf, and Empire had faster establishment than Emerald.

Difference in shade tolerance affects foliage–sapwood response to thinning by two eucalypts

In eucalypt plantations in subtropical Australia, Eucalyptus dunnii exhibits greater diameter increment after thinning than more shade-tolerant Corymbia citriodora. To elucidate the mechanism underlying this difference, we investigated relationships between tree leaf area and sapwood area following thinning in 11-year-old E. dunnii and C. citriodora plantations. There was no significant difference in specific leaf area (SLA) between thinned and unthinned stands in E. dunnii and C. citriodora, whereas crown zone significantly affected SLA in the two eucalypts. At the whole-tree level non-linear leaf area (Al)–sapwood area (As) relationships were measured in both eucalypts by thinning treatment. A significant increase in Al/As ratio was only observed at the upper crown in thinned E. dunnii. The present results suggested the plastic nature of response of leaf characteristics in both eucalypts grown in different light environments and the species-specific pattern of crown-zone leaf responses to thinning in the two species, i.e. the top of the canopy appears to be driving greater growth response to thinning in the less shade tolerant E. dunnii compared with the more shade-tolerant C. citriodora. It is concluded that different thinning regimes should be applied in shade-tolerant and shade-intolerant eucalypt forests.

Growth, allometry and shade tolerance of understory saplings of four subalpine conifers in central Japan

The conifers Abies veitchii, A. mariesii, Picea jezoensis var. hondoensis, Tsuga diversifolia dominate in subalpine forests in central Japan. We expected that species differences in shade tolerance and in aboveground and belowground architecture are important for their coexistence. We examined net production and carbon allocation of understory saplings. Although the four species allocated similar amounts of biomass to roots at a given trunk height, the root-zone area of T. diversifolia was greater than that of the three other species. T. diversifolia often dominates shallow soil sites, such as ridge and rocky slopes, and, therefore, a wide spread of lateral roots would be an adaptation to such edaphic conditions. Crown width and leaf and branch mass were greatest for T. diversifolia and A. mariesii, followed in order by A. veitchii and P. jezoensis var. hondoensis. Although leaf mass of P. jezoensis var. hondoensis was lowest among the four species, species differences were not found in the net production per sapling because net production per leaf mass was greatest for P. jezoensis var. hondoensis. The leaf lifespan was longer in the order A. mariesii, T. diversifolia, P. jezoensis var. hondoensis and A. veitchii. The minimum rate of net production per leaf mass required to maintain the current sapling leaf mass (MRNP(LM)) was lowest in A. mariesii and T. diversifolia, and increased in the order of A. veitchii and P. jezoensis var. hondoensis. A. mariesii and T. diversifolia may survive in shade conditions by a lower MRNP(LM) than the two other species. Therefore, species differences in aboveground and belowground architecture and MRNPLM reflected their shade tolerance and regeneration strategies, which contribute to their coexistence.

New cohort growth and survival in variable retention harvests of a pine ecosystem in Minnesota, USA

There is significant interest in silvicultural systems such as variable retention harvesting (VRH) that emulate natural disturbance and increase structural complexity, spatial heterogeneity, and biological diversity in managed forests. However, the consequences of variable retention harvesting for new cohort growth and survival are not well characterized in many forest ecosystems. Moreover, the relative importance of resource preemption by existing ground layer vegetation after variable retention harvests is unclear. We addressed both in a VRH experiment implemented as a randomized block design replicated four times in red pine forest in Minnesota, USA. Treatments included a thinning with residual trees dispersed evenly throughout the stand (dispersed) and two patch cuts that left 0.1ha gaps (small gap) or 0.3ha gaps (large gap) in a forest matrix. Residual basal area was held near constant in the three harvest treatments. We planted seedlings of three common pines (Pinus banksiana, P. strobus and P. resinosa) and measured light, soil nutrients and growth over seven growing seasons. We hypothesized that forests with equivalent average structures (e.g., basal area) would have higher stand-level seedling growth and survival in aggregated retention versus dispersed retention stands. However, variable retention harvest resulted in relatively small differences in growth and survival across the three retention treatments (although all differed as expected from uncut controls). Species specific responses to overstory treatments were partially related to shade tolerance. Tolerant white pine had high survival across all overstory treatments whereas intolerant red and jack pine had lower survival in uncut controls. In general, jack pine had the strongest growth response to reduction of overstory density. However, both white and jack pine achieved highest growth in the dispersed treatment despite differences in shade tolerance. Regardless of species, shrubs had a strong impact on seedling growth. Indeed, differences in growth were often larger across shrub treatments than among retention treatments. Our results support the hypothesis that shrubs preempt resources and dampen the impacts of different overstory retention patterns on new cohort growth and survival. Our results imply that managers have considerable flexibility to employ various types of retention patterns coupled with planting in red pine ecosystems at least at the levels of retention studied here.

Canopy disturbance and intertree competition: implications for tree growth and recruitment in two yellow birch–conifer stands in Quebec, Canada

Composition, structure, and species-specific patterns of recruitment and growth were characterized in two yellow birch (Betula alleghaniensis Britt.)–conifer stands in Quebec, Canada, to improve our understanding of the dynamics of these complex ecosystems. The mixture of mid- and shade-tolerant species in the canopy, the inverse J-shape stem diameter distribution, and the age distribution were indicative that the two stands were in a late-successional stage. Recruitment of mid-tolerant species above 1.3 m in height appeared to be periodic and synchronized with historical spruce budworm (Choristoneura fumiferana Clem.) outbreaks, while the coniferous component of these mixedwood stands recruited continuously. Results suggest that recruitment of yellow birch and red maple (Acer rubrum L.) requires disturbances of a certain intensity that affect at least 25 % of the forest cover. In contrast, balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) can recruit under the canopy without relying on moderate or large canopy disturbances. Results suggest that the historical disturbance regime, and differences in shade tolerance between species, largely govern the contemporary composition of these stands. This study improves the comprehension of mechanisms that regulate the dynamics of yellow birch-conifer stands and will be useful for the subsequent elaboration of forest management strategies.

One‐sided competition for light promotes coexistence of forest trees that share the same adult height

Summary Coexistence of tree species is usually explained in relation to horizontal heterogeneity of forests caused by disturbance. In contrast, it remains unknown whether one‐sided competition for light in vertically structured forests contributes to stable coexistence of tree species that share the same adult height, even without horizontal heterogeneity. And if so, it is needed to specify the conditions of stable coexistence in terms of demographic and allometric traits between species. To answer these questions, we employ a theoretical model that describes dynamics of tree populations in forests of which vertical structure is expediently divided by height classes. We carry out analytical examination for a forest with two height classes where tree populations are adult in canopy and juvenile in understorey. Demographic processes in the canopy are regulated by foliage density in the canopy, whereas juvenile survival is suppressed by overall foliage density in both classes. A between‐species difference in juvenile/adult ratio of foliage density is required for coexistence equilibrium of two species to exist. The difference in juvenile/adult ratio in equilibrium is determined by demographic and allometric parameters of species. Trade‐offs between demographic parameters are necessary for a coexistence equilibrium which is either stable or unstable. A species with high fecundity and/or shade‐free juvenile survival can stably coexist with a species with high shade‐free growth rate and/or adult survival, whereas it cannot stably coexist with a species with high shade tolerance in growth rate and/or in adult survival. Difference in shade tolerance in juvenile survival does not contribute to stable coexistence. Height‐foliage allometry contributes only additionally to enhance coexistence equilibrium. When we divide forests into three height classes, up to three species can coexist, by means of demographic trade‐offs that bring about interspecific differentiation in vertical foliage distribution. We show all possible cases of coexistence among canopy (C), subcanopy (S) and understorey (U) species in terms of maximum adult height as follows: CCC, CCS, CCU, CSS and CSU. Synthesis. Our theoretical model shows that demographic trade‐offs among tree species with identical demographic responses to shade promotes stable coexistence through vertical foliage partitioning. This mechanism works independently of the coexistence mechanism through horizontal partitioning of patch mosaic, which is associated with interspecific difference in shade tolerance.

Competitive Control of an Exotic Mangrove Species: Restoration of Native Mangrove Forests by Altering Light Availability

AbstractRecently, many studies have focused on the possibility of restoring mangrove ecosystems by introducing fast‐growing mangroves. However, methods for managing an exotic fast‐growing species to restore mangrove ecosystems and at the same time preventing invasion by introduced species remains unclear.Sonneratia apetalaBuch‐Ham is one example of an exotic mangrove with both high ecological value and potential risk for invasion after introduction. To investigate the possibility of reducing the potential for invasion by altering light availability, we simulated different irradiances ofS. apetalaunderstory in the greenhouse. For each irradiance treatment, three levels of competition betweenS. apetalaand native mangrovesAegiceras corniculatum(L.) were used: no competition, intraspecific competition and interspecific competition. Compared withA. corniculatum,S. apetalashowed a significantly higher growth rate for both height and biomass accumulation under full irradiation. Compared to the full irradiation treatment, the shading treatment significantly reduced the height, total biomass and biomass allocation to leaves ofS. apetalaby 61.31, 71.0, and 76.2%, respectively, whereas the growth ofA. corniculatumwas not affected. The results suggested that lowering light availability could inhibit the growth ofS. apetalaand increase the competitiveness ofA. corniculatum. Planting introduced fast‐growing mangroves at a density of approximately 2,000 plants/hm2is an effective strategy for preventing potential invasion and restoring wetland habitats. By taking advantage of the differences in shade tolerance between fast‐growing exotic mangroves and native mangroves, introduction of fast‐growing mangroves in coastal areas could have huge potential for reforesting mangrove ecosystems.

Quantification of the effects of aboveground and belowground competition on growth of seedlings in a conifer–angiosperm forest

Differential shade-tolerance is thought one of the critical components of coexistence of conifer and angiosperm canopy tree species in temperate forests. However, belowground competition for nutrients may also change along light gradients, confounding apparent differences in shade tolerance. Despite this co-variation in light and nutrients, in situ manipulation of belowground competition along a light gradient has not been previously used to investigate conifer–angiosperm seedling performance. In this study we selected conifer–angiosperm seedlings along a light gradient and used trenching to reduce belowground competition for half of the seedlings. The forest is currently dominated by an angiosperm (Beilschmiedia tawa) that is more shade-tolerant than the co-occurring conifers Prumnopitys ferruginea and shade-intolerant Dacrydium cupressinum. Diameter and height growth rates of the fastest growing seedlings (top 25%) across all species were greater for seedlings with reduced belowground competition – increased light did not significantly alter growth rates. For these fast-growing seedlings the diameter growth rates of the coniferous P. ferruginea and D. cupressinum were superior to that of the angiosperm B. tawa. Of the fastest growing seedlings, height growth was also greatest for D. cupressinum across the gradient of light availability. This species was most responsive to light, shoot growth showing a positive interaction between increased light and trenching. Approximately 30% of its seedlings occurred at >10% full sun, and rates of both diameter and shoot growth were increased approximately threefold at the highest light levels, compared with the lowest (c. 2% full sun). Despite the angiosperm’s current dominance of the study forest, the superior performance of the fastest growing conifer seedlings, coupled with their longevity, suggests the conifer species will persist even under current conditions.

Tree dynamics and co-existence in the montane-sub-alpine ecotone: the role of different light-induced strategies

Questions: Is light availability the main factor driving forest dynamics in Pyrenean sub-alpine forests? Do pines and firs differ in growth, mortality and morphological response to low light availability? Can differences in shade tolerance affect predictions of future biome changes in Pyrenean sub-alpine forests in the absence of thermal limitation? Location: Montane–sub-alpine ecotones of the Eastern Pyrenees (NE Spain). Methods: We evaluated morphological plasticity, survival and growth response of saplings of Scots pine, mountain pine and silver fir to light availability in a mixed forest ecotone. For each species, we selected 100 living and 50 dead saplings and measured size, crown morphology and light availability. A wood disk at root collar was then removed for every sapling, and models relating growth and mortality to light were obtained. Results: Fir had the lowest mortality rate (<0.1) for any given light condition. Pines had comparable responses to light availability, although in deep shade Scots pine risked higher mortality (0.35) than mountain pine (0.19). Pines and fir developed opposing strategies to light deprivation: fir employed a conservative strategy based on sacrificing height growth, whereas pines enhanced height growth to escape from shade, but at the expense of higher mortality risk. Scots pine showed higher plasticity than mountain pine for all architectural and morphological traits analysed, having higher adaptive capacity to a changing environment. Conclusions: Our results support the prediction of future biome changes in Pyrenean sub-alpine forests as silver fir and Scots pine may find appropriate conditions for colonizing mountain pine-dominated stands due to land-use change-related forest densification and climate warming-related temperature increases, respectively.

Mid-successional stand dynamics in a cool-temperate conifer-hardwood forest in northern Japan

Stand dynamics was studied over 13 years in a cool-temperate conifer-hardwood forest, northern Japan. A total 30 hardwood species and one conifer, Abies sachalinensis, larger than 1.5 cm DBH were recorded. The total stand density was 1677 trees ha−1 at the beginning, decreasing to 1184 trees ha−1 (30% reduction) over the study period, but the total stand basal area was almost unchanged (about 49 m2 ha−1). This large reduction in total density was mainly due to the death of saplings and infrequent recruitment. Number of recruits gradually decreased with time, while that of dead trees was constant. Cause of death of small trees was mainly due to suppression by tall trees. Skewness of the DBH frequency distribution varied among the species. A less skewed frequency distribution (i.e., few number of saplings) was shown by shade-intolerant species such as Populus maximowiczii and Betula maximowicziana, and a more skewed frequency distribution (i.e., large number of saplings) by shade-tolerant species such as Acer mono and Tilia japonica. DBH frequency distribution changed to less skewed patterns with reduction of density in most species during the census period. Rank of shade tolerance positively correlated with tree density and skewness, and negatively correlated with mean DBH. Skewness also positively correlated with recruitment rates. Furthermore, rank of shade tolerance positively correlated with seed size. These results suggest that shade-intolerant species regenerated immediately after disturbances by wide dispersal of small seeds, but their recruitment was interrupted after that. By contrast, shade-tolerant species were able to recruit even after the ceasation of recruitment of shade-intolerant species, but suffered severe mortality due to the increasing shading with the progress of stand development. This study suggests that the stand is still developing, with changes in species composition and size structure, and that species differences in shade tolerance and seed size are important for the stand structural changes.