Subtropical Montane Forest Research Articles

Mosses and lichens enhance atmospheric elemental mercury deposition in a subtropical montane forest†

Environmental context Mosses and lichens are widely distributed in montane forests and their important role in global biogeochemical cycles has been increasingly recognised. This study of mercury accumulation and sources in mosses and lichens, using mercury isotopic data, provides evidence that they promote atmospheric mercury deposition in these forests, which is an important function that should be incorporated into current mercury mass balance budgets for forests. Rationale Mosses and lichens, which are widely distributed in montane forests, are often used to monitor the atmospheric mercury (Hg) depositions. In this study we hypothesised that atmospheric Hg uptake by mosses and lichens could greatly promote Hg depositions in montane forests. Methodology We comprehensively determined the Hg concentration and isotopic signatures of various species of mosses and lichens in a subtropical montane forest, to quantify the Hg accumulation, influencing factors and potential Hg depositions induced by mosses and lichens. Results Our results show that the higher Hg concentrations in mosses than in lichens are mainly due to their species-specific, morphological and physiological differences. Hg isotopic mixing model results display that uptake of atmospheric elemental Hg (Hg0) contributes 89.2 ± 22.8% of Hg in mosses and 88.4 ± 24.4% in lichens. The lichens growing on trees have a lower atmospheric Hg0 source contribution than on the ground (61.3 ± 42.5% versus 93.6 ± 10.0%) because of the elevated rainfall Hg uptake on trees. The Hg storage in live moss and lichen is 28.0 ± 16.5 and 0.9 ± 1.0 μg m−2, respectively. Given the 1–2-year lifespan of moss, the moss induced atmospheric Hg deposition is almost equivalent to litterfall Hg deposition which was previously used as a proxy for atmospheric Hg0 deposition in forests. Discussion Overall, we suggest mosses and lichens play an important role in atmospheric Hg depositions and recommend more research in montane forests.

Soundscapes of the Yungas Andean forest: Identifying the acoustic footprint of an anuran assemblage

Soundscapes are composed by the conjunction of sound patterns in each space and time. The biophony produced by the advertisement calls of anurans are one of the most outstanding features of a soundscape, particularly in subtropical montane areas such as the Yungas Andean forests of NW Argentina. We recorded soundscapes with automated recording units along an altitudinal gradient and throughout a whole year in the Calilegua National Park. Using a novel combination of visual analysis and acoustic indices we have been able to identify the anuran acoustic fingerprint in the soundscapes of a seasonal subtropical montane forest. In addition, we detected a decrement in using the acoustic communication channel along the altitudinal gradient by anuran assemblages, in agreement with a decrement in species richness. Our results showed a seasonal effect of the vocalization patterns, splitting the group of sounds recorded in two main periods along the year. In this study we presented the first description of Argentina's altitudinal strata of the Yungas Andean forests. This information provides a solid basis for monitoring programs of direct and indirect anthropogenic impacts. Additionally, we highlight the importance of understanding how soundscapes are composed in a naturally protected area and, posit them as a novel ecosystem service that could benefit human health. We emphasise that Natural Soundscapes should be protected and must be included as intangible heritage in the management plans of protected areas in the country. Likewise, the methods proposed in this study encourage settling down the basis for implementing long-term acoustic monitoring of anuran species and other acoustic communities in the Yungas ecoregion.

How the color of reflective materials influences the occurrence of mammals and birds

Color reflective materials have been widely employed in agriculture, airports, and road traffic as signals and to prevent the damage caused by mammals and birds. The negative impacts of such applications on wildlife have been acknowledged, but little is known about the particular effects of different colors applied to these materials. We recorded the occurrence of wildlife using 56 camera traps placed in locations affected by different reflective color sheeting (red, yellow, green, blue, white, mirror and control without disturbance) in a subtropical montane forest of southwestern China. We compared richness and abundance of ground bird and mammal species. The results showed that the yellow reflective material has an attractive effect on birds during daytime compared with the control group, while the red and green ones appear to repel them. However, the general tendency was a reduction of bird species occurring at night because of all the different sources of reflective light. For mammals, no significant difference was found among disturbances during either day or night. Species showed different responses to specific colors but further research in this regard is needed. Based on these experimental findings, we recommend that all reflective materials should be avoided or used carefully within protected areas. Moreover, red and green signals are suitable for airports and agriculture fields to effectively prevent damage and safety concerns inflicted by birds. Biodiversity, Conservation biology, Environmental contamination and remediation, Environmental impacts, Population biology

Elevational Pattern and Control Factors of Soil Microbial Carbon Use Efficiency in the Daiyun Mountain

Microbial carbon use efficiency (CUE) refers to the C transformation to microbial biomass from C uptake. The study of soil microbial CUE is very important for understanding the soil C cycle. Here, CUE, Cgrowth, and Crespiration were measured using the 18O-H2O-DNA labeling method at six elevational sites (980-1765 m) in Daiyun Mountain, a subtropical montane forest, to understand the variation characteristics and influencing mechanisms. The results showed that:CUE varied from 0.1 to 0.4 and increased linearly with elevation; CUE was positively correlated with Cgrowth, Crespiration, and qgrowth but negatively correlated with qCO2, indicating that CUE increased with elevation by increasing microbial growth and inhibiting respiration; and temperature was the first controlling factor for the elevation variation in microbial CUE in the subtropical forest ecosystem.

Effects of stand condition and root density on fine-root dynamics across root functional groups in a subtropical montane forest

Fine roots play key roles in belowground C cycling in terrestrial ecosystems. Based on their distinct functions, fine roots are either absorptive fine roots (AFRs) or transport fine roots (TFRs). However, the function-based fine root dynamics of trees and their responses to forest stand properties remain unclear. Here, we studied the dynamics of AFRs and TFRs and their responses to stand conditions and root density in a subtropical montane mixed forest based on a 2-a root window experiment. Mean (± SE) annual production, mortality, and turnover rate of AFRs were 7.87 ± 0.17 m m−2 a−1, 8.13 ± 0.20 m m−2 a−1and 2.96 ± 0.24 a−1, respectively, compared with 7.09 ± 0.17 m m−2 a−1, 4.59 ± 0.17 m m−2 a−1, and 2.01 ± 0.22 a−1, respectively, for TFRs. The production and mortality of fine roots were significantly higher in high root-density sites than in low-root density sites, whereas the turnover of fine roots was faster in the low root-density sites. Furthermore, root density had a larger positive effect than other environmental factors on TFR production but had no obvious impact on AFR production. Tree species diversity had an apparent positive effect on AFR production and was the crucial driver of AFR production, probably due to a complementary effect, but had no evident impact on TFR. Both tree density and tree species diversity were positively correlated with the mortality of AFRs and negatively related to the turnover of TFRs, suggesting that higher root density caused stronger competition for rooting space and that plants tend to reduce maintenance costs by decreasing TFR turnover. These findings illustrated the importance of root functional groups in understanding root dynamics and their responses to changes in environmental conditions.

Canopy-Level Flux and Vertical Gradients of Hg0 Stable Isotopes in Remote Evergreen Broadleaf Forest Show Year-Around Net Hg0 Deposition.

Vegetation uptake represents the dominant route of Hg input to terrestrial ecosystems. However, this plant-directed sink is poorly constrained due to the challenges in measuring the net Hg0 exchange on the ecosystem scale over a long period. Particularly important is the contribution in the subtropics/tropics, where the bulk (∼70%) of the Hg0 deposition is considered to occur. Using the relaxed eddy accumulation technique, this study presents for the first time a whole ecosystem Hg0 flux record over an evergreen hardwood forest. This tower-based micrometeorological method gauged a cumulated net Hg0 flux of -41.1 μg m-2 over 16 months, suggesting that the subtropical montane forest acts as a large and continuous sink of atmospheric Hg0. The monthly net fluxes were consistently negative (-7.3 to -1.0 μg m-2 month-1) throughout the year, with the smallest absolute values occurring during the mild and dry subseason in spring, which was also the annual lowest in vegetation activity. Colocated measurements of multilevel gradients of Hg0 concentration and its stable isotopic composition support the finding of year-round Hg0 deposition. The stable Hg isotope measurements also show that in-canopy bi-directional Hg0 exchange is prevalent.

Core arbuscular mycorrhizal fungi are predicted by their high abundance-occupancy relationship while host-specific taxa are rare and geographically structured.

Habitat restoration may depend on the recovery of plant microbial symbionts such as arbuscular mycorrhizal (AM) fungi, but this requires a better understanding of the rules that govern their community assembly. We examined the interactions of soil and host-associated AM fungal communities between remnant and restored patches of subtropical montane forests. While AM fungal richness did not differ between habitat types, community membership did and was influenced by geography, habitat and host. These differences were largely driven by rare host-specific AM fungi that displayed near-complete turnover between forest types, while core AM fungal taxa were highly abundant and ubiquitous. The bipartite networks in the remnant forest were more specialized and hosts more specific than in the restored forest. Host-associated AM fungal communities nested within soil communities in both habitats, but only significantly so in the restored forest. Our results provide evidence that restored and remnant forests harbour the same core fungal symbionts, while rare host-specific taxa differ, and that geography, host identity and taxonomic resolution strongly affect the observed distribution patterns of these fungi. We suggest that host-specific interactions with AM fungi, as well as spatial processes, should be explicitly considered to effectively re-establish target host and symbiont communities.

Soil enzyme stoichiometry revealed the changes of soil microbial carbon and phosphorus limitation along an elevational gradient in a Pinus taiwanensis forest of Wuyi Mountains, Southeast China

Understanding changes in soil enzyme activities and ecoenzymatic stoichiometry is important for assessing soil nutrient availability and microbial nutrient limitation in mountain ecosystems. However, the variations of soil microbial nutrient limitation across elevational gradients and its driving factors in subtropical mountain forests are still unclear. In this study, we measured soil properties, microbial biomass, and enzyme activities related to carbon (C), nitrogen (N), and phosphorus (P) cycling in Pinus taiwanensis forests at different altitudes of Wuyi Mountains. By analyzing the enzyme stoichiometric ratio, vector length (VL), and vector angle (VA), the relative energy and nutrient limitation of soil microorganisms and its key regulatory factors were explored. The results showed that β-glucosaminidase (BG) activities increased along the elevational gradient, while the activities of β-N-acetyl glucosaminidase (NAG), leucine aminopeptidase (LAP), acid phosphatase (AcP) and (NAG+LAP)/microbial biomass carbon (MBC) and AcP/MBC showed the opposite trend. Enzyme C/N, enzyme C/P, enzyme N/P, and VL were enhanced with increasing elevation, while VA decreased, indicating a higher degree of microbial P limitation at low elevation and higher C limitation at high elevation. In addition, our results suggested that dissolved organic carbon and microbial biomass phosphorus are critical factors affecting the relative energy and nutrient limitation of soil microorganisms at different elevations. The results would provide a theoretical basis for the responses of soil carbon, nitrogen, and phosphorus availability as well as the relative limitation of microbial energy and nutrition to elevational gradients, and improve our understanding of soil biogeochemical cycle process in subtropical montane forest ecosystems.

Functional diversity loss and change in nocturnal behavior of mammals under anthropogenic disturbance.

In the Anthropocene, understanding the impacts of anthropogenic influence on biodiversity and behavior of vulnerable wildlife communities is increasingly relevant to effective conservation. However, comparative studies aimed at disentangling the concurrent effect of different types of human disturbance on multifaceted biodiversity and on activity patterns of mammals are surprisingly rare. We applied a multiregion community model to separately estimate the effects of cumulative human modification (e.g., settlement, agriculture, and transportation) and human presence (aggregated presence of dogs, people, and livestock) on species richness and functional composition of medium‐ and large‐bodied mammals based on camera trap data collected across 45 subtropical montane forests. We divided the detected mammal species into three trophic guilds–carnivores, herbivores, and omnivores–and assessed the nocturnal shifts of each guild in response to anthropogenic activities. Overall, species richness tended to increase (β coefficient = 0.954) as human modification increased but richness decreased as human presence increased (β = –1.054). Human modification was associated with significantly lower functional diversity (mean nearest taxon distance [MNTD], β = –0.134; standardized effect sizes of MNTD, β = –0.397), community average body mass (β = –0.240), and proportion of carnivores (β = –0.580). Human presence was associated with a strongly reduced proportion of herbivores (β = –0.522), whereas proportion of omnivores significantly increased as human presence (β = 0.378) and habitat modification (β = 0.419) increased. In terms of activity patterns, omnivores (β = 12.103) and carnivores (β = 9.368) became more nocturnal in response to human modification. Our results suggest that human modification and human presence have differing effects on mammals and demonstrate that anthropogenic disturbances can lead to drastic loss of functional diversity and result in a shift to nocturnal behavior of mammals. Conservation planning should consider concurrent effects of different types of human disturbance on species richness, functional diversity, and behavior of wildlife communities.

Ligustrum luciduminvasion decreases abundance and relative contribution of soil fauna to litter decomposition but increases decomposition rate in a subtropical montane forest of northwestern Argentina

Invasive plant species can alter litter decomposition rates through changes in litter quality, environment conditions, and decomposer organisms (microflora and soil fauna), but limited research has examined their direct impact on soil fauna. We assessed the abundance and relative contribution of soil meso- and macrofauna to litter decomposition in a forest invaded by Ligustrum lucidum W.T. Aiton and in a noninvaded forest in a subtropical mountain forest in northwestern Argentina, using litterbags (0.01, 2, and 6 mm mesh size). Additionally, we analyzed the litter quality and soil properties of both forest types. Soil fauna abundance was lower in the invaded forest than in the noninvaded forest. The contribution of soil macrofauna to litter decomposition was important in both forest types, but soil mesofauna contribution was significant only in noninvaded forest. Litter decomposition was significantly faster in the invaded forest, consistent with its higher quality litter compared with the uninvaded forest. Invaded forest had significantly lower litter accumulation, lower soil moisture, and greater soil pH than noninvaded forest. Our results showed that although soil fauna was less abundant and played a less pronounced role in litter decomposition in invaded forest, these changes did not translate into a reduced litter decomposition rate due to the higher quality of litter produced in the invaded forest.

Dynamics of tree mortality in subtropical montane forests of Northwestern Argentina

Tree mortality and its relationships with forest structure and environmental factors have been studied for many decades using permanent plots. In the last decades, plot monitoring showed that tree mortality rates were increasing in tropical and temperate regions. We analyzed tree mortality in subtropical montane forests of Northwestern Argentina to: (i) compare tree mortality rates between secondary and old-growth forests, (ii) describe relationships between tree mortality rates with elevation, climatic variables (mean annual temperature, total annual precipitation, temperature and precipitation seasonality), productivity, plot-mean wood, density and plot-mean square diameter, and (iii) analyze long-term trends of tree mortality rates at plot and species level. We used 54 permanent plots monitored for 25 years (1991–92 to 2016–17) to analyze individual-based mortality and basal area mortality rates. We found that tree mortality rates decreased significantly with elevation, precipitation seasonality, plot-mean wood density and plot-mean square diameter, and increased significantly with total annual precipitation, mean annual temperature and productivity. Individual-based mortality increased between 1991–92 and 2016–17 in old-growth forests. Although the main drivers of increasing tree mortality over time remain unknown, we suggest that it may be related to the increasing precipitation and temperature that occurred in the last decades in this region. Further research with forest plot monitoring is necessary to understand causes of increasing mortality and the consequences for forest structure, composition and dynamics in the long-term.

Biomagnification and trophic transfer of total mercury and methylmercury in a sub-tropical montane forest food web, southwest China

Little is known about the bioaccumulation and trophic transfer of total mercury (THg) and methylmercury (MeHg) via food webs in terrestrial ecosystems, especially in subtropical forest ecosystems. In the present study, THg and MeHg were determined as well as the carbon (δ13C) and nitrogen (δ15N) isotope composition in samples of soils, plants, invertebrates, and songbird feathers to construct food webs in a remote subtropical montane forest in Mt. Ailao, southwest China and assess the bioaccumulation, biomagnification, and trophic transfer of Hg. Results showed that the trophic levels (TLs) of all consumers ranged from 0.8 to 3.3 and followed the order of songbirds > spiders > omnivorous insects > herbivorous insects > plants, and THg and MeHg exhibited a clear biomagnification up the food chain from plants-herbivorous/omnivorous insects-spiders-songbirds. The lowest MeHg concentration was observed in pine needles ranged from 0.104 to 0.949 ng g−1 with only a 1.6% ratio of MeHg to THg (MeHg%), while the highest MeHg concentrations ranged from 425 to 5272 ng g−1 in songbirds with MeHg% values of up to 96%. High values of trophic magnification slope (TMS) for THg (0.22) and MeHg (0.38) were observed in plant-invertebrate-songbird food chain, verifying the significant bioaccumulation of Hg, particularly MeHg, in the remote subtropical forest ecosystem. This study confirmed the production and efficient biomagnification of MeHg in remote subtropical montane forest and the significant bioaccumulation of MeHg in terrestrial top predators.

Onward but not always upward: individualistic elevational shifts of tree species in subtropical montane forests

Ongoing global climate change is driving widespread shifts in species distributions. Trends show frequent upwards shifts of treelines, but information on changes in montane forest below the treeline and in the tropics and subtropics is limited, despite the importance of these areas for biodiversity and ecosystem function. Patterns of species shifts in tropical and subtropical regions are likely to be more complex and individualistic than global averages suggest due to high species diversity and strong influence of competition, alongside direct climatic limitations on distributions. To address the question of how subtropical montane tree species are likely to move as climate changes, we used an extensive national forest inventory to estimate distribution shifts of 75 tree species in Taiwan by comparing the optimum elevation and range edges of adults and juveniles within species. Overall there was a significant difference in optimum elevation of adults and juveniles. Life stage mismatches suggested upward shifts in 35% of species but downward shifts of over half (56%), while 8% appeared stable. Upward elevation shifts were disproportionately common in high elevation species, whilst mid to low elevation species suggested greater variation in shift direction. Whilst previous research on mountain forest range shifts has been dominated by work addressing changes in treeline position, we show that although high elevation species shift up, below the treeline species may shift individualistically, heralding widespread changes in forest communities over coming decades. The wide variation of responses indicated is likely driven by individual species responses to interacting environmental factors such as competition, topography and anthropogenic influences across the broad range of forest types investigated. As global environmental changes continue, more detailed understanding of tree range shifts across a wide spectrum of forests will allow us to prepare for the implications of such changes for biodiversity, ecosystem function and dependent human populations.

Estimation of biomass from shape-specific length-mass equations for arboreal spiders in subtropical montane forest of Taiwan

Accurate estimation of invertebrate biomass is essential for studies of ecosystem structure and function. To estimate seasonal changes in spider biomass on canopies of two coniferous and three broadleaf tree species in plantation and native forests of subtropical Taiwan, 6,554 spiders were collected from February to August 2015. A part of the collection (n = 887) was weighed and measured to develop appropriate body size-mass equations for subtropical montane forest systems. By comparing different equations, we demonstrate that use of shape-specific equations and incorporation of body width measurements provide the most accurate biomass estimates. Generalized whole-fauna equations produced accurate estimates for the entire pooled sample but caused relatively higher biases than shape-specific equations when applied to spider assemblage subgroups. Applying coefficients derived from the best equations, we describe the seasonal variation in spider biomass on five dominant tree species. Compared to broadleaf trees, Taiwan cedar and Japanese cedar supported higher spider biomass and abundance. Spider biomass on the two conifers declined in early spring, then increased over time, and reached its highest in August. In contrast, spider biomass on caudate-leaved chinkapin and Mori oak formed bell-shaped curves with a high peak in late spring. Spider biomass on deciduous Formosan alder remained at a low level from February to June and increased in August. Moreover, phenological patterns of spider biomass differed from those of abundance on some tree species. We expect that regression parameters from our study are appropriate for biomass estimation of spider assemblage in subtropical montane forest systems.

Spatio-temporal dynamics of seedling communities are determined by seed input and habitat filtering in a subtropical montane forest

Spatial and temporal variation in species abundances and distributions of the seedling community, which plays a pivotal role in maintaining species diversity, can help predict future changes in forest communities. We monitored the dynamics of 12,830 seedlings within 405 1-m2 seedling plots in the Badagongshan (BDGS) 25-ha forest dynamic plot over a 6-year period (2012–2017). We presented changes in the relative abundance for 15 dominant seedling species during the last six years, assessed temporal changes in species richness, species turnover, seedling density, species reordering (mean rank shift of the relative abundance; MRS) and community similarity within three topographically defined habitats (ridge, slope and valley), and explored the mechanisms underlying dynamics of seedling communities. Furthermore, we explored differences in species’ ecological indicator values (EIVs) and functional groups for species gained and lost during the study period. Across three habitat types, there were enormous reordering of the 15 dominant seedling species; a few mast-seedling events were clearly identified. Both species richness and seedling density continually declined over the entire census year, except for an increase of species richness during 2012–2013. Species turnover fluctuated temporally in three habitat types; overall, species emigration rate was higher than species immigration rate in three habitats. Valleys with lower soil C:N ratio, light availability and VDCN (vertical distance above the channel network), but higher soil pH and TWI (topographic wetness index), had lower species richness and stem density, and higher species turnover and species reordering than slopes and ridges. At the community-wide scale, significant directional changes in species composition occurred on ridges and slopes. Newly colonizing species were typically more shade- tolerant, water- and temperature- demanding shrub species and grown on soil with low pH but high fertility. In the BDGS plot, species richness and seedling density fluctuated in the first two years and then decreased over time, which reflects that both habitat filtering and seed input regulated temporal dynamics of species composition, but the relative importance varied among studied years. In this subtropical forest, species composition showed obvious directional changes. Shrub species increased more than species of other strata in ridge and slope areas. It is worth noting that an increased dominance of species that are more water-demanding could increase the risk of mortality under global climate change (e.g. drought).

Runoff and soil erosion responses to rainfall and vegetation cover under various afforestation management regimes in subtropical montane forest

AbstractSoil erosion and runoff generation are a major concern in forest and agricultural ecosystem management. However, the tangled coeffects of rainfall and vegetation on runoff and erosion generation are regionally dependent and remain unclear in regions with high erosivity, such as Southeast China where the large‐scale afforestation is being implemented. Here, we present the 4‐year observations of runoff and erosion responses to various storms following three afforestation (assisted natural regeneration [ANR; windrowing harvest residues on surface]; Chinese fir cultivation [YCF]; andCastanopsis carlesiicultivation [YCP] after slash‐and‐burn) since 2012. Stepwise power‐law regressions were used to identify the key variables and formulate the responses. Results show that the YCF and YCP following slash and burn have extremely high erosion rates, over 20 t ha−1 yr−1(twofold higher than the global tolerable threshold), during the first year. In contrast, the erosion rate is only approximately 1.3 t ha−1 yr−1in the ANR. The high erosion rates reveal the environmental vulnerability and the necessity of management in this region. Stepwise regressions suggest total rainfall rather than rainfall intensity as key variable probably because the forest canopy substantially offsets raindrop kinetics. The nonlinear runoff and erosion responses indicate that the risk of soil erosion is extremely high when vegetation cover is less than 40% and rainfall is greater than 80 mm. This study, therefore, suggests that windrowing harvest residues into strips or maintaining a vegetation cover greater than 40% is a sound management practice for mitigating land degradation in this region.

Differential larval phenology affects nestling condition of Green-backed Tit (Parus monticolus) in broadleaf and coniferous habitats, subtropical Taiwan

Trophic interactions between birds and their prey often vary among habitat types, but they are poorly studied in low-latitude regions. We assessed the seasonal effect of larval abundance on the breeding performance of the Green-backed Tit (Parus monticolus), a caterpillar specialist, in broadleaf (mixed-oak forest) and coniferous (conifer plantation) habitats in subtropical Taiwan. We measured the biomass of Lepidoptera and Hymenoptera larvae in five tree species: two evergreen oaks and one deciduous alder in broadleaf habitat and two conifers in coniferous habitat. Alder supported a high larval biomass peak in early spring, dominated by noctuid and sawfly larvae, while the two oaks had later, lower peaks. The diversity of trees in the broadleaf habitat supported a broad food peak, spiking in early spring and gradually declining. In contrast, the coniferous habitat had a comparatively lower larval biomass that increased slightly over the season and included a high percentage of hairy lithosiines. Habitat-specific seasonality in larval abundance affected nestling conditions. Early-brood nestlings in the broadleaf habitat were heavier than those in the coniferous habitat. However, the between-habitat difference disappeared in the late broods because the mass of nestlings in the coniferous habitat increased significantly. We found a linear relationship between nestling condition and the total larval biomass available at demand peaks, but there were no differences in annual breeding density, late-brood frequency, laying date, clutch size, or fledging success between the two habitats. Food availability constrained nestling growth but not survival. Habitat-related trophic interactions are present in these subtropical montane forests.

Intraspecific variation in seed germination and storage behaviour of Cordia tree species of subtropical montane forests of Argentina: Implications for ex situ conservation

Cordia americana, C. saccelia and C. trichotoma are native trees of the subtropical Andean forests of Argentina. Due to their high value as a wood source, these species are under threat from the over-exploitation of their populations and from changes in land use. Knowledge of seed biology may contribute to clarifying their regeneration ecology and establishing management policies and conservation programmes. We studied seed mass, seed germination, seed desiccation tolerance and seed storage behaviour in seeds from different populations of each species. Seed mass differed among the populations of each species. For C. americana and C. saccelia, germination percentages (GP) varied among populations and light and temperature conditions. For all species and populations, GP was not affected by seed population or desiccation treatments, but the time to germination (t50) increased after drying. GP decreased and t50 increased in seeds stored with 8–10% MC at 35 °C for three months for all species and populations. Seeds stored with 8–10% MC at 20 °C and with 3–5% MC at 35 °C also showed deterioration depending on the species. Differences in germination requirements, desiccation tolerance and storage behaviour were not related to seed mass. These results indicate that (1) all Cordia species seeds show orthodox storage behaviour, (2) both moisture content and temperature are key factors in Cordia seed storage and (3) some populations within a species are more sensitive to desiccation and storage conditions than others. Thus, these species and populations could be preserved in seed banks, but the germination, desiccation and storage behaviour variability among populations must be considered before germination and storage protocols are established. This information will be very useful for designing restoration, reforestation, plant propagation and in situ and ex situ conservation programmes for these Cordia species.

Effects of Precipitation on Mercury Accumulation on Subtropical Montane Forest Floor: Implications on Climate Forcing

AbstractProcesses facilitated by precipitation play an important role on mercury (Hg) accumulation on forest floor and therefore key to Hg cycling in forest ecosystems. Sites along the windward slope of 1,250 to 2,400 m at Mt. Ailao, Southwestern China, have higher precipitation than the leeward slope sites. In this study, measurements of Hg concentration and associated stable isotope composition for soil, fresh, and degraded litterfall samples were made at sites along two slopes of Mt. Ailao to quantify the direct and indirect effects of precipitation on Hg accumulation on forest floor. Higher soil Hg concentrations, larger litterfall Hg depositions, and faster litter decomposition rates were observed on the windward slope (1,250–2,400 m). Data of Hg isotopic signatures suggest that Hg in surface soils is mainly derived from litterfall Hg input. Precipitation enhances litterfall Hg deposition by increasing litter biomass production, reduces litter decomposition rate, facilitates short‐term Hg uptake to decomposing litter, and potentially increases microbial activity that increases Hg loss via microbial reduction or runoff. Structural equation modeling results support that the indirect effect of precipitation on increased biomass production merge as the most important factor controlling soil Hg variation. Given the climate forcing on global precipitation pattern and vegetation growth cycle, Hg biogeochemical cycling is likely to continue to evolve under the changing climate.

Linkages between tree architectural designs and life-history strategies in a subtropical montane moist forest

Tree architecture is crucial to maximizing light capture, determined by carbon allocation of individual trees, and consequently characterizes species-specific growth strategies. Its variation and associated life-history strategies have been examined in tropical and temperate forests, but not in subtropical forests. Moreover, a similar architectural pattern was found using a hierarchical Bayesian model in a tropical forest, which differed from most of previous studies. Here, we employed a hierarchical Bayesian model to examine tree architecture differences and associations with adult stature and light requirement among 59 subtropical co-occurring species. Architectural variations among tree species with different seed dispersal and leaf phenology types were analyzed. Most species showed similar architecture in the height of the lowest foliage-tree height relationships (F-H) and the long side of crown- tree height relationships (W1-H), but some species showed interspecific variations in tree height-stem diameter relationships (H-D) among the 59 co-occurring species in the subtropical montane forest. Trees developed deeper and larger crowns at mid-elevation compared to the tropical and temperate forests. Parameters of H-D relationship differed in leaf phenology and dispersal types, and intercepts of F-H relationship and W1-H relationship differed in leaf phenology. Large-statured species had more slender stems, and shallower and narrower crowns at small sizes, but similar crowns at large sizes. Light-demanding species showed weak correlations between architectural variables and light requirement but exhibited wide crowns at the intermediate sizes. In general, size-dependent architectural differentiation was driven mainly by adult stature and light requirement in subtropical forest. Coexistence species showed different life-history strategies in light capture, which may help provide options in forest thinning and harvesting in subtropical forest. Species-specific tree architectural models of 59 co-occurring species represent three-dimensional (3D) structure of this subtropical forest accurately, but also support for future terrestrial laser scanning (TLS) data analysis.