Mixed Subtropical Forest Research Articles

Phylogenetic regionalization of tree assemblages reveals novel patterns of evolutionary affinities in the Atlantic Forest

AbstractAimWe used a phylogenetic approach to group assemblages of woody plant into major vegetation units in the Atlantic Forest, thus for the first time incorporating information on species evolutionary relationships into a bioregionalization of this critical hotspot. A phylogenetic regionalization will provide a spatially explicit framework for answering many basic and applied questions in biogeography, ecology and conservation.LocationAtlantic Forest.TaxonAngiospermsMethodsOur data set comprises 614 genera and 116 families, spread over 1,755 assemblages. To place assemblages in a multivariate evolutionary composition space, we used a phylogenetically informed ordination analysis, and to determine what the main phylogenetic groups of assemblages were, we used K‐means clustering based on phylogenetic dissimilarity of assemblages. To quantify how well environmental variables distinguish the phylogenetic groups found, we implemented classification tree approaches. Then, to explore the evolutionary turnover between the phylogenetic groups, we calculated phylogenetic beta diversity. Finally, we determined the lineages that are most strongly associated with individual phylogenetic groups using an indicator analysis for lineages.ResultsOur analyses suggest that there are seven principal groups, in terms of evolutionary lineage composition, in the Atlantic Forest. The greatest turnover of phylogenetic lineage composition separates tropical evergreen rain forest and semideciduous assemblages from subtropical and highland assemblages. The mixed subtropical forest showed the lowest phylogenetic compositional similarity values with other groups. Tropical rain forest had the highest number of significant indicator lineages, and the highest values of the indicator statistic for lineages.Main conclusionsWe found that the most pronounced evolutionary division separates southern and highland tree assemblages from those occurring under more tropical climates and at lower elevations. Our phylogenetic analyses point to an environmentally driven compositional division, likely based on the regular occurrence of freezing versus non‐freezing temperatures. Precipitation and edaphic regimes that assemblages experience had less definitive effects on their evolutionary lineage composition.

Specific leaf area is a potential indicator of tree species sensitive to future climate change in the mixed Subtropical Forests of southern Brazil

• Functional traits influence plants performance. • We tested whether functional traits could predict the impact of climate change. • Specific leaf area was an indicator of species sensitivity to climate change. • Araucaria angustifolia is highly sensitive to climatic change. Global warming represents one of the most important threats to biodiversity. Because the functional traits of plants influence the performance of individuals under different environmental conditions, we aimed to describe the functional traits of the most frequent tree species found in the Brazilian Mixed Subtropical Forest. We also aimed to test whether functional traits could be used to predict the impact of climate change on the future distribution of tree species. For selected species, certain functional traits were described, namely, wood density, leaf size, specific leaf area, leaf renovation regime, dispersal syndrome, maximum potential height, fruit type, presence of seed dormancy, and the desiccation tolerance of seeds. The geographical distributions of the selected species were modeled using the Maximum Entropy algorithm (MaxEnt) as a function of climatic variation. To predict the impact of climatic changes by 2070 relative to current climate, the best and worst scenarios in relation to the concentration of greenhouse gases (GHG) were used. While the best scenario assumes a strong reduction in GHG anthropogenic emissions, turning negative by 2070, the worst scenario assumes a continuous increase in GHG anthropogenic emissions over time. The functional traits were ordinated by Principal Components Analysis to identify the ecological strategies of each species. The relationship between functional traits and changes to the area of climatic suitability of each species was evaluated using regression trees. Functional traits predicted changes to suitable climatic areas in the worst-case scenario only. The suitable climatic area of more leathery leaf species was predicted to decline by 41.0% on average, whereas that of more membranous leaf species was predicted to decline by 14.0%. In particular, Araucaria angustifolia , which is considered the most representative species of the Mixed Subtropical Forest of Brazil, had the highest sensitivity to climate change. Consequently, our results suggest that this important forest formation will be strongly impacted by climate and will be under severe risk in the future.

Estimation of forest biomass dynamics in subtropical forests using multi-temporal airborne LiDAR data

Abstract Estimating the change in the magnitude and distribution of forest biomass is important for monitoring carbon dynamics and understanding the implications on the terrestrial carbon cycle. In this study, we assessed the capacity of multi-temporal airborne Light Detection and Ranging (LiDAR) data to estimate forest biomass dynamics at a mixed subtropical forest of southeast China, and analyzed the magnitude and spatial patterns of the above ground biomass (AGB) change over a 6-year period. To do so, we evaluated different approaches to estimate change in AGB, specifically direct (i.e., predicting biomass change using the differences in LiDAR metrics) and indirect (i.e., modeling biomass for each point in time and predicting the change as their differences) approaches. Once models were developed, the change in AGB was mapped across the study site and examined in relation to forest type and age. Our results demonstrated that the direct approach (CV-R2 = 0.63, CV-rRMSE = 25.64%) produced more accurate estimates in change of AGB than the indirect approach (CV-R2 = 0.59, CV-rRMSE = 28.35%). Canopy height metrics of delta mean height (∆ hmean) and a number of upper percentile heights (i.e., ∆ h75 and ∆ h95), calculated from the LiDAR first returns, were found to be most sensitive to changes in biomass, whereas metrics based on maximum canopy height or canopy density had less predictive power. Furthermore, differences in point cloud densities did not significantly impact the estimations of AGB and change of AGB at the plot-scale (30 × 30 m). Spatial extrapolation of the AGB change indicated that, in general, most of the forest area had an overall gain in biomass. The middle-aged stands (typically dominated by Quercus acutissima between 41 and 60 years old) show marked growth of biomass (median ∆ AGB = 2.29 Mg ha− 1 year− 1), followed by mature (typically dominated by Pinus massoniana between 31 and 60 years old) (median ∆ AGB = 1.72 Mg ha− 1 year− 1) and young stands (typically consisting of regenerated broadleaved trees younger than 40 years old) (median ∆ AGB = 1.48 Mg ha− 1 year− 1), whereas over-mature stands (typically dominated by Cunninghamia lanceolata older than 35 years) show the lowest growth (median ∆ AGB = 0.76 Mg ha− 1 year− 1). This study demonstrates benefits of using multi-temporal LiDAR data to help identify specific areas for management interventions, to enhance forest productivity, maintain biomass stocks and optimize carbon sequestration.

Insight into the indirect function of isopods in litter decomposition in mixed subtropical forests in China

Aboveground consumers can shape belowground processes in brown-food webs of forests by converting litter into faeces. Woodlice are one of the important aboveground consumer groups driving the dynamics of belowground soil. Although considerable data on litter decomposition exists, the indirect effects of woodlice (different qualities of faeces) on litter decomposition need to be explored further. In this study, we assessed the influence of isopods (Armadillidium vulgare) and its by-products (three contrasting qualities of faeces) on the decomposition of broad-leaf and needle litter via soil incubation. Litter mass loss, soil microbial biomass and soil extracellular enzyme activities treated with different isopod by-products were determined in six-month laboratory incubations.The results showed that after incubation, the indirect effect of fauna (faeces) did not significantly increase broad-leaf litter decomposition. However, faeces of isopods fed on high-quality legume litter significantly increased needle litter decomposition. The effects of isopod faeces on microbial activities were significant: most of the soil microbial biomass and extracellular enzyme activities increased significantly compared with non-faeces treatments in the soil of broad-leaved and coniferous forests; and high-quality faeces strengthened the correlation of litter mass loss with peroxidase and phenol oxidase in coniferous forest. The result suggests that faeces with higher concentrations of nitrogen and labile carbon can mediate the decomposition of refractory materials like lignin and phenolic compounds, which might be highly relevant for the litter decomposition process in ecosystems with high macrofauna abundance. This study infers that the indirect effect of isopods (faeces) on litter decomposition depends on the quality of the litter they consumed and the type of decomposing litter. Isopods indirectly accelerate the nutrient-poor litter decomposition process by converting high-quality litter into faeces. As such, the negative effects of litter recalcitrance on microbial decomposition in mixed forests are indirectly alleviated.

Using Small-Footprint Discrete and Full-Waveform Airborne LiDAR Metrics to Estimate Total Biomass and Biomass Components in Subtropical Forests

An accurate estimation of total biomass and its components is critical for understanding the carbon cycle in forest ecosystems. The objectives of this study were to explore the performances of forest canopy structure characterization from a single small-footprint Light Detection and Ranging (LiDAR) dataset using two different techniques focusing on (i) 3-D canopy structural information by discrete (XYZ) LiDAR metrics (DR-metrics), and (ii) the detailed geometric and radiometric information of the returned waveform by full-waveform LiDAR metrics (FW-metrics), and to evaluate the capacity of these metrics in predicting biomass and its components in subtropical forest ecosystems. This study was undertaken in a mixed subtropical forest in Yushan Mountain National Park, Jiangsu, China. LiDAR metrics derived from DR and FW LiDAR data were used alone, and in combination, in stepwise regression models to estimate total as well as above-ground, root, foliage, branch and trunk biomass. Overall, the results indicated that three sets of predictive models performed well across the different subtropical forest types (Adj-R2 = 0.42–0.93, excluding foliage biomass). Forest type-specific models (Adj-R2 = 0.18–0.93) were generally more accurate than the general model (Adj-R2 = 0.07–0.79) with the most accurate results obtained for coniferous stands (Adj-R2 = 0.50–0.93). In addition, LiDAR metrics related to vegetation heights were the strongest predictors of total biomass and its components. This research also illustrates the potential for the synergistic use of DR and FW LiDAR metrics to accurately assess biomass stocks in subtropical forests, which suggest significant potential in research and decision support in sustainable forest management, such as timber harvesting, biofuel characterization and fire hazard analyses.

Diversity and spatial structure of belowground plant-fungal symbiosis in a mixed subtropical forest of ectomycorrhizal and arbuscular mycorrhizal plants.

Plant–mycorrhizal fungal interactions are ubiquitous in forest ecosystems. While ectomycorrhizal plants and their fungi generally dominate temperate forests, arbuscular mycorrhizal symbiosis is common in the tropics. In subtropical regions, however, ectomycorrhizal and arbuscular mycorrhizal plants co-occur at comparable abundances in single forests, presumably generating complex community structures of root-associated fungi. To reveal root-associated fungal community structure in a mixed forest of ectomycorrhizal and arbuscular mycorrhizal plants, we conducted a massively-parallel pyrosequencing analysis, targeting fungi in the roots of 36 plant species that co-occur in a subtropical forest. In total, 580 fungal operational taxonomic units were detected, of which 132 and 58 were probably ectomycorrhizal and arbuscular mycorrhizal, respectively. As expected, the composition of fungal symbionts differed between fagaceous (ectomycorrhizal) and non-fagaceous (possibly arbuscular mycorrhizal) plants. However, non-fagaceous plants were associated with not only arbuscular mycorrhizal fungi but also several clades of ectomycorrhizal (e.g., Russula) and root-endophytic ascomycete fungi. Many of the ectomycorrhizal and root-endophytic fungi were detected from both fagaceous and non-fagaceous plants in the community. Interestingly, ectomycorrhizal and arbuscular mycorrhizal fungi were concurrently detected from tiny root fragments of non-fagaceous plants. The plant–fungal associations in the forest were spatially structured, and non-fagaceous plant roots hosted ectomycorrhizal fungi more often in the proximity of ectomycorrhizal plant roots. Overall, this study suggests that belowground plant–fungal symbiosis in subtropical forests is complex in that it includes “non-typical” plant–fungal combinations (e.g., ectomycorrhizal fungi on possibly arbuscular mycorrhizal plants) that do not fall within the conventional classification of mycorrhizal symbioses, and in that associations with multiple functional (or phylogenetic) groups of fungi are ubiquitous among plants. Moreover, ectomycorrhizal fungal symbionts of fagaceous plants may “invade” the roots of neighboring non-fagaceous plants, potentially influencing the interactions between non-fagaceous plants and their arbuscular-mycorrhizal fungal symbionts at a fine spatial scale.

The mycorrhizal status of Taiwanese trees and the description of some ectomycorrhizal types

In Taiwanese forests a dependence of mycorrhizal types on the altitude is recognizable: in the lower tropical regions VA-mycorrhizae dominate, whereas in the mixed subtropical forests most of the species show VA-mycorrhizae, but there are also several species with ectomycorrhizae. In the higher mountains ectomycorrhizae predominate. In addition to this relationship between mycorrhizal status and altitude, some tree species belong to typical ectomycorrhizal or VA-mycorrhizal families. Ten ectomycorrhizal types from Taiwanese trees were characterized by macroscopic, microscopic and ultrastructural features. The basic structures of hyphal mantles are the same in Taiwan as in the Black Forest (southwest Germany). Two of the types described and two further types are identical with types from the Black Forest on Picea abies (L.) Karst. Only two fungal partners could be identified (Lactarius, Amphinema), all others are unknown. Some noteworthy observations are: an epidermis-like covering of a hyphal mantle, an ectendomycorrhiza on Pinus taiwanensis Hayata with Amphinema byssoides and wall ingrowths in the outer cortical layer of Castanopsis-mycorrhizae.

Tertiary vegetation, climate, and altitude of the Rio Grande depression, New Mexico–Colorado

Late Eocene to middle Oligocene floras from the area of the present Rio Grande depression represent a time sequence from the upper part of mixed subtropical forest (Bernalillo flora), to an ecotone between broadleaved sclerophyll and mixed conifer forest (Red Rock Ranch flora), to subalpine conifer forest (Hillsboro and Hermosa floras). The implied difference in mean annual temperature of ~ 11°C suggests that altitude increased 2,000 m in 6–8 my. Construction of the Datil-Mogollon volcanic pile, averaging about 1,200 to 1,500 m thick, is thought to be largely responsible for the forest zonation, but regional doming accompanying volcanism may also be involved. The Oligocene subalpine conifer forests now occur in the piñon-juniper belt 900 and 1,200 m below the present subalpine zone, consistent with the subsidence that formed the Rio Grande rift beginning in the late Oligocene/early Miocene and continuing to the present. Later epeirogenic uplift of ~ 1200 m is implied by fossil plants in the Galisteo (~ 40 my bp), Creede (~ 27 my bp) and Tesuque (~ 14 my bp) Formations that border, or are in the rift.