Understory Research Articles

Area-based vs tree-centric approaches to mapping forest carbon in Southeast Asian forests from airborne laser scanning data

Tropical forests are a key component of the global carbon cycle, and mapping their carbon density is essential for understanding human influences on climate and for ecosystem-service-based payments for forest protection. Discrete-return airborne laser scanning (ALS) is increasingly recognised as a high-quality technology for mapping tropical forest carbon, because it generates 3D point clouds of forest structure from which aboveground carbon density (ACD) can be estimated. Area-based models are state of the art when it comes to estimating ACD from ALS data, but discard tree-level information contained within the ALS point cloud. This paper compares area-based and tree-centric models for estimating ACD in lowland old-growth forests in Sabah, Malaysia. These forests are challenging to map because of their immense height. We compare the performance of (a) an area-based model developed by Asner and Mascaro (2014), and used primarily in the neotropics hitherto, with (b) a tree-centric approach that uses a new algorithm (itcSegment) to locate trees within the ALS canopy height model, measures their heights and crown widths, and calculates biomass from these dimensions. We find that Asner and Mascaro's model needed regional calibration, reflecting the distinctive structure of Southeast Asian forests. We also discover that forest basal area is closely related to canopy gap fraction measured by ALS, and use this finding to refine Asner and Mascaro's model. Finally, we show that our tree-centric approach is less accurate at estimating ACD than the best-performing area-based model (RMSE 18% vs 13%). Tree-centric modelling is appealing because it is based on summing the biomass of individual trees, but until algorithms can detect understory trees reliably and estimate biomass from crown dimensions precisely, areas-based modelling will remain the method of choice.

Liana effects on biomass dynamics strengthen during secondary forest succession.

Secondary forests are important carbon sinks, but their biomass dynamics vary markedly within and across landscapes. The biotic and abiotic drivers of this variation are still not well understood. We tested the effects of soil resource availability and competition by lianas on the biomass dynamics of young secondary tropical forests in Panama and assessed the extent to which liana effects were mediated by soil resource availability. Over a five-year period, growth, mortality, and recruitment of woody plants of ≥1cm diameter were monitored in 84 plots in 3-30-year-old secondary forests across the Agua Salud site in central Panama. Biomass dynamics and the effects of lianas and soil resources were examined using (generalized) linear mixed-effect models and a model averaging approach. There was strong spatial and temporal variation in liana biomass within and across the plots. The relative biomass of lianas had a strong negative effect on overall tree growth, growth of understory trees decreased with soil fertility and dry season soil water content, and the effect of lianas on tree mortality varied with soil fertility. Tree recruitment was not associated with any of the predictor variables. Our model indicates that tree biomass growth across our landscape was reduced with 22% due to competition with lianas, and that the effect of lianas increased during succession, from 19% after five years to 32% after 30years. The projected liana-induced growth reduction after 60years was 47%, which was consistent with data from a nearby site. Our study shows that the observed liana proliferation across tropical forests may reduce the sequestration and storage of carbon in young secondary forests, with important implications for the carbon balance of tropical forest landscapes and consequently for global climate change. Our study highlights the need to incorporate lianas and soil variables in research on the biomass dynamics of secondary forest across tropical landscapes, and the need for well-replicated longitudinal studies to cover landscape-level variability in the relevant abiotic and biotic components.

Holocene climate reconstruction based on herbaceous phytolith indices from an AMS 14C-dated peat profile in the Changbai Mountains, northeast China

This study uses new herbaceous phytolith indices to reconstruct the paleoclimate in the Changbai Mountains, NE China. In this study, we collected 52 pairs of herbaceous quadrats and corresponding topsoils: 25 were from the understory (UND) and 7 were from the non-understory (NON) in the Changbai Mountains; whereas the other 20 were from the grassland (GRA) of Songnen Plain for comparing the forest area of the Changbai Mountains. The phytolith analyses of the 104 modern samples provide a guide of using herbaceous phytolith indices as paleoclimate reconstruction. The herbaceous quadrats of the Changbai Mountains contained more long-cell phytoliths and fewer short-cell phytoliths compared to the herbaceous quadrats of the Songnen grassland; and similar situations appeared in the corresponding topsoil phytoliths. The ratio of short cell% to long cell% (S/L) in the topsoil can be used to discriminate grassland (S/L > 1.65) and forest (<1.65), with discriminant accuracy of 80%. Furthermore, in the forest region, S/L in the topsoil is low for the non-understory (NON) (<0.46), and relatively high for the understory (UND) (0.46 < S/L < 1.65), probably due to preservation of short-cell phytoliths. The ratio of rondel% to lanceolate% (Ro/La) reflected the same trend as S/L for the forest region: Ro/La < 0.23 indicating NON, and Ro/La > 0.89 indicating UND. Thus, lower S/L and Ro/La ratios may reflect more development of NON in the forest region under relatively warm conditions, whereas higher S/L and Ro/La values indicate better development of UND with cold climates. These two indices (S/L and Ro/La) from a peat profile in the Changbai Mountains were further used to reconstruct the paleoclimate since 7670 a BP. The phytolith analyses of 33 peat samples from the 326-cm long core showed four ordinal clustering zones: Zone I (7670–4060 a BP) with low mean S/L (0.42) and Ro/La (0.78) was characterized as warm. In Zone II (4060–2580 a BP), S/L and Ro/La fluctuated around mean values of 0.47 and 3.40, respectively; indicating cooler climate than Zone I. Zone III (2580–640 a BP) was characterized by the highest mean values of S/L (0.53) and Ro/La (6.97) in the profile, reflecting the coldest condition in the record. In Zone IV (640 a BP–modern), the average values of S/L and Ro/La were 0.31 and 1.14, respectively. Both indices increased initially and then declined, perhaps reflecting the colder climate of the Little Ice Age, followed by a warming period. The climatic patterns of the Changbai Mountains reconstructed from the herbaceous phytolith indices agreed with the Ic index and pollen analysis from the same peat profile, suggesting that these new herbaceous phytolith indices should be applicable in paleoclimate reconstruction.

Research on Understory Vegetation and Soil Physical-chemical Properties of Teak Plantation with Difference Stand Densities

Research on Understory Vegetation and Soil Physical-chemical Properties of Teak Plantation with Difference Stand Densities

Intra-annual to multi-decadal xylem traits in a tropical moist semi-deciduous forest of Central Africa

A witness of a tree’s past conditions is the wood itself. The main research question of this dissertation is how to assess and reveal the driving forces of the patterns of wood traits on pith-to-bark cross-sections in tropical trees. Cambial and leaf phenology was monitored in the Luki Reserve (Mayombe forest, D.R. Congo). Furthermore, X-ray CT densitometry was explored to assess traits in a reliable way, for multiple species. Variability in phenology is observed for T. superba, which requires traits of individual trees to be fixed on a time axis. Furthermore, X-ray CT is a suitable method for assessing traits in a fast way. Cambial activity of understory trees has shown to be species-specific, whilst many trees show zero xylem growth. Finally, 66 years of tree growth was analysed, while trait analysis revealed a median ring count of only 32, thus implying many non-periodical rings. This work presents methodological improvements to measure traits as continuous variables from pith to bark, but also acknowledges that phenology still remains a key aspect in order to fix traits on a time axis.

Intra-annual to multi-decadal xylem traits in a tropical moist semi-deciduous forest of Central Africa

A witness of a tree’s past conditions is the wood itself. The main research question of this dissertation is how to assess and reveal the driving forces of the patterns of wood traits on pith-to-bark cross-sections in tropical trees. Cambial and leaf phenology was monitored in the Luki Reserve (Mayombe forest, D.R. Congo). Furthermore, X-ray CT densitometry was explored to assess traits in a reliable way, for multiple species. Variability in phenology is observed for T. superba, which requires traits of individual trees to be fixed on a time axis. Furthermore, X-ray CT is a suitable method for assessing traits in a fast way. Cambial activity of understory trees has shown to be species-specific, whilst many trees show zero xylem growth. Finally, 66 years of tree growth was analysed, while trait analysis revealed a median ring count of only 32, thus implying many non-periodical rings. This work presents methodological improvements to measure traits as continuous variables from pith to bark, but also acknowledges that phenology still remains a key aspect in order to fix traits on a time axis. Key words: leaf phenology, wood anatomy, stable isotopes, Mayombe, dendrochronology, X-ray CT densitometry

Long-term regeneration responses to overstory retention and understory vegetation treatments in the northern Rocky Mountains

Classic regeneration cuttings retaining trees at harvest (shelterwood with reserves, group selection) can be analyzed as analogs of variable-retention harvesting. A 1974 silvicultural experiment in the northern Rocky Mountains was analyzed at 38 years to evaluate the long-term effects of retention harvests on stand development, with a focus on both regeneration and retention tree responses. The postharvest understory treatments (understory removed and broadcast burned) effects were also evaluated. Results indicate that overstory retention results in relatively long-term regeneration growth reduction. Compared with the overstory-free condition (clearcut), the shelterwood with reserves and group selection overstories both reduced the regenerated cohort?s basal area, 63 and 44%, respectively. Postharvest burning increased regeneration stem density and also decreased mean regenerated tree size; consequently, these treatment effects were somewhat offsetting, as they produced a zero net difference in regenerated cohort basal area. Considerable regeneration growth reduction associated with retained overstory trees in the shelterwood with reserves was partially mitigated by understory vegetation protection measures that conserved advance regeneration. We conclude that both retention treatments somewhat suppressed regenerated cohort development, but that these impacts were lessened when overstory trees were aggregated and cuttings were in groups, rather than regularly dispersed through the cutting unit.

Light avaliability at the dry and rainy seasons in agrossivicultural system under different fertilizations

This study was conducted in a agrossilvicultural system with two years of deployment, located in Goiânia, Goias, using tree component as the species Tectona grandis L. f. This objective was evaluate the radiation incidence in the seasons dry and rainy under different fertilization. The design was a randomized block, in split plot, factorial arrangement 4 x 2 x 2. The plots received the factors fertilization and measurement of height, being four types of fertilization (control, NPK, sewage sludge and cattle manure) and two heights measure (soil level and 1.3 m above the soil). The subplots were allocated two seasons (dry and rainy), with four repetitions (blocks). They evaluated the photon flux density (PFD) in μmol.m -2 .s -1 and the percentage of shading in the understory. The types of fertilizer did not influence the soil fertility and the light avaliability in any of the seasons and heights of measurement. The percentage (%) shading differed only at soil level, being higher in the rainy season compared to season dry (37.18 vs. 19.80%). In the dry season is reduced (%) shading and the consequent increase in photon reflectance rate at soil level in the agrossilvicultural system in initial stage.

Analyzing deadwood volume of Calabrian pine (Pinus brutia Ten.) in relation to stand and site parameters: a case study in Köprülü Canyon National Park.

The importance of deadwood (DW) in forest ecosystems is widely recognized today. Deadwood is used as a proxy indicator for biodiversity conservation and sustainable management of forests. This research aims to determine the amount and spatial distribution of DW (standing dead trees, stumps, and coarse woody debris) and characterize the changes with few selected parameters in an unmanaged forest reserve of Köprülü Canyon National Park (NP). The data were collected from 387 temporary sample plots with different stand characteristics such as stand age, crown closure, site index, and density, and site parameters like elevation, aspect, slope, and distance to settlement areas of Calabrian pine (Pinus brutia Ten.)-dominated forests. The mean volume of DW was 3.8m3/ha which was 2.4% of the total standing living volume. The volume of standing DW was 0.5m3/ha (13.2%), that of stumps was 0.2m3/ha (5.3%), and that of down DW was 3.1m3/ha (81.5%). Statistically, positive correlation was found between the volume of DW and that of living trees, crown closure, altitude (p<0.01), and stand age (p<0.05). However, negative correlation was found between the number of understory trees (p<0.01) and DW. The results obtained from Calabrian pine (P. brutia Ten.) can be used as reference values for managed forests and can contribute to set the rules in deciding the appropriate level of DW in particularly biodiversity integrated forest management planning.

Seasonal leaf phenology data for 12 tree species in a cool‐temperate deciduous broadleaved forest in Japan from 2005 to 2014

AbstractThis paper reports seasonal data regarding leaf number, leaf length and width, leaf area, leaf angle, and SPAD (leaf chlorophyll content index) for 11 genera (12 species) in a cool‐temperate deciduous broadleaved forest in Japan. Knowing the leaf phenology of tree species is important for accurately evaluating the temporal variability of ecosystem functions (e.g., photosynthesis and evapotranspiration) under rapid climate change. However, there is a lack of freely available long‐term observation data regarding leaf phenological characteristics for many tree species. We collected leaf phenological data from tagged shoots every 1–4 weeks from April or May to October or November each year from 2005 to 2014 in Takayama, Japan (36°08′46″N, 137°25′23″E, 1420 m a.s.l.). We targeted typical dominant, codominant, and understory tree species at the site. To evaluate differences among individuals and between sunlit and shaded leaves, we measured one to four shoots of some species and individuals. Our data provide input, calibration, and validation parameters for a terrestrial ecosystem and for radiative‐transfer models and remote‐sensing observations.

A new species of Jomine Graf-Kumagai (Hymenoptera: Ichneumonidae:Campopleginae) from Brazil.

The genus Jomine Graf-Kumagai has two described species known only from Brazil. A new species, J. paulista Herrera-Florez sp. n. is described and its host is given here. The material used in this work was obtained during a survey of the Geometridae larvae and their parasitoids in an understory at São Paulo, Brazil. An identification key to the species of Jomine is provided.

Difference between evergreen conifer and deciduous hardwood trees in suppressing the growth of Abies sachalinensis understory trees

Difference between evergreen conifer and deciduous hardwood trees in suppressing the growth of Abies sachalinensis understory trees

Quantification of Changes in Light and Temperature Associated with Invasive Amur Honeysuckle (Lonicera maackii)

Biological invasion by nonnative species is considered one of the major threats to the global environment. Amur honeysuckle (Lonicera maackii) is a shrub introduced from Asia which has become invasive in Eastern deciduous forests of North America. An interesting aspect of the life-history of Amur honeysuckle is its extended leaf phenology. It leafs out earlier in the spring than most native shrubs and understory trees and loses its leaves later in the fall. Thus, Amur honeysuckle has the potential to alter the natural light environment and possibly impact native species, particularly spring ephemerals which are dependent on high light levels prior to canopy leaf-out. We tested the hypothesis that light levels are lower in sites with Amur honeysuckle relative to sites with native forest understory and quantified differences between sites. We found that light levels were significantly lower under Amur honeysuckle compared to natural understory, with the greatest reduction occurring during spring. Temperature at ground level was also lower under Amur honeysuckle than under the natural understory during spring. The extended leaf phenology of Amur honeysuckle alters both temperature and light intensity, which may increase both its success as an invader and its impact on native species.

Reproductive Phenology, Seasonality of Canopy and Understorey Trees in a Tropical Evergreen Forest

Reproductive Phenology, Seasonality of Canopy and Understorey Trees in a Tropical Evergreen Forest

Incubation behaviour and care of a nestling by a pair of Black Fantails Rhipidura atra

The Black Fantail Rhipidura atra , endemic to the lower montane forests of New Guinea, builds a typical fantail nest. Observations of a nest placed high up in an understorey tree in the Arfak Mountains in Indonesian New Guinea revealed that the male and female of a pair mostly alternated incubation bouts and contributed almost equally to incubation, care of the nestling and nest-defence. Incubation constancy was ~80%. Observations of Black Fantails mobbing potential nest-predators are described.

Detecting Tree Stems from Volumetric TLS Data in Forest Environments with Rich Understory

The present study introduces a method to identify tree stems from terrestrial laser scanning (TLS) data. We focused on forest environments of diverse and layered structure, which were technically characterized by strong occlusion effects with regards to laser scanning. The number and distribution of tree stems are important information for the management of protective forests against natural hazards, for forest inventory, and for ecological studies. Our approach builds upon a three-dimensional (3D) voxel grid transformation of the original point cloud data, followed by two major steps of processing. Firstly, a series of morphological operations removed leaves and branches and left only potential stem segments. Secondly, the stem segments of each tree were combined by a multipart workflow, which uses shape and neighborhood criteria. At the same time, erroneous fragments and noise were removed from the dataset. As a result, each object in the voxel grid was represented by a single connected component referring to one specific tree stem. Testing the method on nine spatially independent plots provided detection rates of 97% for the number and location of stems from mature trees with a diameter &gt;= 12 cm and 84% for smaller trees with a minimum of 130 cm total tree height. In summary, we obtained a dataset covering the number and locations of the stems from both mature and understory trees, while not aiming at a precise reconstruction of the stem shape.

Understory vegetation dynamics 15 years post-thinning in 50-year-old Douglas-fir and Douglas-fir/western hemlock stands in western Oregon, USA

Recent trends in forest management practices designed to restore or enhance late-successional structure for habitat values typically include provisions for the creation and maintenance of structural and compositional diversity within and among stands. The Pacific Northwest in particular has expanses of young, structurally simple forests that range from high stocking (unthinned and little understory development) to relatively lower stocking having been previously thinned or initially regenerated at low densities. We have remeasured two long-term study sites in Oregon, USA, for 15years to examine structural development and understory persistence at a range of overstory canopy cover, spatial arrangement, and understory treatments (spraying and planting). Understory responses to thinning varied primarily by site and species group, given the range of pre-existing plant communities, and through time. In general, shrub cover increased after thinning, while forb cover increased initially after thinning and then declined. Though spraying effects were still visible 15years after treatment driven by reductions in one dominant understory species, it had little effect on the long-term development of structure at these overstory densities. Indeed, the range of overstory densities and spatial arrangements in this study did not have any large effects because all of the thinning treatments resulted in increased light availability to the understory at least through fifteen years after thinning. Combining more extensive overstory removal and understory treatments likely can be used to stimulate heterogeneous structure and composition development in these forests, including the possible stimulation of persistent early-seral vegetation within older stands.

Plant functional groups within a tropical forest exhibit different wood functional anatomy

Summary Understanding the anatomical basis of plant water transport in forest ecosystems is crucial for contextualizing community‐level adaptations to drought, especially in life‐form‐rich tropical forests. To provide this context, we explored wood functional anatomy traits related to plant hydraulic architecture across different plant functional groups in a lowland tropical rain forest. We measured wood traits in 90 species from six functional groups (mature‐phase, understorey and pioneer trees; understorey and pioneer shrubs; vines) and related these traits to intrinsic water‐use efficiency (WUEi) as a measure of physiological performance. We also examined vessel size distribution patterns across groups to determine trade‐offs in theoretical hydraulic safety vs. efficiency. Some plant functional groups exhibited significant differences in vessel parameters and WUEi. Vessel diameters in vines and pioneer trees were two‐ to threefold greater on average than in understorey trees and shrubs. Contrastingly, vessels in understorey trees and shrubs fell within the smaller size classes, suggesting greater safety mechanisms. In addition to these trends, large vessel dimensions were important predictors of WUEi among the functional groups. We conclude that wood functional anatomy profiles varied across plant functional groups in a tropical rain forest. These groups can therefore serve as a framework for further investigations on structure–function relationships and a sound basis for modelling species responses to drought. A lay summary is available for this article.

Long‐term declines of native trees in an oceanic island's tropical forests invaded by alien plants

AbstractQuestionHow did the native and alien woody plant communities of protected lowland wet forests of a tropical oceanic island change in the presence of understorey invasive alien plants over the medium (21–27 yrs) and longer term (68 yrs)?LocationBel Ombre, Brise Fer and Macchabé forests in the Black River Gorges National Park (BRGNP), Mauritius (20°22′10″–20°28′17″ S, 57°24′45″–57°27′12″ E).MethodsRandom and replicated vegetation plots were sampled in two protected forest areas whose communities of woody plants were surveyed 21 and 27 yrs previously, and in another protected and similar forest that was surveyed 68 yrs earlier, to identify species and measure stem diameters so as to permit comparisons at the three sites over these time periods.ResultsInvasion by woody alien plants has progressed through time at all three sites, comprised mostly of the understorey and shade‐tolerant Strawberry guava (Psidium cattleianum). Concomitantly, although reductions in native woody plant species richness of large trees (≥10 cmDBH) were not statistically significant at the community level, their densities and basal area had roughly halved in 68 yrs. Comparisons with the studies 21–27 yrs previously confirmed the tendency towards a reduction in density of larger trees, besides indicating a trend towards decline in species richness of smaller understorey trees.ConclusionAn unabated replacement of native by alien trees over the longer term is occurring in protected areas of the lowland wet forests of theBRGNPand presumably in other similarly invaded areas. Our work stresses the importance of long‐term monitoring in elucidating impacts of invasive alien plants at the community level, particularly when dealing with slow‐growing and long‐lived species. Plausible mechanisms bringing about the observed changes and that have been found at the same or similar sites, include reduced regeneration, growth, production of flowers and fruits and increased mortality of native trees when these grow among invasive alien plants. The control of invasive alien plants, where they invade tropical forests, should be a central conservation objective even in better preserved and well protected areas.

El impacto del huracán Dean sobre la estructura y composición arbórea de un bosque manejado en Quintana roo, México

Los huracanes son considerados como uno de los factores más determinantes de la estructura y composición de muchos bosques tropicales. En Quintana Roo, estos fenómenos naturales son tan frecuentes que forman parte de la dinámica natural del bosque. El 21 de agosto de 2007, en el centrosur del Estado, ocurrió el huracán Dean, que afectó alrededor de 900,000 ha de la selva mediana subperennifolia. En este estudio se cuantifican los daños ocasionados sobre la vegetación y se analizan los cambios en la composición de especies y la estructura del bosque afectado por el huracán Dean. Se encontró que la composición del bosque no fue afectada significativamente y que el mayor efecto del huracán fue sobre la estructura del bosque. Los árboles más dañados fueron individuos de especies del sotobosque. Los principales tipos de daño fueron desramado, desenraizado y quebrado o ruptura del tronco. Asimismo, basados en fuentes bibliográficas y algunas observaciones durante el trabajo en campo, se discute el efecto que el aprovechamiento forestal puede tener en cuanto a incrementar la susceptibilidad de estos bosques al daño por viento. Se propone disminuir la cantidad de áreas de concentración de madera (bacadillas) durante la extracción forestal, así como incorporar a los planes de manejo forestal, el aprovechamiento de árboles dañados que ofrezcan alguna utilidad. También se propone el monitoreo a largo plazo de la dinámica de los bosques afectados en relación con los no afectados por huracanes.