Heterogeneous Forest Environments Research Articles

A Novel 3D Tree-Modeling Method of Incorporating Small-Scale Spatial Structure Parameters in a Heterogeneous Forest Environment

Currently, 3D tree modeling in a highly heterogeneous forest environment remains a significant challenge for the modeler. Previous research has only focused on morphological characteristics and parameters, overlooking the impact of micro-environmental factors (e.g., spatial-structural diversification and habitat heterogeneity) and providing less structural information about the individual tree and decreasing the applicability and authenticity of 3D tree models in a virtual forest. In this paper, we chose a mixed-forest conversion of Chinese fir (Cunninghamia lanceolata) plantations in a subtropical region of China as our study subject and proposed a novel 3D tree-modeling method based on a structural unit (TMSU). Our approach modified traditional rule-based tree modeling (RTM) by introducing a nonlinear mixed-effect model (NLME) to study the coupling response between the spatial structures and morphological characteristics (e.g., tree height (H), height-to-crown base (HCB), and crown width (CW)) of three dominant trees (e.g., Cunninghamia lanceolata (SM), Machilus pauhoi (BHN), and Schima superba (MH)) and develop a prediction model of the morphological characteristic by incorporating forest-based structural parameters. The results showed that: (1) The NLME model in TMSU was found to better fit the data and predict the morphological characteristics than the OLS model in RTM. As compared to the RTM morphological model, the prediction accuracy of the TMSU model of morphological features was improved by 10.4%, 3.02%, and 17.8%, for SM’s H, HCB, and CW, respectively; 6.5%, 7.6%, and 8.9% for BHN’s H, HCB, and CW, respectively; and 13.3%, 15.7%, and 13.4% for MH’s H, HCB, and CW, respectively. (2) The spatial-structural parameters of crowding (Ci), mingling (Mi), and dominance (Ui) had a significant impact on the morphological characteristics of SM, BHN, and MH in TMSU. The degree of crowding, for example, had a positive relationship with tree height, height-to-crown base, and crown width in SM, BHN, and MH; under the same crowding conditions, mingling was positively correlated with tree crown width in SM, and dominance was positively correlated with tree height but negatively correlated with height-to-crown base in BHN; under the same crowding and mingling, dominance was positively correlated with height-to-crown base in MH. (3) Using 25 scenes based on the value class of Ci,Mi for SM, 25 scenes based on the value class of Ci,Ui for BHN, and 125 scenes based on the value class of Ci,Mi,Ui for MH, we generated the model libraries for the three dominating species based on TMSU. As a result, our TSMU method outperformed the traditional 3D tree-modeling method RTM in a complex and highly heterogeneous spatial structure of a forest stand, and it provided more information concerning the spatial structure based on the neighborhood relationships than the simple morphological characteristics; a higher morphological prediction accuracy with fewer parameters; and the relationship between the spatial-structural parameters and the morphological characteristics of a reference tree.

Forest beta-diversity analysis by remote sensing: How scale and sensors affect the Rao’s Q index

Space-borne remote sensing missions provide robust, timely and continuous data to assess biodiversity in remote or protected areas, where direct field observations can be prohibited by difficult accessibility. The objective of this study was to extend the concept of remote sensing based assessment of beta-diversity to multi-scale domain by multi-resolution optical satellite data. This study was conducted in a reserved forest of western Himalaya, India; a region affected by the invasive Lantana camara L (lantana). We calculated and compared Rao’s Q and Shannon indices at different spatial resolutions (0.5, 5, and 30 m) and scales (window sizes) by using imageries from Pléiades 1A, RapidEye, and Landsat-8 acquired in April 2013, the pre-monsoon season. Rao’s Q index explained diversity more accurately than Shannon index for the three analyzed stand densities. Diversity was better approximated by Rao’s Q index calculated by Pléiades 1A at a resolution of 0.5 m at low stand density. We observed higher correlations of the average coefficient of variation (CV) with Rao’s Q and Shannon indices for areas associated with mixed spectral reflectance caused by overstory and understory vegetation. Furthermore, CV was lower in open areas dominated by lantana. These results indicated a strong scale and spatial resolution dependence of Rao’s Q index on remote sensing-derived spectral heterogeneity information. When applied in heterogeneous forest environments, Rao’s Q index could represent a better remote sensing proxy to estimate beta-diversity than the conventional Shannon index.

Multispecies Phytophthora disease patterns in declining beech stands

AbstractDecline diseases are typically caused by complex abiotic and biotic interactions and characterized by a suite of symptoms indicative of low plant vigour. Diseased trees are frequently infected by Phytophthora, but the complex interactions between pathogen, host and the heterogeneous forest environment mask a comprehensive understanding of the aetiology. In the present study, we surveyed European beech (Fagus sylvatica) stands in Swiss forests with recent increases in bleeding lesions for the presence of Phytophthora. We used a combined approach of analysing soil and bark samples from trees displaying bleeding lesions and trees free from bleeding lesions. Soil baiting revealed a higher prevalence of Phytophthora spp. around trees with bleeding lesions than around trees without bleeding lesions. For the bark samples from bleeding lesions, we used several detection methods. Phytophthora spp. were detected in 74% of the trees by an immunological on‐site diagnostic kit, in 64% by a specific PCR assay, and 38% by isolation on selective media. All samples tested were negative for P. ramorum using qPCR. Overall, nine Phytophthora species were identified by ITS sequencing, the most common of which were P. plurivora, P. gonapodyides, P. × cambivora and P. syringae. We identified distinct species in bleeding lesions and the rhizosphere of the same host tree which suggests a multispecies Phytophthora disease patterns in these declining beech. Among the recovered species, P. × cambivora and P. × serendipita were identified as hybrid genotypes with the former abundant in bleeding lesions.

Micropropagation of Mespilus germanica L.

The data presented in this paper is supporting the research article “Variable seed behavior increases recruitment success of a hardwood tree, Zelkova serrata, in spatially heterogeneous forest environments” (Oyama et al., 2018) [1]. We provided the data of several ecological properties of the two types of the seeds (i.e. shoot seeds vs. single seeds) with distinctly different dispersal behaviors. We provide data of terminal velocity, which was measured by releasing 50 replicates of each seed type from a height of 5.0 m in dead air space in a gymnasium. We also show the data of germination cue [i.e. red:far-red (R:FR) ratios], which was examined in plant growth chambers that received three distinct R:FR ratios (0.1, 0.4, and 1.0; 16 h photoperiod) or no illumination. Further, we show the data of the rates of multi-locus outcrossing rates and biparental inbreeding in each of single- and shoot seeds. The mating system parameters were estimated by assaying a total of 80 shoot seeds and 70 single seeds that were randomly collected from Parent 1 and Parent 2 for five microsatellite loci. Finally, we show the data of hemispherical canopy photographs, which were taken at different distance from the adults using a digital camera equipped with a fisheye lens.

Variable seed behavior increases recruitment success of a hardwood tree, Zelkova serrata, in spatially heterogeneous forest environments

Abstract Variable seed behavior (e.g., seed heteromorphism) plays an important role in enhancing plant fitness by spreading risk in spatially and temporally changing environments. This adaptation is common in herbs but rare in trees. Zelkova serrata, one of the most important commercial tree species in Japan, has two types of seeds: shoot seeds that disperse via a seed-bearing shoot and single seeds that disseminate after separating from shoots. To evaluate whether the seeds of Z. serrata show heteromorphism, we compared several inherent ecological properties (e.g., seed mass, degree of seed dormancy, and dispersal ability) between the two seed types and assessed the effects of variable seed behavior on recruitment success in forest environments. The degree of seed dormancy did not differ between the two seed types. Seed mass increased with a delayed seed dispersal time but did not differ between the two types at any time. Seed dispersal ability was greater in shoot seeds than in single seeds. These inherent seed behaviors suggest that the two types of seeds do not reflect seed heteromorphism. The results, however, indicate that shoot seeds dispersed larger seeds over much greater distances than did single seeds, particularly at later seed dispersal times, whereas a greater number of single seeds were disseminated near adults. To evaluate the effects of variable seed dispersal ability on seedling establishment in forest environments, we measured seedling performance at different distances (≤27.5 m) from adults isolated from one another in the forest understory. Seedling density, survival, and growth did not vary with distance from adults (i.e., there was little negative distance-dependent seedling mortality), which suggests that single seeds can contribute to persistent seedling banks near conspecific adults. To evaluate the advantages of long-distance dispersal of shoot seeds for recruitment on disturbed sites (i.e., gaps), we compared the occurrence and relative abundance of Z. serrata among 1100 plots with different slopes; steep slopes are closely associated with gap creation (e.g., landslides). The occurrence and relative abundance of Z. serrata increased with slope inclination, which suggests that shoot seeds may enhance recruitment success in disturbed sites along steep slopes, thereby generating Z. serrata-dominated forests. This suggests that the variability in seed behavior of Z. serrata may enhance recruitment success in spatially heterogeneous forest environments. Knowledge of the unique reproductive behaviors and the wide range of habitats suitable for this species is important for forest managers when making sustainable timber production plans for Z. serrata.

Mapping of Shorea robusta Forest Using Time Series MODIS Data

Mapping forest types in a natural heterogeneous forest environment using remote sensing data is a long-standing challenge due to similar spectral reflectance from different tree species and significant time and resources are required for acquiring and processing the remote sensing data. The purpose of this research was to determine the optimum number of remote sensing images and map the Sal forest through the analysis of Vegetation Index (VI) signatures. We analyzed the eight days’ composite moderate resolution imaging spectroradiometer (MODIS) time series normalized differential vegetation index (NDVI), and enhanced vegetation index (EVI) for the whole year of 2015. Jeffries-Matusita (J-M) distance was used for the separability index. Performance of EVI and NDVI was tested using random forest (RF) and support vector machine (SVM) classifiers. Boruta algorithm and statistical analysis were performed to identify the optimum set of imageries. We also performed data level five-fold cross validation of the model and field level accuracy assessment of the classification map. The finding confirmed that EVI with SVM (F-score of Sal 0.88) performed better than NDVI with either SVM or RF. The optimum 12 images during growing and post monsoon season significantly decreased processing time (to one-fourth) without much deteriorating accuracy. Accordingly, we were able to map the Sal forest whose area is accounted for about 36% of the 82% forest cover in the study area. The proposed methodology can be extended to produce a temporal forest type classification map in any other location.

A comparison of measured HONO uptake and release with calculated source strengths in a heterogeneous forest environment

Abstract. Vertical mixing ratio profiles of nitrous acid (HONO) were measured in a clearing and on the forest floor in a rural forest environment. For the forest floor, HONO was found to predominantly deposit, whereas for the clearing, net deposition dominated only during nighttime and net emissions were observed during daytime. For selected days, net fluxes of HONO were calculated from the measured profiles using the aerodynamic gradient method. The emission fluxes were in the range of 0.02 to 0.07 nmol m−2 s−1 and thus were in the lower range of previous observations. These fluxes were compared to the strengths of postulated HONO sources. Laboratory measurements of different soil samples from both sites revealed an upper limit for soil biogenic HONO emission fluxes of 0.025 nmol m−2 s−1. HONO formation by light-induced NO2 conversion was calculated to be below 0.03 nmol m−2 s−1 for the investigated days, which is comparable to the potential soil fluxes. Due to light saturation at low irradiance, this reaction pathway was largely found to be independent of light intensity, i.e. it was only dependent on ambient NO2. We used three different approaches based on measured leaf nitrate loadings for calculating HONO formation from HNO3 photolysis. While the first two approaches based on empirical HONO formation rates yielded values in the same order of magnitude as the estimated fluxes, the third approach based on available kinetic data of the postulated pathway failed to produce noticeable amounts of HONO. Estimates based on reported cross sections of adsorbed HNO3 indicate that the lifetime of adsorbed HNO3 was only about 15 min, which would imply a substantial renoxification. Although the photolysis of HNO3 was significantly enhanced at the surface, the subsequent light-induced conversion of the photolysis product NO2 did not produce considerable amounts of HONO. Consequently, this reaction might occur via an alternative mechanism. By explicitly calculating HONO formation based on available kinetic data and simple parameterizations, we showed that (a) for low NOx the light-induced conversion of NO2 on humic acids is already light saturated by the early morning, (b) HONO formation from photolysis of adsorbed HNO3 appears to proceed via an alternative mechanism and (c) estimates of HONO emissions from soil are very sensitive to mass transfer and acidic soils do not necessarily favour HONO emissions.

Canopy-structure effects on surface roughness parameters: Observations in a Great Lakes mixed-deciduous forest

Over forested canopies, the physical structure of vegetation interacts with wind by exerting drag on the flow, thus generating turbulent mixing that is necessary for scalar transport. We use 11 years of above-canopy wind speed measurements from spatially and temporally heterogeneous forest environments to disentangle the effects of different features of changing canopy structure on the surface roughness parameters: displacement height (d), roughness length (z0), and the aerodynamic canopy height (ha). We find a significant increasing long-term trend of dormant-season (leaf-off) ha, which closely resembles the rate of biometrically derived vertical stem growth over years. We show that the values of d and z0 trade-off with higher d and shorter z0 when leaf area is high in the growing season. Using airborne lidar measurements and a footprint model for flux-source location detection, we show that these d and z0 trade-offs also correspond with the spatial differences between taller and shorter subplot patches.We show that incorporating seasonal-scale temporal heterogeneity of d and z0 into surface-flux and ecosystem models will improve their accuracy. However, incorporating simple empirical modifications to surface-structure roughness parameters due to inter-annual variation in canopy height and leaf area did not lead to improved modeling of frictional velocity within this study. Further investigation of structure–roughness relationships is needed to incorporate these aspects. Finally, this study proposes a meteorological-based method for estimating vertical stem growth in undisturbed forest environments by tracking ha over time.

Bionomics of Encarsia scapeata Rivnay (Hymenoptera: Aphelinidae), tritrophic relationships and host-induced diapause

During a survey of whitefly parasitoids in the Israeli Mediterranean forest, we found Encarsia scapeata Rivnay to be the only parasitoid of Trialeurodes lauri Signoret, growing on Arbutus andrachne L. trees. Overall parasitism levels averaged about 10% during the two-year study and correlated inversely with whitefly abundance. Following bud burst, the univoltine whiteflies oviposit on the young leaves (April–May), develop to the early 4th instar and then diapause from May–June to next spring, when their development to mature adults continues. Following a diapause that had apparently been induced by the whitefly host, most adult parasitoids emerged during April, intimately synchronized with their whitefly host. Natural diapause of the whiteflies and the wasps could be experimentally broken by cutting infested branches and keeping them under room conditions. Analyses of slide-mounted material revealed that parasitoid development usually occurred following initiation of post-diapause development in the unparasitized whiteflies of the same age, but occasionally preceded it. This host-dependent phenological plasticity of E. scapeata ensures synchronization with its hosts in the heterogeneous forest environment. In a lab set-up, E. scapeata readily parasitized the non-diapausing whitefly Bemisia tabaci (Gennadius), in which it too did not diapause. Thus, the diapause of E. scapeata is apparently induced by the diapause of its whitefly host. Since it can successfully develop on B. tabaci, E. scapeata, with its flexible developmental strategy, could serve as an addition to the pool of Encarsia species useful for B. tabaci control.

Vegetation type discrimination on Landsat TM data in heterogeneous forested landscape of Western Ghats—Accuracy evaluation from large scale aerial photo maps

In the present study, forest type classification using Landsat TM False Colour Composite (FCC) bands 2, 3, 4 has been evaluated for mapping highly heterogeneous forest environment of Western Ghats (Kerala). Visual interpretation of Landsat TM FCC has been carried out to identify bioclimatic vegetation types. For accuracy estimation maps prepared from 1∶15,000 scale black-and-white aerial photographs have been used as ground check data. For comparison aerial photomap classes have been aggregated to match with Landsat-TM-derived map. The classification accuracy of ten major bioclimatic and landcover types was estimated using systematic sampling procedure. The overall classification accuracy of the forest types for the study area was 88.33%.