Woody Foliage Research Articles

Global-scale assessment and inter-comparison of recently developed/reprocessed microwave satellite vegetation optical depth products

The vegetation optical depth (VOD), a vegetation index retrieved from passive or active microwave remote sensing systems, is related to the intensity of microwave extinction effects within the vegetation canopy layer. This index is only marginally impacted by effects from atmosphere, clouds and sun illumination, and thus increasingly used for ecological applications at large scales. Newly released VOD products show different abilities in monitoring vegetation features, depending on the algorithm used and the satellite frequency. VOD is increasingly sensitive to the upper vegetation layer as the frequency increases (from L-, C- to X-band), offering different capacities to monitor seasonal changes of the leafy and/or woody vegetation components, vegetation water status and aboveground biomass. This study evaluated nine recently developed/reprocessed VOD products from the AMSR2, SMOS and SMAP space-borne instruments for monitoring structural vegetation features related to phenology, height and aboveground biomass.For monitoring the seasonality of green vegetation (herbaceous and woody foliage), we found that X-VOD products, particularly from the LPDR-retrieval algorithm, outperformed the other VOD products in regions that are not densely vegetated, where they showed higher temporal correlation values with optical vegetation indices (VIs). However, LPDR X-VOD time series failed to detect changes in VOD after rainfall events whereas most other VOD products could do so, and overall daily variations are less pronounced in LPDR X-VOD. Results show that the reprocessed VODCA C- and X-VOD have almost comparable performance and VODCA C-VOD correlates better with VIs than other C-VOD products. Low frequency L-VOD, particularly the new version (V2) of SMOS-IC, show a higher temporal correlation with VIs, similar to C-VOD, in medium-densely vegetated biomes such as savannas (R ~ 0.70) than for other short vegetation types. Because the L-VOD indices are more sensitive to the non-green vegetation components (trunks and branches) than higher frequency products, they are well-correlated with aboveground biomass: (R ~ 0.91) across space between predicted and observed values for both SMOS-IC V2 and SMAP MT-DCA. However, when compared with forest canopy height, results at L-band are not systematically better than C- and X-VOD products. This revealed specific VOD retrieval issues for some ecosystems, e.g., boreal regions. It is expected that these findings can contribute to algorithm refinements, product enhancements and further developing the use of VOD for monitoring above-ground vegetation biomass, vegetation dynamics and phenology.

Changes in rainfall distribution promote woody foliage production in the Sahel

Dryland ecosystems comprise a balance between woody and herbaceous vegetation. Climate change impacts rainfall timing, which may alter the respective contributions of woody and herbaceous plants on the total vegetation production. Here, we apply 30 years of field-measured woody foliage and herbaceous mass from Senegal and document a faster increase in woody foliage mass (+17 kg ha−1 yr−1) as compared to herbaceous mass (+3 kg ha−1 yr−1). Annual rainfall trends were partitioned into core wet-season rains (+0.7 mm yr-1), supporting a weak but periodic (5-year cycles) increase in herbaceous mass, and early/late rains (+2.1 mm yr−1), explaining the strongly increased woody foliage mass. Satellite observations confirm these findings for the majority of the Sahel, with total herbaceous/woody foliage mass increases by 6%/20%. We conclude that the rainfall recovery in the Sahel does not benefit herbaceous vegetation to the same extent as woody vegetation, presumably favoured by increased early/late rains.

A method for mapping Australian woody vegetation cover by linking continental-scale field data and long-term Landsat time series

ABSTRACTThere is a significant need to provide nationwide consistent information for land managers and scientists to assist with property planning, vegetation monitoring applications, risk assessment, and conservation activities at an appropriate spatial scale. We created maps of woody vegetation cover of Australia using a consistent method applied across the continent, and made them accessible. We classified pixels as woody or not woody, quantified their foliage projective cover, and classed them as forest or other wooded lands based on their cover density. The maps provide, for the first time, cover density estimates of Australian forests and other wooded lands with the spatial detail required for local-scale studies. The maps were created by linking field data, collected by a network of collaborators across the continent, to a time series of Landsat-5 TM and Landsat-7 ETM+ images for the period 2000–2010. The fractions of green vegetation cover, non-green vegetation cover, and bare ground were calculated for each pixel using a previously developed spectral unmixing approach. Time series statistics, for the green vegetation cover, were used to classify each pixel as either woody or not using a random forest classifier. An estimate of woody foliage projective cover was made by calibration with field measurements, and woody pixels classified as forest where the foliage cover was at least 0.1. Validation of the foliage projective cover with field measurements gave a coefficient of determination, R2,of 0.918 and root mean square error of 0.070. The user’s and producer’s accuracies for areas mapped as forest were high at 92.2% and 95.9%, respectively. The user’s and producers’s accuracies were lower for other wooded lands at 75.7% and 61.3%, respectively. Further research into methods to better separate areas with sparse woody vegetation from those without woody vegetation is needed. The maps provide information that will assist in gaining a better understanding of our natural environment. Applications range from the continental-scale activity of estimating national carbon stocks, to the local scale activities of assessing habitat suitability and property planning.

Measuring seasonal dynamics of leaf area index in a mixed conifer-broadleaved forest with direct and indirect methods

Aims Leaf area index(LAI) is a commonly used parameter for quantifying canopy structure and can be quickly measured by indirect optical methods in a forest stand,but few studies have evaluated the accuracy of optical methods to estimate seasonal variations of LAI in a mixed conifer-broadleaved forest. The aims of this study are to(1) develop a practical field method for directly measuring seasonal variations in LAI for mixed conifer-broadleaved forest;(2) evaluate the accuracy of optical methods(digital hemispherical photography(DHP) and LAI-2000 plant canopy analyzer) for measuring the seasonality of LAI; and(3) determine how much the accuracy of estimating the seasonality of LAI can be improved by using optical methods after correcting for influencing factors(e.g.,woody materials and clumping effects within a canopy).Methods The seasonal variations of LAI in a mixed broadleaved-Korean pine(Pinus koraiensis) forest were estimated from litterfall and used to evaluate optical LAI(effective LAI,Le) measurements using the DHP and the LAI-2000 plant canopy analyzer. We corrected a systematic error due to incorrect automatic photographic exposure for DHP measurements. In addition to optical Le,we also measured the seasonality of other major factors influencing the determination of LAI,including woody-to-total area ratio(α),clumping index(?E) and needle-to-shoot area ratio(γE). Important findings The LAI from different methods all showed a unimodal form,and peaked in early August. Effective LAIs from the optical methods underestimated LAI throughout the growing seasons(from May to November). Le from DHP underestimated LAI by an average of 55%(ranging from 50% to 59%) and from LAI-2000plant canopy analyzer by an average of 27%(ranging from 19% to 35%). The accuracy of Le from DHP after correcting for the automatic exposure,α,?E and γE was greatly improved,but the LAI was underestimated by 6%–15%(with mean value of 9%) from May to November. In contrast,the accuracy of Le from LAI-2000 plant canopy analyzer after correcting for the α,?E and γE was also greatly improved,the difference between corrected Le from LAI-2000 plant canopy analyzer and observed LAI was less than 9%. The results from our study demonstrate that seasonal variations in LAI in mixed conifer-broadleaved forests can be optically measured with high accuracy(85% for DHP and 91% for LAI-2000 plant canopy analyzer),as long as corrections are made for the influences of woody materials and foliage clumping on the measurement.

HIGH TEMPORAL FREQUENCY BIOPHYSICAL AND STRUCTURAL VEGETATION INFORMATION FROM MULTIPLE REMOTE SENSING SENSORS CAN SUPPORT MODELLING OF EVENT BASED HILLSLOPE EROSION IN QUEENSLAND

Abstract. This study demonstrates the potential applicability of high temporal frequency information on the biophysical condition of the vegetation from a time series of the global Moderate Resolution Imaging Spectroradiometer (MODIS) Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) from 2000 to 2006 (collection 4; 8-day composites in 1 km spatial resolution) to improve modelling of soil loss in a tropical, semi-arid catchment in Queensland. Combining the biophysical information from the MODIS FPAR with structural vegetation information from the Geoscience Laser Altimeter System on the Ice, Cloud, and land Elevation Satellite (ICESat) for six vegetation structural categories identified from a Landsat Thematic Mapper 5 (TM) and Enhanced Thematic Mapper 7 (ETM+) woody foliage projective cover product representing floristically and structurally homogeneous areas, dynamic vegetative cover factor (vCf) estimates were calculated. The dynamic vCf were determined in accordance with standard calculation methods used in erosion models worldwide. Time series of dynamic vCf were integrated into a regionally improved version of the Universal Soil Loss Equation (USLE) to predict daily soil losses for the study area. Resulting time series of daily soil loss predictions averaged over the study area coincided well with measures of total suspended solids (TSS) (mg/l) at a gauge at the outlet of the catchment for three wet seasons (R2 of 0.96 for a TSS-event). By integrating the dynamic vCf into modified USLE, the strength of the dependence of daily soil loss predictions to the only other dynamic factor in the equation – daily rainfall erosivity – was reduced.

Variation in Formaldehyde Removal Efficiency among Indoor Plant Species

The efficiency of volatile formaldehyde removal was assessed in 86 species of plants representing five general classes (ferns, woody foliage plants, herbaceous foliage plants, Korean native plants, and herbs). Phytoremediation potential was assessed by exposing the plants to gaseous formaldehyde (2.0 μL·L−1) in airtight chambers (1.0 m3) constructed of inert materials and measuring the rate of removal. Osmunda japonica, Selaginella tamariscina, Davallia mariesii, Polypodium formosanum, Psidium guajava, Lavandula spp., Pteris dispar, Pteris multifida, and Pelargonium spp. were the most effective species tested, removing more than 1.87 μg·m−3·cm−2 over 5 h. Ferns had the highest formaldehyde removal efficiency of the classes of plants tested with O. japonica the most effective of the 86 species (i.e., 6.64 μg·m−3·cm−2 leaf area over 5 h). The most effective species in individual classes were: ferns—Osmunda japonica, Selaginella tamariscina, and Davallia mariesii; woody foliage plants—Psidium guajava, Rhapis excels, and Zamia pumila; herbaceous foliage plants—Chlorophytum bichetii, Dieffenbachia ‘Marianne’, Tillandsia cyanea, and Anthurium andraeanum; Korean native plants—Nandina domestica; and herbs—Lavandula spp., Pelargonium spp., and Rosmarinus officinalis. The species were separated into three general groups based on their formaldehyde removal efficiency: excellent (greater than 1.2 μg·m−3 formaldehyde per cm2 of leaf area over 5 h), intermediate (1.2 or less to 0.6), and poor (less than 0.6). Species classified as excellent are considered viable phytoremediation candidates for homes and offices where volatile formaldehyde is a concern.

How does the global Moderate Resolution Imaging Spectroradiometer (MODIS) Fraction of Photosynthetically Active Radiation (FPAR) product relate to regionally developed land cover and vegetation products in a semi-arid Australian savanna?

Spatio-temporally variable information on total vegetation cover is highly relevant to water quality and land management in river catchments adjacent to the Great Barrier Reef, Australia. A time series of the global Moderate Resolution Imaging Spectroradiometer (MODIS) Fraction of Photosynthetically Active Radiation (FPAR; 2000-2006) and its underlying biome classification (MOD12Q1) were compared to national land cover and regional, remotely sensed products in the dry-tropical Burdekin River. The MOD12Q1 showed reasonable agreement with a classification of major vegetation groups for 94% of the study area. We then compared dry-seasonal, quality controlled MODIS FPAR observations to (i) Landsat-based woody foliage projective cover (wFPC) (2004) and (ii) MODIS bare ground index (BGI) observations (2001-2003). Statistical analysis of the MODIS FPAR revealed a significant sensitivity to Landsat wFPC-based Vegetation Structural Categories (VSC) and VSC-specific temporal variability over the 2004 dry season. The MODIS FPAR relation to 20 coinciding MODIS BGI dry-seasonal observations was significant (ρ < 0.001) for homogeneous areas of low wFPC. Our results show that the global MODIS FPAR can be used to identify VSC, represent VSC-specific variability of PAR absorption, and indicate that the amount, structure, and optical properties of green and non-green vegetation components contribute to the MODIS FPAR signal.

Soil organic matter formation and sequestration across a forested floodplain chronosequence

Successional changes in soil organic matter formation and carbon sequestration across a forested floodplain chronosequence were studied at the Savannah river site, National Environmental Research Park, SC, US. Four floodplain sites were selected for study, three of which are in various stages of recovery from impact due to thermal effluent discharge. The fourth is a minimally disturbed reference site. Forest floor organic matter increases rapidly during early secondary succession, with a maximum of 657 g/m 2 and decreasing to 338 g/m 2 during the later seral stages. Carbon content in the forest floor also reflected this pattern, with levels greatest during early succession and declining thereafter. Changes in carbon pools of the forest floor are primarily driven by changing levels of forest floor biomass in the various stages of succession, rather than element concentrations. The composition of the forest floor from the various stages differed markedly. The percent herbaceous material declined during succession from 74% in an early stage to <1% in the latest seral stage. Conversely, the amount of woody foliage increased from 6.7 to more than 70% in late succession. Measures of the degree of transformation of forest floor litter to soil organic matter using the lignocellulose index (LCI) did not differ between stages of succession. Percent lignin and percent cellulose of the forest floor were similar between stages and ranged from 13.8–16.3, and 30.4–32.5%, respectively. Carbon content of the mineral soil increased with successional stage of the floodplain chronosequence. Soil carbon content ranged from 15.6 kg/m 2 per 0.7 m in the earliest stage of succession to 55.9 kg/m 2 in late succession. Regression analyses indicated that it may take over 50 years for carbon levels to reach 75% of that of the reference site. The evidence also suggests that soil structure was disrupted by the disturbance, producing a greater proportion of microaggregates in early seral stages. The formation of soil macroaggregate structure, which may facilitate the accrual of carbon, appears to be occurring slowly.

Determination of carbon fraction and nitrogen concentration in tree foliage by near infrared reflectances: a comparison of statistical methods

Further evaluation of near infrared reflectance spectroscopy as a method for the determination of nitrogen, lignin, and cellulose concentrations in dry, ground, temperate forest woody foliage is presented. A comparison is made between two regression methods, stepwise multiple linear regression and partial least squares regression. The partial least squares method showed consistently lower standard error of calibration and higher R2 values with first and second difference equations. The first difference partial least squares regression equation resulted in standard errors of calibration of 0.106%, with an R2 of 0.97 for nitrogen, 1.613% with an R2 of 0.88 for lignin, and 2.103% with an R2 of 0.89 for cellulose. The four most highly correlated wavelengths in the near infrared region, and the chemical bonds represented, are shown for each constituent and both regression methods. Generalizability of both methods for prediction of protein, lignin, and cellulose concentrations on independent data sets is discussed. Prediction accuracy for independent data sets and species from other sites was increased using partial least squares regression, but was poor for sample sets containing tissue types or laboratory-measured concentration ranges beyond those of the calibration set.

The Use of NIR in Predicting Nutritive Value of Mediterranean Tree and Shrub Foliage

To upgrade grazing management recommendations in the Mediterranean area, one needs to assess the nutritive value of woody foliages including their changes over time and with location. Using a wide range of native and cultivated foliages, our objective was to evaluate the potential of near infrared (NIR) reflectance spectroscopy to determine foliage chemistry and in vitro digestibility for ruminants. The samples, representative of small ruminant eating bites, were divided into the different plant parts. Samples were carefully conditioned, being air-dried at 60°C; drying times were individually varied to ensure complete dehydration without excessive heating. Samples were analysed for organic matter (OM), nitrogen (N), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL) and in vitro digestibility with a pepsin–cellulase method developed for forages (IVDMD). NIR scans were made with an NIRSystems 5000 instrument and data analysis was performed using ISI software. Partial least squares (PLS) regression equations were developed for IVDMD and each constituent. Nine mathematical treatments, with and without scatter correction, were compared. The database of woody foliage spectra and a reference fodder database were compared in two ways: the first involved a comparison of the spectral variation in each collection while the second measured the Mahalanobis distance of each spectrum in one database from the average spectrum in the other. In the case of N, a broad-based calibration was compared with others derived from various sample sub-sets; these latter were formed either according to sample type or following a proximity analysis of five spectral groups by principal component analysis. NIR predictions of IVDMD were applied to describe the effect of phenological changes in the edible parts of Quercus pubescens Willd. The foliage base is very heterogeneous and wider than the reference fodder base. The fodder base variation does not include the foliage samples. The lowest standard errors of calibration (SEC) and cross-validation (SECV) are comparable to literature results on forest leaves, but better for lignin (SECV of 1.5 compared to SEC values of 2.5–2.9). SECV for IVDMD is satisfactory at almost 2.0 because this value is similar to precision data normally reported for in vitro digestibility estimations on narrower sample sets than the current one. The broad-based calibration for N gave similar or lower standard errors to those obtained using sample sub-sets. One can show that IVDMD values for Quercus pubescens leaves decrease from 65 to 15% with increasing maturity; leaf IVDMD values are approximately 15% higher than the previous year's stem value from May until October. NIR spectroscopy appears to be an adequate technique for the prediction of the nutritive value of Mediterranean foliages from trees and shrubs, with a reliability similar to that obtained from classical fodder analysis procedures. This study shows that broad-based calibrations with PLS regression could be made on extremely diverse sets of data (IVDMD ranging from 28 to 94%), grouping distinct edible plant parts within the same data base.

Palatability of Woody Plants to Browsing Ruminants in a South African Savanna

We recorded food selection by free—ranging kudus (Tragelaphus strepsiceros), impalas (Aepyceros melampus), and domestic goats in the Nylsvley Nature Reserve in South Africa. The predominant vegetation is a deciduous wooded savanna growing on infertile sandy soils; patches of Acacia savanna occur on the more fertile sites of former human settlements. Woody species fall into two basic categories of acceptability to the animals: (1) species favored year—round; and (2) species generally rejected, except during certain periods. Among the latter, some species increase in acceptability during the dry season; others are favored temporarily while new leaves predominate. Some species remain low in acceptability year—round. We propose a palatability classification of woody species, considering features of leaf retention (deciduous vs. evergreen) and spinescence, as well as seasonal variations in acceptability. Estimated annual foliage losses to browsing ungulates were 1—3% for unpalatable deciduous species, compared with 10—30% for most palatable unarmed deciduous and evergreen species. Unpalatable deciduous species dominate the woody foliage biomass on the infertile soils, while palatable but spinescent species make up most of the leaf biomass of trees and shrubs on the more fertile sites. These patterns seem widely typical of African savanna. Plants known to have chemical defenses against vertebrate herbivory are prominent on nutrient—deficient soils, while those with structural defenses are prominent on fertile soils.

The significance of the woody component of semi‐arid savanna vegetation in relation to meat production

Abstract In many semi‐arid savanna areas of southern Africa extensive beef ranching is the main form of land use. Cattle prefer to graze rather than to browse and the woody component of the vegetation is therefore normally underutilized. Beef ranching will remain important but it is suggested that the use of domesticated browsers such as goats and eland in conjunction with cattle would achieve better overall utilization of the vegetation and prevent bush encroachment. Increased meat production would also be expected. However, not enough is known about the effects on the vegetation of stocking with both browsing and grazing animals to allow for the definition of clear management policies. Further information is needed about the woody plant standing crop and seasonal production in various vegetation types, woody species composition, browse quality and availability, the effects of utilization on woody plants, carrying capacity, the management principles for sustained woody foliage production, and the detaile...