Arturo Sanchez-Azofeifa

Biomass resilience of Neotropical secondary forests

Land-use change occurs nowhere more rapidly than in the tropics, where the imbalance between deforestation and forest regrowth has large consequences for the global carbon cycle. However, considerable uncertainty remains about the rate of biomass recovery in secondary forests, and how these rates are influenced by climate, landscape, and prior land use. Here we analyse aboveground biomass recovery during secondary succession in 45 forest sites and about 1,500 forest plots covering the major environmental gradients in the Neotropics. The studied secondary forests are highly productive and resilient. Aboveground biomass recovery after 20 years was on average 122 megagrams per hectare (Mg ha−1), corresponding to a net carbon uptake of 3.05 Mg C ha−1 yr−1, 11 times the uptake rate of old-growth forests. Aboveground biomass stocks took a median time of 66 years to recover to 90% of old-growth values. Aboveground biomass recovery after 20 years varied 11.3-fold (from 20 to 225 Mg ha−1) across sites, and this recovery increased with water availability (higher local rainfall and lower climatic water deficit). We present a biomass recovery map of Latin America, which illustrates geographical and climatic variation in carbon sequestration potential during forest regrowth. The map will support policies to minimize forest loss in areas where biomass resilience is naturally low (such as seasonally dry forest regions) and promote forest regeneration and restoration in humid tropical lowland areas with high biomass resilience.

Carbon sequestration potential of second-growth forest regeneration in the Latin American tropics

Models reveal the high carbon mitigation potential of tropical forest regeneration. Regrowth of tropical secondary forests following complete or nearly complete removal of forest vegetation actively stores carbon in aboveground biomass, partially counterbalancing carbon emissions from deforestation, forest degradation, burning of fossil fuels, and other anthropogenic sources. We estimate the age and spatial extent of lowland second-growth forests in the Latin American tropics and model their potential aboveground carbon accumulation over four decades. Our model shows that, in 2008, second-growth forests (1 to 60 years old) covered 2.4 million km2 of land (28.1% of the total study area). Over 40 years, these lands can potentially accumulate a total aboveground carbon stock of 8.48 Pg C (petagrams of carbon) in aboveground biomass via low-cost natural regeneration or assisted regeneration, corresponding to a total CO2 sequestration of 31.09 Pg CO2. This total is equivalent to carbon emissions from fossil fuel use and industrial processes in all of Latin America and the Caribbean from 1993 to 2014. Ten countries account for 95% of this carbon storage potential, led by Brazil, Colombia, Mexico, and Venezuela. We model future land-use scenarios to guide national carbon mitigation policies. Permitting natural regeneration on 40% of lowland pastures potentially stores an additional 2.0 Pg C over 40 years. Our study provides information and maps to guide national-level forest-based carbon mitigation plans on the basis of estimated rates of natural regeneration and pasture abandonment. Coupled with avoided deforestation and sustainable forest management, natural regeneration of second-growth forests provides a low-cost mechanism that yields a high carbon sequestration potential with multiple benefits for biodiversity and ecosystem services.

Spectral properties of foliose and crustose lichens based on laboratory experiments

Reflectance spectra of rock encrusting lichens were acquired to determine the influence that this vegetation type may have on the reflectance properties of rock exposures located in high latitude and subarctic environments. The samples investigated consist of crustose and foliose lichen species collected from exposures of the Gog quartzite formation in Alberta, Canada. Lichen transmittance was estimated to be <3% throughout the 350–2500-nm spectral region, using spectra measured from the foliose lichen, Umbilicaria torrefacta, as a representative sample of a broader class of lichens. These findings suggest that lichen prevents the transmission of light to the underlying rock substrate. Therefore, the subpixel influence of lichen and rock within a scene can be considered linearly weighted. Discrimination of lichen species is made possible using ratios of reflectance at 400/685 and 773/685 nm. An index using the band ratios 2132/2198 and 2232/2198 nm shows the similarity of lichen spectra in the infrared and a distinguishing feature between rocks with OH bearing minerals and lichen. Thus, spectral unmixing of rock and crustose/foliose lichens may be successfully accomplished using a single lichen end-member for this spectral range.

Gall inducing arthropods from a seasonally dry tropical forest in Serra do Cipó, Brazil

Highly diverse forms of galling arthropods can be identified in much of southeastern Brazils vegetation. Three fragments of a Seasonally Dry Tropical Forest (SDTF) located in the southern range of the Espinhaco Mountains were selected for study in the first survey of galling organisms in such tropical vegetation. Investigators found 92 distinct gall morphotypes on several organs of 51 host plant species of 19 families. Cecidomyiidae (Diptera) was the most prolific gall-inducing species, responsible for the largest proportion of galls (77%) observed. Leaves were the most frequently galled plant organ (63%), while the most common gall morphotype was of a spherical shape (30%). The two plant species, Baccharis dracunculifolia (Asteraceae) and Celtis brasiliensis (Cannabaceae), presented the highest number of gall morphtypes, displaying an average of 5 gall morphotypes each. This is the first study of gall-inducing arthropods and their host plant species ever undertaken in a Brazilian SDTF ecosystem. Given the intense human pressure on SDTFs, the high richness of galling arthropods, and implied floral host diversity found in this study indicates the need for an increased effort to catalogue the corresponding flora and fauna, observe their intricate associations and further understand the implications of such rich diversity in these stressed and vulnerable ecosystems.

On Line Validation Exercise (OLIVE): A Web Based Service for the Validation of Medium Resolution Land Products. Application to FAPAR Products

The OLIVE (On Line Interactive Validation Exercise) platform is dedicated to the validation of global biophysical products such as LAI (Leaf Area Index) and FAPAR (Fraction of Absorbed Photosynthetically Active Radiation). It was developed under the framework of the CEOS (Committee on Earth Observation Satellites) Land Product Validation (LPV) sub-group. OLIVE has three main objectives: (i) to provide a consistent and centralized information on the definition of the biophysical variables, as well as a description of the main available products and their performances (ii) to provide transparency and traceability by an online validation procedure compliant with the CEOS LPV and QA4EO (Quality Assurance for Earth Observation) recommendations (iii) and finally, to provide a tool to benchmark new products, update product validation results and host new ground measurement sites for accuracy assessment. The functionalities and algorithms of OLIVE are described to provide full transparency of its procedures to the community. The validation process and typical results are illustrated for three FAPAR products: GEOV1 (VEGETATION sensor), MGVIo (MERIS sensor) and MODIS collection 5 FPAR. OLIVE is available on the European Space Agency CAL/VAL portal), including full documentation, validation exercise results, and product extracts.

The topographic normalization of hyperspectral data: implications for the selection of spectral end members and lithologic mapping

Abstract Compact Airborne Spectrographic Imager (CASI) hyperspectral data is used to investigate the effects of topography on the selection of spectral end members, and to assess whether the topographic correction improves the discrimination of rock units for lithologic mapping. A publicly available Digital Elevation Model (DEM), at a scale of 1:50,000, is used to model the radiance variation of the scene as a function of topography, assuming a Lambertian surface. Skylight is estimated and removed from the airborne data using a dark object correction. The CASI data is corrected on a pixel-by-pixel basis to normalize the scene to a uniform solar illumination and viewing geometry. The results show that topography has the effect of expanding end member clusters at times resulting in the overlap of clusters and that the correction process can effectively reduce the variation in detected radiance due to changes in local illumination. When topographic effects are embedded in the hyperspectral data, methods typically used for the selection of end members, such as the convex hull method, can miss end members or result in the selection of nonrepresentative pixels as end members. Thus, end members selected by some conventional methods are very likely “incomplete” or “nonrepresentative” if the topographic effect is embedded in the data. As shown in this study, the topographic correction can reveal hidden end members and achieve a better representation of end members via the statistical center of isolated clusters.

Predicting leaf gravimetric water content from foliar reflectance across a range of plant species using continuous wavelet analysis

Leaf water content is an important variable for understanding plant physiological properties. This study evaluates a spectral analysis approach, continuous wavelet analysis (CWA), for the spectroscopic estimation of leaf gravimetric water content (GWC, %) and determines robust spectral indicators of GWC across a wide range of plant species from different ecosystems. CWA is both applied to the Leaf Optical Properties Experiment (LOPEX) data set and a synthetic data set consisting of leaf reflectance spectra simulated using the leaf optical properties spectra (PROSPECT) model. The results for the two data sets, including wavelet feature selection and GWC prediction derived using those features, are compared to the results obtained from a previous study for leaf samples collected in the Republic of Panamá (PANAMA), to assess the predictive capabilities and robustness of CWA across species. Furthermore, predictive models of GWC using wavelet features derived from PROSPECT simulations are examined to assess their applicability to measured data. The two measured data sets (LOPEX and PANAMA) reveal five common wavelet feature regions that correlate well with leaf GWC. All three data sets display common wavelet features in three wavelength regions that span 1732-1736 nm at scale 4, 1874-1878 nm at scale 6, and 1338-1341 nm at scale 7 and produce accurate estimates of leaf GWC. This confirms the applicability of the wavelet-based methodology for estimating leaf GWC for leaves representative of various ecosystems. The PROSPECT-derived predictive models perform well on the LOPEX data set but are less successful on the PANAMA data set. The selection of high-scale and low-scale features emphasizes significant changes in both overall amplitude over broad spectral regions and local spectral shape over narrower regions in response to changes in leaf GWC. The wavelet-based spectral analysis tool adds a new dimension to the modeling of plant physiological properties with spectroscopy data.

Hyperspectral remote sensing of tropical and sub-tropical forests

Tropical Dry Forest Phenology and Discrimination of Tropical Tree Species Using Hyperspectral Data, K.L. Castro-Esau and M. Kalacska Remote Sensing and Plant Functional Groups: Physiology, Ecology, and Spectroscopy in Tropical Systems, M. Alvarez-Anorve, M. Quesada, and E. de la Barrera Hyperspectral Data for Assessing Carbon Dynamics and Biodiversity of Forests, R. Lucas, A. Mitchell, and P. Bunting Effect of Soil Type on Plant Growth, Leaf Nutrient/Chlorophyll Concentration, and Leaf Reflectance of Tropical Tree and Grass Species, J.C. Calvo-Alvarado, M. Kalacska, G.A. Sanchez-Azofeifa, and L.S. Bell Spectral Expression of Gender: A Pilot Study with Two Dioecious Neotropical Tree Species, J.P. Arroyo-Mora, M. Kalacska, B.L. Caraballo, J.E. Trujillo, and O. Vargas Species Classification of Tropical Tree Leaf Reflectance and Dependence on Selection of Spectral Bands, B. Rivard, G.A. Sanchez-Azofeifa, S. Foley, and J.C. Calvo-Alvarado Discriminating Sirex noctilio Attack in Pine Forest Plantations in South Africa Using High Spectral Resolution Data, R. Ismail, O. Mutanga, and F. Ahmed Hyperspectral Remote Sensing of Exposed Wood and Deciduous Trees in Seasonal Tropical Forests, S. Bohlman Assessing Recovery Following Selective Logging of Lowland Tropical Forests Based on Hyperspectral Imagery, J.P. Arroyo-Mora, M. Kalacska, R.L. Chazdon, D.L. Civco, G. Obando-Vargas, and A.A. Sanchun Hernandez A Technique for Reflectance Calibration of Airborne Hyperspectral Spectrometer Data Using a Broad, Multiband Radiometer, T. Miura, A.R. Huete, L.G. Ferreira, E.E. Sano, and H. Yoshioka Assessment of Phenologic Variability in Amazon Tropical Rainforests Using Hyperspectral Hyperion and MODIS Satellite Data, A.R. Huete, Y. Kim, P. Ratana, K. Didan, Y.E. Shimabukuro, and T. Miura Hyperspectral Remote Sensing of Canopy Chemistry, Physiology, and Biodiversity in Tropical Rainforests, G.P. Asner Tropical Remote Sensing -Opportunities and Challenges, J.A. Gamon Index

Relationships between endophyte diversity and leaf optical properties

A single tropical plant species can harbour hundreds of endophyte species within its tissues. Beyond this, little is known about the relationship between endophyte colonization, leaf traits and spectral properties of leaves. We explore these relationships in Coccoloba cereifera, a plant well known for its symbiotic properties. Endophyte richness in C. cereifera was statistically correlated with leaf traits such as water content, the ratio of fresh weight/dry weight and polyphenol/leaf specific weight. Endophyte diversity was also related to spectral vegetation indices of chlorophyll content. The associations among endophyte diversity, leaf traits and spectral reflectance pose new questions and present new opportunities to better understand plant–fungal symbioses and related leaf optical properties.

Progress and opportunities for monitoring greenhouse gases fluxes in Mexican ecosystems: the MexFlux network

Understanding ecosystem processes from a functional point of view is essential to study relationships among climate variability, biogeochemical cycles, and surface-atmosphere interactions. Increasingly during the last decades, the eddy covariance (EC) method has been applied in terrestrial, marine and urban ecosystems to quantify fluxes of greenhouse gases (e.g., CO 2 , H 2 O) and energy (e.g., sensible and latent heat). Networks of EC systems have been established in different regions and have provided scientific information that has been used for designing environmental and adaptation policies. In this context, this article outlines the conceptual and technical framework for the establishment of an EC regional network (i.e., MexFlux) to measure the surface-atmosphere exchange of heat and greenhouse gases in Mexico. The goal of the network is to improve our understanding of how climate variability and environmental change influence the dynamics of Mexican ecosystems. First, we discuss the relevance of CO 2 and water vapor exchange between terrestrial ecosystems and the atmosphere. Second, we briefly describe the EC basis and present examples of measurements in two terrestrial and one urban ecosystems of Mexico. Finally, we describe the conceptual and operational goals at short-, medium-, and long-term scales for continuity of the MexFlux network.