Changes In Canopy Structure Research Articles

Options for monitoring and estimating historical carbon emissions from forest degradation in the context of REDD+.

Measuring forest degradation and related forest carbon stock changes is more challenging than measuring deforestation since degradation implies changes in the structure of the forest and does not entail a change in land use, making it less easily detectable through remote sensing. Although we anticipate the use of the IPCC guidance under the United Framework Convention on Climate Change (UNFCCC), there is no one single method for monitoring forest degradation for the case of REDD+ policy. In this review paper we highlight that the choice depends upon a number of factors including the type of degradation, available historical data, capacities and resources, and the potentials and limitations of various measurement and monitoring approaches. Current degradation rates can be measured through field data (i.e. multi-date national forest inventories and permanent sample plot data, commercial forestry data sets, proxy data from domestic markets) and/or remote sensing data (i.e. direct mapping of canopy and forest structural changes or indirect mapping through modelling approaches), with the combination of techniques providing the best options. Developing countries frequently lack consistent historical field data for assessing past forest degradation, and so must rely more on remote sensing approaches mixed with current field assessments of carbon stock changes. Historical degradation estimates will have larger uncertainties as it will be difficult to determine their accuracy. However improving monitoring capacities for systematic forest degradation estimates today will help reduce uncertainties even for historical estimates.

Ecosystem structure and services in eelgrass Zostera marina and rockweed Ascophyllum nodosum habitats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 437:51-68 (2011) - DOI: https://doi.org/10.3354/meps09276 Ecosystem structure and services in eelgrass Zostera marina and rockweed Ascophyllum nodosum habitats Allison L. Schmidt1,*, Marta Coll1,2, Tamara N. Romanuk1, Heike K. Lotze1 1Department of Biology, Dalhousie University, PO Box 15000, 1355 Oxford Street, Halifax, Nova Scotia B3H 4R2, Canada 2Institut de Ciencies del Mar (ICM-CSIC), Passeig maritim de la Barceloneta, 37−49, 08003 Barcelona, Spain *Email: aschmidt@dal.ca ABSTRACT: Marine vegetated habitats provide essential functions and services to ocean ecosystems and human well-being. It is unclear, however, how different habitat types compare. Using large-scale field surveys, we compared the canopy and community structure between eelgrass and rockweed beds in Atlantic Canada and assessed their nitrogen retention, carbon storage, and habitat services. We then used binary network models of predator–prey interactions to determine food-web structure and its robustness to species loss. Despite disparate 3-dimensional canopy structure, both habitats significantly enhanced overall abundance and diversity of associated flora and fauna, including several commercially important species. Significant differences occurred in the species assemblages within and between habitats and were attributed to different settlement opportunities, food availability, predation risk, and maneuverability. While eelgrass plants had higher nitrogen content, rockweed canopies maintained 8-fold greater biomass and, thus, 14-fold greater nitrogen and 8-fold greater carbon retention per unit area. Both rockweed and eelgrass food webs showed similarities to other temperate and tropical seagrass webs, yet their robustness to the loss of most connected species including primary producers was among the lowest; underscoring their vulnerability to disturbances affecting the functionally dominant primary producers. The present study demonstrates that marine vegetation provides important habitat, nitrogen, and carbon storage services, yet the extent of these services depends on the foundation species and its architecture. Changes in canopy structure will therefore have profound effects on associated food webs and ecosystem services. Thus, as increasing human pressures on coastal ecosystems threaten the continued supply of essential functions and services, the protection of marine vegetated habitats should be a management priority. KEY WORDS: Canopy structure · Nitrogen retention · Carbon storage · Juvenile habitat · Diversity · Food-web structure · Species extinction · Human impacts Full text in pdf format Supplementary material PreviousNextCite this article as: Schmidt AL, Coll M, Romanuk T, Lotze HK (2011) Ecosystem structure and services in eelgrass Zostera marina and rockweed Ascophyllum nodosum habitats. Mar Ecol Prog Ser 437:51-68. https://doi.org/10.3354/meps09276 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 437. Online publication date: September 15, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Physiological interpretation of a hyperspectral time series in a citrus orchard

Hyperspectral remote sensing for monitoring horticultural production systems requires the understanding of how plant physiology, canopy structure, management and solar elevation affect the retrieved canopy reflectance during different stages of the phenological cycle. Hence, the objective of this study was to set up and to interpret a hyperspectral time series for a mature and healthy citrus orchard in the Western Cape province of South Africa considering these effects. Based on the remotely sensed data, biophysical parameters at the canopy level were derived and related to known observed physiological and phenological changes at the leaf level and to orchard management. Fractions of mature fruit, flowers, and sunburnt leaves were considered, and indices related to canopy structure chlorophyll content and canopy water status were calculated. Results revealed small cover fractions of mature fruit, flowers and sunburnt leaves of respectively 2.1%, 3.1% and 7.0%, but the high spectral contrast between flowers and leaves allowed a successful classification of flowering intensity. Furthermore, it was shown that canopy level time series of vegetation indices were sensitive to changes in solar elevation and soil reflectance which could be reduced by applying an empirical soil line correction for the most affected indices. Most trends in vegetation indices at the canopy level could be explained by a combination of changes at the leaf level (chlorophyll, carotenoids, dry matter), changes in canopy structure (leaf area index and leaf angle distribution) and changes in cover fractions of vegetative flushes, flowers and sunburnt leaves. The transformed chlorophyll absorption ratio index over the optimised soil adjusted vegetation index (MCARI/OSAVI) was best related to leaf level trends in chlorophyll content. Seasonal changes in the photochemical reflectance index (PRI) were linked to inverse changes in the carotenoid-to-chlorophyll ratio. Canopy structure indices (the modified triangular vegetation index or MTVI2 and the standardized leaf area index determining index or sLAIDI) were sensitive to changes in leaf area index, average leaf angle as well to management interactions (pruning and harvest). Canopy water status was highly impacted during the spring flush due to expanding leaves that concealed trends in the underlying mature leaves. Seasonal trends in soil and weeds reflectance were related to changes in volumetric soil water content and to the earlier and reduced growth period of non-irrigated weeds.

Preliminary Analysis on the Use of a Process-Based Forest Growth Model of Cryptomeria japonica Planted Forest to Represent the Effects of Canopy Structure Change

The objective of this study is to modify the process-based stand growth model for Cryptomeria japonica in the photosynthetic pro- duction process so as to more reasonably represent the stand growth pattern after thinning. We introduce five leaf strata to the canopy structure, and then parameterize the light-curve for each leaf stratum by Bayesian calibration via the Markov Chain Monte Carlo (MCMC) method. We examine the behavior of the model using the estimated light-curve parameters through a simulation approach. We used the forest stand data derived from repeated measurements of three per- manent plots. The posterior distribution of light-curve parameters derived from MCMC were well converged. We virtually applied three thinning scenarios, upper thinning, random thinning and lower thin- ning, and then simulated stand growth. The modified model could well reflect the changes in canopy structure derived from thinning on the growth pattern after thinning. The results suggest that the multiple light-curve model adopted in this study would be represent more realistic stand dynamics after thinning than single light-curve model adopted in the former model.

Post-flowering leaflet removals increase pod initiation in soybean canopies

Much of the yield variation in soybean ( Glycine max L. Merrill) crops is related to changes in pod and seed number. Pod number is the result of pod initiation and pod abscission while seed number is the result of potential seed per pod and seed abortion. However, the physiological regulation of these processes is not well understood. A field experiment was conducted to investigate the role of post-flowering changes in source size and canopy structure on pod initiation, pod abscission and seed abortion in soybean. Two soybean genotypes: DM48 and A7409 (maturity groups IV and VII, respectively) were used. Leaflet removal treatments (L) consisted of removing none (L0), one (L1) or two (L2) lateral leaflets of every developed trifoliate leaf present. Leaflet removals were applied twice: the first at full bloom and the second shortly after the beginning seed stage. Crop growth rate (CGR), leaf area index (LAI), light interception (LI), and relative leaf growth rate, were determined during the periods in which numerical components are established. For the period between the first and the second leaflet removal, CGR remained unchanged among L treatments in both genotypes because LAI reductions were compensated through an increase in the net assimilation rate of the remaining leaves. The first leaflet removal increased the relative leaf growth rate and the number of pods initiated (PI) and these increases were inversely related to the remaining LAI in both genotypes. Moreover, the inverse relationship between LAI and PI was sustained at LAI below and above critical (i.e ., LAI for 95% LI) and was not related to CGR or LI. The number of pod abscised also increased with the level of leaflet removal during the first and main abscission period in both genotypes and the percentage of pod abscission was directly related to the seed growth rate per unit leaf area during the abscission period. Seed abortion was inversely related to LAI after the second leaflet removal. Only the highest level of leaflet removals (i.e., L2) was able to reduce seed size in both genotypes. Whereas pod abscission, seed abortion and seed size could be related to indicators of canopy assimilatory capability pod initiation was not, suggesting that other physiological mechanism/s operate in the regulation of pod initiation. In addition, our results suggest that early (i.e., at flowering) canopy closure may negatively impact pod initiation in soybean. To the best of our knowledge, this study is the first to document that the number of initiated pods is inversely related to LAI in soybean canopies.

Trends in entropy production during ecosystem development in the Amazon Basin

Understanding successional trends in energy and matter exchange across the ecosystem-atmosphere boundary layer is an essential focus in ecological research; however, a general theory describing the observed pattern remains elusive. This paper examines whether the principle of maximum entropy production could provide the solution. A general framework is developed for calculating entropy production using data from terrestrial eddy covariance and micrometeorological studies. We apply this framework to data from eight tropical forest and pasture flux sites in the Amazon Basin and show that forest sites had consistently higher entropy production rates than pasture sites (0.461 versus 0.422 W m(-2) K(-1), respectively). It is suggested that during development, changes in canopy structure minimize surface albedo, and development of deeper root systems optimizes access to soil water and thus potential transpiration, resulting in lower surface temperatures and increased entropy production. We discuss our results in the context of a theoretical model of entropy production versus ecosystem developmental stage. We conclude that, although further work is required, entropy production could potentially provide a much-needed theoretical basis for understanding the effects of deforestation and land-use change on the land-surface energy balance.

Sensitivity of groundwater recharge under irrigated agriculture to changes in climate, CO2 concentrations and canopy structure

Estimating groundwater recharge in response to increased atmospheric CO2 concentration and climate change is critical for future management of agricultural water resources in arid or semi-arid regions. Based on climate projections from the Intergovernmental Panel on Climate Change, this study quantified groundwater recharge under irrigated agriculture in response to variations of atmospheric CO2 concentrations (550 and 970 ppm) and average daily temperature (+1.1 and +6.4 °C compared to current conditions). HYDRUS 1D, a model used to simulate water movement in unsaturated, partially saturated, or fully saturated porous media, was used to simulate the impact of climate change on vadose zone hydrologic processes and groundwater recharge for three typical crop sites (alfalfa, almonds and tomatoes) in the San Joaquin watershed in California. Plant growth with the consideration of elevated atmospheric CO2 concentration was simulated using the heat unit theory. A modified version of the Penman–Monteith equation was used to account for the effects of elevated atmospheric CO2 concentration. Irrigation amount and timing was based on crop potential evapotranspiration. The results of this study suggest that increases in atmospheric CO2 and average daily temperature may have significant effects on groundwater recharge. Increasing temperature caused a temporal shift in plant growth patterns and redistributed evapotranspiration and irrigation water use earlier in the growing season resulting in a decrease in groundwater recharge under alfalfa and almonds and an increase under tomatoes. Elevating atmospheric CO2 concentrations generally decreased groundwater recharge for all crops due to decreased evapotranspiration resulting in decreased irrigation water use. Increasing average daily temperature by 1.1 and 6.4 °C and atmospheric CO2 concentration to 550 and 970 ppm led to a decrease in cumulative groundwater recharge for most scenarios. Overall, the results indicate that groundwater recharge may be very sensitive to potential future climate changes.

Individual Object Change Detection for Monitoring the Impact of a Forest Pathogen on a Hardwood Forest

Sudden oak death (SOD) has caused widespread mortality in a number of tree and shrub species throughout coastal California. As a result, canopy changes are directly visible from remotely sensed imagery. To quantify changes in horizontal canopy structure to the oak woodlands in China Camp State Park, California, USA, a heavily hit area, we developed a novel change detection technique that tracks changes to individual objects. Using 4-band, 1 m spatial resolution aerial photography, we classified four annual images (2000 to 2003) with object-based image analysis (OBIA) and employed a GIS for our change detection technique. We identified 352 gaps that contained SOD mortality in 2000 and persisted through 2003. Their median areas and perimeters did not change significantly in that time. However, those gaps that increased in size tended to be smaller than those that decreased, indicating increased mortality in newly infected areas. Our new change detection method allowed us to monitor these gaps one-by-one, revealing ecologically meaningful results that would otherwise be obscured in a landscape-scale analysis.

Stream ecosystem responses to the 2007 spring freeze in the southeastern United States: unexpected effects of climate change

AbstractSome expected changes in climate resulting from human greenhouse gas emissions are clear and well documented, but others may be harder to predict because they involve extreme weather events or heretofore unusual combinations of weather patterns. One recent example of unusual weather that may become more frequent with climate change occurred in early spring 2007 when a large Arctic air mass moved into the eastern United States following a very warm late winter. In this paper, we document effects of this freeze event on Walker Branch, a well‐studied stream ecosystem in eastern Tennessee. The 2007 spring freeze killed newly grown leaf tissues in the forest canopy, dramatically increasing the amount of light reaching the stream. Light levels at the stream surface were sustained at levels considerably above those normal for the late spring and summer months due to the incomplete recovery of canopy leaf area. Increased light levels caused a cascade of ecological effects in the stream beginning with considerably higher (two–three times) rates of gross primary production (GPP) during the late spring and summer months when normally low light levels severely limit stream GPP. Higher rates of stream GPP in turn resulted in higher rates of nitrate (NO3−) uptake by the autotrophic community and lower NO3− concentrations in stream water. Higher rates of stream GPP in summer also resulted in higher growth rates of a dominant herbivore, the snail Elimia clavaeformis. Typically, during summer months net NO3− uptake and snail growth rates are zero to negative; however, in 2007 uptake and growth were maintained at moderate levels. These results show how changes in forest vegetation phenology can have dramatic effects on stream productivity at multiple trophic levels and on nutrient cycling as a result of tight coupling of forest and stream ecosystems. Thus, climate change‐induced changes in canopy structure and phenology may lead to large effects on stream ecosystems in the future.

Physiological, morphological and allocation plasticity of a semi-deciduous shrub

The main objective of this study was to look into the phenotypic plasticity of the semi-deciduous Mediterranean shrub, Halimium halimifolium. We studied morphological, allocation and physiological traits to determine which characters were more plastic and contribute in a greater extent to the acclimation ability of the species. We present a phenotypic plasticity index for morphological, physiological and allocation traits, which we have applied in the most contrasted plant communities where the species grows naturally. Data published by Díaz Barradas, M.C., García Novo, F. [1987. The vertical structure of Mediterranean scrub in Doñana National Park (SW Spain). Folia Geobotanica Phytotaxonomica 22, 415–433; 1988. Modificación y extinción de la luz a través de la copa en cuatro especies de matorral en el Parque Nacional de Doñana. Monografias Instituto Pirenaico de Ecologia 4, 503–516; 1990. Seasonal changes in canopy structure in two mediterranean dune shrubs. Journal of Vegetation Science 1, 31–40.], Díaz Barradas, M.C., Zunzunegui, M., García Novo, F. [1999a. Autoecological traits of Halimium halimifolium in contrasted habitats under Mediterranean type climate. Folia Geobotanica 34, 189–208.] and Zunzunegui et al. [Zunzunegui, M., Díaz Barradas, M.C., García Novo, F. 1997. Autoecological notes of Halimium halimifolium. Lagascalia 19, 725–736. Sevilla, Spain; Zunzunegui, M., Díaz Barradas, M.C., Fernández Baco, L., García Novo, F. 1999. Seasonal changes in photochemical efficiency in leaves of Halimium halimifolium a Mediterranean semideciduous shrub. Photosynthetica 36, 17–31; Zunzunegui, M., Díaz Barradas, M.C., García Novo, F. 2000. Different phenotypic response of Halimium halimifolium in relation to groundwater availability. Plant Ecology 148, 165–174; Zunzunegui, M., Díaz Barradas, M.C., Aguilar, F., Ain-Lhout, F., Clavijo, A., García Novo, F. 2002. Growth response of Halimium halimifolium at four sites with different soil water availability regimes in two contrasted hydrological cycles. Plant and Soil 247, 271–28.] have been re-appraised and combined with original data. Phenotypic plasticity index showed that the highest plasticity of the species was physiological, and especially for the traits related with water control. This high physiological plasticity appears mainly between seasons (September–November) rather than between sites. Plasticity in allocation traits showed intermediate values between physiological and morphological traits.

Abrupt changes in annual stemflow with growth in a young stand of Japanese cypress

Stemflow was measured in a planted young stand of Japanese cypress for four years from ages 9 to 12. Canopy cover increased with growth from 55% to 94% during the measurement period. The ratio of stemflow SF to rainfall R, SF/R (the funneling ratio FR that represents the efficiency in collecting stemflow), was 5.9% (81.3) at age 9 on an annual basis; however, it abruptly fell to 2.8% (30.0) at age 10. Following the drop, SF/R recovered gradually with growth, reaching 3.8% at age 11 and 4.3% at 12, while FR remained almost constant at values of around 30. The relation between R and SF/R analyzed quarterly on a rain event basis revealed that changes in canopy structure and/or tree architecture

Temperate-like stand dynamics in relict Mediterranean-fir (Abies pinsapo, Boiss.) forests from southern Spain

• Introduction and statement of the research questions: Gap dynamics have been widely studied in forests of Abies spp. from temperate and boreal regions. The local microclimate and competition for light have been identified as the main factors controlling changes in species composition and canopy structure, however little is known on dynamics of such forests in Mediterranean. • Experimental design and aims: We studied forest structure and dynamics of Abies pinsapo stands in southern Spain, in contrasting habitats and successional status. In addition past regeneration patterns and their relationship to canopy structure, disturbances and forest-use history were investigated. • Results: Stands structure attributes were within the range described for temperate conifer biomes. The age structure revealed two main cohorts comprised of a few > 100 year-old trees and abundant younger trees established in a single recruitment event after the stands were protected in the 1950s. Initial growth-rate analyses indicated that A. pinsapo regenerated mainly in small canopy gaps, while only 15% recruited from the forest understorey. For the last ten years, basal area increment was lower than 10 cm 2 y −1 in 91% of studied trees and growth rate differences between trees narrowed.

Impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana

AbstractThe lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (5 °16′54″N, 52 °54′44″W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93‐day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 g C m−2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 g C m−2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 g C m−2), emphasizing that environmental conditions, such as during a severe drought, modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance.

Leaf litterfall, fine-root production, and decomposition in shrublands with different canopy structure induced by grazing in the Patagonian Monte, Argentina

Selective sheep grazing in the Patagonian Monte induces the reduction of total and perennial grass cover, species replacement within life forms, and the increase in dominance of long-lived evergreen woody plants with slow growth rates and high concentration of secondary compounds in leaves. We hypothesized that these changes in the canopy structure induced by sheep grazing will affect the mass, chemistry and decomposability of leaf litter and fine roots. We selected two sites in the Patagonian Monte, representative of ungrazed and grazed vegetation states. At each site, we assessed canopy structure (total cover and absolute and relative grass and shrub cover), monthly leaf litterfall, and fine-root biomass and production in the upper soil (15 cm). We also estimated the rates of mass, C, soluble phenolics, lignin and N decay in litterbags containing both leaf litter and fine roots of each site under field conditions during two consecutive years. The ungrazed site exhibited higher total plant cover, absolute and relative grass- and shrub-cover than the grazed one. Leaf litterfall was lower at the grazed site than at the ungrazed site. Fine-root production did not vary between sites. Leaf litter and fine root tissues had higher concentration of secondary compounds at the grazed than at the ungrazed site. However, fine roots showed lower mass and C decay than leaf litter, attributable to the predominant secondary compound (lignin and soluble phenolics, respectively). Leaf litter decomposed slower but released more N during decay at the ungrazed than at the grazed site, probably due to its low concentration of secondary compounds. We concluded that changes in canopy structure induced by grazing disturbance such as those explored in our study could reduce leaf litterfall mass and increase the concentration of secondary compounds of both leaf litter and fine roots leading to slow N release to soil during decay.

Intraspecific changes in forest canopy allometries during self‐thinning

Summary 1Leaves are the key active sites for energy and matter transfer in plants, and therefore the total one-sided area of leaves per square metre of ground (leaf area index, LAI) is a critical variable used for scaling up from plant to ecosystem level properties. 2A commonly held belief is that LAI remains constant during the self-thinning phase of stand development, and allometric relationships between tree density, mean tree size and leaf area (or leaf mass) are frequently used to provide a mechanistic explanation for the observed thinning relationships. 3We investigated variations in leaf allometry, stand LAI and other canopy properties along a developmental sequence of naturally occurring mono-specific self-thinning stands of mountain beech (Nothofagus solandri var. cliffortioides) in New Zealand. 4Stand age had a consistent significant effect on both the slope and the intercept of both the leaf mass and the leaf area allometric relationships (increasing slope, decreasing intercept). This was due to trees of a given basal area having more leaf area (or leaf mass) when growing in a neighbourhood of smaller trees, than equivalently sized individuals surrounded by a lower density of trees larger than itself. 5A peaked (non-constant) relationship was observed between LAI and stand age during self-thinning, with the mean LAI values peaking in intermediately aged large sapling stands (7·08) compared with the small sapling stands (5·42) and older pole stands (5·70). Stand level leaf mass per unit area (LMA) varied with canopy height and stand age, being highest at the top of canopies and in older stands. 6We propose that the observed increase in canopy depth during the early stages of stand development (but after canopy closure has occurred) could be driving the increase in stand LAI due to a more even distribution of light within the canopy. 7Our findings suggest that the commonly held assumption of constant LAI should be abandoned in favour of the notion of leaf area being at a dynamic maximum during self-thinning, with the maximum possible leaf area being influenced by age-related changes in canopy structure that occur during stand development.

Isotopic variation of snow cover and streamflow in response to changes in canopy structure in a snow‐dominated mountain catchment

AbstractIsotopic composition of snow cover and streamflow was determined in a snow‐dominated, forested watershed to quantify the spatial variability and processes that alter stable isotope (oxygen‐18, 18O and deuterium, 2H) composition under different forest canopy conditions (clear‐cut, partial‐cut (thinned), and unimpacted forest). Snow sampling was carried out on 4 days in late winter and early spring 2006. Meteorological data, precipitation, and streamflow were continuously monitored during the study. Isotope analyses of precipitation samples were conducted weekly through the 2005–2006 snow season. Values of δ18O varied between − 22·0 and − 9·5‰ , and δ2H varied between − 170 and − 76‰ . Isotope concentrations from snowpack samples varied between − 17·5 and − 13·8‰ for δ18O, and between − 129 and − 102‰ for δ2H. These ranges reflect differences in precipitation, accumulation, sublimation, and melting of the snow cover. Streamflow samples were collected during the snowmelt season from two locations every alternate day from the beginning of April until the end of May. Streamflow and snow from a partial‐cut and an uncut forest were enriched in the heavy isotopes (18O and 2H) relative to streamflow and snow from a clear‐cut forest. Based on the low water contents of the snowpack under dense canopies, we infer that the isotope enrichment resulted primarily from sublimation of snow intercepted by the canopy, with more enrichment in denser canopies. There was no significant correlation between snowpack isotope concentration and altitude. Results indicate that variations in canopy structure can alter snow isotope composition. This finding will provide a useful index of snowpack sublimation, and thus, improved parameterization of distributed hydrological models. Copyright © 2008 John Wiley & Sons, Ltd.

Sensitivity of volatile monoterpene emission to changes in canopy structure: a model‐based exercise with a process‐based emission model

This paper investigates the dependence of monoterpene emissions at the canopy scale on total leaf area and leaf distribution. Simulations were carried out for a range of hypothetical but realistic forest canopies of the evergreen Quercus ilex (holm oak). Two emission models were applied that either did (SIM-BIM2) or did not (G93) account for cumulative responses to temperature and light. Both were embedded into a canopy model that considered spatial and temporal variations of foliage properties. This canopy model was coupled to a canopy climate model (CANOAK) to determine the micrometeorological conditions at the leaf scale. Structural properties considerably impacted monoterpene emission. The sensitivities to changes in total leaf area and to leaf area distribution were found to be of similar magnitude. The two different models performed similarly on a whole-year basis but showed clear differences during certain episodes. The analysis showed that structural indices have to be carefully evaluated for proper scaling of emission from leaves to canopy. Further research is encouraged on seasonal dynamics of emission potentials.

Satellite Remote Sensing of Terrestrial Net Primary Production for the Pan-Arctic Basin and Alaska

We applied a terrestrial net primary production (NPP) model driven by satellite remote sensing observations of vegetation properties and daily surface meteorology from a regional weather forecast model to assess NPP spatial and temporal variability for the pan-Arctic basin and Alaska from 1982 to 2000. Our results show a general decadal trend of increasing NPP for the region of approximately 2.7%, with respective higher (3.4%) and lower (2.2%) rates for North America and Eurasia. NPP is both spatially and temporally dynamic for the region, driven largely by differences in productivity rates among major biomes and temporal changes in photosynthetic canopy structure and spring and summer air temperatures. Mean annual NPP for boreal forests was approximately 3 times greater than for Arctic tundra on a unit area basis and accounted for approximately 55% of total annual carbon sequestration for the region. The timing of growing season onset inferred from regional network measurements of atmospheric CO2 drawdown in spring was inversely proportional to annual NPP calculations. Our findings indicate that recent regional warming trends in spring and summer and associated advances in the growing season are stimulating net photosynthesis and annual carbon sequestration by vegetation at high latitudes, partially mitigating anthropogenic increases in atmospheric CO2. These results also imply that regional sequestration and storage of atmospheric CO2 is being altered, with potentially greater instability and acceleration of the carbon cycle at high latitudes.

The Interactive Effects of Fire and Diversity on Short-Term Responses of Ecosystem Processes in Experimental Mediterranean Grasslands

We conducted a field experiment using constructed communities to test whether species richness contributed to the maintenance of ecosystem processes under fire disturbance. We studied the effects of diversity components (i.e., species richness and species composition) upon productivity, structural traits of vegetation, decomposition rates, and soil nutrients between burnt and unburnt experimental Mediterranean grassland communities. Our results demonstrated that fire and species richness had interactive effects on aboveground biomass production and canopy structure components. Fire increased biomass production of the highest-richness communities. The effects of fire on aboveground biomass production at different levels of species richness were derived from changes in both vertical and horizontal canopy structure of the communities. The most species-rich communities appeared to be more resistant to fire in relation to species-poor ones, due to both compositional and richness effects. Interactive effects of fire and species richness were not important for belowground processes. Decomposition rates increased with species richness, related in part to increased levels of canopy structure traits. Fire increased soil nutrients and long-term decomposition rate. Our results provide evidence that composition within richness levels had often larger effects on the stability of aboveground ecosystem processes in the face of fire disturbance than species richness per se.

Relating SAR image texture to the biomass of regenerating tropical forests

An accurate global carbon budget requires information on terrestrial carbon sink strength. Regenerating tropical forests are known to be important terrestrial carbon sinks but information on their location, extent and biomass (from which carbon content can be estimated) is incomplete. The use of remotely sensed data in optical wavelengths has been of limited use due to both the weak relationship between optical radiation and forest biomass and near‐constant cloud cover in the tropics. L‐band Synthetic Aperture Radar (SAR) backscatter, however, is related positively to biomass (but only up to an asymptote of around 40–90 T ha−1) and can be obtained independently of cloud cover. Both canopy structure and biomass change over time as pioneer species are replaced by early and late regenerating species. These structural changes are related to an increase in (i) tree height, (ii) tree species richness and (iii) canopy thickness and influence the roughness of the canopy surface and consequently SAR image texture. Therefore, we investigated the degree to which textural information could be used to increase the correlation between image tone (backscatter) and biomass. Field data were used to estimate the biomass of 37 regenerating forests plots in Brazilian Amazonia. Texture measures derived from local statistics, the grey level co‐occurrence matrix (GLCM) and the variogram were evaluated using simulated images on the basis of their ability to identify significant differences in image texture independently of image contrast. The selected texture measures were applied to L‐band JERS‐1 (Japanese Earth Resources Satellite) SAR images and the correlation between backscatter and biomass was determined for regenerating tropical forests. A strong correlation was found for the texture measures and biomass. The r a 2 (adjusted coefficient of determination), measuring the correlation between backscatter and biomass, increased from 0.74 to 0.82 with the addition of GLCM‐derived contrast. The addition of image texture (GLCM‐derived contrast) to image tone (backscatter) potentially increases the accuracy with which JERS‐1 SAR data can be used to estimate biomass in tropical forests.