Influences of canopy structure and physiological traits on flux partitioning between understory and overstory in an eastern Siberian boreal larch forest

Boreal forests play an important role in the global balance of energy and CO₂. Our previous study of elaborate eddy covariance observations in a Siberian boreal larch forest, conducted both above the forest canopy and at the forest floor, revealed a significant contribution of latent heat flux (LE) from the cowberry understory to the whole ecosystem LE. Thus, in the present study, we examined what factors control the partitioning of whole ecosystem LE and CO₂ flux into the understory and overstory vegetation, using detailed leaf-level physiology (for both understory and overstory vegetation) and soil respiration property measurements as well as a multilayer soil-vegetation-atmosphere transfer (SVAT) model. The modeling results showed that the larch overstory's leaf area index (LAI) and vertical profile of leaf photosynthetic capacity were major factors determining the flux partitioning in this boreal forest ecosystem. This is unlike other forest ecosystems that tend to have dense LAI. We concluded that control of the larch overstory's LAI had a relationship with both the coexistence of the larch with the cowberry understory and with the water resources available to the total forest ecosystem.     

Relationships between simulated water stress and mortality and growth rates in underplanted Toona ciliata Roem. in subtropical Argentinean plantations

Toona ciliata Roem. (Australian red cedar) requires a nurse-tree overstory to prevent damage from drought and irradiation in some regions of north-eastern Argentina. T. ciliata was planted in the understory of Pinus taeda L. (625 stems/ha), Pinus elliottii Engelm. × Pinus caribaea Morelet (625 stems/ha), and Grevillea robusta A. Cunn. (833 stems/ha) nurse trees, which were thinned to 0, 25, 50, 75 and 100% of the initial densities. We measured initial T. ciliata mortality and growth as well as Leaf Area Index (LAI) based on light transmission. T. ciliata soil water availability and its effect on early growth and mortality were examined by modelling drought stress using the two-dimensional forest hydrology model ForWaDy. Simulated patterns in T. ciliata water stress for the different overstory treatments were consistent with observed patterns of mortality. Early mortality was lowest with a G. robusta overstory, with corresponding lowest drought stress values and high modelled soil water contents in the top soil layer in intermediate and high overstory densities. Mortality was highest with a P. elliottii × P. caribaea overstory in treatments with the highest modelled drought stress values in the most open treatments. The model supported our field observations by indicating that water stress was an important limitation to T. ciliata survival and growth on our study sites. The linkage between T. ciliata establishment success, early growth and soil water availability as indicated by ForWaDy, leads us to conclude that the model is a suitable stand management tool for guiding establishment of T. ciliata plantations.     

Controls on vegetation structure in Southwestern ponderosa pine forests, 1941 and 2004

Long-term studies can broaden our ecological understanding and are particularly important when examining contingent effects that involve changes to dominance by long-lived species. Such a change occurred during the last century in Southwestern (USA) ponderosa pine (Pinus ponderosa) forests. We used five livestock grazing exclosures established in 1912 to quantify vegetation structure in 1941 and 2004. Our objectives were to (1) assess the effects of historical livestock grazing on overstory structure and age distribution, (2) assess the effects of recent livestock grazing and overstory on understory vegetation, and (3) quantify and explain changes in understory vegetation between 1941 and 2004. In 1941, canopy cover of tree regeneration was significantly higher inside exclosures. In 2004, total tree canopy cover was twice as high, density was three times higher, trees were smaller, and total basal area was 40% higher inside exclosures. Understory species density, herbaceous plant density, and herbaceous cover were negatively correlated with overstory vegetation in both years. Most understory variables did not differ between grazing treatments in 1941 but were lower inside exclosures in 2004. Differences between grazing treatments disappeared once overstory effects were accounted for, indicating that they were due to the differential overstory response to historical livestock grazing practices. Between 1941 and 2004, species density declined by 34%, herbaceous plant density by 37%, shrub cover by 69%, total herbaceous cover by 59%, graminoid cover by 39%, and forb cover by 82%. However, these variables did not differ between grazing treatments or years once overstory effects were accounted for, indicating that the declines were driven by the increased dominance of the overstory during this period. Our results demonstrate that historical livestock grazing practices are an aspect of land-use history that can affect ecosystem development. Grazing history must be considered when extrapolating results from one site to another. In addition, the understory vegetation was more strongly controlled by the ponderosa pine overstory than by recent livestock grazing or by temporal dynamics, indicating that overstory effects must be accounted for when examining understory responses in this ecosystem.     

Mortality of large trees and lianas following experimental drought in an Amazon forest

Severe drought episodes such as those associated with El Ni?o Southern Oscillation (ENSO) events influence large areas of tropical forest and may become more frequent in the future. One of the most important forest responses to severe drought is tree mortality, which alters forest structure, composition, carbon content, and flammability, and which varies widely. This study tests the hypothesis that tree mortality increases abruptly during drought episodes when plant-available soil water (PAW) declines below a critical minimum threshold. It also examines the effect of tree size, plant life form (palm, liana, tree) and potential canopy position (understory, midcanopy, overstory) on drought-induced plant mortality. A severe, four-year drought episode was simulated by excluding 60% of incoming throughfall during each wet season using plastic panels installed in the understory of a 1-ha forest treatment plot, while a 1-ha control plot received normal rainfall. After 3.2 years, the treatment resulted in a 38% increase in mortality rates across all stems >2 cm dbh. Mortality rates increased 4.5-fold among large trees (>30 cm dbh) and twofold among medium trees (10-30 cm dbh) in response to the treatment, whereas the smallest stems were less responsive. Recruitment rates did not compensate for the elevated mortality of larger-diameter stems in the treatment plot. Overall, lianas proved more susceptible to drought-induced mortality than trees or palms, and potential overstory tree species were more vulnerable than midcanopy and understory species. Large stems contributed to 90% of the pretreatment live aboveground biomass in both plots. Large-tree mortality resulting from the treatment generated 3.4 times more dead biomass than the control plot. The dramatic mortality response suggests significant, adverse impacts on the global carbon cycle if climatic changes follow current trends.     

Shifts in southern Wisconsin forest canopy and understory richness, composition, and heterogeneity

We resurveyed the under- and overstory species composition of 94 upland forest stands in southern Wisconsin in 2002-2004 to assess shifts in canopy and understory richness, composition, and heterogeneity relative to the original surveys in 1949-1950. The canopy has shifted from mostly oaks (Quercus spp.) toward more mesic and shade-tolerant trees (primarily Acer spp.). Oak-dominated early-successional stands and those on coarse, nutrient-poor soils changed the most in canopy composition. Understories at most sites (80%) lost native species, with mean species density declining 25% at the 1-m2 scale and 23.1% at the 20-m2 scale. Woody species have increased 15% relative to herbaceous species in the understory despite declining in absolute abundance. Initial canopy composition, particularly the abundance of red oaks (Quercus rubra and Q. velutina), predicted understory changes better than the changes observed in the overstory. Overall rates of native species loss were greater in later-successional stands, a pattern driven by differential immigration rather than differential extirpation. However, understory species initially found in early-successional habitats declined the most, particularly remnant savanna taxa with narrow or thick leaves. These losses have yet to be offset by compensating increases in native shade-adapted species. Exotic species have proliferated in prevalence (from 13 to 76 stands) and relative abundance (from 1.2% to 8.4%), but these increases appear unrelated to the declines in native species richness and heterogeneity observed. Although canopy succession has clearly influenced shifts in understory composition and diversity, the magnitude of native species declines and failure to recruit more shade-adapted species suggest that other factors now act to limit the richness, heterogeneity, and composition of these communities.     

Regulation of algal community development in a Macrocystis pyrifera forest

The effects of small and large-scale roughness, overstory development, competition for space with sessile animals, and grazing on algal community development in a subtidal Macrocystis pyrifera forest were examined using specially prepared concrete blocks as substrata. Variation in small-scale roughness (crevices and grooves in the order of 0.1 to 3 mm width and depth) had no significant effects on community composition. However, M. pyrifera colonization, algal diversity, and sessile animal biomass were higher near the upper horizontal edges of blocks and concrete prisms. This “edge” effect may result from a combination of increased spore and larval settlement and enhanced growth of plants and animals associated with the turbulent eddies formed around these obstructions. Natural and experimentally produced variations in the algal overstory demonstrated that the presence of an overstory can reduce algal diversity and cover beneath. Caging experiments suggest that predatory fishes and sea-stars indirectly affect the algal community by removing sessile animals (primarily bryozoans) which compete with the algae for space. The exclusion of grazers resulted in increased growth of Gigartina spp. Selective grazing on this genus may account for its reduced abundance in the study area.     

Intertype mark correlation function: A new tool for the analysis of species interactions

The spatial pattern of the different species in complex ecosystems reflects the underlying ecological processes. In this paper a second order moment function is proposed and tested to analyse the spatial distribution of a mark, which could be a tree characteristic such as diameter or height, between two different types of points, which could be two different tree species. The proposed function was a conditional density function based on the intertype K_rs(d) function, incorporating as test function the correlation of the marks between pairs composed of points of different types. The results obtained in simulated and real plots prove that the function is capable of revealing the scale at which spatial correlation of the mark between two types of points exists. The proposed function allows the spatial association between individuals of different species at different life stages to be identified. This analysis may reveal information on species ecology and interspecific interactions in forest ecosystems.     

Communal roosting sites are potential ecological traps: experimental evidence in a Neotropical harvestman

Situations in which animals preferentially settle in low-quality habitat are referred to as ecological traps, and species that aggregate in response to conspecific cues, such as scent marks, that persist after the animals leave the area may be especially vulnerable. We tested this hypothesis on harvestmen (Prionostemma sp.) that roost communally in the rainforest understory. Based on evidence that these animals preferentially settle in sites marked with conspecific scent, we predicted that established aggregation sites would continue to attract new recruits even if the animals roosting there perished. To test this prediction, we simulated intense predation by repeatedly removing all individuals from 10 established roosts, and indeed, these sites continued to attract new harvestmen. A more likely reason for an established roost to become unsuitable is a loss of overstory canopy cover caused by treefalls. To investigate this scenario, without felling trees, we established 16 new communal roosts by translocating harvestmen into previously unused sites. Half the release sites were located in intact forest, and half were located in treefall gaps, but canopy cover had no significant effect on the recruitment rate. These results support the inference that communal roost sites are potential ecological traps for species that aggregate in response to conspecific scent.     

Floristic composition of arid off –shore islands in Abu Dhabi,United Arab Emirates

Data on flora and vegetation of 14 off-shore islands representing different habitat types were studied for investigating floristic composition, vegetation types and correlation with their habitats and ecosystem. The results demonstrate considerable plant distribution and diversity among the islands within the limited spectrum of species; encompassing a total of 47 species, belonging to 43 genera under 24 families. The most representative families were Amaranthaceae (9 species), Fabaceae (4 species), Poaceae (4 species) and Asteraceae and Aizoaceae (3 species each). Fourteen families are represented by only one species. The mangrove species, Avicennia marina, occurs throughout the coast of Abu Dhabi in discontinuous patches and in different water salinities. The studies also seek to underline that dominant species that constitutes the flora of Abu Dhabi are salt tolerant in nature. Compared to other Arabian Peninsula ecosystems, UAE perhaps has a higher coastal: mainland area ratio, which has contributed to a natural dominance of salt tolerant species among the community. The studies show 40% similarity among islands with respect to the species diversity. The floristic composition of the off-shore islands also indicates a need to consider these sites as protected sites.     

Crustacean habitat potential mapping in a tidal flat using remote sensing and GIS

To make a macrofaunal (crustacean) habitat potential map, the spatial distribution of ecological variables in the Hwangdo tidal flat, Korea, was explored. Spatial variables were mapped using remote sensing and a geographic information system (GIS) combined with field observations. A frequency ratio (FR) and logistic regression (LR) model were employed to map the macrofauna potential area for the Ilyoplax dentimerosa, a crustacean species. Spatial variables affecting the tidal macrofauna distribution were selected based on abundance and biomass and used within a spatial database derived from remotely sensed data of various types of sensors. The spatial variables included the intertidal digital elevation model (DEM), slope, distance from a tidal channel, tidal channel density, surface sediment facies, spectral reflectance of the near infrared (NIR) bands and the tidal exposure duration. The relation between the I. dentimerosa and each spatial variable was calculated using the FR and LR. The species was randomly divided into a training set (70%) to analyse habitat potential using FR and LR and a test set (30%) to validate the predicted habitat potential map. The relations were overlaid to produce a habitat potential map with the species potential index (SPI) value for each pixel. The potential habitat maps were compared with the surveyed habitat locations such as validation data set. The comparison results showed that the LR model (accuracy is 85.28%) is better in prediction than the FR (accuracy is 78.96%) model. The performance of models gave satisfactory accuracies. The LR provides the quantitative influence of variables on a potential habitat of species; otherwise, the FR shows the quantitative influence of a class in each variable. The combination of a GIS-based frequency ratio and logistic regression models and remote sensing with field observations is an effective method to determine locations favorable for macrofaunal species occurrences in a tidal flat.     

More asymmetric tree competition brings about more evapotranspiration and less runoff from the forest ecosystems: A simulation study

The present paper reports how stand size-structure dynamics due to competition between different-sized trees affect long-term forested water balance in Japanese cool-temperate planted stands (evergreen coniferous Cryptomeria japonica and deciduous coniferous Larix kaempferi stands) using a fully coupled multi-layered meteorological surface physics—terrestrial ecosystems model. The simulation captured the well-known annual variation in leaf area index (LAI) accurately with stand age in monocultured and even-aged stands; the occurrence of maximum LAI during the early growth stage and then a gradual decline followed by a steady state after the maximum LAI. The simulations also detected a high dependency of annual evapotranspiration (AETr) on LAI with stand age that is well known by prior observational researches. In the C. japonica (shade-tolerant late-successional species) stand, the relationship between annual net primary productivity of an individual tree (NPP_ind) and individual tree mass (w) changed from linear to a convex curve during self-thinning, indicating that the degree of asymmetric tree competition intensified with forest stand development. The higher degree of competitive asymmetry characterized by the convex-shaped NPPind-w relationship produced greater size inequality, i.e., the formation of trees stratified by height. Under such conditions, AETr and annual transpiration (ATr) were mainly regulated by larger trees. On the other hand, the NPPind-w relationships in the L. kaempferi (shade-intolerant early-successional species) stand were linear throughout the simulated period, indicating the lower degree of competitive asymmetry. Under such conditions, the growth of intermediate-sized trees was enhanced and these trees became a dominant source of AETr (and also ATr) during self-thinning. Furthermore, the sensitivity analysis of the effects of ecophysiological parameters such as foliage profile (i.e., vertical distribution of leaf area density) of an individual tree (distribution pattern is described by the parameter η), the maximum carboxylation velocity (V_cmax0) and biomass allocation pattern of individual plant growth (μ₁) on AETr, ATr and annual runoff (AR_off) showed that the temporal trends of AETr, ATr, AR_off and NPPind-w relationships were completely the same as those in the control simulations. However, the NPPind-w relationship during self-thinning indicated higher degrees of competitive asymmetry when η or V_cmax0 were greater than those in the control simulation and generated greater AETr and ATr and thus smaller AR_off. We found that more asymmetric tree competition brings about greater size inequality between different-sized trees and thus more evapotranspiration and less runoff in a forest stand. Overall, our simulation approach revealed that not only LAI dynamics but also plant competition, and thus size-structure dynamics, in a forest ecosystem are essential to long-term future projections of forested water balance.     

The potential of marine live-bait introductions into oceanic islands

The likely introduction of non-indigenous species into the coastal ecosystems of oceanic islands through live-bait utilizations was studied. A store survey identified the species that are traded as live fishing-bait. Only Polychaeta species were identified as imported live-bait on São Miguel Island and all specimens were identified as Perinereis linea. Reponses to surveys of 77 anglers showed that: 44 % harvest from native sources, 44 % buy live-bait and 12 % do both; 56 % of the anglers’ fish on a weekly basis; 31 % dispose of the bait into the sea. A field survey at five sites where fishing rods are routinely utilized was developed to investigate if the non-indigenous polychaetes sold as fishing-bait are already established in the natural environment of the Azores archipelago. Three species of Nereididae were identified: the native Neanthes nubila and P. oliveirae and the cryptogenic P. cultrifera. The escalating utilization of live-bait argues for a change in the habits of fishermen with respect to the discarding of leftover bait, as the higher the volume of discards the higher becomes the probability of non-indigenous species establishment successes, especially on oceanic islands characterized by vulnerable ecosystems with simpler trophic webs.     

Using spatial models to establish climatic limiters of plant species’ distributions

Plant species’ climatic range limiters provide clues to reconstruct past climates, restore ecosystems, and manage agricultural systems. However, precise climatic limiters are unknown for many important species, and determining them typically involves long-term autecological studies. A new method presented here automatically and quantitatively infers limiters for a plant species using its documented, digitized distribution. The method uses available and accessible elevation and climate datasets from the US Geological Survey (USGS) and NOAA, along with common off-the-shelf (COTS) geographic information software technology (GIS) to determine which variables in the plant distribution climate space are actually limiting the range by restricting its movement into surrounding territory. The method utilizes precision climate interpolation allowing for independent variables in addition to latitude and longitude, via a software package developed at Australian National University (ANUSPLIN). For this first run, elevation and slope were included as independent variables for interpolating precipitation and temperature surfaces. The model defined limits for five Sonoran Desert plant species: Carnegiea gigantea, Cercidium microphyllum, Encelia farinosa, Ferocactus acanthodes, and Larrea tridentata. Results were tested against environmental factors outlined in autecological studies. Important model-derived climatic constraints to the distribution of C. gigantea include insufficient monsoon precipitation, low winter and monsoon temperatures, and excessive monsoon and fall precipitation. The distribution of C. microphyllum is constrained by cold winter and fall temperatures, excessive spring and summer precipitation and insufficient fall precipitation. E. farinosa is restricted by frigid winter temperatures and too much summer rainfall. Key factors limiting F. acanthodes are cold winter temperatures and inadequate fall and monsoon precipitation. An inordinate amount of precipitation during the summer, monsoon, and fall constrict the range of L. tridentata, along with an abnormally cool summer or monsoon. Results indicate that the method adequately resolves plant range limiters consistent with the autecological record. Future changes to the model are offered to improve results.     

Examining the effects of alternative management strategies on landscape-scale forest patterns in northeastern Minnesota using LANDIS

Spatial modeling of forest patterns can provide information on the potential impact of various management strategies on large landscapes over long time frames. We used LANDIS, a stochastic, spatially-explicit, ecological landscape model to simulate 120 years of forest change on the Nashwauk Uplands, a 328,000 ha landscape in northeastern Minnesota that lies in the transition between boreal and temperate forests. We ran several forest management scenarios including current harvesting practices, no harvests, varied rotation ages, varied clearcut sizes, clustered clearcuts, and landowner coordination. We examined the effects of each scenario on spatial patterns of forests by covertype, age class, and mean and distribution of patch sizes. All scenarios reveal an increase in the spruce-fir (Picea-Abies) covertype relative to the economically paramount aspen-birch (Populus-Betula) covertype. Our results also show that most covertypes occur in mostly small patches <5 ha in size and the ability of management to affect patch size is limited by the highly varied physiography and landuse patterns on the landscape. However, coordination among landowners, larger clearcuts, and clustered clearcuts were all predicted to increase habitat diversity by creating some larger patches and older forest patches. These three scenarios along with the no harvest scenario also create more old forest than current harvesting practices, by concentrating harvesting on some portion of the landscape. The no harvest scenario retained large, fire-regenerated aspen-birch patches. Harvests fragment large aspen-birch patches by changing the age structure and releasing the shade-tolerant understory species. More sapling forest, and larger sapling patches resulted from the shortened rotation scenario.     

Effects of Long-Term Ungulate Exclusion and Recent Alien Species Control on the Preservation and Restoration of a Hawaiian Tropical Dry Forest

Abstract: Although the destruction of tropical rain forests receives much attention, tropical dry forests are in general far more threatened and endangered. Eliminating grazing ungulates is often considered a key first step toward protecting these ecosystems, but few studies have investigated the long-term effects of this technique. We examined the effects of ungulate exclusion from a 2.3-ha native dry-forest preserve on the island of Hawaii by comparing its present flora to the flora of an adjacent area subjected to continuous grazing since the preserve was fenced over 40 years ago. Relative to this adjacent area, the fenced preserve contained a more diverse flora with substantially greater coverage of native overstory and understory species. Until recently, however, regeneration of native canopy trees within the preserve appears to have been thwarted by a dominant herbaceous cover of alien fountain grass (   Pennisetum setaceum ) and predation by alien rodent species. Our results indicate that although ungulate exclusion may be a necessary and critical first step, it is not sufficient to adequately preserve and maintain Hawaii's remaining tropical dry forest remnants. Our recent efforts to control the dominant alien species within the fenced preserve suggest that this practice may facilitate both the regeneration of native species and the colonization and potential invasion of new alien plants. Comparisons of seedlings of the dominant native canopy tree Diospyros sandwicensis growing in sites both dominated by and free of fountain grass suggested that fountain grass inhibits Diospyros seedling growth and photosynthesis but may increase survival if seedlings are protected from ungulates.     

Longleaf pine (Pinus palustris) and hardwood dynamics in a fire-maintained ecosystem: A simulation approach

Longleaf pine (Pinus palustris) savannas of the southeastern U.S. represent an archetype of a fire dependent ecosystem. They are known to have very short fire return intervals (∼1-3 years) that perpetuate understory plant diversity (up to 50 species m⁻²), support pine recruitment, and suppress fire sensitive hardwoods. Understanding the relationships that regulate longleaf and southern hardwoods is especially critical. With decreased fire frequency, insufficient intensity, or lack of underground competition, a woody mid-story rapidly develops, dominated by fire sensitive trees and shrubs that in-turn suppress more fire dependent species (including pine seedlings). This may occur in forest gaps, where pine-needle abundance is diminished, reducing fire spread potential. The interactions between longleaf pine, hardwoods, forest fuels, and fire frequency are complex and difficult to understand spatially. The objective of this study was to develop a spatially explicit longleaf pine-hardwood stochastic simulation model (LLM), incorporating tree demography, plant competition, and fuel and fire characteristics. Data from two longleaf pine study sites were used to develop and evaluate the model with the goal to incorporate simple site-specific calibration parameters for model versatility. Specific model components included pine seed masting, hardwood clonal sprouting, response to fire (re-sprouting, mortality), and tree density driven competition effects. LLM spatial outputs were consistent with observed forest gap dynamics associated with pine seedling establishment and hardwood encroachment. Changes in fire frequency (i.e., fire probability = 0.35-0.05) illustrated a shift in community structure from longleaf pine dominated to a hardwood dominated community. This approach to assessing model response may be useful in characterizing longleaf ecosystem resilience, especially at intermediate fire frequencies (e.g., 0.15) where the community may be sensitive to small changes in the fire regime. Height distributions and population densities were similar to in situ findings (field and LIDAR data) for both study sites. Height distributions output by the LLM illustrated fluctuations in population structure. The LLM was especially useful in determining knowledge gaps associated with fuel and fire heterogeneity, plant-plant interactions, population structure and its temporal fluctuations, and hardwood demography. This is the first known modeling work to simulate interactions between longleaf pine and hardwoods and provides a foundation for further studies on fire and forest management, especially in relation to ecological forestry practices, restoration, and site-specific applications.     

A Natural Experiment on the Impact of Overabundant Deer on Forest Invertebrates

Abstract:  In large parts of North America and Europe, deer overabundance threatens forest plant diversity. Few researchers have examined its effects on invertebrate assemblages. In a natural experiment on Haida Gwaii (British Columbia, Canada), where Sitka black-tailed deer ( Odocoileus hemionus sitkensis ) were introduced, we compared islands with no deer, with deer for fewer than 20 years, and with deer for more than 50 years. We sampled invertebrates in three habitat categories: forest edge vegetation below the browse line, forest interior vegetation below the browse line, and forest interior litter. In forest edge vegetation, invertebrate abundance and species density decreased with increasing length of browsing history. In forest interior vegetation, decrease was significant only on islands with more than 50 years of browsing. Insect abundance in the vegetation decreased eightfold and species density sixfold on islands browsed for more than 50 years compared with islands without deer. Primary consumers were most affected. Invertebrates from the litter showed little or no variation related to browsing history. We attributed the difference between vegetation-dwelling and litter-dwelling invertebrates to differences in the effect of browsing on their habitat. In the layer below the browse line deer progressively removed the habitat. The extent of litter habitat was not affected, but its quality changed. We recommend more attention be given to the effect of overabundant ungulates on forest invertebrate conservation with a focus on edge and understory vegetation in addition to litter habitat.     

Waterfowls habitat modeling: Simulation of nest site selection for the migratory Little Tern (Sterna albifrons) in the Nakdong estuary

This paper aims to find patterns in nest site selection by Little Terns Sterna albifrons, in the Nakdong estuary in South Korea. This estuary is important waterfowl stopover and breeding habitat, located in the middle of the East Asia-Australasian Flyway. The Little Tern is a common species easily observed near the seashore but their number is gradually declining around the world. We investigated their nests and eggs on a barrier islet in the Nakdong estuary during the breeding season (May to June, 2007), and a pattern for the nest site selection was identified using genetic programming (GP). The GP generated a predictive rule-set model for the number of Little Tern nests (training: R² = 0.48 and test: 0.46). The physical features of average elevation, variation of elevation, plant coverage, and average plant height were estimated to determine the influence on nest numbers for Little Tern. A series of sensitivity analyses stressed that mean elevation and vegetation played an important role in nest distribution for Little Tern. The influence of these two variables could be maximized when elevation changed moderately within the sampled quadrats. The study results are regarded as a good example of applying GP to vertebrate distribution patterning and prediction with several important advantages compared to conventional modeling techniques, and can help establish a management or restoration strategy for the species.     

A process-based model designed for filling of large data gaps in tower-based measurements of net ecosystem productivity

In this paper we present a simple hybrid gap-filling model (GFM) designed with a minimum number of parameters necessary to capture the ecological processes important for filling medium-to-large gaps in Flux data. As the model is process-based, the model has potential to be used in filling large gaps exhibiting a broad range of micro-meteorological and site conditions. The GFM performance was evaluated using “Punch hole” and extrapolation experiments based on data collected in west-central New Brunswick. These experiments indicated that the GFM is able to provide acceptable results (r² > 0.80) when >500 data points are used in model parameterization. The GFM was shown to address daytime evolution of NEP reasonably well for a wide range of weather and site conditions. An analysis of residuals indicated that for the most part no obvious trends were evident; although a slight bias was detected in NEP with soil temperature. To explore the portability of the GFM across ecosystem types, a transcontinental validation was conducted using NEP and ancillary data from seven ecosystems along a north-south transect (i.e., temperature–moisture gradient) from northern Europe (Finland) to the Middle East (Israel). The GFM was shown to explain over 75% of the variability in NEP measured at most ecosystems, which strongly suggests that the GFM maybe successfully applied to forest ecosystems outside Canada.