Oak Canopy Research Articles

Photosynthetic responses to temperature across leaf-canopy-ecosystem scales: a 15-year study in a Californian oak-grass savanna.

Ecosystem CO2 fluxes measured with eddy-covariance techniques provide a new opportunity to retest functional responses of photosynthesis to abiotic factors at the ecosystem level, but examining the effects of one factor (e.g., temperature) on photosynthesis remains a challenge as other factors may confound under circumstances of natural experiments. In this study, we developed a data mining framework to analyze a set of ecosystem CO2 fluxes measured from three eddy-covariance towers, plus a suite of abiotic variables (e.g., temperature, solar radiation, air, and soil moisture) measured simultaneously, in a Californian oak-grass savanna from 2000 to 2015. Natural covariations of temperature and other factors caused remarkable confounding effects in two particular conditions: lower light intensity at lower temperatures and drier air and soil at higher temperatures. But such confounding effects may cancel out. At the ecosystem level, photosynthetic responses to temperature did follow a quadratic function on average. The optimum value of photosynthesis occurred within a narrow temperature range (i.e., optimum temperature, T opt): 20.6 ± 0.6, 18.5 ± 0.7, 19.2 ± 0.5, and 19.0 ± 0.6 °C for the oak canopy, understory grassland, entire savanna, and open grassland, respectively. This paradigm confirms that photosynthesis response to ambient temperature changes is a functional relationship consistent across leaf-canopy-ecosystem scales. Nevertheless, T opt can shift with variations in light intensity, air dryness, or soil moisture. These findings will pave the way to a direct determination of thermal optima and limits of ecosystem photosynthesis, which can in turn provide a rich resource for baseline thresholds and dynamic response functions required for predicting global carbon balance and geographic shifts of vegetative communities in response to climate change.

Natural Regeneration of Oak and Hornbeam under the Canopy and Log Cabins in the State Enterprise "Korsun-Shevchenko Forestry"

The reproduction of hornbeam both natural and cultural is an important issue nowadays. Seed propagation for this species is considered to be the best way to reproduce. The regularities of the process of regeneration under the canopy of oak and hornbeam forests and log cabins in fresh oak forests in Korsun-Shevchenkivskyi forestry are the key problems of the research presented. After having conducted the research we have obtained the results stating that in mature stands of the Korsun-Shevchenko forestry fresh oak dominated for fullness of the cover. Furthermore, all log cabins show intense natural seed recovery. However, the composition of the natural seed recovery is not always correlated with the composition of the felled tree stand. The feature of beech seed recovery is that it undergrowth kept under a tent spaces, self-seeding and appears in log cabins after logging parent stand. Thus we shoul summarize that forest recovery process in fresh oak and hornbeam forests of state enterprise "Korsun-Shevchenko forestry" is satisfactory. In normal conditions oak and hornbeam of forestry bloom and bear fruit every year, but abundant crops depend on weather conditions once in 3-5 years. Under a canopy of plantations of populations of the common oak in blocks of Korsun-Shevchenko forestry through intensive expansion of grass cover and shrubs, and with not enough seats of oak and lack of proper care resumes is unsatisfactory. The most successful is a natural renewal of hornbeam populations.

Does large-scale N fertilization have time-delayed effects on insects community structure by changing oak quantity and quality?

The increased atmospheric deposition of nitrogen (N) may indirectly affect herbivorous insects by deposition-induced changes in host quantity and quality. To avoid the “lamp effect” that can occur in small-scale N fertilizations, large-scale N fertilization (ca. 9 ha, 100 kg N ha−1 year−1) experiments were performed in a deciduous, broad-leaved, cool temperate forest. The initial responses of mature oak canopy trees (Quercus crispula) and their herbivorous insects to N fertilization were evaluated by measuring the growth and leaf qualities of the trees. The feeding guilds and community structures of the herbivorous insects at control and fertilized sites before (2012) and after (2013–2014) N fertilization were then determined. In 2014, N fertilization enhanced plant growth. In 2013 but not 2014, N fertilization increased N content and decreased the carbon/nitrogen (C/N) ratio in leaves. Despite these changes in plant traits in 2013, N fertilization had no effect on either feeding guilds (chewing herbivory, galler density, and miner density) or community structures (species richness, diversity index, and relative abundance) of herbivorous insects in the same year. However, in 2014, the diversity index decreased significantly, whereas species richness and abundance were unchanged. This suggests that species-specific responses to changes in leaf qualities following N fertilization, in the form of altered insect fecundity, impact the diversity index of herbivorous insects, albeit with a 1-year lag time. Thus, our large-scale N fertilization experiment show the time-delayed bottom-up effects of N fertilization on insect community structure.

Influence of regional nighttime atmospheric regimes on canopy turbulence and gradients at a closed and open forest in mountain-valley terrain

Stable stratification of the nocturnal lower boundary layer inhibits convective turbulence, such that turbulent vertical transfer of ecosystem carbon dioxide (CO2), water vapor (H2O) and energy is driven by mechanically forced turbulence, either from frictional forces near the ground or top of a plant canopy, or from shear generated aloft. The significance of this last source of turbulence on canopy flow characteristics in a closed and open forest canopy is addressed in this paper. We present micrometeorological observations of the lower boundary layer and canopy air space collected on nearly 200 nights using a combination of atmospheric laser detection and ranging (lidar), eddy covariance (EC), and tower profiling instrumentation. Two AmeriFlux/Fluxnet sites in mountain-valley terrain in the Western U.S. are investigated: Wind River, a tall, dense conifer canopy, and Tonzi Ranch, a short, open oak canopy. On roughly 40% of nights lidar detected down-valley or downslope flows above the canopy at both sites. Nights with intermittent strong bursts of “top-down” forced turbulence were also observed above both canopies. The strongest of these bursts increased sub-canopy turbulence and reduced canopy virtual potential temperature (θv) gradient at Tonzi, but did not appear to change the flow characteristics within the dense Wind River canopy. At Tonzi we observed other times when high turbulence (via friction velocity, u*) was found just above the trees, yet CO2 and θv gradients remained large and suggested flow decoupling. These events were triggered by regional downslope flow. Lastly, a set of turbulence parameters is evaluated for estimating canopy turbulence mixing strength. The relationship between turbulence parameters and canopy θv gradients was found to be complex, although better agreement between the canopy θv gradient and turbulence was found for parameters based on the standard deviation of vertical velocity, or ratios of 3-D turbulence to mean flow, than for u*. These findings add evidence that the relationship between canopy turbulence, static stability, and canopy mixing is far from straightforward even within an open canopy.

Growth and physiology of a dominant understory shrub, Hamamelis virginiana, following canopy disturbance in a temperate hardwood forest

As global climatic changes increase plant susceptibility to large-scale disturbances such as drought and pathogens, understory responses to these disturbances will become increasingly important to long-term forest dynamics. To better understand understory responses to canopy disturbance, we measured changes in the growth and physiology of the dominant understory shrub, American witch-hazel (Hamamelis virginiana L.), in response to girdling of canopy oaks in a temperate hardwood forest of the northeastern United States. Changes in the growth and physiology of H. virginiana may be important to the regeneration of northeastern temperate forests, as this common shrub largely shapes the microenvironment for seedlings on the forest floor where it occurs. Canopy disturbance by girdling resulted in significant increases in light and soil nitrogen availability. In response to these environmental changes, basal-area growth of H. virginiana increased by an average 334%. This growth increase corresponded to significant increases in foliar nitrogen, respiration, and leaf chlorophyll and carotenoid concentrations. These findings indicate improved environmental conditions and increased growth for this understory shrub following the loss of dominant canopy trees. This study suggests that following large-scale canopy disturbance, H. virginiana and shrubs like it may play an important role in competing for soil N and shading seedlings of regenerating canopy species.

Forest plant community as a driver of soil biodiversity: experimental evidence from collembolan assemblages through large‐scale and long‐term removal of oak canopy treesQuercus petraea

Plant–soil interactions are increasingly recognized to play a major role in terrestrial ecosystems functioning. However, few studies to date have focused on slow dynamic ecosystems such as forests. As they are vertically stratified by multiple vegetation strata, canopy tree removal by thinning operations could alter forest plant community through tree canopy opening. Very little is known about cascading effects on soil biodiversity.We conducted a large‐scale, multi‐site assessment of collembolan assemblage response to long‐term canopy tree removal in sessile oakQuercus petraeatemperate forests. A total of 33 experimental plots were studied covering a large gradient of canopy tree basal area, stand age and local abiotic contexts.Collembolan abundance strongly declined with canopy tree removal in early forest successional stage and this was mediated by negative effect of understory plant community composition changes, i.e. shift from moss and forb to tree seedling, fern, shrub and grass species. Negative effect of this composition shift on collembolan species richness was largely offset by positive effect of the increase in understory plant species richness. This gives support to both the plant mass‐ratio and functional diversity hypotheses. Collembolan functional groups had contrasting response patterns, which were mediated by different ecological factors. Epedaphic (r‐strategist) abundance and species richness increased with canopy tree removal in relation with the increase in understory plant species richness. In contrast, euedaphic (K‐strategist) abundance and species richness declined with canopy tree removal in early forest successional stage in relation with changes in understory plant community composition and species richness, as well as microclimatic conditions.Overall, our study provides experimental evidence that forest plant community can be a strong driver of collembolan assemblages. It also emphasizes the role of trees as foundation species of forest ecosystems that can shape soil biodiversity through their regulation of understory plant community and ecosystem abiotic conditions.

Interactions among habitat, management, and demography for an invasive annual grass

Effective long-term management of noxious plant species depends on our ability to identify and manage ecological processes-driving invasion and to use site-specific information to design realistic management strategies and goals. However, there is a surprising lack of research that investigates relationships among habitat characteristics, weed demography, and management efforts. We investigated the interactions among these factors using the invasive annual grass medusahead (Elymus caput-medusae). In Yuba County, California, we seeded medusahead in densities from 0 to 50,000 seeds/m2 in open grassland and oak woodland habitats. We also exposed plots to defoliation none, once, or twice in a season and captured how medusahead germination, establishment, and persistence responded to experimental treatments. We found that medusahead establishment was higher in the grassland, compared to the woodland habitat, likely due, in part, to the presence of litter under oak canopies. After a single defoliation event, medusahead persistence was higher in the oak, but not the grassland plots. We also found that defoliation once or twice reduced medusahead density. However, a single clipping treatment actually resulted in increased seed production. This was likely a compensatory response by a younger cohort, and provides an explanation for why single control efforts do not generally result in successful long-term outcomes. This work highlights the complex relationships between density-dependent and density-independent processes that may influence invasion dynamics.

Monitoring Understory Composition of Blue Oak Woodlands on Conservation Easements

Conservation easements are an increasingly popular strategy for conserving biological diversity on private land. Long-term vegetation monitoring on conservation easements can provide critical information on persistence of biological diversity and abundance of invasive species. We sampled understory plant composition on five of The Nature Conservancy’s conservation easements in the Mt. Lassen foothills of Northern California. We established 73 plots of 10-meter radius, measured species composition with the point-intercept method, and compiled a full species list for each plot in 2005 and 2006. We found significant differences in the relative cover of native and non-native annual grasses and annual forbs among easement properties. Relative cover of native plants was significantly higher in herbaceous plots (50 percent) than in plots with blue oak (Quercus douglasii) canopy (21 percent). We found medusahead (Taeniatherum caput-medusae) in 64 percent of plots and yellow star thistle (Centaurea solstitialis) in 9 percent of plots. Overlap of species composition between years was correlated with difference in date sampled each year but not correlated with confidence in plot relocation. Our analysis of community diversity and relative abundance provides a baseline for future change. Finally, we make recommendations for the design of future monitoring efforts on conservation easements.

Intraspecific variation in epiphyte functional traits reveals limited effects of microclimate on community assembly in temperate deciduous oak canopies

Forest canopies are heterogeneous environments where changes in microclimate over short distances create an opportunity for niche‐based filtering of canopy‐dwelling species assemblages. This environmental filtering may not occur if species' physiological capacities are flexible or if rapid dispersal alleviates compositional differences. I assess the role of humidity, light and temperature gradients in structuring epiphyte communities in temperate deciduous oak (Quercus) canopies and determine whether gradients filter species with fixed traits or whether environmental constraints act primarily to alter individual phenotypes. I measured environmental conditions and seven functional traits related to water and light acquisition on individual macrolichens at 60 sample locations in northern red oaks Quercus rubra in two Piedmont forests in North Carolina, USA. The effects of environmental variables on individual‐level traits and community composition were evaluated using linear mixed models and constrained ordination (RDA). In general, traits and community composition responded weakly to environmental variables and trait variation within taxa was high. Cortex thickness exhibited the strongest response, such that individuals with thicker cortices were found in samples experiencing lower humidity and higher light levels. Overall, gradients of humidity, light and temperature were not strong environmental filters that caused large changes in community composition. This was probably due to phenotypic variability within taxa that enabled species to persist across the full range of environmental conditions measured. Thus, humidity affected the phenotype of individuals, but did not limit species distributions or alter community composition at the scale of branches within trees. Community and trait responses were primarily associated with site‐level differences in humidity, suggesting that in these forests landscape‐scale climatic gradients may be stronger drivers of epiphyte community assembly than intra‐canopy environmental gradients.

The path back: oaks (Quercusspp.) facilitate longleaf pine (Pinus palustris) seedling establishment in xeric sites

AbstractUnderstanding plant–plant facilitation is critical for predicting how plant community function will respond to changing disturbance and climate. In longleaf pine (Pinus palustrisMill.) ecosystems of the southeastern United States, understanding processes that affect pine reproduction is imperative for conservation efforts that aim to maintain ecosystem resilience across its wide geographic range and edaphic gradients. Variation in wildland fire and plant–plant interactions may be overlooked in “coarse filter” restoration management, where actions are often prescribed over a variety of ecological conditions with an assumed outcome. For example, hardwood reduction techniques are commonly deemed necessary for ecological restoration of longleaf pine ecosystems, as hardwoods are presumed competitors with longleaf pine seedlings. Natural regeneration dynamics are difficult to test experimentally given the infrequent and irregular mast seed events of the longleaf pine. Using a long‐term, large‐scale restoration experiment and a long‐term monitoring data site at Eglin Air Force Base, Florida (USA), this study explores the influence of native fire‐intolerant oaks on longleaf regeneration. We test for historical observations of hardwood facilitation against the null hypothesis of competitive exclusion. Our results provide evidence of hardwood facilitation on newly germinated longleaf pine seedlings (<2 yr old) after two mast seeding events (1996, 2011). Using regression‐tree and Kaplan–Meier survival analyses, we found that deciduous oak midstory density was the most significant variable associated with longleaf pine seedling survival rates in the first 2 yr after germination. We found that as few as 43 oak midstory stems ha−1were sufficient to facilitate seedling survival, but as many as 1400 stems ha−1maintained facilitation without competitive exclusion of seedlings. We found that 1.5‐yr‐old pine seedlings were more moisture stressed under more open canopy conditions when compared to those immediately adjacent to a midstory oak canopy. Recognition that deciduous oaks are important facilitators of longleaf seedling establishment on xeric sites represents a significant departure from conventional wisdom and current management practices that has largely focused on competitive exclusion. This points to a critical role of a deciduous oak midstory of moderate densities for long‐term ecosystem resilience in xeric longleaf pine ecosystems in light of climate uncertainty.

Influence of river channelization and the invasive shrub, Ligustrum sinense, on oak (Quercus spp.) growth rates in bottomland hardwood forests

AbstractQuestionDo river channelization and a common invasive shrub, Ligustrum sinense Lour. (Chinese privet), affect tree growth rates in forested riverine wetlands?LocationThree sites along the Wolf River, in and near Memphis, Tennessee, USA.MethodsWe cored and analysed 83 oak trees within three study sites. Correlations of river channelization and climatic variables with basal area increments (BAI) and detrended BAI (SFS) were analysed to investigate channelization effects. Significant correlations were removed from BAI chronologies (BAI‐HR) to isolate the effect of L. sinense. We investigated effects of L. sinense on tree growth using a before–after/control–impact (BACI) experimental design with one location impacted by invasion (INV), two control locations that were not invaded (NON and REF) and covariates of tree age and size. We conducted a two‐factor mixed effects ANCOVA to determine if there was a significant interaction (BACI) effect.ResultsChannelization promoted faster canopy oak growth in all sites, spring drought significantly slowed growth in NON, while summer precipitation promoted wood production in NON. Investigation of L. sinense impact on tree growth revealed a significant BACI effect, such that trees in INV grew slower after invasion than trees in the non‐invaded control sites (NON and REF).ConclusionsWe suggest that faster growth after channelization may be a consequence of increased aerobic conditions, by enabling higher oxygen availability to tree roots. However, many of the obligate bottomland tree species struggle to regenerate in drier, post‐channelized conditions. Thus, native drought‐tolerant species may have an advantage in the sub‐canopy and regeneration layers of these altered forests. Instead, L. sinense, an invasive and drought‐tolerant species, has invaded most locations adjacent to the channelized portion of the Wolf River. L. sinense presence reduces the channelization advantage by slowing growth of canopy oaks and possibly contributing to accelerated mortality. These results suggest an emerging shift to a commonly held paradigm with respect to invasive shrub species. Not only do invasive shrubs crowd out other small woody species and herbaceous plants, but they also have the ability to impact the structure of the forest canopy.

Surface runoff and soil erosion under eucalyptus and oak canopy

AbstractTo assess potential differences in stormwater runoff and sediment yield between plots of blue gum eucalyptus (Eucalyptus globulus) and coast live oak (Quercus agrifolia), we measured runoff, sediment yield, water repellency and soil moisture at eight paired sites. Eucalyptus has been associated in many studies worldwide with elevated soil water repellency and increased runoff, a likely contributor to soil erosion. To better understand these connections and their relationship to land cover, there is a need for studies employing either rainfall simulators or natural rainfall. Our research employs the latter, and was subject to contrasting hydrologic conditions in the two years of the study. Fieldwork was conducted from October 2006 to February 2008 in the San Francisco Bay Area of central California. During the 2006–2007 winter wet season, runoff was significantly higher under eucalypts than at paired oak sites, and in the early phases of the season was connected with elevated water repellency. However, sediment yield at all sites during the 2006–2007 hydrologic year was below the detection limit of the Gerlach sediment collection traps, possibly due to a limited wet season, and only appeared as suspended sediment captured in overflow buckets. Intensive rainfall events in January 2008 however created substantial runoff of sediment and litter with significantly greater yield at oak sites compared to paired eucalyptus sites. Water repellency likely had little effect on runoff during these events, and the primary cause of greater erosion under oaks is the thinner cover of leaf litter in comparison to eucalyptus. Our study is limited to undisturbed sites with intact litter cover that have not experienced recent wildfires; if disturbed, we would expect a different picture given the propensity for crown fires of eucalypts, enhancement of rainsplash erosion, and the likely greater potential for stream‐connected sediment yield from post‐disturbance soil erosion events.

Short-term changes in height–diameter relation of two maple species and European cornel of understory in an oak forest in Hungary on the basis of two-parameters model

Forest understory species such as shrub and herbaceous layer, have received little attention in long-term studies. Knowledge of the diameter and the height of trees are fundamental for developing growth and yield models in forest stands. Overstory composition of the Sikfőkut Project site was dominated by sessile oak–Turkey-oak forest (Quercetum petraeae-cerris Soo 1963). Similarly to other European countries an oak decline occurred in Hungary oak woodlands at the end of 1970’s and about 63% of the oak trees perished in our site. The potential for oak species regeneration was a very low over the period of 1982-2012. Four nonlinear height-diameter functions were fitted and evaluated for Sikfőkut site based on a data set consisting of 2025 individuals for three dominant woody species (Acer campestre L., Acer tataricum L. and Cornus mas L.) and detected any short-term changes in these equations following dieback of oak canopies. These height– diameter equations increase our knowledge of the growth of these species; therefore will enable us to improve management planning in oak forests.

Diversity of gall wasps (Hymenoptera: Cynipidae) associated with oak trees (Fagaceae: Quercus) in a fragmented landscape in Mexico

Habitat fragmentation reduces the available habitat area and increases both the distance between fragments and the amount of fragment edges. Therefore, there are more probabilities of plant population size reduction and species extinction. In the same way, biotic and abiotic changes associated with forest fragmentation can dramatically alter plant growth and phenological patterns. We conducted a 3-year study to analyze effects of habitat fragmentation and seasonal variation on host plant quality (quantity of leaves, diameter at breast height, tree height), gall abundance and species richness in a temperate oak forest. Our results show that host plant quality was significantly higher in isolated oaks and small fragments, increasing the abundance and species richness of oak gall wasp species in most fragmented habitats. Oak canopy cover is altered by forest fragmentation, there being higher production of leaves on trees that are more exposed to fragmentation, and can provide important resources for maintaining gall wasp species diversity in a fragmented landscape. We found higher gall wasp richness and abundance in autumn than in the spring, which matches with the higher quantity of leaves in this season.

Ice storms as a successional pathway forFagus grandifoliaadvancement inQuercus rubradominated forests of southern New England

On 11 December 2008, a severe ice storm affected large portions of southern New England. We report the results of a study investigating differential damage among tree species. Past studies surveying ice-damaged forests have relied heavily on ocular estimations of canopy damage. We compare this method with damage estimates based on the cross-sectional area of downed woody material and quantitative comparisons of tree height and canopy projection in damaged and undamaged stands. Ocular estimates and changes in canopy height and projection were unreliable. Estimates based on the amount of woody debris provide a more robust measure of storm damage. We assess damage in two forest tracts with a dominant red oak (Quercus rubra L.) canopy (42% of total basal area) and an American beech (Fagus grandifolia Ehrh.) dominated understory (50% of all stems > 1.3 m). Species’ standing basal area was well correlated with the amount of newly downed woody debris (r = 0.69, p < 0.001); accordingly, oak species constituted approximately 57% of all newly downed woody debris, and ANOVA showed that oak species were significantly more impacted by ice damage than other species present (p < 0.001). Our findings indicate that canopy species provide an “umbrella effect”, shielding less dominant lower strata trees from the worst effects of ice load. Oak was also the largest contributor to older downed woody debris, indicative of a recurrent historical pattern of differential canopy disturbance driven by strata and relative dominance. These findings suggest that periodic ice events play an important role in facilitating the advancement of shade-tolerant tree species into the canopy from lower strata.

Oak canopy arthropod communities: which factors shape its structure?

Canopy of forest ecosystems has been recognized as a habitat that supports a wide variety of plants, vertebrates, invertebrates, and microbes. Within the invertebrate group, arthropods are characterized by their great abundance, diversity, and functional importance. Particularly in temperate forests, species of the genus Quercus (oaks) are one of the most important tree canopy groups, for its diversity and dominance. Different studies have shown that the oak canopy contains a high diversity of arthropods suggesting their importance as habitat for this group of organisms. In this review, we investigated the factors that determine the establishment, organization, and maintenance of arthropod communities in the oak canopy. In general, it was found that there is a lack of literature that addresses the study of oak canopy arthropod communities. Also, the following patterns were found: (a) the research has covered a wide variety of topics; however, there are differences in the depth to which each topic has been analyzed, (b) there are ambiguous criteria to define the structure of the canopy, (c) groups with different habitat preferences belonging to different guilds and uneven development stages have been studied, avoiding generalizations about patterns found, (d) the standardization in sampling techniques and collection has been difficult, (e) bias exists towards the study of phytophagous insects belonging to the Coleoptera, Hymenoptera, and Lepidoptera orders, and (f) there are few studies in other groups of arthropods, for example, acorn borers, whose activity has an impact on the fitness and dispersion of the host plants. Finally, we propose that the detection and study of patterns in oak canopy communities can be of great value to propose management and conservation strategies in these forests.

Effect of host-plant genetic diversity on oak canopy arthropod community structure in central Mexico

BackgroundRecently it has been proposed that the genetic diversity of foundation species influences the structure and function of the community by creating locally stable conditions for other species and modulating ecosystem dynamics. Oak species are an ideal system to test this hypothesis because many of them have a wide geographical distribution, and they are dominant elements of the forest canopy. In this study we explored the response of canopy arthropod community structure (diversity and biomass) to the level of genetic diversity of Quercus crassipes and Q. rugosa, two important canopy species. Also, we examined the effect of oak species and locality on some community structure parameters (diversity, biomass, rare species, and richness of arthropod fauna) of canopy arthropods. In total, 160 canopies were fogged in four localities at the Mexican Valley (ten trees per species per locality per season).Results Q. crassipes registered the highest number of rare species, diversity index, biomass, and richness in comparison with Q. rugosa. We found a positive and significant relationship between genetic diversity parameters and canopy arthropod diversity. However, canopy arthropod biomass registered an inverse pattern. Our results support the hypothesis that the genetic diversity of the host-plant species influences the assemblage of the canopy arthropod community.ConclusionsThe pattern found in our study provides a powerful tool when trying to predict the effects of the genetic diversity of the host-plant species on different community structure parameters, which permits assignment of a new conservation status to foundation species based on their genetic diversity.

Land change in eastern Mediterranean wood-pasture landscapes: the case of deciduous oak woodlands in Lesvos (Greece).

In Mediterranean Europe, wood-pasture landscapes with oak woodlands as emblematic ecosystems are undergoing rapid land-use change, which may threaten their legacy as hotspots of biodiversity, ecosystem services, and cultural heritage. The objective of this study was to quantify land cover changes and transitions as well as the dynamics of oak woodland patterns and densities over 50 years in two municipalities at the center and edges of Quercus macrolepis distribution in Northern Lesvos (Greece). We used aerial photographs from 1960 and WorldView-2 satellite images from 2010 to process land cover maps and metrics, and to calculate oak canopy cover with a point-grid sampling approach. Spatiotemporal dynamics of land cover change were generally high--especially between oak woodlands and grass- and shrub-lands, resulting in a more heterogeneous and fragmented landscape in 2010. Surprisingly, oak woodland area remained stable with marginal losses in one study site and gains in the other one. Oak canopy cover increased by 8 and 9%. Spatial hotspots of change were mountainous and peripheral phrygana areas with expanding oak stands, as well as river valleys and near urban areas with expanding olive groves and grass- and shrublands in former complex cultivation and oak stands. We conclude that the parallel processes of abandonment of crop cultivation and intensification of livestock grazing have been less detrimental to oak woodlands than supposed. To ensure long-term persistence of oak woodlands in the face of ongoing rural depopulation and land-use intensification, environmental and agricultural policies should better address their specificities as anthropogenic habitats.

Influence of forest type and host plant genetic relatedness on the canopy arthropod community structure of Quercus crassifolia

Quercus crassifolia is an oak species with characteristics of foundation species, which is a canopy dominant element of different forest types that supports a wide diversity of associated species. Therefore, it is an excellent system to address important ecological questions. We analyzed the effect of individual genetic relatedness of the host plant, forest type (Abies-Quercus, Quercus-Pinus, and Quercus forest), and season (dry vs. rainy) on the canopy arthropod community structure. Thirty oak canopies were fogged (five individuals/season/forest type). We identified 442 arthropod species belonging to 22 orders. The highest values of density, diversity, and richness were recorded during the rainy season for each forest type. Also, the non-metric multidimensional scaling (NMDS) analysis showed a separation of the host tree species for each forest type. During the rainy season, the highest values of density, diversity, and richness in each forest type were recorded. A separation of host tree was found for each forest type. In general, diversity and richness of canopy arthropods showed the following pattern: Abies-Quercus > Quercus-Pinus > Quercus, while density showed an inverse pattern. An increase of the diversity of canopy arthropods is significantly related to an increase of host plant genetic diversity, independently of the type of forest and of the season. In terms of conservation, if arthropod species respond to genetic differences among host plants, it becomes important to conserve genetic diversity of foundation species, since it is fundamental to preserve diversity of their associated arthropod communities.

Influence of woody tissue and leaf clumping on vertically resolved leaf area index and angular gap probability estimates

Leaf area index L is a key vegetation parameter that can be used in soil–vegetation–atmosphere exchange modeling. To represent the structure of ecosystems in vertically distributed modeling, vertically resolved L distributions as well as vertical and angular gap probability Pgap distributions are needed, but they are rarely available. On the experimental side, studies often neglect woody plant components when using indirect methods for L or Pgap observations. This can lead to significantly biased results, particularly in semi-arid savannah-type ecosystems with low L values.The objective of this study is to compare three non-destructive leaf area index measurement techniques in a sparse savannah-type cork oak canopy in central Portugal in order to derive vertically resolved L as well as vertically and angularly resolved Pgap. We used the established LAI-2000 device as well as fast digital cover photography (DCP), which was vertically and angularly distributed. We applied object-based image analysis to DCP to exclude woody plant components. We compared the results with vertically distributed LAI-2000 measurements and with vertical estimates based on easily measurable crown parameters.Height and angularly distributed DCP was successfully applied here for the first time. It delivers gap probability Pgap and effective leaf area index Le measurements that are comparable to the established LAI-2000. The height and angularly dependent leaf clumping index Ω could be determined with DCP, which led to a 30% higher total leaf area index L for DCP compared to LAI-2000. The exclusion of woody tissue from DCP yields on average a 6.9% lower leaf area index L. Including Ω and excluding woody tissue, the L of DCP matched precisely with direct measurements using litter traps. However, the set-up and site-specific adjustment of the image analysis algorithm remains challenging. We propose a special filter for LAI-2000 to enhance data quality when used in open canopies. Finally, if height-dependent observations are not feasible, ground-based observations of crown parameters can be used to derive very reasonable L height distributions from a single, ground-based L observation.