Deciduous Canopy Research Articles

Response to basal resources by stream macroinvertebrates is shaped by watershed urbanization, riparian canopy cover, and season.

Riparian reforestation is a common restoration action in urban streams, but relatively little is known about the influence of local riparian vegetation in the face of watershed-scale urban land cover. Allochthonous organic matter and benthic algae are important basal energy resources in streams, but the roles of watershed urbanization vs near-stream vegetation in the availability of these resources are not well understood. Our goal was to understand how the interaction of land cover at 2 spatial scales (watershed vs reach) and seasonal dynamics shape basal resources and their effects on macroinvertebrate communities. We assessed relationships between seasonal patterns in standing stocks of particulate organic matter (POM) and benthic periphyton and macroinvertebrate community composition in openand closed-canopy reaches of 4 urban and 4 reference streams in northern Kentucky, USA. POM standing stocks were not strongly influenced by watershed or riparian condition. Benthic algal biomass was greater in urban than in reference streams in all seasons and in open than in closed riparian canopies in summer when light levels are most affected by a deciduous canopy. Relationships between macroinvertebrate functional feeding group (FFG) biomass and their primary food resources were influenced by watershed land use and season, but riparian canopy effects were minor. The proportion of collectors varied by season, whereas the proportion of shredders was higher in reference than urban streams. Scraper biomass was influenced by benthic algal biomass and varied seasonally, whereas predator biomass was driven by prey-insect biomass. Periphyton density was affected by the interaction of watershedand reach-scale land cover and was the only basal resource strongly related to consumer taxa. Watershed land use influences the stream ecosystem, but local riparian canopy may be important in limiting benthic algal accumulation.

Tropical forest temperature thresholds for gross primary productivity

AbstractTropical forests are hyper‐diverse and perform critical functions that regulate global climate, yet they are also threatened by rising temperatures. Canopy temperatures depart considerably from air temperatures, sometimes by as much as air temperatures are projected to increase by the end of this century; however, canopy temperatures are rarely measured or considered in climate change analyses. Our results from near‐continuous thermal imaging of a well‐studied tropical forest show that canopy temperatures reached a maximum of ~34°C, and exceeded maximum air temperatures by as much as 7°C. Comparing different canopy surfaces reveals that bark was the warmest, followed by a deciduous canopy, flowers, and coolest was an evergreen canopy. Differences among canopy surfaces were largest during afternoon hours, when the evergreen canopy cooled more rapidly than other canopy surfaces, presumably due to transpiration. Gross primary productivity (GPP), estimated from eddy covariance measurements, was more strongly associated with canopy temperatures than air temperatures or vapor pressure deficit. The rate of GPP increase with canopy temperatures slowed above ~28–29°C, but GPP continued to increase until ~31–32°C. Although future warming is projected to be greater in high‐latitude regions, we show that tropical forest productivity is highly sensitive to small changes in temperature. Important biophysical and physiological characteristics captured by canopy temperatures allow more accurate predictions of GPP compared to commonly used air temperatures. Results suggest that as air temperatures continue to warm with climate change, canopy temperatures will increase at a ~40% higher rate, with uncertain but potentially large impacts on tropical forest productivity.

Characteristics and abundance of large and small instream wood in a Carpathian mixed-forest headwater basin

The effect of instream wood on stream hydraulics and geomorphic processes depends on wood and channel dimensions. We investigated abundance and characteristics (i.e., wood orientation, proportion of spanned channel width, stability and decay classes) of large wood (LW; defined here as having a length ≥ 1 m and a diameter ≥ 0.1 m) and small wood (SW; including two categories with length ≥ 0.5 m and diameter ≥ 0.1 m or length ≥ 1 m and diameter ≥ 0.05 m) in three steep, confined headwater channels of medium-high mountain ranges of the Western Carpathians (Central Europe). Results show that SW is more frequent than LW, however, active-channel LW load varied between 26 and 305 m3∙ha−1, whereas SW showed much lower active-channel load (8–16 m3∙ha−1). Differences between LW and SW active-channel volumes were considerably smaller in streams under dominant deciduous canopy. In these streams, morphological steps – created exclusively by SW – were more frequent than LW steps. This higher frequency of SW in streams surrounded by a deciduous tree canopy can be explained by the continuous supply of branches rather than entire dead trees. On the other hand, the volume and frequency of LW was related to the proportion of conifers in the valley corridor. We observe very high active-channel load in two channel reaches for which values exceeded most of those observed in similarly small streams across the globe. We also observe an unusually large proportion of instream wood (both LW and SW) oriented parallel to the flow direction, which might suggest a higher mobility of bed material in the flysch-dominated headwater channels of our study site.

Refoliation of deciduous canopy trees following severe insect defoliation: comparison of Fagus crenata and Quercus crispula

Deciduous trees can survive severe defoliation by herbivores and often refoliate in the same season. Refoliation following severe defoliation represents compensatory regrowth to recover foliage biomass. Although the relationship between defoliation intensity and degree of refoliation at the individual level has been quantified following artificial defoliation for saplings and small trees, no study has examined the relationship for canopy trees and interspecific differences in this relationship. In this study, defoliation by gypsy moths in an outbreak year and subsequent refoliation were visually surveyed for canopy trees of Fagus crenata (n = 80) and Quercus crispula (n = 113) in central Japan. Defoliation and refoliation estimates were scored in 10% classes as the ratio to foliage present before defoliation. The degree of refoliation and the proportion of refoliated trees were high in severely defoliated trees. For 60 and 100% defoliated trees, respective refoliations were 2 and 66% for F. crenata, and 37 and 88% for Q. crispula. All of the 90 and 100% defoliated trees refoliated. These results indicate that severely defoliated trees show an increased need for refoliation to maintain metabolism. Beta regression analysis showed that Q. crispula possessed higher refoliation capability than F. crenata. This is likely associated with the relatively large storage reserves and recurrent growth flush pattern of oak species, which are strong characteristics of oaks and adaptive for response to herbivory and catastrophic disturbances. Interspecific differences in refoliation capability may exert differential effects on forest ecosystem processes, such as influencing the growth of understory species.

City Profile: Sligo, Ireland

W hen I pulled into Sligo on the morning bus with a dog-eared copy of W. B. Yeats’s Collected Poems, I carried two wishes: first, that it would stop raining. And second, that I might uncover some of the vital, inspiring force behind my favorite poet. One gets over the rain. Located on the coastal edge of County Sligo in the northwest of Ireland, Sligo rests on the neck of land between Sligo Bay and the placid Lough Gill. Riverside restaurants, shops, and lively pubs line the town center, where the swinging doors of little cafés disclose the smell of black currant scones or the flash of jam jars and bottles of cordial. Visitors’ maps lead to abbeys, churches, and other historical sites around town, but somehow, people seem to gravitate toward Wine Street, where the Yeats Memorial Building stands. Lovers of Irish poetry have good reason to venture to a less-trafficked town like Sligo. Yeats’s early work draws deeply from the natural features and fairy stories of the area where he spent much of his youth, and his footprints linger. With a car, a bicycle, or a sturdy pair of walking boots, one can retrace the journey of “The Stolen Child” through the deciduous canopy of old Slishwood to the rustling waterfall of Glen-Car, where the fairies swing from fern fronds. Bus and ferry can bring you to the famous lake isle of Innisfree that hummed peacefully in Yeats’s memory amid the bustle of London, or to the Salley Gardens where he would rendezvous with Maud Gonne, ever aloof. The more solemn-minded make their way to the cemetery where Yeats lies interred “Under bare Ben Bulben’s head / In Drumcliff churchyard” and ruminate on the lines cut into his simple headstone. Despite the area’s many draws, travelers from too far afield are regarded as something of a pleasant surprise. Tours are more likely to be filled with visitors from another county than curious continentals or pond-hopping Americans. Let slip a foreign accent and you may find yourself caught up in a chat with a lifelong resident. Should your dialogue take a turn toward poetry, you may discover one of Sligo’s greatest charms: here, literature never quite becomes history. Sligo is a place of poetry without pomp. Verse is scrawled on the walls, written into folk songs, and etched into the memories of those raised with rhymes on their tongues. Yeats’s legacy is borne proudly and revisited frequently. One exemplar of this (and for me, one of the town’s great treasures) is the Hamilton Gallery, which, in addition to exhibiting artwork from a vast range of contemporary Irish artists, holds an annual invitational exhibition reflecting on some aspect of Yeats’s work. Each of these special shows is a culmination of the unique kind of presence with which Sligo is gifted—one that allows its inhabitants, and perhaps its pilgrims, to poignantly reenvision the life and work of W. B. Yeats. Grant Schatzman is a WLT intern and a writer, editor, and student at the University of Oklahoma. Notebook city profile Sligo, Ireland by Grant Schatzman LEFT PHOTO: DAVE GUNN. RIGHT PHOTO: KEITH EWING left Sligo’s River Garavogue. right Yeats’s grave in St. Columba’s churchyard. WORLDLIT.ORG 5 ...

City Profile: Sligo, Ireland

W hen I pulled into Sligo on the morning bus with a dog-eared copy of W. B. Yeats’s Collected Poems, I carried two wishes: first, that it would stop raining. And second, that I might uncover some of the vital, inspiring force behind my favorite poet. One gets over the rain. Located on the coastal edge of County Sligo in the northwest of Ireland, Sligo rests on the neck of land between Sligo Bay and the placid Lough Gill. Riverside restaurants, shops, and lively pubs line the town center, where the swinging doors of little cafés disclose the smell of black currant scones or the flash of jam jars and bottles of cordial. Visitors’ maps lead to abbeys, churches, and other historical sites around town, but somehow, people seem to gravitate toward Wine Street, where the Yeats Memorial Building stands. Lovers of Irish poetry have good reason to venture to a less-trafficked town like Sligo. Yeats’s early work draws deeply from the natural features and fairy stories of the area where he spent much of his youth, and his footprints linger. With a car, a bicycle, or a sturdy pair of walking boots, one can retrace the journey of “The Stolen Child” through the deciduous canopy of old Slishwood to the rustling waterfall of Glen-Car, where the fairies swing from fern fronds. Bus and ferry can bring you to the famous lake isle of Innisfree that hummed peacefully in Yeats’s memory amid the bustle of London, or to the Salley Gardens where he would rendezvous with Maud Gonne, ever aloof. The more solemn-minded make their way to the cemetery where Yeats lies interred “Under bare Ben Bulben’s head / In Drumcliff churchyard” and ruminate on the lines cut into his simple headstone. Despite the area’s many draws, travelers from too far afield are regarded as something of a pleasant surprise. Tours are more likely to be filled with visitors from another county than curious continentals or pond-hopping Americans. Let slip a foreign accent and you may find yourself caught up in a chat with a lifelong resident. Should your dialogue take a turn toward poetry, you may discover one of Sligo’s greatest charms: here, literature never quite becomes history. Sligo is a place of poetry without pomp. Verse is scrawled on the walls, written into folk songs, and etched into the memories of those raised with rhymes on their tongues. Yeats’s legacy is borne proudly and revisited frequently. One exemplar of this (and for me, one of the town’s great treasures) is the Hamilton Gallery, which, in addition to exhibiting artwork from a vast range of contemporary Irish artists, holds an annual invitational exhibition reflecting on some aspect of Yeats’s work. Each of these special shows is a culmination of the unique kind of presence with which Sligo is gifted—one that allows its inhabitants, and perhaps its pilgrims, to poignantly reenvision the life and work of W. B. Yeats. Grant Schatzman is a WLT intern and a writer, editor, and student at the University of Oklahoma. Notebook city profile Sligo, Ireland by Grant Schatzman LEFT PHOTO: DAVE GUNN. RIGHT PHOTO: KEITH EWING left Sligo’s River Garavogue. right Yeats’s grave in St. Columba’s churchyard. WORLDLIT.ORG 5 ...

Seasonal changes in photosynthesis and starch content in Japanese fir (Abies firma Sieb. et Zucc.) saplings under different levels of irradiance

In response to irradiance seasonality, saplings under brighter conditions increased leaf biomass with high photosynthesis to realize high growth, whereas understory saplings depend on photosynthesis during canopy leaf fall, and larger root biomass contributed to storage. We studied the changes in photosynthesis, biomass partitioning, and starch content in Abies firma saplings in a mixed deciduous forest in southwest Japan. Saplings were examined under high, intermediate, and low irradiance levels. The relative irradiance at intermediate and low irradiance levels increased significantly during winter and spring due to leaf fall in the deciduous canopy trees. The maximum photosynthetic rates (P max) under low irradiance were lower than those under high irradiance throughout the year. The needle daily carbon balance in summer was negative under low irradiance, whereas the balance became positive in winter and spring due to increases in irradiance. The needle daily carbon balance in intermediate- and high-irradiance saplings remained positive year-round, although the midday photosynthetic depression suppressed the daily needle carbon gain under high irradiance. The starch content in needles, branches, and roots was higher in spring due to high photosynthetic production, and then decreased in summer under all irradiance levels. Root starch under low irradiance levels may be used to maintain carbon balance during summer, thereby contributing to survival. High needle biomass coupled with a high P max facilitated carbon gain under high and intermediate irradiance, whereas high relative root biomass under low irradiance may enhance storage ability. Overall, A. firma saplings seemed to acclimate to different irradiance levels with seasonal changes through changes in photosynthetic traits, starch storage, and biomass partitioning.

Spatial Heterogeneity of the Forest Canopy Scales with the Heterogeneity of an Understory Shrub Based on Fractal Analysis

Spatial heterogeneity of vegetation is an important landscape characteristic, but is difficult to assess due to scale-dependence. Here we examine how spatial patterns in the forest canopy affect those of understory plants, using the shrub Canada buffaloberry (Shepherdia canadensis (L.) Nutt.) as a focal species. Evergreen and deciduous forest canopy and buffaloberry shrub presence were measured with line-intercept sampling along ten 2-km transects in the Rocky Mountain foothills of west-central Alberta, Canada. Relationships between overstory canopy and understory buffaloberry presence were assessed for scales ranging from 2 m to 502 m. Fractal dimensions of both canopy and buffaloberry were estimated and then related using box-counting methods to evaluate spatial heterogeneity based on patch distribution and abundance. Effects of canopy presence on buffaloberry were scale-dependent, with shrub presence negatively related to evergreen canopy cover and positively related to deciduous cover. The effect of evergreen canopy was significant at a local scale between 2 m and 42 m, while that of deciduous canopy was significant at a meso-scale between 150 m and 358 m. Fractal analysis indicated that buffaloberry heterogeneity positively scaled with evergreen canopy heterogeneity, but was unrelated to that of deciduous canopy. This study demonstrates that evergreen canopy cover is a determinant of buffaloberry heterogeneity, highlighting the importance of spatial scale and canopy composition in understanding canopy-understory relationships.

Using ground penetrating radar to assess the variability of snow water equivalent and melt in a mixed canopy forest, Northern Colorado

Snow is an important environmental variable in headwater systems that controls hydrological processes such as streamflow, groundwater recharge, and evapotranspiration. These processes will be affected by both the amount of snow available for melt and the rate at which it melts. Snow water equivalent (SWE) and snowmelt are known to vary within complex subalpine terrain due to terrain and canopy influences. This study assesses this variability during the melt season using ground penetrating radar to survey multiple plots in northwestern Colorado near a snow telemetry (SNOTEL) station. The plots include south aspect and flat aspect slopes with open, coniferous (subalpine fir, Abies lasiocarpa and engelman spruce, Picea engelmanii), and deciduous (aspen, populous tremuooides) canopy cover. Results show the high variability for both SWE and loss of SWE during spring snowmelt in 2014. The coefficient of variation for SWE tended to increase with time during snowmelt whereas loss of SWE remained similar. Correlation lengths for SWE were between two and five meters with melt having correlation lengths between two and four meters. The SNOTEL station regularly measured higher SWE values relative to the survey plots but was able to reasonably capture the overall mean loss of SWE during melt. Ground Penetrating Radar methods can improve future investigations with the advantage of non-destructive sampling and the ability to estimate depth, density, and SWE.

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.

Effects of canopy composition and disturbance type on understorey plant assembly in boreal forests

AbstractQuestionsWhat are the relative roles of disturbance type and canopy composition on understorey plant assemblages? Are these two environmental filters of equal importance in driving understorey patterns? Does a trait‐based approach improve understanding of plant assemblage responses in disturbed boreal forests?LocationEastern boreal forests of North America, Québec, Canada.MethodsWe sampled understorey plant assemblages in ca. 30‐yr‐old forest stands originating from three types of disturbance (clear‐cutting, fire and spruce budworm outbreak) and two dominant canopy compositions (coniferous and deciduous). For each disturbance × canopy combination, at least eight stands were sampled. The results were analysed with a combination of multivariate (RDA, PERMANOVA), univariate (IndVal) and trait‐based (fourth‐corner) approaches.ResultsOverall, canopy composition was a more important driver than disturbance type for understorey plant communities. Species richness and particularly the abundance of herbaceous species were highest under deciduous canopies, whereas bryophytes and lichens were more diverse and abundant under coniferous canopies. Light‐demanding species with abundant seed production were mostly restricted to deciduous canopies. Some patterns were also explained by disturbance type, but these were mostly associated with the presence/absence of non‐abundant species or species groups such as lichens.ConclusionsWe propose that the higher effect of canopy composition compared with disturbance type can be explained by two factors. First, the effect of canopy composition tends to remain present for decades during stand development, whereas the effect of the disturbance type tends to dissipate progressively after the stand‐initiating disturbance. Second, in boreal forests, most understorey plant species possess reproduction strategies (such as vegetative reproduction) that make them well adapted to persist in stands affected by any type of disturbance. At the landscape level, maintaining the right proportion of deciduous and coniferous stands through forest management could ensure that understorey ecosystem processes and plant diversity are maintained. However, creating or maintaining specific post‐disturbance attributes could be important for the conservation of species affiliated with specific substrates.

Propagule Pressure and Disturbance Drive the Invasion of Perennial False-Brome (Brachypodium sylvaticum)

An ecosystem's invasibility is influenced by changes in biotic and abiotic resistances, which often occur due to shifts in the prevailing disturbance regime. The susceptibility of a community to intrusion by nonnative species may interact with propagule pressure to determine the extent of a biological invasion. We examined how propagule pressure, forest community structure, and disturbance interact to influence the invasibility of temperate Pacific Northwest forests by the newly invasive grass, perennial false-brome (Brachypodium sylvaticum). Our goal was to identify factors enabling shifts from establishment to population growth in B. sylvaticum populations at the edge of its expanding range. Ecological sampling methods were used to identify patterns in B. sylvaticum habitat. An inverse relationship between the amount of B. sylvaticum and all perennial vegetation types and soil litter depth was found, suggesting that disturbance might play a role in B. sylvaticum population establishment or growth. An experimental study was then performed to test the effects of disturbance, propagule pressure, and habitat on B. sylvaticum seedling establishment in sites where B. sylvaticum was already naturalized. We found evidence that disturbance of the soil and vegetation led to increased B. sylvaticum seedling recruitment within naturalized sites, especially where conditions of high propagule pressure and deciduous forest canopy existed. In contrast, B. sylvaticum populations dominated by coniferous forest canopy were much more invasible than deciduous forests and did not show increased seedling recruitment in response to our disturbance treatments. Our study shows how propagule pressure and plant community dynamics interact to alter the invasibility of Pacific Northwest forests allowing B. sylvaticum to transition from establishment to population growth thus allowing this weed to cause greater negative impacts on the ecosystem.

Long-term base cation weathering rates in forested catchments of the Canadian Shield

A number of methods exist for estimating mineral weathering rates. Yet, quantifying this crucial biogeochemical reaction in the field has always been a challenge because mineral weathering takes place in open systems whose initial state conditions are not well known and where material inputs and outputs vary in time and space. Here, using the soil profile mass balance method, we estimated long-term weathering rates of base cations (BCs) for a set of 21 watersheds, and we investigated the links between environmental variables and soil properties and the spatial variation in BC weathering rates in the study area. The watersheds are located in southern Quebec and vary with respect to hydro-climatic conditions, soil properties and forest cover. Average long-term estimates of annual BC weathering rates for the study area were 0.16, 0.10, 0.09 and 0.06kmolcha−1year−1 for Ca, Mg, Na and K, respectively. Overall, redundancy analysis (RDA) indicated that soil surface area, percent deciduous canopy cover, elevation, as well as soil albite content were the most significant variables explaining together 56% of the total variation in BC weathering rates. Consistent with previous findings, our results showed that, beside soil properties, climate-related environmental variables played key roles in determining the variability of BC weathering rates in the study area. In the context of global climate change, more insights are needed for a better understanding of the effects of discrete climatic variables on BC weathering rates.

Contrasting traits, contrasting environments, and considerations on population dynamics under a changing climate: an ecophysiological field study of two co‐dominant tree species

AbstractThe increase in light availability resulting from canopy changes or opening is not always beneficial and can inhibit photosynthesis of tree seedlings already under other environmental stress. Tree seedlings' responses to compounded abiotic stress depend on their life‐history traits, and understanding the variations of such responses is important for understanding population dynamics under a changing climate. In this study we investigate how the photosynthesis of juveniles of two canopy tree species with different life‐history traits, Abies sachalinensis and Betula ermanii, differs in two contrasting sites at a sub‐boreal forest in northern Japan—one under a deciduous canopy (Closed site) and the other at a wide canopy opening (Open site). Seedlings at the Open site had low Fv/Fm (quantum yield of photosystem II) for a longer period than those at the Closed site. Abies sachalinensis at the Closed site showed lower Fv/Fm in spring than those at the Open site, but recovered after the canopy's new leaves flushed, indicating its acclimation to the shaded condition. Mean Pmax (light‐saturated photosynthetic rate at ambient CO2 levels) of A. sachalinensis seedlings was affected by site and air temperature, while B. ermanii seedlings were also affected by precipitation. Only B. ermanii's seedlings presented growth in the period studied, in spite of observed mid‐day drops to Fv/Fm attributed to water‐deficit‐related photoprotection. Results suggest that the climate change predicted for the Hokkaido area may increase the competitive advantage of broad‐leaved deciduous species, such as B. ermanii, in relation to evergreen conifers like A. sachalinensis.

Forest canopy interactions with nucleation mode particles

Abstract. Ultrafine particle size distributions through a deciduous forest canopy indicate that nucleation mode particle concentrations decline with depth into the canopy, such that number concentrations at the bottom of the canopy are an average of 16% lower than those at the top. However, growth rates of nucleation mode particles (diameters 6–30 nm) are invariant with height within the canopy, which implies that the semi-volatile gases contributing to their growth are comparatively well-mixed through the canopy. Growth rates of nucleation mode particles during a meteorological drought year (2012) were substantially lower than during a meteorologically normal year with high soil water potential (2013). This may reflect suppression of actual biogenic volatile organic compound (BVOC) emissions by drought and thus a reduction in the production of condensable products during the drought-affected vegetation season. This hypothesis is supported by evidence that growth rates during the normal year exhibit a positive correlation with emissions of BVOC modeled on observed forest composition, leaf area index, temperature and photosynthetically active radiation (PAR), but particle growth rates during the drought-affected vegetation season are not correlated with modeled BVOC emissions. These data thus provide indirect evidence that drought stress in forests may reduce BVOC emissions and limit growth of nucleation mode particles to climate-relevant sizes.

A novel index of leaf RGR predicts tree shade tolerance

Summary Plant traits responsible for shade tolerance are controversial. An important feature of shade‐tolerant trees is the ability to maintain a positive whole‐plant carbon balance [i.e. positive relative growth rate (RGRplant)] in low‐light environments, but a positive RGRplant does not always ensure continuous growth. To grow successfully in shaded environments, a plant must increase its leaf biomass with time. However, because RGRplant is determined by whole‐plant biomass change, RGRplant can be positive without any increment of leaf mass. Therefore, we developed a new index focussing on the leaf carbon balance to evaluate growth potential in shaded understoreys. We applied this to cool–temperate forest trees, such as Abies firma (evergreen conifer), Fagus crenata and F. japonica (deciduous broad‐leaved trees), and compared their shade tolerance. We termed the new index ‘RGRleaf’ expressed using net assimilation rate (NARleaf), leaf lifespan (LL), leaf mass per area (LMA) and leaf partitioning rate (LP), as [(NARleaf × LP)/LMA – (1/LL)]. RGRleaf >0 shows a positive leaf carbon balance, leading to continuous growth. RGRleaf allows a quantitative analysis of traits affecting the leaf carbon balance. We planted seedlings of each species in different light environments (open site, deciduous canopy site and evergreen canopy site) and measured their traits. RGRleaf and RGRplant were strongly correlated, but RGRplant was positive even when RGRleaf was negative (i.e. no potential of continuous growth). The negative RGRleaf values appeared correspond to low survival rates. We found that in the deciduous canopy site, A. firma showed higher RGRleaf, RGRplant and survival rates compared with F. japonica and F. crenata. Analyses of RGRleaf and its traits explained that A. firma's relatively high NARleaf and long LL are effective in maintaining a positive leaf carbon balance. Especially in deep shade (i.e. very low NARleaf), a prolonged LL is essential for maintaining a positive leaf carbon balance. These results suggest that in cool–temperate forests, evergreen plants can be more shade‐tolerant than deciduous ones.

Leaf nitrogen distribution in relation to crown architecture in the tall canopy species, Fagus crenata.

The theory of optimal leaf N distribution predicts that the C gain of plants is maximized when the N content per unit area (N(area)) scales with light availability, but most previous studies have demonstrated that the N distribution is not proportional to light availability. In tall trees, the leaves are often clustered on twigs (leaf cluster) and not evenly distributed within the crowns. Thus, we hypothesized that the suboptimal N distribution is partly caused by the limited capacity to translocate N between leaf clusters, and consequently, the relationship between light and N(area) differs for leaves in different clusters. We investigated the light availability and N content of all individual leaves within several leaf clusters on tall trees of a deciduous canopy species Fagus crenata in Japan. We observed that the within-cluster leaf N distribution patterns differed from the between-cluster patterns and the slopes of the relationships between light and N(area) were lower within clusters than between clusters. According to the detailed analysis of the N distribution within leaf clusters, N(area) was greater for current-year shoots with greater light availability or a larger total leaf area. The latter pattern was probably caused by the greater sink strength of the current-year shoots with a larger leaf area. These N distribution patterns suggest that leaf clusters are fairly independent with respect to their N use, and the productivity of real F. crenata crowns may be less than optimal.

Inland flights of young red‐eyed vireos Vireo olivaceus in relation to survival and habitat in a coastal stopover landscape

Inland dispersal of migrating land birds away from the coast, often opposite to the direction of migration, occurs frequently. Many of these movements may involve migrants seeking improved stopover conditions farther inland, but direct study of inland flights and of the ecological factors influencing their occurrence is limited. We used an automated telemetry array and ground‐tracking to assess flight behaviours, survival, and habitat use of young red‐eyed vireos Vireo olivaceus during fall migration at a coastal island and an inland stopover site in southwest Nova Scotia. We recorded inland flights for 41% (11/27) of individuals that departed the island. At least 25% of 16 individuals tagged at the inland site also relocated within the landscape prior to continuing migration, but due to the higher proportion of ambiguous flights at the inland site (44%) compared to the island (15%), we could not be sure if actual proportions of relocations differed between sites. Mortality on the island (at least 10 of 39 individuals) was significantly higher than at the inland site (0 of 16 individuals). At mainland sites near the coast where we found 6 of 11 individuals after they relocated away from the island, mortality remained high (2/6). Lack of deciduous canopy cover may have contributed to the high mortality on the island, but coastal mainland sites had a relatively high amount of deciduous canopy cover, similar to at the inland site where there was no mortality. Although coastal stopover sites may be important for migrating songbirds, especially before or after making a large water crossing, our results show that mortality can be much higher, and habitat poorer, at the coast compared to farther inland. Therefore, relocating inland may be an adaptive strategy for individuals that initially settle at the coast and that need to rest and refuel before they continue migration.

Spatial quantification of leafless canopy structure in a boreal birch forest

Leafless deciduous canopies in boreal regions affect the energy available for snowmelt and reduce overall surface albedo during winter, thereby exerting a strong influence on weather and climate. In this work, ground-based measurements of leafless canopy structure, including hemispherical photography, terrestrial laser scanning (TLS) and manual tree surveys were collected at 38 sites in an area of mountain birch forest in northern Sweden in March 2011 and 2012. Photo-derived sky view fraction was strongly inversely correlated (r<−0.9) to the total tree basal area in a 5m radius around the photo site. To expand findings to wider areas, maps of canopy height for a 5km×3km area were obtained from airborne lidar (ALS) data collected during summer 2005. Canopy heights derived from TLS were used to validate the ALS estimates, and simple models were developed to establish relationships between hemispherical sky view and ALS canopy height (RMSE<5%). The models and ALS data provide useful methods for estimating canopy radiative transfer and biomass over wide areas of birch forest, despite the relatively low ALS resolution (∼1 return m−2).

Clutch Sizes, Fledging Success, and Nest-site Characteristics of Sharp-shinned Hawks in Kentucky

Because Sharp-shinned Hawks (Accipiter striatus) are among the most secretive of North America's forest-breeding raptors, little is known about their breeding biology, including the characteristics of their nesting habitat. In 2009 and 2010, we searched forest stands in Kentucky and located 11 nests, all in pines (Pinus spp.). Nests were at a mean height of 18.6 ± 1.4 m in trees with a mean height of 23.7 m. Comparison of the characteristics of nest sites and randomly selected unused sites revealed significant differences (P = 0.021). Discriminant analysis revealed that six variables (foliage cover, mean tree height, basal area, percent deciduous canopy cover, distance from edge, and distance from road) permitted the best discrimination between used and random sites. Sharp-shinned Hawks nested in areas closer to edges and in areas with denser stands of taller conifers and denser understory. All nests were in stands of young (∼25–50 years), even-aged conifers about 18–25 m in height. Nest sites were also closer to edges where stands of dense pines transitioned into areas with more, shorter deciduous trees and less foliage cover than nest sites. These adjacent areas may provide better foraging habitat for nesting Sharp-shinned Hawks because small birds, their primary prey, are more abundant in mixed stands than in dense stands of conifers where they nested.