Dominant Canopy Species Research Articles

The role of isohydric and anisohydric species in determining ecosystem-scale response to severe drought.

Ongoing shifts in the species composition of Eastern US forests necessitate the development of frameworks to explore how species-specific water-use strategies influence ecosystem-scale carbon (C) cycling during drought. Here, we develop a diagnostic framework to classify plant drought-response strategies along a continuum of isohydric to anisohydric regulation of leaf water potential (Ψ(L)). The framework is applied to a 3-year record of weekly leaf-level gas exchange and Ψ measurements collected in the Morgan-Monroe State Forest (Indiana, USA), where continuous observations of the net ecosystem exchange of CO2 (NEE) have been ongoing since 1999. A severe drought that occurred in the middle of the study period reduced the absolute magnitude of NEE by 55%, though species-specific responses to drought conditions varied. Oak species were characterized by anisohydric regulation of Ψ(L) that promoted static gas exchange throughout the study period. In contrast, Ψ(L) of the other canopy dominant species was more isohydric, which limited gas exchange during the drought. Ecosystem-scale estimates of NEE and gross ecosystem productivity derived by upscaling the leaf-level data agreed well with tower-based observations, and highlight how the fraction of isohydric and anisohydric species in forests can mediate net ecosystem C balance.

Differential radial growth response of three coexisting dominant tree species to local and large‐scale climate variability in a subtropical evergreen broad‐leaved forest of China

AbstractSubtropical evergreen broad‐leaved forests (EBF) face great pressure from global climate change. However, little consensus exists related to how coexisting trees in these forests will respond to climatic change. We used tree rings to establish climate‐growth relationships of three coexisting dominant canopy tree species in an EBF located in the Gutianshan National Nature Reserve, Zhejiang Province, in eastern China. Our results emphasize highly species‐specific radial growth responses to both local and large‐scale climate variability. The radial growth of Pinus massoniana was enhanced by high minimum autumn and low winter temperatures as well as La Niña events. Positive growth responses in Castanopsis eyrei were linked to high minimum summer and spring temperatures. Low winter temperatures and summer sunshine also increased the growth of Schima superba. We modeled future tree‐ring growth using two climate change scenarios. Under both an intermediate (Representative Concentration Pathway, RCP 4.5) and a high emission climate change scenario (RCP 8.5), we projected further growth acceleration in C. eyrei, but a reduced growth rate in S. superb. Growth of P. massoniana was not predicted to change under the RCP 4.5 scenario, but was predicted to increase significantly under the RCP 8.5 scenario. These results suggest that climate change will have repercussions for the competitive balance among these tree species in subtropical forests, and the diverging responses of individual tree species need to fully considered in any models of the effects of climate change on the EBF and in future management plans.

Ecophysiological and foliar nitrogen concentration responses of understorey Acacia spp. and Eucalyptus sp. to prescribed burning.

Eucalyptus spp. is a dominant tree genus in Australia and most Eucalyptus spp. are canopy dominant species. In Australian natural forests, Eucalyptus spp. commonly are associated with understorey legumes which play a crucial role for ecological restoration owing to their nitrogen (N) fixing ability for replenishing the soil N lost after frequent prescribed burning. This study aimed to explore to what extent physiological responses of these species differ 7 and 12years after last fire. Two most common understorey Acacia spp., Acacia leiocalyx and A. disparrima, as well as one non-leguminous Eucalyptus resinifera, were studied due to their dominance in the forest. Both A. leiocalyx and A. disparrima showed higher carbon (C) assimilation capacity, maximum photosynthetic capacity, and moderate foliar C/N ratio compared with E. resinifera. A. leiocalyx showed various advantages compared to A. disparrima such as higher photosynthetic capacity, adaptation to wider light range and higher foliar total N (TNmass). A. leiocalyx also relied on N2-fixing ability for longer time compared to A. disparrima. The results suggested that the two Acacia spp. were more beneficial to C and N cycles for the post burning ecosystem than the non-N2-fixing species E. resinifera. A. leiocalyx had greater contribution to complementing soil N cycle long after burning compared to A. disparrima.

Assessing the utility WorldView-2 imagery for tree species mapping in South African subtropical humid forest and the conservation implications: Dukuduku forest patch as case study

Indigenous forest biome in South Africa is highly fragmented into patches of various sizes (most patches<1km2). The utilization of timber and non-timber resources by poor rural communities living around protected forest patches produce subtle changes in the forest canopy which can be hardly detected on a timely manner using traditional field surveys. The aims of this study were to assess: (i) the utility of very high resolution (VHR) remote sensing imagery (WorldView-2, 0.5–2m spatial resolution) for mapping tree species and canopy gaps in one of the protected subtropical coastal forests in South Africa (the Dukuduku forest patch (ca.3200ha) located in the province of KwaZulu-Natal) and (ii) the implications of the map products to forest conservation. Three dominant canopy tree species namely, Albizia adianthifolia, Strychnos spp. and Acacia spp., and canopy gap types including bushes (grass/shrubby), bare soil and burnt patches were accurately mapped (overall accuracy=89.3±2.1%) using WorldView-2 image and support vector machine classifier. The maps revealed subtle forest disturbances such as bush encroachment and edge effects resulting from forest fragmentation by roads and a power-line. In two stakeholders’ workshops organised to assess the implications of the map products to conservation, participants generally agreed amongst others implications that the VHR maps provide valuable information that could be used for implementing and monitoring the effects of rehabilitation measures. The use of VHR imagery is recommended for timely inventorying and monitoring of the small and fragile patches of subtropical forests in Southern Africa.

Fuel flammability and fire responses of juvenile canopy species in a temperate rainforest ecosystem

Historically, rainforests have been considered vulnerable to fire. Recent research, however, has shown that many rainforest species can survive fire by resisting burning and by resprouting and seeding post-fire. We investigated the response of a warm temperate rainforest community to fire by burning juveniles of the dominant canopy tree species (Doryphora sassafras, Syzygium smithii and Wollemia nobilis) and examining litter flammability in a controlled environment. The three species resprouted after the experimental burn, predominantly from buds on the stem that were below the soil surface. Higher fire temperatures resulted in reduced overall plant height and resprouting from buds lower on the stem. Increasing proportions of W. nobilis litter generated fires with higher intensities and fuel consumption compared with rainforest angiosperm litter. Moreover, fuel moisture content decreased with increasing W. nobilis litter proportions. Higher litter flammability may result in increased likelihood of fire ignition and fire severity near W. nobilis trees, which would negatively impact the juveniles of all three rainforest species. Alternatively, after lower-temperature fires (e.g. in rainforest angiosperm litter), W. nobilis may have an advantage over the other species because of faster-growing resprouts occurring higher on the stem.

Die-out of Manilkara hexandra from Bundala National Park, Sri Lanka: Causes and some possible underlying mechanisms

Bundala National Park (BNP) is a biologically diverse wetland habitat where a sizable area of Tropical Semi-deciduous (TSD) forests of Sri Lanka exists. Manilkara hexandra is the only dominant canopy tree species in these forests. However, the species appears to be dying out from BNP. With the aim of revealing the causes and possible underlying reasons for the die-out of the species, the population size, spatial distribution, natural regeneration and the healthiness of individuals of M. hexandra in BNP were examined in twenty five 50x50 m2 plots in three belt transects which were established across different forest categories in BNP. The major alien exotic plants in these plots were also enumerated. Results revealed that the tree die-back and poor natural regeneration were among the major causes for the die-out of M. hexandra from BNP, which had altered the population structure and distribution of the species over space. Live individuals of the species were absent in some degraded sites especially those invaded by Prosopis juliflora. Presence of over-mature cohorts, occurrence of tree cankers and presence of the aggressive invader, P. juliflora appear to affect the die-back of M. hexandra. This study provides a clue that there is a possibility of dying-back of the remaining healthy trees of M. hexandra in TSD forests of BNP in the near future, unless the threats imposed upon M. hexandra are uplifted through strategic management activities.

Functional relationships between leaf hydraulics and leaf economic traits in response to nutrient addition in subtropical tree species

Leaves can be both a hydraulic bottleneck and a safety valve against hydraulic catastrophic dysfunctions, and thus changes in traits related to water movement in leaves and associated costs may be critical for the success of plant growth. A 4-year fertilization experiment with nitrogen (N) and phosphorus (P) addition was done in a semideciduous Atlantic forest in northeastern Argentina. Saplings of five dominant canopy species were grown in similar gaps inside the forests (five control and five N + P addition plots). Leaf lifespan (LL), leaf mass per unit area (LMA), leaf and stem vulnerability to cavitation, leaf hydraulic conductance (K(leaf_area) and K(leaf_mass)) and leaf turgor loss point (TLP) were measured in the five species and in both treatments. Leaf lifespan tended to decrease with the addition of fertilizers, and LMA was significantly higher in plants with nutrient addition compared with individuals in control plots. The vulnerability to cavitation of leaves (P50(leaf)) either increased or decreased with the nutrient treatment depending on the species, but the average P50(leaf) did not change with nutrient addition. The P50(leaf) decreased linearly with increasing LMA and LL across species and treatments. These trade-offs have an important functional significance because more expensive (higher LMA) and less vulnerable leaves (lower P50(leaf)) are retained for a longer period of time. Osmotic potentials at TLP and at full turgor became more negative with decreasing P50(leaf) regardless of nutrient treatment. The K(leaf) on a mass basis was negatively correlated with LMA and LL, indicating that there is a carbon cost associated with increased water transport that is compensated by a longer LL. The vulnerability to cavitation of stems and leaves were similar, particularly in fertilized plants. Leaves in the species studied may not function as safety valves at low water potentials to protect the hydraulic pathway from water stress-induced cavitation. The lack of rainfall seasonality in the subtropical forest studied probably does not act as a selective pressure to enhance hydraulic segmentation between leaves and stems.

Effects of Acidic Deposition and Soil Acidification on Sugar Maple Trees in the Adirondack Mountains, New York

We documented the effects of acidic atmospheric deposition and soil acidification on the canopy health, basal area increment, and regeneration of sugar maple (SM) trees across the Adirondack region of New York State, in the northeastern United States, where SM are plentiful but not well studied and where widespread depletion of soil calcium (Ca) has been documented. Sugar maple is a dominant canopy species in the Adirondack Mountain ecoregion, and it has a high demand for Ca. Trees in this region growing on soils with poor acid-base chemistry (low exchangeable Ca and % base saturation [BS]) that receive relatively high levels of atmospheric sulfur and nitrogen deposition exhibited a near absence of SM seedling regeneration and lower crown vigor compared with study plots with relatively high exchangeable Ca and BS and lower levels of acidic deposition. Basal area increment averaged over the 20th century was correlated (p < 0.1) with acid-base chemistry of the Oa, A, and upper B soil horizons. A lack of Adirondack SM regeneration, reduced canopy condition, and possibly decreased basal area growth over recent decades are associated with low concentrations of nutrient base cations in this region that has undergone soil Ca depletion from acidic deposition.

Forest herb layer response to long-term light deficit along a forest developmental series

Temperate deciduous forest communities are slow-changing systems, with herbaceous understorey communities displaying a delayed response to overstorey canopy and light dynamics. While light availability constrains herbaceous understorey diversity and composition in space and time, its response in the long-term absence of light has seldom been quantified, particularly as it is often confounded by covariation in soil conditions. We studied a developmental high-forest series in two widespread NW-European temperate deciduous forest communities with different dominant canopy tree species: Stellario-Carpinetum (Oak-hornbeam canopy) and Milio-Fagetum (Beech canopy). All plots had soil conditions which were not significantly different, enabling investigation into the direct effects of the long-term absence of light on the herbaceous understorey, disentangled from the confounding effects of soil variation.Plant species richness measures declined with canopy cover continuity in the herb layer of the oak-hornbeam stands, whereas richness in the herb layer of the beech stands displayed a unimodal response. Nonetheless, in both plant communities, species richness and closed-forest species richness were negatively affected by the extended absence of light in stands with the longest period of continuous canopy cover. The long-term limitation or decline in quantitative and qualitative light availability as a result of extended periods of canopy cover was shown to be the primary driver behind losses in alpha-diversity, community composition turn-over and individual species dynamics. Heliophilous species were lost from both communities, while closed-forest species also declined, as a direct consequence of the prolonged period without ample light on the forest floor. This study demonstrates how the herb layer is affected by the absence of light on the forest floor mediated by long periods of continuous canopy cover. Despite different temporal responses in herb layer richness and composition between different shade-casting canopy species, the eventual outcome in the prolonged absence of light is independent of dominant canopy species.

High spatial resolution three-dimensional mapping of vegetation spectral dynamics using computer vision

High spatial resolution three-dimensional (3D) measurements of vegetation by remote sensing are advancing ecological research and environmental management. However, substantial economic and logistical costs limit this application, especially for observing phenological dynamics in ecosystem structure and spectral traits. Here we demonstrate a new aerial remote sensing system enabling routine and inexpensive aerial 3D measurements of canopy structure and spectral attributes, with properties similar to those of LIDAR, but with RGB (red-green-blue) spectral attributes for each point, enabling high frequency observations within a single growing season. This “Ecosynth” methodology applies photogrammetric “Structure from Motion” computer vision algorithms to large sets of highly overlapping low altitude (<130m) aerial photographs acquired using off-the-shelf digital cameras mounted on an inexpensive (<USD$4000), lightweight (<2kg), hobbyist-grade unmanned aerial system (UAS). Ecosynth 3D point clouds with densities of 30–67pointsm−2 were produced using commercial computer vision software from digital photographs acquired repeatedly by UAS over three 6.25ha (250m×250m) Temperate Deciduous forest sites in Maryland USA. Ecosynth point clouds were georeferenced with a precision of 1.2–4.1m horizontal radial root mean square error (RMSE) and 0.4–1.2m vertical RMSE. Understory digital terrain models (DTMs) and canopy height models (CHMs) were generated from leaf-on and leaf-off point clouds using procedures commonly applied to LIDAR point clouds. At two sites, Ecosynth CHMs were strong predictors of field-measured tree heights (R2 0.63 to 0.84) and were highly correlated with a LIDAR CHM (R 0.87) acquired 4days earlier, though Ecosynth-based estimates of aboveground biomass and carbon densities included significant errors (31–36% of field-based estimates). Repeated scanning of a 50m×50m forested area at six different times across a 16 month period revealed ecologically significant dynamics in canopy color at different heights and a structural shift upward in canopy density, as demonstrated by changes in vertical height profiles of point density and relative RGB brightness. Changes in canopy relative greenness were highly correlated (R2=0.87) with MODIS NDVI time series for the same area and vertical differences in canopy color revealed the early green up of the dominant canopy species, Liriodendron tulipifera, strong evidence that Ecosynth time series measurements can capture vegetation structural and spectral phenological dynamics at the spatial scale of individual trees. The ability to observe canopy phenology in 3D at high temporal resolutions represents a breakthrough in forest ecology. Inexpensive user-deployed technologies for multispectral 3D scanning of vegetation at landscape scales (<1km2) heralds a new era of participatory remote sensing by field ecologists, community foresters and the interested public.

Relationships between Carabid Beetle Communities and Forest Stand Parameters: Taxon Congruence or Habitat Association?

We sampled ground beetles (Coleoptera: Family Carabidae) at the Furman Forest in northeast Greenville County, SC, and compared species richness and community attributes with tree stand richness, diversity, and composition. Beetles were collected by pitfall trap 1 night/week for 9 weeks from June to August 2011 in 24 plots (200 m2) varying in tree abundance (11–131 trees/plot), mean tree size (6.5–26.0 cm DBH), species richness (2–13 species/plot), Simpson's diversity (1.6–9.1/plot), and composition. We collected 286 carabids representing 13 genera and 26 species, including a new state record for South Carolina, Cyclotrachelus hypherpiformis. Carabid abundance, species richness, and diversity were unrelated to tree abundance, richness, or diversity. However, carabid abundance and richness were positively correlated with the abundance of Liriodendron tulipifiera (Tulip Poplar), suggesting a preference for mesic habitats. Total carabid abundance and the abundance and dominance of Carabus goryi (the most abundant species) were also positively correlated with mean tree size (DBH), suggesting a preference for older stands. Carabid diversity, abundance, and community structure were associated with habitat type and stand age (as indicated by dominant canopy species and tree size) and not canopy tree species richness or diversity.

Hydrologic variation of stemflow yield across co‐occurring dominant canopy trees of varying mortality

ABSTRACTConcern over forest dieback due to environmental change and the long residence times of standing dead trees necessitates understanding the impact of forest health on the redistribution of precipitation by forest canopies. Stemflow represents a critical point source input of water and nutrients to forest ecosystems. We investigate the variation in water storage capacity, stemflow volume and stemflow funnelling ratios from two co‐occurring dominant canopy species, Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar), across three different mortality classes: live, stressed (girdled) and standing dead. Over 25 rainfall events, interspecific differences in stemflow volume distributions were significant over all (U = 45 881, p &lt; 0·0001), leaf‐off (U = 11 285, p &lt; 0·0001) and leaf‐on (U = 11 582, p &lt; 0·0001) events. Stemflow funnelling ratios were greater in F. grandifolia (26·0 ± 1·2) compared with L. tulipifera (4·9 ± 0·4). Minimum precipitation threshold amounts required to initiate stemflow were lower for F. grandifolia compared with L. tulipifera, and lower for live and stressed compared with dead. Mean stemflow volume from both species was 1·5 ± 0·2 l stem−1 event−1 from dead stems, 89·2 ± 7·7 l stem−1 event−1 from stressed stems and 91·3 ± 8·9 l stem−1 event−1 from live stems. The results of this study improve our understanding of the influence of mortality on rainfall partitioning and stemflow fluxes and may give insight into how mortality generating factors such as pest defoliation and climate change may alter stemflow relationships in forested ecosystems. Copyright © 2013 John Wiley &amp; Sons, Ltd.

The Relative Importance of Fungal Infection, Conspecific Density and Environmental Heterogeneity for Seedling Survival in a Dominant Tropical Tree

AbstractA gap remains in our understanding of how host‐specific fungal pathogens impact negative density dependence (NDD). Here, we investigated survival of Cinnamomum subavenium Miq. seedlings, the dominant canopy species in a seasonal tropical evergreen forest, Thailand. It is infected by a host‐specific fungus that is easily identifiable in the field. We quantified the effects of conspecific seedling and adult density on fungal infection and seedling survival over a wide range of environmental heterogeneity in elevation, understory vegetation and presence of forest gaps. Generalized linear mixed models (GLMMs) for seedling survival revealed that fungal infection significantly reduced survival and had the strongest effect on seedling survival as compared with conspecific density and environmental heterogeneity. Adult conspecific density was not, however, significantly correlated with the probability of infection, and conspecific seedling density was positively associated with increased infection only at high elevations. In contrast to infection, we found a significant positive correlation between conspecific seedling density and the probability of seedling survival. Consequently, our results demonstrate that fungal infection can have major impacts on seedling survival, but not in a manner consistent with local NDD effects on seedlings, as assumed in the Janzen–Connell hypothesis. Our study provides an example of how quantifying the interaction between environmental heterogeneity and a host‐specific plant‐pathogen can yield unexpected insights into the dynamics of seedling populations. The combined effects of host‐specific pathogens and environmental heterogeneity on survival of dominant seedling species may ultimately provide a chance for rarer species to recruit.

Removal of nutrient limitations in forest gaps enhances growth rate and resistance to cavitation in subtropical canopy tree species differing in shade tolerance

A 4-year fertilization experiment with nitrogen (N) and phosphorus (P) was carried out in natural gaps of a subtropical forest in northeastern Argentina. Saplings of six dominant canopy species differing in shade tolerance were grown in five control and five N + P fertilized gaps. Hydraulic architectural traits such as wood density, the leaf area to sapwood area ratio (LA : SA), vulnerability to cavitation (P50) and specific and leaf-specific hydraulic conductivity were measured, as well as the relative growth rate, specific leaf area (SLA) and percentage of leaf damage by insect herbivores. Plant growth rates and resistance to drought-induced embolisms increased when nutrient limitations were removed. On average, the P50 of control plants was -1.1 MPa, while the P50 of fertilized plants was -1.6 MPa. Wood density and LA : SA decreased with N + P additions. A trade-off between vulnerability to cavitation and efficiency of water transport was not observed. The relative growth rate was positively related to the total leaf surface area per plant and negatively related to LA : SA, while P50 was positively related to SLA across species and treatments. Plants with higher growth rates and higher total leaf area in fertilized plots were able to avoid hydraulic dysfunction by becoming less vulnerable to cavitation (more negative P50). Two high-light-requiring species exhibited relatively low growth rates due to heavy herbivore damage. Contrary to expectations, shade-tolerant plants with relatively high resistance to hydraulic dysfunction and reduced herbivory damage were able to grow faster. These results suggest that during the initial phase of sapling establishment in gaps, species that were less vulnerable to cavitation and exhibited reduced herbivory damage had faster realized growth rates than less shade-tolerant species with higher potential growth rates. Finally, functional relationships between hydraulic traits and growth rate across species and treatments were maintained regardless of soil nutrient status.

Seedling recruitment factors in low‐diversity Hawaiian wet forest: towards global comparisons among tropical forests

Recruitment limitations determine forest community regeneration patterns. Source limitation and dispersal limitation contribute to overall seed limitation, while environmental conditions and habitat associations influence establishment limitation. Several hypotheses have made contradictory predictions for how the relative importance of these limitations should vary with diversity. However, comparative data have not been available for low‐diversity tropical forests. We quantified recruitment limitations using 2.5 yrs of seed rain and seedling distribution data collected within a 4 ha forest dynamics plot in low‐diversity native‐dominated Hawaiian wet forest. We further quantified seedling irradiance and substrate habitat associations and niche overlap (using Pianka's niche overlap index). Additionally, we compared recruitment limitations and the frequency of seedling habitat associations across forests using the few available published data from sites employing similar field and analytical methods. In Hawaiian wet forest, seed dispersal more strongly limited recruitment than did establishment limitation across species, with 11 of 18 species completely seed limited (i.e., no seeds found). However, the relative importance of limitations varied greatly among species. For the three most abundant species, habitat conditions more strongly limited regeneration than did seed arrival, especially for the dominant canopy species, Metrosideros polymorpha, which was not seed limited. Most species were significantly associated with specific ranges of irradiance and/or substrates. Although habitat associations may indicate niche differentiation, Hawaiian species also showed significant niche overlap. Across the three forests compared, community‐wide mean seed and establishment limitation values were similar, despite wide variation in diversity. However, recruitment limitations differed strongly among species within forests due to species' life‐history differences. While seed limitation in Hawaiian forest was as high as in high‐diversity forests, mechanisms may differ; seed limitation in Hawaii may arise from loss of pollinators and dispersers rather than from a high proportion of rare species as occurs in high‐diversity forests. The strong habitat associations in Hawaiian forest relative to high‐diversity forests supported theoretical expectations that lower species diversity should increase the importance of habitat associations. However, these habitat associations were not linked to niche differentiation in Hawaii. Our findings suggest that high recruitment limitation may facilitate coexistence despite niche overlap in low‐diversity Hawaiian forest.

Tree species diversity and related mechanism in an evergreen broad-leaved forest in Ailao Mountains, Yunnan, China

There is no enough data or evidence to reach a firm conclusion for tree species diversity and related mechanism in an evergreen broad-leaved forest in Ailao Mountains, Yunnan, China. A 6-hm2 plot was established in Ailao Mountains State Nature Reserve for the purpose of monitoring long-term dynamics of tree populations. All free-standing trees with diameter at breast height (DBH) ≥ 1 cm were tagged, mapped, measured (girth) and identified to species in the plot. The spatial distribution patterns of four dominant canopy tree species in the plot were analyzed using a point pattern analysis Ripley’s L-function. A total of 12131 free-standing individuals with DBH ≥ 1 cm were recorded in the plot, including 68 species belonging to 49 genera and 25 families. Lithocarpus hancei had the largest basal area and the largest importance value. Camellia forrestii, an understory tree species was ranked the second in terms of importance value, although it showed the highest abundance (1712 individuals). The four canopy dominant species had a large number of seedlings and saplings and tend to be patchily distributed. And the spatial distributions of 26 tree species with ≥40 individuals was examined at each life history stage (diameter at breast height ≥1 cm), and 37 of 57 life history stages showed aggregated distribution pattern. It showed that it may be not density dependence but habitat heterogeneity as a prevalent mechanism for regulating the population spatial structure of most tree species in the subtropical forest studied here. Key words: Evergreen broad-leaved forest, habitat heterogeneity, spatial distribution pattern, tree species diversity.

Biogeochemistry of beetle-killed forests: Explaining a weak nitrate response

A current pine beetle infestation has caused extensive mortality of lodgepole pine (Pinus contorta) in forests of Colorado and Wyoming; it is part of an unprecedented multispecies beetle outbreak extending from Mexico to Canada. In United States and European watersheds, where atmospheric deposition of inorganic N is moderate to low (<10 kg⋅ha⋅y), disturbance of forests by timber harvest or violent storms causes an increase in stream nitrate concentration that typically is close to 400% of predisturbance concentrations. In contrast, no significant increase in streamwater nitrate concentrations has occurred following extensive tree mortality caused by the mountain pine beetle in Colorado. A model of nitrate release from Colorado watersheds calibrated with field data indicates that stimulation of nitrate uptake by vegetation components unaffected by beetles accounts for significant nitrate retention in beetle-infested watersheds. The combination of low atmospheric N deposition (<10 kg⋅ha⋅y), tree mortality spread over multiple years, and high compensatory capacity associated with undisturbed residual vegetation and soils explains the ability of these beetle-infested watersheds to retain nitrate despite catastrophic mortality of the dominant canopy tree species.

Succession and disturbance in an endangered red spruce−Fraser fir forest in the southern Appalachian Mountains, North Carolina, USA

Red spruce-Fraser fir forests are geographically limited to high elevations in the Appalachian Mountains (USA) and are considered to be endangered in the USA. We investigated the successional status and radial growth patterns in the heavily disturbed red spruce Picea rubens Sarg. and Fraser fir Abies fraseri (Pursh) Poir. forest of Roan Mountain, Tennessee and North Carolina. This study elucidates the complexity of second-growth red spruce development after logging and disturbances by balsam woolly adelgid Adelges piceae Ratz. We documented precise temporal information of stand age, disturbance regimes, recruitment patterns, and the successional trajectory of the spruce-fir forest community. We used radial growth patterns of red spruce samples to detect the frequency and magnitude of disturbance. Red spruce was the oldest dominant canopy species, although Fraser fir had high recruitment rates over the past 80 yr. Changes in forest structure and species richness coincided with stand-wide disturbance events such as balsam woolly adelgid infestation and widespread early twentieth-century logging. The competitive advantage of Fraser fir over red spruce has resulted in an even-aged Fraser fir-dominant forest that occupies a relatively early stage of successional development. This study provides a 130 yr environmental history to assist land managers in the southern Appalachian Mountains as they develop long-term restoration plans for this unique ecosystem.

The role of canopy gaps in the regeneration of coastal dune forest

AbstractIn regenerating coastal dune forest, the canopy consists almost exclusively of a single species, Acacia karroo. When these trees die, they create large canopy gaps. If this promotes the persistence of pioneer species to the detriment of other forest species, then the end goal of a restored coastal dune forest may be unobtainable. We wished to ascertain whether tree species composition and richness differed significantly between canopy gaps and intact canopy, and across a gradient of gap sizes. In three known‐age regenerating coastal dune forest sites, we measured 146 gaps, the species responsible for gap creation, the species most likely to reach the canopy and the composition of adults, seedlings and saplings. We paired each gap with an adjacent plot of the same area that was entirely under intact canopy and sampled in the same way.Most species (15 of 23) had higher abundance in canopy gaps. The probability of self‐replacement was low for A. karroo even in the largest gaps. Despite this predominance of shade‐intolerant species, regenerating dune forest appears to be in the first phase of succession with ‘forest pioneers’ replacing the dominant canopy species. The nature of these species should lead to successful regeneration of dune forest.

The macrofungal diversity and community of Atlantic oak &lt;i&gt;(Quercus petraea&lt;/i&gt; and &lt;i&gt;Q. robur)&lt;/i&gt; forests in Ireland

The oak species Quercus petraea and Q. Robur are dominant canopy tree species of native deciduous forests in Ireland and coastal regions of Western Europe. These forests are typically plant species-rich, and can also have a rich fungal flora. This survey examined macrofungi found in five native oak sites across Ireland over three years. Overall, 94 macrofungal species belonging to 39 genera were discovered with Mycena, Lactarius, Russula and Cortinarius the most species-rich genera. The species accumulation curve did not show signs of levelling off, indicating that more sampling would reveal more new species. Species richness estimation using the Chao2 estimator indicated that up to 135 species may be present across all of our plots, with individual plots receiving estimates from 19 to 61 species per plot. Sampled-based rarefaction analysis showed no significant differences in macrofungal species richness between our plots. The five most common species were Laccaria amethystina, L. laccata, Stereum hirsutum, Armillaria mellea and Cortinarius flexipes . Comparisons of the results with results from oak forests in similar regions found that the communities in Great Britain were most similar to those found in Ireland. There were some key oak forest distinguishing fungal species from the family Boletaceae lacking from Irish oak forests. It is hypothesised that the historic deforestation of Ireland, caused a reduction of suitable habitats for Irish oak associated macrofungi, leading to the unspecific mycota found in the oak forests of this study. The threats to Atlantic oak forests in Ireland are briefly discussed.