Intact Canopy Research Articles

Avian responses to an extreme ice storm are determined by a combination of functional traits, behavioural adaptations and habitat modifications.

The extent to which species’ traits, behavior and habitat synergistically determine their response to extreme weather events (EWE) remains poorly understood. By quantifying bird and vegetation assemblages before and after the 2008 ice storm in China, combined with interspecific interactions and foraging behaviours, we disentangled whether storm influences avian reassembly directly via functional traits (i.e. behavioral adaptations), or indirectly via habitat variations. We found that overall species richness decreased, with 20 species detected exclusively before the storm, and eight species detected exclusively after. These shifts in bird relative abundance were linked to habitat preferences, dietary guild and flocking behaviours. For instance, forest specialists at higher trophic levels (e.g. understory-insectivores, woodpeckers and kingfishers) were especially vulnerable, whereas open-habitat generalists (e.g. bulbuls) were set to benefit from potential habitat homogenization. Alongside population fluctuations, we found that community reassembly can be rapidly adjusted via foraging plasticity (i.e. increased flocking propensity and reduced perching height). And changes in preferred habitat corresponded to a variation in bird assemblages and traits, as represented by intact canopy cover and high density of large trees. Accurate predictions of community responses to EWE are crucial to understanding ecosystem disturbances, thus linking species-oriented traits to a coherent analytical framework.

Introduced deer at low densities do not inhibit the regeneration of a dominant tree

Deer have been introduced to forests worldwide as non-native invasive species. Red deer (Cervus elaphus scoticus) were introduced to New Zealand in 1851, became abundant throughout its forests, then their populations declined to current, typically low densities. It is uncertain whether browsing by red deer at low densities reduces growth and survival of seedlings of the dominant trees in New Zealand forests. We investigated this experimentally in a cool temperate rain forest dominated by mountain beech (Fuscospora cliffortioides, Nothofagaceae). Mountain beech regeneration depends on stand-level disturbances. Red deer are thought to exert strongest effects on regeneration in canopy gaps. Our factorial design was creation of canopy gaps, by felling trees, contrasted with intact canopies, and fencing to completely exclude deer, and unfenced treatments. We measured growth and mortality of mountain beech seedlings (initially 15–135cm tall) in plots after 6years. Seedling growth rates were much greater in canopy gaps than under intact canopies. They were greatest in gaps from which deer were excluded and the seedlings that were largest when gaps were created grew most rapidly. Mortality of seedlings was largely related to initial size and rates were greater in canopy gaps because of self-thinning. We conclude that red deer, at current low densities, affect the regeneration of the dominant canopy tree of these forests slightly, but at levels that are unlikely to prevent canopy replacement. Forest managers should focus efforts on managing deer and their effects on forest regeneration in the period that follows major canopy disturbance.

Influence of Land Use Activities on Riparian Vegetation, Soil and Water Quality: An Indicator of Biodiversity Loss, South West Mau Forest, Kenya

Watershed and riparian areas of Mau Forest Complex in Kenya are experiencing increased threats due to unsustainable land use activities geared towards economic growth amidst growing population. This study was carried out to examine effects of land use activities on riparian vegetation, soil and water quality along two major rivers (Chemosit and Kipsonoi) of South West Mau Forest (SWMF). Land use activities adjacent to these rivers and biodiversity disturbance on the riparian zone were identified and underpinned to changes on Total Nitrogen, Total Phosphorous, Potassium, Sulphur, Cadmium, Copper, Lead, Total Suspended Solids and soil Organic Carbon. Three sampling sites designated(upstream, midstream and downstream) were identified and established along each river as guided by existing land use activities represented by forest, tea plantation and mixed agricultural farming respectively. At each sampling site, a 200 m × 50 m section was systematically marked on each side of the river bank; the longest side being parallel to the river flow and divided into three belts transects each 20 m × 50 m, spaced 70 m apart. Six distinct land use activities (indigenous forest, food crop, tree and tea farming, livestock keeping and urban settlement) were identified as the major land use activities in SWMF. Plant species richness decreased and overall riparian disturbance increased from upstream (intact canopy with native vegetation) to mid-stream and downstream as epitomized by the structure, biodiversity disturbance resulting from extensive and intensive farming, intrusion of exotic species to livestock grazing and urban settlement. Variation among sampling sites in Total Suspended Solids, pH, Total Nitrogen, Phosphorus and Potassium were associated to different land use activities along the riparian zone. Total Nitrogen and water pH showed significant sensitivity to land use changes (p < 0.05). Put together these results indicate loss of biodiversity, riparian disturbance hence a need to adopt environmental-friendly land use planning and sustainable farming systems in SWMF.

Influence of grazing and vegetation type on post-fire floristic and lifeform composition in Tasmania, Australia

Fire and herbivory are important disturbances in vegetation globally. These disturbances are widely applied in combination for conservation and livestock management. Little is known regarding the relative effects on species composition of post-fire grazing, grazing by itself, burning by itself, the absence of both of these disturbances or of the variation of their influences between vegetation types. At seven sites in Tasmania, Australia, in sedgeland, heathy forest and grassland, the covers and heights of tracheophytes were measured before and for 2 years after the commencement of a fire experiment that nested grazing within burning. Burning followed by grazing, largely by native vertebrates, tended to result in greater changes in species and lifeform composition than either grazing by itself or burning by itself. Heathy forest and sedgeland responded primarily to fire rather than grazing. Heathy forest shifted to a new state with burning while sedgeland began a return to its pre-burn state. Grazing after burning most strongly affected the lowland tussock grassland, while also strongly influencing the height of highland tussock grasslands. Intact canopies in eucalypt forest after fire prevented a return to the original understorey while grazing animals turn tussock grassland into lawn after fire. In all cases, the effects of grazing after burning are incremental rather than strongly synergistic.

The Positive Interaction Between Two Nonindigenous Species, Casuarina (Casuarina Equisetifolia) and Acacia (Acacia Mangium), in the Tropical Coastal Zone of South China: Stand Dynamics and Soil Nutrients

The role of mixed forests in tropical coastal South China is unclear due to a long history of afforestation with a Casuarina (C asuarina equisetifolia) monoculture. In this study, we determined how the stand dynamics and soil nutrients in monoculture stands of C asuarina equisetifolia were influenced by Acacia ( Acacia mangium), a fast-growing pioneer species, when the two tree species were combined in two initial proportions. We also compared the canopy conditions of mixed and monoculture stands of C. equisetifolia at the young stage. Over a period of ten years, the density of stems was relatively low in C. equisetifolia × Acacia mangium mixed stands compared to C. equisetifolia monoculture stands. By contrast, the aboveground biomass, understory diversity and soil nutrients were relatively high in C. equisetifolia × A. mangium mixed stands, particularly when the initial mixing proportion of A. mangium was greater. Moreover, C. equisetifolia can protect A. mangium in the windy coastal environment by ensuring evenly distributed crown growth, intact canopy conditions, and high leaf area index (LAI) during the young stage. In conclusion, the two species had a positive interaction in the mixed forests, which suggests that coastal conservation managers need to shift from their traditional focus on C. equisetifolia single-species afforestation to multi-tree species mixed afforestation.

Species interactions can maintain resistance of subtidal algal habitats to an increasingly modified world

Current trends in habitat loss have been forecast to accelerate under anticipated global change, thereby focusing conservation attention on identifying the circumstances under which key species interactions retard habitat loss. Urbanised coastlines are associated with broad-scale loss of kelp canopies and their replacement by less productive mats of algal turf, a trend predicted to accelerate under ocean acidification and warming (i.e. enhanced CO2 and temperature). Here we use kelp forests as a model system to test whether efforts to maintain key species interactions can maintain habitat integrity under forecasted conditions. First, we assessed whether increasing intensity of local human activity is associated with more extensive turf mats and sparser canopies via structured field observations. Second, we experimentally tested the hypothesis that intact canopies can resist turf expansion under enhanced CO2 and temperature in large mesocosms. In the field, there was a greater proportion of turf patches on urbanised coasts of South Australia than in agricultural and urban catchments in which there was a greater proportion of canopy-forming algae. Mesocosm experiments revealed this expansion of turfs is likely to accelerate under increases in CO2 and temperature, but may be limited by the presence of intact canopies. We note that even in the presence of canopy, increases in CO2 and temperature facilitate greater turf covers than occurs under contemporary conditions. The influence of canopy would likely be due to shading of the understorey turfs which, in turn, can modify their photosynthetic activity. These results suggest that resistance of habitat to change under human-dominated conditions may be managed via the retention of key species and their interactions. Management that directly reduces the disturbance of habitat-forming organisms (e.g. harvesting) or reverses loss through restoration may, therefore, reinforce habitat resistance in an increasingly stressful world.

Seed dispersal by rodents in a lowland forest in central Panama

Abstract:We studied the removal of seeds of three species of large-seeded tree (Astrocaryum standleyanum, Attalea butyraceaandDipteryx oleifera) from three different heights within six study plots in a lowland forest in central Panama. Fresh fruits with intact seeds fitted with industrial sewing bobbins were placed within semi-permeable exclosures. Removed seeds were tracked to deposition sites, and seed fate was determined. Removals were likely perpetrated by two small rodents, the strictly terrestrialProechimys semispinosusand the scansorialSciurus granatensis, because they were the most abundant small rodents in the study site during the study period and were of sufficient size to remove large seeds. Rodent abundance and fruit availability were estimated by conducting censuses. Nine microhabitat variables were measured at each deposition site to determine if these two rodents were preferentially depositing seeds in sites with certain characteristics or were randomly depositing seeds. During the study, rodents handled 98 seeds, 85 of which were not predated upon and could potentially germinate. Removal rates were not influenced by rodent abundance or fruit availability. Seeds were most frequently moved &lt;3 m and deposited with the fruit eaten and the seed intact. However, some seeds did experience relatively long-distance dispersal (&gt;10 m). Rodents preferentially deposited seeds in locations with large logs (&gt;10 cm diameter), dense herbaceous cover, and an intact canopy. The number of large logs was different from random locations. Despite not being able to determine long-term fate (greater thanc. 1 y), we show that these small rodents are not primarily seed predators and may in fact be important mutualists by dispersing seeds relatively long distances to favourable germination sites.

Response of invasive Chromolaena odorata and two coexisting weeds to contrasting irradiance and nitrogen

Chromolaena odorata is a widespread exotic weed in southern China and other regions of the world. To better understand its invasive strategies, we compared leaf pigment contents and gas-exchange traits of the invader with its two coexisting species (native Urena lobata and invasive Bidens pilosa) under combined conditions of irradiance (full, medium, and low) and nitrogen (full, medium, and low) supplies. The chlorophyll (Chl) a+b content of U. lobata was the highest and the Chl a/b ratio of C. odorata was the lowest among the three weed species. In most treatments, leaf pigment, light-saturated photosynthetic rate (P max), and light saturation point (LSP) of all the species increased, while their Chl a/b ratios decreased with the increasing nitrogen. The P max and LSP of U. lobata were greater than those of the coexisting weeds under full irradiance (FI), but significantly declined with the decreasing irradiance. The invasive weeds, especially C. odorata, showed lower P max and LSP under FI, but they showed slight decrease under low irradiance. Compared to U. lobata, C. odorata exhibited the lower light compensation point (LCP) in most treatments, higher LSP under low and medium irradiance, and lower dark respiration rate under FI. In addition, all the three species showed similar responses to different irradiance and nitrogen conditions, mean phenotypic plasticity index (MPPI) of most photosynthetic variables of the two invasive species was lower than that of U. lobata. These results suggested that C. odorata behaved as a facultative shadetolerant weed, being able to grow in moderately sheltered environments; the lower MPPI might be one of the important competitive strategies during its invasion. However, its invasion should be limited to some very shady habitats. In the field, control should be mainly directed against populations growing in the open or nutrient-rich habitats, where its expansion speed could be much faster. Deep shade by intact canopies or luxuriant forests might be an effective barrier against its invasion.

Divergent responses of leaf herbivory to simulated hurricane effects in a rainforest understory

Hurricanes are major disturbances in many forests, but studies showing effects of natural hurricanes on herbivory rates have yielded mixed results. Forest managers could benefit from a better understanding of the effects of disturbances on herbivory to manage for particular recovery or restoration goals after anthropogenic or natural disturbances, such as logging and windstorms. I measured herbivory on eight understory plant species that are common pioneer and non-pioneer species in a rainforest in Puerto Rico, following experimental manipulation of forest plots to simulate the two major effects of a hurricane (canopy opening and a detrital pulse). I expected that greater leaf production and leaf quality would result from canopy trimming and detritus (debris) addition to the forest floor, respectively, and that both treatments would enhance herbivory rates independently and especially in combination. I found a significant interaction of trim and debris treatments that affected plant species within pioneer and non-pioneer plant groups differently: a debris pulse or canopy trimming alone stimulated understory herbivory over time on non-pioneer and pioneer plants, respectively, but the combination of these two treatments had no effect on herbivory rates. Specifically, herbivory was higher on pioneer plants in plots where the canopy was trimmed but debris had not been added, whereas herbivory was higher on non-pioneer plants in plots where debris was added to the forest floor under intact canopy conditions. Therefore, different mechanisms apparently controlled herbivory of pioneer and non-pioneer species. Pioneer plants likely experienced enhanced herbivory in trimmed plots in part because of the increased densities of pioneer plants responding to canopy trimming; pioneer plants were temporarily less abundant in debris addition plots. Non-pioneer species may have experienced greater herbivory in debris addition plots in part because of increased foliar quality resulting from enhanced nutrient availability associated with the debris pulse. Future, complementary greenhouse and field mesocosm experiments that manipulate the factors likely contributing to these results would help to reconcile results from previous studies that have documented both increases and decreases in herbivory or certain herbivore taxonomic groups resulting from natural hurricanes. Understanding the mechanisms that affect herbivory after hurricanes is important because herbivory can affect nutrient cycling, plant community structure, and ultimately forest recovery after disturbance.

Population dynamics in canopy gaps: nonlinear response to variable light regimes by an understory plant

Gap-dependent species are typically understood to have higher population growth rates (λs) when they are exposed to higher light transmittance. I investigated the relationship between both diffuse light and direct light transmittance and λ for the gap-dependent plant Trollius laxus using 5 years of data from 20 subpopulations (11 in created, experimental canopy gaps; 9 in intact canopy control areas). There was a nonlinear (unimodal) relationship between diffuse light and λ for T. laxus under the wide range of light levels encountered at the gap and control subpopulations [4–58 % diffuse photosynthetic photon flux density (PPFD)]. There was no relationship between direct light and λ. However, in the gaps, where light levels were generally greater than 20 % PPFD, both diffuse light and direct light had strong negative linear relationships with λ. Therefore, under wide-ranging light regimes, plant populations may show complicated, nonlinear responses to gap formation. Furthermore, gap-dependent plant populations may even decline in the brightest gaps. These results demonstrate that future studies on forest plant population dynamics should strive to include populations from a wide variety of light regimes, and avoid broadly categorizing light regimes as simply “gap” or “non-gap.”

Understanding the key mechanisms of tropical forest responses to canopy loss and biomass deposition from experimental hurricane effects

To date, it is not clear which are the factors that most influence tropical forest recovery from hurricanes. Increased canopy openness and increased detritus (debris) deposition are two of the most likely factors, but due to their simultaneous occurrence during a hurricane, their relative effects cannot be separated without a manipulative experiment. Hence, in the Luquillo Experimental Forest (LEF) of Puerto Rico, the Luquillo Long-Term Ecological Research Program (LTER) has undertaken experimental manipulations in replicated 30×30m plots to simulate the major effects of hurricane disturbance–increased canopy openness and debris addition to the forest floor. Using a factorial experiment enabled investigation of the separate and combined effects of canopy opening and debris on this wet tropical forest; the experimental outcomes may help direct forest management decisions in similar disturbance-prone environments. In this first article of the special issue, we (1) provide details of the design and methodology for this manipulative experiment (the Canopy Trimming Experiment, CTE), (2) report some principal abiotic responses to treatments, and (3) introduce the subject areas of the 12 additional CTE manuscripts in this special issue. The physical conditions created by canopy and understory treatment and the amounts of debris added to CTE plots were similar to the LEF’s conditions following Hurricane Hugo (a category 4 storm) in 1989; although more wood and a 37% (1.5cm) deeper litter layer was present in the CTE. Our selective cutting and removal of the forest canopy above 3m, which included trimming 234 palm trees and 342 non-palm trees, greatly altered the understory micro-environment by increasing light levels and decreasing litter moisture for 18months; throughfall and soil moisture were elevated in trim plots for 3months. In plots where the canopy was trimmed and the debris (6kgm−2) was added to the forest floor, the canopy debris persisted on the forest floor for at least 4years; debris decomposed more quickly in plots with intact canopies. The diverse collection of papers in this special issue provide mechanistic understandings of response patterns of tropical forest biota (microbes, plants, animals) and processes (decomposition, herbivory, nutrient cycling, primary production) to canopy and understory disturbance that resembles a major (⩾category 3) hurricane. Although measurements for this experiment are on-going to further identify the mechanisms of long-term forest change resulting from hurricanes, we include findings up to the first seven years post-treatment at this time.

Coqui frog populations are negatively affected by canopy opening but not detritus deposition following an experimental hurricane in a tropical rainforest

Hurricanes, cyclones, and typhoons are common disturbances in many island and coastal forests. There is a lack of understanding of the importance to forest biota of the two major physical aspects that occur simultaneously during a hurricane: canopy disturbance and detritus (debris) deposition onto the ground. Using a replicated factorial design, our study involved experimentally determining the independent and interactive effects of canopy opening and debris additions to the forest floor on densities of coqui frogs (Eleutherodactylus coqui). Coquies are the dominant amphibian, and second most common vertebrate species, in the Luquillo Experimental Forest (LEF), a montane, tropical rainforest in northeastern Puerto Rico that frequently experiences hurricanes. Frogs were sampled in all twelve 30×30m plots at three periods prior to installing treatments (July 2003, January 2004, July 2004), and at months 1, 3, 6, and 12 post-treatment. The degree of canopy opening and amount of debris deposited onto the forest floor by our experimental treatments closely mimicked conditions resulting from Hurricane Hugo, a severe hurricane that passed over the LEF in 1989. Based on findings from past studies involving natural hurricanes in the LEF, we predicted that coqui densities would increase in response to debris additions, and decrease or remain unchanged in response to canopy disturbance. However, we found that debris deposition had no significant effect on coqui density and that the opening of the canopy was the dominant aspect affecting coqui by significantly reducing their densities. We identified several possible explanations for the decreased coqui densities in open-canopy plots, including decreased litter moisture and insect prey, and temporal and spatial scales associated with disturbance that may have influenced coqui behavior. Following natural hurricanes, and in light of our findings from experimental hurricane impacts, we expect that coquies benefit from patches of intact canopy while suffering reduced densities in open-canopy settings. Furthermore, based on our study and other experimental forest studies involving frogs, future forest practices that remove significant canopy should probably be viewed as having an initially (up to 1year) negative effect on the frog community.

Seven-year responses of trees to experimental hurricane effects in a tropical rainforest, Puerto Rico

We experimentally manipulated key components of severe hurricane disturbance, canopy openness and detritus deposition, to determine the independent and interactive effects of these components on tree recruitment, forest structure, and diversity in a wet tropical forest in the Luquillo Experimental Forest, Puerto Rico. Canopy openness was increased by trimming branches, and we manipulated debris by adding or subtracting the trimmed materials to the trimming treatments, in a 2×2 factorial design replicated in three blocks. Tree (stems ⩾1cm diameter at breast height) responses were measured during the 9-year study, which included at least 1year of pre-manipulation monitoring. When the canopy was trimmed, stem densities increased >2-fold and rates of recruitment increased >25-fold. Deposition of canopy debris did not markedly affect stem densities but did have small yet significant effects on tree basal area. Basal area increased about 10% when debris was added to plots with intact canopies; the other treatments exhibited smaller or no increases in basal area over time. Much of the dynamics of stem densities were due to changes in the smallest size class (1–2.5cm diameter), which responded with a pulse of recruitment in the canopy trimmed treatments, and a steady loss in plots with intact canopies. The decreases in stem densities in the plots with intact canopies is attributed to observed on-going forest thinning from the last natural severe hurricane disturbance in 1998. Given these repeated hurricane effects, our study enabled an experimental test of the Intermediate Disturbance Hypothesis (IDH), for which we predicted an increase in species diversity in canopy trimmed treatments and a loss of species in the treatments with intact canopies. Measured patterns of diversity gave partial support to the predictions of IDH, although raw species richness of sampled plots fit the predictions better than richness adjusted for differences in stem densities among treatments. Ordination of species responses in the community identified a guild of pioneer species responding to the trimmed treatments, but not the debris additions, amongst substantial background variation in species composition unrelated to the experimental treatments. These results are consistent with a growing consensus that, while trade-offs of resilience and resistance govern many species responses to hurricane disturbance, other environmental and historical factors are equally or more important in governing community dynamics in hurricane-disturbed forests.

Response of forest bird communities to forest gap in winter in southwestern China

Although forest gap ecology is an important field of study, research remains limited. By plot setting and point counted observation, the response of birds to forest gaps in winter as well as bird distribution patterns in forest gaps and intact canopies were studied in a north tropical monsoon forest of southwestern China from November 2011 to February 2012 in the Fangcheng Golden Camellia National Nature Reserve, Guangxi. The regression equation of bird species diversity to habitat factor was Y1=0.611+0.002 X13+0.043 X2+0.002 X5-0.003 X8+0.006 X10+0.008 X1 and the regression equation of bird species dominance index to habitat factor was Y3=0.533+0.001 X13+0.019 X2+0.002 X3-0.017 X4+0.002 X1. There were 45 bird species (2 orders and 13 families) recorded in the forest gap, accounting for 84.9% of all birds (n=45), with an average of 9.6 species (range: 2-22). Thirty-nine bird species (5 orders and 14 families) were recorded in non-gap areas, accounting for 73.6% of all birds (n=39), with an average of 5.3 species (range: 1-12). These results suggested that gap size, arbor average height (10 m from gap margin), arbor quantity (10 m from gap margin), shrub quantity (10 m from gap margin), herbal average coverage (1 m from gap margin) and bare land ratio were the key forest gap factors that influenced bird diversities. On the whole, bird diversity in the forest gap was greater than in the intact canopy. Spatial distributions in the forest gaps were also observed in the bird community. Most birds foraged in the "middle" and "canopy" layers in the vertical stratification. In addition, "nearly from" and "close from" contained more birds in relation to horizontal stratification. Feeding niche differentiation was suggested as the main reason for these distribution patterns.

Spatial heterogeneity in ecologically important climate variables at coarse and fine scales in a high-snow mountain landscape.

Climate plays an important role in determining the geographic ranges of species. With rapid climate change expected in the coming decades, ecologists have predicted that species ranges will shift large distances in elevation and latitude. However, most range shift assessments are based on coarse-scale climate models that ignore fine-scale heterogeneity and could fail to capture important range shift dynamics. Moreover, if climate varies dramatically over short distances, some populations of certain species may only need to migrate tens of meters between microhabitats to track their climate as opposed to hundreds of meters upward or hundreds of kilometers poleward. To address these issues, we measured climate variables that are likely important determinants of plant species distributions and abundances (snow disappearance date and soil temperature) at coarse and fine scales at Mount Rainier National Park in Washington State, USA. Coarse-scale differences across the landscape such as large changes in elevation had expected effects on climatic variables, with later snow disappearance dates and lower temperatures at higher elevations. However, locations separated by small distances (∼20 m), but differing by vegetation structure or topographic position, often experienced differences in snow disappearance date and soil temperature as great as locations separated by large distances (>1 km). Tree canopy gaps and topographic depressions experienced later snow disappearance dates than corresponding locations under intact canopy and on ridges. Additionally, locations under vegetation and on topographic ridges experienced lower maximum and higher minimum soil temperatures. The large differences in climate we observed over small distances will likely lead to complex range shift dynamics and could buffer species from the negative effects of climate change.

Decreased carbon limitation of litter respiration in a mortality-affected piñon–juniper woodland

Abstract. Microbial respiration depends on microclimatic variables and carbon (C) substrate availability, all of which are altered when ecosystems experience major disturbance. Widespread tree mortality, currently affecting piñon–juniper ecosystems in southwestern North America, may affect C substrate availability in several ways, for example, via litterfall pulses and loss of root exudation. To determine piñon mortality effects on C and water limitation of microbial respiration, we applied field amendments (sucrose and water) to two piñon–juniper sites in central New Mexico, USA: one with a recent (&lt; 1 yr), experimentally induced mortality event and a nearby site with live canopy. We monitored the respiration response to water and sucrose applications to the litter surface and to the underlying mineral soil surface, testing the following hypotheses: (1) soil respiration in a piñon–juniper woodland is water- and labile C-limited in both the litter layer and mineral soil; (2) piñon mortality reduces the C limitation of litter respiration; and (3) piñon mortality enhances the C limitation of mineral soil respiration. Litter respiration at both sites responded to increased water availability, yet surprisingly, mineral soil respiration was not limited by water. Consistent with hypothesis 2, C limitation of litter respiration was lower at the recent mortality site compared to the intact canopy site. Applications to the mineral soil showed evidence of reduction in CO2 flux on the girdled site and a non-significant increase on the control. We speculate that the reduction may have been driven by water-induced carbonate dissolution, which serves as a sink for CO2 and would reduce the net flux. Widespread piñon mortality may decrease labile C limitation of litter respiration, at least during the first growing season following mortality.

Bryophyte persistence following major fire in eucalypt forest of southern Australia

The significance of variation in fire severity is not well understood for bryophyte species richness and composition. This is despite fire being a major factor in determining bryophyte richness and composition in temperate forests. We documented the species richness of mosses and liverworts in 42 sites of Mountain Ash (Eucalyptus regnans) forest in eastern Australia. We compared two age classes: long unburned stands and 72year old stands following a major fire in February 2009. Within these two age classes, we surveyed sites of contrasting fire severity: (1) unburned, (2) subject to moderate severity fire (intact canopy) and (3) subject to high severity fire (burned canopy). At each site, we surveyed bryophytes in 10m×100m transects, which was large enough to include a variety of microhabitats. Roughly 60% of the variation in species richness (r2=0.61, p<0.001) and composition (R=0.57, p<0.001) was explained by fire severity. High severity fire removed all bryophytes and only pioneer species were present 2years later. In contrast, the moderate severity fire sites were often species rich because they harboured pioneer bryophytes and species associated with long unburned forest. A key finding was the importance of small unburned patches that contained understorey trees and logs for boosting bryophyte richness. Practices such as salvage logging that remove biological legacies are inconsistent with the conservation of bryophyte diversity in this landscape.

Occurrence of the Sunda colugo (Galeopterus variegatus) in the tropical forests of Singapore: A Bayesian approach

Dermopterans are taxonomically-unique mammals, but little is known about their habitat requirements. The Sunda colugo (Galeopterus variegatus), which is one of only two living species of dermopterans confined to Southeast Asia, reportedly occurs in tropical forests, plantations, and gardens. Based on their ecology, however, we predict that tropical forests are likely to be their primary habitats. Here, we investigate environmental variables that account for the occurrence of G. variegatus in Singapore using Bayesian inference. Our results show that G. variegatus was only detected in transects with over 95% canopy cover, which was ultimately the most important predictor of colugo occurrence. Tropical forests, including disturbed forests, with relatively intact canopies are therefore vital for colugos to persist.

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.

Impact of invasion of Acer platanoides on canopy structure and understory seedling growth in a hardwood forest in North America

Invasion by exotic plant species is known to affect native communities and ecosystems, but the mechanisms of the impacts are much less understood. In a field study, we examined the effects of a tree invader, Acer platanoides (Norway maple, NM), on canopy structure and seedling growth in the understory of a North American deciduous forest. The experimental site contains a monospecific patch of A. platanoides and a mixed patch of A. platanoides with its native congener, A. rubrum (red maple, RM). In the study, we examined canopy characteristics of three types of trees in the forests, i.e., RM trees in the mixed forest, NM trees in the mixed forest, and NM trees in its monospecific patch. Height growth and biomass production of RM and NM seedlings under intact canopies and newly created gaps of the three types of trees were followed for two growing seasons. We found that removal of half of the canopy from focal trees increased canopy openness and light transmission to the forest floor, but to a greater extent under NM trees than under RM trees. Seedlings of these two Acer species varied greatly in biomass production under canopies of the same type of trees and in their responses to canopy opening. For example, seedlings of the exotic NM grown under the native RM trees in the mixed forests increased biomass production by 102.4% compared to NM seedlings grown under conspecific trees. The native RM seedlings grown under NM trees, however, reduced biomass production by 23.5% compared to those grown under conspecific trees. It was also observed that RM was much more responsive in biomass production to canopy opening than NM. For instance, total seedling biomass increased by 632.2% in RM, but by only 134.6% in NM in response to the newly created gaps. In addition, we found that NM seedlings allocated a greater portion of biomass below-ground as canopy openness increased, whereas the same trend was not observed in RM seedlings. Our results thus demonstrated that invasion of NM significantly altered canopy structure and community dynamics in the hardwood forest. Because the exotic NM seedlings are able to grow well under the native RM trees, but not vice versa, NM will likely expand its distribution in the forests and make it an ever increasingly serious tree invader in its non-native habitats, including North America.