Canopy Removal Research Articles

Impacts of Vegetation Removal on Urban Mediterranean Stream Hydrology and Hydraulics

Given the widespread presence of non-native vegetation in urban and Mediterranean watersheds, it is important to evaluate how these sensitive ecosystems will respond to activities to manage and restore native vegetation conditions. This research focuses on Del Cerro, a tributary of the San Diego River in California, where non-native vegetation dominates the riparian zone, creating flooding and fire hazards. Field data were collected in 2018 to 2021 and consisted of water depth, streamflow, and stream temperature. Our data set also captured baseline conditions in the floodplain before and after the removal of burned non-native vegetation in November 2020. Observed changes in hydrologic and geomorphic conditions were used to parameterize and calibrate a two-dimensional hydraulic model to simulate urban floodplain hydraulics after vegetation removal. We utilized the U.S. Army Corps of Engineers’ Hydrologic Engineering Center River Assessment System (HEC-RAS) model to simulate the influence of canopy loss and vegetation disturbance and to assess the impacts of vegetation removal on stream restoration. We simulated streamflow, water depth, and flood extent for two scenarios: (1) 2019; pre-restoration where non-native vegetation dominated the riparian area, and (2) 2021; post-restoration following the removal of non-native vegetation and canopy. Flooding after restoration in 2021 was more frequent compared to 2019. We also observed similar flood extents and peak streamflow for storm events that accumulated half the amount of precipitation as pre-restoration conditions. Our results provide insight into the responses of small urban stream reaches to the removal of invasive vegetation and canopy cover.

Soil nutrients mediate the indirect effects of shrub canopy removal: How distance from shrubs affects the herbs and grasses community in a shrub‐encroached grassland

AbstractUnderstanding community processes is essential to predict community dynamics and succession processes. To explore how shrub canopy removal frequency (hereafter ‘removal frequency’) and distance from shrubs affect herbs and grasses community assembly in a shrub‐encroached grassland, we carried out a 4‐year shrub canopy removal experiment with three removal frequencies (no removal, removal once, and removal twice per year) in a Caragana microphylla shrub‐encroached grassland, and assessed community assembly mechanisms directly beneath shrubs (0 m from shrubs, i.e., in the centre of the shrub) and in shrub interspaces (at least 2 m from shrubs) under each removal frequency treatment using both functional trait‐based and phylogenetic‐based approaches. Removal frequency positively affected standard effect sizes (SESs) of the mean pairwise distance (MPD) for multi‐trait, specific leaf area (SLA) and leaf dry matter content (LDMC), denoted by SES.MPDMulti‐trait, SES.MPDSLA, and SES.MPDLDMC, indirectly via regulating soil nitrogen (N) and soil carbon (C) content, while it negatively affected SES.MPDHeight indirectly via regulating soil available phosphorus (P) content. Distance from shrubs negatively affected SES.MPDHeight indirectly via regulating soil available P content, and negatively affected SES.MPDLDMC indirectly via regulating soil C content. The trait‐based approach was more powerful than the phylogenetic‐based one in explaining the responses of community assembly processes to environmental changes. These findings highlight the importance of shrub canopy removal and distance from shrubs in affecting soil nutrient status and consequently community assembly processes, which provides a new insight into how canopy removal or fertile island effects affect community assembly in the shrub‐encroached grassland regions.

Independent Effects of Species Removal and Asynchrony on Invariability of an Intertidal Rocky Shore Community

Ecological stability depends on interactions between different levels of biological organization. The insurance effects occur when increasing species diversity leads to more temporally invariable (i.e., more stable) community-level properties, due in part to asynchronous population-level fluctuations. While the study of insurance effects has received considerable attention, the role of dominant species that contribute with particular functional traits across different level of organizations is less understood. Using a field-based manipulative experiment, we investigated how species richness and different types of parameters at the population level, such as the invariability of dominants, population invariability, and population asynchrony, influence the community invariability. The experiment involved the repetitive removal of the canopy forming algaMazzaella laminarioides(hereafter “Mazzaella”) during 32 months in two rocky intertidal sites of northern-central Chile. We predicted that the invariability of dominants enhances community invariability, that the effect of multispecies population-level parameters on community invariability are dependent on species richness, and that subdominant algae are unable to fully compensate the loss of canopies of the dominant species. Biomass of algae and mobile invertebrates was quantified over time. We observed independent effects ofMazzaellaremoval and community-wide asynchrony on community invariability. While canopy removal reduced community invariability, population asynchrony boosted community invariability regardless of the presence of canopies. In addition, filamentous and foliose algae were unable to compensate the loss of biomass triggered by the experimental removal ofMazzaella. Canopy removal led to a severe decrement in the biomass of macrograzers, while, at the same time, increased the biomass of mesograzers. Asynchrony stemmed from compensatory trophic responses of mesograzers to increased abundances of opportunistic algae. Thus, further work on consumer-resource interactions will improve our understanding of the links between population- and community-level aspects of stability.

Can’t see the flowers for the trees: factors driving floral abundance within early-successional forests in the central Appalachian Mountains

Silviculture can be a powerful tool for restoring and enhancing habitat for forest-dependent wildlife. In eastern North America, regenerating timber harvests support abundant wildflowers that provide essential forage for native pollinators. Factors driving floral resource availability within regenerating forests remain almost entirely unstudied. Recent efforts to increase the area of regenerating forests (<10 years old) through overstory removal harvest in the central Appalachian Mountains provide an opportunity to investigate the development of forest wildflower communities following canopy removal. We conducted 1208 surveys of blooming plants across 143 harvests, recording 1 525 245 flowers representing 220 taxa spanning 47 families. The number of flowers within recently harvested stands was negatively associated with fern and sapling cover but positively associated with grass and bramble ( Rubus spp.) cover. Early in the growing season, more flowers bloomed in older regenerating stands (e.g., >5 years old), but this pattern reversed by the end of the growing season. Ultimately, our study demonstrates that the abundance of flowers available to pollinators within regenerating hardwood stands varies with factors associated with advancing succession. Recognizing the potential trade-off between woody regeneration (i.e., saplings) and pollinator forage availability may benefit forest managers who intend to provide floral resources to flower-dependent wildlife like pollinators via silviculture.

Application of swat hydrological model to assess the impacts of land use change on sediment loads

Controlling and reducing the watershed's erosion and sedimentation is essential to ensure the continuity of projects implemented to develop land and water resources and improve sustainability, performance, and longevity. Sediment control is also critical in managing the river basin in limiting the transport of solids, improving water quality, sustaining aquatic life, and preventing damage to downstream aquatic environments and ecosystems. Estimating the potential effects of land-use changes on surface runoff and soil erosion requires distributed hydrological modeling methods. In addition to naturally occurring sediments, changes in land-use types for different applications can be a primary cause for the increase in sediment rates in the watershed. This study used the Soil and Water Assessment Tool (SWAT), a rainfall-runoff model, to evaluate land use/cover changes (i.e., deforestation) and their impact on sediment load under different scenarios. For the baseline (no changes) scenario, the watershed is calibrated using the flow and sediment data measured from the rain gauge station during the time step to estimate the post-deforestation changes at the sub-catchment scale of the study area. The study results indicated that the total surface runoff and sediment yield for the selected sub-catchment in the deforestation scenario with the highest spatial distribution, due to the high erosivity (24% increase) of excessive surface runoff after deforestation, sediment yield increased 3.5-fold. In contrast, due to the removal of trees and vegetation's canopy, the evapotranspiration, leaf area index, and dissolved oxygen transported into reach showed the inverse ratios, and the values decreased by 5%, 24, and 17%, respectively, in compared with the baseline scenario. In terms of watershed management, therefore, the application of hydrological models such as SWAT rainfall-runoff and erosion models can be a helpful method for decision-makers to apply for the protection of forests from intensive impacts such as deforestation and limiting their socio-environmental effects.

Carbon dioxide fluxes of a mountain grassland: Drivers, anomalies and annual budgets

The potential of grasslands to mitigate climate change by carbon (C) sequestration in soils depends on agricultural management and the response of the grassland C cycle to a warming and more variable climate. A 15-year time series of eddy covariance carbon dioxide (CO2) flux measurements on a medium-intensively managed grassland at 1000 m above sea level in Switzerland was analysed to assess how CO2 fluxes respond to environmental drivers as well as grazing and cutting events. Further, the effects of management, recent warming trends and anomalous weather conditions on the annual C sequestration potential were assessed. To this end, C budgets including atmospheric and management-related C fluxes (fertilization, cutting/grazing) were estimated. Generally, the main environmental drivers of CO2 fluxes were light and temperature. The removal of the aboveground canopy by management significantly reduced photosynthesis and induced a saturation in the photosynthetic response to light at lower intensities compared to periods without management. Ecosystem respiration remained largely unaffected by management. With a net ecosystem exchange of −357 (± 76) g C m−2 year−1 and a net biome production of −154 (± 80) g C m−2 year−1 (including management C fluxes), the grassland on average acted as a net C sink. Recent climate warming favors spring CO2 assimilation due to earlier starting vegetation periods. However, the warming also resulted in an increased ecosystem respiration. Further, anomalous and especially unfavorable weather conditions for photosynthesis and regrowth following harvest events induced several periods of an anomalously increased net CO2 release. In the year 2015, such release anomalies contributed to an annual net C loss. Under future climatic conditions, the C sequestration potential at the mountain site will depend on the extent to which spring photosynthesis is offset by such climate-management interactions and a warming-induced increase in ecosystem respiration.

Lidar Inspection for Indigenous Architecture at Caguana Ceremonial Complex, Borikén

The virtual removal of forest canopies through light detection and ranging (lidar) has enhanced archaeological interpretations of settlement patterns in tropical zones. Although lidar collections of Indigenous landscapes in the Caribbean Archipelago are limited, resolutions from open-access lidar datasets reveal coarse regional settlement patterns and large-scale architecture planning. In this article we inspect the Caguana Ceremonial complex in Utuado, Borikén (Puerto Rico), using a 2016 lidar dataset available through the National Oceanic and Atmospheric Administration portal. Visual comparisons between known Indigenous sites, surface anomalies, and site inspections in the three sectors under study identified plazas, possible ancient paths into the Caguana complex, a possible agricultural area west of the site, and the ANG-4 site. This study, the first application of lidar inspections in Puerto Rican archaeology, demonstrates that open-access data can help guide research and save time in field surveys, thus improving our ability to protect the Indigenous cultural heritage hidden under forest canopies.

Macroalgal canopies reduce beta diversity in intertidal communities

Abstract Species diversity in a habitat is often termed alpha diversity. As it influences various community properties, many studies have investigated its drivers. For instance, intertidal macroalgal canopies limit understory thermal stress during low tides and thus often increase alpha diversity. More recently, beta diversity has also become of interest. Beta diversity measures the change in species composition across space and is another important attribute of communities because it influences their multifunctionality, productivity, and resilience. Using data from a field experiment done in Atlantic Canada, we tested the hypothesis that fucoid macroalgal canopies limit beta diversity in intertidal communities. This prediction stems from previous evidence that such canopies limit thermal variation across the substrate during low tides, an important consideration because spatial thermal changes influence spatial variability in species composition. To test our hypothesis, we compared two treatments (full canopy cover and canopy removal) created the year before on intertidal areas that were originally all fully covered by canopies. Separately for each treatment, we calculated beta diversity as the Bray-Curtis dissimilarity between nearby quadrats using species abundance data. Overall, fucoid macroalgal canopies significantly reduced beta diversity, showing that these foundation species can have opposing effects on alpha and beta diversity.

Coral Forests: How Mangroves Provide Refuge to Corals from Light Stress on the Shallow Reef

Given increasing reports of corals living among roots under mangrove canopies, we used field surveys and reciprocal transplants to test the hypothesis that mangroves are a refuge for corals from the high solar irradiance and temperatures of adjacent shallow reefs. We found that live coral cover and species richness in mangroves rivaled or exceeded that of reefs. Our experimental manipulation of light in mangroves and on adjacent reefs indicated that light intensity is a key environmental parameter mediating coral bleaching and survival. We suggest the role of mangroves acting as coral refugia will become increasingly important with global climate change. Photo 1: Large Siderastrea siderea coral colony observable just below the water’s surface under the mangrove canopy. These large corals can make up 15–51% of the coral cover in the mangrove forest of Bocas del Toro, Panama. Surveying the corals within the mangrove forest requires both snorkeling and climbing the trees to avoid harming the corals growing in the shallow water. Photo credit: Heather A. Stewart, McGill University/Smithsonian Tropical Research Institute. Photo 2: To characterize the coral community in the mangrove forest and adjacent shallow reef, coral surveys were conducted with 1-m2 quadrats quantifying cover, richness, diversity, abundance, and identity of live coral species. Photo credit: Heather A. Stewart, McGill University/Smithsonian Tropical Research Institute. Photo 3: Treatments included natural conditions in each of these habitats, plus experimental addition of shading on the reef to mimic the mangrove canopy, and experimental removal of the mangrove canopy to mimic light conditions on the reef. The corals represented two species observed more frequently in mangroves (Montastraea cavernosa and Pseudodiploria clivosa), two species observed more frequently on the reef (Diploria labyrinthiformis and Porites astreoides), and two that were observed in similar frequency in both habitats (Colpophyllia natans and Orbicella faveolata). We found that the proportion of coral bleaching and mortality increased with light intensity across all coral species except Diploria labyrinthiformis. Photo credit: Heather A. Stewart, McGill University/Smithsonian Tropical Research Institute. Photo 4: Close-up of Montastraea cavernosa colony with polyps extended within the mangrove canopy. This coral species typically grows in a plate morphology and with coloration such as blue or green hues that differ from domed morphology and red, yellow, or brown hues on the adjacent reef, indicating some differences in traits associated with light conditions under the canopy. Photo credit: Heather A. Stewart, McGill University/Smithsonian Tropical Research Institute. These photographs illustrate the article “Caribbean mangrove forests act as coral refugia by reducing light stress and increasing coral richness” by Heather A. Stewart, David I. Kline, Lauren J. Chapman, Andrew H. Altieri published in Ecosphere. https://doi.org/10.1002/ecs2.3413.

Managing climate change microrefugia for vascular plants in forested karst landscapes

Microrefugia are small areas that support favourable climate and allow species to persist during regional and global climate changes. Dolines in karst landscapes may provide such areas for many climate change-vulnerable species. Here we provide a better understanding on how plant species indicate changes in their environment (temperature, soil moisture and light availability) after a few years of partial canopy removal from dolines and their close surroundings (logged areas: >1 ha). We place our results in the context of the most widely used forest management practices within the study area (Mecsek Mts, Hungary), in addition to presenting a general framework for the maintenance of doline microrefugia in forested karst landscapes. Three types of habitats were investigated: dolines before logging, dolines after logging, and the forested plateau. Three large dolines and three sites on the plateau were selected for vegetation sampling. All dolines were sampled before logging and 5–10 years after partial canopy removal. Logging resulted in a 50–80% reduction of canopy cover in the dolines and their close surroundings. We established a transect across each doline from north to south passing through doline bottoms, and across each plateau site. We estimated the percentage cover of vascular plant species (tree saplings – up to 1 m in height, shrubs and herbs) along the transects using 1 m × 1 m vegetation plots, determined the diagnostic species of the doline and plateau habitats, and used multivariate methods and linear mixed-effects models during analyses. Plant species indicated clear gradients of the main microclimatic factors within the dolines and that significant changes took place after logging. Canopy removal caused substantial changes in the main microclimatic factors of most doline microhabitats (e.g., south-facing slopes). The vegetation of the dolines before logging indicated moister conditions than that of the plateau and cooler and shadier conditions than that of the dolines after logging. These and our previous results suggest that logging may directly and indirectly influence dolines to be microrefugia under global warming. By applying our framework to refugia conservation and management for the karst landscape in the Mecsek Mts, we can conclude that the protection of old forests and natural forest dynamics in as many large dolines as possible and the implementation of close-to-nature forestry practices may be essential to maintain regional biodiversity in the long run.

Effects of Rhododendron removal on soil bacterial and fungal communities in southern Appalachian forests

Rhododendron maximum, a native ericaceous evergreen shrub, is expanding in forests of the southern Appalachian region following eastern hemlock (Tsuga canadensis) mortality due to hemlock woolly adelgid (Adelges tsugae) infestations. The goal of our study was to examine soil microbial community responses to experimental R. maximum removal treatments. The experiment was implemented as a 2 × 2 factorial design, including two R. maximum canopy removal levels (cut vs. not cut) combined with two forest floor removal levels (burned vs. not burned). These treatments were designed as potential management strategies to facilitate hardwood tree establishment in forests that have experienced T. canadensis declines. We sampled soils after removals and characterized bacterial and fungal communities using amplicon sequencing. Shrub removal did not affect bacterial or fungal α diversity but did affect both bacterial and fungal community composition. Relative abundances of bacterial phyla and fungal classes exhibited no differences among R. maximum removal treatments. However, specific bacterial and fungal taxa that were responsive to R. maximum removal (i.e., differentially abundant sequences) did exhibit clear patterns at high taxonomic levels. Specifically, taxa that responded negatively to R. maximum removal were found primarily in two bacterial phyla (Proteobacteria and Bacteroidetes) and one fungal class (Archaeorhizomycetes) while positive responders were clustered in several other bacterial phyla (e.g., Actinobacteria, Planctomycetes, Cyanobacteria). Fungal functional guilds also responded to R. maximum removal, including negative responses of ericoid mycorrhizae and positive responses of arbuscular mycorrhizae and wood saprotrophs. Effects of R. maximum removal on soil microbial communities were minor overall, but clear effects on some key functional groups were evident (i.e., mycorrhizal fungi), suggesting that microbial responses to R. maximum removal may influence recovery of forests in the southern Appalachian region.

Nitric acid dry deposition associated with equilibrium shift of ammonium nitrate above a forest by long-term measurement using relaxed eddy accumulation

The dry deposition process of nitrogen compounds still has considerable uncertainty due to the complex compound behavior in the atmosphere. To enhance understanding of the nitric acid (HNO3) dry deposition process that largely contributes to the total nitrogen deposition, we associate this process with the equilibrium shift of ammonium nitrate (NH4NO3) to HNO3 and ammonia (NH3) near the surface. We obtained the flux of HNO3 and PM2.5 components above a forest in suburban Tokyo using a relaxed eddy accumulation (REA) system incorporating the denuder/filter-pack sampling technique. We conducted continuous samplings on a weekly basis over a long-term period, from October 14, 2016 to October 3, 2018, including leafy and leafless conditions. The measured deposition velocities of fine NO3− particles were significantly (p < 0.05) larger than those of fine SO42− particles and similar to those of HNO3, regardless of the leafy and leafless periods. The larger deposition velocities of fine NO3− particles caused by the equilibrium shift of NH4NO3 were found to be similar to previous measurements at the same site. The measured deposition velocities of HNO3 were low and included many emission cases compared to those of fine NO3− particles. The lower HNO3 deposition velocities were associated with the equilibrium shift of NH4NO3 to the gas phase, causing the suppressed deposition and apparent emission of HNO3, particularly during the leafless period. The emission of HNO3 is possibly due to high HNO3 concentration near the surface, which is attributed to a small removal of the leafless canopy. The turbulence enhanced both the upward and downward fluxes of HNO3. These results will contribute to the better understanding for the dynamics of the nitrogen compounds in the atmosphere and the accurate assessment for the nitrogen deposition.

Drought stress and hurricane defoliation influence mountain clouds and moisture recycling in a tropical forest

Mountain ranges generate clouds, precipitation, and perennial streamflow for water supplies, but the role of forest cover in mountain hydrometeorology and cloud formation is not well understood. In the Luquillo Experimental Forest of Puerto Rico, mountains are immersed in clouds nightly, providing a steady precipitation source to support the tropical forest ecosystems and human uses. A severe drought in 2015 and the removal of forest canopy (defoliation) by Hurricane Maria in 2017 created natural experiments to examine interactions between the living forest and hydroclimatic processes. These unprecedented land-based observations over 4.5 y revealed that the orographic cloud system was highly responsive to local land-surface moisture and energy balances moderated by the forest. Cloud layer thickness and immersion frequency on the mountain slope correlated with antecedent rainfall, linking recycled terrestrial moisture to the formation of mountain clouds; and cloud-base altitude rose during drought stress and posthurricane defoliation. Changes in diurnal cycles of temperature and vapor-pressure deficit and an increase in sensible versus latent heat flux quantified local meteorological response to forest disturbances. Temperature and water vapor anomalies along the mountain slope persisted for at least 12 mo posthurricane, showing that understory recovery did not replace intact forest canopy function. In many similar settings around the world, prolonged drought, increasing temperatures, and deforestation could affect orographic cloud precipitation and the humans and ecosystems that depend on it.

Intertidal Canopy-forming Seaweeds Modulate Understory Seaweed Photoprotective Compounds.

Foundation species provide physical structure that enhances the diversity and abundance of associated organisms. Canopy-forming seaweeds are known to act as foundation species on rocky shores by lowering temperature and desiccation stress. Direct solar radiation, including ultraviolet (UV) light, can also reduce photosynthetic rates in algae, cause oxidative stress and DNA damage. The reduction in UV exposure provided by an algal canopy could therefore be important for understory organisms, including the red alga Chondrus crispus on New England's (USA) rocky shores, and this relationship may be more important at higher tidal elevations with increased low-tide exposure time. In field experiments, we investigated the relationship between tidal elevation and an index of C. crispus UV exposure, the concentration of UV-absorbing pigments. Low on the shore, C. crispus grew without a canopy. Higher on the shore, in the mid-intertidal zone, C. crispus was found under the canopy-forming rockweed, Fucus distichus subsp. evanescens. At this elevation, C. crispus was shaded (>50%; >1m above MLLW). We performed a canopy removal experiment that spanned the mid-zone where C. crispus and F. distichus subsp. evanescens co-occur and the low-zone (no canopy). Following canopy removal in the mid-zone, UV pigment concentrations increased with tidal elevation. After accounting for the effect of elevation, removal of the algal canopy resulted in UV-protective pigment concentrations 2-fold higher than in un-manipulated control plots. These results suggest that amelioration of solar UV exposure might be another mechanism by which canopy seaweeds, acting as foundation species, facilitate understory seaweeds on rocky shores.

Removing riparian Rhododendron maximum in post-Tsuga canadensis riparian forests does not degrade water quality in southern Appalachian streams

In the past century, the evergreen woody shrub, Rhododendron maximum, has experienced habitat expansion following foundational tree species die-off in eastern US deciduous forests. Rhododendron can potentially alter stream chemistry, temperature, trophic dynamics, and in-stream decomposition rates, given its dominance in riparian areas. Here we conducted two operational-scale (3 ha) riparian treatments that removed rhododendron through cutting alone (CR, canopy removal), or removing both the rhododendron canopy and forest floor using cutting and prescribed fire (CFFR, canopy and forest floor removal). We expected that rhododendron shrub removal, with or without soil organic horizon removal, would increase soil nutrient availability and subsequently alter stream pH, acid neutralizing capacity (ANC), inorganic nitrogen (NO3-N, NH4-N), total dissolved inorganic nitrogen, dissolved organic carbon (DOC), calcium (Ca), potassium (K), and magnesium (Mg). We hypothesized that responses would occur more quickly in the CFFR treatment. Treatments reduced shrub-, but not tree basal area. Treatments lowered soil N, but not C. Stream chemistry responses to treatments varied between CR and CFFR and were transient, generally with pH, N, and some cations declining, and aluminum (Al) and DOC showing a pulse increase. By removing rhododendron, the remaining deciduous trees likely accelerated N uptake as soil moisture availability increased. This could partially explain why we observed lower than expected stream nutrients (NO3-N, Ca, and Mg) after treatments. Initial rhododendron slash on the forest floor coupled with incomplete consumption of the O-horizon on the CFFR treatment likely elevated DOC in the upper soil horizons and mobilized Al. From a management perspective, using these treatments to restore structure and function to riparian forests in the wake of eastern hemlock mortality, with or without fire, would most likely not result in short-term diminished water quality that is common when overstory trees are harvested and may even lower stream NO3-N concentrations long term.

Restoring native forests from Pinus radiata plantations: Effects of different harvesting treatments on the performance of planted seedlings of temperate tree species in central Chile

Extensive areas of native vegetation have been cleared to establish commercial exotic tree plantations in south-central Chile, a region known as a world biodiversity hotspot. Despite increasing societal demands to restore native forests in parts of the landscape, documented experiences for this form of restoration are lacking. We conducted a landscape-replicated experiment to test the influence of different harvesting treatments (clearcut, strip-cutting and unharvested control) on the early establishment of native tree species in 20-year-old Pinus radiata plantations. Group plantings of shade-intolerant (Nothofagus dombeyi; Nothofagus obliqua), semi-tolerant (Nothofagus alpina; Laurelia sempervirens) and shade–tolerant species (Aextoxicon punctatum; Cryptocarya alba) were established across the treatments, and seedling performance and water status were monitored during the first two growing seasons. Mean survival was significantly higher in the strip-cuttings (77%) and control (70%) than in the clearcuts (38%), while mean height and root collar diameter growth were significantly higher in the strip-cuttings (16 cm year−1; 0.2 cm year−1) and clearcuts (16 cm year−1; 0.2 cm year−1) than in the control (5 cm year−1; 0.1 cm year−1). Shade-intolerant and semi-tolerant species showed the highest growth responses to openings. Leaf water potential was significantly higher in seedlings in the strip-cuttings than those in the control and clearcuts, and stomatal conductance was significantly higher in the strip-cuttings and clearcuts than in the control. Higher seedling performances and lower water stress in the strip-cutting treatment suggest that partial canopy removal is a suitable method for artificial regeneration of native tree species with different shade tolerances for native forest restoration from P. radiata plantations.

Responses of Watsonia fourcadei and other geophytes to burning and slashing treatments in South Outeniqua Sandstone Fynbos

The often mass flowering of Watsonia and other geophyte species in the first year after a fire in the South African fynbos vegetation is well known, but it has rarely been quantified. Many fynbos geophytes also flower after the fynbos canopy was physically removed, but these flowering responses have also not been quantified. A study comparing the flowering response of geophytes after physical removal versus fire removal of the fynbos canopy was conducted to establish to what degree these species are fire dependant. It was also done to improve our understanding of fynbos geophyte ecology, especially towards establishing if the flowering response of these plants is due to fire related factors per se, or not.Vegetative growth, flowering response, seed set and seedling establishment of Watsonia fourcadei were recorded after two treatments, burning and physical removal of vegetation (slashing) in two veld ages (5- and 16 years). Responses of other co-occurring geophytic species to these treatments were also recorded. The number of vegetatively active W. fourcadei plants doubled and flowering percentage increased from 2.3% to 38.7% in the first year after the fire. In the second year after the fire the number of vegetatively active W. fourcadei plants was similar to those in the first year after the fire, but flowering percentage decreased to pre-fire levels. About 50% of W. fourcadei plants were dormant 5 years after the fire and > 90% were dormant in 16-year old fynbos. Flowering percentages of W. fourcadei in slashed 5-year old fynbos did not differ significantly from burned 16-year old fynbos. The flowering stimulus of W. fourcadei was thus not due to fire associated factors per se. Seed predation of W. fourcadei seed capsules decreased from 46.9% before the fire to 7.1% after the fire. Number of viable seed released increased from 15.8 seed mˉ² pre-fire to 1170.5 seed mˉ² post-fire and 233.1 seedlings mˉ² established after the fire. The 74-fold increase in seed release in the burned fynbos could not be ascribed to higher cross pollination success as about 40% of the flowers were autogamous. The number of vegetatively active geophytic species increased from 2.3 species mˉ² pre-fire to 7.9 species mˉ² post-fire in 16-year old burned fynbos and 4.0 species mˉ² in the slashed fynbos. Most (76%) of these geophytic species flowered after the fynbos was burned and 24% of the species flowered in the slashed fynbos. Only some of the geophytic species were thus dependent on fire to stimulate flowering. A repeated short cycle disturbance regime (ca. 5 years) of burning and/or slashing may result in a super-abundance of Watsonia plants that can displace smaller geophytic species. Previous hypotheses on proximate reasons for the Watsonia post-fire flowering that are rejected are: (i) greater visibility of the plants; (ii) heating of the soil and corms by fire and; (iii) increased availability of phosphorous and/or other minerals in the post-fire environment. Smoke as a factor to induce flowering in W. fourcadei growing under natural conditions is questioned.

Effects of canopy cover and neighboring vegetation on the early development of planted Austrocedrus chilensis and Nothofagus dombeyi in north Patagonian degraded forests

Austrocedrus chilensis and Nothofagus dombeyi, are endemic forest species of ecological and productive importance in the Andean-Patagonian region of Argentina. Both species grow in pure or mixed stands. In the last decades, several A. chilensis stands have been degraded by different disturbances that have compromised their natural regeneration. Plantation of seedlings of both species may be an alternative to help restore degraded A. chilensis stands. In this study we determined, in degraded A. chilensis stands grown in a xeric and a mesic site, the effects of canopy cover, the presence/absence of neighboring herbaceous vegetation and the interaction between these factors, on the performance (i.e. survival and growth) of planted N. dombeyi and A. chilensis seedlings, during three growing seasons. Results showed that in both xeric and mesic sites, survival and growth of either species were reduced when canopy cover was below 30%. Removal of neighboring vegetation improved survival of both species at the xeric site, and improved growth of both species at the mesic site. Canopy cover and removal of neighboring vegetation seem to interact by improving survival and growth of A. chilensis, while for N. dombeyi the effects of these factors, when present, are independent, both improving survival and growth. Austrocedrus chilensis has greater capacity than N. dombeyi to tolerate the high radiation and low soil moisture combination, so this species is more recommendable for planting at most exposed conditions (no canopy cover at xeric sites), but both species could be successfully used for restoring degraded A. chilensis stands.

Impact of fire on montane snowpack energy balance in Snow Gum forest stands

Forest stands fundamentally alter hydrology of a region through impacting area micrometeorology and corresponding variability in snow accumulation and melt. Bushfires significantly change these interactions through removal of forest canopy, darkening of tree stems, and post-fire stem decay. This study quantified the impact of pre- and post-bushfire E. pauciflora (Snow Gum) forest stands on snowpack energy balance in the Snowy Mountains of Southeast Australia. Forest canopy cover in undisturbed forest stands moderated snowpack energy exchange through reductions to incoming shortwave radiation and turbulent fluxes. Energy flux to the snowpack was at a maximum in the fire-disturbed forest due to lower snowpack albedo resulting in greater net shortwave radiation and an increased sensible heat emission from decaying tree stems. The fire-disturbed forest also experienced the largest evaporation rate with 8.1% of snowpack SWE being lost to the atmosphere. Dominant energy fluxes to the snowpack were shortwave radiation in the unforested area and fire-disturbed forest stand, and sensible heat in the undisturbed forest stand.

More severe disturbance regimes drive the shift of a kelp forest to a sea urchin barren in south-eastern Australia

Climate change is influencing the frequency and severity of extreme events. This means that systems are experiencing novel or altered disturbance regimes, making it difficult to predict and manage for this impact on ecosystems. While there is established theory regarding how the frequency of disturbance influences ecosystems, how this interacts with severity of disturbance is difficult to tease apart, as these two are inherently linked. Here we investigated a subtidal kelp (Ecklonia radiata) dominated community in southern Australia to assess how different disturbance regimes might drive changes to a different ecosystem state: sea urchin barrens. Specifically, we compared how the frequency of disturbance (single or triple disturbance events over a three month period) influenced recruitment and community dynamics, when the net severity of disturbance was the same (single disturbance compared to triple disturbances each one-third as severe). We crossed this design with two different net severities of disturbance (50% or 100%, kelp canopy removal). The frequency of disturbance effect depended on the severity of disturbance. When 50% of the canopy was removed, the highest kelp recruitment and recovery of the benthic community occurred with the triple disturbance events. When disturbance was a single event or the most severe (100% removal), kelp recruitment was low and the kelp canopy failed to recover over 18 months. The latter case led to shifts in the community composition from a kelp bed to a sea-urchin barren. This suggests that if ecosystems experience novel or more severe disturbance scenarios, this can lead to a decline in ecosystem condition or collapse.