The effect of emerald ash borer-caused tree mortality on the invasive shrub Amur honeysuckle and their combined effects on tree and shrub seedlings

Invasive insects and plants are major threats to the health and viability of North American forests. Emerald ash borer (Agrilus planipennis) (EAB) may cause extensive changes to forest composition due to rapid ash (Fraxinus spp.) mortality. Invasive shrubs like Amur honeysuckle (Lonicera maackii) may benefit from EAB and have negative effects on woody seedlings. We predict that ash mortality has positive effects on seedling abundance, recruitment, and survival, but that these effects are influenced by L. maackii basal area and/or cover. We sampled 16 sites, representing a chronosequence of ash mortality throughout western Ohio. We tested whether L. maackii growth and fecundity varied in relation to ash decline. We also investigated effects of ash decline, stand basal area (BA), L. maackii BA and percent cover on woody seedling abundance, recruitment, and survival using linear mixed models evaluated with Akaike’s Information Criterion. These same responses were also investigated for four seedling groups: L. maackii, invasive plants (excluding L. maackii), shade tolerant natives, and shade intolerant natives. We found a significant positive relationship between ash decline and L. maackii BA growth. Lower seedling species richness corresponded with greater L. maackii BA and better ash condition. Greater L. maackii BA was also associated with lower seedling abundance and recruitment, as well as abundance and recruitment of shade-tolerant species, and recruitment of shade-intolerant species. Sites with poorer ash condition and greater L. maackii BA had more L. maackii seedlings. These findings indicate that the negative effects of L. maackii are more important to future forest composition than ash decline; however ash decline increases L. maackii growth, hence exacerbating the effects of this invasive shrub.     

Fire affects the occurrence of small mammals at distinct spatial scales in a neotropical savanna

Fire is a major disturbance event that affects biomes worldwide, altering vegetation structure and flora and fauna assemblages. Here, we investigated the effects of an extensive wildfire (~?6240 ha) on small mammal assemblages in savanna woodland (cerradão) at two spatial scales (meso- and macrohabitat) in a neotropical savanna (Brazilian Cerrado). At each spatial scale, we assessed relationships between habitat structure and small mammal species composition and abundance before and after the fire in four natural patches (one burned, three unburned) using partial redundancy analysis. From July 2009 to October 2013, we captured 1319 individuals belonging to 14 species. Our results showed that the fire had consequences for small mammal assemblage at both scales. After the fire, the burned patch differed from the other patches in vegetation attributes and species composition. At a fine scale, fire increased the herbaceous layer and decreased the litter layer and understory obstruction. On a larger scale, the main consequences of fire on vegetation structure were increased variation in litter depth, tree diameter, and distance to the nearest tree. We observed a relationship between mesohabitat structure and the abundance of species with different habitat requirements during the post-fire succession. Fire favored the invasion of generalist species from open Cerrado habitats (rodents Calomys tener, Calomys expulsus, Cerradomys scotti, and Necromys lasiurus) at the expense of more specialized forest species. Our results reinforce the relevance of incorporating multi-scale habitat heterogeneity in future studies assessing the effects of fire on wildlife.     

Cover thresholds for impacts of an exotic grass on the structure and assembly of a wet prairie community

Potential impacts of an exotic grass, Hemarthria altissima, on restoration of wet prairie community structure (species richness and cover of indicator species) and assembly processes (temporal turnover rates of plant species) on the Kissimmee River floodplain in Central Florida, USA, were evaluated over a 12-year period before and after restoration of hydrologic regimes (2001), and implementation of herbicide treatments (2006–2007) to control its spread. Thresholds for impacts were derived from comparisons of sample sites with variable levels of H. altissima cover. Prior to herbicide treatments, cover of H. altissima exhibited a logistic increase over time, with peak colonization and expansion occurring during major flood events. Mean post-restoration cover of three native wet prairie indicator species (Polygonum punctatum, Panicum hemitomon, and Luziola fluitans) increased to 37.8 ± 3.4 % in plots in which H. altissima cover was <12 %, and did not exceed 15 % in any plots with H. altissima cover >30 %. Prior to and after herbicide treatments, these indicator species largely accounted for observed differences in wet prairie community structure (i.e., cover of wetland forbs and grasses) between heavily infested sites and plots with low or no cover of H. altissima. The cover threshold at which H. altissima began to have these community-level effects was 40–50 %, but lower species richness was found only where H. altissima cover was >80 %. Increasing cover of H. altissima led to a significant decline in temporal turnover rates of plant species (P < 0.001, r² = 0.10), but also was largely due to plots with very high (>75 %) cover of H. altissima. Mean temporal turnover rates of plant species increased significantly (P = 0.03) after herbicide treatments and subsequently were highest during an ensuing flood pulse. However, 2–3 years after herbicide treatments, regrowth of H. altissima reestablished high cover (mean = 59 ± 9.5 %) in over half of the treated plots. The ability of H. altissima to establish dominant cover in restored hydrologic conditions on the Kissimmee River floodplain, and documented regrowth following herbicide treatments, increase the potential for this exotic grass species to be a pervasive threat to successful reestablishment of wet prairie community structure and assembly processes.     

The importance of fire refugia in the recolonization of a fire-sensitive conifer in northern Patagonia

Seed dispersal and seedling establishment are essential for plant recolonization after disturbances, especially for plants that rely exclusively on sexual reproduction such as post-fire colonizer trees. Fire refugia may play a key role not only allowing trees to survive fire, but also functioning as seed sources after it. The estimation of seed dispersal and seedling establishment are essential for assessing plant recolonization ability, understanding landscape dynamics and determining which areas may not be able to recover due to lack of seed arrival. Here we study the post-fire recolonization ability of Austrocedrus chilensis (Cordilleran Cypress) from fire refugia in burned areas of northwest Patagonia, Argentina. We mapped all female trees, saplings and seedlings within and around fire refugia, recorded the reproductive capacity of female trees and characterized the microsite conditions for establishment. We used an inverse modelling approach and Approximate Bayesian Computation to estimate the seed dispersal kernel and the probability of seedling establishment. We found that the average dispersal distance of an A. chilensis seed was 88.52 m. The dispersal kernel was fat-tailed, meaning that A. chilensis has the capacity of producing accelerating expansions. Large woody debris, litter, and the protection of shrubs were the most important factors associated with the presence of recruits. We highlight the importance of fire refugia as seed sources for the recolonization of burned areas and thus the relevance of protecting these places to allow the persistence of fire-sensitive species.     

Fire Elicits an Adaptive Reproductive Strategy Shift from Host Plant Quantity to Quality in a Capital Breeding Species

Capital breeding species, those that do not acquire resources over their reproductive period, are hypothesized to have more flexible reproductive strategies than income breeding species, enabling the former to better cope with environmental changes. Yet, empirical study of this life history attribute in a changing environment is rare. Hemileuca eglanterina (Saturniidae), a strict capital breeding, day-flying moth, should employ a different reproductive strategy to exploit temporary increases in host plant nutrient quality following fire. In wetlands, where one half was burned and the other left unburned, the number of eggs/clutch was positively correlated with host plant abundance in the absence of fire, suggesting that H. eglanterina uses a resource abundance matching reproductive strategy by default. However, following fire, H. eglanterina laid greater numbers of eggs/clutch and did not adjust clutch size to host plant abundance, appearing to shift to a host plant quality based reproductive strategy. Coinciding with the fire-induced shift in reproductive strategy, host plants from burned habitat contained a greater proportion of N-containing compounds in their foliage than plants from unburned habitat, and larvae fed only leaves from the burned habitat had significantly greater survival than siblings fed unburned foliage. These results suggest the shift in reproductive strategy by H. eglanterina following fire was adaptive and that capital breeding species can cope with sudden environmental changes via alternative reproductive strategies.     

Fire severity drives variation in post-fire recruitment and residual seed bank size of <Emphasis Type="Italic">Acacia</Emphasis> species

Very high-severity fires are a component of many fire-prone ecosystems, yet are often viewed as detrimental to vegetation. However, species in such systems are likely to have adapted to persist under a fire regime that includes high-severity fires. We examined how fire severity affects post-fire recruitment and residual seed banks of Acacia species and whether severity may affect plant responses to fire intervals. Nine sites of either high or low burn severity were identified after a large-scale mixed-severity fire in Warrumbungle National Park, south-eastern Australia. Transects were used to sample above-ground woody plant density. Seed bank size was surveyed by soil extraction from two depths and manual searching for seeds. Residual soil seed bank and recruitment were compared across the two burn severities. Acacia seedling density was higher in areas burnt at high severity, indicating that increased severity triggers increased germination from the seed bank. Size of residual seed bank was smaller after high-severity fire, but varied between species, with few Acacia cheelii seeds remaining despite high above-ground abundance. In contrast, A. penninervis retained a small residual seed bank. There was little evidence of negative effects on populations of Acacia species after high-severity burns. However, we found that high fire severity may impact on the ability of a species to persist in response to a subsequent short fire interval. Fire management for maintaining biodiversity needs to consider other key aspects of the fire regime, including severity and season, rather than focusing solely on fire frequency.     

Allelopathic potentials of exotic invasive and native trees over coexisting understory species: the soil as modulator

Ailanthus altissima and Robinia pseudoacacia are two aggressive exotic tree species invading riparian ecosystems in Central Spain. We explored their allelopathic potentials as a possible mechanism explaining their success in these ecosystems. Specifically, we aimed (1) to compare the phytotoxic effects of the exotic and native (Fraxinus angustifolia and Populus alba) trees on the fitness of several understory plants coexisting in riparian ecosystems, and (2) to assess the capacity of the riparian soil to modulate the phytotoxic effects. In laboratory bioassays, aqueous leaf litter extracts from the donor tree species at field-realistic concentrations were tested on different fitness indicators of 13 understory target species, using germination paper and soil as substrates in petri dishes. Using germination paper, we found species-specific effects between donor and target species, but the phytotoxicity of the exotic trees as a group was not greater than that of the natives. Nevertheless, the exotic R. pseudoacacia was the most effective donor species reducing the radicle growth of the target species. Over riparian soil substrate, the aqueous leaf litter extracts did not produce any phytotoxic effect on the target species, except in one case. Altogether, our results highlight the importance of using both a native control when assessing the phytotoxicity of nonnative plants and also the natural soil in the modulation of phytotoxic effects. Ignoring both factors in laboratory bioassays would have led to the overestimation of the phytotoxicity of the exotic species as a mechanism contributing to their invasion success.     

Duff Distribution Influences Fire Severity and Post-Fire Vegetation Recovery in Sagebrush Steppe

Woody plant expansion is a global phenomenon that alters the spatial distribution of nutrients, biomass, and fuels in affected ecosystems. Altered fuel patterns across the landscape influences ecological processes including fire behavior, fire effects, and can impact post-fire plant germination and establishment. The purpose of this study was to determine how accumulations of ground fuels beneath western juniper (Juniperus occidentalis ssp. occidentalis) canopies, composed of litter and duff, affect post-fire species response in sagebrush steppe and to quantify fuel loading patterns. Field sampling and analysis was conducted across environmental gradients following the 2007 Tongue-Crutcher Wildfire in southwestern Idaho to determine conditions that were most influential in post-fire vegetation recovery patterns. Duff depth and fire severity were determined to be the most influential factors affecting post-fire vegetation response. Decreasing species richness and native perennial grass cover was represented along the increasing duff depth gradient. Species response grouped by fire severity revealed significant presence of cheatgrass (Bromus tectorum) in low severity sites and a dominance of snowbrush ceanothus (Ceanothus velutinus) in higher severity sites. Determining sub-crown surface fuel characteristics offers the potential to predict future patterns and processes as they relate to burn severity and vegetation recovery components in developing woodlands.     

Fire frequency effects on soil and pollinators: what shapes sexual plant reproduction?

Increased fire frequency can significantly erode both soil properties and plant–pollinator interactions affecting plant reproductive success but they have seldom been assessed simultaneously. Here, we evaluate soil properties, pollinator assemblage and the reproductive success of two native Fabaceae herbs, Desmodium uncinatum and Rhynchosia edulis, growing in unburned, low and high fire frequency sites of Chaco Serrano across two consecutive years. Desmodium uncinatum is outcrossing with a high dependence on pollinators, whereas R. edulis is autogamous and completely independent of pollinators. We found that soil water content, nitrates and electrical conductivity significantly decreased in low and high fire frequency sites. Pollinator richness and composition visiting each plant species was similar across all fire frequency scenarios. However, fruit set of the exogamous D. uncinatum was strongly reduced in frequently burned sites, whereas fruit set of the autogamous R. edulis showed no significant changes. In both species, the probability of setting fruits was positively related to soil quality across fire frequency scenarios, implying that decreased reproduction was mainly driven by limitation of abiotic resources shaped by increased fire frequency. Because the pollinator-dependent D. uncinatum has a higher reproductive cost, reduced soil quality induced by fire frequency had stronger effects on its reproduction. Chronic reduction of sexual reproduction in frequently burned sites with depleted soils will limit population recruitment with negative consequences on long-term plant population persistence.     

Restoration rocks: integrating abiotic and biotic habitat restoration to conserve threatened species and reduce fire fuel load

With rapid urban expansion, biodiversity conservation and human asset protection often require different regimes for managing wildfire risk. We conducted a controlled, replicated experiment to optimise habitat restoration for the threatened Australian pink-tailed worm-lizard, Aprasia parapulchella while reducing fire fuel load in a rapidly developing urban area. We used dense addition of natural rock (30 % cover) and native grass revegetation (Themeda triandra and Poa sieberiana) to restore critical habitat elements. Combinations of fire and herbicide (Glyphosate) were used to reduce fuel load and invasive exotic species. Rock restoration combined with herbicide application met the widest range of restoration goals: it reduced fire fuel load, increased ant occurrence (the primary prey of A. parapulchella) in the short-term and increased the growth and survival of native grasses. Lizards colonised the restored habitat within a year of treatment. Our study documents an innovative way by which conflicts between biodiversity conservation and human asset protection can be overcome.     

Do novel weapons that degrade mycorrhizal mutualisms promote species invasion?

Non-native plants often dominate novel habitats where they did not co-evolve with the local species. The novel weapons hypothesis suggests that non-native plants bring competitive traits against which native species have not adapted defenses. Novel weapons may directly affect plant competitors by inhibiting germination or growth, or indirectly by attacking competitor plant mutualists (degraded mutualisms hypothesis). Japanese knotweed (Fallopia japonica) and European buckthorn (Rhamnus cathartica) are widespread plant invaders that produce potent secondary compounds that negatively impact plant competitors. We tested whether their impacts were consistent with a direct effect on the tree seedlings (novel weapons) or an indirect attack via degradation of seedling mutualists (degraded mutualism). We compared recruitment and performance using three Ulmus congeners and three Betula congeners treated with allelopathic root macerations from allopatric and sympatric ranges. Moreover, given that the allelopathic species would be less likely to degrade their own fungal symbiont types, we used arbuscular mycorrhizal (AMF) and ectomycorrhizal (ECM) tree species to investigate the effects of F. japonica (no mycorrhizal association) and Rhamnus cathartica (ECM association) on the different fungal types. We also investigated the effects of F. japonica and R. cathartica exudates on AMF root colonization. Our results suggest that the allelopathic plant exudates impact seedlings directly by inhibiting germination and indirectly by degrading fungal mutualists. Novel weapons inhibited allopatric seedling germination but sympatric species were unaffected. However, seedling survivorship and growth appeared more dependent on mycorrhizal fungi, and mycorrhizal fungi were inhibited by allopatric species. These results suggest that novel weapons promote plant invasion by directly inhibiting allopatric competitor germination and indirectly by inhibiting mutualist fungi necessary for growth and survival.     

Effects of <Emphasis Type="Italic">Prangos ferulacea</Emphasis> aqueous and hydroalcoholic extracts obtained from different organs on the regeneration of <Emphasis Type="Italic">Trifolium resupinatum</Emphasis>

Prangos ferulacea is one of the widely used, nutritional and popular fodders in livestock industry. This species is also considered as an important option in rangeland restoration and management. In this study, the comparative phytotoxic activity of aqueous and hydroalcoholic extracts obtained from different organs (flower, shoot and leaf) of P. ferulacea on proline content, seed germination and seedling growth of Trifolium resupinatum has been investigated. According to the results, the hydroalcoholic extract of P. ferulaceae flower possesses the highest total phenolic and flavonoid content and the uppermost phytotoxic effect on T. resupinatum. The extracts significantly decreased seed germination and seedling growth of T. resupinatum and increased the proline content. Our findings indicate that hydroalcoholic extract induced a stronger oxidative stress in T. resupinatum. Finally, based on the results, aqueous allelochemicals that originated from P. ferulacea played a significant role in the successful propagation and development of T. resupinatum in rehabilitated pastures. According to our results, the phytotoxicity effect of the hydroalcoholic extract was significantly higher than that of the aqueous extract. Since in nature, the allelopathic interaction between plants is closer to the aqueous method, primary evaluations of rangeland restoration using this method is suggested.     

Shade tolerance of <Emphasis Type="Italic">Ailanthus altissima</Emphasis> revisited: novel insights from southern Switzerland

The tree of heaven (Ailanthus altissima (Mill.) Swingle) is considered to be an early-successional, gap-obligate pioneer species with vigorous height growth, low shade tolerance, early fecundity and large seed production. It is a highly invasive species in many temperate and Mediterranean ecosystems outside its natural range, especially after disturbance. Due to its low shade tolerance, the potential of A. altissima to colonise undisturbed forests is thought to be low. In this study we analysed the potential of juvenile A. altissima to grow and survive in sweet chestnut (Castanea sativa Mill.) forests in southern Switzerland. We used hemispherical photography to assess the light conditions of 204 individuals of A. altissima (31 % generative, 69 % vegetative) aged between 1 and 7 years (median: 3 years) in six sites. Generative (seed-borne) and vegetative (clonal ramet) offspring of A. altissima are able to grow in light conditions well below the requirements of shade-intolerant tree species such as European larch (Larix decidua Mill.) and Scots pine (Pinus sylvestris L.). The relatively low light conditions found to be sufficient for the growth and survival of generative regeneration of A. altissima suggest a higher shade tolerance for this species than previously stated, at least for early regeneration. Consequently, the colonisation frontier of A. altissima should be intensively monitored in both forest openings but also in closed canopy forests in the vicinity of seed-bearing A. altissima.     

Mechanisms of influence of invasive grass litter on germination and growth of coexisting species in California

In grasslands, litter has been recognized as an important factor promoting grass persistence and the suppression of forbs. The invasive European annual grass Bromus diandrus (ripgut brome) is widespread throughout California, where it produces a persistent and thick litter layer. The native grass, Stipa pulchra, is also common in some grassland settings and can also produce persistent litter, yet it is typically associated with more forbs. Very little is known about the mechanisms through which these two common grass species influence seedling establishment of both exotic invasive and native herbs. Here, we evaluated the effect of B. diandrus and S. pulchra litter on seedling establishment of two invasive (the grass B. diandrus and the forb Centaurea melitensis) and two native (the grass S. pulchra, and the forb Clarkia purpurea) herbaceous plants in a greenhouse setting. Our results showed that B. diandrus litter cover hindered seedling establishment of the four species tested, but that the degree and mechanism of inhibition was dependent on which species was tested, life form (e.g. monocot/dicot) and seed size. Seedling emergence of the two forb species was more vulnerable to litter cover than either grass species and both forbs had smaller seed size. After germination, only seedling biomass of B. diandrus itself was reduced by litter (both B. diandrus and S. pulchra). We found no significant effects of leachate of either grass species on seedling emergence of any species, while a high concentration of B. diandrus leachates inhibited root growth of all species including B. diandrus seedlings. Stipa pulchra litter leachates did not affect S. pulchra or C. melitensis seedlings although it did suppress B. diandrus and C. purpurea seedling growth. Our findings provide direct experimental evidence for the mechanism of effect of litter on these coexisting invasive and native species. Such evidence helps advance our understanding of role of B. diandrus and S. pulchra litter in California grassland.     

Potential allelopathic effects of the tropical legume <Emphasis Type="Italic">Sesbania virgata</Emphasis> on the alien <Emphasis Type="Italic">Leucaena leucocephala</Emphasis> related to seed carbohydrate metabolism

Allelopathy has been considered a key mechanism to explain the invasiveness of some species. It is well known that invasive plants can affect native plants by producing novel allelochemicals but some exotic plant species may be also sensitive to allelochemicals released by native species, providing a tool to reduce growth and impacts of invasive exotic species. Here, using growth chamber experiments we tested the mutual potential allelopathic effects of Sesbania virgata (a native dominant species) and the alien Leucaena leucocephala seeds. S. virgata was unaffected by seed leachates of L. leucocephala, indicating that, under lab conditions, this legume presents resistance to the phytotoxic compounds produced by seeds of this alien species. In contrast, germination and seedling growth of L. leucocephala were strongly affected by the phytochemicals produced by seeds of S. virgata. A delay in endospermic mobilization of storage carbohydrates (raffinose-family oligosaccharides and galactomannan) was observed in the alien species. These potential allelopathic effects could not be attributed sole to the presence neither of the phytoxic catechin nor of ABA in seed leachates of S. virgata. Our findings indicate that the in vitro behavior of S. virgata is consistent with its aggressiveness in natural environment and suggest sesbanimide as a potential candidate as implicated in the noxious effects of S. virgata on the alien species.     

Fire and Grazing Influence Site Resistance to <Emphasis Type="Italic">Bromus tectorum</Emphasis> Through Their Effects on Shrub,Bunchgrass and Biocrust Communities in the Great Basin (USA)

Shrubs, bunchgrasses and biological soil crusts (biocrusts) are believed to contribute to site resistance to plant invasions in the presence of cattle grazing. Although fire is a concomitant disturbance with grazing, little is known regarding their combined impacts on invasion resistance. We are the first to date to test the idea that biotic communities mediate the effects of disturbance on site resistance. We assessed cover of Bromus tectorum, shrubs, native bunchgrasses, lichens and mosses in 99 burned and unburned plots located on similar soils where fires occurred between 12 and 23 years before sampling. Structural equation modeling was used to test hypothesized relationships between environmental and disturbance characteristics, the biotic community and resistance to B. tectorum cover. Characteristics of fire and grazing did not directly relate to cover of B. tectorum. Relationships were mediated through shrub, bunchgrass and biocrust communities. Increased site resistance following fire was associated with higher bunchgrass cover and recovery of bunchgrasses and mosses with time since fire. Evidence of grazing was more pronounced on burned sites and was positively correlated with the cover of B. tectorum, indicating an interaction between fire and grazing that decreases site resistance. Lichen cover showed a weak, negative relationship with cover of B. tectorum. Fire reduced near-term site resistance to B. tectorum on actively grazed rangelands. Independent of fire, grazing impacts resulted in reduced site resistance to B. tectorum, suggesting that grazing management that enhances plant and biocrust communities will also enhance site resistance.     

Diurnal temperature-related variations in photosynthetic enzyme activities of two C<Subscript>4</Subscript> species of Chenopodiaceae grown in natural environment

The effects of the diurnal variations in ambient temperature on some C₃ and C₄ enzymes in the Salsola dendroides and Suaeda altissima species of Chenopodiaceae family were studied during the intensive vegetation period. Activities of phosphoenolpyruvate carboxylase (PEPC) and cytosolic aspartate aminotransferase (AsAT) were shown to decrease in both species in the afternoon and evening. The activity of the mitochondrial AsAT decreased in S. altissima, remained relatively constant in S. dendroides during the day. The activity of alanine aminotransferase was high in the S. dendroides species in the morning and evening and decreased in the S. altissima species by the evening. Glucose-6-phosphate activated PEPC in both species throughout the day. The study of the redox status-regulated C₃ enzymes showed temperature-related increases in NADP-glyceraldehyde 3-phosphate dehydrogenase activity in both plants, in fructose-2,6-bisphosphatase activity in the S. altissima species, and in NADP-MDH activity in the S. dendroides species in the afternoon.     

Optimal prescribed burn frequency to manage foundation California perennial grass species and enhance native flora

Grasslands can be diverse assemblages of grasses and forbs but not much is known how perennial grass species management affects native plant diversity except in a few instances. We studied the use of late-spring prescribed burns over a span of 11 years where the perennial grass Poa secunda was the foundation species, with four additional years of measurements after the final burn. We evaluated burn effects on P. secunda, the rare native annual forb Amsinckia grandiflora and local native and exotic species. Annual burning maintained P. secunda number, resulted in significant expansion, the lowest thatch and exotic grass cover, the highest percentage of bare ground, but also the lowest native forb and highest exotic forb cover. Burning approximately every 3 years maintained a lower number of P. secunda plants, allowed for expansion, and resulted in the highest native forb cover with a low exotic grass cover. Burning approximately every 5 years and the control (burned once from a wildfire) resulted in a decline in P. secunda number, the highest exotic grass and thatch cover and the lowest percentage of bare ground. P. secunda numbers were maintained up to 4 years after the final burn. While local native forbs benefited from burning approximately every 3 years, planted A. grandiflora performed best in the control treatment. A. grandiflora did not occur naturally at the site; therefore, no seed bank was present to provide across-year protection from the effects of the burns. Thus, perennial grass species management must also consider other native species life history and phenology to enhance native flora diversity.     

Can perennial dominant grass <Emphasis Type="Italic">Miscanthus sinensis</Emphasis> be nurse plant in recovery of degraded hilly land landscape in South China?

Perennial C₄ grasses, especially Miscanthus sinensis, are widely distributed in the degraded lands in South China. We transplanted native and exotic tree seedlings under the canopy of M. sinensis to assess the interaction (competition or facilitation) between dominant grass M. sinensis and tree seedlings. The results of growth, chlorophyll fluorescence, and ultrastructure showed that negative effects may be stronger in perennial dominant grass M. sinensis. Although M. sinensis buffered the air temperature, improved soil structure, and increased soil phosphorus content, these beneficial effects were outweighed by the detrimental effect, especially overshading. To ensure the establishment of target native species in M. sinensis communities in degraded lands of South China, restoration strategies should include removing aboveground vegetation, planting target species seedlings in openings to reduce the effects of canopy shading, and/or selecting competition-tolerant target species. Also, seedlings of exotic species used in restoration engineering cannot be directly planted under the canopy of M. sinensis.     

Post-fire Aleppo pine growth,C and N isotope composition depend on site dryness

Key message

The post-fire growth responses and changes in wood C and N isotope composition depend on site water availability and fire severity in Mediterranean Aleppo pine forests.

Abstract

Mediterranean forests are subjected to recurrent wildfires and summer droughts. Under warmer and drier conditions, it is required to determine how Mediterranean pines recover after wildfires, and how this translates into changes in tree radial growth and function (e.g. intrinsic water-use efficiency—iWUE). We analysed four Aleppo pine areas located in SE Spain affected by 1994 wildfires and subjected to different water availability, ranging from mesic to semi-arid conditions. We combined dendrochronological analyses with δ¹³C and δ¹⁵N wood isotopes to quantify the changes in radial growth (expressed as Basal Area Increment—BAI) and functional responses (iWUE and N cycling) to three fire severities (unburned sites, low and medium severities). We expected that the post-fire release in nutrients and a reduction in competition for water would enhance radial growth. We found that fire did not significantly alter growth patterns at the driest sites, but increased BAI at the wettest sites. δ¹³C was significantly (P ≤ 0.01) more negative only in burned stands located at the wettest site indicating a decreased iWUE and thus improved water availability. However, the δ¹⁵N was higher in severely burned than in unburned plots from all sites but the wettest site, indicating a potential fertilization effect of fire in sites subjected to mild drought severity. Site water availability determined how fire affected subsequent modifications in growth and tree functioning of Aleppo pine forests, that is, changes in iWUE and N cycling. Therefore, site dryness should be explicitly considered to forecast the growth and functioning responses of Mediterranean pine forests to the predicted increasing recurrence of fire events due to global warming.