Establishment of Broad‐leaved Thickets in Serengeti,Tanzania: The Influence of Fire,Browsers, Grass Competition,and Elephants1

The role of Euclea divinorum in the establishment of broad‐leaved thickets was investigated in Serengeti National Park, Tanzania. Thickets are declining due to frequent fires, but have not reestablished when fires have been removed. Seedlings of E. divinorum, a fire‐resistant tree, were found in grassland adjacent to thickets and as thicket canopy trees and may function to facilitate thicket establishment. Seedlings of thicket species were abundant under E. divinorum canopy trees but not in the grassland, indicating that E. divinorum can facilitate forest establishment. We examined E. divinorum establishment in grassland by measuring survival and growth of seedlings with respect to fire, browsers, elephants, and competition with grass. Seedling survival was reduced by fire (50%), browsers (70%), and competition with grass (50%), but not by elephants. Seedling growth rate was negative unless both fire and browsers, or grass was removed. Establishment of thickets via E. divinorum is not occurring under the current conditions in Serengeti of frequent fires, abundant browsers, and dense grass in riparian areas. Conditions that allowed establishment may have occurred in 1890–1920s during a rinderpest epizootic, and measurements of thicket canopy trees suggest they established at that time.     

Limited flooding tolerance of juveniles restricts the distribution of adults in an understory shrub (Itea virginica; Iteaceae)

Juvenile plants often have tight microhabitat associations because of specific requirements for seed germination and subsequent establishment. Due to their larger size, adults may be more adept at coping with stress. However, few studies consider the role of ontogeny in structuring plant populations, even though phenotypic expression can change through life history. In cypress-tupelo swamps of the United States, understory species often grow on microsites above floodwaters. In a field survey of one such species, Itea virginica, we found that more than 98% of seedlings occurred on elevated microsites, which were relatively infrequent. However, this strict association relaxed through ontogeny, with nearly 8% of subadults and adults rooted directly on the forest floor. We hypothesized that flooding inhibits juvenile establishment on the forest floor. In greenhouse experiments, we investigated the effects of flooding and substrate on Itea performance. Seeds had similar germination rates on drained swamp soil and cypress knee wood. Seedling growth was high on unflooded soil, but declined precipitously when submerged. Finally, performance of seedlings, but not older plants, decreased with flood severity. Our results highlight the importance of assessing stress tolerance over multiple life history stages because limitations of juveniles can constrain the distribution patterns of future ontogenetic stages.     

Comparative seed biology and co-existence of two fynbos shrub species

Abstract. Fire-prone fynbos communities include numerous species which are difficult to distinguish in terms of conventional niche axes since they are morphologically similar and share the same broad life-history traits. These species compete for space after each fire and lottery theory predicts that those with dissimilar per capita regeneration would not co-exist in the long-term. We studied seed production, soil seed bank dynamics, germination and post-fire seedling establishment and mortality of two obligate reseeding, morphologically similar shrubs which co-occur in dune fynbos throughout the southwestern Cape. Passerina paleacea produced 30 x more plump seeds and maintained soil seed banks between 1.5 x (pre-dispersal) and 2.6 x (post-dispersal) times larger than Phylica ericoides. Seeds of both species showed a high degree of dormancy although germination was stimulated by direct fire-related cues for Phylica only. Approximately 4 x more Passerina seedlings than Phylica seedlings were counted at the end of the winter germination period after a mild autumn fire. However, seedling mortality in the first five months of the dry summer was more than twice as high for Passerina than for Phylica. We suggest that the long-term co-existence of these two species does not result from similar post-fire regeneration success but rather from population instabilities arising from differential regeneration in relation to fire regime. The results predict that hot fires followed by dry summers would favour Phylica over Passerina as the former has fire-stimulated germination and greater drought tolerance; cool fires followed by moist summers would favour Passerina.     

The costs of leaving home: ants disperse myrmecochorous seeds to low nutrient sites

Summary Leucospermum conocarpodendron (L.) Buek (Proteaceae) seedlings were excavated several months after a fire in Cape fynbos. Seedlings under burnt parental skeletons had short hypocotyls (mean 25 mm) indicating passive dispersal whereas seedlings in the open were more deeply buried (mean 48 mm) by ants. Soil nutrient concentrations at the site of germination were negatively related to depth of burial and distance from parent. Ant dispersal resulted in seedlings emerging in soils with lower nutrient concentrations than passively dispersed seeds. Tissue analysis supported the soil results with lower P content in seedlings from open (ant dispersed) sites. Seedling survival in the first year of establishment was also lower in open sites, but not significantly so. However seedlings were slightly taller in the open. The results of this study, the first on naturally occurring intraspecific variation in myrmecochory, strongly contradict current explanations for the high incidence of myrmecochory in nutrient poor environments.     

Improving restoration success through microsite selection: an example with planting sagebrush seedlings after wildfire

Post‐fire restoration of foundation plant species, particularly non‐sprouting shrubs, is critically needed in arid and semi‐arid rangeland, but is hampered by low success. Expensive and labor‐intensive methods, including planting seedlings, can improve restoration success. Prioritizing where these more intensive methods are applied may improve restoration efficiency. Shrubs in arid and semi‐arid environments can create resource islands under their canopies that may remain after fire. Seedlings planted post‐fire in former canopy and between canopies (interspace) may have different survival and growth. We compared planting Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) seedlings post‐fire in former sagebrush canopy and interspace microsites at five locations. Four growing seasons after planting, seedling survival was 46 and 7% in canopy and interspace microsites, respectively. Sagebrush cover was 5.8 times greater in canopy compared to interspace microsites. Sagebrush survival and cover were likely greater because of less competition from herbaceous vegetation as well as benefiting from resource island effects in canopy microsites. Initially, post‐fire abundance of exotic annual grasses was less in canopy microsites, but by the third year post‐fire it was substantially greater in canopy microsites, indicating that resource availability to seedlings was greater, at least initially, in canopy microsites. These results suggest microsites with greater likelihood of success should be identified and then utilized to improve restoration success and efficiency. This is important as the need for restoration greatly exceeds resources available for restoration.     

Seed size,establishment sites and species coexistence in a Chilean rain forest

Abstract. Seedling densities on the forest floor and on elevated microsites (logs and stumps) were compared for eight woody species in a temperate rain forest in southern Chile. Degree of association with elevated microsites varied significantly between species, showed no systematic relationship with reported shade tolerance, but was significantly negatively correlated with seed mass. Large-seeded Podocarpus nubigena established preferentially on undisturbed forest floor sites, whereas seedlings of small-seeded species such as Nothofagus nitida and Laurelia philippiana were found mainly on fallen logs and stumps. The abundance of large seedlings and saplings of N. nitida on logs/stumps, and the growth forms of canopy trees, confirm that recruitment of this species occurs mainly on decaying wood. The relationship between seed size and microsite preferences may be caused by effects of seed size on (1) ability to establish in forest floor litter and (2) retention of seeds on logs. Seedling occupancy of logs and stumps varied with state of decay. Few seedlings of any species were present on logs in the early stages of decay. N. nitida established earlier than the other species, attaining maximum abundance on wood in the middle decay classes. Species richness and overall seedling abundance were highest on wood in advanced stages of decay. Seed size differences are suggested as a determinant of differential utilization of forest floor heterogeneity, and hence of plant species coexistence.     

Linking seed dispersal,germination and seedling recruitment in the invasive species <Emphasis Type="Italic">Berberis darwinii</Emphasis> (Darwin’s barberry)

Seedling recruitment is a multi-phased process involving seed production, dispersal, germination, seedling establishment and subsequent survival. Understanding the factors that determine success at each stage of this process is of particular interest to scientists and managers seeking to understand how invasive species spread and persist, and identify critical stages for management. To understand the factors and processes influencing recruitment of the invasive species Berberis darwinii Hook. (Darwin’s barberry), temporal and spatial patterns of seed dispersal, germination and seedling establishment were examined. Seed dispersal from a large source population was measured over two fruiting seasons, and subsequent patterns of seedling emergence and survival within each cohort were measured. Seed longevity was tested under both natural and artificial conditions. Seeds were widely dispersed by birds, up to 450 m from the source population. Dispersal was essential to seedling establishment, as few seedlings survived beneath the parent canopy. Seeds were relatively short-lived in the soil under both field and glasshouse conditions, with few surviving for more than 1 year. Patterns of newly emerged seedlings largely reflected patterns of seed rain, but seedling survival was significantly affected by distance from source population, seedling density and light environment. These results suggest that recruitment of B. darwinii is dependent on dispersal of seeds to favourable microsites. Management priorities should include the removal of fruiting plants, and seedling control in highlight areas.     

Soil seed banks and post-fire seed deposition across a forest - fynbos ecotone in the Cape Province

Abstract. The relative sizes and composition of soil seed banks, the influence of fire and the post-fire deposition of seeds were investigated in a riparian forest and adjacent fynbos and transitional vegetation in Swartboskloof. Brief complementary studies of soil seed banks were conducted in poorly-developed forest and scree forest soils. Numbers of species in each vegetation type were very similar, but there were fewer seeds in riparian forest soil than in the transitional and fynbos zones. These patterns were not repeated in poorly-developed forest and scree forest. No effects of fire on soil seed banks were detected. Forest soil had relatively large numbers of seeds stored at 10 to 15 cm deep, with many zoochorous and few myr-mecochorous seeds. Anemochorous and ornithochorous seeds of forest species formed a major component of seed deposition within the transitional and fynbos zones in the first year after fire. The numbers of anemochorous forest seeds in the fynbos declined with distance from the forest edge. The deposition of ornithochorous forest seeds was less closely related to distance from the source, and was not exclusively associated with the presence of tall or fruit-bearing shrubs. Regeneration after canopy-destroying disturbance in the forest is likely to emanate from the soil seed banks of pioneer species which now or previously occurred on forest margins. Seed availability does not appear to limit colonization of fynbos by forest species soon after fire.     

The effects of date of planting on field establishment of serotinous cape Proteaceae

Season of fire have marked effects on the germination and establishment of serotinous shrubs of the family Proteaceae in fynbos vegetation. To investigate reasons for this, we simulated the effects of different fire seasons by planting seeds into cleared fynbos and then followed their progress. Four species of Proteaceae were planted monthly at four sites over two and a half years. Exclosures were used to exclude rodent seed predators. Germination was confined largely to the three winter months (June–Aug.). Seeds planted from January–June had higher germination than those planted in the second half of the year. Higher levels of regeneration noted after fires in the first half of the year, were previously hypothesised to be results of predation. However, we obtained similar results despite the exclusion of seed predators. Monthly minimum temperature was strongly correlated with germination percentage but monthly rainfall was not. Loss of seed viability may be important, in determining post-fire seedling densities. Differential seedling mortality of earlier and late germinants appears to be unimportant in determining establishment levels. Our results nevertheless support the current practice of restricting management fires in fynbos to the summer-autumn period.     

Impact of graminoid cover on postfire growth of nonsprouting Protea seedlings in the eastern Fynbos Biome of South Africa

Large tracts of lowland and foothill landscape in the bimodal rainfall, eastern Fynbos Biome of South Africa lack an overstorey of nonsprouting, serotinous Proteaceae (proteoids). Scattered stands of proteoids in the grassy fynbos that dominate these landscapes suggest that proteoids have the potential to be more widespread. Here, we assessed whether interactions between the resprouting graminoid (predominantly C4 grasses) understorey and the proteoid overstorey could explain the sparseness of proteoids in grassy fynbos. We quantified postfire seedling growth and graminoid cover for three proteoid (Protea) species in beneath‐proteoid canopy and open microsites at sixteen locations in the eastern Fynbos Biome. Contrary to studies undertaken in proteoid fynbos west of our study area, we found no consistent differences between graminoid cover and growth of proteoid seedlings in beneath‐canopy and open microsites. Nor did we find consistent negative relationships between graminoid cover and seedling growth. We conclude that graminoid–proteoid interactions do not explain the sparseness of proteoids in the eastern Fynbos Biome.     

Quercus rugosa seedling dynamics in relation to its re-introduction in a disturbed Mexican landscape

Abstract. In order to define the ‘regeneration niche’ and then promote the re-introduction of Quercus rugosa into a disturbed area we studied seed predation, germination, seedling survival and growth of this species at three different sites: the forest interior, the forest border and a disturbed site, along a disturbance gradient. Acorn removal on the ground was high at the sites, with higher removal rates from 25-seed clusters than from 5- and 1-seed clusters. More seeds were removed at the forest border than at the other two sites, although in all cases some seeds remained in the soil for periods long enough for them to germinate and produce seedlings. Seed germination and seedling establishment were more successful and similar in the forest interior and the forest border, and much less successful at the disturbed site, due to acorn desiccation. Seedling survival was strongly affected by site, with the highest survival at the forest border and the lowest survival at the disturbed site after a year. The subsequent dry season, which was particularly harsh, caused a drop in survival both at the forest border and the disturbed site. In the former, a closer analysis revealed that partially shaded microsites enhanced survival, while in the latter overall survival was very low, with approximately 5 % of the seedlings surviving, compared to 50 % final survival at the other sites. There was a positive correlation between seed size and seedling survival at the forest border. The three size variables measured (seedling height, basal diameter and crown area) did not increase noticeably during the 20-month study period at the forest interior, while growth still occurred at the forest border and the disturbed site. However, during the two dry seasons there were large drops in mean seedling height and crown area at the disturbed site, due to more frequent dieback, causing large variation in seedling size. These results show that extensive re-introduction of this species to the disturbed area will probably fail under present conditions, and that careful selection or duplication of microsites that mimic the partial shade of the forest border is a sound method for improving oak establishment at this site.     

Fruit removal,pyrene dispersal,post-dispersal predation and seedling establishment of a bird-dispersed tree

The recruitment of a dioecious bird-dispersed tree, the hollyIlex aquifolium (Aquifoliaceae), was studied consideringthe stages of fruit removal by birds, seed rain, post-dispersal seed predation,seed germination and seedling survival. The main objective was to test theeffect of different microhabitats within a beech forest on recruitment stages.Migrant thrushes were the main dispersers of this tree whose fruit crops wereentirely removed during two study years. Seed rain was greatest beneath hollytrees regardless of their sex and lowest in the open sites. Post-dispersal seedpredation was examined by two experiments and did not differ betweenmicrohabitats despite its quantitative importance (about 70%). Seedlingemergence, which probably corresponded to seeds from several cohorts, wasgreater beneath trees than in open sites and the density of second-yr to 5cm seedlings depended on the presence-absence of ungulateherbivores and litter. While the former had a detrimental effect, the latterhada beneficial effect on seedling abundance. Seedling survival showed nosignificant variations between microhabitats but depended on seedling densityinsome microhabitats (holly, beech). Finally, the initial seed arrival seemed todetermine microhabitat suitability for holly seedling establishment. However,under heavy browsing the density of seedlings may be strongly reduced leadingtomicrohabitat homogeneity for holly seedling establishment.     

Direct and indirect interactions among plants explain counterintuitive positive drought effects on an eastern Mediterranean shrub species

Coexistence of woody and herbaceous plants may be governed by a complex set of direct and indirect interactions, whose relative importance have been rarely assessed. We experimentally studied woody species establishment in a mixed plant community by disentangling the potential role of such biotic interactions and the effect of environmental variations on them. Seedling establishment of the common eastern Mediterranean shrub species Sarcopoterium spinosum was investigated under different rainfall and light conditions, combined with the effect of the presence of adult shrubs and annual neighbors. We predicted that seedlings will be directly affected by competition with annuals with increasing water availability, while direct effects of adult shrubs will be positive via amelioration of water stress. Indirect effects were expected beneath shrub canopies due to reduced water stressed and light availability for both annuals and shrub seedlings, which may intensify competition between annuals and shrub seedlings. To test these predictions we performed field and garden experiments in which we combined manipulation of shrub and annual presence with manipulations of water availability and light conditions to simulate the effect of shrub canopy. In contrast to our prediction, shrub seedling establishment was not facilitated but inhibited by adult shrubs because of light limitation. As expected, annuals had direct negative effects on shrub seedlings under wet conditions, which shifted to neutral or positive effects under dry conditions. Thus, interactions among shrubs and annuals, and in particular the release from competition during drought years, leads to a counterintuitive positive effect of drought on shrub seedling establishment. Our findings point to the importance of experimentally studying multidimensional interactions for coexistence of different life forms and to the underestimated role of light for success in water‐limited ecosystems.     

Love of Nurse Plants is Not Enough for Restoring Oak Forests in a Seasonally Dry Tropical Environment

The highest concentration of oak species in the world occurs in Mexico, but human activities have strongly degraded these oak forests. Mexican oaks have high economic, social, and cultural value, and restoring these forests is of paramount importance for the people of Mexico. Here, we propose a method for restoring oak forests using native shrubs that colonize degraded areas as nurse plants for oak seedlings. To test the viability of this proposal, seedling transplant experiments were performed in a degraded area near a protected oak forest relict. Two pioneer shrubs were identified as potential nurse species: Mimosa luisana and Senecio sp. The target oak species was Quercus castanea . Oak seedlings were located beneath the canopies of both shrubs and in the surrounding area without shrub cover. Water is a limiting resource for oak establishment in seasonally dry environments; therefore, we included irrigation systems in our experimental design to determine whether the combination of nurse plants plus watering led to higher rate of survival than the presence of nurse species alone. Seedling survival without watering was less than 20% both beneath nurse species and in the surrounding habitat. When water was supplied, survival rate beneath nurse species increased up to 58% while survival in the surrounding habitat did not differ from that observed in treatments without watering. Our results indicate that survival rate of oak seedlings is increased by the presence of nurse plants only when water is supplied. This suggests that restoration of oak forests in these degraded areas requires both nurse plants and watering.     

Influence of conspecific and heterospecific adults on riparian tree species establishment during encroachment of a humid palm savanna

Woody plant encroachment of savanna ecosystems has been related to altered disturbance regimes, mainly fire suppression and herbivore exclusion. In contrast, neighbourhood interactions among resident and colonising woody species have received little attention, despite their likely influence on the pattern and rate of tree establishment. We examined how resident palm trees (Butia yatay) and established adults of two riparian forest tree species (Allophylus edulis and Sebastiania commersoniana) influenced seed arrival and seedling performance of the latter two species in a humid savanna of east-central Argentina. Seed traps and seedlings of both riparian species were placed in herbaceous openings, and beneath palm, conspecific and heterospecific adult trees in two unburned savanna patches, and were monitored for 2 years. Only seeds of the bird-dispersed Allophylus arrived in palm microsites, yet survival of Allophylus seedlings near adult palms was limited by animal damage through trampling and burrowing, a non-trophic mechanism of apparent competition. Seeds of both riparian species dispersed into conspecific microsites, although adult trees selectively reduced growth of conspecific seedlings, a pattern consistent with the “escape hypothesis”. Further, survival of Sebastiania increased in the moister Allophylus microsites, suggesting a one-way facilitative interaction between woody colonisers. Our results indicate that dispersal facilitation by resident savanna trees may be critical to riparian species invasion after fire suppression. Distance-dependent effects of conspecific and heterospecific adult trees could contribute to shape the subsequent dynamics of woody seedling establishment. Overall, we show that indirect interactions can play a prominent role in savanna encroachment by non-resident woody species.     

Disentangling the effects of facilitation on restoration of the Atlantic Forest

Facilitation is an important ecological mechanism with potential applications to forest restoration. We hypothesized that different facilitation treatments, distance from the forest edge and time since initiation of the experiment would affect forest restoration on abandoned pastures. Seed and seedling abundance, species richness and composition were recorded monthly during two years under isolated trees, bird perches and in open pasture. Seed arrival and seedling establishment were measured at 10 m and 300 m from the forest edge. We sampled a total of 131,826 seeds from 115 species and 487 seedlings from 46 species. Isolated trees and bird perches increased re-establishment of forest species; however, species richness was higher under isolated trees. Overall, abundance and richness of seeds and seedlings differed between sampling years, but was unaffected by distance from the forest edge. On the other hand, species composition of seeds and seedlings differed among facilitation treatments, distance from the forest edge and between years. Seedling establishment success rate was larger in large-seeded species than medium- and small-seeded species. Our results suggest that isolated trees enhance forest re-establishment, while bird perches provide a complementary effort to restore tree abundance in abandoned pastures. However, the importance of seed arrival facilitation shifts toward establishment facilitation over time. Arriving species may vary depending on the distance from the forest edge and disperser attractors. Efforts to restore tropical forests on abandoned pastures should take into account a combination of both restoration strategies, effects of time and proximity to forest edge to maximize regeneration.     

Role of nurse plants in Araucaria Forest expansion over grassland in south Brazil

Abstract Araucaria Forest expansion over grassland takes place under wet climate conditions and low disturbance and it is hypothesized that isolated trees established on grassland facilitate the establishment of forest woody species beneath their canopies. Forest with Araucaria angustifolia is a particular type of Brazilian Atlantic Forest and the main forest type on the highland plateau in south Brazil, often forming mosaics with natural Campos grassland. The objectives of this paper were to evaluate the role of isolated shrubs and trees as colonization sites for seedlings of Araucaria Forest woody species on grassland, to determine which species function as preferential nurse plants in the process and the importance of vertebrate diaspore dispersal on the structure of seedling communities beneath nurse plants. The study was conducted in São Francisco de Paula, Rio Grande do Sul State, where we sampled isolated shrubs and trees in natural grassland near Araucaria Forest edges. Seedlings were counted and identified, and seedling diaspore dispersal syndromes, size and colour were registered. We detected 11 woody species with a potential role in nucleating grassland colonization by forest species. Beneath the canopies of nurse plants more forest species seedlings were found compared with open field grassland and the seedlings had diaspores mostly dispersed by vertebrates. Also, more seedlings were found under the canopy of A. angustifolia than beneath other nurse plant species. We conclude that A. angustifolia trees established on grassland act as nurse plants, by attracting disperser birds that promote colonization of the site by other forest species seedlings, and that under low level of grassland disturbance, conservation of frugivorous vertebrate assemblages may increase forest expansion over natural grassland and also facilitate the regeneration of degraded forest areas.     

Fire,canopy cover and seedling dynamics in Mediterranean shrubland of northeastern Spain

Abstract. Seedling establishment and survival of the main woody species of early-successional shrubland in northeastern Spain were studied from 1992 to 1995 with emphasis on the importance of vegetation cover (existence of open areas and the situation beneath the plant canopy) and microhabitat (occurrence of stones, litter and bare soil). In the absence of fire, vegetation cover (measured at a scale of 30cm × 30 cm) was not correlated with seedling emergence of most species, nor with growth and survival of seedlings up to one year old. Seedlings older than one year showed a similar pattern: their density was not significantly different in both kinds of habitats. The emergence of seedlings was mainly associated with the presence of mature plants – which can provide seeds – and with the absence of unsuitable microhabitats (large stones, deep litter and bare soil). In April 1994 a wildfire burned the study area. This enabled a study of the pattern of post-fire establishment. After the wildfire, seedling emergence of several species increased and most species produced seedlings with higher survival and growth rates than in the period before the fire. Pre-fire cover, however, did not show significant effects on post-fire seedling dynamics in most cases.     

Fine-scale spatial heterogeneity and seed size determine early seedling survival in a desert perennial shrub (<Emphasis Type="Italic">Ericameria nauseosa:</Emphasis> Asteraceae)

In heterogenous landscapes, seeds settle in some microsites more readily than others, independently of whether those microsites are suitable for germination and subsequent growth, and survival of seedlings. Wild seeds and seedlings of Ericameria nauseosa var. oreophila in the sand-dune ecosystem near Mono Lake, California show both concordance and conflict in where seeds are retained and where seedlings flourish. Using a field experiment, we followed performance of seeds and seedlings (i.e., the rate of germination and successful emergence, initial seedling size, seedling growth and survival over first growing season), by planting seeds of known sizes in pre-identified microsites (windward and lee aspects of interspaces between shrubs, under shrub canopies, and under snag canopies, respectively). Heavier seeds were more likely to germinate and emerge successfully and resulted in initially larger seedlings than lighter seeds. These initially larger seedlings subsequently remained larger over the growing season and lived longer than initially smaller seedlings. Independent of seed and initial seedling size, seedlings that germinated under the canopy of adult shrubs grew larger and survived longer than seedlings that germinated in interspaces (open space with little or no vegetation) or under snags (dead adult shrubs). Seedlings grown under the canopy of adult shrubs experienced significantly less solar radiation and wind-deposited sand than seedlings grown in interspace or snag microsites. Sand burial more than 1 cm was lethal for seedlings. The two variables of seed size and microsite type had by far greater impact on eventual growth and survival of seedlings than did aspect, and the effects of the former two variables were independent of each other. This study amplifies the body of work on E. nauseosa at this site demonstrating that the earliest events in the life history of this long-lived perennial shrub appear to persist through time despite the harsh and variable environment.     

Climatic warming strengthens a positive feedback between alpine shrubs and fire

Climate change is expected to increase fire activity and woody plant encroachment in arctic and alpine landscapes. However, the extent to which these increases interact to affect the structure, function and composition of alpine ecosystems is largely unknown. Here we use field surveys and experimental manipulations to examine how warming and fire affect recruitment, seedling growth and seedling survival in four dominant Australian alpine shrubs. We found that fire increased establishment of shrub seedlings by as much as 33‐fold. Experimental warming also doubled growth rates of tall shrub seedlings and could potentially increase their survival. By contrast, warming had no effect on shrub recruitment, postfire tussock regeneration, or how tussock grass affected shrub seedling growth and survival. These findings indicate that warming, coupled with more frequent or severe fires, will likely result in an increase in the cover and abundance of evergreen shrubs. Given that shrubs are one of the most flammable components in alpine and tundra environments, warming is likely to strengthen an existing feedback between woody species abundance and fire in these ecosystems.