Contrasting Population Dynamics of the Endemic New Caledonian Conifer Araucaria laubenfelsii in Maquis and Rain Forest

This study compares demographic parameters and population dynamics for high disturbance (maquis) and low disturbance (rain forest) environments of the montane conifer, Araucaria laubenfelsii, in New Caledonia. The establishment, growth, survival and reproduction of ca 2500 individuals were followed in permanent plots over 10 yr. Growth and survival rates for A. laubenfelsii show that it is a long-lived, slow growing tree, with evidence of suppression in the sapling size classes in mature rain forest. Growth rates for all size classes are generally faster in maquis than rain forest. Transition matrix analyses estimated positive rates of population increase (λ values>1), with populations expanding in maquis, and stable in mature forest. Araucaria laubenfelsii is able to regenerate continuously in maquis and early successional rain forest, but recruitment is limited in older stands. Life table response experiment analyses showed that reproduction, and transitions from sapling to mature tree stage, contributed positively to λ in maquis, but negatively in forest. Araucaria laubenfelsii on Mont Do can be considered a long-lived pioneer, with early maquis colonizers helping to drive succession from maquis to forest. While opportunities for recruitment decline with time as rain forest sites develop a closed canopy, occasional gap phase recruitment, combined with disturbance by cyclones, landslides and fire, provide opportunities to ensure species persistence. Understanding contrasting population dynamics of A. laubenfelsii in maquis and rain forest will better facilitate conservation management of this species, particularly given current high rates of land conversion and degradation in New Caledonia. Abstract in French is available at http://www.blackwell-synergy.com/loi/btp     

Changes in two Minnesota forests during 14 years following catastrophic windthrow

Abstract. We measured tree damage and mortality following a catastrophic windthrow in permanent plots in an oak forest and a pine forest in central Minnesota. We monitored changes in forest structure and composition over the next 14 years. Prior to the storm, the oak forest was dominated by Quercus ellipsoidalis, and the pine forest by Pinus strobus. The immediate impacts of the storm were to differentially damage and kill large, early‐successional hardwoods and pines. Subsequent recovery was characterized by the growth of late‐successional hardwoods. In both forests the disturbance acted to accelerate succession. Ordination of tree species composition confirmed the trend of accelerated succession, and suggested a convergence of composition between the two forests.     

Factors influencing the distribution and growth of dwarf bamboo, <Emphasis Type="Italic">Fargesia nitida</Emphasis>, in a subalpine forest in Wolong Nature Reserve,southwest China

Dwarf bamboos impose intense resource competition in subalpine coniferous forests, and their exclusive densities have crucial impacts on tree regeneration and understory species diversity. We studied the factors influencing the distribution and growth of dwarf bamboo, Fargesia nitida, in a subalpine forest in southwest China. TWINSPAN, based on an attribute matrix, could divide the subalpine forest into 11 sub-associations, and more clearly reflected ecological functional features of the subalpine forest than analysis based on a species matrix. TWINSPAN was also generally consistent with DCA ordination based on the attribute matrix. DCA and DCCA ordination showed relationships between the distribution of F. nitida population and environment factor. The first DCCA axis showed topography and disturbance gradients (except fallen trees and broken branches); the second DCCA axis showed canopy density and composition gradients. Stepwise multiple regression analyses showed that distribution (culm density and coverage) of F. nitida decreased significantly with landslide and slope aspect, and increased significantly with soil status. The light condition had positive effects on growth and size of bamboo. A stable environment in the northern slope and more broadleaved species dominating in canopy would increase the dwarf bamboo biomass. Thus, the disturbance regimes, the slope aspect and the BA of evergreen conifer trees can provide useful guidelines for the control and management of F. nitida populations, and in helping to understand the succession and regeneration of subalpine forest in this region.     

Estimation of tree replacement patterns in an Appalachian Picea-Abies forest

Abstract. Patterns of tree species replacement in a Picea-Abies forest, determined by several different methods, are compared and the methods are assessed. Methods are grouped as either understory-based or gap-based estimates of replacement. The understory-based methods characterize canopy-understory interactions with spatial statistics, sapling density measurement, sapling frequency measurement, and successor sapling identification beneath live canopy trees. The gap-based methods include sapling density measurement, sapling frequency measurement, and successor sapling identification in tree-fall gaps. Methods except those based on frequency indicate a strong trend of replacement of all canopy species by Abies. Understory-based methods may underestimate canopy recruitment of intolerant trees, while gap-based methods relying on sapling density or frequency may overestimate recruitment of intolerant trees. Estimates based on the selection of successor saplings in the understory or in gaps are reliable. Gap successor estimates consider the process of gap capture and are useful in analyses of forest dynamics.     

黑龙江省大兴安岭林区火烧迹地森林更新及其影响因子

林火干扰是大兴安岭森林更新的影响因子之一,研究火烧迹地森林更新的影响因子(立地条件、火前植被、火干扰特征)对理解生态系统的结构、功能和火后演替轨迹具有重要意义。选取呼中及新林林业局55个代表性火烧样地,利用增强回归树分析法分析了火烧迹地森林更新的影响因素。结果表明:(1)立地条件是影响针、阔叶树更新苗密度的主要因素;海拔对针叶树更新苗密度的影响最大;坡度对阔叶树更新苗密度影响最大;(2)距上次火烧时间对针叶树更新苗比重影响最大,其次是林型;(3)中度林火干扰后森林更新状况好于轻度和重度火烧迹地。根据火烧迹地森林更新调查分析可知:林型影响火后演替模式,火前为针叶树或阔叶树纯林,火后易发生自我更新(火后树种更新组成与火前林型相同),而针阔混交林在火干扰影响下易于发生序列演替(火后初期以早期演替树种更新为主)。     

Early post-fire tree regeneration in a Picea-Vaccinium forest in northern Sweden

Abstract. Age and size structure of saplings of Picea abies, Pinus sylvestris and Betula pubescens were examined in a 26-yr old forest fire area in a Picea abies-Vaccinium myrtillus forest in northern Sweden. Picea, which is a shade-tolerant species, had its maximum regeneration prior to the shade-intolerant Pinus. The shift from Picea to Pinus regeneration in the late 1970s, did not seem to be related to variations in summer temperature. Instead, it is suggested that Picea established in the shade created by dead trees, and, that increased reindeer browsing of Betula in combination with a simultaneous thinning of the tree layer, favoured Pinus recruitment. These regeneration patterns do not confirm conventional views of post-fire succession in Sweden.     

Composition and Dynamics of Functional Groups of Trees During Tropical Forest Succession in Northeastern Costa Rica

We compared the functional type composition of trees ≥10 cm dbh in eight secondary forest monitoring plots with logged and unlogged mature forest plots in lowland wet forests of Northeastern Costa Rica. Five plant functional types were delimited based on diameter growth rates and canopy height of 293 tree species. Mature forests had significantly higher relative abundance of understory trees and slow-growing canopy/emergent trees, but lower relative abundance of fast-growing canopy/emergent trees than secondary forests. Fast-growing subcanopy and canopy trees reached peak densities early in succession. Density of fast-growing canopy/emergent trees increased during the first 20 yr of succession, whereas basal area continued to increase beyond 40 yr. We also assigned canopy tree species to one of three colonization groups, based on the presence of seedlings, saplings, and trees in four secondary forest plots. Among 93 species evaluated, 68 percent were classified as regenerating pioneers (both trees and regeneration present), whereas only 6 percent were classified as nonregenerating pioneers (trees only) and 26 percent as forest colonizers (regeneration only). Slow-growing trees composed 72 percent of the seedling and sapling regeneration for forest colonizers, whereas fast-growing trees composed 63 percent of the seedlings and saplings of regenerating pioneers. Tree stature and growth rates capture much of the functional variation that appears to drive successional dynamics. Results further suggest strong linkages between functional types defined based on adult height and growth rates of large trees and abundance of seedling and sapling regeneration during secondary succession.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp     

Insects and light interact to mediate vine colonization of fast growing Microberlinia bisulcata tree seedlings in gaps of an African rain forest

Vines thrive in lowland tropical forests, yet the biotic factors underlying their colonization of host tree seedlings and saplings remain surprisingly understudied. Insect herbivores presumably could influence this process, especially where disturbance has opened the canopy (i.e., gaps)—temporary areas of higher primary productivity favoring the recruitment of vines and trees and invertebrates in forests—but their impact on vine colonization has never been experimentally tested. Using data from an insect herbivore exclusion (mesh-netting cages) experiment conducted in an African rain forest (Korup, Cameroon), I logistically modeled the probability of vines colonizing seedlings of three co-dominant species (Microberlinia bisulcata vs. Tetraberlinia bifoliolata and T. korupensis) in paired shaded understory and sunny gap locations (41 blocks across 80 ha, starting n = 664 seedlings) in a 1–2-yr period (2008–2009). Vine colonization occurred almost exclusively in gaps, occurring on 16% of seedlings there. Excluding herbivores in gaps doubled colonization of the light-demanding and faster growing M. bisulcata but had negligible effects on the two shade-tolerant, slower growing and less palatable Tetraberlinia species, which together were twice as susceptible to vines under natural forest gap conditions (controls). When protected from herbivores in gaps, more light to individual seedlings strongly increased vine colonization of M. bisulcata whereas its well-lit control individuals supported significantly fewer vines. These results suggest vines preferably colonize taller seedlings, and because light-demanding tree species grow faster in height with more light, they are more prone to being colonized in gaps; however, insect herbivores can mediate this process by stunting fast growing individuals so that colonization rates becomes more similar between co-occurring slow and fast growing tree species. Further influencing this process might be associational resistance or susceptibility to herbivores linked to host species’ leaf traits conferring shade-tolerant ability as seedlings or saplings. A richer understanding of how vines differentially influence forest regeneration and species composition may come from investigating vine–tree–herbivore interactions across light gradients, ideally via long-term studies and intercontinental comparisons. Abstract in French is available with online material.     

Herbivores differentially limit the seedling growth and sapling recruitment of two dominant rain forest trees

Resource heterogeneity may influence how plants are attacked and respond to consumers in multiple ways. Perhaps a better understanding of how this interaction might limit sapling recruitment in tree populations may be achieved by examining species’ functional responses to herbivores on a continuum of resource availability. Here, we experimentally reduced herbivore pressure on newly established seedlings of two dominant masting trees in 40 canopy gaps, across c. 80 ha of tropical rain forest in central Africa (Korup, Cameroon). Mesh cages were built to protect individual seedlings, and their leaf production and changes in height were followed for 22 months. With more light, herbivores increasingly prevented the less shade-tolerant Microberlinia bisulcata from growing as tall as it could and producing more leaves, indicating an undercompensation. The more shade-tolerant Tetraberlinia bifoliolata was much less affected by herbivores, showing instead near to full compensation for leaf numbers, and a negligible to weak impact of herbivores on its height growth. A stage-matrix model that compared control and caged populations lent evidence for a stronger impact of herbivores on the long-term population dynamics of M. bisulcata than T. bifoliolata. Our results suggest that insect herbivores can contribute to the local coexistence of two abundant tree species at Korup by disproportionately suppressing sapling recruitment of the faster-growing dominant via undercompensation across the light gradient created by canopy disturbances. The functional patterns we have documented here are consistent with current theory, and, because gap formations are integral to forest regeneration, they may be more widely applicable in other tropical forest communities. If so, the interaction between life-history and herbivore impact across light gradients may play a substantial role in tree species coexistence.     

A Flood Plain Palm Forest in the Luquillo Mountains of Puerto Rico Five Years After Hurricane Hugo1

Long-term studies are needed to understand the dynamics of tropical forests, particularly those subject to periodic disturbances such as hurricanes. We studied a flood plain Prestoea montana palm forest in the Luquillo Mountains of Puerto Rico over a 15-yr period (1980–1995), which included the passage of Hurricane Hugo in September 1989. The passage of the hurricane caused the dominant species to become more dominant and created low instantaneous tree mortality (1% of stems) and reductions in tree biomass (-16 Mg/ha/yr) and density, although not in basal area. Five years after the hurricane, the palm flood plain forest had exceeded its prehurricane aboveground tree biomass, tree density, and basal area. Aboveground tree biomass accumulated at a rate of 9.2 Mg/ha/yr, 76 percent of which was due to palms. Before the hurricane this rate was on the order of 3 Mg/ha/yr. Forest floor litter decreased to prehurricane levels (6.7 Mg/ha), within 5 yr, mostly due to the disappearance of woody litter. Thirteen tree species not represented in the canopy entered the forest by regeneration, and 2 species suffered almost 20 percent/yr mortality over a 5-yr period after the storm (floodplain average of 2%/yr). Delayed tree mortality was twice as high as instantaneous tree mortality after the storm and affected dicotyledonous trees more than it did palms. Regencration of dicotyledonous trees, palms, and tree ferns was influenced by a combination of factors including hydroperiod, light, and space. Redundancy Data Analysis showed that the area near the river channel was the most favorable for plant regeneration. Palm regeneration was higher in locations with longer hydroperiods, while regeneration of dicotyledonous trees was higher in areas with low risk of flooding. This study shows how a periodic disturbance provides long-term opportunities for species invasions and long-term ecosystem response at the patch scale of < 1 ha.     

Variations in resistance to canopy disturbances and their interactions with the spatial structure of major species in a cool‐temperate forest

Question: How does typhoon‐related disturbance (more specifically, disturbance in the understorey due to tree‐fall and branch‐fall) affect different species mortality rates in a vertically well‐structured forest community? Location: Cool‐temperate, old‐growth forest in the Daisen Forest Reserve, Japan. Methods: We investigated the canopy dynamics and mortality rate trends of trees ≥5 cm diameter at breast height in a 4‐ha study plot, and analysed the effects of tree diameter and spatial structure on the mortality risks for major tree species in the understorey. Results: Significant differences were found in the mortality rates and proportions of injured dead stems between census periods, which were more pronounced in the understorey than in the canopy. Acer micranthum, which showed increased mortality during typhoon disturbance periods, had a clumped distribution. In contrast, Acer japonicum and Viburnum furcatum, which showed similar mortality rates between census periods, had a loosely clumped spatial distribution and a negative association with canopy trees, respectively. In the understorey stems of Acanthopanax sciadophylloides and Fagus crenata, whose spatial distribution patterns depended on canopy gaps, significant increases in mortality rates were observed only during severe typhoon‐related disturbance periods. Conclusions: The sensitivity of trees to typhoon‐related canopy disturbance is more pronounced in the lower layers of vertically structured forest communities. Differences in mortality patterns generated through the combined effects of spatial variation in disturbance regime and species‐specific spatial distribution patterns (spatial aggregation, association with canopy trees, and canopy gap dependency) contribute to the co‐existence of understorey species in forest communities that are subject to typhoon‐related disturbance.     

Linking responses of native and invasive plants to hurricane disturbances: implications for coastal plant community structure

Hurricane disturbances produce significant changes in forest microclimates, creating opportunities for seedling regeneration of native and invasive plant species alike. However, there is limited information on how changes in microclimates and pre-existing forest conditions affect native and invasive plants responses to hurricane disturbances. In this manipulative study, we examined the responses of three common shrub/small stature tree species, two of which are native to the coastal region of the southeastern USA (Baccharis halimifolia and Morella cerifera) and one that is invasive (Triadica sebifera), to two key components of hurricane disturbance (canopy damage and saline storm surge). In a greenhouse, we grew seedlings of these species under a range of shade levels that mimicked pre-and post-hurricane canopy conditions for wet pine forest and mixed hardwood forest, two forest communities common in coastal areas of the southeastern USA. Seedlings were subjected to saline storm surges equivalent to full strength sea water for 3 days. Seedling responses (mortality and growth) to the treatments were monitored for 16 months. All species benefitted from higher canopy openness. Storm surge effects were short-lived and seedlings readily recovered under high light conditions. The storm surge had stronger negative effects on survival and growth of all species when coupled with high shade, suggesting storm surge has greater negative impacts on seedlings where hurricane winds cause minimal or no canopy damage. The invasive T. sebifera was by far more shade tolerant than the natives. Survival of T. sebifera seedlings under highly shaded conditions may provide it a competitive edge over native species during community reassembly following tropical storms. Differential responses of native and invasive species to hurricane disturbances will have profound consequences on community structure across coastal forest stands, and may be regulated by legacies of prior disturbances, community structure, extent of canopy damage, and species’ tolerance to specific microclimates.

     

Dispersal mode,shade tolerance,and phytogeographical affinity of tree species during secondary succession in tropical montane cloud forest

Secondary succession following land abandonment, represented by a chronosequence of 15 old fields (0–80 years old) and two old-growth forests, was studied in the tropical montane cloud forest region of Veracruz, Mexico. The objective was to determine successional trajectories in forest structure and species richness of trees ≥5 cm DBH, in terms of differences in seed dispersal mode, shade tolerance, and phytogeographical affinity. Data were analyzed using AIC model selection and logistic regressions. Mean and maximum canopy height reached values similar to old-growth forest at 35 and 80 years, respectively. Species richness and diversity values were reached earlier (15 and 25 years, respectively) while basal area and stem density tended to reach old-growth forest values within 80 years. Along the chronosequence, the proportion of species and individuals of wind-dispersed trees declined, that of bird dispersed small seeded trees remained constant, while that of gravity and animal dispersed large seeded trees increased; shade-intolerant species and individuals declined, while intermediate and shade-tolerant trees increased. Shade-tolerant canopy trees were rare during succession, even in the old-growth forest. Tropical tree species were more frequent than temperate ones throughout the chronosequence, but temperate tree individuals became canopy dominants at intermediate and old-growth forest stages.     

Disturbance effects on herbaceous layer vegetation and soil nutrients in Populus forests of northern lower Michigan

Abstract. Recent disturbance models have identified changes in resource availability as factors that control plant community response. Soil nutrient resources typically are assumed to change following forest disturbance, usually with nutrient availablity increasing initially and subsequently decreasing through later stages of succession. We examined the effects of disturbance (clearcut harvesting with a brief recovery period) on soil organic matter, pH and extractable soil nutrients in successional aspen forests of northern lower Michigan to determine relationships of these variables to changes in herbaceous layer vegetation. Two site types were identified: drymesic (glacial outwash sands, low in organic matter) and mesic (calcareous clay till, high in organic matter). Extractable nutrient concentrations were 1.5 to 3 times higher in the A₁ horizon of mesic sites than those of dry-mesic sites. Soil pH and cations increased after disturbance on mesic sites, but not on dry-mesic sites. Patterns of change with disturbance were less pronounced in lower horizons on both site types. Herblayer species diversity increased after disturbance on mesic sites, but with decreases in the importance of shade-tolerant tree species and Maianthemum canadense. Species characteristic of open habitats (e.g. Pteridium aquilinum, Rubus spp., Fragaria virginiana, and Diervilla lonicera), increased in importance. Soil factors, species composition and diversity on dry-mesic sites changed little after disturbance, with Pteridium aquilinum and ericaceous species remaining dominant in both mature (55–82 yr) and disturbed (≤ 15 yr) stands. These results suggest that soil nutrient resources do not always change through secondary succession and that patterns of change can be distinctly site-dependent. Disturbance response patterns in the herbaceous layer of these aspen forests are also site-dependent.     

Extant and potential vegetation of an old-growth maritime Ilex opaca forest

The extant and potential (seed bank) vegetation of a rare maritime holly forest on Fire Island, New York was described to assess whether treefall gaps act as a mechanism for the persistence of the species composition of this plant community over time. The Sunken Forest overstory is dominated by Ilex opaca, Amelanchier canadensis and Sassafras albidum. A survey of canopy gaps indicated canopy openings compose 11.3% of the land within the Sunken Forest (16 ha). The composition and density of the seed bank were described using the emergence method. Germination from soil samples placed in the greenhouse was monitored over 2 years. Sixteen species germinated with an average propagule density of 215±41 germinants per square metre. An early successional species (Rhus copallinum) dominated the seed bank, but the late-successional, shade-tolerant I. opaca was also present. Though only one species in the seed bank did not appear in the current vegetation, species abundance differed between vegetation strata. The mean cover and density of the ground-layer flora were higher beneath treefall gaps than closed canopy. Sapling density did not differ between the two canopy conditions, but the dominant species differed with A. canadensis occupying several closed canopy plots and P. serotina saplings appearing more often in gap plots. Most of the dominant canopy species are present in the seed bank and ground layer but are not present in the shrub and sapling layer, with the exception of A. canadensis. Current (2002) sapling density is lower than three decades ago for all species except P. serotina, which is now the dominant woody species in the Sunken Forest understory. The results of this study indicate that if the cause of the sapling reduction is lessened or removed, the characteristic species of the overstory of this unusual plant community may rebound and redevelop a sapling and shrub layer akin to that present before the increase in Odocoileus virginianus on the island.     

Fire-induced shifts in overstory tree species composition and associated understory plant composition in Glacier National Park,Montana

In Rocky Mountain forests, fire can act as a mechanism of change in plant community composition if postfire conditions favor establishment of species other than those that dominated prefire tree communities. We sampled pre and postfire overstory and postfire understory species following recent (1988–2006) stand-replacing fires in Glacier National Park (GNP), Montana. We identified changes in relative density of tree species and groups of species (xerophytes vs. mesophytes and reseeders vs. resprouters) in early succession. Postfire tree seedling densities were adequate to maintain prefire forest structure, but relative densities among species were variously changed. Changes were directly related to individual species’ response to severe fires. Most notably, relative density of the mesophytic resprouter quaking aspen (Populus tremuloides) and the xerophytic reseeder lodgepole pine (Pinus contorta) increased substantially following fire, with a concomitant decline in proportional abundance of other tree species that, in some cases, dominated stands before fire. Trends identified in our study suggest that forest community shifts toward those dominated by lodgepole pine and quaking aspen are occurring in GNP. Cover of understory species was not affected by tree species composition or density. These forest communities will likely change throughout succession with the addition of shade-intolerant species in early seral stages and shade-tolerant species later in succession. However, with increased fire frequency, the lodgepole pine-dominated postfire communities observed in our study may become more common throughout time.     

Seedling and Sapling Dynamics of Treefall Pits in Puerto Rico1

Seedling and sapling dynamics in a Puerto Rican rain forest were compared between forest understory and soil pits created by the uprooting of 27 trees during Hurricane Hugo. Soil N and P, organic matter, and soil moisture were lower and bulk densities were higher in the disturbed mineral soils of the pits than in undisturbed forest soils ten months after the hurricane. No differences in N and P levels were found in pit or forest soils under two trees with N–fixing symbionts (Inga laurina and Ormosia krugii) compared to soils under a tree species without N–fixing sym–bionts (Casearia arborea), but other soil variables (Al, Fe, K) did vary by tree species. Forest plots had greater species richness of seedlings (<10 cm tall) and saplings (10–100 cm tall) than plots in the soil pits (and greater sapling densities), but seedling densities were similar between plot types. Species richness and seedling densities did not vary among plots associated with the three tree species, but some saplings were more abundant under trees of the same species. Pit size did not affect species richness or seedling and sapling densities. Recruitment of young Cecropia schreberiana trees (>5 m tall) 45 months after the hurricane was entirely from the soil pits, with no tree recruitment from forest plots. Larger soil pits had more tree recruitment than smaller pits. Defoliation of the forest by the hurricane created a large but temporary increase in light availability. Recruitment of C. schreberiana to the canopy occurred in gaps created by the treefall pits that had lower soil nutrients but provided a longer–term increase in light availability. Treefall pits also significantly altered the recruitment and mortality of many understory species in the Puerto Rican rain forest but did not alter species richness.     

The effects of environmental variables and human disturbance on woody species richness and diversity in a bamboo–deciduous forest in northeastern Thailand

Variations in species richness and diversity at a local scale are affected by a number of complex and interacting variables, including both natural environmental factors and human-made changes to the local environment. Here we identified the most important determinants of woody species richness and diversity at different growth stages (i.e. adult, sapling and seedling) in a bamboo–deciduous forest in northeast Thailand. A total of 20 environmental and human disturbance variables were used to determine the variation in species richness and diversity. In total, we identified 125 adult, 111 sapling (within fifty 20 × 20-m plots) and 89 seedling species (within one hundred and twenty 1 × 1-m subplots). Overall results from stepwise multiple regression analyses showed that environmental variables were by far the most important in explaining the variation in species richness and diversity. Forest structure (i.e. number of bamboo clumps and canopy cover) was important in determining the adult species richness and diversity (R ² = 0.48, 0.30, respectively), while topography (i.e. elevation) and human disturbance (i.e. number of tree stumps) were important in determining the sapling species richness and diversity (R ² = 0.55, 0.39, respectively). Seedling species richness and diversity were negatively related to soil phosphorus. Based on our results, we suggest that the presence of bamboos should be incorporated in management strategies for maintaining woody species richness and diversity in these forest ecosystems. Specifically, if bamboos cover the forest floor at high densities, it may be necessary to actively control these species for successful tree establishment.     

Resistance to wildfire and early regeneration in natural broadleaved forest and pine plantation

The response of an ecosystem to disturbance reflects its stability, which is determined by two components: resistance and resilience. We addressed both components in a study of early post-fire response of natural broadleaved forest (Quercus robur, Ilex aquifolium) and pine plantation (Pinus pinaster, Pinus sylvestris) to a wildfire that burned over 6000 ha in NW Portugal. Fire resistance was assessed from fire severity, tree mortality and sapling persistence. Understory fire resistance was similar between forests: fire severity at the surface level was moderate to low, and sapling persistence was low. At the canopy level, fire severity was generally low in broadleaved forest but heterogeneous in pine forest, and mean tree mortality was significantly higher in pine forest. Forest resilience was assessed by the comparison of the understory composition, species diversity and seedling abundance in unburned and burned plots in each forest type. Unburned broadleaved communities were dominated by perennial herbs (e.g., Arrhenatherum elatius) and woody species (e.g., Hedera hibernica, Erica arborea), all able to regenerate vegetatively. Unburned pine communities presented a higher abundance of shrubs, and most dominant species relied on post-fire seeding, with some species also being able to regenerate vegetatively (e.g., Ulex minor, Daboecia cantabrica). There were no differences in diversity measures in broadleaved forest, but burned communities in pine forest shared less species and were less rich and diverse than unburned communities. Seedling abundance was similar in burned and unburned plots in both forests. The slower reestablishment of understory pine communities is probably explained by the slower recovery rate of dominant species. These findings are ecologically relevant: the higher resistance and resilience of native broadleaved forest implies a higher stability in the maintenance of forest processes and the delivery of ecosystem services.