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1.
Ecology ; : e02999, 2020 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-32004379

RESUMO

Identifying the environmental drivers of population dynamics is crucial to predict changes in species abundances and distributions under climate change. Populations of the same species might differ in their responses as a result of intraspecific variation. Yet the importance of such differences remains largely unexplored. We examined the responses of latitudinally distant populations of the forest moss Hylocomiastrum umbratum along microclimate gradients in Sweden. We transplanted moss mats from southern and northern populations to 30 sites with contrasting microclimates (i.e., replicated field common gardens) within a forest landscape, and recorded growth and survival of individual shoots over 3 yr. To evaluate the importance of intraspecific variation in responses to environmental factors, we assessed effects of the interactions between population origin and microclimate drivers on growth and survival. Effects on overall performance of transplanted populations were estimated using the product of survival and growth. We found differences between southern and northern populations in the response to summer temperature and snowmelt date in one of three yearly transitions. In this year, southern populations performed better in warm, southern-like conditions than in cold, northern-like conditions; and the reverse pattern was true for northern populations. Survival of all populations decreased with evaporation, consistent with the high hydric demands and poikilohydric nature of mosses. Our results are consistent with population adaptation to local climate, and suggest that intraspecific variation among populations can have important effects on the response of species to microclimate drivers. These findings highlight the need to account for differential responses in predictions of species abundance and distribution under climate change.

2.
Glob Chang Biol ; 26(2): 471-483, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31833152

RESUMO

Climate warming is likely to shift the range margins of species poleward, but fine-scale temperature differences near the ground (microclimates) may modify these range shifts. For example, cold-adapted species may survive in microrefugia when the climate gets warmer. However, it is still largely unknown to what extent cold microclimates govern the local persistence of populations at their warm range margin. We located 99 microrefugia, defined as sites with edge populations of 12 widespread boreal forest understory species (vascular plants, mosses, liverworts and lichens) in an area of ca. 24,000 km2 along the species' southern range margin in central Sweden. Within each population, a logger measured temperature eight times per day during one full year. Using univariate and multivariate analyses, we examined the differences of the populations' microclimates with the mean and range of microclimates in the landscape, and identified the typical climate, vegetation and topographic features of these habitats. Comparison sites were drawn from another logger data set (n = 110), and from high-resolution microclimate maps. The microrefugia were mainly places characterized by lower summer and autumn maximum temperatures, late snow melt dates and high climate stability. Microrefugia also had higher forest basal area and lower solar radiation in spring and autumn than the landscape average. Although there were common trends across northern species in how microrefugia differed from the landscape average, there were also interspecific differences and some species contributed more than others to the overall results. Our findings provide biologically meaningful criteria to locate and spatially predict potential climate microrefugia in the boreal forest. This opens up the opportunity to protect valuable sites, and adapt forest management, for example, by keeping old-growth forests at topographically shaded sites. These measures may help to mitigate the loss of genetic and species diversity caused by rear-edge contractions in a warmer climate.

3.
Nat Ecol Evol ; 3(5): 744-749, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30936433

RESUMO

Macroclimate warming is often assumed to occur within forests despite the potential for tree cover to modify microclimates. Here, using paired measurements, we compared the temperatures under the canopy versus in the open at 98 sites across 5 continents. We show that forests function as a thermal insulator, cooling the understory when ambient temperatures are hot and warming the understory when ambient temperatures are cold. The understory versus open temperature offset is magnified as temperatures become more extreme and is of greater magnitude than the warming of land temperatures over the past century. Tree canopies may thus reduce the severity of warming impacts on forest biodiversity and functioning.


Assuntos
Florestas , Microclima , Temperatura Ambiente , Mudança Climática
4.
Glob Chang Biol ; 24(7): 2952-2964, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-29635859

RESUMO

Species are often controlled by biotic factors such as competition at the warm edge of their distribution range. Disturbances at the treeline, disrupting competitive dominance, may thus enable alpine species to utilize lower altitudes. We searched for evidence for range expansion in grazed, fire-managed Ethiopian subalpine Erica heathlands across a 25-year chronosequence. We examined vascular plant composition in 48 plots (5 × 5 m) across an altitudinal range of 3,465-3,711 m.a.s.l. and analyzed how community composition changed in relation to increasing competition over time (using a Shade index based on Erica shrub height and cover) and altitude. Species' habitats and altitudinal ranges were derived from literature. Time since fire explained more variation (r2  = .41) in species composition than altitude did (r2  = .32) in an NMDS analysis. Community-weighted altitudinal optima for species in a plot decreased strongly with increasing shade (GLM, Standardized Regression Coefficient SRC = -.41, p = .003), but increased only weakly with altitude (SRC = .26, p = .054). In other words, young stands were dominated by species with higher altitudinal optima than old stands. Forest species richness increased with Log Shade index (SRC = .12, p = .008), but was unaffected by altitude (SRC = -.07, p = .13). However, richness of alpine and heathland species was not highest in plots with lowest Shade index, but displayed a unimodal pattern with an initial increase, followed by a decrease when shading increased (altitude was not significant). Our results indicate that disturbance from the traditional patch burning increases the available habitat for less competitive high-altitude plants and prevents tree line ascent. Therefore, maintaining, but regulating, the traditional land use increases the Afro-alpine flora's resilience to global warming. However, this system is threatened by a new REDD+ program attempting to increase carbon storage via fire suppression. This study highlights the importance of understanding traditional management regimes for biodiversity conservation in cultural landscapes in an era of global change.


Assuntos
Mudança Climática , Fogo , Desenvolvimento Vegetal , Plantas/classificação , África , Altitude , Biodiversidade
5.
Ecol Evol ; 8(23): 11484-11491, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30598750

RESUMO

Dispersal is a fundamental biological process that can be divided into three phases: release, transportation, and deposition. Determining the mechanisms of diaspore release is of prime importance to understand under which climatic conditions and at which frequency diaspores are released and transported. In mosses, wherein spore dispersal takes place through the hygroscopic movements of the peristome, the factors enhancing spore release has received little attention. Here, we determine the levels of relative humidity (RH) at which peristome movements are induced, contrasting the response of species with perfect (fully developed) and specialized (reduced) peristomes. All nine investigated species with perfect peristomes displayed a xerochastic behavior, initiating a closing movement from around 50%-65% RH upon increasing humidity and an opening movement from around 90% RH upon drying. Five of the seven species with specialized peristomes exhibited a hygrochastic behavior, initiating an opening movement under increasing RH (from about 80%) and a closing movement upon drying (from about 90%). These differences between species with hygrochastic and xerochastic peristomes suggest that spore dispersal does not randomly occur regardless of the prevailing climate conditions, which can impact their dispersal distances. In species with xerochastic peristomes, the release of spores under decreasing RH can be interpreted as an adaptive mechanism to disperse spores under optimal conditions for long-distance wind dispersal. In species with hygrochastic peristomes, conversely, the release of spores under wet conditions, which decreases their wind long-distance dispersal capacities, might be seen as a safe-site strategy, forcing spores to land in appropriate (micro-) habitats where their survival is favored. Significant variations were observed in the RH thresholds triggering peristome movements among species, especially in those with hygrochastic peristomes, raising the question of what mechanisms are responsible for such differences.

7.
Trends Ecol Evol ; 32(5): 335-345, 2017 05.
Artigo em Inglês | MEDLINE | ID: mdl-28284373

RESUMO

Given the serious limitations of production-oriented frameworks, we offer here a new conceptual framework for how to analyze the nexus of food security and biodiversity conservation. We introduce four archetypes of social-ecological system states corresponding to win-win (e.g., agroecology), win-lose (e.g., intensive agriculture), lose-win (e.g., fortress conservation), and lose-lose (e.g., degraded landscapes) outcomes for food security and biodiversity conservation. Each archetype is shaped by characteristic external drivers, exhibits characteristic internal social-ecological features, and has characteristic feedbacks that maintain it. This framework shifts the emphasis from focusing on production only to considering social-ecological dynamics, and enables comparison among landscapes. Moreover, examining drivers and feedbacks facilitates the analysis of possible transitions between system states (e.g., from a lose-lose outcome to a more preferred outcome).


Assuntos
Agricultura , Biodiversidade , Conservação dos Recursos Naturais , Abastecimento de Alimentos , Ecossistema
8.
Proc Biol Sci ; 283(1838)2016 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-27629036

RESUMO

The expansion of pollinator-dependent crops, especially in the developing world, together with reports of worldwide pollinator declines, raises concern of possible yield gaps. Farmers directly reliant on pollination services for food supply often live in regions where our knowledge of pollination services is poor. In a manipulative experiment replicated at 23 sites across an Ethiopian agricultural landscape, we found poor pollination services and severe pollen limitation in a common oil crop. With supplementary pollination, the yield increased on average by 91%. Despite the heterogeneous agricultural matrix, we found a low bee abundance, which may explain poor pollination services. The variation in pollen limitation was unrelated to surrounding forest cover, local bee richness and bee abundance. While practices that commonly increase pollinators (restricted pesticide use, flower strips) are an integral part of the landscape, these elements are apparently insufficient. Management to increase pollination services is therefore in need of urgent investigation.


Assuntos
Agricultura/métodos , Abelhas , Polinização , Animais , Produtos Agrícolas , Etiópia , Flores , Pólen
9.
PLoS One ; 10(5): e0126639, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25961306

RESUMO

Bird and arthropod predation is often associated with natural pest control in agricultural landscapes, but the rates of predation may vary with the amount of tree cover or other environmental factors. We examined bird and arthropod predation in three tree-rich and three tree-poor landscapes across southwestern Ethiopia. Within each landscape we selected three tree-rich and three tree-poor homegardens in which we recorded the number of tree species and tree stems within 100 × 100 m surrounding the central house. To estimate predation rates, we attached plasticine caterpillars on leaves of two coffee and two avocado shrubs in each homegarden, and recorded the number of attacked caterpillars for 7-9 consecutive weeks. The overall mean daily predation rate was 1.45% for birds and 1.60% for arthropods. The rates of arthropod predation varied among landscapes and were higher in tree-poor landscapes. There was no such difference for birds. Within landscapes, predation rates from birds and arthropods did not vary between tree-rich and tree-poor homegardens in either tree-rich or tree-poor landscapes. The most surprising result was the lack of response by birds to tree cover at either spatial scale. Our results suggest that in tree-poor landscapes there are still enough non-crop habitats to support predatory arthropods and birds to deliver strong top-down effect on crop pests.


Assuntos
Artrópodes , Aves , Comportamento Predatório , Árvores , Animais , Etiópia
10.
PLoS One ; 10(3): e0120085, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25803452

RESUMO

Secondary succession is changing the character of many temperate forests and often leads to closed-canopy stands. In such forests set aside for conservation, habitat management alternatives need to be tested experimentally, but this is rarely done. The Swedish Oak Project compares two often debated alternatives: minimal intervention and non-traditional active management (conservation thinning) on plots of each type replicated at 25 sites. We study responses of several taxa, and here report results for land molluscs. They are considered to be sensitive to more open, drier forest and we predicted a negative effect of the thinning (26% reduction of the basal area; mean value for 25 experimental forests). We sampled molluscs in the litter in ten 20 x 25 cm subplots, and by standardised visual search, in each plot. In total, we recorded 53 species of snails and slugs (24 369 individuals) and the mean species richness in plots was 17. Two seasons after thinning, mean (± SE) species richness had decreased by 1.4 (± 0.9) species in thinning plots, but increased by 0.7 (± 1.0) species in minimal intervention plots, a significant but small change with considerable variation among sites. In matched comparisons with minimal intervention, thinning reduced the overall abundance of molluscs. Most species responded negatively to thinning - but only five of the 53 species were significantly affected, and reproduction seemed to be negatively affected in only one species. An ordination analysis did not reveal any particular change in the species community due to thinning. Thus, the negative effect of conservation thinning on land molluscs was apparently mild - one reason was that many trees, shrubs and other forest structures remained after the treatment. Conservation thinning may be recommended, since other taxa are favoured, but minimal intervention is also a useful form of management for molluscs and saproxylic taxa.


Assuntos
Biodiversidade , Conservação dos Recursos Naturais/métodos , Florestas , Moluscos , Animais , Moluscos/classificação , Moluscos/fisiologia , Densidade Demográfica , Reprodução , Estações do Ano , Suécia
11.
Ambio ; 44 Suppl 1: S60-8, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25576281

RESUMO

Microrefugia are sites that support populations of species when their ranges contract during unfavorable climate episodes. Here, we review and discuss two aspects relevant for microrefugia. First, distributions of different species are influenced by different climatic variables. Second, climatic variables differ in the degree of local decoupling from the regional climate. Based on this, we suggest that only species limited by climatic conditions decoupled from the regional climate can benefit from microrefugia. We argue that this restriction has received little attention in spite of its importance for microrefugia as a mechanism for species resilience (the survival of unfavorable episodes and subsequent range expansion). Presence of microrefugia will depend on both the responses of individual species to local climatic variation and how climate-forcing factors shape the correlation between local and regional climate across space and time.


Assuntos
Ecossistema , Mudança Climática
12.
Ambio ; 44 Suppl 1: S113-26, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25576286

RESUMO

Wetlands provide multiple ecosystem services, the sustainable use of which requires knowledge of the underlying ecological mechanisms. Functional traits, particularly the community-weighted mean trait (CWMT), provide a strong link between species communities and ecosystem functioning. We here combine species distribution modeling and plant functional traits to estimate the direction of change of ecosystem processes under climate change. We model changes in CWMT values for traits relevant to three key services, focusing on the regional species pool in the Norrström area (central Sweden) and three main wetland types. Our method predicts proportional shifts toward faster growing, more productive and taller species, which tend to increase CWMT values of specific leaf area and canopy height, whereas changes in root depth vary. The predicted changes in CWMT values suggest a potential increase in flood attenuation services, a potential increase in short (but not long)-term nutrient retention, and ambiguous outcomes for carbon sequestration.


Assuntos
Mudança Climática , Ecossistema , Áreas Alagadas
13.
PLoS One ; 9(11): e112943, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25387233

RESUMO

Most species distribution models assume a close link between climatic conditions and species distributions. Yet, we know little about the link between species' geographical distributions and the sensitivity of performance to local environmental factors. We studied the performance of three bryophyte species transplanted at south- and north-facing slopes in a boreal forest landscape in Sweden. At the same sites, we measured both air and ground temperature. We hypothesized that the two southerly distributed species Eurhynchium angustirete and Herzogiella seligeri perform better on south-facing slopes and in warm conditions, and that the northerly distributed species Barbilophozia lycopodioides perform better on north-facing slopes and in relatively cool conditions. The northern, but not the two southern species, showed the predicted relationship with slope aspect. However, the performance of one of the two southern species was still enhanced by warm temperatures. An important reason for the inconsistent results can be that microclimatic gradients across landscapes are complex and influenced by many climate-forcing factors. Therefore, comparing only north- and south-facing slopes might not capture the complexity of microclimatic gradients. Population growth rates and potential distributions are the integrated results of all vital rates. Still, the study of selected vital rates constitutes an important first step to understand the relationship between population growth rates and geographical distributions and is essential to better predict how climate change influences species distributions.


Assuntos
Briófitas/fisiologia , Ecossistema , Florestas , Crescimento Demográfico , Especificidade da Espécie , Suécia , Temperatura Ambiente
14.
Conserv Biol ; 27(5): 1031-40, 2013 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-23772911

RESUMO

Knowledge about how forest margins are utilized can be crucial for a general understanding of changes in forest cover, forest structure, and biodiversity across landscapes. We studied forest-agriculture transitions in southwestern Ethiopia and hypothesized that the presence of coffee (Coffea arabica)decreases deforestation rates because of coffee's importance to local economies and its widespread occurrence in forests and forest margins. Using satellite images and elevation data, we compared changes in forest cover over 37 years (1973-2010) across elevations in 2 forest-agriculture mosaic landscapes (1100 km(2) around Bonga and 3000 km(2) in Goma-Gera). In the field in the Bonga area, we determined coffee cover and forest structure in 40 forest margins that differed in time since deforestation. Both the absolute and relative deforestation rates were lower at coffee-growing elevations compared with at higher elevations (-10/20% vs. -40/50% comparing relative rates at 1800 m asl and 2300-2500 m asl, respectively). Within the coffee-growing elevation, the proportion of sites with high coffee cover (>20%) was significantly higher in stable margins (42% of sites that had been in the same location for the entire period) than in recently changed margins (0% of sites where expansion of annual crops had changed the margin). Disturbance level and forest structure did not differ between sites with 30% or 3% coffee. However, a growing body of literature on gradients of coffee management in Ethiopia reports coffee's negative effects on abundances of forest-specialist species. Even if the presence of coffee slows down the conversion of forest to annual-crop agriculture, there is a risk that an intensification of coffee management will still threaten forest biodiversity, including the genetic diversity of wild coffee. Conservation policy for Ethiopian forests thus needs to develop strategies that acknowledge that forests without coffee production may have higher deforestation risks than forests with coffee production and that forests with coffee production often have lower biodiversity value.


Assuntos
Agricultura/métodos , Coffea , Conservação dos Recursos Naturais , Árvores , Etiópia , Geografia , Comunicações Via Satélite , Clima Tropical
15.
Glob Chang Biol ; 19(5): 1470-81, 2013 May.
Artigo em Inglês | MEDLINE | ID: mdl-23504984

RESUMO

Recent studies from mountainous areas of small spatial extent (<2500 km(2) ) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m(2) units (community-inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1-km(2) units; (2) the relationship between CiT range and topographically and geographically derived predictors at 1-km resolution; and (3) whether spatial turnover in CiT is greater than spatial turnover in GiT within 100-km(2) units. Ellenberg temperature indicator values in combination with plant assemblages explained 46-72% of variation in LmT and 92-96% of variation in GiT during the growing season (June, July, August). Growing-season CiT range within 1-km(2) units peaked at 60-65°N and increased with terrain roughness, averaging 1.97 °C (SD = 0.84 °C) and 2.68 °C (SD = 1.26 °C) within the flattest and roughest units respectively. Complex interactions between topography-related variables and latitude explained 35% of variation in growing-season CiT range when accounting for sampling effort and residual spatial autocorrelation. Spatial turnover in growing-season CiT within 100-km(2) units was, on average, 1.8 times greater (0.32 °C km(-1) ) than spatial turnover in growing-season GiT (0.18 °C km(-1) ). We conclude that thermal variability within 1-km(2) units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains.


Assuntos
Biota , Mudança Climática , Fenômenos Fisiológicos Vegetais , Europa (Continente) , Geografia , Modelos Teóricos , Temperatura Ambiente
16.
Trends Ecol Evol ; 28(6): 341-6, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23419539

RESUMO

Extinction debts can result from many types of habitat changes involving mechanisms other than metapopulation processes. This is a fact that most recent literature on extinction debts pays little attention to. We argue that extinction debts can arise because (i) individuals survive in resistant life-cycle stages long after habitat quality change, (ii) stochastic extinctions of populations that have become small are not immediate, and (iii) metapopulations survive long after that connectivity has decreased if colonization-extinction dynamics is slow. A failure to distinguish between these different mechanisms and to simultaneously consider both the size of the extinction debt and the relaxation time hampers our understanding of how extinction debts arise and our ability to prevent ultimate extinctions.


Assuntos
Ecossistema , Extinção Biológica , Animais , Conservação dos Recursos Naturais , Modelos Biológicos , Plantas , Dinâmica Populacional , Processos Estocásticos , Fatores de Tempo
17.
PLoS One ; 7(7): e41987, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22870183

RESUMO

It is well-known that many species with small diaspores can disperse far during extended temporal scales (many years). However, studies on short temporal scales usually only cover short distances (in, e.g., bryophytes up to 15 m). By using a novel experimental design, studying the realized dispersal, we extend this range by almost two orders of magnitude. We recorded establishment of the fast-growing moss Discelium nudum on introduced suitable substrates, placed around a translocated, sporulating mother colony. Around 2,000 pots with acidic clay were placed at different distances between 5 m and 600 m, in four directions, on a raised bog, with increased pot numbers with distance. The experiment was set up in April-May and the realized dispersal (number of colonized pots) was recorded in September. Close to the mother colony (up to 10 m), the mean colonization rates (ratio of colonized pots) exceeded 50%. At distances between 10 and 50 m colonization dropped sharply, but beyond 50 m the mean colonization rates stabilized and hardly changed (1-3%). The estimated density of spores causing establishments at the further distances (2-6 spores/m²) was realistic when compared to the estimated spore output from the central colonies. Our study supports calculations from earlier studies, limited to short distances, that a majority of the spores disperse beyond the nearest vicinity of a source. The even colonization pattern at further distances raises interesting questions about under what conditions spores are transported and deposited. However, it is clear that regular establishment is likely at the km-scale for this and many other species with similar spore output and dispersal mechanism.


Assuntos
Briófitas/fisiologia , Esporos/fisiologia
18.
Oecologia ; 167(4): 1093-101, 2011 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21706332

RESUMO

The extent to which a plant assemblage might recolonize a disturbed system is in general related to the availability of propagule sources and sites with appropriate conditions for establishment. Both these factors might be sensitive to aspects of spatial heterogeneity. Microtopographic variation may enhance initial resistance by reducing the impact of the disturbance and facilitating establishment of incoming propagules by providing shaded "safe-sites". This study explores the influence of microtopographic heterogeneity (caused by variation in surface boulder cover) on the recolonization of closed-canopy forest floor bryophytes using a chronosequence of 75 spruce-dominated forests in south-central Sweden (2-163 years after clear-cutting). We found that high boulder cover did increase survival and subsequent persistence in young forests at both investigated scales (i.e. 1,000 and 100 m(2)), although this pattern became less evident on the smaller spatial scale. Species accumulation in boulder-poor subplots was not different when surrounded by boulder-rich compared with boulder-poor subplots suggesting short-distance recolonization from boulder-created refugia to be of little importance during recolonization. To conclude, it seems that boulders increase initial resistance to clear-cutting for this bryophyte guild, but that the subsequent recolonization process is more likely to depend on external propagule sources and factors affecting establishment such as the microclimate in the developing stand.


Assuntos
Briófitas/fisiologia , Ecossistema , Agricultura Florestal , Monitoramento Ambiental , Dinâmica Populacional , Especificidade da Espécie , Suécia , Árvores
19.
Ecol Appl ; 20(6): 1648-63, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20945765

RESUMO

Forested freshwater ecosystems worldwide are threatened by a number of anthropogenic disturbances, such as water pollution and canalization. Transient or permanent deforestation can also be a serious threat to organisms in forested watersheds, but its effects on different types of freshwater systems has been little studied. We investigated lotic bryophyte communities on rock and soil in subtropical cloud laurel forests on La Gomera Island in the Canary Islands, Spain, and asked whether the response to forest clear-cutting varied among the communities associated with dripping walls, streams, and waterfalls. We compared three successional forest stages: ancient forests (> 250 years), young forests (20-50 years after clear-cutting), and open stands (5-15 years after clear-cutting). In each of 56 study sites we sampled general vegetation and substrate data in a 0.01-ha plot and took composition data of bryophyte species in 3 + 3 subplots of 1 x 1 m. The general pattern of decline in species richness and change in species composition after forest clear-cutting was stronger for streamside assemblages compared to assemblages on dripping walls and in waterfalls. The change in species numbers on rocks was larger than that on soils, because a guild of species growing on soil (but not on rocks) were favored by disturbance and thus increased in the disturbed sites. Most of the sensitive species could be classified as typical laurel forest species. Mosses were generally more tolerant to forest clear-cutting than were liverworts. We suggest that streamsides are more sensitive to disturbance than waterfalls and dripping walls because of a larger variation in microclimate before than after clear-cutting and because they are more easily invaded by early-successional species (both bryophytes and highly competitive vascular plants). We propose that special care should be taken along small streams within disturbed watersheds if bryophyte assemblages and threatened species should be protected. The susceptibility to anthropogenic pressures is probably rather high in ecosystems that do not regularly experience large-scale stand-replacing disturbances, especially on oceanic islands because of isolation and a small total habitat area for focal organisms.


Assuntos
Briófitas/fisiologia , Ecossistema , Agricultura Florestal/métodos , Árvores , Demografia , Monitoramento Ambiental , Espanha , Água
20.
Ecology ; 90(4): 1042-54, 2009 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-19449698

RESUMO

Landscape heterogeneity causes spatial variation in disturbance regimes and resilience. We asked whether the resilience of bryophyte (liverwort and moss) assemblages to clear-cutting differs between streamside and upland boreal forests in northern Sweden. We hypothesized that bryophyte survival and recolonization rates are higher in streamside areas, thus raising resilience. Conversely, disturbance-intolerant but also invading species should be more frequent here, potentially reducing resilience. In each of 18 sites, we compared two 0.1-ha plots (one streamside and one upland) located in old forest that had never been clear-cut with two matching plots in young stands established after clear-cutting of old forests 30-50 years earlier. We used the magnitude of the difference in assemblages between old and young stands as a measure of change and, therefore, resilience (large difference implying low resilience). Species assemblages were more resilient in streamside than in upland forests. Species composition changed significantly in upland but not in streamside forests. Reductions in species richness were more pronounced in upland forests for total richness and for eight subgroups of species. Two results indicated lower survival/recolonization in upland forests: (1) species had a stronger association with old stands in upland areas, and (2) among species present in both the old streamside and old upland plot in a site, fewer appeared in the young upland than in the corresponding streamside plot. Simultaneously, a higher proportion of species invaded streamside areas; 40 of the 262 species encountered in streamside forests increased their occupancy by two or more sites compared to only two of 134 species in uplands. We suggest that in boreal forests spatial variation in resilience of assemblages of forest organisms intolerant of canopy removal is related to factors governed mainly by topography. More generally, we argue that landscape-scale variation in resilience of assemblages is influenced by spatial variation in (1) stress and resource availability, (2) number of disturbance-intolerant species, and (3) magnitude of environmental changes brought about by a disturbance with a specific intensity. We also suggest that rapid recovery in the short term does not necessarily imply higher long-term ability to return to the pre-disturbance state.


Assuntos
Briófitas/fisiologia , Ecossistema , Rios , Árvores/fisiologia , Animais , Dinâmica Populacional
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