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133 results for “Ecotone”

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dryad36/100

Data from: Contrasting species decline but high sensitivity to increasing water stress on a mixed pine-oak ecotone

1. Forest decline under environmental stress is expressed by regeneration failure and accelerated mortality in all ontogenic stages at the population level. Characterizing functional traits and mechanisms that best capture species decline and mortality is essential to assess forest dynamics. 2. We analyzed sensitivity to increasing water stress in two species with different water-use strategies on a mixed Quercus pyrenaica - Pinus sylvestris forest where adult pines express vulnerability to climate change but oaks do not. We compared dynamics of radial growth, wood δ13C and sapwood nonstructural carbohydrates (NSC) in response to drought at different time scales in both species and two age-cohorts in pine. 3. Both species were very sensitive to water stress, which influenced trait phenotypic plasticity at short- and long-time scales. Water-use strategy in pines of both ages was more conservative than in the more drought-tolerant oak. Both species showed negative growth trends despite increasing iWUE. Recent growth of pines is slower than it was in the past. Carbon isotope discrimination trends in young pines suggested increasing leaf gas exchange constraints. NSC were far from depletion in both species and all pine ages. Intra- and inter-annual NSC variability was higher in oaks than in pines and in soluble sugars (SS) than in starch. SS were lowest in young pines. Sensitivity of NSC to contrasting climatic years was low in pines, which NSC mostly remained homeostatic. The sensitivity to climate expressed suggests different C-allocation strategies, with less coupling between radial growth and current year photosynthesis in young pines. 4. Synthesis. Pines expressed negative responses to increased water stress regardless of age, showing rising gas-exchange constraints through tighter stomatal control of water losses than oaks. Young pines showed similar functional responses to water stress than old pines in decline, which suggests species-level vulnerability and could be regarded as early-warning signals anticipating mortality in pines. Yet, given the high sensitivity to drought also expressed by the non-declining oak, it would have been difficult to unequivocally disentangle species decline based only on the traits analysed.

opencc-zeroJul 2020View details →

dryad36/100

Data from: Nitrogen enrichment accelerates mangrove range expansion in the temperate-tropical ecotone

Climate change and nutrient enrichment are two phenomena impacting coastal ecosystems. In coastal wetlands, mangroves in temperate-tropical ecotones are encroaching on adjacent saltmarshes, a pattern that is primarily attributed to warmer winter temperatures. Climate change is also expected to increase the vulnerability of coastal wetlands to eutrophication, and increases in nutrient availability may further mediate the rate of mangrove expansion. We investigated the consequences of nutrient enrichment on coastal wetlands in the mangrove-saltmarsh ecotone near the temperate edge of mangrove distribution along the northeast coast of Florida. We tested the hypothesis that nutrient enrichment enhances the ongoing, climate-driven expansion of mangroves into areas historically dominated by saltmarshes by increasing mangrove growth and cover, allowing them to outcompete and overgrow adjacent saltmarsh plants. We manipulated nitrogen (N) and phosphorus (P) availability and measured the effects on growth, cover, diversity, leaf traits and nutrient dynamics of Avicennia germinans. We found that A. germinans shrubs growing in the saltmarsh-mangrove ecotone in northern Florida grew taller, increased their canopies, and had higher reproductive output when enriched with N compared to control plants and P-enriched plants. Nutrient enrichment did not alter Sarcocornia perennis growth, and increased Batis maritima height but did not alter density or biomass. Nitrogen addition caused an increase in A. germinans cover and decreases in B. maritima cover and Simpson's index of diversity, suggesting that N enrichment, an ongoing phenomenon, can hasten the invasion of mangroves into saltmarshes by favoring mangrove growth and reproduction without significantly enhancing saltmarsh plant growth.

opencc-zeroAug 2020View details →

dryad36/100

Data from: Varieties of the highly dispersible and hypervariable tree, Metrosideros polymorpha, differ in response to mechanical stress and light across a sharp ecotone

PREMISE OF THE STUDY: The drivers of isolation between sympatric populations of long-lived and highly-dispersible conspecific plants are not well understood. In the Hawaiian Islands the landscape-dominant tree, Metrosideros polymorpha, displays extraordinary phenotypic differences among sympatric varieties despite high dispersibility of its pollen and seeds, thereby presenting a unique opportunity to investigate how disruptive selection alone can maintain incipient forms. Stenophyllous M. polymorpha var. newellii is a recently evolved tree endemic to the waterways of east Hawai'i Island that shows striking neutral genetic differentiation from its ancestor, wet-forest var. glaberrima, despite sympatry of these forms. We looked for evidence for, and drivers of, differential local adaptation of these varieties across the range of var. newellii. METHODS: For paired populations of these varieties, we compared seedling performance under contrasting light conditions and a strong water current characteristic of the riparian zone. We also conducted a reciprocal transplant experiment and contrasted adult leaf anatomy. KEY RESULTS: Results suggest that the riparian zone is harsh and that selection involving the mechanical stress of rushing water, and secondarily light, lead to significant reciprocal immigrant inviability in adjacent forest and riparian environments. The strongest adaptive divergence between varieties was seen in leaves and seedlings from the site with the sharpest ecotone, coincident with the strongest genetic isolation of var. newellii observed previously. CONCLUSIONS: These findings suggest that disruptive selection across a sharp ecotone contributes to the maintenance of an incipient riparian ecotype from within a continuous population of a long-lived and highly dispersible tree species.

opencc-zeroJul 2019View details →

dryad36/100

Higher vascular plant abundance associated with decreased ecosystem respiration after 20 years of warming in the forest-tundra -ecotone

The ongoing climate warming is promoting shrub abundance in high latitudes, but the effect of this phenomenon on ecosystem functioning is expected to depend on whether deciduous or evergreen species increase in response to warming. To explore effects of long-term warming on shrubs and further on ecosystem functioning, we analyzed vegetation and ecosystem CO2 exchange after 20 years of warming in the forest-tundra ecotone in sub-arctic Sweden. A previous study conducted nine years earlier had found increased evergreen Empetrum nigrum ssp. hermaphroditum in the forest and increased deciduous Betula nana in the tundra. Following current understanding, we expected a continued increase in shrub abundance that would be stronger in tundra than in forest. We expected warming to increase ecosystem respiration (Re) and gross primary productivity (GPP), with a greater increase in Re in tundra due to increased deciduous shrub abundance, leading to a less negative net ecosystem exchange (NEE) and reduced ecosystem C sink strength. As predicted, vascular plant abundances were higher in the warmed plots with a stronger response in tundra than in forest. However, whereas B. nana had increased in abundance since the last survey, E. hermaphroditum abundance had declined due to several moth and rodent outbreaks during the past decade. In contrast to predictions, Re was significantly lower in the warmed plots irrespective of habitat, and GPP increased marginally only in the forest. The lower Re and a higher GPP under warming in the forest together led to increased net C sink. Re was negatively associated with the total vascular plant abundance. Our results highlight the importance of disturbance regimes for vegetation responses to warming. Climate warming may promote species with both a high capacity to grow under warmer conditions and a resilience towards herbivore outbreaks. Negative correlation between Re and total vascular plant abundance further indicates that the indirect impacts of increased plants on soil microclimate may become increasingly important for ecosystem CO2 exchange in the long run, which adds to the different mechanisms that link warming and CO2 fluxes in northern ecosystems.

opencc-zeroOct 2023View details →

zenodo36/100

Figure 1 in Bird checklist and contributions to conservation of the Atlantic forest-cerrado ecotone in Três Lagoas municipality, Brazil

Figure 1. Três Lagoas Municipality map, Atlantic forest-cerrado ecotone and survey and localities (1-31).

opencc-by-nc-4.0Oct 2023View details →

zenodo36/100

Figure 3 in Seasonality effect on ant (Hymenoptera: Formicidae) activity in an ecotonal environment in the state of Piauí, Brazil

Figure 3. Non-metric multidimensional scaling – NMDS of ant composition according to seasonality in an ecotonal area between the Caatinga and Cerrado biomes at Floriano, Piauí, Brazil.

opencc-by-nc-4.0Jan 2022View details →

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Figure 2 in Seasonality effect on ant (Hymenoptera: Formicidae) activity in an ecotonal environment in the state of Piauí, Brazil

Figure 2. Number of ant species (average values) collected according to the seasons studied in a transition area between the Caatinga and Cerrado biomes in Floriano, Piauí, Brazil. The lines link the number of species caught in each collection point.

opencc-by-nc-4.0Jan 2022View details →

dryad36/100

Data from: Changes of Chinese forest-grassland ecotone in geographical scope and landscape structure from 1990 to 2020

Forest-grassland ecotone (FGE) has essential ecological and economic value. Unfortunately, it is impacted greatly by environmental changes and anthropogenic disturbance, and is considered one of the most severely threatened biomes in China. To protect Chinese FGE, identifying its exact boundary and exploring its landscape structure dynamic are badly needed, especially on nationwide scale at one-year temporal resolution. Here, we mapped the annual FGE distribution of China from 1990 to 2020, investigated its changing trends of area, location and landscape patterns, and revealed the underlying driving factors. Our results showed that FGE area over the 31 years totaled 1,011,870 km2, covering about 10.54% of China's land. The FGE area first increased from 1990 and peaked in 1999, and then kept decreasing until 2020. The FGE gravity center has moved accumulatively 590.15 km over the 31 years, with the net moving distance of 228.76 km southwestward. From 1990 to 2020, forest area increased continuously while grassland and cropland area decreased, but these three landscape types had been dominating the FGE. The increase in forest area was largely converted from grassland. The decline in grassland mainly resulted from its conversion into cropland and forest. Meanwhile, the conversion of cropland to grassland supplemented grassland loss to a certain extent. At landscape level, the total area with decreased fragmentation is larger than that with increased fragmentation. Returning Farmland to Grassland Project and land reclamation were primary drivers for changes of fragmentation in the northern and middle part of the FGE, while temperature and precipitation were primary drivers in southern part. Our results will improve the understanding into the dynamic trends of distribution and pattern of FGE at nationwide scale, and thus help to optimize the designing of ecological projects and protective schemes for FGE as a unique and integral biome.

opencc-zeroMay 2024View details →

zenodo36/100

Carbon loss due to grassland reclamation in the agro-pastoral ecotone of northern China

The conversion of grasslands to cropland can significantly impact the terrestrial carbon cycle, yet the effects on soil organic carbon (SOC) are not well quantified due to a lack of large-scale sampling data. This study aims to quantify changes in SOC resulting from grassland reclamation in the agropastoral ecotone of northern China through paired sampling of 101 cropland plots and 101 adjacent grassland control plots. Results indicate that grassland reclamation led to an average 16.07% decrease in surface SOC content (0–10 cm). Over 80% of the study area experienced a loss in SOC, while less than 20% showed an increase. These findings underscore the significant impact of grassland reclamation on SOC depletion and highlight the importance of land management strategies to mitigate carbon loss in this region.

opencc-by-4.0Sep 2024View details →

dryad36/100

Data for: Responses of soil phosphorus cycling and bioavailability to plant invasion in river-lake ecotones

The invasion of exotic plants in the river-lake ecotone has seriously affected the nutrient cycling processes in wetland soil. The South American species Alternanthera philoxeroides (Mart.) Griseb. is rapidly invading the river-lake ecotone in subtropical China, and has become the dominant species in the river-lake ecotone. However, there have been few studies on the effects of A. philoxeroides invasion on soil phosphorus (P) cycling and bioavailability in this ecotone. Herein, we measured the bioavailable P fractions, physicochemical properties and nutrient content in the surface soils of the native plant (Zizania latifolia (Griseb.) Turcz and Nelumbo nucifera Gaertn.) communities and the adjacent invasive A. philoxeroides communities in three river-lake ecotones with different nutrient substrates in the subtropical Dongting Lake basin over a three-year period to reveal the effects of A. philoxeroides invasion on the morphology and concentrations of soil bioavailable P. The principal coordinate analysis results showed that A. philoxeroides invasion significantly altered the bioavailable P concentrations in the soil of native plant communities in the different river-lake ecotones, and this effect was not disturbed by the heterogeneity of the soil matrix. However, the effects of invasion into different native plant communities on the fractions of soil bioavailable P were different. Compared with native Z. latifolia and N. nucifera communities, A. philoxeroides invasion increased the concentration of inorganic P by 39.5% and 3.7%, respectively, and the concentration of organic P decreased by 32.7% and 31.9%, respectively. Meanwhile, the invasion promoted P cycling and accumulation in the river-lake ecotone, which resulted in average decreases in the soil N:P and C:P ratios of 7.9% and 12.5%, respectively. These results highlight the impact of exotic plant invasions on nutrient cycling in wetland ecosystems in the river-lake ecotone, and this process may be detrimental to the late recovery of native plants.

opencc-zeroMar 2023View details →

dryad36/100

Tree biomass does not correlate with soil carbon stocks in forest-tundra ecotones along a 1100 km latitudinal gradient in Norway

Due to climate warming, forests are expanding to higher elevations and latitudes at the expense of tundra vegetation. While the subsequent increase in aboveground biomass is well-documented, there is much speculation regarding the effects on soil organic carbon (SOC) stocks. To provide insight into the consequences of tree encroachment into treeless tundra, we sampled SOC stocks across 36 forest-tundra ecotones along a 1100 km latitudinal gradient in Norway. Our results show that SOC stocks vary greatly within, as well as among treeline ecotones, and that SOC stocks do not correlate with tree biomass and tree species. SOC stocks do increase with temperature, and vary with slope steepness, slope aspect, and soil parent material. Applying a 'space-for-time substitution' perspective, our findings suggest that tree encroachment into tundra is unlikely to have immediate consequences for SOC stocks.

opencc-zeroJul 2023View details →

dryad36/100