Dynamics Of Natural Ecosystems Research Articles

Greenhouse gas emissions from alternative futures of deforestation and agricultural management in the southern Amazon

The Brazilian Amazon is one of the most rapidly developing agricultural areas in the world and represents a potentially large future source of greenhouse gases from land clearing and subsequent agricultural management. In an integrated approach, we estimate the greenhouse gas dynamics of natural ecosystems and agricultural ecosystems after clearing in the context of a future climate. We examine scenarios of deforestation and postclearing land use to estimate the future (2006-2050) impacts on carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) emissions from the agricultural frontier state of Mato Grosso, using a process-based biogeochemistry model, the Terrestrial Ecosystems Model (TEM). We estimate a net emission of greenhouse gases from Mato Grosso, ranging from 2.8 to 15.9 Pg CO(2)-equivalents (CO(2)-e) from 2006 to 2050. Deforestation is the largest source of greenhouse gas emissions over this period, but land uses following clearing account for a substantial portion (24-49%) of the net greenhouse gas budget. Due to land-cover and land-use change, there is a small foregone carbon sequestration of 0.2-0.4 Pg CO(2)-e by natural forests and cerrado between 2006 and 2050. Both deforestation and future land-use management play important roles in the net greenhouse gas emissions of this frontier, suggesting that both should be considered in emissions policies. We find that avoided deforestation remains the best strategy for minimizing future greenhouse gas emissions from Mato Grosso.

Do arbuscular mycorrhizal fungi with contrasting life-history strategies differ in their responses to repeated defoliation?

Arbuscular mycorrhizal (AM) fungi obligatorily depend on carbon (C) resources provided via the plant and therefore fluctuations in C availability may strongly and differently affect AM fungi with different life-history strategies (LHS). In the present study, we examined the effect of repeated defoliation of in vitro grown barrel medic (Medicago truncatula) on the spore and auxiliary cell (AC) production dynamics of a presumed r-strategist (Glomus intraradices) and a presumed K-strategist (Dentiscutata reticulata). Glomus intraradices modulated the production of spores directly to C availability, showing direct investment in reproduction as expected for r-strategists. In contrast, AC production of D. reticulata was not affected after a single defoliation and thus showed higher resistance to fluctuating C levels, as expected for K-strategists. Our results demonstrate that plant defoliation affects the production of extraradical C storage structures of G. intraradices and D. reticulata differently. Our results contribute towards revealing differences in LHS among AM fungal species, a step further towards understanding their community dynamics in natural ecosystems and agroenvironments.

Do arbuscular mycorrhizal fungi with contrasting life-history strategies differ in their responses to repeated defoliation?

Arbuscular mycorrhizal (AM) fungi obligatorily depend on carbon (C) resources provided via the plant and therefore fluctuations in C availability may strongly and differently affect AM fungi with different life-history strategies (LHS). In the present study, we examined the effect of repeated defoliation of in vitro grown barrel medic (Medicago truncatula) on the spore and auxiliary cell (AC) production dynamics of a presumed r-strategist (Glomus intraradices) and a presumed K-strategist (Dentiscutata reticulata). Glomus intraradices modulated the production of spores directly to C availability, showing direct investment in reproduction as expected for r-strategists. In contrast, AC production of D. reticulata was not affected after a single defoliation and thus showed higher resistance to fluctuating C levels, as expected for K-strategists. Our results demonstrate that plant defoliation affects the production of extraradical C storage structures of G. intraradices and D. reticulata differently. Our results contribute towards revealing differences in LHS among AM fungal species, a step further towards understanding their community dynamics in natural ecosystems and agroenvironments.

Forest Management and Biodiversity Conservation Based on Natural Ecosystem Dynamics in Northern Europe: The Complexity Challenge

Recent research in northern Europe has revised many long-held conceptions of the complexity of forest ecosystems and their natural structure and dynamics. The unveiling of the picture of natural characteristics of forest ecosystem structure and dynamics reveals much more diversity than its traditional complement, highlighting the importance of non-stand-replacing disturbances and the associated heterogeneous and dynamic stand and landscape structures. This increasing detail is a reflection of a fundamental change in the ecological understanding of forests as complex ecosystems. In particular, the generalization that the boreal forest is regulated by fierce stand-replacing disturbances, leading to the dominance of even-aged stand successions, has been disproved. However, this misconception has, until now, been repeated and used to legitimize the dominant practice of clear-cutting as a nature-based way to manage the forest. The practical conclusion of this review paper is that the dominating forest management model in North European boreal forests, which is based on the clear-cut harvesting of timber and growing of even-aged stands, is in contradiction with the variable and complex characteristics of the disturbance-succession cycle observed in naturally dynamic forests with negligible human impact. As a consequence, the structural variation of the boreal forest under management has been grossly truncated compared with its natural range. Because of this, and due to the scarcity of protection areas in many regions of northern Europe, it is not likely that the conservation of native biodiversity and ecological sustainability will be attained, assuming that the model of forest management remains unchanged. Thus, there is a strong incentive for change in the prevailing forest management model toward one that is based on natural ecosystem dynamics and an understanding of forests as complex systems.

Architectural differentiation reflects bacterial community structure in stream biofilms

Laboratory studies have documented the extensive architectural differentiation of biofilms into complex structures, including filamentous streamers generated by turbulent flow. Still, it remains elusive whether this spatial organization of natural biofilms is reflected in the community structure. We analyzed bacterial community differentiation between the base and streamers (filamentous structures floating in the water) of stream biofilms under various flow conditions using denaturing gradient gel electrophoresis (DGGE) and sequencing. Fourth-corner analysis showed pronounced deviation from random community structure suggesting that streamers constitute a more competitive zone within the biofilm than its base. The same analysis also showed members of the alpha-Proteobacteria and Gemmatimonadetes to preferentially colonize the biofilm base, whereas beta-Proteobacteria and Bacteroidetes were comparatively strong competitors in the streamers. We suggest this micro-scale differentiation as a response to the environmental dynamics in natural ecosystems.

Land use and disturbance effects on the dynamics of natural ecosystems of the Monte Desert: Implications for their management

The complex interactions between human activity and natural processes determine non-linear dynamics in ecosystems that can difficult their management. Human settlements in arid lands contribute to the modification of disturbance regimes, including the introduction of new disturbances and the elimination of others. In consequence, they can alter the functional mechanisms that allow systems to overcome limiting factors, leading to desertification. In this revision, we evaluated the effects of the changes on disturbance regimes produced by the different forms of land transformation on the structure and function of ecosystems of the Monte Biogeographical Province, in Argentinean arid west. Two approaches were used: the analysis of land use history and the analysis of the effects of the main disturbances on the dynamics of different communities. We concluded that throughout the history of the Monte Desert, the joint action of natural and anthropic agents has resulted in complex dynamics that lead most area of the Monte to a moderate to severe status of desertification. The modification of the disturbance regime had strong consequences for several aspects of the dynamics of communities, such as species composition and diversity, water dynamics, soil conditions, trophic structure and productivity of Monte Desert ecosystems. However, disturbance regimes could be managed to promote favorable transitions in ecosystems and, therefore, could be a tool for optimizing productivity of agro-ecosystems, and recovering and conserving natural ecosystems.

Special issue: Restoring and designing ecosystems for a crowded planet

Given increasing rates of consumption of our natural resources, the study of ecosystem services and restoration ecology will become more and more relevant because functional ecosystems represent the natural capital upon which our economies depend for ecosystem goods and services. Ecological restoration may occur through different activities: 1) rehabilitating disaster areas; 2) increasing the production capacity of degraded land; 3) improving the quality of existing nature reserves; and 4) enhancing the conservation of nature. But what can be done when degradation is extreme? Creation of new ecosystems (designer ecosystems) may be the only way. The goal of this special issue is threefold: 1) to consider how a perspective of ecosystem functioning may be realistically used in a restoration or ecological design context; 2) to evaluate the extent to which ecosystem services are being re-established in degraded habitats; and 3) to assess whether designed ecosystems are successfully fulfilling the expectations of restoration ecology in terms of structure and ecosystem function. Several examples of innovative recent studies of designer ecosystems focused both on plants and animals are presented. These involve tropical and temperate forests, riparian trees along urban streams, wetlands, and coastal dunes. In addition, the relevance of natural ecosystem dynamics for restoration projects and designer ecosystems is reviewed.

Marine Ecological Research in New Zealand: Developing Predictive Models through the Study of No‐Take Marine Reserves

Abstract: New Zealand established its first no‐take marine reserve more than 25 years ago. Twenty no‐take marine reserves have now been created, although few of these are considered comparable. We considered whether existing conceptual models of population and community structure based only on data from exploited systems lack the baseline information of natural states necessary to make accurate predictions for new reserves. Three of the oldest and best‐studied reserves are situated on the northeastern coast of New Zealand. These reserves are considered broadly comparable replicates, and research has shown the recovery of previously exploited predator populations and the reestablishment of trophic controls over community structure and productivity. None of the major changes was predicted when the reserves were created. All the observations from and experimental tests of hypotheses in these three ecologically comparable reserves have provided predictive models for future reserves. Recent surveys in newly created reserves, however, suggest that these models are bioregion and habitat specific. In these new reserves the recovery of previously exploited predators was predicted but did not always occur. Where trends were correctly predicted, the speed and amplitude of the changes were not accurately predicted. Research in New Zealand suggests that it is not yet possible to predict explicit outcomes for newly created reserves and less possible to predict detailed results for systems of reserves. Results from a representative system of reserves, including all major habitats within all bioregions and broadly comparable reserves, are needed. Such a system will enable the range and variety of natural ecosystem dynamics to be investigated and provide the controls necessary to measure the effects of exploitation.

Development of a spatial terrestrial nitrogen model for application to Douglas-fir forest ecosystems

Though field data indicate that biogeochemical properties are heterogeneous, biogeochemical models are often applied without regard to local variation. In this paper, we examine how the spatial scale used to represent heterogeneity in ecosystem modeling affects aggregated forest stand nitrogen (N) dynamics. We conduct this spatial analysis using measured local variation in forest carbon and nitrogen distributions. By coupling field and modeling approaches, we address spatial scaling in the context of natural ecosystem dynamics. We model spatially explicit N dynamics in Douglas-fir ( Pseudotsuga menziesii) forests using reaction-diffusion equations, in which Michaelis–Menten functions represent nitrogen transfer between plant, microbial, and soil pools, and nitrogen transport is approximated using diffusion. A stability analysis of the reaction terms in the absence of diffusion shows the model is very resilient to perturbation; consequently limit-cycle or oscillatory dynamics are not observed. The model is sensitive to variation in the maximum rate of plant nitrogen uptake as well as the Michaelis–Menten half-saturation constant for plant N uptake. The spatial scale of modeled heterogeneity does not significantly affect aggregated N dynamics in the Douglas-fir system; spatial resolution mainly affects the variance of stand nitrogen values. Analysis of post-perturbation dynamics shows that stand productivity is significantly reduced under frequent perturbations, especially when microbial biomass pools are seriously degraded.

Simulating past and future dynamics of natural ecosystems in the United States

Simulations of potential vegetation distribution, natural fire frequency, carbon pools, and fluxes are presented for two DGVMs (Dynamic Global Vegetation Models) from the second phase of the Vegetation/Ecosystem Modeling and Analysis Project. Results link vegetation dynamics to biogeochemical cycling for the conterminous United States. Two climate change scenarios were used: a moderately warm scenario from the Hadley Climate Centre and a warmer scenario from the Canadian Climate Center. Both include sulfate aerosols and assume a gradual CO2 increase. Both DGVMs simulate a reduction of southwestern desert areas, a westward expansion of eastern deciduous forests, and the expansion of forests in the western part of the Pacific Northwest and in north‐central California. Both DGVMs predict an increase in total biomass burnt in the next century, with a more pronounced increase under the Canadian scenario. Under the Hadley scenario, both DGVMs simulate increases in total carbon stocks. Under the Canadian scenario, both DGVMs simulate a decrease in live vegetation carbon. We identify similarities in model behavior due to the climate forcing and explain differences by the different structure of the models and their different sensitivity to CO2. We compare model output with data to enhance our confidence in their ability to simulate potential vegetation distribution and ecosystem processes. We compare changes in the area of drought‐induced decreases in vegetation density with a spatial index derived from the Palmer Drought Severity Index to illustrate the ability of the vegetation to cope with water limitations in the future and the role of the CO2 fertilization effect.

Optimizing minirhizotron sample frequency for an evergreen and deciduous tree species

• When using minirhizotrons to study fine dynamics in natural ecosystems, it is important to determine how sample collection frequency influences estimates of fine root production and mortality. Minirhizotron images were collected twice per week from mature Pseudotsuga menziesii and Tilia cordata trees and analyzed to estimate fine root production and mortality. These data were used to create data sets reflecting sample frequencies of 1, 2, 4 or 8wk. • When the sampling interval is long, fine roots can appear and disappear between samplings, leading to underestimates of production and mortality. For example, with an 8-wk sample frequency, 24 and 35% of the fine root production in P. menziesii and T. cordata , respectively, is not measured. Fine root mortality displays the same sensitivity to sample frequency. • Our experimental observations supported the previously published simulation analysis, which provides an estimate of the proportion of fine roots missed at different sample frequencies and is a tool that can be used to select a sample frequency to balance production and mortality accuracy with sampling and analytical effort.

Basing silviculture on natural ecosystem dynamics: an approach applied to the southern boreal mixedwood forest of Quebec

We present a method in which fundamental knowledge of natural ecosystem dynamics of the southern boreal forest may be used as a basis for a new silvicultural approach aimed at maintaining biodiversity and long-term ecosystem productivity under management. The natural disturbance regime of the southern boreal forest of Quebec is characterized by intense crown fires. Natural forest dynamics following fire on mesic sites involve a gradual replacement of stands of broadleaf species by mixedwood then softwood stands. This succession is accompanied by a decrease in soil fertility and in ecosystem productivity. In the absence of fire, spruce budworm outbreaks contribute in regenerating mature, fir-dominated forests and in reintroducing a hardwood component into stands. Current silvicultural practices promote successive rotations of similarly composed stands. Attaining softwood regeneration following harvest of softwood stands often necessitates site preparation, planting and control of competitive species, including economically and ecologically valuable hardwoods. At the landscape level this strategy may contribute to decreasing stand diversity by favouring replacement of mixedwood stands by hardwood or softwood stands. Natural dynamics indicate that a silvicultural approach favouring species replacement while, at the landscape level preserving a representative proportion of hardwood, mixedwood and softwood stands would be more appropriate. The advantages of such an approach are discussed in comparison with current practices.