| A comparison of methods to assess long-term changes in Sonoran Desert vegetation. | Munson, S.M. | 2011 |
KeywordsArid ; Climate ; Desert Laboratory ; Line-point intercept ; National Park Service ; Plant cover ; Plant species ; Semiarid ; Vegetation monitoring AbstractKnowledge about the condition of vegetation cover and composition is critical for assessing the structure and function of ecosystems. To effectively quantify the impacts of a rapidly changing environment, methods to track long-term trends of vegetation must be precise, repeatable, and time- and cost-efficient. Measuring vegetation cover and composition in arid and semiarid regions is especially challenging because vegetation is typically sparse, discontinuous, and individual plants are widely spaced. To meet the goal of long-term vegetation monitoring in the Sonoran Desert and other arid and semiarid regions, we determined how estimates of plant species, total vegetation, and soil cover obtained using a widely-implemented monitoring protocol compared to a more time- and resource-intensive plant census. We also assessed how well this protocol tracked changes in cover through 82 years compared to the plant census. Results from the monitoring protocol were comparable to those from the plant census, despite low and variable plant species cover. Importantly, this monitoring protocol could be used as a rapid, "off-the shelf" tool for assessing land degradation (or desertification) in arid and semiarid ecosystems. AuthorsS.M. Munson, R.H. Webb, J.A. Hubbard Year Published2011 PublicationJournal of Arid Environments LocationsDOI10.1016/j.jaridenv.2011.04.032 |
| Economics of Flexible Versus Conservative Stocking Strategies to Manage Climate Variability Risk. | Torell, L. A | 2010 |
KeywordsBouteloua gracilis, climate forecast, drought, grazing flexibility, linear programming, stocking strategies, Climate Hub AbstractRecommended strategies for dealing with drought include maintaining a conservative stocking rate, maintaining grazing flexibility by having yearlings as one of multiple enterprises on the ranch, and leaving a significant amount of herbaceous production at the end of the grazing season. We perform an economic analysis of these grazing strategies using a bio-economic multiperiod linear programming model with variable annual forage production and beef prices. We evaluate the economics of conservative versus flexible grazing where stock numbers are adjusted to match forage conditions. The deterministic model estimates that a flexible grazing strategy could nearly double net returns relative to a conservative strategy, but realizing this substantial economic potential means higher production costs, and it depends on a quality climate forecast that is not currently available. Maintaining grazing flexibility was determined to be very important for managing variable forage conditions, and its importance increased with the level of variability. Without annual variation in forage production, over 80% of available forage would optimally be allocated to cow-calf production. As forage variability increased to levels observed on the arid rangelands of the western United States, a 50:50 forage allocation between cow-calf and yearling enterprises was found to be optimal, but optimal cow numbers decreased over time as dry conditions force herd reductions. As compared to a cow-calf ranch only, adding flexible yearling enterprises increased average annual net ranch returns by 14% with conservative stocking and by up to 66% with flexible grazing. Herd expansion beyond a conservative level should occur with yearlings because adjusting cow numbers is too expensive relative to the potential short-term gain, even if forage conditions are known with certainty. AuthorsL. A Torell, Subramanian Murugan, Octavio A Ramirez Year Published2010 PublicationRangeland Ecology & Management LocationsDOI10.2111/REM-D-09-00131.1 This article contributed by:
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| Phenology of a northern hardwood forest canopy. | RICHARDSON, ANDREW D. | 2006 |
Keywordsbud break;climate change;growing season length;Harvard Forest;Hubbard Brook Experimental Forest;leaf fall;leaf out;northern hardwood forest;phenology;senescence AbstractWhile commonplace in other parts of the world, long-term and ongoing observations of the phenology of native tree species are rare in North America. We use 14 years of field survey data from the Hubbard Brook Experimental Forest to fit simple models of canopy phenology for three northern hardwood species, sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). These models are then run with historical meteorological data to investigate potential climate change effects on phenology. Development and senescence are quantified using an index that ranges from 0 (dormant, no leaves) to 4 (full, green canopy). Sugar maple is the first species to leaf out in the spring, whereas American beech is the last species to drop its leaves in the fall. Across an elevational range from 250 to 825 m ASL, the onset of spring is delayed by 2.7±0.4 days for every 100 m increase in elevation, which is in reasonable agreement with Hopkin's law. More than 90% of the variation in spring canopy development, and just slightly less than 90% of the variation in autumn canopy senescence, is accounted for by a logistic model based on accumulated degree-days. However, degree-day based models fit to Hubbard Brook data appear to overestimate the rate at which spring development occurs at the more southerly Harvard Forest. Autumn senescence at the Harvard Forest can be predicted with reasonable accuracy in sugar maple but not American beech. Retrospective modeling using five decades (1957-2004) of Hubbard Brook daily mean temperature data suggests significant trends (P≤0.05) towards an earlier spring (e.g. sugar maple, rate of change=0.18 days earlier/yr), consistent with other studies documenting measurable climate change effects on the onset of spring in both North America and Europe. Our results also suggest that green canopy duration has increased by about 10 days (e.g. sugar maple, rate of change=0.21 days longer/yr) over the period of study. AuthorsRICHARDSON, ANDREW D.,BAILEY, AMEY SCHENCK,DENNY, ELLEN G.,MARTIN, C. WAYNE,O'KEEFE, JOHN Year Published2006 PublicationGlobal Change Biology LocationsDOI10.1111/j.1365-2486.2006.01164.x |
| Snow depth, soil freezing, and fluxes of carbon dioxide, nitrous oxide and methane in a northern hardwood forest. | GROFFMAN, PETER M. | 2006 |
Keywordscarbon dioxide;methane;nitrogen;nitrous oxide;northern hardwood forest;snow;soil freezing;winter climate change AbstractSoil-atmosphere fluxes of trace gases (especially nitrous oxide (N2O)) can be significant during winter and at snowmelt. We investigated the effects of decreases in snow cover on soil freezing and trace gas fluxes at the Hubbard Brook Experimental Forest, a northern hardwood forest in New Hampshire, USA. We manipulated snow depth by shoveling to induce soil freezing, and measured fluxes of N2O, methane (CH4) and carbon dioxide (CO2) in field chambers monthly (bi-weekly at snowmelt) in stands dominated by sugar maple or yellow birch. The snow manipulation and measurements were carried out in two winters (1997/1998 and 1998/1999) and measurements continued through 2000. Fluxes of CO2 and CH4 showed a strong seasonal pattern, with low rates in winter, but N2O fluxes did not show strong seasonal variation. The snow manipulation induced soil freezing, increased N2O flux and decreased CH4 uptake in both treatment years, especially during winter. Annual N2O fluxes in sugar maple treatment plots were 207 and 99 mg N m-;2 yr-;1 in 1998 and 1999 vs. 105 and 42 in reference plots. Tree species had no effect on N2O or CO2 fluxes, but CH4 uptake was higher in plots dominated by yellow birch than in plots dominated by sugar maple. Our results suggest that winter fluxes of N2O are important and that winter climate change that decreases snow cover will increase soil:atmosphere N2O fluxes from northern hardwood forests. AuthorsGROFFMAN, PETER M.,HARDY, JANET P.,DRISCOLL, CHARLES T.,FAHEY, TIMOTHY J. Year Published2006 PublicationGlobal Change Biology LocationsDOI10.1111/j.1365-2486.2006.01194.x |
| Ecosystem response to nutrient enrichment across an urban airshed in the Sonoran Desert | Hall, Sharon J. | 2011 |
KeywordsAmbrosia; arid ecosystem; Larrea tridentata; N deposition; nitrogen fertilization; Pectocarya spp.; phosphorus; Sonoran Desert, Arizona, USA; urban environments; winter ephemeral annual plants AbstractRates of nitrogen (N) deposition have increased in arid and semiarid ecosystems, but few studies have examined the impacts of long-term N enrichment on ecological processes in deserts. We conducted a multiyear, nutrient-addition study within 15 Sonoran Desert sites across the rapidly growing metropolitan area of Phoenix, Arizona (USA). We hypothesized that desert plants and soils would be sensitive to N enrichment, but that these effects would vary among functional groups that differ in terms of physiological responsiveness, proximity to surface N sources, and magnitude of carbon (C) or water limitation. Inorganic N additions augmented net potential nitrification in soils, moreso than net potential N mineralization, highlighting the important role of nitrifying microorganisms in the nitrate economy of drylands. Winter annual plants were also responsive to nutrient additions, exhibiting a climate-driven cascade of resource limitation, from little to no production in seasons of low rainfall (winter 2006 and 2007), to moderate N limitation with average precipitation (winter 2009), to limitation by both N and P in a season of above-normal rainfall (winter 2008). Herbaceous production is a potentially important mechanism of N retention in arid ecosystems, capable of immobilizing an amount equal to or greater than that deposited annually to soils in this urban airshed. However, interannual variability in precipitation and abiotic processes that limit the incorporation of detrital organic matter into soil pools may limit this role over the long term. In contrast, despite large experimental additions of N and P over four years, growth of Larrea tridentata, the dominant perennial plant of the Sonoran Desert, was unresponsive to nutrient enrichment, even during wet years. Finally, there did not appear to be strong ecological interactions between nutrient addition and location relative to the city, despite the nearby activity of nearly four million people, perhaps due to loss or transfer pathways that limit long-term N enrichment of ecosystems by the urban atmosphere. AuthorsHall, Sharon J.; Sponseller, Ryan A.; Grimm, Nancy B.; Huber, David; Kaye, Jason P.; Clark, Christopher; Collins, Scott L. Year Published2011 PublicationEcological Applications LocationsDOI10.1890/10-0758.1 This article contributed by:Ecological Society of America |
| Combined effects of climate, resource availability, and plant traits on biomass produced in a Mediterranean rangeland | Chollet, Simon | 2014 |
Keywordsclimate variability, dominance hypothesis, forage production, functional complementarity, functional structure of communities, grazing, interannual variation, nutrient and water availability, response and effect framework AbstractBiomass production in grasslands, a key component of food provision for domestic herbivores, is known to depend on climate, resource availability, and on the functional characteristics of communities. However, the combined effects of these different factors remain largely unknown. The aim of the present study was to unravel the causes of variations in the standing biomass of plant communities using a long-term experiment conducted in a Mediterranean rangeland of Southern France. Two management regimes, sheep grazing and grazing associated with mineral fertilization, were applied to different areas of the study site over the past 25 years. Abiotic (temperature, available water, nutrients) and biotic (components of the functional structure communities) factors were considered to explain interannual and spatial variations in standing biomass in these rangelands.
Standing biomass was highly predictable, with the best model explaining 80% of variations in the amount of biomass produced, but the variation explained by abiotic and biotic factors was dependent on the season and on the management regime. Abiotic factors were found to have comparable effects in both management regimes: The amount of biomass produced in the spring was limited by cold temperatures, while it was limited by water availability and high temperatures in the summer. In the fertilized community, the progressive change in the functional structure of the communities had significant effects on the amount of biomass produced: the dominance of few productive species which were functionally close led to higher peak standing biomass in spring. AuthorsChollet, Simon, Rambal, Serge, Fayolle, Adeline, Hubert, Daniel, Foulquié, Didier and Garnier, Eric Year Published2014 PublicationEcology LocationsDOI10.1890/13-0751.1 This article contributed by:Ecological Society of America |
| Operational approaches to managing forests of the future in Mediterranean regions within a context of changing climates | Stephens, Scott L | 2010 |
Keywordsclimate change, historical variability, restoration, forest policy, Sierra Nevada, Sierra San Pedro Martir, mixed conifer, Jeffrey pine, ponderosa pine, upper montane, Climate Hub AbstractMany US forest managers have used historical ecology information to assist in the development of desired conditions. While there are many important lessons to learn from the past, we believe that we cannot rely on past forest conditions to provide us with blueprints for future management. To respond to this uncertainty, managers will be challenged to integrate adaptation strategies into plans in response to changing climates. Adaptive strategies include resistance options, resilience options, response options, and realignment options. Our objectives are to present ideas that could be useful in developing plans under changing climates that could be applicable to forests with Mediterranean climates. We believe that managing for species persistence at the broad ecoregion scale is the most appropriate goal when considering the effects of changing climates. Such a goal relaxes expectations that current species ranges will remain constant, or that population abundances, distribution, species compositions and dominances should remain stable. Allowing fundamental ecosystem processes to operate within forested landscapes will be critical. Management and political institutions will have to acknowledge and embrace uncertainty in the future since we are moving into a time period with few analogs and inevitably, there will be surprises. AuthorsStephens, Scott L, Millar, Constance I and Collins, Brandon M Year Published2010 PublicationEnvironmental Research Letters Locations- Baja California, Mexico (30.8406, -115.284)
- California, United States (36.7783, -119.418)
- Forests in California, USA, and Baja California, Mexico; Vegetation types in the Sierra Nevada, the mountains of southern California, and the Sierra San Pedro Martir (SSPM), Mexico. (37.7333, -119.567)
- Forests in California, USA, and Baja California, Mexico; Vegetation types in the Sierra Nevada, the mountains of southern California, and the Sierra San Pedro Martir (SSPM), Mexico. (30.75, -115.217)
DOI10.1088/1748-9326/5/2/024003 This article contributed by:
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| Biodiversity and global health—hubris, humility and the unknown | Stephens, Carolyn | 2012 |
KeywordsNo keywords available AbstractIn November 2011, botanists on a remote island off Papua New Guinea discovered a new species of orchid—uniquely and mysteriously night-flowering [1]. New to science, and with so much more to understand, this flower is threatened by deforestation [2]. Also in November 2011, a survey of 583 conservation scientists reported a unanimous (99.5%) view that 'it is likely a serious loss of biological diversity is underway at a global extent' and that, for scientists, 'protection of biological diversity for its cultural and spiritual values and because of its usefulness to humans were low priorities, which suggests that many scientists do not fully support the utilitarian concept of ecosystem services' [3]. In terms of management, some scientists now advocate controversial conservation strategies such as triage (prioritization of species that provide unique or necessary functions to ecosystems) [4, 5].
Meanwhile, there are many scientists who contend that there is an urgent need to improve our understanding of the importance of biodiversity for human health and well-being, arguing that only an anthropocentric view of biodiversity within a paradigm 'ecosystem service' will enable decision-makers to prioritize the theme [6–9]. A 2011 UN report argues that this need for understanding is especially urgent in fragile and vulnerable ecosystems where communities depend directly on the resources of their environment [10].
Here we have a paradox: international conservation scientists think that we cannot protect biodiversity on the basis of its cultural and spiritual value, nor its usefulness to humans. Other scientists argue that using a utilitarian ecosystem services framework is the only way to get humans to protect biodiversity. Meanwhile, communities directly dependent on biodiverse ecosystems are often those who best understand and protect biodiversity, for exactly these reasons of use and spiritual connection, but they do not hold only a utilitarian view of their environment and its diversity. These communities often define their own 'health' as integrally linked to the 'health' of the ecosystem, and they see themselves as an integral part of the ecosystem [11].
It is generally accepted that the destruction of biodiverse ecosystems internationally is not by communities directly dependent on these ecosystems, but from processes such as deforestation, mining, resource extraction and biopiracy, generated by external human demand [12–16]. Rich countries and their populations are currently particularly responsible for the resource extraction that impacts negatively on biodiversity and on the well-being of local communities [17]. However, increasingly, urban populations in every country demand resources and products from biodiverse regions, and with rising urban populations this threat is likely to increase.
To illustrate, we can take one example. Amazonia is one of Earth's most important biodiverse tropical moist forest ecosystems. As the Amazonian forest reaches the Andes it becomes a contiguous and equally vital ecosystem: the Yungas or Cloud Forest [18]. These two sister forests are amongst the most biodiverse ecosystems of the world, spanning several Latin American countries (including Brazil, Argentina, Peru, Bolivia, Venezuela, Colombia and Ecuador), and over 7 million square kilometres [18, 19]. For millennia, across modern geopolitical boundaries, Amazonia/Yungas has been protected by over 1000 different indigenous peoples [20]. In turn, Amazonia/Yungas has provided health and spiritual well-being for indigenous peoples via food, medicines, home and culture [21]. Using a utilitarian view of the ecosystem, these forests also provide the world with some of its most important ecosystem services in terms of forest and food resources, current and potential new medicines, rainfall regulation and a global carbon sink [19, 22].
In terms of protection of these ecosystems, there is evidence that recognized 'indigenous territories' within Amazonia/Yungas are better protected, in terms of biodiversity and environmental damage, than other conservation units such as national or regional reserves [23, 24]. Yet deforestation, resource extraction and climate change threaten all parts of the Amazonia/Yungas [19, 25–28], and indigenous communities, amongst the most marginalized peoples in Latin America [29], are experiencing increasing threats to their territories, and their health and well-being [20]. Figures 1–3 show different aspects of the Andean Yungas and high mountain ecosystems of Argentina. The ecosystems are highly biodiverse. We are only beginning to understand the extent of their importance for human well-being, and these incredible forests are at risk from deforestation, mining and climate change. AuthorsStephens, Carolyn Year Published2012 PublicationEnvironmental Research Letters LocationsDOI10.1088/1748-9326/7/1/011008 This article contributed by:
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| Groundwater depletion during drought threatens future water security of the Colorado River Basin | Castle, Stephanie L. | 2014 |
KeywordsColorado River Basin, drought, GRACE, groundwater, water management, groundwater depletion, 1217 Time variable gravity, 1884 Water supply, 1829 Groundwater hydrology, 1857 Reservoirs (surface), 1876 Water budgets AbstractStreamflow of the Colorado River Basin is the most overallocated in the world. Recent assessment indicates that demand for this renewable resource will soon outstrip supply, suggesting that limited groundwater reserves will play an increasingly important role in meeting future water needs. Here we analyze 9 years (December 2004 to November 2013) of observations from the NASA Gravity Recovery and Climate Experiment mission and find that during this period of sustained drought, groundwater accounted for 50.1 km3 of the total 64.8 km3 of freshwater loss. The rapid rate of depletion of groundwater storage (−5.6 ± 0.4 km3 yr−1) far exceeded the rate of depletion of Lake Powell and Lake Mead. Results indicate that groundwater may comprise a far greater fraction of Basin water use than previously recognized, in particular during drought, and that its disappearance may threaten the long-term ability to meet future allocations to the seven Basin states. AuthorsCastle, Stephanie L., Thomas, Brian F., Reager, John T., Rodell, Matthew, Swenson, Sean C. and Famiglietti, James S. Year Published2014 PublicationGEOPHYSICAL RESEARCH LETTERS LocationsDOI10.1002/2014GL061055 |
| Future dryness in the southwest US and the hydrology of the early 21st century drought | Cayan, D. R. | 2010 |
Keywordsclimate change, regional modeling, sustainability, water resources AbstractRecently the Southwest has experienced a spate of dryness, which presents a challenge to the sustainability of current water use by human and natural systems in the region. In the Colorado River Basin, the early 21st century drought has been the most extreme in over a century of Colorado River flows, and might occur in any given century with probability of only 60%. However, hydrological model runs from downscaled Intergovernmental Panel on Climate Change Fourth Assessment climate change simulations suggest that the region is likely to become drier and experience more severe droughts than this. In the latter half of the 21st century the models produced considerably greater drought activity, particularly in the Colorado River Basin, as judged from soil moisture anomalies and other hydrological measures. As in the historical record, most of the simulated extreme droughts build up and persist over many years. Durations of depleted soil moisture over the historical record ranged from 4 to 10 years, but in the 21st century simulations, some of the dry events persisted for 12 years or more. Summers during the observed early 21st century drought were remarkably warm, a feature also evident in many simulated droughts of the 21st century. These severe future droughts are aggravated by enhanced, globally warmed temperatures that reduce spring snowpack and late spring and summer soil moisture. As the climate continues to warm and soil moisture deficits accumulate beyond historical levels, the model simulations suggest that sustaining water supplies in parts of the Southwest will be a challenge. AuthorsCayan, D. R., Das, T., Pierce, D. W., Barnett, T. P., Tyree, M. and Gershunov, A. Year Published2010 PublicationProceedings of the National Academy of Sciences LocationsDOI10.1073/pnas.0912391107 |