Colonization Potential of Oaks under Climate Change

by Elizabeth Medford

While the impact of climate change on a variety of animal populations and their ranges has been studies extensively in the past, the study of the impact of warming on tree species also provides useful information for policymaking. A variety of different modeling systems apply different variables and make predictions about tree species distribution in the future as temperatures rise. In this study however, Prasad et al. (2013) combine two different commonly used technologies to overcome the constraint of computation time and allow assessment of colonization potential for oak species. Four oak species were chosen to focus on because they are strongly climate-driven species: black oak, post oak, chestnut oak, and white oak. Using the DISTRIB and SHIFT models together the authors were able to determine the future dominant forest types in the northeastern United States. This study determined that even under optimistic conditions ignoring some influential factors, only a small fraction of suitable oak habitat is likely to be occupied by oaks within 100 years. The authors urge that the information garnered in this study be used to inform assisted migration practices for vulnerable tree species. They additionally call for further studies focusing on how each individual species will adapt to increases in temperature. Continue reading

Predicting Species Range Shifts Under Climate Change

by Cameron Lukos

Global climate change is causing long lasting effects on all of Earth’s natural systems. A consequence of these changes is species range shifting. Accurately predicting these shifts is very difficult and many methods have been criticized. The standard bioclimate envelope models (BEMS) have been criticized as too simple because they do not incorporate biotic interactions or evolutionary adaptation. BEMs are widely used though. Kubish et al. (2013) wanted to determine the evolutionary conditions of dispersal, because local adaptation or interspecific competition may be of minor importance for predicting future shifts. They used individual-based simulations at two different temperatures as well as competing simulations. Their results show that in single-species scenarios excluding adaptation, species follow optimal habitat conditions or go extinct if their connection to the environment becomes too weak. With competitors, their results were dependent on habitat fragmentation. If a species was highly connected to its habitat, the range shifted as predicted; if a species was only moderately connected to its environment, there was a lag time, and with low connectivity to the environment, the result was extinction. Based on this work, Kubisch et al. determined that the BEMs may work well as long as habitats are well connected and there is no difficulty dispersing. Continue reading

Resilience or Decline of Species under Climate Change?

by Samantha Thompson

Species have widely been affected by changes in global climate but to what extent is uncertain, though predictions of species decline are often urgent. For example, one prominent analysis predicted that 15 to 37% of species would be endangered or extinct by 2050 (Moritz, 2013). Another predicts more than a 50% loss of climatic range by 2080 for some 57% of widespread species of plants and 34% of animals (Moritz, 2013). Montane taxa are expected to lose range area as they shift northward with warming (Moritz, 2013). Craig Moritz et al. point out that fossil records suggests that most species have persisted through past climate change, whereas forecasts of future impacts predict large-scale range reduction and extinction. Moritz et. al. explore the apparent contradiction between observed past and predicted future species responses summarizing salient concepts and theories and by reviewing broad-scale predictions of future response and evidence from paleontological and phylogeographic studies of past responses at millennial or greater time scales. Bringing the two ideas together, the authors consider evidence for species responses to recent twentieth century climate changes and place them in a management context. Continue reading

Native Bee Species Disappearing, but Pollination Still OK So Far

by Lia Metzger

Over the past decade, bee populations have been decreasing significantly in North America. While many studies have investigated why there has been a decrease, few have researched the long-term change in species richness, in interaction between pollinators and plants, or in function of pollinators. Burkle et al. (2013) studied the loss of species of plant-pollinators, focusing on bees, and forbs, their interactions, and the function of bees over 120 years. Using data collected by Charles Robertson from 1888 to 1891 and data collected in 2009 and 2010 from natural habitats near Carlinville, Illinois, USA, the authors quantified and analyzed the changes in the network structure, bee diversity, and phenologies of bees and forbs. Additionally, data from 1971 to 1972 in Carlinville were used to investigate the changes in bee diversity, quality of pollination, and bee visitation rates to Claytonica virginica. Over 120 years, a substantial number of species interactions and bee species were lost and bee phenologies shifted significantly. The authors found that richness of bee species and the rate of visitation to C. virginica declined dramatically in the last 40 years and that there was a loss of redundancy in bee species. Continue reading

High and Distinct Range-Edge Genetic Diversity despite local Bottlenecks

 

by Cameron Lukos

The genetic consequences of being at the edge of species ranges has been the subject of much debate. Populations that occur at low latitude ranges are expected to retain high unique genetic diversity. Less favorable environments that limit population size at the range edges may have caused genetic erosion that has a stronger effect than past events. This study by Assis et al. (2013) provided a test of whether the population declines at the peripheral range might be shown in decreasing diversity and increasing population isolation and differentiation. The authors compared population genetic differentiation and diversity with trends in abundance along a latitudinal gradient to the furthest extents of the range of a sea kelp, Saccorhiza polyschides. Assis et al. also looked at recent bottleneck events to determine whether the recent recoded distributional shifts had a negative impact on the population size. They found that there was decreasing population density and increasing spatial fragmentation and local extinction at the southern edge. The genetic data revealed two distinct groups and a central mixed group. As the authors had predicted there was higher differentiation and evidence of bottleneck at the southern edge but instead of a decrease there was an increase in genetic diversity suggesting that extinction and recolonization had not reduced diversity and that this may be evidence of a process of shifting genetic baselines. Continue reading

Asian Tiger Mosquitoes Expanding in Northeastern US

by Sarah King

Mosquitoes are known for dispersing many different kinds of diseases that affect human health. Asian tiger mosquitoes (Aedes albopictus), originating in Southeast Asia, are among the most invasive and widespread species of mosquitoes in the world. This species has been the cause of the reemergence of several mosquito-borne diseases such as chikungunya and dengue, and in the United States it is largely responsible for the reemergence of West Nile Virus. Using census information, temperature data, precipitation data, CO2 emissions forecasts, and generated maps of Ae. albopictus population distributions, Rochlin and his collgues (2013) statistically modeled projections of Ae. albopictus expansion through the next seventy years (2020s, 2050s, and 2080s). Their modeling shows that the range of Ae. albopictus will grow over the next seventy years to Continue reading

Disequilibrium between Tree Species Distributions and Regional Temperatures

by Cortland Henderson

Correlations between geographic distributions of plant species and the current climate have been identified, suggesting that species ranges will shift upwards if global temperatures rise. These links, however, are based on models that do not establish whether or not plant species are at equilibrium with the current climate, and are incapable of differentiating between naturally occurring shifts and climate-induced shifts. García-Valdés et al. (2013) examine the ten most common tree distributions throughout the Iberian Peninsula by creating a new species distribution model that relaxes built-in assumptions that tree species and climate are currently at equilibrium. Their model successfully removed previous biases and found that tree species are not at equilibrium Continue reading

Climate Change Forces Species to Shift Niches

 

by Cameron Lukos

In order for species to survive environmental change and avoid extinction, they have to be able to either track suitable environmental conditions or adapt to the changed environment.  Whether and how species adapt to environmental change is largely unknown.  Wasof et al. (2013) examined specifically the realized niche width (ecological amplitude), and the realized niche position (ecological optimum).  A realized niche is the actual space that a species inhabits and the resources it can access as a result of limiting biotic factors present in the habitat.  They created the niche width from a beta diversity metric, which increases if the focus species co occurs with other species.  Wasof et al. used a detrended correspondence analysis (DCA) to represent the locations of the niche positions and then developed their own approach to run species specific DCAs to allow the focal species to shift its realized niche while others stayed put.  Wasof et al. concluded that none of the 26 species maintained their realized niche width and position along the latitudinal gradient.  A few species shifted their realized niche width but all of the species shifted their position.  Most of the species that shifted their position shifted their realized niche for areas where soil nutrients and pH were poorer and more acidic.  The results suggest that these plants are locally adapting or have plasticity.  The pattern Continue reading

Financial Costs Necessary to Meet Biodiversity Conservation Targets by 2020

In order to slow a worldwide loss of biodiversity, the Convention on Biological Diversity (CBD) created the Strategic Plan for Biodiversity 2011-2020. Participating countries created conservation targets to be met by 2020. However, a lack of data on the costs involved to meet their goals has made financing difficult. Using threatened bird populations to create a model, McCarthy et al. (2012) analyzed the financial costs necessary to meet two of the CBD’s most urgent goals. By examining expert estimates on current and predicted costs of conservation actions, the authors calculated the expected costs necessary to reclassify globally threatened species to the next lowest category of extinction risk. They also conducted a separate analysis of the costs needed to expand protection of globally important sites for biodiversity. Both analyses found a need for increased investment in biodiversity conservation, particularly in financially poor but biodiversity-rich countries. The results should guide discussions on the costs necessary to fund the strategic plan.–Katie Huang
McCarthy, D.P, Donald, P.F., Scharlemann, J.P.W., Buchanan, G.M., Balmford, A., Green, J.M.H., Bennun, L.A., Burgess, N.D., Fishpool, L.D.C., Garnett, S.T., Leonard, D.L., Maloney, R.F., Morling, P., Schaefer, H.M., Symes, A., Wiedenfeld, D.A., Butchart, S.H.M., 2012. Financial costs of meeting global biodiversity conservation targets: current spending and unmet needs. Science 338, 946–949.

                McCarthy et al. modeled the financial costs necessary to meet the CBD’s targets of preserving species and site biodiversity. They chose to focus on these goals for their urgency and overlap with the conservationist movement. The authors used data from birds, the best-known organism class, as the basis for their model. In order to determine the costs of species conservation, McCarthy et al. sampled 211 globally threatened bird species. They asked experts to estimate current conservation expenditures and the costs of actions needed to reclassify each species to the next lowest category of extinction risk. They modeled midrange cost estimates as a function of breeding distribution extent, degree of forest dependence, mean Gross Domestic Product per km2 of breeding range states, and mean Purchasing Power Parity of breeding range states. The model they created based on the sample was used to estimate costs for all globally threatened bird species. To estimate the cost of site conservation, the authors modeled the costs of conserving terrestrial Important Bird Areas (IBAs) using socioeconomic and site-specific variables for 396 sites across 50 countries. Both analyses applied the bird models to all taxa to create a total estimate for the cost of implementing the strategic plan.
                The authors found that the estimated median cost for conservation actions needed to downlist one species within 10 years would be $0.848 million. The estimated total cost to downlist the 1,115 globally threatened bird species would be approximately $1.23 billion annually, assuming that there would be no overlap in the effects of various conservation actions. However, as only 20% of actions are species-specific, McCarthy et al. revised the minimum total to $0.875 billion annually. Of that sum, $0.379 to $0.614 billion is needed in lower-income countries, which would likely require financial assistance. Additionally, the total amount is susceptible to increase due to possible intensification in affecting factors such as climate change. The authors also found that for their sample of 211 bird species, a majority of the median $0.065 million spent annually was primarily concentrated on a few species. Only 3% of all species received adequate funding. To address the inequity in distribution, an additional $0.769 to $1.08 billion per year is needed. By applying the model to all taxa, the authors estimated that a total range of $3.41 to $4.76 billion is necessary to conserve all known threatened species as outlined in the CBD Strategic Plan, with the latter figure assuming no cost-sharing among species.
                Based on their model of the costs of site conservation, the authors found that it would cost $7.18 billion annually to maintain currently protected IBAs. To expand protection to currently unprotected and partially protected IBAs, it would cost a total of $50.7 billion per year. Thus, the total amount required to fully protect all IBAs would equal $57.8 billion annually. Of that sum, $17.48 billion is needed in lower-income countries. Expanding coverage to more diverse taxa than just birds would cost $76.1 billion annually. Based on current data of conservation expenditures, the authors estimate that the amount spent on managing protected, partially protected, and unprotected IBAs is deficient in both lower- and higher-income countries.
                As actions for species and site conservation are likely to overlap, the authors estimate that the combined cost to reach these targets is approximately $78.1 billion annually, but these costs would also likely contribute to other CBD goals. However, aside from monetary deficiency, there are still obstacles to conserving biodiversity. Even with increased investment, the CBD must prioritize which sites and species it will focus most on preserving. It also needs to manage the inequity between resources in higher- and lower-income countries, as many of the latter are financially poor but rich in biodiversity. The results of the study should help implement the CBD’s strategic plan by providing the financial guidelines necessary for its funding.

Forest Composition in Mediterranean Mountains is Projected to Shift Along the Entire Elevational Gradient Under Climate Change

Mountainous areas in southern Europe act as wet-cool microclimate refugia in a warm-dry region for genetically unique and endemic species. However, recent predictions suggest that species rich regions within the Mediterranean mountains are at great risk to climate change because changes in atmospheric dynamics will cause these areas to become warmer and drier. Therefore, evaluating the effects of future climate change on the diversity, composition, and distribution of Mediterranean mountainous species is essential to the persistence of their genetic heritage. By using high spatial resolution data, generalized linear models, and machine learning models, Ruiz-Labourdette et al. (2011) modeled the current and future distributions of 15 tree species in two connected mountain ranges in the Iberian Peninsula across the elevational gradient. The distributions were modeled as functions of climate, lithology, and soil water availability. Additionally, Ruiz-Labourdette et al. analyzed potential changes in the composition of tree communities. The authors’ models predicted an upward migration of Mediterranean tree communities to higher elevations, an expansion of drought and high temperature tolerant tree species’ ranges, and a decline in temperate, cold-adapted tree communities with moderate water requirements. Furthermore, the mountain lowlands showed the largest projected changes in species distribution. Ultimately, these findings indicate that climate change may result in a loss of tree species diversity within these mountain ranges.—Megan Smith

Ruiz-Labourdette, D., Dogues-Bravo, D., Ollero, H.S., Schmitz, M.F., Pineda, F.D., 2011. Forest Composition in Mediterranean Mountains is Projected to Shift Along the Entire Elevational Gradient Under Climate Change. Journal of Biogeography 39:1. DOI: 10.1111/j.1365-2699.2011.02592.x

The varied topography within the Mediterranean Mountains created a variety of microclimates that acted as refugia for species that thrived in warm environments during periods of adverse climatic conditions. Additionally, the mountains protected other species that grew in cold and wet environments from post-glacial warming period. As a result, mountain species’ isolation in refugia resulted in one of the highest rates of endemism in Europe.

The study area encompassed a mountainous region of 71,700 km2 in southern Europe and included two large mountain ranges: the Central Mountain Range, located in the central west part of the Iberian Peninsula, and the Iberian Mountain Range, located in the central east part of the peninsula. The Iberian Mountains are primarily composed of limestones, calcarenites, marls, evaporates, dolomites, and sandstones. The Central Mountains consist of granite, metamorphic materials, a homogenous siliceous substratum, and limestone. A map showing the location of the Central Iberian Mountain Ranges, as well as the elevations of the highest summits in these mountain ranges, was displayed.

Forest composition varies between the two mountain ranges. The wetter, northern areas contain forests of temperate and broadleaf species. Mountainous regions with a more continental climate consist of pine forests, while the lower mountainous regions contain sub-Mediterranean deciduous forests. Additionally, wet-warm Mediterranean forests are found to the west of the study area, while warmer and drier piedmont environments and the shaded low-elevation mountainous areas contain tree species resilient to summer droughts.

Spatial distribution models (SDMs) are used to project climate changes in areas that have a suitable climate for the species in question. However, most SDMs utilize low-resolution biological and climatic datasets that cannot identify small patches with suitable conditions. These small patches might reduce the negative effects of climate change by providing microrefugia for communities. Therefore, Ruiz-Labourdette et al. utilized high-resolution data in their study to examine the topographic complexities and microrefugia present in the Iberian mountain ranges. Ultimately, this method achieved a more accurate representation of species distribution and community composition.

The authors modeled the current and future distributions of 15 tree species in Iberian Peninsula mountain ranges as functions of climate, lithology, and soil-water availability using generalized linear models and data mining models. Ruiz-Labourdette et al. also mapped the variation in the composition of current and potential forest communities in the study region using a multivariate ordination of a matrix of presence/absence of tree species. Two IPCC Special Report on Emission Scenarios (SRES) (A2 and B2) between the years of 2041–70 and 2071–2100 were used to model the study area’s future forest composition.

Forest species data were collected from a forest map of Spain at a scale of 1:50,000. The map was rasterized to a 500 x 500 m grid to create a data matrix of the current presence/absence of tree species in 286,688 cells. Tree species that occurred in more than 500 cells were incorporated in the study. Lithological data were collected from a geological map of the Iberian Peninsula and were classified into six lithological groups. Additionally, the authors incorporated soil hydromorphology into their study by calculating the topographic ratio (TR), which assesses the effects of topography on water drainage.

Ten climatic variables were used to model the potential distribution of tree species. These variables were obtained from monthly measurements recorded at 752 rainfall stations and 197 temperature stations that belong to the observation network of the Spanish State Meteorology Agency. Current climate conditions were recorded for the period 1961–90. For the periods 2041–70 and 2071–2100, the IPCC SRES scenarios A2 and B2 were used. The scenarios differ in the amount of carbon emitted from energy and industrial sources by 2100, with A2 being the most severe. The global models were downscaled to a regional scale to make the information on current and future climatic conditions available at the level of individual weather stations. These data were used to develop climatic maps. To construct climatic maps in a 500 x 500 m grid format, current and future climate data were inserted over the study area using multivariate stepwise regressions that incorporated quantitative geographic data (elevation, distance from coast, latitude, longitude, and slope) and qualitative data (drainage basins and aspect). Hydromorphology of the soils in the future scenarios was calculated by applying the expected increase or decrease in yearly rainfall volume to the current hydromorphology map.

GLM and data mining (gradient boosting) species distribution models were used to create alternative species spatial projections. The models were validated by splitting the data into two groups. Two-thirds of the data were used for calibration and one-third was used to evaluate and validate the models. Two probability maps were constructed for each species, one using GLM and the other using the gradient boosting technique. Binary presence/absence maps were created from probability maps using a threshold to maximize the kappa statistic, which defines the similarity between the binary map and the available biological evidence. Ruiz-Labourdette et al. chose between the GLM and gradient boosting models based on the kappa value obtained with the validation subset. They selected the model that best explained the current species distribution. Species were only modeled if they achieved a kappa value > 0.4 in one of two models. The model that was selected and validated for each species was applied to the future climate scenarios. A table displaying the kappa values obtained for each tree species in the GLM and gradient-boosting models was constructed.

Using the results of the models, the authors created a presence/absence matrix for all the tree species in the five scenarios examined (current; B2 for 2041–70; A2 for 2041–70; B2 for 2071–2100; and A2 for 2071–2100). This matrix was analyzed by multiple correspondence analyses (MCA) to identify trends in the variation of the current and future compositions of species. A table displaying the contributions of the tree species to the first axis of the MCA analysis was constructed.

Ruiz-Labourdette et al. incorporated 12 of the 15 species in their study that achieved acceptable kappa values. Gradient-boosting models were selected for the majority of the species (8 species).

The authors observed the largest changes in distribution for Mediterranean species such as xeric conifers and sclerophyllous evergreen species that are tolerant of high temperatures and summertime drought. These species ranges were expected to increase by 350% under the most severe climate change scenario (A2). Interestingly, their future range only occurred in regions in which the elevation did not differ from the elevation of their original range. This suggests that these species may spread from their present range and colonize flat piedmont and low-elevation mountainous areas. In contrast, Ruiz-Labourdette et al. found that Eurosiberian coniferous and broad-leaved species (species that prefer cold and wet environments) would experience a significant decrease in range. This decrease ranged from 80–99%, depending on the climate scenario. The Eurosiberian species are also expected to undergo the largest elevational displacement: upward between 200 and 550 m. As a result, the tree line would rise, and these tree species would colonize treeless areas that are now occupied by high-mountain grasslands. Unfortunately, it is likely that areas with climatic conditions suitable for their survival would disappear from the central and southern massifs.

The models also predicted that the ranges of sub-Mediterranean species (semi-deciduous oak trees, sub-Mediterranean gymnosperms, and sub-Mediterranean phreatophytes) would remain constant or decrease slightly under different climate scenarios (between 5% and 70%). These species optimal growing conditions may also occur at slightly higher elevations, compensating for the warming and water deficits. A figure displaying the current and projected distributions of three tree species in the Central and Iberian Mountain Ranges under the A2 climate scenario was constructed. Additionally, a graph displaying the potential change in the distribution of all the tree species in each three groups was constructed.

The authors’ models revealed that shifts in tree communities would occur as a result of an increase in the area where the climate is Mediterranean. The proportion of Mediterranean forests, especially the perennial sclerophyllous species, will increase, as will the range of xerophyllous vegetation. This species currently occupies marginal areas in warm, dry, sheltered piedmont enclaves. However, in the future, they may become the dominant vegetation within these regions. Semi-deciduous and deciduous species now found in flat piedmont and low elevation areas that require a moderate amount of water are predicted to decline. Furthermore, coniferous forests that grow in cold regions, as well as the Eurosiberian broadleaf forests that grow in wet and cold conditions, will experience a latitudinal displacement towards the north and a reduction in range. They will disappear entirely from the westernmost mountains. Instead, oak forests will become the dominant forests within these regions. A figure displaying the changes in tree communities projected for the Central and Iberian Mountain Ranges in the Iberian Peninsula was constructed.

Overall, Ruiz-Labourdette et al.’s results indicate that climate warming and a decrease in the availability of water will alter the abundance and diversity of mountain tree biota. Tree species resilient to high temperatures and drought that occupy lower elevations could increase in range and elevation, while species that persist in cold and wet environments may decline as a result of water stress. However, changes in the spatial extent of species ranges and in community composition will be greatest at lower, rather than at higher, elevations. Therefore, changes in tree species’ distributions and forest communities will occur across the entire range of elevation among these mountainous regions.