Abundance of Dendroctonus frontalis and D. mexicanus (Coleoptera: Scolytinae) along altitudinal transects in Mexico: Implications of climatic change for forest conservation.

Bark beetle infestations have historically been primary drivers of stand thinning in Mexican pine forests. However, bark beetle impacts have become increasingly extensive and intense, apparently associated with climate change. Our objective was to describe the possible association between abundance of bark beetle flying populations and the occurrence of given value intervals of temperature, precipitation and their balance, in order to have a better comprehension of the climatic space that might trigger larger insect abundances, an issue relevant in the context of the ongoing climatic change. Here, we monitored the abundance of two of the most important bark beetle species in Mexico, Dendroctonus frontalis and D. mexicanus. We sampled 147 sites using pheromone-baited funnel traps along 24 altitudinal transects in 11 Mexican states, from northwestern Chihuahua to southeastern Chiapas, from 2015 to 2017. Through mixed model analysis, we found that the optimum Mean Annual Temperatures were 17°C-20°C for D. frontalis in low-elevation pine-oak forest, while D. mexicanus had two optimal intervals: 11-13°C and 15-18°C. Higher atmospheric Vapor Pressure Deficit (≥ 1.0) was correlated with higher D. frontalis abundances, indicating that warming-amplified drought stress intensifies trees' vulnerability to beetle attack. As temperatures and drought stress increase further with projected future climatic changes, it is likely that these Dendroctonus species will increase tree damage at higher elevations. Pine forests in Mexico are an important source of livelihood for communities inhabiting those areas, so providing tools to tackle obstacles to forest growth and health posed by changing climate is imperative.

Assisted migration and the rare endemic plant species: the case of two endangered Mexican spruces.

Background: In the projected climate change scenarios, assisted migration might play an important role in the ex situ conservation of the threatened plant species, by translocate them to similar suitable habitats outside their native distributions. However, it is unclear if such habitats will be available for the Rare Endemic Plant Species (REPS), because of their very restricted habitats. The aims of this study were to perform a population size assessment for the REPS Picea martinezii Patterson and Picea mexicana Martínez, and to evaluate the potential species distributions and their possibilities for assisted migration inside México and worldwide. Methods: We performed demographic censuses, field surveys in search for new stands, and developed distribution models for Last Glacial Maximum (22,000 years ago), Middle Holocene (6,000 years ago), current (1961-1990) and future (2050 and 2070) periods, for the whole Mexican territory (considering climatic, soil, geologic and topographic variables) and for all global land areas (based only on climate). Results: Our censuses showed populations of 89,266 and 39,059 individuals for P. martinezii and P. mexicana, respectively, including known populations and new stands. Projections for México indicated somewhat larger suitable areas in the past, now restricted to the known populations and new stands, where they will disappear by 2050 in a pessimistic climatic scenario, and scarce marginal areas (p = 0.5-0.79) remaining only for P. martinezii by 2070. Worldwide projections (based only on climate variables) revealed few marginal areas in 2050 only in México for P. martinezii, and several large areas (p ≥ 0.5) for P. mexicana around the world (all outside México), especially on the Himalayas in India and the Chungyang mountains in Taiwan with highly suitable (p ≥ 0.8) climate habitats in current and future (2050) conditions. However, those suitable areas are currently inhabited by other endemic spruces: Picea smithiana (Wall.) Boiss and Picea morrisonicola Hayata, respectively. Conclusions: Assisted migration would only be an option for P. martinezii on scarce marginal sites in México, and the possibilities for P. mexicana would be continental and transcontinental translocations. This rises two possible issues for future ex situ conservation programs: the first is related to whether or not consider assisted migration to marginal sites which do not cover the main habitat requirements for the species; the second is related to which species (the local or the foreign) should be prioritized for conservation when suitable habitat is found elsewhere but is inhabited by other endemic species. This highlights the necessity to discuss new policies, guidelines and mechanisms of international cooperation to deal with the expected high species extinction rates, linked to projected climate change.

Global field observations of tree die-off reveal hotter-drought fingerprint for Earth's forests.

Earth's forests face grave challenges in the Anthropocene, including hotter droughts increasingly associated with widespread forest die-off events. But despite the vital importance of forests to global ecosystem services, their fates in a warming world remain highly uncertain. Lacking is quantitative determination of commonality in climate anomalies associated with pulses of tree mortality-from published, field-documented mortality events-required for understanding the role of extreme climate events in overall global tree die-off patterns. Here we established a geo-referenced global database documenting climate-induced mortality events spanning all tree-supporting biomes and continents, from 154 peer-reviewed studies since 1970. Our analysis quantifies a global "hotter-drought fingerprint" from these tree-mortality sites-effectively a hotter and drier climate signal for tree mortality-across 675 locations encompassing 1,303 plots. Frequency of these observed mortality-year climate conditions strongly increases nonlinearly under projected warming. Our database also provides initial footing for further community-developed, quantitative, ground-based monitoring of global tree mortality.

Distribution and conservation of species is misestimated if biotic interactions are ignored: the case of the orchid Laelia speciosa.

The geographic distribution of species depends on their relationships with climate and on the biotic interactions of the species. Ecological Niche Models (ENMs) mainly consider climatic variables only and may tend to overestimate these distributions, especially for species strongly restricted by biotic interactions. We identified the preference of Laelia speciosa for different host tree species and include this information in an ENM. The effect of habitat loss and climate change on the distribution of these species was also estimated. Although L. speciosa was recorded as epiphyte at six tree species, 96% of the individuals were registered at one single species (Quercus deserticola), which indicated a strong biotic interaction. We included the distribution of this host tree as a biotic variable in the ENM of L. speciosa. The contemporary distribution of L. speciosa is 52,892 km2, which represent 4% of Mexican territory and only 0.6% of the distribution falls within protected areas. Habitat loss rate for L. speciosa during the study period was 0.6% per year. Projections for 2050 and 2070 under optimistic and pessimistic climate change scenarios indicated a severe reduction in its distribution. Climaticaly suitable areas will also shift upwards (200-400 m higher). When estimating the distribution of a species, including its interactions can improve the performance of the ENMs, allowing for more  accurate estimates of the actual distribution of the species, which in turn allows for better conservation strategies.

Suitable climatic habitat changes for Mexican conifers along altitudinal gradients under climatic change scenarios.

The high biodiversity of the Mexican montane forests is concentrated on the Trans-Mexican Volcanic Belt, where several Protected Natural Areas exist. Our study examines the projected changes in suitable climatic habitat for five conifer species that dominate these forests. The species are distributed sequentially in overlapping altitudinal bands: Pinus hartwegii at the upper timberline, followed by Abies religiosa, the overwintering host of the Monarch butterfly at the Monarch Butterfly Biosphere Reserve, P. pseudostrobus, the most important in economic terms, and P. devoniana and P. oocarpa, which are important for resin production and occupy low altitudes where montane conifers merge with tropical dry forests. We fit a bioclimatic model to presence-absence observations for each species using the Random Forests classification tree with ground plot data. The models are driven by normal climatic variables from 1961 to 1990, which represents the reference period for climate-induced vegetation changes. Climate data from an ensemble of 17 general circulation models were run through the classification tree to project current distributions under climates described by the RCP 6.0 watts/m2 scenario for the decades centered on years 2030, 2060 and 2090. The results suggest that, by 2060, the climate niche of each species will occur at elevations that are between 300 to 500 m higher than at present. By 2060, habitat loss could amount to 46-77%, mostly affecting the lower limits of distribution. The two species at the highest elevation, P. hartwegii and A. religiosa, would suffer the greatest losses while, at the lower elevations, P. oocarpa would gain the most niche space. Our results suggest that conifers will require human assistance to migrate altitudinally upward in order to recouple populations with the climates to which they are adapted. Traditional in situ conservation measures are likely to be equivalent to inaction and will therefore be incapable of maintaining current forest compositions.

Common garden comparisons confirm inherited differences in sensitivity to climate change between forest tree species.

The natural distribution, habitat, growth and evolutionary history of tree species are strongly dependent on ecological and genetic processes in ecosystems subject to fluctuating climatic conditions, but there have been few experimental comparisons of sensitivity between species. We compared the responses of two broadleaved tree species (Fagus sylvatica and Quercus petraea) and two conifer tree species (Pinus sylvestris and Picea abies) to climatic transfers by fitting models containing the same climatic variables. We used published data from European provenance test networks to model the responses of individual populations nested within species. A mixed model approach was applied to develop a response function for tree height over climatic transfer distance, taking into account the climatic conditions at both the seed source and the test location. The two broadleaved species had flat climatic response curves, indicating high levels of plasticity in populations, facilitating adaptation to a broader range of environments, and conferring a high potential for resilience in the face of climatic change. By contrast, the two conifer species had response curves with more pronounced slopes, indicating a lower resilience to climate change. This finding may reflect stronger genetic clines in P. sylvestris and P. abies, which constrain their climate responses to narrower climatic ranges. The response functions had maxima that deviated from the expected maximum productivity in the climate of provenance towards cooler/moister climate conditions, which we interpreted as an adaptation lag. Unilateral, linear regression analyses following transfer to warmer and drier sites confirmed a decline in productivity, predictive of the likely impact of ongoing climate change on forest populations. The responses to mimicked climate change evaluated here are of considerable interest for forestry and ecology, supporting projections of expected performance based on "real-time" field data.

Total Mercury in Plant Tissue from a Mining Landscape in Western Mexico.

Environmental impacts of mining activities are well known, particularly on-site degradation, but long term effects are less known. Mercury content from vegetation samples from a mine dump and surrounding forests was quantified for understanding the fate of this element in the local the environment. The study area, Tlalpujahua, Michoacán, México, has a mining history going back more than 400 years. Including gold and silver extraction by means of mercury amalgamation for 352 years (1554-1906). Mercury was present in all sampled materials. The highest values correspond to wood samples from the mine dump (13.84 ± 3.88 ppm), while wood samples from adjacent forests had 4.3 ± 2.4 ppm, almost twice as much as coniferous needles, shrub leaves and corn seeds (2.2 ± 0.34 ppm). The highest concentration was found for J. deppeana wood (16.05 ± 2.3 ppm). The capacity of accumulating mercury by Juniperus trees when growing on the mine dumps suggests that this species has a potential to be used for biosequestration purposes.

Adaptive and plastic responses of Quercus petraea populations to climate across Europe.

How temperate forests will respond to climate change is uncertain; projections range from severe decline to increased growth. We conducted field tests of sessile oak (Quercus petraea), a widespread keystone European forest tree species, including more than 150 000 trees sourced from 116 geographically diverse populations. The tests were planted on 23 field sites in six European countries, in order to expose them to a wide range of climates, including sites reflecting future warmer and drier climates. By assessing tree height and survival, our objectives were twofold: (i) to identify the source of differential population responses to climate (genetic differentiation due to past divergent climatic selection vs. plastic responses to ongoing climate change) and (ii) to explore which climatic variables (temperature or precipitation) trigger the population responses. Tree growth and survival were modeled for contemporary climate and then projected using data from four regional climate models for years 2071-2100, using two greenhouse gas concentration trajectory scenarios each. Overall, results indicated a moderate response of tree height and survival to climate variation, with changes in dryness (either annual or during the growing season) explaining the major part of the response. While, on average, populations exhibited local adaptation, there was significant clinal population differentiation for height growth with winter temperature at the site of origin. The most moderate climate model (HIRHAM5-EC; rcp4.5) predicted minor decreases in height and survival, while the most extreme model (CCLM4-GEM2-ES; rcp8.5) predicted large decreases in survival and growth for southern and southeastern edge populations (Hungary and Turkey). Other nonmarginal populations with continental climates were predicted to be severely and negatively affected (Bercé, France), while populations at the contemporary northern limit (colder and humid maritime regions; Denmark and Norway) will probably not show large changes in growth and survival in response to climate change.

North American vegetation model for land-use planning in a changing climate: a solution to large classification problems.

Data points intensively sampling 46 North American biomes were used to predict the geographic distribution of biomes from climate variables using the Random Forests classification tree. Techniques were incorporated to accommodate a large number of classes and to predict the future occurrence of climates beyond the contemporary climatic range of the biomes. Errors of prediction from the statistical model averaged 3.7%, but for individual biomes, ranged from 0% to 21.5%. In validating the ability of the model to identify climates without analogs, 78% of 1528 locations outside North America and 81% of land area of the Caribbean Islands were predicted to have no analogs among the 46 biomes. Biome climates were projected into the future according to low and high greenhouse gas emission scenarios of three General Circulation Models for three periods, the decades surrounding 2030, 2060, and 2090. Prominent in the projections were (1) expansion of climates suitable for the tropical dry deciduous forests of Mexico, (2) expansion of climates typifying desertscrub biomes of western USA and northern Mexico, (3) stability of climates typifying the evergreen-deciduous forests of eastern USA, and (4) northward expansion of climates suited to temperate forests, Great Plains grasslands, and montane forests to the detriment of taiga and tundra climates. Maps indicating either poor agreement among projections or climates without contemporary analogs identify geographic areas where land management programs would be most equivocal. Concentrating efforts and resources where projections are more certain can assure land managers a greater likelihood of success.

Projections of suitable habitat for rare species under global warming scenarios.

PREMISE OF THE STUDY: Modeling the contemporary and future climate niche for rare plants is a major hurdle in conservation, yet such projections are necessary to prevent extinctions that may result from climate change. • METHODS: We used recently developed spline climatic models and modified Random Forests statistical procedures to predict suitable habitats of three rare, endangered spruces of Mexico and a spruce of the southwestern USA. We used three general circulation models and two sets of carbon emission scenarios (optimistic and pessimistic) for future climates. • KEY RESULTS: Our procedures predicted present occurrence perfectly. For the decades 2030, 2060, and 2090, the ranges of all taxa progressively decreased, to the point of transient disappearance for one species in the decade 2060 but reappearance in 2090. Contrary to intuition, habitat did not develop to the north for any of the Mexican taxa; rather, climate niches for two taxa re-materialized several hundred kilometers southward in the Trans-Mexican Volcanic Belt. The climate niche for a third Mexican taxon shrank drastically, and its two mitotypes responded differently, one of the first demonstrations of the importance of intraspecific genetic variation in climate niches. The climate niche of the U.S. species shrank northward and upward in elevation. • CONCLUSION: The results are important for conservation of these species and are of general significance for conservation by assisted colonization. We conclude that our procedures for producing models and projecting the climate niches of Mexican spruces provide a way for handling other rare plants, which constitute the great bulk of the world's endangered and most vulnerable flora.