Selected Publications

 

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For more recent publications follow this link.

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Ding, C., Schreiber, S.G., Roberts, D.R., Hamann, A. and Brouard, J.S. 2017. Post-glacial biogeography of trembling aspen inferred from habitat models and genetic variance in quantitative traits. Scientific Reports 7:4672, DOI: 10.1038/s41598-017-04871-7.
Using species distribution models and information on genetic structure, we reconstructed a historical biogeography of trembling aspen in North America. A southeast to northwest gradient of decreasing genetic variance in quantitative traits suggests recolonisation of boreal Canada and Alaska from refugia in the eastern United States, with separate southwestern refugia for the Rocky Mountain regions. We did not find evidence for Beringian refugia. Stable habitat, where aspen clones may have survived multiple glaciations, was predicted in Mexico and the eastern United States, but not in the west where some of the largest aspen clones have been documented.
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Yeaman, S., Hodgins, K.A., Lotterhos, K.E., Suren, H., Nadeau, S., Degner, J.C., Nurkowski, K.A., Smets, P., Wang, T., Gray, L.K., Liepe, K.J., Hamann, A., Holliday, J.A., Whitlock, M.C., Rieseberg, L.H. & Aitken, S.N. 2016. Convergent local adaptation to climate in distantly related conifers. Science 353:1431–1433.
Science Perspectives companion piece: Hancock, A. M. 2016. How conifers adapt to the cold. Science 353: 1362–1363.
We usually assume that adaptation to climate is complex and involves many traits, many genes and many gene variants, allowing evolution to find a great variety of ways for trees to thrive under various environmental conditions. Here we show that even after evolving independently for 140 million years, lodgepole pine and interior spruce use a limited number and a high proportion of shared genes to adapt to the climate in which they live. The findings suggest that trees may be more restricted in their ability to adapt to climate than expected.
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Montwé, D., Isaac-Renton, M.G., Hamann, A. and Spiecker, H. 2016. Drought tolerance and growth in populations of a wide-ranging tree species indicate climate change risks for the boreal north. Global Change Biology 22: 806–815.
It is often assumed that climate change will lead to positive growth responses in northern latitudes. However, in this paper we show that natural plant populations adapted to boreal environments lack critical drought tolerance traits and may therefore not be able to take advantage of more favorable growing conditions expected under climate change. The research is based on whole-tree dendrochronological analysis at the driest sites of the Illingworth provenance trial series, one of the world's largest genetic field tests. These highly-valued test plantations have become available for destructive sampling after the trees were killed by the mountain pine beetle epidemic.
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Roberts, D.R. and Hamann, A. 2016. Climate refugia and migration requirements in complex landscapes. Ecography 39: 1238–1246.
All of today's species have proven their ability to cope with climate change during the glacial-interglacial cycles of the Quaternary, but future migration requirements involve different geographic barriers and new climate refugia. Here, we show that migration requirements to reach the nearest climate refugia in the future still exceed the fastest reconstructed post-glacial migration requirements, and that qualitatively different migration patterns may emerge in the future for some species.
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Liepe, K. J., Hamann, A., Smets, P., Fitzpatrick, C.R. and Aitken, S.N. 2016. Adaptation of lodgepole pine and interior spruce to climate: implications for reforestation in a warming world. Evolutionary Applications 9: 409–419.
In a series of common garden experiments, we quantify adaptation to local climate conditions in hundreds of populations of two widespread North American conifers, lodgepole pine and interior spruce. We infer adaptation strategies of tree populations do different macroclimatic regions within their range, and develop scientific knowledge for assisted gene flow applications to address climate change.
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Gray, L.K., Hamann, A., John, S., Rweyongeza, D., Barnhardt, L. and Thomas, B.R. 2016. Climate change risk management in tree improvement programs: selection and movement of genotypes. Tree Genetics & Genomes 12: 23, DOI: 10.1007/s11295-016-0983-1.
Building on 35 years of tree improvement research for for white spruce, we analyzed data from 135,000 seed transfers in 44 genetic tests established by industry and government agencies in Alberta. We show how the risk of planting maladapted trees can be minimized by selecting seed sources from origins with warmer temperatures, or by eliminating genotypes from breeding programs that are sensitive to anticipated future climate environments. However, adaptation to cold appears to be a prevalent driver for genetic population differentiation in spruce, thus limiting how far material may be moved under present climate conditions.
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Wang, T., Hamann, A., Spittlehouse, D.L., and Carroll, C. 2016. Locally downscaled and spatially customizable climate data for historical and future periods for North America. PLoS One 11: e0156720.
This is the most up-to-date reference for users of our high-resolution interpolated climate databases and the corresponding software to interactively query these datasets. Interpolated grids and software packages for the entire North American continent are avialable for anonymous download (http://tinyurl.com/ClimateNA and http://tinyurl.com/ClimateWNA). Equivalent databases have also been developed for Europe (http://tinyurl.com/ClimateEU) and South America (http://tinyurl.com/ClimateSA).
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Hamann, A. , Roberts, D.R., Barber, Q.E., Carroll, C. and Nielsen, S.E. 2015. Velocity of climate change algorithms for guiding conservation and management. Global Change Biology 21: 997–1004.
The velocity of climate change is a widely used analytical approach (including in the 5th IPCC report) to assess climate change vulnerability of species, ecosystems, or protected areas. In this paper, we provide improved algorithms to better support conservation and forest management applications.Sample code is available here and velocity grids for western North America can be downloaded at http://tinyurl.com/VelocityWNA,
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Carroll, C., Lawler, J.J., Roberts, D.R., Hamann, A. 2015. Biotic and climatic velocity identify contrasting areas of vulnerability to climate change. PLoS One 10: e0140486.
A case study for the western hemisphere as to how to apply the new methodological approach listed above (Hamann et al 2015). The introduction also provides an excellent overview of various concepts of velocity calculations (climaic, biotic, bioclimatic, forward, reverse). Data for the full North American continent are available here: http://adaptwest.databasin.org/pages/adaptwest-velocitywna
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Schreiber, S.G. Hacke, U.G. and Hamann, A. 2015. Variation of xylem vessel diameters across a climate gradient: insight from a reciprocal transplant experiment with a widespread boreal tree. Functional Ecology 29: 1392-1401.
A large-scale transplant experiment across western Canada showed that the best performing populations showed the highest degree of plasticity, which can be used as a selection criterion for genotypes in assisted migration programs to address climate change.
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Gapare, W.J., Ivkovic, M, Liepe, K.J., Hamann, A. and Low, C.B. 2015. Drivers of genotype by environment interaction in radiata pine as indicated by multivariate regression trees. Forest Ecology and Management 353: 21-29.
We analyze genotype × environment interactions in arguably the largest datasets for plantation forestry in the world. We show that in some environments, substantial productivity gains are possible over status-quo deployment strategies for radiata pine.
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Montwé, D. Spiecker, H. and Hamann, A. 2015. Five decades of growth in a genetic field trial of Douglas-fir reveal trade-offs between productivity and drought tolerance. Tree Genetics & Genomes 11: 29, DOI: 10.1007/s11295-015-0854-1.
In this study, we combine dendrochronological research with genetic field trials to quantify genotype × environment interactions observed over time. Our results show evidence for trade-offs between productivity and drought resilience.
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Roberts, D.R. and Hamann, A. 2015. Glacial refugia and modern genetic diversity of 22 western North American tree species. Proceedings of the Royal Society B: Biological Sciences 282: 20142903, DOI: 10.1098/rspb.2014.2903.
North American tree species, subspecies, and genetic varieties have primarily evolved in a landscape of extensive continental ice. Here, we use species distribution models, genetic marker information, and fossil pollen data to reconstruct glacial refugia and post-glacial migration paths. We evaluate hypotheses regarding Beringian refugia, the origin of Pacific Northwest inland rainforests, and the evolution of subspecies in widespread conifers. Download links for additional maps of glacial habitat reconstructions (22 species, 27MB PDF), and supplementary stistics (Tables S1-S4, 0.5MB PDF)
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Isaac-Renton, M.G., Roberts, D.R. Hamann, A. and Spiecker, H. 2014. Douglas-fir plantations in Europe: a retrospective test of assisted migration to address climate change. Global Change Biology 20: 2607–2617.
Can bioclimate envelope models reliably guide assisted migration under observed and projected climate change? This study uses North American species introductions to Europe as a retrospective experiment on how trees respond when subjected to climate regime shifts. Based on a meta-analysis of 2800 provenance transfers, we conclude that climate envelope models can predict growth of introduced populations reasonably well with some exception, and that climate trends observed over the last three decades warrant changes to current use of Douglas-fir planting stock in Europe. The complete provenance trial database is available upon request.
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Schreiber, S.G., Ding, C., Hamann, A., Hacke, U.G., Thomas, B.R. and Brouard, J.S. 2013. Frost hardiness vs. growth performance in trembling aspen: an experimental test of assisted migration. Journal of Applied Ecology 50: 939949.
This study demonstrates that assisted migration prescriptions may have considerable potential to enhance forest productivity. In the case of aspen, even 1000+ km long-distance seed transfers in a north-west direction were successful, with excellent survival rates and markedly increased productivity after 10 years. We conclude that benefits in productivity outweigh potential risks associated with northward transfer of aspen planting stock under both current and projected future climate conditions.
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Worrall, J.J., Rehfeldt, G.E., Hamann, A., Hogg, E.H., Marchettia, S.B., Michaelian, M., Gray, L.K. 2013. Recent declines of Populus tremuloides in North America linked to climate. Forest Ecology and Management 299: 3551.
From 2000 to 2010, over 3.2 million ha of aspen decline (crown thinning, branch dieback, and mortality) were mapped in North America. We show that warm, dry cliamte extremes are strongly implicated in most episodes, which may subsequently be amplified and prolonged by insect pests and diseases. A bioclimatic habitat model shows that decline tended to occur in marginally suitable climate habitat, and that climatic suitability decreased markedly in the period leading up to decline in almost all decline regions.
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Hamann, A. and Aitken, S.N. 2013. Conservation planning under climate change: accounting for adaptive potential and migration capacity in species distribution models Diversity and Distributions 19: 268–280.
This is a methods paper enabeling a more sensible interpretation of species distribution model projections. Similar to the widely used ‘no migration’ and ‘unlimited migration’ scenarios, we employ more refined biological response scenarios to evaluate the potential effects of genetic adaptation to local environments and the capacity of species to adapt and migrate. As an example application, we evaluate how future-proof the protected area system of British Columbia is.
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Gray, L. K. and Hamann, A. 2013. Tracking suitable habitat for tree populations under climate change in western North America. Climatic Change 117: 289–303.
Our latest magnum opus regarding tree species distribution modeling at the population level for western North America. Consensus maps representing habitat suitability and uncertainties, considering a comprehensive set of climate change scenarios are downloadable as PDFs here: black spruce | Douglas-fir | Engelmann Spruce | lodgepole pine | Pacific silver fir | ponderosa pine | Sitka spruce | tamarack | trembling aspen | western hemlock | western larch | western redcedar | western white pine | white spruce | yellow cedar. The corresponding GIS files are available upon request from AH.
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Schreiber, S.G., Hamann, A., Hacke, U.G. and Thomas, B.R. 2013. Sixteen years of winter stress: an assessment of cold hardiness, growth performance and survival of hybrid poplar clones at a boreal planting site. Plant Cell & Environment 36: 419–428.
In this study, we evaluated the effect of winter stress on growth and survival of 47 hybrid poplar clones in a long-term field experiment. We found that trees with narrow xylem vessels showed reduced freezing-induced embolism and superior productivity at age 16. Cold hardiness of living tissues and the timing of leaf senescence and budbreak were not related to growth or survival, pinpointing small vessel diameters as an essential adaptive trait for poplar hybrids in boreal planting environments.
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Gylander, T., Hamann, A. Brouard, J. S. and Thomas, B. R. 2012. The potential of aspen clonal forestry in Alberta: breeding regions and estimates of genetic gain from selection. PLoS One 7: e44303.
Here, we synthesize the results of a decade-long research effort by an industrial tree improvement cooperative. We assess the degree to which growth traits are inherited (broad sense heritabilities), and estimate gains from selection and clonal deployment of aspen planting stock. The genetic data are also more generally interpreted with respect to movement of plant material within Alberta, so that planting stock is well adapted to environmental conditions..
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Roberts, D. R. and Hamann, A. 2012. Method selection for species distribution modelling: are temporally or spatially independent evaluations necessary? Ecography 35: 792–802.
In this comprehensive method comparison, we evaluate how our novel ecosystem-based climate envelope modeling approach fares against a set of popular species distribution models. A by-product of this research turned out to be the main scientific insight: Assesments of model accuracy against truly independent test data (fossil records, new regions) were quite highly correlated with standard cross-validation techniques, broadly affirming the validity of other method comparisons using semi-independent data-splitting approaches.
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Roberts, D. R. and Hamann, A. 2012. Predicting potential climate change impacts with bioclimate envelope models: a palaeoecological perspective.Global Ecology and Biogeography 21: 121–133.
It is widely thought that bioclimate envelope model projections may be compromised by no-analogue climates. In this paper we show that habitat projections for the 21st century are likely well within model capabilities. We could approximately reconstruct ecosystem distributions for the mid- to late-Holocene, but models proved unreliable for the Late Pleistocene, where no-analogue climates and niche constancy issues became apparent.
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Gray, L. K., Gylander, T., Mbogga, M. S., Chen, P. and Hamann, A. 2011. Assisted migration to address climate change: recommendations for aspen reforestation in western Canada. Ecological Applications. 21: 1591–1603.
We bring together results from genetic field trials, remote sensing, climatology, and modeling to develop assisted migration prescriptions for aspen in western Canada. Our intention is to develop more dependable guidelines by synthesizing information from a variety of data sources and by drawing on independent modeling, experimental, and empirical research approaches.
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Gray, L. K. and Hamann, A. 2011. Strategies for reforestation under uncertain future climates: guidelines for Alberta, Canada. PLoS One 6: e22977, URL: http://dx.plos.org/10.1371/journal.pone.0022977.
In this case study for Alberta, we develop hands-on recommendations to modify reforestation practices in the face of uncertain future climates. We also contribute a discussion as to why bioclimate envelope models are a useful tool for matching species and locally adapted genotypes with the most likely planting environments.
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Beaubien, E. and Hamann, A. 2011. Spring flowering response to climate change between 1936 and 2006 in Alberta, Canada. BioScience. 61: 514–524.
If there is anyone in Alberta unconvinced that climate change is a reality, this paper provides virtually irrefutable evidence collected literally in the backyard of hundreds of Albertans. Since the 1930s monthly temperatures in spring have increased by up to 5.3 °C, and the earliest-blooming plant species have advanced their flowering dates by two weeks. At the same time, they also have become more vulnerable to spring frosts.
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Schreiber, S.G., Hacke, U.G., Hamann, A. and Thomas, B.R. 2011. Genetic variation of hydraulic and wood anatomical traits in hybrid poplar and trembling aspen. New Phytologist 190: 150160.
Performance of forest trees is usually thought of as a balance between investing in growth versus survival traits. In this study we unexpectedly found that small vessel diameters, restrictive stomatal control, and robust hydraulic properties are associated with the fastest growing trees. Some of these traits may be used for early selection, and selecting conservatively for survival traits does not appear to compromise growth performance of aspen and hybrid poplars in a boreal planting environment.
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Hamann, A., Gylander, T. and Chen, P. 2011. Developing seed zones and transfer guidelines with multivariate regression trees. Tree Genetics & Genomes 7: 399408.
In this methods paper we introduce a new multivariate approach to analyze geographic patterens of adaptive genetic variation as well as neutral genetic marker traits. Regression trees link genetic information to geographic variables or spatial polygons for the delineation of seed zones and the development of seed transfer guidelines. Sample code and sample data is included at the end if you want to try it out!
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Chen, P., Welsh, C. and Hamann, A. 2010. Geographic variation in growth response of Douglas-fir to inter-annual climate variability and projected climate change. Global Change Biology 16: 33743385.
We usually expect climate change to affect tree species at their southern and low-elevation range limits. This dendrochronology study shows that the opposite is the case for Douglas-fir. Why? Populations of wide-ranging species are differenty adapted and will all occupy climates at or beyond the limits of their individual niches. An important implication is that we should not rely on models that assume a uniform species response to predict potential climate change impacts.
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Mbogga, M. S., Wang, X. and Hamann, A. 2010. Bioclimate envelope model predictions for natural resource management: dealing with uncertainty. Journal of Applied Ecology 47: 731740.
We use an analysis of variance approach to evaluate which model parameters, modeling methods, and input data matter in bioclimate envelope modeling. Differences due to climate change predictions generally outweigh uncertainty due to ecological models and their assumptions. Nevertheless, we find some strong interaction terms between ecological and climate models. These interactions point to where ecological models can be improved most efficiently, and narrow the range of projections that practitioners need to consider.
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Li, H., Wang, X. and Hamann, A. 2010. Genetic adaptation of aspen (Populus tremuloides) populations to spring risk environments: a novel remote sensing approach. Canadian Journal of Forest Research 40: 20822090.
Required heatsum is a genetic trait that determines the timing of budbreak in spring. We use sattelite observations and interpolated climate data to infer required heatsum and validate the results against experimental data from a genetic common garden trial. To our knowledge this is the first time that genetic variation in any trait has been revealed for all populations of a species across a large geographic area.
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O'Neill, G., Hamann, A. and T. L. Wang. 2008. Accounting for population variation improves estimates of the impact of climate change on species’ growth and distribution. Journal of Applied Ecology 45: 10401049.
Virtually all species distribution models predict the realized niche of species using census data in the form of species inventory plots. Here we present a model for lodgepole pine that predicts growth within the fundamental niche of the species. It is parameterized with data from the arguably largest reciprocal transplant experiment in existence.
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Hamann, A., and T. L. Wang. 2006. Potential effects of climate change on tree species and ecosystem distribution in British Columbia. Ecology 87: 27732786.
Probably the most cited paper in this list. We introduce a novel climate envelope modeling technique and demonstrate how the climate space of BC's ecological zones shifts under various climate change scenarios. Gordon Campbell used figures and data for a presentation at the 2008 Premier's Summit Meeting, and the projections were displayed at the Royal BC Museum in 2007.
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Woods, A., Coates, K. D., and Hamann, A. 2005. Is an unprecedented Dothistroma needle blight epidemic related to climate change? Bioscience 55: 761769.
This paper makes a convincing case that an unprecendented outbreak of Dothistroma needle blight (a native disease in Brtish Columbia) is caused by a directional long-term trend toward higher summer precipitation. We are not sure if this trend in precipitation can be attributed to global climate change processes, but we show that the usual cyclical suspects (PDO, El-Nino) are not responsible.
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Hamann, A., S. N. Aitken, and A. D. Yanchuk. 2004. Cataloguing in situ protection of genetic resources for major commercial forest trees in British Columbia. Special Issue, Forest Ecology and Management 197: 295305.
Why should we worry about conservation of the most common species? While species extinctions certainly deserve attention, we also want to avoid losing uniquely adapted populations within a species. Genotypes are not easy to identify and may be lost without anyone taking notice. This paper proposes a novel conservation framework to avoid such losses, and evaluates the effectiveness of major protected area expansion by the New Democratic government from 1996-1999.
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Hamann, A. 2004. Flowering and fruiting phenology of a Philippine submontane rain forest: climatic factors as proximate and ultimate causes. Journal of Ecology 92: 2431.
Climate can be the trigger for leaf-out, flowering and fruiting, but it can also be the evolutionary cause for a particular timing of these phenological events. This is obvious for temperate forests with pronounced seasons. Here I investigate what's going on in an aseasonal tropical rainforest across a wide range of species: a dazzeling variety of proximate triggers and ultimate causes.
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Hamann, A., G. Namkoong, and M. P. Koshy. 2002. Improving precision of breeding values by removing spatially autocorrelated variation in forestry field experiments. Silvae Genetica 51: 210215.
Probably the best paper in this list that nobody cites except myself and my students :-) We use kriging to remove residual errors in field experiments that are due to microsite variation. Works for non-genetic field experiments too.
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Hamann, A. and Curio, C. 1999. Interactions between frugivores and fleshy fruit trees in a Philippine submontane rainforest. Conservation Biology 13: 766773.
We highlight the importance of fruit-eating animals for fruit-trees and vice versa. If one functional group is in severe decline, the other is likely to follow, which is unfortunately the case for the study area.
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Hamann, A., El-Kassaby, Y.A., Koshy, M.P. and Namkoong, G. 1998. Multivariate analysis of allozymic and quantitative trait variation in Alnus rubra: geographic patterns and evolutionary implications. Canadian Journal of Forest Research 51: 210215.
A methods paper that has been cited in several multivariate statistics textbooks as an example for the use of canonical correlation analysis. The method revealed interpretable relationships between genetic and environmental data that was invisible to univariate approaches. There is also an interesting reconstruction of glacial refugia and post-glacial migration routes based on genetic marker data from red alder.
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Hamann, A. 1998. Adventitious root formation in cuttings of loblolly pine (Pinus taeda L .): developmental sequence and effects of maturation. Trees - Structure and Function 12: 175180.
A tedious anatomical study that answered when and why you can stop waiting for loblolly pine cuttings to root. Rooted cutting orchards are used for clonal forestry with the species.