Scientists & Staff
Current ResearchMy main research focus investigates the role of competition by understory plants and herbivory by ungulates and small mammals in the diversity and abundance of tree seedlings in the understory before overstory gap formation. Furthermore, I am involved in several projects elucidating the role mammalian herbivores play in the maintenance of herbaceous plant communities across a wide latitudinal gradient.
Research InterestsI plan on continuing my research programs on the maintenance of herbaceous species diversity in both temperate and tropical systems. I also plan on examining the potential for developing alternatives to herbicide application for the control of understory herbaceous interference. Additional research interests involve regeneration of forest systems following catastrophic wind disturbance and subsequent salvaging as well as the impact of soil-borne pathogens on early tree establishment.
Why This Research is ImportantAmong the many factors that determine forest understory diversity prior to any overstory disturbance, competition and herbivory are typically thought of as preeminent. Understanding how these two factors, alone and in concert, act to promote or reduce plant diversity is key to the sustainable management of forest resources.
- University of Pittsburgh, Ph.D. Ecology and Evolutionary Biology, 2005
- University of North Carolina, Greensboro, M.S. Department of Biological Sciences, 1998
- University of North Carolina, Greensboro, B.A. Department of Biological Sciences, 1993
- University of Pittsburgh, Graduate Certificate Latin American Studies, 2005
- Ecological Society of America
Featured Publications & Products
- De Jager, Nathan R.; Drohan, Patrick J.; Miranda, Brian M.; Sturtevant, Brian R.; Stout, Susan L.; Royo, Alejandro A.; Gustafson, Eric J.; Romanski, Mark C. 2017. Simulating ungulate herbivory across forest landscapes: A browsing extension for LANDIS-II. Ecological Modelling. 350: 11-29.
- Royo, Alex; Peterson, Chris J.; Stanovick, John S.; Carson, Walter P. 2016. Evaluating the ecological impacts of salvage logging: can natural and anthropogenic disturbances promote coexistence?. Ecology. 97(6): 1566-1582.
- Kern, Christel C.; Burton, Julia I.; Raymond, Patricia; D'Amato, Anthony W.; Keeton, William S.; Royo, Alex; Walters, Michael B.; Webster, Christopher R.; Willis, John L. 2017. Challenges facing gap-based silviculture and possible solutions for mesic northern forests in North America. Forestry 90: 4-17.
- Royo, Alex; Kramer, David W.; Miller, Karl V.; Nibbelink, Nathan P.; Stout, Susan L. 2016. The canary in the coal mine: Sprouts as a rapid indicator of browse impact in managed forests. Ecological Indicators. 69: 269-275.
- Pendergast, Thomas H.; Hanlon, Shane M.; Long, Zachary M.; Royo, Alex; Carson, Walter P. 2016. The legacy of deer overabundance: long-term delays in herbaceous understory recovery. Canadian Journal of Forest Research. 46(3): 362-369.
Publications & Products
- Flower, Charles; Fant, Jeremie; Hoban, Sean; Knight, Kathleen; Steger, Laura; Aubihl, Elijah; Gonzalez-Meler, Miquel; Forry, Stephen; Hille, Andrea; Royo, Alejandro. 2018. Optimizing conservation strategies for a threatened tree species: In situ conservation of white ash (Fraxinus americana L.) genetic diversity through insecticide treatment. Forests
- Averill, Kristine M; Mortensen, David A; Smithwick, Erica A H; Kalisz, Susan; McShea, William J; Bourg, Norman A; Parker, John D; Royo, Alejandro A; Abrams, Marc D; Apsley, David K; Blossey, Bernd; Boucher, Douglas H; Caraher, Kai L; DiTommaso, Antonio; Johnson, Sarah E; Masson, Robert; Nuzzo, Victoria A. 2017. A regional assessment of white-tailed deer effects on plant invasion. AoB PLANTS. 10(1). 22 p.
- Barrette, Martin; Bélanger, Louis; De Grandpré, Louis; Royo, Alejandro A. 2017. Demographic disequilibrium caused by canopy gap expansion and recruitment failure triggers forest cover loss. Forest Ecology and Management
- Flower, Charles E.; Aubihl, Elijah; Fant, Jeremie; Forry, Stephen; Hille, Andrea; Knight, Kathleen S.; Oldland, William K.; Royo, Alejandro A.; Turcotte, Richard M. 2017. In-situ genetic conservation of white ash (Fraxinus americana) at the Allegheny national forest. In: Sniezko, Richard A.; Man, Gary; Hipkins, Valerie; Woeste, Keith; Gwaze, David; Kliejunas, John T.; McTeague, Brianna A., tech. cords. 2017. Gene conservation of tree species—banking on the future. Proceedings of a workshop. Gen. Tech. Rep. PNW-GTR-963. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 165-169.
- McWilliams, William H.; Westfall, James A.; Brose, Patrick H.; Lehman, Shawn L.; Morin, Randall S.; Ristau, Todd E.; Royo, Alejandro A.; Stout, Susan L. 2017. After 25 years, what does the Pennsylvania Regeneration Study tell us about oak/hickory forests under stress?. In: Kabrick, John M.; Dey, Daniel C.; Knapp, Benjamin O.; Larsen, David R.; Shifley, Stephen R.; Stelzer, Henry E., eds. Proceedings of the 20th Central Hardwood Forest Conference; 2016 March 28-April 1; Columbia, MO. General Technical Report NRS-P-167. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 280-290.
- Royo, Alejandro A.; Kramer, David W.; Miller, Karl V.; Nibbelink, Nathan P.; Stout, Susan L. 2017. Spatio-temporal variation in foodscapes modifies deer browsing impact on vegetation. Landscape Ecology. 32(12): 2281-2295.
- Sinacore, Katherine; Hall, Jefferson Scott; Potvin, Catherine; Royo, Alejandro A.; Ducey, Mark J.; Ashton, Mark S.; Joseph, Shijo. 2017. Unearthing the hidden world of roots: Root biomass and architecture differ among species within the same guild. PLOS ONE
- Chips, Michael J.; Yerger, Ellen H.; Hervanek, Arpad; Nuttle, Tim; Royo, Alex; Pruitt, Jonathan N.; McGlynn, Terrence P.; Riggall, Cynthia L.; Carson, Walter P. 2015. The indirect impact of long-term overbrowsing on insects in the Allegheny National Forest region of Pennsylvania. Northeastern Naturalist. 22(4): 782-797.
- McWilliams, William H.; Westfall, James A.; Brose, Patrick H.; Dey, Daniel C.; Hatfield, Mark; Johnson, Katherine; Laustsen, Kenneth M.; Lehman, Shawn L.; Morin, Randall S.; Nelson, Mark D.; Ristau, Todd E.; Royo, Alejandro A.; Stout, Susan L.; Willard, Thomas; Woodall, Christopher W. 2015. A regeneration indicator for Forest Inventory and Analysis: history, sampling, estimation, analytics, and potential use in the midwest and northeast United States. Gen. Tech. Rep. NRS-148. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 74 p.
- Huebner, Cynthia D.; Steinman, Jim; Hutchinson, Todd F.; Ristau, Todd E.; Royo, Alejandro A. 2014. The distribution of a non-native (Rosa multiflora) and native (Kalmia latifolia) shrub in mature closed-canopy forests across soil fertility gradients. Plant and Soil. 377(1-2): 259-276.
- Nuttle, Tim; Royo, Alejandro A.; Adams, Mary Beth; Carson, Walter P. 2013. Historic disturbance regimes promote tree diversity only under low browsing regimes in eastern deciduous forest. Ecological Monographs. 83: 3-17.
- Peterson, Chris J.; Krueger, Lisa M.; Royo, Alejandro A.; Stark, Scott; Carson, Walter P. 2013. Disturbance size and severity covary in small and mid-size wind disturbances in Pennsylvania northern hardwoods forests. Forest Ecology and Management. 302: 273-279.
- Royo, Alejandro A.; Ristau, Todd E. 2013. Stochastic and deterministic processes regulate spatio-temporal variation in seed bank diversity. Journal of Vegetation Science. 24: 724-734.
- Stout, Susan L.; Royo, Alejandro A.; deCalesta, David S.; McAleese, Kevin; Finley, James C. 2013. The Kinzua Quality Deer Cooperative: can adaptive management and local stakeholder engagement sustain reduced impact of ungulate browsers in forest systems?. Boreal Environment Research. 18(suppl. A): 50-64.
- Dey, Daniel C.; Royo, Alejandro A.; Gardiner, Emile S.; Cardenas, Luis Mario. 2012. Sustaining Quercus humboltii and Colombobalanus excelsa on the Colombian landscape: preservation or conservation - a research perspective. In: Butnor, John R., ed. Proceedings of the 16th Biennial Southern Silvicultural Research Conference; 2011 February 14-17; Charleston, SC. Gen. Tech. Rep. e-GTR-SRS-156. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station: 88-90.
- Dey, Daniel C.; Royo, Alejandro A.; Gardiner, Emile S.; Cardenas, Luis Mario. 2012. Sustaining Quercus humboldtii and Colombobalanus excelsa on the Colombian landscape: preservation or conservation - a research perspective. In: Butnor, John R., ed. 2012. Proceedings of the 16th biennial southern silvicultural research conference. e-Gen. Tech. Rep. SRS-156. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 90-92.
- Huebner, Cynthia D.; Hutchinson, Todd; Ristau, Todd; Royo, Alejandro; Steinman, James. 2012. Documenting the Regional and local distribution of Kalmia latifolia and Rosa multiflora in West Virginia, Ohio, and Pennsylvania Forests along a soil fertility gradient. In: Potter, Kevin M.; Conkling, Barbara L., eds. 2012. Forest health monitoring: 2009 national technical report. Gen. Tech. Rep. SRS-167. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 211-217.
- Royo, Alejandro A.; Knight, Kathleen S. 2012. White ash (Fraxinus americana) decline and mortality: the role of site nutrition and stress history. Forest Ecology and Management. 286: 8-15.
- Royo, Alejandro A.; Knight, Kathleen S.; Himes, Jamie M.; Will, Ashley N. 2012. White ash (Fraxinus americana) health in the Allegheny plateau region, Pennsylvania: Evaluating the relationship between FIA phase 3 crown variables and a categorical rating system. In: McWilliams, Will; Roesch, Francis A. eds. 2012. Monitoring Across Borders: 2010 Joint Meeting of the Forest Inventory and Analysis (FIA) Symposium and the Southern Mensurationists. e-Gen. Tech. Rep. SRS-157. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 123-129.
- Goetsch, Chandra; Wigg, Jennifer; Royo, Alejandro A.; Ristau, Todd; Carson, Walter P. 2011. Chronic over browsing and biodiversity collapse in a forest understory in Pennsylvania: Results from a 60 year-old deer exclusion plot. The Journal of the Torrey Botanical Society. 138(2): 220-224.
- Kain, Morgan; Battaglia, Loretta; Royo, Alejandro; Carson, Walter P. 2011. Over-browsing in Pennsylvania creates a depauperate forest dominated by an understory tree: results from a 60-year-old deer exclosure. Journal of the Torrey Biological Society. 138(3): 322-326.
- Royo, Alejandro A.; Heartsill-Scalley, Tamara; Moya, Samuel; Scatena, Fred N. 2011. Non-arborescent vegetation trajectories following repeated hurricane disturbance: ephemeral versus enduring responses. Ecosphere. 2(7): art 77. doi: 10.1890/ES11-0018.1
- Dey, Daniel C.; Royo, Alejandro A.; Brose, Patrick H.; Hutchinson, Todd F.; Spetich, Martin A.; Stoleson, Scott H. 2010. An ecologically based approach to oak silviculture: a synthesis of 50 years of oak ecosystem research in North America. Revista Columbia Forestal. 13(2): 201-222.
- Knight, Kathleen S.; Herms, Daniel A.; Cardina, John; Long, Robert; Rebbeck, Joanne; Gandhi, Kamal J.K.; Smith, Annemarie; Klooster, Wendy S.; Herms, Catherine P.; Royo, Alejandro A. 2010. Emerald ash borer aftermath forests: The dynamics of ash mortality and the responses of other plant species. In: Michler, Charles H.; Ginzel, Matthew D., eds. 2010. Proceedings of symposium on ash in North America; 2010 March 9-11; West Lafayette, IN. Gen. Tech. Rep. NRS-P-72. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 11.
- Reinhart, Kurt O.; Royo, Alejandro A.; Kageyama, Stacie A.; Clay, Keith. 2010. Canopy gaps decrease microbial densities and disease risk for a shade-intolerant tree species. Acta Oecologica. 36: 530-536.
- Royo, Alejandro A.; Carson, Walter P. 2010. The formation of dense understory layers in forests worldwide: consequences and implications for forest dynamics, biodiversity, and succession. In: Pye, John M.; Rauscher, H. Michael; Sands, Yasmeen; Lee, Danny C.; Beatty, Jerome S., tech. eds. Advances in threat assessment and their application to forest and rangeland management. Gen. Tech. Rep. PNW-GTR-802. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 469-496.
- Royo, Alejandro A.; Collins, Rachel; Adams, Mary Beth; Kirschbaum, Chad; Carson, Walter P. 2010. Pervasive interactions between ungulate browsers and disturbance regimes promote temperate forest herbaceous diversity. Ecology. 91(1): 93-105.
- Royo, Alejandro A.; Stout, Susan L.; deCalesta, David S.; Pierson, Timothy G. 2010. Restoring forest herb communities through landscape-level deer herd reductions: Is recovery limited by legacy effects? . Biological Conservation. 143: 2425-2434.
- Krueger, Lisa M.; Peterson, Chris J.; Royo, Alejandro; Carson, Walter P. 2009. Evaluating relationships among tree growth rate, shade tolerance, and browse tolerance following disturbance in an eastern deciduous forest. Canadian Journal of Forest Research. 39: 2460-2469.
- Royo, A.A. 2008. P.A. Thomas and J. Packham: Ecology of woodlands and forests: Description, dynamics, and diversity [book review]. Landscape Ecology. 23(6): 755-756.
- Royo, Alejandro A.; Bates, Ramona M.; Lacey, Elizabeth P. 2008. Demographic constraints in three populations of Lobelia boykinii, a rare wetland endemic. Journal of the Torrey Botanical Society. 135(2): 189-199.
- Royo, Alejandro A.; Carson, Walter P. 2008. Direct and indirect effects of a dense understory on tree seedling recruitment in temperate forests: habitat-mediated predation versus competition. Canadian Journal of Forest Research. 38: 1634-1645.
- Royo, Alejandro A.; Carson, Walter P. 2006. On the formation of dense understory layers in forests worldwide: consequences and implications for forest dynamics, biodiversity, and succession. Canadian Journal of Forest Research 36:1345-1362
- Banta, Joshua A.; Royo, Alejandro A.; Kirschbaum, Chad; Carson, Walter P. 2005. Plant communities growing on boulders in the Allegheny National Forest: Evidence for boulders as refugia from deer and as a bioassay of overbrowsing. Natural Areas Journal. 25(1): 10-18.
- Comisky, Lauren; Royo, Alejandro A.; Carson, Walter P. 2005. Deer browsing creates rock refugia gardens on large boulders in the Allegheny National Forest, Pennsylvania. American Midland Naturalist. 154: 201-206.
- Reinhart, Kurt O.; Royo, Alejandro; Van der Putten, Wim H.; Clay, Keith. 2005. Soil feedback and pathogen activity in Prunus serotina throughout its native range. Journal of Ecology 93:890-898
- Royo, Alejandro A.; Carson, Walter P. 2005. The herb community of a tropical forest in central Panama: dynamics and impact of mammalian herbivores. Oecologia
National Research Highlights
Effective browse pressure indicators are necessary to adaptively manage forest landscapes with resident deer. Hardwood tree stump sprouts are a reliable and easily measured phytoindicator in disturbed forests. Deer browsing reduced sprout height by 39 percent when averaged across tree species. Browse impacts on sprout height at local (2.5 acre) scales is a valuable indicator of estimated deer densities at larger (1 square mile) scale.
International Symposium Improves Understanding of Disturbance and Salvage Logging and Forest Sustainability
The Forest Service’s Northern Research Station along with the University of Pittsburgh and the Carnegie Museum of Natural History sponsored an international symposium in May 2015 where international research teams and forest managers addressed the ecological and economic costs and benefits of disturbance and salvage logging in diverse forest biomes and disturbances.
Community composition of seeds stored in forest soils becomes increasingly divergent over time
Hurricane disturbance caused pronounced and persistent changes in the non-tree species composition of a subtropical wet forest. A unique long-term Forest Service dataset tracked the response and recovery of tropical forest herb, shrub, and vine communities to multiple hurricanes over 21 years on the 13-ha Bisley Experimental Watersheds in the Luquillo Experimental Forest, Puerto Rico.
Landscape-level Deer Herd Reductions Restore Forest Understory Plant Communities but Not Species Diversity
Since 2001, NRS scientist Alejandro Royo has tracked the response of herbaceous plant communities to deer herd reductions throughout the 70,000-acre Kinzua Quality Deer Cooperative (KQDC) in northwestern Pennsylvania.