Current Research interest
The Rehm lab focuses on how climate change and invasive species are impacting ecological communities. We are particularly interested in how human induced global change is causing major rearrangements in communities and resulting in large-scale biodiversity loss.
We work across spatial and temporal scales; from leaves to communities and from climate past to the future. This research uses a variety of experimental, theoretical and modeling techniques to apply this research across systems such as US southeastern grasslands, eastern US deciduous forests, tropical islands, and tropical montane forests
We work across spatial and temporal scales; from leaves to communities and from climate past to the future. This research uses a variety of experimental, theoretical and modeling techniques to apply this research across systems such as US southeastern grasslands, eastern US deciduous forests, tropical islands, and tropical montane forests
Grassland restoration long-term success
Grasslands are some of the most biodiverse yet imperiled communities on the globe with over 90% of native grasslands lost in the US Southeast alone. Efforts are now underway to restore grasslands to conserve these unique system. However, rarely are global change drivers such as climate change or invasive species considered in restoration planning.
We are experimentally testing how the interaction of invasive plants and climate change will impact the long-term success of restoration efforts using a combination of open-top warming chambers (OTCs), automated rain-out shelters, climate monitoring and vegetation sampling.
We have partnered with the Southeastern Grasslands Initiative and USGS to improve restoration designs and inform managers on how to make their projects resilient to these future pressures.
Grasslands are some of the most biodiverse yet imperiled communities on the globe with over 90% of native grasslands lost in the US Southeast alone. Efforts are now underway to restore grasslands to conserve these unique system. However, rarely are global change drivers such as climate change or invasive species considered in restoration planning.
We are experimentally testing how the interaction of invasive plants and climate change will impact the long-term success of restoration efforts using a combination of open-top warming chambers (OTCs), automated rain-out shelters, climate monitoring and vegetation sampling.
We have partnered with the Southeastern Grasslands Initiative and USGS to improve restoration designs and inform managers on how to make their projects resilient to these future pressures.
Plant phenology, temperature extremes, and climate change
Plants rely on environmental cues for their phenological cycle such as bud break in the spring or leaf drop in the fall. With climate change those environmental cues are changing leading to mismatches between the optimal and actual timing of phenological events. In addition, climate extremes such as high temperatures in the summer are becoming more severe potentially moving outside what plants can handle. Using simple heating and freezing assays we are testing the thermal tolerance of eastern US trees as well as tracking phenology to determine which species are in danger during climate change. Some species may be able to adjust their phenological timing and thermal tolerances while others may not, leading to winners and losers in the forest. |
What is preventing forest restoration on a tropical island?
The Hawaiian islands have one of the most unique species assemblages on the planet but ongoing habitat loss and the introduction of non-native species has caused precipitous declines or extinctions of many Hawaiian island endemics. On the big island of Hawaii, mid to high elevation forest has been severely impacted through clearing for ungulate grazing and the subsequent introduction of non-native plants that outcompete native trees. Efforts are now underway to restore native plant communities with the goal of improving overall ecosystem functioning and providing important habitats for many of the endangered native bird species. I am working to understand why past efforts to restore mid-elevation Hawaiian forests have fallen short of their goals, specifically testing how the presence on non-native grasses inhibits the recruitment of native plants. |
Tropical Treeline dynamics
Tropical treelines represent the sharp transition from closed canopy cloud forest to open alpine vegetation and occur at elevations between 3500-4500 meters above sea level throughout much of the Andes. The treeline ecotone can be an important climate indicator as it marks the point where climate becomes cold enough that non-woody vegetation such as grasses is favored over the upright woody stems of trees. If treeline elevation is determined by temperature then any increase in global temperatures should cause treelines to shift further upslope. However, despite rising temperatures over the past 100 years, tropical treelines remain remarkably stationary. I used a series of experimental, observational, and modeling studies to determine which aspects of climate affect tropical treeline distributions. I focused on temperature extremes rather than mean temperatures to see how species and the treeline ecotone will respond to ongoing and future climate change |
The Ecological role of avian seed dispersers
The loss of native seed dispersers can result in large disruptions to ecosystem structure and function. On the island of Guam an introduced snake species (Boiga irregularis) has resulted in a complete defaunation of native bird species. Almost 70% of all native tree species on Guam are dispersed by birds so losing these dispersal vectors may lead to drastic changes in community composition and regeneration patterns. Conversely, other islands in the Mariana Island chain such as Rota and Saipan still maintain a healthy bird assemblage because the snake is only found on Guam. I am working to investigate how the loss of native avifauna can have cascading effects on the forest community. Our findings will hopefully guide future management decisions on how to restore seed dispersal services to Guam and other tropical island systems. For more information please visit the project website. |