Native tree species prosper while exotics falter during gap-phase regeneration, but only where deer densities are near historical levels

Throughout eastern North America, chronic white-tailed deer overbrowsing and widespread exotic plant invasions degrade native plant diversity and abundance. However, because deer densities are high across entire regions, it is challenging to find large areas where deer have been at low density for l...

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Bibliographic Details
Published in:	New forests Vol. 55; no. 5; pp. 1083 - 1100
Main Authors:	Yacucci, Anthony C., Carson, Walter P., Martineau, Jenna C., Burns, Curtis D., Riley, Brian P., Royo, Alejandro A., Diggins, Thomas P., Renne, Ian J.
Format:	Journal Article
Language:	English
Published:	Dordrecht Springer Netherlands 01-09-2024 Springer Nature B.V
Subjects:	Abundance Biomedical and Life Sciences Canopies Canopy gaps Deer Density Forestry Height Indicators Indigenous plants Indigenous species Introduced plants Introduced species Invasive species Life Sciences Plant diversity Plant species Quercus Regeneration Species diversity Species richness Gap-phase dynamics Exotic establishment regeneration Native plant diversity Canopy tree recruitment Oak Historic deer density
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Summary:	Throughout eastern North America, chronic white-tailed deer overbrowsing and widespread exotic plant invasions degrade native plant diversity and abundance. However, because deer densities are high across entire regions, it is challenging to find large areas where deer have been at low density for long periods. We predicted native plant diversity and abundance would be significantly higher during gap-phase regeneration where deer have been maintained at low densities (~ 7 deer/km²) compared to where deer have been chronically overabundant. Simultaneously, we predicted that exotic plant diversity and abundance would be lower in gaps where deer have been maintained at low versus high densities. We also evaluated whether deer density interacts with gap age, gap size, and gaps in dry versus more mesic forest patches. We studied 41 gaps throughout an 88 km 2 fenced military post where deer were maintained near pre-European-settlement densities for 67 years and in nearby forests where deer have been overabundant for decades. Native species richness, diversity, and cover were 37–65% higher, and exotic species cover was 80% lower in canopy gaps at low relative to high deer density. Stem height and density of multiple native canopy tree species (e.g., two Quercus spp.) were 5-20-fold higher within canopy gaps at low deer density. Moreover, 10 native woody species were indicators of low deer density, including three Quercus species, whereas no native woody species were indicators of high deer density. Deer were the primary filter underlying these different patterns in diversity, abundance, and plant height. Our findings demonstrate that gaps develop a vigorous and diverse native sapling layer, with far fewer exotics, in areas of low deer density without a history of chronic overbrowsing. We propose that military posts may be conservation and native plant regeneration hotspots wherever they regularly cull deer.
ISSN:	0169-4286 1573-5095
DOI:	10.1007/s11056-023-10022-w