Invasion Dynamics of Amur Honeysuckle in Southwest Ohio David L. Gorchov, Dept. of Biology Mary C. Henry, Dept. of Geography Miami University, Oxford, OH
Lonicera maackii Native to east Asia Introduced to U.S. in 1897; naturalized in 24 eastern states Partly self-compatible (Goodell and Iler 2007) Seeds dispersed by birds (Bartuszevige & Gorchov 2006) & deer (Castellano & Gorchov 2013, Guiden unpubl.) Seedlings establish in sun or shade (Luken & Goessing 1995) Extended leaf phenology (can find all individuals)
1. Importance of stand invasibility vs. propagule pressure in invasions
40 woodlots in agricultural landscape Darke and Preble counties, OH
Lonicera maackii cover weakly correlated with some woodlot measures Correlation coeff. (r) Stand age -0.40 tree cover in 1938 aerial photo -0.38 tree cover in 1962/63 aerial photo -0.37 Woodlot area Perimeter : area ratio Tree basal area
Woodlot L. maackii cover correlated with land cover in 1500 m buffer land cover in 1500 m buffer r %Crops -0.69 % Developed 0.44 %Forest 0.62 %Pasture 0.68 % Recreational Grass % Water 0.36 L. maackii cover not correlated with road density, latitude, or composition of woodlot perimeter in 1938 or 1962/3
Stepwise regression of woodlot L. maackii cover on predictors: % crop in 1500 m buffer was first predictor to enter; no other variable improved fit
1. Conclusions Landscape, more than woodlot characteristics, determine cover of this invader Propagule pressure more important than stand invasibility L. maackii invasion impeded by cropland Absence of propagule sources? Deterrent to movement of seed dispersers?
2. Relative importance of diffusion vs. long-distance dispersal in invasion of exotic species Fragmented habitat (forested patches in agricultural matrix)
Diffusion (expanding front)
Diffusion: subsequent recruitment from outside the patch propagule pressure
Long-distance dispersal
Long-distance dispersal
Long-distance dispersal
Long-distance dispersal: Subsequent recruitment from within patch Founder effect
Understanding of dispersal can inform management of invasives Diffusion: target edge of current range Long-distance dispersal: patrol for colonists X X X
Age structure of 28 populations in s. Darke Co. 14 pops.: all shrubs or 30 largest X-sections of stems Rings counted by 2-3 persons 689 shrubs; >1200 stems
Oldest shrub in each woodlot 8 14 8 7 8 14 13 21 11 1219 13 Long-distance dispersal, followed by diffusion 7 18 12 15 13 13 13 11 16 9 16 19 8 16 12 15
4436500 4435500 1992 X and Y axes correspond to UTM coordinates of woodlot centers in south-central Darke County Size of bubble corresponds to # of L. maackii shrubs in a woodlot in a given year 4434500 4433500 4432500 1992 4431500 4430500 4429500 4428500 689000 690000 691000 692000 693000 694000 695000 696000 697000
4436500 1997 4435500 4434500 4433500 Long-distance dispersal, followed by diffusion 4432500 1997 4431500 4430500 4429500 4428500 689000 690000 691000 692000 693000 694000 695000 696000 697000
2002 4436500 4435500 4434500 Long-distance dispersal, followed by diffusion 4433500 4432500 2002 1997 4431500 4430500 4429500 4428500 689000 690000 691000 692000 693000 694000 695000 696000 697000
Early phase of invasion: long distance dispersal after ~ 8 yrs: diffusion Closest pop. 4 yrs older Distance to closest sourcec (m) 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 1988 1990 1992 1994 1996 1998 2000 2002 2004 Establishment Year
Who is dispersing L. maackii seeds 4 km? Peter Guiden, MS thesis (Miami U)
Do later-establishing pops. to grow faster? (expected if diffusion important) NO Σ oldest 9 years Year pop. established
Age structure expected under diffusion vs. long-distance disperal predicted age structure number of individuals N(long) N(short) age
Immigration rate for a population (x i ) # shrubs in oldest 3 age classes / 3 x 145 =0.67/yr Age
Mean of x i for 28 pops. used as global immigration rate X = 0.87/yr x i Regression of pop. imm. rate vs. year of establishment not sig.
Recruitment from parents within the population assumed to equal total recruitment - immigration y i = n i -X yrs 8-9 yrs 5-7 Age For pop. 145, within pop. recruitment accounts for 34% of recruits in years 5-7 and 83% in years 8-9 On avg. (14 pops.), within-pop. recruitment accounts for 46% of recruits in years 5-7 and 77% in years 8-9
Early growth of new populations is due to both immigration (propagule pressure) and reproduction within the pop., but after 8 years is due mostly to within-pop. recruitment
2. Conclusions Long-distance dispersal important early in invasion Immigration rates are low, and soon exceeded by recruitment from within pop. Management: patrol for colonists X
Thanks! USDA NRI Competitive Grants Program, Mary Henry (MU) & Oscar Rocha (Kent State), co-pis Peter Frank, Steve Castellano, Doug Noe, Sujan Khanal, Holly Andrews, Charlotte Freeman