In the southern Great Plains of USA, encroachment by trees and shrubs in historically open wooded ‘savanna’ is attributed to factors such as fire suppression and overgrazing. This study evaluated the efficacy of reintroduction of prescribed burning and also herbicide application, to reduce invading honey mesquite Prosopis glandulosa,aiming to restore savanna habitat and increase grass and herb diversity, near Vernon town (33°53′N, 99°02′W) north Texas.
Prior to treatment the site was dominated by mesquite (average canopy cover 50% and tree height 2.4 m) and had been cattle grazed at moderate intensity (12-15 ha/cow) for 50 years. Four replicates of four treatments (replicate plots 4 ha; randomized design) were applied:
1) winter burn (January-February 1996);
2) aerial spray of 0.28 kg/ha clopyralid via fixed-wing aircraft (2 July 1996);
3) aerial spray of 0.28 kg/ha clopyralid + 0.28 kg/ha triclopyr (C + T) applied as (2);
4) untreated (control).
n 1999, mortality and regrowth of 80 to 120 mesquite were evaluated (i.e. dead; stem sprouts only; basal sprouts only; or stem sprouts + basal sprouts) along two randomly located 200 m transects per plot. Mesquite canopy cover and live height was recorded in 2001 and 2004. End of growing season grass and forb production (clipping and drying samples) and species composition was quantified in 2002, 2003 and 2004, within randomly located quadrats.
In burn plots, fire intensity was high but mesquite had low mortality and high basal sprouting. Clopyralid application resulted in moderate mortality with low basal sprouting of survivors, and C + T high mortality but high basal sprouting.
In C + T and clopyralid plots (6 to 8 years post-treatment) grass and forb production increased, but mesquite regrowth limited recovery in burn plots.
Herbaceous diversity was increased in burned and C + T plots (decreased cool-season (C3)perennial grass dominance and increased warm season (C4) perennial grasses and/or C3 forbs). Control and clopyralid plots (mesquite overstory maintained) had lower herbaceous diversity (C3 perennial grasses dominant).
The authors consider that the clopyralid treatment represents the best restoration technique as it reduced mesquite canopy cover to historic levels and incurred some benefits to herbaceous recovery.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://onlinelibrary.wiley.com/doi/10.1111/j.1526-100X.2006.00150.x/full