Removal Of Aboveground Biomass Research Articles

Vegetation Recovery Following High-intensity Wildfire and Silvicultural Treatments in Sand Pine Scrub

We hypothesized that clear-cutting mimics natural high-intensity disturbance by wildfire followed by salvage logging in sand pine scrub, and tested whether vegetation adapted to recovery from fire would respond similarly to another type of biomass removal. We measured plant community composition and structural characteristics in three replicated disturbance treatments and in mature sand pine forest (MF). Treatments were: (1) high- intensity burn, salvage logged and naturally regenerated (HIBS); (2) clear-cut, roller- chopped, and broadcast-seeded (RC); and (3) clear-cut and bracke-seeded (BK). All treat- ments were sampled 5-7 yr postdisturbance. Nonwoody plant species richness and diversity were significantly lower in MF than in disturbance treatments. Ruderal species were more abundant in HIBS and RC, but not to the exclusion of the characteristic suite of native scrub species. Shrub richness and diversity did not differ, but some species responded differently among treatments. Differences may be due to season of disturbance or rhizome depth (e.g., Serenoa repens (Bartr.) Small vs. Sabal etonia Swingle ex Nash.). Oak stem density was signif- icantly lower in HIBS and RC. Most structural characteristics were similar in HIBS, RC and BK but differed from MF. Results suggest that many scrub species responded similarly to aboveground biomass removal and the consequent structural and microclimatic conditions across these disturbance types. We suggest that plant resiliency traits, which evolved in re- sponse to the selective pressures of high-intensity disturbance and harsh environmental con- ditions, confer resiliency to human-caused disturbance as well. Mechanical biomass removal may be a suitable ecosystem management practice where burning is impractical. Due to the absence of a virgin (unsalvaged) burn treatment or pretreatment data and the short-term scope of this study, interpretation of results should be made with caution.

Creosotebush vegetation after 50 years of lagomorph exclusion.

In 1939, an experiment was established on the Jornada Experimental Range to evaluate the effects of shrub removal, rabbit exclusion, furrowing, and seeding in creosotebush [Larrea tridentata (DC.) Cov] vegetation. Sixteen plots (21.3×21.3 m) were laid out in four rows of four plots per row with a buffer zone of 7.6 m between plots and rows. A barbed wire fence excluded cattle and poultry wire fencing excluded lagomorphs. Treatments were factorially applied at two levels. Plant cover in the plots was sampled in 1938 (before treatment), 1947, 1956, 1960, 1967 and 1989 with randomly located, line-intercept transects. Data from all sampling dates were analyzed as a split plot in time and main effects for 1989 tested by analysis of variance for a 2×4 factorial experiment. There were significant (P<0.10) year x treatment interactions. Seeding and furrowing treatments were ineffective but lagomorph exclusion and shrub clearing treatments resulted in significant treatment differences for several species. In 1989, basal area of spike dropseed (Sporobolus contractus A.S. Hitchc.) was 30-fold greater on the lagomorph excluded than on the lagomorph unexcluded treatment. Canopy cover of honey mesquite (Prosopis glandulosa Torr. var. glandulosa), tarbush (Flourensia cernua DC.) and mariola (Parthenium incanum H.B.K.) were affected by lagomorph exclusion. None of the responses were viewed as successional in nature. They principally represented individual species sensitivities to either absence of a primary herbivore or removal of aboveground shrub biomass. Though the physical treatments could be regarded as relatively severe disturbances of the system, the impacts on community vegetation dynamics were relatively insignificant.

Effect of defoliation intensity on aboveground and belowground relative growth rates.

According to a simple growth model, grazed and ungrazed plants may have equal absolute growth rates provided that the relative growth rate (RGR) of grazed plants increases exponentially with grazing intensity (proportion of biomass removed). This paper reports results from an experiment designed to determine whether plants of two grass species subjected to a gradient of defoliation intensities, from 0 to 100% aboveground biomass removal, showed such a response. The relationship between aboveground RGR and defoliation intensity was exponential and closely matched the theoretical relationship of equal absolute growth rate. Thus, plants showed the same aboveground growth regardless of defoliation intensity thanks to an exponential stimulation of RGR by defoliation. Belowground RGR was depressed by defoliation of more than 20% of the above-ground biomass. In spite of the drastic modification imposed by the treatments on the relative proportions of different plant parts, after a 42-day recovery period basic allometric relationships, such as root:shoot and leafarea: weight ratios, were not affected by defoliation intensity. Exponential aboveground compensatory responses represent a key feedback process resulting in constant aboveground growth regardless of defoliation intensity and appear to be a simple consequence of strong commitments to certain allometric relationships.