Organic matter removal in loblolly pine (Pinus taeda L.) plantations increased ground layer diversity 16 years after treatment

Background/Question/Methods

Soil organic matter serves as an indicator of soil “quality” and contributes to soil productivity. Silvicultural activities and biomass harvesting can affect the depth and amount of organic matter on the forest floor. There are no well documented comparisons of the long term effect of organic matter manipulation on the ground layer vegetation (below 1.4 m). We investigated the impact of experimental organic matter manipulation 16 years after treatment in a loblolly pine (Pinus taeda L.) plantation in west-central Alabama. We examined the cover, richness, diversity, and biomass of the ground layer vegetation. Twelve 0.16 ha plots were established in a randomized complete block design with three treatments and four replications. The three treatments, imposed after harvesting a 33-year old plantation and immediately before replanting, were: 1) removed all forest floor and slash material, 2) control – no forest floor manipulation, and 3) double - all forest floor and slash material from treatment 1 was added. In each plot we established fifteen 1m² randomly located subplots. We determined the cover of each species by visual estimation. We compared the vegetation biomass, cover, richness, and diversity in the treatments using a mixed effects model and Tukey adjustment for multiple comparisons (α=0.05).

Results/Conclusions

Ground layer diversity was significantly different among the three treatments (p<0.001). Shannon’s diversity index was 0.94, 0.77, and 0.55 in the removal, control, and double treatments, respectively. Ground layer diversity in the removal treatment was greater than in both, the control (p=0.080) and in the double treatment (p<0.001). The control treatment was significantly more diverse than the double treatment (p=0.011). Similarly, plant richness, total plant cover and the cover of herbaceous, graminoid, and woody species were all significantly greater in the removal treatment (all p<0.05). Our results indicated that there was no negative effect of organic matter removal on the studied parameters. These results are also consistent with findings that there are no differences in above ground productivity of the loblolly pine trees among the treatments.