The effects of post-harvest residue on plantation forest soils and early growth of redwood and Douglas-fir seedlings in Humboldt County California

Forest harvest residue (slash) usefulness has been up for debate among private timberland owners, public land managers, and the timber industry for decades. The disposal of slash, viewed as having low ecological value, has received considerable attention as wildfire risk has made burning it harder. In recent years, forest scientists and ecologists have recognized the importance of decaying wood and its relationship to forest growth and regeneration. At this site in Northern California, we looked at whether forest harvest residue enriches soil near slash windrows through soils coring and lab analyses, looking for primary limited nutrients nitrate (NO3-N) and ammonium (NH4-N). This study looks at the growth responses of newly planted Douglas-fir seedlings and clonal redwood nursery stock, with respect to their distance to slash piles. In our findings, there was no clear relationship to distance to piles in terms of soil nutrients, however there was an increase in basal area of planted Douglas-fir and redwood farther away from slash piles. Soil analyses showed no clear relationship to early slash decay and soil nutrient replenishment, however this study only looked at the early stages between one year after harvest and the second year. Further research is needed over a longer timeframe to determine if and when slash piles might affect soil chemistry, and we recommend including a range of sites to expand the scope of inference beyond our two study sites that were close together and located outside redwood’s natural range