A decade of streamwater nitrogen and forest dynamics after a mountain pine beetle outbreak at the Fraser Experimental Forest, Colorado

摘要: Forests of western North America are currently experiencing extensive tree mortality from a variety bark beetle species, and insect outbreaks projected to increase under warmer, drier climates. Unlike the abrupt biogeochemical changes typical after wildfire timber harvesting, outcomes poorly understood. The mountain pine (Dendroctonus ponderosae) began attack lodgepole (Pinus contorta) at Fraser Experimental Forest in 2002 spread throughout research area by 2007. We compared streamwater nitrogen (N) 2003 through 2012 with data previous two decades four watersheds distinct forest management histories, stand structures, responses outbreak. Watersheds dominated old-growth had larger trees lost 85% overstory 44% total basal beetles. In contrast, managed containing mixture second-growth (30–60 year old) (250- 350-year higher density subcanopy trees, smaller mean diameter, lower beetle-induced (~26% area). Streamwater nitrate concentrations were significantly during outbreak than pre-outbreak levels snowmelt base flow seasons. mixed-age stands, unaffected Beetle elevated inorganic N export 43 74% though amounts released low (0.04 0.15 kg ha−1) relative atmospheric inputs (<2% annual deposition). Increased height, foliar measured residual live augmented demand for N, far excess change Reallocation soil resources understory vegetation helps explain high nutrient retention affected outbreaks.