Canadian Forest Service Publications
Effects of disturbance on understory succession in upland and lowland boreal forests and implications for woodland caribou Rangifer tarandus caribou. 2016. Mallon, E.E.; Turetsky, M.R.; Thompson, I.D.; Fryxell, J.M.; Wiebe, P.A. Forest Ecology and Management 364:17-26.
Issued by: Great Lakes Forestry Centre
Catalog ID: 36576
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Boreal forest development is influenced by both natural and anthropogenic disturbances that alter stand structure and nutrient cycling over decadal timescales. The effects of disturbance on boreal forests is likely to be modified by soil moisture, given that disturbance severity, vegetation structure and plant productivity vary between upland and lowland forest stands. Future changes in boreal vegetation dynamics are predicted to have consequences for a range of ecosystem services including climate feedbacks and wildlife management. Here, as part of a broader study on habitat use and forage of woodland caribou, we investigated the effects of soil drainage class (upland vs. lowland), disturbance (wildfire vs. timber harvest), and stand age on understory plant species richness, cover, biomass, productivity, and foliar C/N. Due to faster nutrient turnover rates in upland soils, we predicted that understory vegetation in uplands would be more productive, biodiverse and nutrient-rich than in lowlands. We also expected disturbance to lead to greater changes in understory vegetation in uplands, given that both fire and timber harvesting tend to be more severe in drier ecosystems. Our results showed that plant understory characteristics varied primarily between soil drainage classes, with few differences between stands recovering from wildfire or timber harvesting. Contrary to our predictions, lowland understory vegetation had greater total understory plant species richness, aboveground net primary productivity, and foliar C/N compared to upland understory vegetation. We also found no difference in total understory vegetation percent cover, productivity or foliar C/N between burned and harvested stands. Understory net primary productivity decreased with time following disturbance in uplands but increased nonlinearly with stand age in lowlands. Greater productivity in lowlands was attributed primarily to evergreen shrubs, though graminoids also were more productive in lowlands than in uplands. Our study has implications for the threatened woodland caribou with respect to the nutritional aspects of their habitat selection. Our results suggest that the commonly held assertion that, by selecting lowlands, caribou face a trade-off between lower predation risk and lower forage quality may be incorrect and requires further examination.
Plain Language Summary
As part of a broader study on habitat use and forage patterns of threatened woodland caribou, we studied the effects of disturbance on forest understory productivity across stands varying in age and drainage conditions. We found that lowlands had greater understory species richness, aboveground net primary productivity and foliar C/N comparable to uplands. These results have implications for woodland caribou management, as they show that lowlands provide equal or greater amounts of caribou forage than uplands. Caribou do not face a forage quality trade-off by selecting lowlands with respect to the nutritional aspects of their habitat selection, which was a commonly held assertion.