No abstract

Forests are vital to maintaining headwater stream integrity in forested biomes, which ensures the delivery of aquatic ecosystem services downstream. Forest harvesting, however, can alter land–water linkages and compromise stream integrity. Historically, the main effects of forestry on streams have been documented by studies that used relatively few (mainly abiotic) indicators and which focused on single harvesting events. However, forest management is expected to intensify in the future to meet increasing global wood demand and it is likely that our present understanding does not adequately capture the cumulative effects that streams will be subjected to under intensive forest management. To address this, we assessed the effects of varying forest management intensities on the integrity of 15 forest headwater streams in northwestern New Brunswick, Canada. We used a comprehensive approach to link multiple biotic and abiotic indicators of stream ecosystem integrity to reach‐ and catchment‐level characteristics including forest management (e.g., cumulative harvesting over time, road density, forest condition). Most indicators detected the gradient in forest management intensity with abiotic indicators responding most strongly. Streams in catchments with highest management intensity (especially road density) tended to have higher fine inorganic sediment deposition and entrainment, water cations and carbon, dissolved organic matter humification, and water temperature. These abiotic differences were associated with higher biofilm biomass and shredder densities, but lower leaf decomposition. Evidence from our multi‐indicator approach elucidated a potential effects pathway of higher inorganic sediment content in biofilms of organic matter potentially limiting or altering its use by microbial and benthic macroinvertebrate (BMI) communities and resulting in reduced leaf decomposition rates. Overall, this study shows that current best management practices in an intensively managed watershed (and legacy effects from past management such as older road systems) do not fully protect against an increased delivery of terrestrial materials to streams with resulting habitat and biotic changes, but that they are mostly effective at preventing the impairment of BMI communities.

No abstract

The Canadian boreal zone provides extractive goods and services (provisioning ecosystem services (PrES)) to domestic and global markets and makes a significant contribution to the Canadian economy. The intensity and location of these extractive activities, however, may positively or negatively affect the availability of other benefits that the Canadian and global society receive from the boreal. Where PrES compete, managing these activities along with their impacts to boreal ecosystems becomes a balancing act between the need for resource extraction and the continued availability of the other benefits from ecosystems. Management measures and policies are more likely to succeed if they are designed with foresight, which means accounting for how demand, a key driver of change in the boreal, may change in the future. To help this process, we present three divergent, yet plausible future scenarios based on the analysis of: (i) the capacity of the boreal to provide wood products, fossil fuels, metals and minerals, and hydropower and other renewables; (ii) past trends (1985–2015) and key events in the demand for these PrES; (iii) the interaction of demand for PrES with other drivers of change to the boreal zone; and (iv) the synergies and trade-offs between PrES. We find that historically and currently the capacity of the boreal to provide these PrES exceeds the amount currently supplied. However, the capacity of different PrES and location of extractive activities are spatially dispersed creating a spatial and temporal patchwork of associated risks to local ecosystem integrity and the supply of non-PrES. In addition, these scenarios suggest that the future of boreal PrES is very uncertain and highly dependent on how other drivers of change (namely governance and geopolitics, societal values and climate change) play out in the future. Given the spatial complexity, we find that the cumulative effect of these drivers (e.g., climate change) will determine what paths unfold for different areas of the boreal, and we conclude that careful consideration and planning must be given to ensure that the balance between PrES and non-PrES is maintained.

Our understanding of how forest management practices affect the relative importance of autochthonous vs. allochthonous resource use by headwater stream food webs is relatively poor. To address this, we used stable isotope (C, N, and H) analyses of food sources and macroinvertebrates from 15 streams in New Brunswick (Canada) and assessed how different catchment conditions arising from the gradient in forest management intensity affect the contribution of autochthonous resources to these food webs. Aquatic primary production contributed substantially to the biomass of invertebrates in these headwater streams, especially for scrapers and collector‐gatherers (25–75%). However, the contribution of algae to food webs decreased as forest management intensity (road density and associated sediments, water cations/carbon, and dissolved organic matter humification) increased, and as canopy openness decreased. This trend was probably due to an increase in the delivery of organic and inorganic terrestrial materials (dissolved and in suspension) in areas of greater harvesting intensity and road density, which resulted in more heterotrophic biofilms. Overall, results suggest that, despite the presence of riparian buffers, forest management can affect stream food web structure via changes in energy flows, and that increased protection should be directed at minimizing ground disturbance in areas with direct hydrological connection to streams and at reducing dissolved and particulate matter inputs from roads and stream crossings in catchments with high degrees of management activity.

No abstract

The Canadian boreal zone provides ecosystem services from local to global scales. Either directly or indirectly, demands for these services have and will continue to serve as drivers of change in the region. Here we present evidence for past, present, and potential future demand for maintaining nonprovisioning ecosystem services (NPrES), defined as indirect and nonmarketable services obtained from ecosystems as a driver of change in the boreal zone. Our evidence of demand stems from federal and provincial policies, actions by Indigenous peoples, and nongovernmental initiatives that aim to maintain the sustainability of natural resource extraction and ecosystem condition of the boreal. Presently, the demand for NPrES influences decisions related to natural resource development (e.g., forestry) that in turn impacts the condition of the boreal zone. Informed by the present conditions and past trends, three future scenarios to the year 2050 are presented that contrast in their trajectory—status quo, increased demand for NPrES, and decreased demand for NPrES. We also summarize the interactions among other drivers of change in the boreal and the synergies and trade-offs among the different types of demand for NPrES. Ultimately, sustainability of the boreal zone and the ecosystem services it provides will result from a complex suite of interacting drivers of change, where the balance of demands for provisioning and NPrES will continue to influence regional conditions.

Riparian zones contain areas of strong hydrological connectivity between land and stream, referred to as variable source areas (VSAs), and are considered biogeochemical control points. However, little is known about whether VSAs influence stream communities and whether this connectivity is affected by forest management. To address this, we used multiple biotic and abiotic indicators to (1) examine the influence of VSAs on riparian vegetation and stream ecosystems by comparing VSA and non-VSA reaches and (2) explore how forest management may affect the influence of VSAs on stream ecosystems. We detected some significant differences between VSA and non-VSA reaches in the riparian vegetation (greater understory and lower tree density) and stream ecosystem indicators (greater dissolved organic matter aromaticity, microbial biomass, peroxidase activity and collector-gatherer density, and lower dissolved organic carbon concentrations, algal biomass, and predatory macroinvertebrate density), which suggests that VSAs may create a more heterotrophic ecosystem locally. However, we show some evidence that forest management activities (specifically, road density) can alter the influence of VSAs and eliminate the differences observed at lower forest management intensities, and that the most hydrologically connected areas seem more sensitive to disturbance. Therefore, we suggest that the heterogeneity in hydrological connectivity along riparian zones should be considered when planning forest harvesting operations and road building (e.g., wider riparian buffers around VSAs).