Forest Investment Account (FIA) - Forest Science Program
FIA Project Y081097

    Recovery processes of small streams and their riparian areas from clear-cutting and partial harvest riparian management
Project lead: Richardson, John (University of British Columbia)
Contributing Authors: Reiss, Aya Elaine; Hofer, Nancy; Richardson, John S.; MacIsaac, Erland A.; Moore, R. Dan; Marczak, Laurie B.; Miquelajauregui, Yosune; Deguise, Isabelle E.; Kiffney, Peter M.; Feller, Michael C.; Hinch, Scott G.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Headwater streams comprise 75-90% of the total stream length of most temperate river networks (Gomi et al. 2002) and thus contribute disproportionately to river network structure and function. Consequently, the physical and biological diversity of main stem rivers are partially a function of materials received from these small streams (Rice et al. 2001, Kiffney et al. 2006, Wipfli et al. 2007). Headwater streams may also provide a critical buffer against projected increases in air temperature resulting from climate warming. Riparian buffers are commonly used to maintain shade and minimize increases in stream temperature (e.g., Kiffney et al. 2003, Gomi et al. 2006), particularly for the protection of cold-water species such as salmon and trout. Buffers also provide for ongoing supplies of organic matter, trapping of sediments and nutrients, future supplies of wood, riparian habitat, etc. (Richardson 2004, Richardson et al. 2005). Therefore, understanding forest harvest impacts on headwater streams has implications for habitat quality and quantity headwaters, and perhaps for the overall river network. Sustainable forest management requires that ecosystem processes and their elements are maintained on the landscape. Maintenance of ecosystem processes can occur if the ecosystem is resistant to changes brought about by forest management, if the system is protected against all changes, or if the system and its processes recover relatively quickly from disturbance. Riparian forest management is intended to mitigate impacts of forest harvesting, but it is clear that some significant change still occurs, even with reserves of 30 m or more (e.g. Cockle & Richardson 2003, Kiffney et al. 2003). In that case, the questions of interest become: 1) how large are the changes?; 2) can the system and its components recover?; 3) at what rates does the system recover?; 4) does the trajectory of recovery converge on control and pre-treatment levels; and 5) are the recovery dynamics aided by the riparian forest reserves? Relatively few studies have examined rates and trajectories of recovery dynamics, and existing studies focused on individual variables such as streamflow (Hicks et al. 1991) and stream temperature (Johnson & Jones 2000). The Malcolm Knapp Riparian Management experiment offers a unique opportunity to document stream and riparian recovery rates within two distinct forest management strategies: clear-cutting with fixed width riparian reserves vs. partial harvest. Since the study is in a 70 year old second growth stand, changes are also occurring in unharvested controls, and with our replicated-BACI study design, we are able to track changes in baseline conditions also. We have made detailed measurements of system components for 16 small streams and their riparian areas for a period of 7 years after harvesting (13 of those streams), and for 3 streams with 50% harvest of riparian areas for <2 years. The initial part of this project compared 13 streams before and after harvesting for 30 m reserves (n = 3), 10 m reserves (n = 3), clearcut to the banks (n = 4), contrasted with 3 control systems (Kiffney et al. 2003). Our measurements are both extensive and intensive and include water temperature, streamwater turbidity and chemistry, geomorphology and in-stream wood, organic matter flux (inputs and outputs), algal dynamics, stream and terrestrial invertebrates, fish and amphibians, riparian vegetation dynamics (understory and overstory), large wood dynamics (standing and downed wood), and windthrow. Each of these elements is linked in order to understand ecosystem changes resulting from different forest management approaches. We documented significant changes in streamwater temperature (Moore et al. 2005) and chemistry (Feller 2005), light flux and algal biomass, even in the 30-m fixed width reserve treatment within the first two years after logging (Kiffney et al. 2003). Some of these changes persisted five years after logging. Regrowth of vegetation in the riparian zone (primarily deciduous), especially in the 10-m and no reserve treatments, has dampened changes in light flux, algal growth and stream temperatures, but has increased litter inputs during leaf fall. Initial regrowth of understory vegetation in the partial-harvest stands is more like that in the no-reserve treatment but with the added benefit of large overstory trees for a future LWD supply. In the 10 and 30 m buffers, most trees windthrown in the early years of the study are still suspended above the channel. The long-term nature of our studies has allowed us to document these recovery patterns, which is vital for assessing the efficacy of protecting stream structure and function under different riparian management strategies. These studies will allow us to develop empirical models to predict ecological short-term (1-5 years) changes associated with riparian harvest (model currently under development). Understanding short-term and long-term changes is critical for sustainable forest management around aquatic ecosystems. Although we have observed that some elements are approaching recovery (e.g., riparian inputs), other measures (e.g., invertebrate abundance or diversity) may take a longer time to recover. We will address the need to document long-term recovery of these streams and their riparian areas by sampling the fixed width riparian reserve treatments and the partial harvest watersheds for three more years. Furthermore, this work will capitalise on considerable investment in describing the initial changes of these systems to different kinds of riparian management (Kiffney et al. 2003). Continuing our measurements will also allow us to calibrate models to predict longer-term changes (5-10+ years) associated with forest harvest. The importance of our project to forest management in BC and across North America increased in 2004/2005 when we added an additional riparian management technique: partial harvest. Specifically, we added three additional streams that received a treatment of 50% removal of basal area of trees in the riparian areas. The 50% removal streams are still exhibiting large changes diverging from control streams. FSP funding to Feller for an LTRI infrastructure maintenance/upgrade earlier this year will facilitate this work by providing more reliable and comprehensive stream physical data from the six instrumented watersheds that are included in our study. We have gained considerable information from this study relevant to both the basic ecology and management of small watersheds at a reasonable level of investment. The potential for considerable gains in our understanding of these small streams are high including: (1) the long-term recovery dynamics of forests and streams from different management approaches; and (2) models that predict both short (1-5 years) and long-term (5-15 years) effects of riparian management on these systems.
Related projects:  FSP_Y092097FSP_Y103097


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Updated August 16, 2010 

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