Forest Investment Account (FIA) - Forest Science Program
FIA Project Y092068

    Ecosystem functioning in small streams and their riparian areas in response to partial harvest riparian management.
Project lead: Marczak, Laurie (University of British Columbia)
Author: Kominoski, John Stephen
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Forest and stream food webs are widely viewed as energetically coupled, particularly with respect to the contributions of riparian forests to stream ecosystems. Increasingly, researchers are recognizing the reciprocal nature of connections between streams and forest, with streams providing critical inputs to riparian forests [1]. Stream food webs receive important subsidies of energy from terrestrial invertebrate and detrital inputs, downstream transport from small headwaters and spawning migrations. Inputs of particulate organic matter from riparian forests represent an important energy source for stream production [2] while accidental inputs of terrestrial invertebrates are a major prey category directly available for stream consumers such as fish [3]. Conversely, stream ecosystems subsidize forest food webs through emerging aquatic invertebrates that are prey for a variety of terrestrial consumers [4, 5] and as conduits for marine nutrients in the form of salmon carcasses [6-8]. The intent of the proposed research is to clarify the effects of forest harvesting in either disrupting or enhancing the magnitude of subsidies to stream environments and the reciprocal feedback to terrestrial habitats.
In recent years, concurrent with an increased awareness of the importance of dynamic functioning of ecosystems, there has been an upsurge of interest in the dynamic consequences of resources subsidies for maintaining ecosystem function and patterns of biodiversity [6, 8-10]. Landuse changes such as forestry can fundamentally alter the flux of materials between terrestrial settings and aquatic systems. It has been clearly shown in a range of habitats that these changes in subsidy quantity or pattern have important effects on patterns of biodiversity [11].

Forest harvesting frequently converts coniferous stands to deciduous forest at least in the short term. These forests exhibit considerable variation in their contribution of both falling terrestrial invertebrates and organic matter to streams [12]. At the same time, reforestation efforts that focus on softwoods may result in a decrease in deciduous inputs to streams [13]. Stream canopies may shift towards greater deciduous cover with harvesting and back towards coniferous cover through either natural succession of due to direct reforestation efforts. Although the consequences of timber harvesting for both streams and forest ecosystems have been extensively investigated over the past several decades, less is understood about the consequences of post-harvest forest succession on the connections between stream and riparian ecosystems. Regenerating forests in the coastal region are frequently dominated by red alder (Alnus rubra) and vine maple (Acer circinatum) in addition to quick growing shrubs such as salmonberry (Rubus spectabilis). Although these deciduous trees and shrubs are not considered valuable from the perspective of either timber production or as a source of wood for fish habitat, red alder in particular has the potential to alter both terrestrial productivity [14] and diversity [15] as well as stream productivity and diversity [13, 16]. Wipfli [10] and Allan [12] found that red alder may provide greater inputs of terrestrial invertebrates to drift-feeding fishes than systems with little alder. Alder leaf litter to streams is more nutritious and more quickly broken down than similar coniferous material [14] and streams flowing through areas with a deciduous canopy tend to export greater absolute quantities of aquatic invertebrates during emergence than similar streams under deciduous canopies [Richardson unpublished data, 17]. Current provincial guidelines for timber harvest recognize the need for protection along fish-bearing or drinking water streams. Streams without fish or streams less than 1.5m wide at bankfull currently receive no mandatory riparian reserves during harvesting [18]. Not only do these streams typically drain into lower salmon-bearing reaches, they may also be strongly influenced by their surrounding terrestrial habitats due to their high perimeter to area ratio. We do not yet have experimental evidence of how sequential shifts in the types of resources entering streams from different canopy types may alter the diversity of stream invertebrates or change key ecosystem functions such as detrital processing or rates of secondary production that may eventual spiral upwards to fish populations or back to terrestrial habitats through altered timing of aquatic insect emergence patterns.

The goal of the proposed project is to determine if (a) changes in the composition of leaf litter inputs (e.g. from Douglas-fir needles to red alder leaf litter) results in changes in the abundance and diversity of benthic invertebrates, and (b) how this shift translates into changes in rates of detrital processing and secondary production and (c) whether these shifts ultimately translate into changes in stream invertebrate emergence pattern or abundance. The proposed project will clarify how forest harvesting operations may alter the riparian connection with headwater streams and reciprocal subsidies from streams to riparian forests. This will provide immediately applicable results in terms of understanding the need for, and the effects of, maintenance of riparian vegetation during forest harvest operations. Research testing the generality of these patterns will improve understanding of how aquatic ecosystems respond to anthropogenic and natural trajectories of forest change.

(1) Helfield, J.M. and R.J. Naiman, Ecosystems, 2006. 9(2): p. 167-180. (2)Wallace, J.B., et al. Science, 1997. 277: p. 102-104. (3)Wipfli, M.S., Land. Urban Plan. 2005. 72: p. 205-213. (4)Paetzold, A., et al. Fresh. Biol. 2006. 51: p. 1103-1115. (5)Collier, K.J., et al. Fresh. Biol. 2002. 47: p. 1651-1659. (6)Zhang, Y., et al., Proc. R. Soc. B. 2003. 270: p. 2117-2123. (7)Helfield, J.M. and R.J. Naiman Oecologia, 2002. 135: p. 573-582. (8)Hocking, M. and T.E. Reimchem. BMC Ecology, 2002. 2(4). (9)Szepanski, M.M., et al. Oecologia, 1999. 120: p. 327-335. (10)Wipfli, M.S., et al. CJFAS, 1999. 56: p. 1600-1611. (11)Marczak, L.B., et al. Ecology, in press. (12)Allan, J.D., et al. CJFAS, 2003. 60: p. 309-320. (13)Wipfli, M.S. and J. Musslewhite, Hydrobiologia, 2004. 520: p. 153-163. (14)Binkley, D., et al. 1994, Oregon State University Press: Corvallis, Oregon. p. 57-72. (15)Newton, M. and E.C. Cole. 1994, Oregon State University Press: Corvalis, Oregon. p. 106-115. (16)Piccolo, J.J. and M.S. Wipfli. CJFAS 2002. 59: p. 503-523. (17)Jackson, J.K. and S.G. Fisher. Ecology, 1986. 67(3): p. 629-638. (18)Province of British Columbia. Riparian Management Area Guidebook. 1995.
Related projects:  FSP_Y081068FSP_Y103068


Executive summary (0.9Mb)

To view PDF documents you need Adobe Acrobat Reader, available free from the Adobe Web Site.

Updated August 16, 2010 

Search for other  FIA reports or other Ministry of Forests and Range publications.

Please direct questions or comments regarding publications to