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- Title
Tree ring δN as validation of space-for-time substitution in disturbance studies of forest nitrogen status.
- Authors
Kranabetter, J.; Meeds, J.
- Abstract
Forest ecosystem nitrogen (N) response to disturbance has often been examined by space-for-time substitution, but there are few objective tests of the possible variation in disturbance type and intensity across chronosequence sites. We hypothesized that tree ring δN, as a record of ecosystem N status, could validate chronosequence assumptions and provide isotopic evidence to corroborate N trends. To test this we measured soil N availability, soil δN, and foliar N attributes of overstory Douglas-fir ( Pseudotsuga menziesii) and understory western hemlock ( Tsuga heterophylla) across three old-growth stands and nine second-growth plantations on southeast Vancouver Island, British Columbia (Canada). Increment cores for wood δN were retrieved from three co-dominant Douglas-fir per plot. Bulk soil δN was well aligned with both foliar and recent wood δN, demonstrating the utility of wood δN in monitoring ecosystem N status. Strongly contrasting trends in tree ring δN were evident among second-growth stands, with most trees from plantations older than 50 years exhibiting steep declines (3-4‰) in δN but with no temporal trends detected for younger plantations. The discrepancy in tree ring δN suggests disturbance history varied considerably among second-growth sites, likely because of greater slash loads and hotter broadcast burns on older cutblocks. As a consequence, the pattern of increased soil N availability and foliar N concentration with time since disturbance derived from the chronosequence could not be validated. Tree ring δN may provide insights into disturbance intensity, especially fire, and correlations with foliar N concentration could inform the extent of changes in stand nutrition.
- Subjects
NITROGEN content of forest soils; DENDROCHRONOLOGY; ECOLOGICAL disturbances; SOIL chronosequences; NATURAL isotopic abundance; DOUGLAS fir; WESTERN hemlock
- Publication
Biogeochemistry, 2017, Vol 134, Issue 1-2, p201
- ISSN
0168-2563
- Publication type
Article
- DOI
10.1007/s10533-017-0355-4