Channel Islands Nation Park: Terrestrial vegetation monitoring annual report - 2016

Abstract

This report presents the data collected in 2016 as part of the long-term terrestrial vegetation monitoring program at Channel Islands National Park. The purposes of the monitoring program are to document the long-term trends in the major vegetation communities within the park. The data collected are from 30 m point-line intercept transects. In the past, each transect was sampled annually. However, beginning in 2012 the program began adding randomly located transects to improve the representativeness of the sampling, and transitioned to a rotating panel design. Now only a core subset of the transects are read annually. Non-core transects are assigned to one of four panels, and those transects are read only once every four years. A summary analysis of the 2016 data shows that: 165 transects were read. The 165 transects were distributed across all five islands: Santa Rosa Island (n = 87), Santa Cruz Island (n = 33), Santa Barbara Island (n = 18), Anacapa Island (n = 9) and San Miguel Island (n = 11). Relative native plant cover averaged 63% across all islands and sampled communities while absolute native plant cover averaged 32%. Among plant communities, relative percent native cover ranged from a low of 1% in seablite scrub to a high of 98% in oak woodland. In general, the number of vegetation data points recorded per transect positively correlates with average rainfall, which is reflected in the number of “hits” or transect points intersecting vegetation. When precipitation declined there is a corresponding drop in the number of hits. In 2016, however this was not the case. Even though rainfall increased as compared to the previous 4 years (18.99 inches in 2016 vs an average of 6.32 for the previous 4 years), the average number of hits was only 64. To put this into perspective, the highest average number of hits was 240 in 1993, an El Niño year of high precipitation. The number of vegetation communities sampled varied by island with the larger islands having more communities. In 2016, there were 15 communities sampled on Santa Rosa Island, 12 communities on Santa Cruz Island, 7 communities on San Miguel Island, 7 communities on Santa Barbara Island, and 7 communities on Anacapa Island. Twenty-six vegetation types were sampled in 2016. Of these, 13 occurred on more than one island. The most commonly shared community was Valley/Foothill grassland which was found in one form or another on all five islands within the park. The next most commonly shared communities were coastal sage scrub and coastal scrub, which were found on four islands. Coastal bluff scrub and coreopsis scrub were monitored on three islands. Four communities—ironwood, mixed woodland, oak woodland, riparian, and seacliff scrub—were monitored on two islands, and 12 communities—Torrey pine woodland, shrub savannah, seablite scrub, Santa Cruz Island pine, perennial iceplant, lupine scrub, fennel, coastal strand, coastal marsh, cactus scrub, boxthorn scrub, barren, and Baccharis scrub—were each monitored on one island.