Channel Islands National Park: Terrestrial vegetation annual report - 2015

Rodriguez, Dirk

This report presents the data collected in 2015 as part of the long-term terrestrial vegetation monitoring program at Channel Islands National Park (Figure E1). 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 on 4 of the 5 islands–Santa Barbara Island, Anacapa Island, Santa Cruz Island, and San Miguel Island–within the park to improve the representativeness of the sampling, and transitioned to a rotating panel design. Now, for those 4 islands 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. The implementation of the new monitoring design will not be implemented on Santa Rosa Island until 2017. A summary analysis of the 2015 data shows that: • 162 transects were read. • The 162 transects were distributed across all five islands: Santa Rosa Island (n = 85), Santa Cruz Island (n = 33), Santa Barbara Island (n = 17), Anacapa Island (n = 13) and San Miguel Island (n = 14). • Relative native plant cover averaged 61% across all islands and sampled communities while absolute native plant cover averaged 37% across all islands and sampled communities. For plant communities, relative percent native cover ranged from a low of 6% in barren types to a high of 99% in ironwood groves. • In general, the number of vegetation data points recorded per transect appears to correlate with average rainfall. In other words, as rainfall increases, vegetation cover increases and this is reflected in the number of “hits” or transect points containing vegetation. When precipitation declined there was a corresponding drop in the number of hits. In 2015, as a result of 4 years of below average rainfall, the average number of hits was 88. To put this into perspective the highest average number of hits was 240 in 1993. • Due to the random placement of the monitoring transects, by chance, not all communities on an island may be monitored. In addition, due to the rotating design used by the CHIS monitoring program, a community may not be monitored in all years if it is solely represented by transects within the rotating panels. Knowing the number of communities monitored versus the total number of known communities on an island, can help a reviewer gauge how accurate the monitoring program may be in detecting island-wide change in a particular year. In 2015, 12 of the 16 communities were sampled on Santa Rosa Island; 7 of 10 communities on Santa Cruz Island (NPS section) were sampled; 7 of the 9 known communities on San Miguel Island were sampled; 7 of the 8 known communities on Santa Barbara Island were sampled; and 5 of the 7 known communities on Anacapa Island were monitored. • 23 different vegetation types were sampled in 2015. Of these, 12 occurred on more than 1 island. The most commonly shared community was Valley/Foothill grassland which was found in one form or another on all 5 islands within the park. The next most common shared communities were coreopsis scrub, coastal sage scrub, coyote brush scrub, and island chaparral which were shared on 3 islands, although not necessarily on the same 3 islands. The other 5 shared communities—caliche scrub, coastal bluff scrub, coastal scrub, herbaceous scrub, mixed woodland, oak woodland, and riparian were shared on 2 islands each.

Channel Islands National Park: Terrestrial vegetation annual report - 2015

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