The question at heart deals with relative costs. As with increasing alpha, using a one-tailed test requires justification and can provoke criticism because we do not have prior knowledge as to the direction of future population change. Increasing sampling effort will increase power to detect ongoing trends, but past a certain threshhold, the phenomenon of diminishing returns takes effect. Number of plots will be partly determined by availability of sites, e.g., you may only have one pond on your refuge. Counts per year depend on time available and how many plots are to be monitored.
Time conquers all .
Perhaps the major point to consider when planning monitoring programs is the dominating effect of time over most survey variables. A key question to ask is how much time one is willing or able to wait for conclusive results. For most five-year surveys, budgetary and logistical constraints would preclude the detection of trend levels useful for management purposes. With every added year, however, required sample size drops markedly before leveling out in the 10-20 year range. Increase within year effort for shorter term surveys .