WASHINGTON -- The Drug Enforcement Administration destroyed fewer marijuana plants in 2012 and 2013 combined than it did in 2010 alone, according to newly available statistics, although officials did not suggest this was an agency goal.

The DEA destroyed 4,395,240 plants in 2013, up slightly from the 3,933,959 plants it destroyed in 2012. Both numbers pale in comparison to the 10 million-plus plants destroyed in both 2009 and 2010.

In the DEA's fiscal year 2015 budget request to Congress, officials said that the agency's successful enforcement efforts had "forced drug traffickers to cultivate marijuana plants on private property, whereas in prior years, marijuana plants were typically grown on public land."

The private grows, DEA officials said, had made it more difficult for the agency to keep its numbers up. "[S]earch warrants are required to pursue investigations on private land," they noted.

Another factor in the lower totals for destroyed plants, the officials suggested, was "the introduction and cultivation of a new, more robust species of marijuana plant. It is called a 'supersized' marijuana plant and it can reach heights of five feet or more and produce up to several pounds of marijuana from a single stalk."

In their budget proposal, DEA officials said the agency must "continuously modify its enforcement strategies to keep pace with the various adaptations and evolutionary techniques employed by trafficking organizations and other criminal enterprises."