An L1-L2 blockchain ecosystem combines high transaction throughput with secure asset settlement, making it likely to play a central role in the migration of financial markets to blockchain-based infrastructure. We provide an economic model of endogenous financial activity within an L1-L2 ecosystem to assess its potential economic value. We demonstrate that liquidity provision and trading volume are likely to migrate from L1 to L2, potentially leading to a situation where L1 is unable to support any meaningful activity alongside L2. Crucially, because the security of an L1-L2 ecosystem is anchored in the L1, reductions in L1 financial activity may weaken the overall system's security. We characterize the conditions under which this outcome arises and show that sufficiently low L1 settlement fees allow L1 and L2 activity to coexist.