Dynamics of young stellar clusters as planet-forming environments

Most stars and thus most planetary systems do not form in isolation. The larger star-forming environment affects protoplanetary disks in multiple ways: Gravitational interactions with other stars truncate disks and alter the architectures of exoplanet systems; external irradiation from nearby high-mass stars truncates disks and shortens their lifetimes; and the remaining gas and dust in the environment affect dynamical evolution (if removed by feedback processes) and provide some shielding for disks from external irradiation. The dynamical evolution of the region regulates when and how long various feedback mechanisms impact protoplanetary disks. Density is a key parameter that regulates the intensity and duration of UV irradiation and the frequency of dynamical encounters. The evolution of larger star-forming complexes may also play an important role by mixing populations. Observations suggest that clusters are not a single-age population but multiple populations with small age differences, which may be key to resolving several timescale issues (i.e., proplyd lifetimes, enrichment). In this review, we consider stellar clusters as the ecosystems in which most stars and therefore most planets form. We review recent observational and theoretical results and highlight upcoming contributions from facilities expected to begin observations in the next 5 years. Looking further ahead, we argue that the next frontier is large-scale surveys of low-mass stars in more distant high-mass star-forming regions. The future of ecosystem studies is bright as faint low-mass stars in more distant high-mass star-forming regions will be routinely observable in the era of extremely large telescopes.