LUCKNOW, India — Wildfires that have killed at least seven people in recent weeks were burning through pine forests in the mountains of northern India on Monday, including parts of two tiger reserves. With dense smoke billowing in the skies, authorities urged villagers to be on alert and tourists to avoid traveling to the Himalayan foothills. After state firefighters were unable for months to put out the fires, the Indian government sent air force helicopters over the weekend to drop water on blazes covering nearly 8 square miles of pine forests. [...] the thick smoke and remote, mountainous terrain were making the job difficult for about 9,000 firefighters, army soldiers and forest guards sent to battle the flames, Gupta said. The fires were worsening the already-high air pollution over northern India, while also destroying forest ecosystems and affecting nesting birds and other animals.