Terrain.treeMaximumFullLODCount
var treeMaximumFullLODCount: int;
int treeMaximumFullLODCount;
treeMaximumFullLODCount as int
Description

Maximum number of trees rendered at full LOD.

This is an easy setting to prevent too many trees being rendered at too high resolution in dense forests. Since there will be no fade if treeMaximumFullLODCount is exceeded you should tweak the treeBillboardDistance to not include unnecessary trees that are not being seen but, still rendered.
	function Start () {
		Terrain.activeTerrain.treeMaximumFullLODCount = 200;
	}
using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Start() {
        Terrain.activeTerrain.treeMaximumFullLODCount = 200;
    }
}
import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Start() as void:
		Terrain.activeTerrain.treeMaximumFullLODCount = 200