[code:1]spanning-tree mode pvst [/code:1]
Per vlan spanning tree was enabled which mean per lan group (vlan) you have segmented in your network into more then one loop redundancy (spanning tree) groups.
no spanning-tree vlan 88 [/code:1]
states that loop protection is disabled on that vlan and no spanning-tree is taking place
switchport trunk encapsulation dot1q
switchport trunk native vlan 87[/code:1]
This code states that on Port-channel1 vlan 87 will act as the native vlan meaning if any frames are not tagged into a specific vlan it will default to vlan 87.
Explains spanning tree very well. Per vlan spanning-tree is only different in that it blocks sets blocking states per vlan not per trunk link. (trunking still must be enabled)
Edit: I could be a bit more descriptive but I have a job interview to go to at 3pm it's 12:00 noon. If you have any more questions after viewing the flash about spanning tree I would be glad to help explain.