The Midrash uses the mitzvah of orlah as an opportunity to offer a paean not just to those who study Torah, but also to machzikei torah, supporters of Torah study:
וכי תבואו אל הארץ ונטעתם כל עץ מאכל הדא הוא דכתיב: (משלי ג)עץ חיים היא למחזיקים בה. אמר רב הונא בשם ר' אחא: שלא יהיו דברי תורה בעיניך, כאדם שיש לו בת בוגרת והוא רוצה להשיאה לאחד, אלא (שם ב)בני אם תקח אמרי ומצותי תצפון
אתך, אם יש לך זכות קח אמרי
אילו נאמר עץ חיים היא לעמלים בה לא היתה תקומה לשונאי ישראל, אלא למחזיקים. אילו נאמר אשר לא ילמד לא היתה תקומה לשונאי ישראל, אלא (דברים כז)אשר לא יקים את כל דברי התורה הזאת, לכך נאמר: עץ חיים היא למחזיקים בה
What does the planting of fruit trees have to do with Torah study? One can take a mystical approach and read the Midrash as associating the idea of planting trees with the idea of the eitz hachaim and eitz hada'as. Torah study, the eitz hachaim, is the means of redeeming the world from the original sin caused by Adam first partaking of the eitz hada'as. The Midrash's meaning is entirely symbolic -- our task is to replant the eitz chaim, to return it to primacy.
However, the Midrash can also be understood in a way that does not rob planting of its concrete meaning (see Shem m'Shmuel). The lesson is that entering the land, planting trees and developing Eretz Yisrael, is an inseparable mission from that of learning and supporting Torah. A Torah based society can only be achieved in the physical boundaries of Eretz Yisrael, and Eretz Yisrael can only successfully be built with spiritual goals in mind.
The Chasam Sofer famously comments that the dispute between Rabbi Yishmael and R' Shimon bar Yochi (Brachos 35) over how to balance the obligation of Torah study with the need to plant and tend the field (i.e. to make a living) applies only in chutz la'aretz. In Eretz Yisrael, all would agree that one may and must tend to the fields as this is the mitzvah of yishuv ha'aretz. In light of our Midrash I would not take the Chasam Sofer's conclusion to mean that Eretz Yisrael demands an unavoidable concession to bitul Torah, but rather quite the reverse -- in Eretz Yisrael alone those occupations which would otherwise be considered bitul Torah take on the positive value of being the means of being machzik Torah.
Last night I went to learn for a bit and daven ma'ariv at a local Beis Medrash which treats yesterday and today as any other day, as is the common practice in most yeshivos. A local synagogue had a celebration marking Yom ha'Atzmaut, but that local synagogue does not have a thriving beis medrash where people learn every night. There are gardeners tending to the planting of trees and celebrating their growth, and there are those who are sitting and being machzik Torah and learning Torah, but sadly, these worlds rarely intersect. Our Midrash sees them as ideally going hand in hand.
The fruit of a tree may not be eaten for three years until the tree develops and grows. The fruits of the spiritual and physical rebuilding of Eretz Yisrael are still immature, but it's never to early to express our hakaras hatov for their renewel and to remind ourselves of the ideals that motivate our efforts.